Showing papers in "Soil Use and Management in 2009"

Soil compaction and soil management - a review.

Abstract: Soil compaction is an important component of the land degradation syndrome which is an issue for soil management throughout the world. It is a long standing phenomenon not only associated with agriculture but also with forest harvesting, amenity land use, pipeline installation, land restoration and wildlife trampling. This review concentrates on the impact of soil compaction on practical soil management issues, an area not previously reviewed. It discusses in the context of the current situation, the causes, identification, effects and alleviation of compaction. The principal causes are when compressive forces derived from wheels, tillage machinery and from the trampling of animals, act on compressible soil. Compact soils can also be found under natural conditions without human or animal involvement. Compaction alters many soil properties and adverse effects are mostly linked to a reduction in permeability to air, water and roots. Many methods can be used to measure the changes. In practical situations, the use of visual and tactile methods directly in the field is recommended. The worst problems tend to occur when root crops and vegetables are harvested from soils at or wetter than field capacity. As discussed by a farmer, the effects on crop uniformity and quality (as well as a reduction in yield) can be marked. By contrast, rendzinas and other calcareous soils growing mainly cereals are comparatively free of compaction problems. The effect of a given level of compaction is related to both weather and climate; where soil moisture deficits are large, a restriction in root depth may have severe effects but the same level of compaction may have a negligible effect where moisture deficits are small. Topsoil compaction in sloping landscapes enhances runoff and may induce erosion particularly along wheeltracks, with consequent off-farm environmental impacts. Indirect effects of compaction include denitrification which is likely to lead to nitrogen deficiency in crops. The effects of heavy tractors and harvesters can to some extent be compensated for by a reduction in tyre pressures although there is concern that deep-seated compaction may occur. Techniques for loosening compaction up to depths of 45 cm are well established but to correct deeper problems presents difficulties. Several authors recommend that monitoring of soil physical conditions, including compaction, should be part of routine soil management.

Harmonized soil profile data for applications at global and continental scales: updates to the WISE database

Abstract: Version 3.1 of the ISRIC-WISE database holds selected site and horizon data for some 10 250 soil profiles from 149 countries. Profile data were extracted from a wide range of sources and harmonized with respect to the original (1974) and revised (1988) Legend of the FAO-Unesco Soil Map of the World. Profiles have been described, sampled, and analysed according to methods and standards in use in the originating countries; analytical results for the same property cannot always be compared directly; as a result the amount of measured data available for modelling is sometimes much less than expected. WISE was specifically developed for land-related applications at continental and global scales

Effects of 10 years of conservation tillage on soil properties and productivity in the farming-pastoral ecotone of Inner Mongolia, China

Abstract: Soil degradation and subsequent yield decline are the main factors limiting further development of agriculture on the farming–pastoral transition zone of China. A 10-year field experiment was conducted in Inner Mongolia to compare the long-term effects of no-tillage with straw cover (NT), subsoiling with straw cover (ST), rototilling with straw cover (RT) and traditional tillage (TT) using ploughs on soil properties and productivity in a spring wheat–oat cropping system. Long-term conservation tillage increased soil organic matter in the top 20 cm by 21.4%, total N by 31.8% and Olsen’s P by 34.5% in the 0–5 cm layer compared to traditional tillage. Mean percentage of macro-aggregates (>0.25 mm, +20%) and macroporosity (>60 lm, +52.1%) also improved significantly in the 0– 30 cm soil layer (P < 0.05). The largest yield improvements coupled with greatest water use efficiency (WUE) were achieved by no-tillage with straw cover. Ten-year mean crop yields increased by 14.0% and WUE improved by 13.5% compared to traditional tillage due to greater soil moisture and improved soil physical and chemical status. These improvements in soil properties and productivity are of considerable importance for the seriously degraded soils in semiarid Inner Mongolia, as well as for food security, sustainable agriculture and carbon storage in the farming–pasture transition regions of China.

Nitrous oxide fluxes and denitrification sensitivity to temperature in Irish pasture soils

Abstract: Nitrous oxide (N2O) emissions from grazed pastures constitute approximately 28% of total global anthropogenic N2O emissions. The aims of this study were to investigate the effect of inorganic N fertilizer application on fluxes of N2O, quantify the emission factors (EFs) for a sandy loam soil which is typical of large areas in Ireland and to investigate denitrification sensitivity to temperature. Nitrous oxide flux measurements from a cut and grazed pasture field for 1 year and denitrification laboratory incubation were carried out. The soil pH was 7.3 and had a mean organic C and N content at 0–20 cm of 44.1 and 4.4 g/kg dry weight, respectively. The highest observed peaks of N2O fluxes of 67 and 38.7 g N2O-N per hectare per day were associated with times of application of inorganic N fertilizer. Annual fluxes of N2O from control and fertilized treatments were 1 and 2.4 kg N2O-N per hectare, respectively. Approximately 63% of the annual flux was associated with N fertilizer application. Multiple regression analysis revealed that soil nitrate and the interaction between soil nitrate and soil water content were the main factors controlling N2O flux from the soil. The derived EF of 0.83% was approximately 66% of the IPCC default EF value of 1.25% as used by the Irish EPA to estimate greenhouse gases (GHGs) in Ireland. The IPCC-revised EF value is 0.9%. A highly significant exponential regression (r2 = 0.98) was found between denitrification and incubation temperature. The calculated Q10 ranged from 4.4 to 6.2 for a temperature range of 10–25 °C and the activation energy was 47 kJ/mol. Our results show that denitrification is very sensitive to increasing temperature, suggesting that future global warming could lead to a significant increase in soil denitrification and consequently N2O fluxes from soils.

