Showing papers in "Soil & Tillage Research in 2009"

A review of the effects of tillage systems on some soil physical properties, water content, nitrate availability and crops yield in the Argentine Pampas

Abstract: Fil: Alvarez, Roberto. Universidad de Buenos Aires. Facultad de Agronomia; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario; Argentina

Reference bulk density and critical degree-of-compactness for no-till crop production in subtropical highly weathered soils

Abstract: The concept of degree of compactness (DC), referred to as field bulk density (BD) as a percentage of a reference bulk density (BD ref ), was developed to characterize compactness of soil frequently disturbed, but for undisturbed soil such as under no-tillage critical degree of compactness values have not been tested. The objective of this study was to compare methods to determine BD ref and limits of DC and BD for plant growth under no-tillage in subtropical soils. Data from the literature and other databases were used to establish relationships between BD and clay or clay plus silt content, and between DC and macroporosity and yield of crops under no-tillage in subtropical Brazil. Data of BD ref reached by the soil Proctor test on disturbed soil samples, by uniaxial compression with loads of 200 kPa on disturbed and undisturbed soil samples, and 400, 800 and 1600 kPa on undisturbed soil samples, were used. Also, comparisons were made with critical bulk density based on the least limiting water range (BDc LLWR) and on observed root and/or yield restriction in the field (BDc Rest). Using vertical uniaxial compression with a load of 200 kPa on disturbed or undisturbed samples generates low BD ref and high DC-values. The standard Proctor test generates higher BD ref -values, which are similar to those in a uniaxial test with a load of 1600 kPa for soils with low clay content but lower for soils with high clay content. The BDc LLWR does not necessarily restrict root growth or crop yield under no-tillage, since field investigations led to higher BDc Rest-values. A uniaxial load greater than 800 kPa is promising to determine BD ref for no-tillage soils. The BD ref is highly correlated to the clay content and thus pedotransfer functions may be established to estimate the former based on the latter. Soil ecological properties are affected before compaction restricts plant growth and yield. The DC is an efficient parameter to identify soil compaction affecting crops. The effect of compaction on ecological properties must also be further considered.

Effects of conservation agriculture techniques on infiltration and soil water content in Zambia and Zimbabwe

Abstract: The adoption of conservation agriculture (CA), based on minimal soil movement, permanent soil cover with crop residues or growing plants and crop rotation has advanced rapidly in the Americas and Australia over the last three decades. One of the immediate benefits of CA in dryland agriculture is improved rainfall-use efficiency through increased water infiltration and decreased evaporation from the soil surface, with associated decreases in runoff and soil erosion. This paper focuses on the effect of CA techniques on soil moisture relations in two researcher-managed trials in Zambia and Zimbabwe. In 2005/2006 and 2006/2007, we found significantly higher water infiltration on both sites on CA fields compared to conventionally ploughed fields. At Henderson Research Station, Zimbabwe, on a sandy soil, a direct seeded CA treatments had a 49% and 45% greater infiltration rate than the conventionally tilled plots after a simulated rainfall in both seasons. At Monze Farmer Training Centre, Zambia, on a finertextured soil, the same treatment had 57% and 87% greater infiltration rate than the conventionally tilled control treatment in both seasons. Treatments that included reduced tillage and surface residue retention had less water runoff and erosion on runoff plots at Henderson Research Station, Zimbabwe. On average, soil moisture was higher throughout the season in most CA treatments than in the conventionally tilled plots. However, the full potential of CA in mitigating drought was not evident as there was no significant drought period in either season. Results suggest that CA has the potential to increase the productivity of rainfall water and therefore reduce the risk of crop failure, as was apparent at the Monze Farmer Training Centre, Zambia, in 2005/2006 when a period of moisture stress at tassling affected CA treatments less than the conventionally tilled treatment.

Effects of 11 years of conservation tillage on soil organic matter fractions in wheat monoculture in Loess Plateau of China

Abstract: The Loess Plateau in northwest China is one of the most eroded landscapes in the world, and it is urgent that alternative practices be evaluated to control soil erosion. Our objective was to determine how three different tillage practices for monoculture of winter wheat ( Triticum aestivum L.) affected soil organic carbon (SOC) and N content after 11 years. Conventional tillage with residue removal (CT), shallow tillage with residue cover (ST), and no-tillage with residue cover (NT) were investigated. Carbon and N in various aggregate-size classes and various labile organic C fractions in the 0–15- and 15–30-cm soil layers were evaluated. The ST and NT treatments had 14.2 and 13.7% higher SOC stocks and 14.1 and 3.7% higher total N (N t ) stocks than CT in the upper 15 cm, respectively. Labile C fractions: particulate organic C (POC), permanganate oxidizable C (KMnO 4 -C), hot-water extractable C (HWC), microbial biomass C (MBC) and dissolved organic C (DOC) were all significantly higher in NT and ST than in CT in the upper 15 cm. KMnO 4 -C, POC and HWC were the most sensitive fractions to tillage changes. The portion of 0.25–2 mm aggregates, mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates from ST and NT treatments were larger than from CT at both 0–15- and 15–30-cm soil depths. The ST and NT treatments had significantly higher SOC and N t in the 0.25–2 mm fraction at both depths and significantly higher N t content in the upper 15 cm. Positive significant correlations were observed between SOC, labile organic C fractions, MWD, GMD, and macroaggregate (0.25–2 mm) C within the upper 15 cm. We conclude that both variants of conservation tillage (NT and ST) increase SOC stock in the rainfed farming areas of northern China and are therefore more sustainable practices than those currently being used.

Conservation farming strategies in East and Southern Africa: yields and rain water productivity from on-farm action research.

Abstract: Improved agricultural productivity using conservation farming (CF) systems based on non-inversion tillage methods, have predominantly originated from farming systems in sub-humid to humid regions where water is not a key limiting factor for crop growth. This paper presents evidence of increased yields and improved water productivity using conservation farming in semi-arid and dry sub-humid locations in Ethiopia, Kenya, Tanzania and Zambia. Results are based on on-farm farmer and research managed experiments during the period 1999–2003. Grain yield of maize (Zea mays L.) and tef (Eragrostis Tef (Zucc)) from conventional (inversion) tillage are compared with CF with and without fertilizer. Rain water productivity (WPrain) is assessed for the locations, treatments and seasons. Results indicate significantly higher yields (p

Evaluation of precision land leveling and double zero-till systems in the rice–wheat rotation: Water use, productivity, profitability and soil physical properties

