Showing papers on "Sowing published in 2002"

Restoration of species‐rich grassland on arable land: assessing the limiting processes using a multi‐site experiment

Abstract: Summary 1 Agricultural intensification has resulted in the reduction and fragmentation of species-rich grasslands across much of western Europe. 2 We examined the key ecological processes that limit the creation of diverse grassland communities on ex-arable land in a multi-site experiment over a wide variety of soil types and locations throughout lowland Britain. 3 The results showed it was possible to create and maintain these communities successfully under a hay-cutting and grazing management regime. Furthermore, there was a high degree of repeatability of the treatment effects across the sites. 4 Lack of seed of desirable species was the key factor limiting the assembly of diverse grassland communities. Sowing a species-rich seed mixture of ecologically adapted grassland plants was an effective means of overcoming this limitation. Community assembly by natural colonization from the seed bank and seed rain was a slow and unreliable process. However, there was no evidence to suggest that sowing a species-poor grass-dominated seed mixture made the vegetation any less susceptible to colonization by desirable species than allowing natural regeneration to take place. 5 Deep cultivation caused significant reductions in soil P and K concentrations across the sites. This had a significant beneficial effect on the establishment and persistence of sown forbs in all years. It also resulted in a significant reduction in the number of unsown weedy grasses. However, for both variables these differences were very small after 4 years. 6 Sowing a nurse crop significantly reduced the number of unsown grass species, but had no beneficial effect on the establishment of desirable species. 7 Treatments sown with the species-rich seed mixture following deep cultivation corresponded most closely to the specified target communities defined by the UK National Vegetation Classification. Natural regeneration and treatments sown with the species-poor seed mixture were much less similar to the target. The sites on circum-neutral soils achieved the greatest degree of similarity to the target. Those on calcareous and acid soils failed to achieve their targets and most closely resembled the target for neutral soils. This reflected the poor performance of the sown preferential species for these communities.

The role of the seed bank in gap regeneration in a calcareous grassland community

Abstract: We conducted a factorial field experiment in order to investigate the role of the soil seed bank in gap recolonization in a calcareous grassland, using 240 experimental gaps (10 X 10 cm). Experimental manipulations included the elimination of the seed bank (by sterilizing the soil), the elimination of short-distance seed rain by removing all flow- erheads in 2 X 2 m plots, and the prevention of lateral clonal spread by surrounding gap soil with 41-pum nylon mesh. The influence of competition on regeneration was also studied, by planting an adult individual of Filipendula vulgaris or Festuca rubra in the center of some gaps. There were 130 species of vascular plants in the established vegetation. Twenty-five species also occurred as seedlings; 51 species were recorded in the seed bank, of which only two were not present in the growing vegetation. There were on average 2362 seeds/ m2 in a 10 cm deep soil layer. Species relative abundances in the established vegetation and in the seed bank were not significantly correlated. Eighty-four vascular plant species emerged from seeds in the experimental gaps. The seed bank contributed on average 5.4 seedlings per gap, short-distance seed rain ( 0.5 m) seed rain 2.7 seedlings. Thirty-one vascular plant species arrived in experimental gaps by lateral clonal spread. Of these, only one was not recorded as a seedling in the experimental gaps. There were on average 2.7 clonally spread shoots per gap. Species with smaller seeds were present in significantly greater numbers in the seed bank than in the vegetation and were also more common colonizers of experimental gaps. There was no evidence of competition or facilitation between seed- lings, or between seedlings and adults. It was concluded that the soil seed bank has an important functional role in a perennial grassland community as a means for population maintenance for many species. Thirty-six percent of the regeneration in small gaps was due to the seed bank, and one may expect that this proportion will increase in larger gaps.