Carbon stocks in Scottish peatlands

Abstract: Various estimates have suggested that the peatlands of Scotland are a significant deposit of fixed carbon. However, these have been based upon rather imprecise estimates of peat depth. Using previously unused archived data, we have mapped peat depth across the country and then used these values to obtain an improved value of the total carbon stock within peatlands, as well as indicating their spatial distribution. We included peat deposits that occur in combination with other soils in soil map units other than ‘blanket’ or ‘basin’ peat. We obtained an area-weighted mean peat depth of 2.0 m, which is slightly shallower than previous estimates. Using values of bulk density and % carbon from the Scottish soils database, the total peatland carbon stock came to 1620 Mt, which represents 56% of the total carbon in all Scottish soils.

Determining soil organic carbon for agricultural soils: a comparison between the Walkley & Black and the dry combustion methods (north Belgium)

Abstract: Mapping soil organic carbon (SOC) and establishing any change over time are important because of CO2 fluxes between soil and atmosphere and cropland decreases in SOC. The latter is one of the main causes of soil fertility decline and increased erodibility. As most analytical methods underestimate total SOC content, correction factors are needed to avoid methodological bias when comparing SOC data from sampling campaigns using different analytical procedures. The traditional method for SOC analysis used to be, and in most cases still is wet oxidation in potassium dichromate, better known as the Walkley & Black method. In this study, we aim to estimate correction factors for the classic and modified version of the Walkley & Black method for different land use and soil type combinations for agricultural soils in north Belgium. General correction factors of 1.47 for the classic Walkley & Black method and 1.20 for the modified Walkley & Black method are proposed. The results show that sandy grassland soils are characterised by lower recoveries than silt loam grassland soils. Furthermore, the correction factor appears to increase with soil wetness.

A lysimeter study of nitrate leaching from grazed grassland as affected by a nitrification inhibitor, dicyandiamide, and relationships with ammonia oxidizing bacteria and archaea

Abstract: Nitrate (NO 3 - ) can contribute to surface water eutrophication and is deemed harmful to human health if present at high concentrations in the drinking water. In grazed grassland, most of the NO 3 - -N leaching occurs from animal urine-N returns. The objective of this study was to determine the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO 3 - leaching in three different soils from different regions of New Zealand under two different rainfall conditions (1260 mm and 2145 mm p.a.), and explore the relationships between NO 3 - -N leaching loss and ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The DCD nitrification inhibitor was found to be highly effective in decreasing NO 3 - -N leaching losses from all three soils under both rainfall conditions. Total NO 3 - -N leaching losses from the urine patch areas were decreased from 67.7-457.0 kg NO 3 - -N/ha to 29.7-257.4 kg NO 3 - -N/ha by the DCD treatment, giving an average decrease of 59%. The total NO3 - -N leaching losses were not significantly affected by the two different rainfall treatments. The total NO 3 - -N leaching loss was significantly related to the amoA gene copy numbers of the AOB DNA and to nitrification rate in the soil but not to that of the AOA. These results suggest that the DCD nitrification inhibitor is highly effective in decreasing NO 3 - leaching under these different soil and rainfall conditions and that the amount of NO 3 - -N leached is mainly related to the growth of the AOB population in the nitrogen rich urine patch soils of grazed grassland.

Use of agricultural by-products to study the pH effects in an acid tea garden soil

Abstract: The amelioration of an acid Alfisol from a tea garden was studied by incorporating various plant materials: canola straw, wheat straw, rice straw, corn straw, soybean straw, peanut straw, faba bean straw, Chinese milk vetch shoot and pea straw prior to incubation for a maximum of 65 days. Soil pH increased after incubation with all the incorporated materials with the legumes causing the largest increases. The final soil pH was correlated with ash alkalinity (r 2 = 0.73), base cations (r 2 = 0.74) and N content (r 2 = 0.93) of the applied materials. It was assumed that the incubation released the base cations in plant materials as they decomposed which ultimately increased the base cation saturation of the soil. Similarly, soil exchangeable Al was also decreased with the incorporation of the legume plant materials and corn straw and rice straw. Our investigation demonstrated that legumes are the preferred choice for controlling the soil acidity and also for reducing the toxicity of Al in acid soils.