Abstract: In recent years conventional production technologies in the rice–wheat (RW) system have been leading to deterioration of soil health and declining farm profitability due to high inputs of water and labour Conservation agriculture (CA)-based resource-conserving technologies (RCTs) vis-a-vis zero-till (ZT), raised-bed planting and direct-seeded rice (DSR) have shown promise as alternatives to conventional production technologies to overcome these problems The integration of CA-based RCTs with precision agriculture (PA)-based technologies in a systems perspective could provide a better option for sustainable RW production systems In this study we attempted to evaluate conservation and precision agriculture (CPA)-based RCTs as a double-ZT system integrated with laser-assisted precision land leveling (PLL) in the RW system A field experiment was conducted in the western IGP for 2 years to evaluate various tillage and crop establishment methods under PLL and traditional land leveling (TLL) practices to improve water productivity, economic profitability and soil physical quality Irrespective of tillage and crop establishment methods (TCE), PLL improved RW system productivity by 74% in year 2 as compared to traditional land leveling Total irrigation water savings under PLL versus TLL were 12–14% in rice and 10–13% in wheat PLL improved RW system profitability by US$113 ha −1 (year 1) to $175 ha −1 (year 2) Yields were higher in conventionally transplanted rice followed by direct-drill-seeded rice after ZT In wheat, yields were higher in ZT when followed by DSR than in the conventional-till (CT) system RW system productivity under double ZT was equivalent to that of the conventional method Among different TCE, conventional puddled-transplanted rice-CT wheat required 12–33% more water than other TCE techniques Compared with CT systems, double ZT consumed 12–20% less water with almost equal system productivity and demonstrated higher water productivity The CT system had higher bulk density and penetration resistance in 10–15 and 15–20 cm soil layers due to compaction caused by the repeated wet tillage in rice The steady-state infiltration rate and soil aggregation (>025 mm) were higher under permanent beds and double ZT and lower in the CT system Under CT, soil aggregation was static across seasons, whereas it improved under double no-till and permanent beds Similarly, mean weight diameter of aggregates was higher under double ZT and permanent beds and increased over time The study reveals that to sustain the RW system, CPA-based RCTs could be more viable options: however, the long-term effects of these alternative technologies need to be studied under varying agro-ecologies

Long-term tillage effects on soil carbon storage and carbon dioxide emissions in continuous corn cropping system from an alfisol in Ohio.

Abstract: The experiment designed to quantify the effects of long-term tillage practices on soil organic carbon (SOC) storage and CO2 emissions, was conducted on long-term tillage and continuous corn (Zea mays L.). The experimental plots were established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. It consisted of moldboard plow till (MT) chisel till (CT), and no-till (NT) laid out in a randomized block design with four replications. After 43 yrs of continuous corn, the pool of SOC in the top 30 cm depth was significantly greater under NT (80.0 ± 3.7 Mg C ha−1) than under CT (45.3 ± 1.7 Mg C ha−1) and MT (44.8 ± 3.7 Mg C ha−1). A large proportion (68–74%) of SOC, in the 0–30 cm depth originated from corn residues (C4-C). On average, MT, CT and NT treatments sequestered C4-C in the top 30 cm at a rate of 0.73, 0.71 and 1.37 Mg ha−1 yr−1. The average daily CO2 fluxes (g CO2-C m−2 d−1) were greater under MT (2.14) and CT (2.07) than under NT (1.61). In addition, the daily CO2 fluxes were highest in summer (2.62–3.77 g CO2-C m−2 d−1), the lowest in winter (0.75–0.87 g CO2-C m−2 d−1), and were positively correlated with air (R2 = 0.78, P < 0.01) and soil temperatures in the top 20 cm (R2 = 0.76, P < 0.01) and negatively with soil water content (R2 = 0.57, P < 0.05). Tillage management had a significant influence on average daily CO2 fluxes during summer and autumn but not during winter and spring. Annual CO2 emissions calculated by extrapolating daily CO2 fluxes were significantly higher under MT (6.6 ± 0.3 Mg CO2-C ha−1 yr−1) and CT (6.2 ± 0.4 Mg CO2-C ha−1 yr−1) than under NT (5.5 ± 0.5 Mg CO2-C ha−1 yr−1; LSD = 0.25 Mg CO2-C ha−1 yr−1). These results indicated that, during the growing season, NT reduced CO2 emissions by an average of 0.7 and 0.6 Mg C ha−1 yr−1 compared to MT and CT, respectively.

Nitrous oxide and methane emissions from long-term tillage under a continuous corn cropping system in Ohio

Abstract: Nitrous oxide (N 2 O) and methane (CH 4 ) emitted by anthropogenic activities have been linked to the observed and predicted climate change. Conservation tillage practices such as no-tillage (NT) have potential to increase C sequestration in agricultural soils but patterns of N 2 O and CH 4 emissions associated with NT practices are variable. Thus, the objective of this study was to evaluate the effects of tillage practices on N 2 O and CH 4 emissions in long-term continuous corn ( Zea mays ) plots. The study was conducted on continuous corn experimental plots established in 1962 on a Crosby silt loam (fine, mixed, mesic Aeric Ochraqualf) in Ohio. The experimental design consisted of NT, chisel till (CT) and moldboard plow till (MT) treatments arranged in a randomized block design with four replications. The N 2 O and CH 4 fluxes were measured for 1-year at 2-week intervals during growing season and at 4-week intervals during the off season. Long-term NT practice significantly decreased soil bulk density ( ρ b ) and increased total N concentration of the 0–15 cm layer compared to MT and CT. Generally, NT treatment contained higher soil moisture contents and lower soil temperatures in the surface soil than CT and MT during summer, spring and autumn. Average daily fluxes and annual N 2 O emissions were more in MT (0.67 mg m −2 d −1 and 1.82 kg N ha −1 year −1 ) and CT (0.74 mg m −2 d −1 and 1.96 kg N ha −1 year −1 ) than NT (0.29 mg m −2 d −1 and 0.94 kg N ha −1 year −1 ). On average, NT was a sink for CH 4 , oxidizing 0.32 kg CH 4 -C ha −1 year −1 , while MT and CT were sources of CH 4 emitting 2.76 and 2.27 kg CH 4 -C ha −1 year −1 , respectively. Lower N 2 O emission and increased CH 4 oxidation in the NT practice are attributed to decrease in surface ρ b , suggesting increased gaseous exchange. The N 2 O flux was strongly correlated with precipitation, air and soil temperatures, but not with gravimetric moisture content. Data from this study suggested that adoption of long-term NT under continuous corn cropping system in the U.S. Corn Belt region may reduce GWP associated with N 2 O and CH 4 emissions by approximately 50% compared to MT and CT management.