Yield and Soil Fertility Trends in a 20-Year Rice–Rice–Wheat Experiment in Nepal

Abstract: The rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system occupies about 13.5 million ha in South Asia and is important for the region's food security. We examined the long-term yield trends, changes in soil nutrient fractions (both total and available), and nutrient balances in a 20-yr rice-rice-wheat experiment conducted in the Indo-Gangetic plain of Nepal. The yield of first rice crop fertilized with recommended NPK fertilizer or farmyard manure (FYM) declined an average of 0.09 or 0.07 Mg ha -1 yr -1 , respectively. These 20-yr trends explained only 20 to 21% of the variability in yield, and inexplicable shorter-term yield trends were observed. Likewise, wheat yield declined at 0.05 Mg ha -1 yr -1 (with both NPK and FYM) over the 20 yr. However, the yield of second rice crop did not decline over that period. The total and available N and P, and total and labile C contents of soil from Year 10 to 20 were either maintained or increased, but total K and available K declined. The apparent K balance showed net losses of 62.3 and 15.2 kg K ha -1 yr -1 with NPK and FYM treatments, respectively. Depletion of soil K and inadequate K fertilization seems to be the primary reasons of limited and declining yield of first rice and wheat crop. In addition, the yield of wheat declined because of a delay in sowing, which was estimated to be 0.04 Mg ha -1 for each day delay in sowing. The study showed that the current local fertilizer recommendations, particularly for K, for the rice-rice-wheat system are inadequate.

Rehabilitation of Degraded Areas of Central Amazonia Using Direct Sowing of Forest Tree Seeds

Abstract: Deforestation in the Amazon Basin is still increasing, and the rehabilitation of these lands continues to be a challenge. Autoecological studies of most Amazonian species are rare, and efficient techniques for restoration of forested habitats have yet to be developed. The aim of this study was to test direct sowing as a rehabilitation technique for sites with different degrees of disturbance: bare soil, pasture, and secondary and mature forests in Central Amazonia, Brazil. At each site, we sowed seeds of 11 native tree species. Throughout the following year we evaluated germination and seedling survival. The germination differed according to the study site and species. Seedling survival in degraded sites was higher than in other areas. After 1 year in the bare soil site, 33% of the sown seeds of eight species developed seedlings; in the pasture the establishment was 23%, in secondary forest 15%, and in mature forest 12% of only four species. The only widespread survivor with more than 45% emergence in all perturbed sites was Caryocar villosum. No pioneer seedlings remained after 1 year. There was a positive correlation between seed size and survival. Large-seeded non-pioneer species seem to be more suitable for direct sowing than small-seeded species. We recommend a combination of direct sowing and planting of seedlings as an appropriate means to accelerate the rehabilitation of degraded areas in Central Amazonia.

Soil microbial community structure in relation to vegetation management on former agricultural land

Abstract: Agricultural overproduction has led the European Union to encourage long-term abandonment of agricultural land. To enhance the transition of agricultural land to natural grasslands or forests different management practices in relation to vegetation can be used. The aim of this study was to understand the interactions between plant and associated soil microbial communities during the succession of agricultural land. A field experiment was established on newly abandoned agricultural land where the development of the soil microbial community was studied in plots after sowing a mixture of 15 plant species and in plots that were left to be naturally colonized by plants. The plants sown contained five species each of grasses, legumes and forbs representing three functional groups. A subset of these plots were inoculated with soil cores from a later successional stage. Adjacent soils with ongoing agricultural practices and deciduous beech forest were also studied. The microbial community composition and biomass were studied by determining fatty acid signatures (PLFA, NFLA) of soil microorganisms. The microbial community had changed within 2 years from that of the agricultural field diverging into one type present in sown plots and another in plots that were naturally colonized by plants. Sowing plant seed mixtures promoted growth of the bacterial community and sarophytic fungi. Respiration measurements showed higher microbial activity and biomass in sown plots. Bait plants for arbuscular mycorrhizal (AM) fungi and NLFA 16:1ω5 showed that the biomass of AM-fungi was reduced when seed mixtures were sown, which also decreased the formation of mycorrhizal associations on plant roots.

Effect of autumn and winter mycorrhizal cover crops on soil properties, nutrient uptake and yield of sweet corn in Pennsylvania, USA

Abstract: We investigated the effects of an autumn sowing of contrasting cover crops (oats, rye and a combination of oats and rye) on soil aggregate stability, mycorrhizal colonization, phosphorus uptake and yield of sweet corn planted the following summer. Rye is a common cover crop in the middle Atlantic region of the United States of America. It grows slowly in the autumn, survives the winter, grows rapidly in the spring and flowers in the summer. Thus, herbicide is commonly used to kill rye prior to planting spring crops. Oats, in contrast, grows rapidly in the autumn but is killed by frost during the winter. Thus, with oats, potentially less herbicide is needed to prepare the field for spring planting. When compared to fallow, oats was as effective as rye in increasing mycorrhizal colonization of sweet corn, density of mycorrhizal hyphae, and soil aggregate stability. An oats cover crop may thus be a viable alternative to rye. The combination of cover crops (rye and oats), however, was significantly better than single species of cover crops in terms of sweet corn mycorrhizal colonization, P uptake and yield of sweet corn.