Soil alteration due to erosion, ploughing and levelling of vineyards in north east Spain

Abstract: Since the 1970s and 1980s, the vineyard areas in the Mediterranean region of north east Spain have undergone profound transformation to allow greater mechanization. This has involved land levelling, deep ploughing and the elimination of traditional soil conservation measures. Recently the EU Common Agricultural Policy encourages this through the vineyard restructuring and conversion plans (Commission Regulation EC No 1227 ⁄ 2000 of 31 May 2000) by subsidizing up to 50% of the cost of soil preparation such as soil movement and land levelling. A clear example of the problems that this causes is in the Penede`s vineyard region (Catalonia, north east Spain), and the present research analyses the changes in soil properties caused by erosion, deep ploughing and land levelling. The study was carried out in an area of 30 000 ha for which a Soil Information System at a scale of 1:50 000 was developed based on 394 field observations (89 soil profiles and 251 auger hole samples down to 120 cm). The results show that 74% of the described soil profiles are disturbed with evidence of soil mixing and ⁄ or profile truncation due to erosion, deep ploughing and ⁄ or land levelling. The evidence from the topsoils is mainly the presence of fragments of calcic or petrocalcic horizons, marls and sandstones. Other important properties for crops such as organic matter (OM) content and soil depth show statistically significant differences between disturbed soils and undisturbed soils (22.3-33.3% OM content depletion and 35.1% soil depth reduction). These results confirm that the soils of the region are significantly altered by mechanical operations which also influence soil erosion and contribute to global warming effect through depletion of soil OM.

The role of lysimeters in the development of our understanding of soil water and nutrient dynamics in ecosystems

Abstract: This paper considers the development of lysimeters and their role in the evolution of our understanding of the dynamics of water and plant nutrients in ecosystems. Lysimeters are delineated volumes of soil. They can be divided into those filled with repacked soil, and those enclosing an undisturbed monolith. The original repacked lysimeter was developed to investigate the concept that all life stems from water, and is considered to be the first quantitative experiment in history. It focussed on the growth of a willow tree and how much of the increment was derived from the soil solids. From this start some 360 years ago lysimeters quickly contributed to the quantification of the transpiration stream and the differentiation of water loss by evaporation from the soil from loss via the leaves of plants. Chronologically, further development began about 210 years ago with the exploration of whether precipitation could account for all the water moving from the land to the oceans, and was the origin of springs. In part, this required a careful quantification of soil evaporation, runoff and deep drainage. This in turn led to the quantification of the soil water balance. As a result, we are able to predict indices, such as crop water use efficiency, drainage and irrigation requirements, contributions to stream flow, groundwater recharge and nutrient loss by leaching. Recognition that the quantification of drainage and leaching required soils of natural structure and profile integrity resulted in the building of the first monolith lysimeter and the development of 'pan' or 'Ebermayer' lysimeters. Improved technology allowed a better understanding of the role of soil in the regional water balance through the development of small diameter lysimeters that could be transported to a central location subject to the same climatic variables. In contrast, other technological changes allowed the impact of typical soil management operations carried out using regular machinery to be applied on field-scale lysimeters. The contribution of the different types of lysimeter to the development of our understanding of soil use and management is considered.

Effects of four tillage systems on soil structure and soil microbial biomass in organic farming

Abstract: Tillage modifies soil structure and crop residue distribution and in turn affects the ability of soil micro-organisms to degrade soil organic matter and release nutrients for crop growth. In organic farming, soil microbiological activity is of primary importance as nutrient supply is mainly dependent on the degradation of soil organic matter by soil micro-organisms. The aim of this work was therefore to study, in organic farming, the effects of four tillage systems [mouldboard ploughing (MP), shallow mouldboard ploughing (SMP), reduced tillage (RT) and shallow soil tillage (ST)] on soil structure, soil microbial biomass (SMB) and its potential activity (Cmin) during the first year following the treatments. To study simultaneously the effects of soil structure modifications and crop residue distribution on SMB and Cmin, we adopted a sampling scheme based on a morphological description of soil profiles. We distinguished and sampled compacted and non-compacted clods (Δ and Γ clods) at three depths (0–5, 5–15 and 15–30 cm). This method enabled us to have a precise estimation of the effects of tillage treatments on SMB and Cmin. MP reduced compacted zones and limited unfavourable conditions for microbial growth and enabled a homogenous distribution of SMB in the soil profile. At the opposite, the ST increased compacted zones in the soil profile and limited SMB development below the top few centimetres. The SMP and the RT systems appeared as intermediate techniques. RT seemed to be a conservation tillage technique which could be used in organic farming.

Effect of selected organic materials and inorganic fertilizer on the soil fertility of a Humic Nitisol in the central highlands of Kenya

Abstract: The effect on soil fertility of applying particular organic resources to a humic Nitisol in the central highlands of Kenya was studied. The organic resources (Calliandra calothyrsus, Leucaena trichandra, Tithonia diversifolia, Mucuna pruriens, Crotalaria ochroleuca and cattle manure) were either applied solely or along with inorganic fertilizer in a cropping trial using maize as the experimental crop. After 4 years of continuous cultivation and manuring, soil fertility effects varied among treatments. Cattle manure proved to be the most effective and improved soil fertility by increasing pH, cations (Ca, K and Mg), and C. Calliandra, Leucaena, Tithonia and herbaceous legumes generally reduced soil pH, C and N but increased Ca, K and Mg. Cattle manure is therefore an important resource for maintaining soil organic matter (SOM) in the area and in other similar areas with arable-livestock systems. Reduction of soil C and N by the high quality organic materials suggests that their role in maintaining SOM in the long-term is limited in this area. A sound nutrient management system should strive to make a balance between maximizing crop production and sustaining soil quality.