Soil restoration using composted plant residues: Effects on soil properties

Abstract: Organic soil amendments are increasingly being examined for their potential for soil restoration. In this paper, different composted plant residues consisting of leguminous (red clover, Trifolium pratense L.) (TP) and non-leguminous (rapeseed, Brassica napus L.) (BN) plants and the combination of both plant residues (red clover + rapeseed, Trifolium pratense L. + Brassica napus L. at a ratio 1:1) (TP + BN) were applied during a period of 4 years for restoring a Xelloric Calciorthid soil located near Seville (Guadalquivir Valley, Andalusia, Spain). The effect of the organic soil amendments on plant cover, soil physical (structural stability, bulk density), chemical (C/N ratio), and biological properties (microbial biomass, soil respiration and enzymatic activities (dehydrogenase, urease, β-glucosidase, phosphatase and arylsulfatase activities)) were determined. Organic amendments were applied at rate of 7.2 and 14.4 t organic matter ha −1 . All composted plant residues had a positive effect on soil physical properties. At the end of the experimental period and at the high rate, soil structural stability was highest in the BN (28.3%) treatment, followed by the TP + BN (22.4%) and the TP (14.5%) treatments and then the control. Soil bulk density was higher in the BN (30.9%), followed by TP + BN (26.2%) and TP (16.1%) treatments with respect to the control. However, soil biological properties (biomass C and the enzymatic activities) were particularly improved by the TP + BN treatment, followed by TP, BN and the control. After 4 years, the percentage of plant cover increased 87.2% in the TP + BN amended soil with respect to the control, followed by TP (84.1%) and BN (83.8%). These differences were attributed to the different chemical composition of the composts applied to the soils and their mineralization, controlled by the soil C/N ratio. The application of TP + BN compost with a C/N ratio of 18, resulted a more favourable soil biological properties and plant cover than the application of TP (C/N ratio = 8.8) and BN (C/N ratio = 47.7) composts.

Effects of mulching and catch cropping on soil temperature, soil moisture and wheat yield on the Loess Plateau of China

Abstract: Soil management can notably influence crop production under dryland farming in semiarid areas. Field experiments were conducted, from October 2001 to September 2004, with an attempt to evaluate the effects of field management regimes on thermal status at an upland site; and soil water and wheat production in a winter wheat (Triticum aestivum L.) system at upland, terrace land and bottom land sites on the Loess Plateau, China. The field management regimes tested were: (i) the conventional practice (winter wheat followed by a ploughed summer bare fallow); (ii) conventional management, but a catch crop growing for certain time during fallow period used as green manure (after the wheat harvest, a catch crop were directly sown, instead of ploughing, and then incorporated into the soil roughly one month before wheat sowing); and (iii) wheat straw mulch (0.8 kg m−2), covering the soil throughout the year during the experimental period (no summer ploughing, straw was removed during wheat sowing). Soil temperature under catch cropping was lower during certain period of its growing by about 2 °C, slightly higher for short spells after incorporation and before wheat harvest, no observed effects during the rest time of a year relative to conventional practice at the upland site. Moreover, soil water storage levels under catch cropping were comparable with those of the conventional practice for all three years, but wheat yield substantially declined in the last year. Mulching showed different responses for the three land sites. At the upland site, daily mean soil temperatures under mulching at 10 cm depth were decreased in the warmer period by 0–4 °C, and increased in the colder period by 0–2 °C when compared to those of non-mulched soil. At upland and bottom land sites, mulching conserved an average of 28 and 20 mm more water in the upper 100 cm soil layer at the time of wheat sowing, respectively, than conventional practice. However, at the terrace, mulching had little effect on soil water storage, nor on wheat grain yield, relative to conventional practice. Therefore, considering the limited availability of mulch material in this region and the economic benefits, it is recommended that mulching may be beneficial to upland or bottom land, but not to terraced land. In addition, the application of catch cropping in this study did not show positive effects, the more comprehensive evaluation of this approach would be further needed.

Soil management effects on runoff, erosion and soil properties in an olive grove of Southern Spain

Abstract: Rainfall, runoff and soil loss from 6 m × 12 m plots were recorded during 7 years (2000–2006) in an experiment in which three different soil management systems were compared in a young olive grove installed on a heavy clay soil, near Cordoba, Southern Spain. The no-tillage (NT) system, kept weed-free with herbicides, had both the largest soil loss (6.9 t ha−1 year−1) and the highest average annual runoff coefficient (11.9%). By contrast, a cover crop (CC) of barley, reduced the soil losses to 0.8 t ha−1 year−1 and the average annual runoff coefficient to 1.2%. Conventional tillage (CT), had intermediate values of soil loss (2.9 t ha−1 year−1) and an average runoff coefficient of 3.1%. The different treatments were established 4 years after planting the olive trees, and a significant decrease in soil and runoff losses was observed with time as the olive trees grew and their canopies developed. Measurements at the end of the experiment showed a significant improvement in the topsoil properties of the CC treatment as compared to CT and NT. The soil under NT presented a significant degradation with respect to traditional CT management. Organic matter values were 2.0, 1.4 and 1.0%, and stability in water of macroaggregates was 0.452, 0.418 and 0.258 kg kg−1 for CC, CT and NT, respectively. These results indicate that the use of a cover crop can be a simple, feasible soil and water conservation practice in olive groves on rolling lands in the region. A key factor in its practical use is to establish it early enough to protect the soil in the critical initial years of the grove, when most of the soil is unprotected by the small olive canopy.

Stratification ratio of soil organic matter pools as an indicator of carbon sequestration in a tillage chronosequence on a Brazilian Oxisol

Abstract: Long-term no-tillage (NT) leads to profile stratification of soil organic matter (SOM) pools, and the soil organic carbon (SOC) stratification ratio (SR) is an indicator of soil quality. The objective of this report is to assess the feasibility of using SOC-SR as an index for estimating SOC sequestration in NT soils. The effect of a plow tillage (PT) and NT chronosequence on the SR of SOM pools was assessed in an Oxisol in Southern Brazil (50°23′W and 24°36′S). The chronosequence consisted of six sites: (i) native field (NF); (ii) PT of the native field (PNF-1) involving conversion of natural vegetation to cropland; (iii) NT for 10 years (NT-10); (iv) NT for 20 years (NT-20); (v) NT for 22 years (NT-22); (vi) conventional tillage for 22 years (CT-22). Soil samples were collected from four depths (0–5 cm; 5–10 cm; 10–20 cm; 20–40 cm layer) and soil parameters comprised by SOM pools [i.e., C, N, S, particulate organic C (POC), particulate N (PN), stable C (SC) and stable N (SN), microbial biomass C (MBC) and microbial biomass N (MBN), basal respiration (BR), dissolved organic C (DOC), total polysaccharides (TP) and labile polysaccharides (LP)] were measured. In undisturbed NF soil, the SR of all parameters increased with increase in soil depth. In contrast, the SR decreased in PT, and the SOM was uniformly distributed in the soil profile. All NT treatments restored the SR, and were characterized with higher values of all measured parameters compared to NF. The SR for SOC ranged from 1.12 to 1.51 for CT-22 compared with 1.64–2.61 SR for NT surface and sub-soil layers, respectively. The SR for POC and PN were higher than those for stable C and N. However, SR for the biological pools (e.g., MBC, MBN and BR) were the highest and strongly correlated with the rate of SOC sequestration. An increase in SR of SOC was also positively correlated with the rate and amount of SOC sequestered. Regression analyses indicated a strong correlation between SR of SOC and all parameters monitored in this study. The data showed that the SR of SOC is an efficient indicator of C sequestration in long-term NT management.