Azospiriflum Inoculation Mitigates Water Stress Effects in Maize Seedlings

Abstract: Water stress in maize (Zea mays, L) after planting slows down germination and initial seedling growth. This study determined that seed inoculation with Azospirillum brasilense BR11005 could mitigate negative water stress effects in seedlings. Pots containing a mixture of sand and vermiculite were divided in three lots and irrigated with a nutrient solution, to 200 g moist kg - 1 bed dry weight (HM), 100 g kg - 1 bed dry weight (MM), or to 50 g kg - 1 bed dry weight (LM), respectively. The first lot corresponded to well irrigated pots and the other two, to 50% and 75% water supply reduction, respectively. Hybrid DK 636 maize seeds were treated during imbibition with either 10 7 live or autoclaved (control) A. brasilense cells seed - 1 , pre-germinated in a humid chamber, and planted in the pots. All seedlings were then grown in a greenhouse at their corresponding water regimes, for up to 15 d after planting. Total aerial biomass (TAB) and foliar area (FA) was determined in shoots. Relative water content (RWC), water content (WC), and water potential (Ψ) were determined in leaves. Free proline concentration was determined in both leaves and roots. In addition, surface and dry weight (DW) were determined in roots. Seed inoculation with Azospirillum improved both leaf RWC and WC, prevented a significant Ψ drop in leaves, increased root growth, TAB and FA, and promoted proline accumulation in both leaves and roots, in seedlings grown for 15 d at 75% water supply reduction.

Effect of mineral nitrogen on nitrogen nutrition and biomass partitioning between the shoot and roots of pea (Pisum sativum L.).

Abstract: The effect of mineral N availability on nitrogen nutrition and biomass partitioning between shoot and roots of pea (Pisum sativum L., cv Baccara) was investigated under adequately watered conditions in the field, using five levels of fertiliser N application at sowing (0, 50, 100, 200 and 400 kg N ha−1). Although the presence of mineral N in the soil stimulated vegetative growth, resulting in a higher biomass accumulation in shoots in the fertilised treatments, neither seed yield nor seed nitrogen concentration was affected by soil mineral N availability. Symbiotic nitrogen fixation was inhibited by mineral N in the soil but it was replaced by root mineral N absorption, which resulted in optimum nitrogen nutrition for all treatments. However, the excessive nitrogen and biomass accumulation in the shoot of the 400 kg N ha−1 treatment caused crop lodging and slightly depressed seed yield and seed nitrogen content. Thus, the presumed higher carbon costs of symbiotic nitrogen fixation, as compared to root mineral N absorption, affected neither seed yield nor the nitrogen nutrition level. However, biomass partitioning within the nodulated roots was changed. The more symbiotic nitrogen fixation was inhibited, the more root growth was enhanced. Root biomass was greater when soil mineral N availability was increased: root growth was greater and began earlier for plants that received mineral N at sowing. Rooting density was also promoted by increased mineral N availability, leading to more numerous but finer roots for the fertilised treatments. However, the maximum rooting depth and the distribution of roots with depth were unchanged. This suggested an additional direct promoting effect of mineral N on root proliferation.

Cropping system influence on planting water content and yield of winter wheat

Abstract: Many dryland producers in the central Great Plains of the USA express concern regarding the effect that elimination of fallow has on soil water content at winter wheat (Triticum aestivum L.) planting and subsequent yields. Our objectives were to quantify cropping system effects (fallow weed control method and crop sequence), including corn (Zea mays L.) (C) and proso millet (Panicum miliacium L.) (M), on soil water at winter wheat planting and subsequent grain yield, and to determine the frequency of environmental conditions which would cause wheat yield to drop below 2500 kg ha -1 for various cropping systems. Crop rotations evaluated from 1993 through 2001 at Akron, CO, were W-F, W-C-F, W-M-F, and W-C-M (all no-till), and W-F (conventional till). Yields were correlated with soil water at planting: kg ha -1 = 373.3 + 141.2 × cm (average and wet years); kg ha -1 = 897.9 + 39.7 × cm (dry years). Increasing cropping intensity to two crops in 3 yr had little effect on water content at wheat planting and subsequent grain yield, while continuous cropping and elimination of fallow reduced soil water at planting by 11.8 cm and yields by 450 to 1650 kg ha -1 , depending on growing season precipitation. No-till systems, which included a 12- to 15-mo fallow period before wheat planting nearly always produced at least 2500 kg ha -1 of yield under normal to wet conditions, but no cropping system produced 2500 kg ha -1 under extremely dry conditions.