The effect of soil texture and organic amendment on the hydrological behaviour of coarse-textured soils

Abstract: To gain more insight into the hydrological behaviour of coarse-textured soils, the physical properties of artificially created soil mixtures with different texture were determined. The mixtures were prepared according to the specifications of the United States Golf Association (USGA) for constructing putting greens. In addition, the effect of 10 vol.% organic matter addition was studied. The soil moisture retention and hydraulic conductivity relationships of the different mixtures were determined and their hydrological behaviour was studied using the numerical model SoWaM. Both texture and organic matter addition substantially affected the hydraulic properties. Hydraulic conductivity significantly increased with increasing coarseness while moisture retention decreased. On the other hand, organic matter addition reduced saturated hydraulic conductivity by a factor of 10 to 100 and distinctly increased moisture retention capacity. The amounts of total available water were increased by the addition of organic matter between 144% (slightly coarse texture) and 434% (very coarse texture). Results indicate that the mixtures can contain only 2–16% plant available water and therefore need frequent irrigation to maintain plant growth. Addition of organic matter seems a good solution to reduce the irrigation water requirements but it increases the risk of ponding or runoff because of large reductions in the saturated hydraulic conductivity sometimes to below the rate of 3.6 m/day recommended by the USGA

Impact of Acacia auriculiformis on the chemical fertility of sandy soils on the Batéké Plateau, D.R. Congo.

Abstract: A 17-year chronosequence of Acacia auriculiformis fallows on Arenosols of the BatekePlateau (D.R. Congo) was surveyed and compared with virgin savannah soils to assess chemical soil fertility changes induced by these N-fixing trees. Significant increases in organic carbon content, total nitrogen content, cation exchange capacity and sum of base cations were found after relatively short fallow periods of only 4 years and did not only affect the forest floor, but extended to at least 50 cm depth. The Acacia act as a major source of organic matter (OM), hence increasing organic carbon and nitrogen content and decreasing the C ⁄ N ratio. The increased OM content suggests that humification processes are the main cause of the significant decrease in pH. Total exchangeable cations initially increased slowly but doubled (topsoil 0-25 cm) and tripled (subsoil 25-50 cm) after 10 years. The point of zero net proton charge was systematically lower than soil pH and decreased with increasing OM content, thereby increasing the cation exchange capacity, although concurrent acidification retarded a significant benefi- cial impact at field pH on Acacia fallows of 10 years and older. Although the chemical soil fertility improves steadily with time, after 8 years of Acacia fallow the absolute amounts of available nutrients are still small and slash and burn practices are required to liberate the nutrients stored in the remain- ing biomass and litter before each new cropping period.

Aggregate stability in organically and conventionally farmed soils

Abstract: A range of factors that influence aggregate stability and soil erodibility were analysed for soils sampled from land managed under contrasting agricultural methods. These included: an organic farm; a conventional farm that incorporated organic fertilizers; a conventional farm that only used inorganic fertilizers; and a non-cultivated control site. The stability of aggregates that compose the bulk soil structure (macroaggregates), and aggregates that were mobilized from the soil by simulated rainfall and surface runoff (microaggregates), were evaluated in terms of the soil fragmentation fractal dimension, organic carbon content and ATP (adenosine 5¢-triphosphate; a signature of live biomass) concentration. The results were used to interpret the existing physical condition of the soils, the (microbial) processes that contribute to that physical structure, and how both pedogenic processes and existing soil quality are influenced by agricultural methods. The soils sampled for this study were demonstrated to be multi-fractal in nature: soils with greater bulk density were composed of more stable macroaggregates, which, in turn, fragmented into larger, more stable micro-aggregates, rendering the entire soil structure less erodible. Soil erodibility and sustainable soil management should therefore be approached at multiple scales. The primary control on both macro- and micro-aggregate stability was determined to be the organic matter input to the soil, as represented by measurements of organic carbon and ATP. Organic content was greatest for the non-cultivated soil, which reflects the degradation of organic reserves in cultivated soils. For cultivated soils, it was not possible to differentiate aggregate stability for soils managed under organic or conventional (i.e. using biological and inorganic fertilizers) farming practices, but aggregates of soils that only received artificial fertilizers consistently exhibited less stability.