Conservation agriculture as a sustainable option for the central Mexican highlands

Abstract: Tropical highlands of the world are densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen all over this agro-ecological zone. Based on selected soil quality indicators, i.e. time-to-pond, aggregate distribution and stability (expressed as the mean weight diameter (MWD) for dry and wet sieving, respectively) and soil moisture, from a representative long-term sustainability trial initiated in 1991 in Central Mexico (2240 masl; 19.31°N, 98.50°W; Cumulic Phaeozem), some insights into the feasibility of conservation agriculture (CA) as part of a sustainable production system in the tropical highlands are given. Zero tillage plots with crop residue removal showed low aggregate distribution (average MWD = 1.34 mm) and stability (average MWD = 0.99 mm) resulting in top layer slaking, increased erosion and low time-to-pond values. Retaining the residue in the field with zero tillage avoided the above-mentioned negative evolution for both aggregate distribution as stability (average MWD = 2.77 and 1.51 mm, respectively) and even improved the physical conditions of the soil as compared to conventional practice. Throughout the growing season the lowest soil moisture content was found in zero tillage without residue (average over the entire growing season = 20.5% volumetric moisture content), the highest in zero tillage with residue retention (average = 29.7%) while conventional tillage had intermediate soil moisture values (average = 27.4%). Zero tillage without residue retention had most days of soil moisture values under permanent wilting point, while zero tillage with residue retention had the least. Taking into account these results, zero tillage with residue retention can clearly be a part of an integrated watershed management scheme towards sustainable agriculture in the tropical highlands. It is clear that to develop new management practices to improve water use, reduce erosion and enhance human labor/animal power focus must be on the use of conservation agriculture both for rainfed as well as irrigated production systems and be fine tuned for each system.

Effects of agricultural management on surface soil properties and soil–water losses in eastern Spain

Abstract: In Spain, agriculture triggers soil degradation and erosion processes. New strategies have to be developed to reduce soil losses and recover or maintain soil functionality in order to achieve a sustainable agriculture. An experiment was designed to evaluate the effect of different agricultural management on soil properties and soil erosion. Five different treatments (ploughing, herbicide, control, straw mulch and chipped pruned branches) were established in “El Teularet experimental station” located in the Sierra de Enguera (Valencia, Spain). Soil sampling was conducted prior to treatment establishment, and again after 16 months, to determine soil organic matter content (OM), aggregate stability (AS), and microbial biomass carbon content (C mic ). Fifty rainfall simulations tests (55 mm during one hour, 5-year return period) were applied to measure soil and water losses under each treatment. The highest values of OM, AS and C mic were observed in the straw-covered plot, where soil and water losses were negligible. On the contrary, the plot treated with herbicides had the highest soil losses and a slight reduction in C mic . Soil erosion control was effective after 16 months on the plots where vegetation was present while on the ploughed and herbicide-treated plots, the practices were not sustainable due to large water and soil losses. Except for the straw mulch plot, soil properties (OM, AS, C mic ) were not enhanced by the new land managements, but soil erosion control was achieved on three of the five plots used (weeds, weeds plus straw and weeds plus chipped pruned branches). Erosion control strategies such as weeds, weeds plus straw mulch and weeds plus chipped branches mulch are highly efficient in reducing soil losses on traditional herbicide-treated and ploughed agricultural land. However, it takes longer to recover other soil properties such as OM, AS, and C mic .

Changes of soil enzyme activities under different tillage practices in the Chinese Loess Plateau

Abstract: The effects of middle term (7 years) consistent tillage practices on the catalase (CAT), urease (URE) and invertase (INV) activities were investigated during the whole winter wheat growing period on a loess soil in Luoyang (east edge of the Chinese Loess Plateau, Henan province, China). Field plots, set up in 1999, included following tillage practices: subsoiling with mulch (SS), no-till with mulch (NT), reduced tillage (RT), and a conventional control (CT). A clear redistribution of soil organic carbon (SOC) and total nitrogen (TN) was found along the slope in RT and CT, however, no difference was observed between studied enzyme activities along different slope positions. SS had higher winter wheat yield than other treatments, which was attributed to the increased soil water content and improvement of soil fertility. Changes in soil temperature and soil moisture content influenced the magnitude of the enzyme activities, but not the ranking of the different treatments during most of the season. SS consistently had higher enzyme activities compared to other treatments. This indicated that seasonal fluctuations did not obscure effects associated with soil tillage practices and enzyme activities could reflect the effects of conversion of soil tillage practices on soil quality. Time within the growing season had a clear impact upon the enzyme activities. Comparatively higher enzyme activities were observed in the stages with vigorous vegetative growth of winter wheat than in stages with productive growth.

Short-term effects of tillage and manure on some soil physical properties and maize root growth in a sandy loam soil in western Iran.

Abstract: Careful soil management is the key to sustainable agricultural production. Tillage practices are critical components of soil management systems which significantly affect soil characteristics and plant development. There is little information concerning the combined impacts of tillage systems and manure application on soils and root development in the western part of Iran. A study was conducted to investigate short-term changes of soil bulk density (BD), soil cone index (CI) and maize (Zea mays L.) root length density (RLD) under different management regimes. The study was carried out on a sandy loam soil (fine loamy, mixed, mesic Calcixerollic Xerochrepts, USDA). The effects of three tillage systems (no-till, NT; chisel plow, CP; and moldboard plow, MP) at three composted cattle manure rates: 0 (M0), 30 (M30), and 60 Mg (dry weight) ha ―1 (M60), were studied on BD, Cl and RLD. The experiment was carried out in a split-plot design with tillage as the main plot and manure application as the sub-plot. Three replicates of the treatments were applied in a randomized block design. The soil and root samplings were done when 100% of the tassels appeared. Tillage methods and manure applications had significant effects on RLD in the upper soil layers. Tillage affected RLD in the order of MP > CP > NP and manure effects on RLD were in the order of M60 > M30 > M0. The effects were not significant for the lower soil layers. The MP system had higher values of RLD with lower values of both Cl and BD. The NT system resulted in lower RLD and higher CI and BD values. The increased BD and Cl of the topsoil in the NT treatment restricted root growth. The mean BD values (average of all soil layers and manure treatments) were 1.43, 1.37 and 1.26 Mg m ―3 for NT, CP and MP, respectively. Adding manure to the soil significantly increased RLD in the order: M60 > M30 > M0. There were also significant differences in CI and BD among manure treatments. The mean CI values (average of all soil layers and tillage systems) were 1.43, 1.22 and 1.06 MPa for M0, M30 and M60, respectively. The positive diminishing effects on CI and BD of manure applications may be attributable to manure incorporation and improvement of the physical quality of the soil with low organic carbon content. The significant overall relation between RLD and CI demonstrated the dominant effect of soil mechanical impedance on root growth. The manure application seems to be able to compensate to a significant degree for the increased mechanical impedance with no-till. The results indicate short-term beneficial effects of manure application on maize root length density as well as on soil physical properties when combined with the tillage systems.