Quantifying terrestrial carbon stocks: examining the spatial variation in two upland areas in the UK and a comparison to mapped estimates of soil carbon

Abstract: Intensive field surveys were undertaken in two upland catchments in the UK, Plynlimon in mid-Wales and Glensaugh in North East Scotland. The survey was to examine the spatial variation across the area and to assess the accuracy of the database underpinning the soil carbon map for the UK. In each area three 1-km2 squares were sampled on a 200-m grid, with samples taken from both the organic and mineral horizons. Carbon stock was estimated, from the sample data, for each 1-km2 square and compared with values from the UK database for that square. The results showed large differences between some squares, particularly for Plynlimon. In this area, the overall discrepancy between field and database values was 45%, compared with 8% for Glensaugh. Various sources of uncertainty were examined, including bulk density, organic horizon depth, and the proportion of different soil types within a square. The value for bulk density, assumed to determine carbon stock, had a significant effect on the estimates. In both catchments the organic layer showed a gradual decrease in bulk density with depth, resulting in a large proportion of the carbon being stored in the top part of the profile. The soil types, mapped during the survey, also showed large differences from those previously identified for each 1-km2 square. This would have a considerable effect on the estimates of carbon stock within the UK database. It highlights that caution needs to be used when interpreting the UK soil map at this spatial scale.

Phytoremediation of selenium‐contaminated soils: the efficiency of different cropping systems

Abstract: Field experiments were conducted at two locations in the seleniferous region of northwestern India from 2001 to 2006 to evaluate the efficiency of four cropping systems in removing Se from contaminated soil containing 2843–4345 lg Se per kg in the surface layer (0–15 cm). Rapeseed (Brassica napus) followed by arhar (Cajanus cajan), sunn hemp (Crotalaria juncea) or cotton (Gossypium arboretum) and wheat (Triticum aestivum) followed by rice (Oryza sativa) were the four cropping systems. The total biomass generated by Brassica-based systems ranged from 16 to 21 t ⁄ ha when harvested at maturity. Corresponding values for a wheat–rice sequence were 22–26 t ⁄ ha. Among the different crops at both the experimental sites, the highest Se content was recorded in leaves (157–209 mg ⁄ kg), grains (64–201 mg ⁄ kg) and stems (42–93 mg ⁄ kg) of Brassica and the lowest in the shoots (10–27 mg ⁄ kg), grains (5–13 mg ⁄ kg) and straw (13–20 mg ⁄ kg) of the rice crop. Except for S and P, concentrations of other nutrients (Zn, Cu, Mn and Fe) were not significantly affected by variations in the Se content of plants. Significant correlation coefficients were observed between Se and S (r = 0.838, P £ 0.001), Se and P (r = 0.817, P £ 0.001) at the peak flowering stage (n = 16), and r = 0.743, P £ 0.001 and r = 0.498, P £ 0.05, respectively, at the maturity stage (n = 16). Total Se removal through harvested biomass of rapeseed-based cropping sequences varied from 716 to 1374 g ⁄ ha ⁄ yr at peak flowering and 736–949 g ⁄ ha ⁄ yr at the maturity stage. Corresponding values for a wheat–rice system were 435–492 and 370–517 g ⁄ ha ⁄ yr, respectively. The amount of Se recycled through leaf senescence ranged from 255 to 500 g ⁄ ha ⁄ yr for Brassica-based cropping systems. In the wheat–rice system, Se addition through irrigation varied from 170 to 243 g ⁄ ha ⁄ yr and was three to four times more than that added in Brassica-based systems. On completion of the phytoremediation experiments at site I, Se removal through harvested biomass at maturity was 1.7–5.1% of total Se in the soil down to a depth of 120 cm and 4.8–13.2% at site II. Analysis showed that Se losses under different crop rotations were 18.5–24.5% at site I and 21–33% at site II of total soil Se. Thus, at both sites 16–20% of total Se lost from the soil was unexplained. Results show that Brassica-based cropping systems lead to significant reductions in Se capital of contaminated soil over 2–3 years. Although a long-term commitment is required, adoption of Brassica-based systems as a regular agricultural practice must lead to sustainable management of seleniferous soils.

Resource flows, crops and soil fertility management in smallholder farming systems in semi-arid Zimbabwe

Abstract: Poor soil fertility and erratic rains are major constraints to crop production in semi-arid environments. In the smallholder farming systems of sub-Saharan Africa, these constraints are manifested in frequent crop failures and endemic food insecurity. We characterized a semi-arid smallholder farming system in south-western Zimbabwe to assess crop production, nutrient use and factors that constrain productivity. The farming system was studied using resource flow mapping, farmer interviews and calculations of crop production over three cropping seasons (2002/2003, 2003/2004 and 2004/2005) to capture variability between years. Farmers were categorized into three groups: better resourced, medium resourced and poorly resourced. Better resourced farmers produced adequate grain for basic household consumption, except in the drought year (2002/2003). Poorly resourced farmers had large grain deficits, whereas the medium resourced class had smaller deficits. Better resourced and medium resourced farmers produced adequate amounts of staple cereal in two of the seasons, while poorly resourced farmers produced inadequate amounts of food in all three seasons. All farmers produced less than 300 kg/ha of legumes per season. Lack of seed was cited as the main reason for poor legume production. Better resourced farmers used animal manure (2000-5000 kg per season) and some fertilizer on their cereal crops, while the medium resourced group used less manure (1000 kg or less) and no fertilizer. The use of manure varied strongly across the years. Poorly resourced farmers used no nutrient inputs on any of their crops. All groups had negative nitrogen balances during the three cropping seasons, although the values varied strongly between seasons. Investigation of the potential strategies for developing sustainable production systems are required to address the problems of food security in the semi-arid parts of the country and the region.