The influence of cover crops and tillage on water and sediment yield, and on nutrient, and organic matter losses in an olive orchard on a sandy loam soil

Abstract: Is the cover crop practice suitable for soil and water conservation in olive tree cropping? Rainfall, runoff, sediments, nutrient and organic carbon losses from 8 x 60 m plots were measured during four hydrological years (2002-2007) in a field trial, in which two different soil management systems were used to confirm this hypothesis: a cover crop (CC), and conventional tillage (CT). The plots were located in a private olive tree farm on a sandy-loam soil, near Seville, southern Spain. The cover crop, as compared to conventional tillage, efficiently reduced runoff and sediment yield down to tolerable levels, 5.68% of the rainfall being converted to runoff, and the soil loss reaching 0.04 kg m ―2 year ―1 , as the average of four years. Additionally, in the cover crop treatment, the values of the nutrient export either dissolved in the runoff water or adsorbed in the sediment, were lower than the analogous values of the conventional tillage treatment: 0.631 and 0.065 kg m- 2 year ―1 of organic carbon and nitrogen, respectively, 0.175 and 0.0333 kg m ―2 year ―1 of soluble K and P, respectively, and 0.010 and 0.002 kg m ―2 year ―1 of available K and P, respectively. The adoption of a cover crop as a soil management practice can be a feasible way to reach sustainability in many olive-cropped soils of southern Spain, although this method is not always easy to implement due to technical problems such as seed selection, its maintenance, and the choice of the correct killing date to avoid water competition. These difficulties could explain the slow rate of its adoption by many farmers. Further exploration of these aspects is required, as well as a specific agricultural extension campaign.

Soil aggregation and distribution of carbon and nitrogen in different fractions under long-term application of compost in rice–wheat system

Abstract: Soil organic matter improves the physical, chemical and biological properties of soil, and crop residue recycling is an important factor influencing soil organic matter levels. We studied the impact of continuous application of rice straw compost either alone or in conjunction with inorganic fertilizers on aggregate stability and distribution of carbon (C) and nitrogen (N) in different aggregate fractions after 10 cycles of rice–wheat cropping on a sandy loam soil at Punjab Agricultural University research farm, Ludhiana, India. Changes in water stable aggregates (WSA), mean weight diameter (MWD), aggregate-associated C and N, total soil C and N, relative to control and inorganically fertilized soil were measured. Total WSA were significantly ( p = 0.05) higher for soils when rice straw compost either alone or in combination with inorganic fertilizers was applied as compared to control. The application of rice straw compost either alone or in combination with inorganic fertilizers increased the macroaggregate size fractions except for 0.25–0.50 mm fraction. The MWD was significantly ( p = 0.05) higher in plots receiving rice straw compost either alone at 8 tonnes ha −1 (0.51 mm at wheat harvest and 0.41 mm at rice harvest) or at 2 tonnes ha −1 in combination with inorganic fertilizers (0.43 and 0.38 mm) as compared to control (0.34 and 0.33 mm) or inorganically fertilized plots (0.33 and 0.31 mm). The macroaggregates had higher C and N density compared to microaggregates. Application of rice straw compost at 2 tonnes ha −1 along with inorganic fertilizers (IN + 2RSC) increased C and N concentration significantly over control. The C and N concentration increased further when rice straw compost at 8 tonnes ha −1 (8RSC) was added. It is concluded that soils can be rehabilitated and can sustain the soil C and N levels with the continuous application of rice straw compost either alone or in combination with inorganic fertilizers. This will also help in controlling the rising levels of atmospheric carbon dioxide.

No-tillage improvement of soil physical quality in calcareous, degradation-prone, semiarid soils

Abstract: Many soils in the semiarid Mediterranean Ebro Valley of Spain are prone to physical and chemical degradation due to their silty texture, low organic matter content, and presence of carbonates, gypsum or other soluble salts. Rainfed agriculture on these soils is also hindered by the scarcity of water. No-tillage can increase plant-available water and soil organic matter, thus helping overcome most factors limiting crop production in this area. Our objective was to determine how conventional- and no-tillage practices affected soil physical quality indicators and water availability in an on-farm study in the Ebro Valley. Soil samples were collected from 0 to 5-, 5 to 15-, and 15 to 30-cm depth increments within adjacent farmer-managed conventional- and no-tillage fields in 2007 and 2008. Both fields were managed for continuous barley (Hordeum vulgare L.) production. The soil at both sites is a silt loam (Haplic Calcisol). Aggregate-size distribution and stability, soil water retention characteristics, organic carbon, and total carbonates were determined in 2007. Pore-size distribution was estimated from the water retention curve. Penetration resistance, soil bulk density and field water content during the entire crop growing season were measured for both fields in 2008. Aggregate dry mean weight diameter and stability in water were 1.2 and 2.2 times greater, respectively, under no-tillage than conventional tillage due to reduced mechanical disturbance and increased soil organic carbon content. Bulk density was 1.12 times greater (P < 0.1) under no-tillage only in the 0–5-cm depth. Two times greater penetration resistance to a depth of 15 cm in this treatment was related to bulk density and aggregates stability. Field water content was greater with no-tillage than conventional tillage during the driest months in 2008. The volume of equivalent diameter pores (0.2–9 μm) was 1.5 times higher under no-tillage. This increased plant-available water content and doubled barley production under no-tillage in 2008, which was a very dry year. We conclude that despite the greater penetration resistance under no-tillage, increased water availability as a result of improved structure characteristics was more important for crop yield. This suggests that producers should seriously consider adopting no-tillage practices for soil conservation in semiarid degraded areas like the one studied.