Effect of different management strategies on soil quality of citrus orchards in Southern Italy

Abstract: Twenty-six soil samples were collected from 13 paired orchards (organically vs. conventionally managed) homogeneous for age, rootstock and cultivars, belonging to the Eastern Sicily Organic Citrus farm Network. The soil quality was evaluated by chemical and biochemical indicators. The total organic C, humification parameters and isoelectric focusing of extracted organic matter were measured to quantify the size of relevant soil C pools. In addition, C turnover was evaluated by determining microbial C mineralization, C microbial biomass and by calculating the mineralization and metabolic quotient (qCO2). The results obtained demonstrated that organic citrus soils were characterized by a general increase in all the organic matter pools, which means a greater C supply for soil metabolic processes. This observed trend did not directly influence the organic matter turnover, indicating that the organic approach could act as a soil C-sink. The soil microflora of organically managed soils showed an improved efficiency in use of energy and organic resources, corresponding to an increased ability of soils under organic management to sustain biological productivity in the long term.

Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

Abstract: In southern New Zealand, grazing of forage crops is common practice to satisfy feed requirements of animals in winter when pasture growth is limited. This practice has been shown to cause soil physical damage and increased loss of surface water contaminants sediment and phosphorus (P) to water bodies. Strategies to mitigate the loss of sediment and P were trialled on a Pallic soil type (Aeric Fragiaquept) in the North Otago Rolling Downlands of New Zealand. All sites were irrigated and measurements were made of losses in overland and sub-surface flow from intensive cattle or sheep grazed, winter forage crops, and sheep grazed pasture. Two mitigations (restricted grazing of crop to three hours and the application of aluminium sulphate) were assessed for their potential to decrease contaminant loss from cropland. Volumes of surface runoff and loss of total P, filterable reactive P and sediment showed significant differences (P sheep crop (67 mm) > sheep pasture (33 mm). The contribution of irrigation water to overland flow water, as a result of saturation-excess conditions, varied between treatments with more loss under cattle crop (20% of total) compared with sheep crop (15%) and sheep pasture (11%). These differences are probably an effect of soil physical condition and highlight the importance of accurate irrigation scheduling to keep soil moisture below field capacity. Restricted winter grazing and alum application after grazing significantly (P < 0.05) decreased P losses in surface runoff under cattle (from 1.4 to 0.9 kg P ⁄ ha) and sheep (from 1.0 to 0.7 kg ⁄ P ⁄ ha) grazed crop plots by about 30%. In cattle grazed plots, restricted grazing also decreased suspended sediments (SS) by 60%. The use of restricted grazing is suggested as a means of decreasing P and SS loss from grazed winter forage crops. The use of alum shows some promise for decreasing P losses, but requires further work to determine its long-term effectiveness and use in other soils and management regimes.

Participatory soil survey: experience in working with a Mesoamerican indigenous community

Abstract: In traditional rural societies that still represent the majority of small farmers worldwide, the use ofconventional soil survey information frequently fails because it does not take into account or underes-timates soil knowledge and experience of local people. Innovative approaches have been proposed toutilize the soil knowledge of rural communities through the participation of local farmers. This paperreports experience of participatory soil survey in the Purhe´pecha community of San Francisco Picha´t-aro in the volcanic highlands of central Mexico. Ethnographic and ethnopedologic techniques wereapplied to acquire soil and land data. Local soil knowledge was incorporated through plenary work-shops designed to produce a participatory soil map based on a Purhe´pecha soil classification. This soilmap reflects farmers’ soil–landscape understanding and correlates fairly well with a scientific soil mapof the same area because in both approaches terrain plays a key role in the delineation of soil units.Participatory soil mapping promoted cooperation between local and external participants and formedthe basis for an agreed land-use plan.

Evaluating chemical and physical quality indicators for a structurally fragile tropical soil.

Abstract: In tropical regions with well-defined wet and dry seasons, repeated wetting and drying cycles can harden exposed soils and inhibit root growth. While this phenomenon has been well documented, the relationships between plant productivity and chemical and physical soil parameters have not been well defined. The current study identifies the abiotic parameters that best relate to measures of plant development, specifically to corn productivity. The primary goal of this research was to provide information to improve agricultural sustainability in humid tropical ecosystems. The effects of using plant residues as a cover on a sandy soil were studied. Four leguminous species were planted in an alley cropping system, Leucaena leucocephala, Cajanus cajan, Clitoria fairchildiana and Acacia mangium, and corn was planted in January 2007 between legume rows. We measured the most important chemical and physical soil parameters. Yield indicators included cob weight and the weight of 100 kernels. The application of plant residues altered soil conditions and increased rootable soil volume. This change was associated with an increase by 10% in water retention above field capacity in the uppermost soil layer of the residue-covered sections of the experiment. In the control sections cobs were up to three times lighter (31.43-93.38 g) in the bare soil control than those from residue-covered sections of the experiment. Dynamic indicators related to nutrient absorption and crop evapotranspiration, such as the number of days with water stress and rootable soil volume, were the most suitable indicators for assessing soil quality. The response of corn was best related to complex physical indicators, including the amount of N applied via legume residues.