Soil quality impacts of residue removal for bioethanol production

Abstract: Global energy demand of 424 EJ year −1 in 2000 is increasing at the rate of 2.2% year −1 . There is a strong need to increase biofuel production because of the rising energy costs and the risks of global warming caused by fossil fuel combustion. Biofuels, being C-neutral and renewable energy sources, are an important alternative to fossil fuels. Therefore, identification of viable sources of biofuel feedstock is a high priority. Harvesting lignocellulosic crop residues, especially of cereal crops, is being considered by industry as one of the sources of biofuel feedstocks. Annual production of lignocellulosic residues of cereals is estimated at 367 million Mg year −1 (75% of the total) for the U.S., and 2800 million Mg year −1 (74.6% of the total) for the world. The energy value of the residue is 16 × 10 6 BTU Mg −1 . However, harvesting crop residues would have strong adverse impact on soil quality. Returning crop residues to soil as amendments is essential to: (a) recycling plant nutrients (20–60 kg of N, P, K, Ca per Mg of crop residues) amounting to 118 million Mg of N, P, K in residues produced annually in the world (83.5% of world's fertilizer consumption), (b) sequestering soil C at the rate of 100–1000 kg C ha −1 year −1 depending on soil type and climate with a total potential of 0.6–1.2 Pg C year −1 in world soils, (c) improving soil structure, water retention and transmission properties, (d) enhancing activity and species diversity of soil fauna, (e) improving water infiltration rate, (f) controlling water runoff and minimizing risks of erosion by water and wind, (g) conserving water in the root zone, and (h) sustaining agronomic productivity by decreasing losses and increasing use efficiency of inputs. Thus, harvesting crop residues as biofuel feedstock would jeopardize soil and water resources which are already under great stress. Biofuel feedstock must be produced through biofuel plantations established on specifically identified soils which do not compete with those dedicated to food crop production. Biofuel plantations, comprising of warm season grasses (e.g., switch grass), short rotation woody perennials (e.g., poplar) and herbaceous species (e.g., miscanthus) must be established on agriculturally surplus/marginal soils or degraded/desertified soils. Plantations established on such soils would restore degraded ecosystems, enhance soil/terrestrial C pool, improve water resources and produce biofuel feedstocks.

Conservation tillage: Short- and long-term effects on soil carbon fractions and enzymatic activities under Mediterranean conditions

Abstract: Short- and long-term field experiments are necessary to provide important information about how soil carbon sequestration is affected by soil tillage system; such systems can also be useful for developing sustainable crop production systems. In this study, we evaluated the short- and long-term effects of conservation tillage (CT) on soil organic carbon fractions and biological properties in a sandy clay loam soil. Both trials consisted of rainfed crop rotation systems (cereal–sunflower–legumes) located in semi-arid SW Spain. In both trials, results were compared to those obtained using traditional tillage (TT). Soil samples were taken in flowering and after harvesting of a pea crop and collected at three depths (0–5, 5–10 and 10–20 cm). The soil organic carbon fractions were measured by the determination of total organic carbon (TOC), active carbon (AC) and water soluble carbon (WSC). Biological status was evaluated by the measurement of soil microbial biomass carbon (MBC) and enzymatic activities [dehydrogenase activity (DHA), o -diphenol oxidase activity (DphOx), and β-glucosidase activity (β-glu)]. The contents of AC and MBC in the long-term trial and contents of AC in the short-term trial were higher for CT than TT at 0–5 cm depth for both sampling periods. Furthermore, DHA and β-glucosidase values in the July sampling were higher in the topsoil under conservation management in both trials (short- and long-term). The parameters studied tended to decrease as depth increased for both tillage system (TT and CT) and in both trials with the exception of the DphOx values, which tended to be higher at deeper layers. Values of DHA and β-glu presented high correlation coefficients ( r from 0.338 to 0.751, p ≤ 0.01) with AC, WSC and TOC values in the long-term trial. However, there was no correlation between either TOC or MBC and the other parameters in the short-term trial. In general, only stratification ratios of AC were higher in CT than in TT in both trials. The results of this study showed that AC content was the most sensitive and reliable indicator for assessing the impact of different soil management on soil quality in the two experiments (short- and long-term). Conservation management in dryland farming systems improved the quality of soil under our conditions, especially at the surface layers, by enhancing its storage of organic matter and its biological properties, mainly to long-term.

Greenhouse gas emission from direct seeding paddy field under different rice tillage systems in central China.

Abstract: Agricultural tillage practices play an important role in the production and/or consumption of green house gas (GHG) that contributes substantially to the observed global warming. Central China is one of the world's major rice producing areas but a few studies have tried to characterize the mechanisms of GHG release from rice paddy field and quantify global warming (GWPs) based on GHGs emission on this region. In this study four tillage systems consisting of no-tillage with no fertilizer (NT0), conventional tillage with no fertilizer (CT0), no-tillage with compound fertilizer (NTC) and conventional tillage with compound fertilizer (CTC) applications in rice ( Oryza sativa L.) cultivation were compared in terms of the carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) emissions from different tillage systems of the subtropical region of China during the rice growing season in 2008. GWPs based on CO 2 , CH 4 and N 2 O's cumulative emissions were also compared. Tillage and fertilization had no influence on CO 2 emissions. No-tillage had no effect on N 2 O emissions but significantly affected CH 4 emissions. Application of fertilizer significantly affected CH 4 and N 2 O emissions. Higher CH 4 emissions and lower N 2 O emissions were observed in CTC than in NTC. Cumulative CH 4 emission flux in NTC was 51.68 g CH 4 m −2 while it was 65.96 g CH 4 m −2 in CTC, 28% ( p 2 O emission flux in CTC was 561.00 mg N 2 O m −2 , and was 741.71 mg N 2 O m −2 in NTC, 33% ( p 2 O emissions between NT0 and CT0 systems, but significant in CH 4 emissions. GWP of CTC was 26011.58 kg CO 2 ha −1 , which was 12% higher than that in NTC (23361.3 kg CO 2 ha −1 ), therefore our findings show that no-tillage system was an effective strategy to reduce GWP from rice paddies in central China and thus can serve as a good agricultural system for environmental conservation.

Influence of crop residue management, cropping system and N fertilizer on soil N and C dynamics and sustainable wheat (Triticum aestivum L.) production

Abstract: Management of N is the key for sustainable and profitable wheat production in a low N soil. We report results of irrigated crop rotation experiment, conducted in the North West Frontier Province (NWFP), Pakistan, during 1999–2002 to evaluate effects of residue retention, fertilizer N application and mung bean (Vigna radiata) on crop and N yields of wheat and soil organic fertility in a mung bean–wheat sequence. Treatments were (a) crop residue retained (+residue) or (b) removed (� residue), (c) 120 kg N ha � 1 applied to wheat, (d) 160 kg N ha � 1 to maize or (e) no nitrogen applied. The cropping system was rotation of wheat with maize or wheat with mung bean. The experiment was laid out in a spit plot design. Postharvest incorporation of crop residues significantly (p < 0.05) increased the grain and straw yields of wheat during both years. On average, crop residues incorporation increased the wheat grain yield by 1.31 times and straw yield by 1.39 times. The wheat crop also responded strongly to the previous legume (mung bean) in terms of enhanced grain yield by 2.09 times and straw yield by 2.16 times over the previous cereal (maize) treatment. Application of fertilizer N to previous maize exerted strong carry over effect on grain (1.32 times) and straw yield (1.38 times) of the following wheat. Application of N fertilizer to current wheat produced on average 1.59 times more grain and 1.77 times more straw yield over the 0 N kg ha � 1 treatment. The N uptake in wheat grain and straw was increased 1.31 and 1.64 times by residues treatment, 2.08 and 2.49 times by mung bean and 1.71 and 1.86 times by fertilizer N applied to wheat, respectively. The soil mineral N was increased 1.23 times by residues, 1.34 times by mung bean and 2.49 times by the application of fertilizer N to wheat. Similarly, the soil organic C was increased 1.04-fold by residues, 1.08 times by mung bean and 1.00 times by the application of fertilizer N. We concluded that retention of residues, application of fertilizer N and involvement of legumes in crop rotation greatly improves the N economy of the cropping system and enhances crop productivity in low N soils.

Soil organic carbon sequestration in relation to organic and inorganic fertilization in rice–wheat and maize–wheat systems

Abstract: Soil organic carbon (SOC) pool is the largest among the terrestrial pools The restoration of SOC pool in arable lands represents a potential sink for atmospheric CO 2 The management and enhancement of SOC is important for sustainable agriculture The cropping system and soil type influence crop biomass under different fertilization Data from two long-term field experiments on rice–wheat and maize–wheat systems in progress since 1971, were analyzed to assess the impact of fertilization practices on SOC stocks in sandy loam soils (typic ustipsament) The treatments in rice–wheat included (i) farmyard manure (FYM alone @ 20 t ha −1 , applied at the time of pre-puddling tillage), (ii) N 120 P 30 K 30 (120 kg N, 30 kg P 2 O 5 and 30 kg K 2 O ha −1 ), (iii) N 120 P 30 (same as in (ii) except that K application was omitted), (iv) N 120 (same as in (ii) except that P and K application was omitted) and (v) control (without any FYM or inorganic fertilizer) Similar treatments were studied in maize–wheat except that the amounts of N, P 2 O 5 and K 2 O were 100, 50 and 50 kg ha −1 , respectively In rice–wheat system, the SOC concentration at different depths in 0–60 cm soil profile was higher (18–62 g kg −1 ) in FYM-treated plots followed by 17–53 g kg −1 in NPK plots, compared to 09–30 g kg −1 in unfertilized plots Balanced fertilization improved the SOC concentration Similar trend was found in maize–wheat system In the 60-cm soil profile the total SOC stocks in both the cropping systems were highest in FYM (313 and 233 Mg ha −1 in rice–wheat and maize–wheat system) followed by balanced fertilization (296 and 213 Mg ha −1 ) and lowest in unfertilized control (214 and 187 Mg ha −1 ) The SOC concentration in rice–wheat soils was 54 and 30% higher in FYM and NPK plots than in maize–wheat system Improved SOC content enhances soil quality, reduces soil erosion and degradation, and increases soil The soils under rice–wheat sequestered 55% higher SOC in FYM plots and 70% higher in NPK plots than in maize–wheat These results document the capacity of optimally fertilized rice–wheat system to sequester higher C as compared to maize–wheat system

Influence of soil tillage systems on aggregate stability and the distribution of C and N in different aggregate fractions

Abstract: Soil aggregation is influenced by the tillage system used, which in turn affects the amount of C and N in the different aggregate fractions. This study assessed the impact of different tillage systems on soil aggregates by measuring the aggregate stability, the organic carbon (C org ) and the total nitrogen (N tot ) contents within different aggregate fractions, and their release of dissolved organic carbon (DOC). Soil samples were collected from the top 0 to 10 cm of a long-term tillage experiment at Fuchsenbigl (Marchfeld, Austria) where conventional tillage (CT), reduced tillage (RT), and minimum tillage (MT) treatments were applied to a Chernozem fine sandy loam. The stable aggregates (1000–2000 μm) were subject to dispersion by the soil aggregate stability (SAS or wet sieving) method after Kemper and Rosenau (1986), and the ultrasonic method of Mayer et al. (2002). Chemical analysis of the soil was obtained for the aggregate fractions 630–1000, 250–630 and 63–250 μm gathered from the ultrasonic method. Using the SAS method, CT and RT had the least amounts of stable aggregates (18.2% and 18.9%, respectively), whereas MT had twice as much stable aggregates (37.6%). Using the ultrasonic method, MT also had the highest amount of water stable aggregates in all three fractions (1.5%, 3.7%, and 35%, respectively), followed by RT (1%, 2.3%, 32.3%), and CT (0.8%, 1.7%, 29.1%). For comparison, a reference soil, EUROSOIL 7 (ES-7) was also analysed (40%, 6.7%, and 12.1%). The highest amounts of C org and N tot were measured under MT in all three fractions, with 8.9%, 3.8%, and 1.3% for C org , and 0.4%, 0.3%, and 0.1% for N tot . Apart from the fraction 630–1000 μm, the aggregates of RT and CT contained org and N tot values of MT. The C/N ratio was least favourable for CT (42.6) in the aggregate fraction 630–1000 μm. The DOC release from stable aggregates after 10 min of ultrasonic dispersion was highest from MT soil (86.7 mg l −1 ). The values for RT and CT were 21% and 25% below this value. The results demonstrate that tillage type influences both aggregate stability and aggregate chemical composition. This research confirms that CT interferes more with the natural soil properties than RT and MT. Furthermore, MT has the highest potential to sequester C and N in this agriculturally used soil.

Impact of reduced tillage on carbon and nitrogen storage of two Haplic Luvisols after 40 years

Abstract: It is broadly accepted that reduced tillage increases soil organic carbon (Corg) and total nitrogen (N) concentrations in arable soils. However, the underlying processes of sequestration are not completely understood. Thus, our objectives were to investigate the impact of a minimum tillage (MT) system (to 5–8 cm depth) on aggregates, on particulate organic matter (POM), and on storage of Corg and N in two loamy Haplic Luvisols in contrast to conventional tillage (CT) (to 25 cm). Surface soils (0–5 cm) and subsoils (10–20 cm) of two experimental fields near Gottingen, Germany, were investigated. Each site (Garte-Sud and Hohes Feld) received both tillage treatments for 37 and 40 years, respectively. In the bulk soil of both sites Corg, N, microbial carbon (Cmic), and microbial N (Nmic) concentrations were elevated under MT in both depths. Likewise, water-stable macroaggregates (>0.25 mm) were on average 2.6 times more abundant under MT than under CT but differences in the subsoils were generally not significant. For surface soils under MT, all aggregate size classes <1 mm showed approx. 35% and 50% increased Corg concentrations at Garte-Sud and Hohes Feld, respectively. For greater macroaggregates (1–2, 2–10 mm), however, differences were inconsistent. Elevations of N concentrations were regular over all size classes reaching 61% and 52%, respectively. Density fractionation of the surface soils revealed that tillage system affected neither the yields of free POM nor occluded POM nor their Corg and N concentrations. Moreover, more Corg and N (15–238%) was associated within the mineral fractions investigated under MT in contrast to CT. Overall, similar to no-tillage, a long-term MT treatment of soil enhanced the stability of macroaggregates and thus was able to physically protect and to store more organic matter (OM) in the surface soil. The increased storage of Corg and N did not occur as POM, as reported for no-tillage, but as mineral-associated OM.