Soil metal immobilization and ryegrass uptake of lead, copper and zinc as affected by application of organic materials as soil amendments in a short-term greenhouse trial

Abstract: Green waste compost, peat, coir and wood bark were applied to metal-contaminated mine waste at the rates of 1 %, 10% and 20% on dry weight basis, and perennial ryegrass grown over a period of 6 weeks. Addition of amendments led to increased biomass yield in all soils when compared with the non-amended soil. EDTA extractable Pb, Cu and Zn was significantly reduced in amended soil, while leaf and root metal concentrations were also significantly reduced by the application of amendments, especially at applied rates of 10% and 20%. Coir, green waste compost and wood bark stood out as amendments which were consistent in reducing soil extractable and plant tissue Pb, Cu and Zn; while peat rates above 10% enhanced solubility of Cu and Zn because of a lowering of the soil pH.

Estimation and analysis of soil hydraulic properties through infiltration experiments: comparison of BEST and DL fitting methods

Abstract: The BEST method (Beerkan estimation of soil transfer parameters through infiltration experiments) appears promising and easy to estimate not only saturated hydraulic conductivity but also water retention and hydraulic characteristics. However, few tests have been conducted to test the methodology. This study involved field BEST infiltration experiments for three layers (surface, 15 and 30 cm) for each of three soils with different soil textures under grassland. By comparing BEST with DL (differentiated linearization method), we found that the DL method did not produce a good estimate of the soil hydraulic properties and neither did it identify the transient flow state. The BEST method resulted in reasonable results and is therefore promising. However, with BEST we encountered some anomalies when calculating hydraulic properties in some cases with too few data points under the transient flow state. We show that the application of BEST field experiments requires a wide range of soil water content from initial to saturated states so as to include sufficient transient flow. The soil hydraulic properties determined using the BEST method showed contrasting characteristics between different soil textures with higher saturated hydraulic conductivity under coarse texture and lower values under loam textures, especially with highly compacted soils. Vertical variation in soil hydraulic properties was significant, and the surface layer had a lower saturated hydraulic conductivity partly caused by compaction (high bulk density) or by remnants of grass plants. Further research on the effects of compaction and grass plants on soil hydraulic properties is needed.

Comparison of soil properties of native forests, Pinus patula plantations and adjacent pastures in the Andean highlands of southern Ecuador: land use history or recent vegetation effects?

Abstract: In the high Andes of Ecuador scarcity of farmland has led to accelerated deforestation, in particular over the last 40 years. Soil mis-management has caused the rapid decline of soil fertility and most farmland has been irreversibly transformed into grassland or tree plantations. The present study assessed whether pastures and particularly pine plantations were associated with less soil nutrients. The soils from six sites each of native forests and Pinus patula plantations, and their adjacent pastures were sampled in a geographically large area in the Paute watershed, south Ecuador. Soil analyses showed statistically significant differences for soil cations and effective cation exchange capacity (ECEC) only. ECEC was highest in soils from native forests and their adjacent pastures (6.4 cmol/kg) compared to pine plantations and their pastures (4.2 cmol/kg). Mean soil organic matter and pH were similar in native forests/pastures (39% SOM; pH 5.4) and in plantations/pastures (40% SOM; pH 5). As pasture soils had ECEC concentrations statistically similar to those of their adjacent forest or plantation, they do not form a single homogeneous land use type based on soil nutrients. Therefore, this study cannot conclude that the presence of pines alone has caused soil degradation, but instead that the soil at the site was already degraded before pines were planted. This study proposes the scenario that pine plantations are established in pastures as a last resort, when the soils are already strongly degraded, and more profitable land uses are not available. Farmers are reluctant to use fertile land for tree plantations, and only the planting of well-known species, such as pines, is officially encouraged.

The influence of soil and biosolids type, and microbial immobilisation on nitrogen availability in biosolids‐amended agricultural soils – implications for fertiliser recommendations

Abstract: Soil microbial biomass interactions influencing the mineralisation of N in biosolids-amended agricultural soil were investigated under field conditions in two soil types, a silty clay and a sandy silt loam, with contrasting organic matter contents. Soil treatments included: dewatered raw sludge (DRAW); dewatered and thermally dried, mesophilic anaerobically digested biosolids (DMAD and TDMAD, respectively); lime-treated unstabilised sludge cake (LC); and NH4Cl as a mineral salt control for measuring nitrification kinetics. Soil mineral N and microbial biomass N (MBN) concentrations were determined over 90 days following soil amendment. Despite its lower total and mineral N contents, TDMAD had a larger mineralisable pool of N than DMAD, and was an effective rapid release N source. Increased rates of mineralisation and nitrification of biosolids-N were observed in the silty clay soil with larger organic matter content, implying increased microbial turnover of N in this soil type compared with the sandy silt loam, but no significant difference in microbial immobilisation of biosolids-N was observed between the two soil types. Thus, despite initial differences observed in the rates of N mineralisation, the overall extent of N release for the different biosolids tested was similar in both soil types. Therefore, the results suggest that fertiliser guidelines probably do not need to consider the effect of soil type on the release of mineral N for crop uptake from different biosolids products applied to temperate agricultural soils.