Effect of land use and management on the early stages of soil water erosion in French Mediterranean vineyards

Abstract: The effect of changes in land use on the early stages of soil water erosion was studied on brown calcareous soils (Calcic Luvisols), a widespread type of soil suitable for wine-growing in the French Mediterranean area. This type of soil is subject to high intensity rainfall events. Rainfall of 60 mm/h was simulated on dry soil for several types of land use including scrubland, fallow and several wine-growing strategies (chemical and mechanical inter-row weeding, grassing, straw mulching, rock fragment cover and clearing rock fragments). No soil loss was observed for fallow and scrubland. The highest runoff rates and soil losses were observed for chemically weeded vineyards, with however, a reduction of soil losses when the prunings were left on the soil. Vineyards mulched with straw or with rock fragment cover were protected against runoff and soil erosion. As the grassing was recent, it was only partially effective, although several indicators showed that it might be promising in the future. A method of ranking the land uses in terms of protection against runoff and soil losses was derived from the experimental data. The statistical relationships between runoff, soil losses and various surface properties (soil cover including litter, weeds and rock fragments, crusts) and properties of the 0–5 cm topsoil layer (aggregate stability, carbon organic content, and porosity) were determined. The rate of initial crusts, the crusting with the rains, the aggregate stability, the carbon organic content and the soil porosity were significantly related to the runoff. The soil cover and the crusting with the rains were significantly related with the water turbidity. All theses parameters were significantly related to soil losses. However, runoff was poorly related to the water turbidity. The causality links between the results and the ranking of the land uses are discussed.

Soil nitrous oxide emissions in long-term cover crops-based rotations under subtropical climate.

Abstract: It has been shown that cover crops can enhance soil nitrous oxide (N2O) emissions, but the magnitude of increase depends on the quantity and quality of the crop residues. Therefore, this study aimed to evaluate the effect of long-term (19 and 21 years) no-till maize crop rotations including grass [black oat (Avena strigosa Schreb)] and legume cover crops [vetch (Vigna sativa L.), cowpea (Vigna unguiculata L. Walp), pigeon pea (Cajanus cajan L. Millsp.) and lablab (Dolichos lablab)] on annual soil N2O emissions in a subtropical Acrisol in Southern Brazil. Greater soil N2O emissions were observed in the first 45 days after the cover crop residue management in all crop rotations, varying from � 20.2 � 1.9 to 163.9 � 24.3 m gNm � 2 h � 1 . Legumebased crop rotations had the largest cumulative emissions in this period, which were directly related to the quantity of N (r 2 =0 .60, p= 0.13) and inversely related to the lignin:N ratio (r 2 =0 .89, p= 0.01) of the cover crop residues. After this period, the mean fluxes were smaller and were closely related to the total soil N stocks (r 2 =0 .96,p = 0.002). The annual soil N2O emission represented 0.39–0.75% of the total N added by the legume

A method for predicting soil susceptibility to the compaction of surface layers as a function of water content and bulk density.

Abstract: Identifying the vulnerability of soils to compaction damage is becoming an increasingly important issue when planning and performing farming operations. Soil compaction models are efficient tools for predicting soil compaction due to agricultural field traffic. Most of these models require knowledge of the stress/strain relationship and of mechanical parameters and their variations as a function of different physical properties. Since soil compaction depends on the soil's water content, bulk density and texture, good understanding of the relations between them is essential to define suitable farming strategies according to climatic changes. In this work we propose a new pedotransfer function for 10 representative French soils collected from cultivated fields, a vineyard and forests. We investigate the relationship between soil mechanical properties, easily measurable soil properties, water content and bulk density. Confined compression tests were performed on remoulded soils of a large range of textures at different initial bulk densities and water contents. The use of remolded samples allowed us to examine a wide range of initial conditions with low measurement variability. Good linear regression was obtained between soil precompression stress, the compression index, initial water content, initial bulk density and soil texture. The higher the clay content, the higher the soil's capacity to bear greater stresses at higher initial water contents without severe compaction. Initial water content plays an important role in clayey and loamy soils. In contrast, for sandy soils, mechanical parameters were less dependent on initial water content but more related to initial bulk density. These pedotransfer functions are expected to hold for the soils of tilled surface layers, but further measurements on intact samples are needed to test their validity.

Carbon sequestration in agricultural soils in the Cerrado region of the Brazilian Amazon

Abstract: The introduction of crop management practices after conversion of Amazon Cerrado into cropland influences soil C stocks and has direct and indirect consequences on greenhouse gases (GHG) emissions. The aim of this study was to quantify soil C sequestration, through the evaluation of the changes in C stocks, as well as the GHG fluxes (N 2 O and CH 4 ) during the process of conversion of Cerrado into agricultural land in the southwestern Amazon region, comparing no-tillage (NT) and conventional tillage (CT) systems. We collected samples from soils and made gas flux measurements in July 2004 (the dry season) and in January 2005 (the wet season) at six areas: Cerrado, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT), in each case after a 2-year period of rice under CT. Soil samples were analyzed in both seasons for total organic C and bulk density. The soil C stocks, corrected for a mass of soil equivalent to the 0–30-cm layer under Cerrado, indicated that soils under NT had generally higher C storage compared to native Cerrado and CT soils. The annual C accumulation rate in the conversion of rice under CT into soybean under NT was 0.38 Mg ha −1 year −1 . Although CO 2 emissions were not used in the C sequestration estimates to avoid double counting, we did include the fluxes of this gas in our discussion. In the wet season, CO 2 emissions were twice as high as in the dry season and the highest N 2 O emissions occurred under the NT system. There were no CH 4 emissions to the atmosphere (negative fluxes) and there were no significant seasonal variations. When N 2 O and CH 4 emissions in C-equivalent were subtracted (assuming that the measurements made on 4 days were representative of the whole year), the soil C sequestration rate of the conversion of rice under CT into soybean under NT was 0.23 Mg ha −1 year −1 . Although there were positive soil C sequestration rates, our results do not present data regarding the full C balance in soil management changes in the Amazon Cerrado.