Carbon, nitrogen, phosphorus and enzymatic activity under different land uses in a tropical, dry ecosystem

Abstract: We compared total C, N and P, available forms of N and P and dehydrogenase, urease and acid phosphatase activities in soils from primary forests, 26-year-old pastures and 26-year-old secondary forests in the tropical dry forest region of Chamela, Jalisco, Mexico. We hypothesized that, because of their natural regeneration and greater plant diversity, secondary forest soils would have higher fertility and enzyme activities than pasture soils and would be more similar to primary forest soils. We predicted also that enzymes would be better indicators of land-use effects on soil fertility than nutrients. Only one nutrient, available phosphorus, and one enzyme, acid phosphatase, were significantly and consist- ently affected by land use. As expected, these parameters were greater in primary and secondary forests than in pastures. Principal components analysis using all variables placed secondary forests intermediate between primary forests and pastures, as predicted, and total C, N and P, available P, ammonium, phosphatase, urease and the C:P ratio were the variables associated with this spatial arrangement of land uses. We conclude that secondary forest soils showed improved fertility and were overall closer to primary forests than to pastures in most variables measured.

Simulating nitrate retention in soils and the effect of catch crop use and rooting pattern under the climatic conditions of Northern Europe

Abstract: This model analysis of catch crop effects on nitrate retention covered three soil texture classes sand, loamy sand, sandy loam) and three precipitation regimes in a temperate climate representative for northern Europe (annual precipitation 709-1026 mm) for a period of 43 years. Simulations were made with two catch crops (ryegrass and Brassica) with different rooting depths, and soil N effects in the next spring were analysed to 0.25, 0.75 and 2.0 m depth to represent the catch crop effect on following crops with different rooting depths. Nitrate retained without a catch crop was generally located in deeper soil layers. In the low precipitation regime the overall fraction of nitrate retained in the 0-2.0 m soil profile was 0.23 for the sandy soil, 0.69 for the loamy sand and 0.81 for the sandy loam. Ryegrass reduced leaching losses much less efficiently than Brassica, which depleted nitrate in the 0-0.75 m soil layer more completely, but also in the deeper soil layer, which the ryegrass could not reach. A positive N effect (Neff, spring mineral N availability after catch crop compared with bare soil) was found in the 0-0.25 m layer (i.e. shallow rooting depth of a subsequent main crop) in all three soil texture classes, with on average 10 kg N ha-1 for ryegrass and 34 kg N ha-1 for Brassica. Considering the whole soil profile (0-2.0 m deep rooting of next crop), a positive Neff was found in the sandy soil, whereas generally a negative Neff was found in the loamy sand and especially the sandy loam. The simulations showed that for shallow-rooted crops, catch crop Neff values were always positive, whereas Neff for deeper-rooted crops depended strongly on soil and annual variations in precipitation conditions. These results are crucial both for farmers crop rotation planning and for design of appropriate catch crop strategies with the aim of protecting the aquatic environment.

Soil aggregation and organic carbon in short-term stockpiles.

Abstract: Surface mining is known to drastically reduce soil organic carbon (OC) pools through various mechanisms associated with topsoil salvage, stockpiling and respreading. Stockpiling is an important management practice; however, the effects of this practice on reductions and recovery of soil aggregation and aggregate OC are poorly understood. Objectives of this research were to monitor soil aggregation and aggregate OC in the surface of a short-term stockpile ( < 3 yr) followed by a second movement of stockpiled soils to a temporary location. Samples were analysed for aggregate size distribution, aggregate fractions, OC, and organic matter turnover using 13 C natural abundance. Macroaggregate proportions increased and microaggregate proportions decreased after 3 yr of storage, possibly indicating recovery of soil structure. Following the removal of the stockpile and placement in a temporary pile, macroaggregation decreased and free silt and clay fractions increased relative to initially stockpiled soils. The second disturbance resulted in greater destruction of aggregate structure than the initial disturbance during topsoil salvage. Aggregate organic matter (as indicated by OC) increased significantly between the early sampling of the stockpiled soils (< 1 yr in storage) and the placement of the topsoil in a temporary pile in macroaggregates and remained the same for microaggregates. Organic matter not protected within aggregates decreased with storage time as this material was available for utilization by microbes while aggregate protected organic matter (OM) remained unchanged or slightly increased for macro- and microaggregates with stockpile storage time. Aggregate δ 13 C values did not indicate inclusion of new OM within soil aggregates after 3 yr of topsoil stockpiling. Short-term stockpiling was beneficial for aggregation in the surface layers where plant roots and microbial communities were active; however, subsequent movement of the topsoil resulted in a greater loss of soil aggregation relative to the initial topsoil salvage without impacting soil OC.