A review of research on seedbed preparation for small grains in Sweden

Abstract: Seedbed preparation research in Sweden over the past 35 years is reviewed. In Swedish farming, spring sown small grains are the dominant crop, but their establishment is often problematic. The spring is the driest season and this may cause poor crop emergence, particularly in clay and clay loam soils, where the seedbed often becomes coarse and non-uniform and dries out quickly. In silty soils, the major problem is surface layer hardening that hampers seedling emergence. Seedbed problems have attracted considerable research interest. A method to characterize seedbed properties based on frame sampling is presented. A survey of seedbeds in farm fields showed that the water content at traditional spring sowing of small grains (as soon as the soils are dry enough for harrowing) is usually below wilting point to a depth of 3 cm in soils with >25% clay, but in coarse-textured soils, there is usually plant available water up to the soil surface. The function of seedbeds was investigated by establishing seedbeds with predetermined properties and sowing depths in shallow plastic boxes. Under dry weather conditions, good emergence of small grain crops could always be achieved without irrigation, provided the seed was placed directly onto a firm seedbed base with a water content at least 0.05 g g−1 greater than that at a matric tension of 1500 kPa and was covered by a 4 cm deep seedbed with >50% aggregates <5 mm. The risk of poor emergence due to surface layer hardening depended much more on the sowing depth than on the aggregate sizes of the seedbed. Several series of field trials are also summarized. In trials on silty soils, a fine seedbed increased both number of plants and crop yield by 5% as compared to a coarse seedbed. In clay and clay loam soils, natural factors, particularly previous freezing and thawing, affected seedbed characteristics more than the choice of harrows and their adjustment or the number of harrowings. In most soils, rolling after sowing improved final emergence of cereals by 4% and grain yield by 2%. Very early sowing in wet soils, without any preceding seedbed preparation, increased crop yield by about 20% in sandy soils, and was often advantageous even in clay soils. On the basis of our experimental results, the goals of seedbed preparation for cereals are specified by means of seedbed models.

Effect of host genotype on indigenous bacterial endophytes of cotton (Gossypium hirsutum L.)

Abstract: The purpose of this study was to determine if populations of indigenous bacterial endophytes in seed, stem and root tissue of cotton seedlings are influenced by host genotype. Growth chamber and field experiments were conducted to test the hypothesis that host genotype has an effect on endophytic bacterial populations in seed tissues and the developing cotton seedling. Initially, population densities of bacteria within seed of nine cotton cultivars were very low (i.e.,

Responses of wheat grain yield and quality to seed rate

Abstract: Four field experiments were conducted to investigate the effects of seed rate on yield and quality of wheat. Despite some small and inconsistent effects of seed rate on radiation-use efficiency and harvest index, the responses of PAR interception, above-ground biomass and grain yield generally followed similar asymptotic increases as seed rate increased. In one experiment, when nitrogen fertilizer was withheld, biomass and grain yields did not respond to increases in seed rate despite increases in PAR interception. In one experiment, grain yield followed a parabolic response to seed rate with apparent reductions in yield at very high seed rates. Plants compensated for low population densities by increased production and survival of tillers and, to a lesser extent, increased grain numbers per ear. Net tiller production continued until the main stems flowered or later. Effects of seed rate on grain specific weight and thousand grain weight were small and inconsistent. Hagberg falling number increased linearly with seed rate in three experiments, associated with quicker maturation of the crop. Grain protein concentration declined with increase in sowing rate according to linear divided by linear or linear plus exponential models depending on whether the grain yield response was asymptotic or parabolic. Discolouration of the grain with blackpoint increased with seed rate in the most susceptible cultivar, namely Hereward. The economic consequences of these effects on yield and quality are discussed.

Soil seed banks and the effects of meadow management on vegetation change in a 10‐year meadow field trial

Abstract: Summary 1 Enhancement of plant species diversity is often an objective in grassland management for wildlife conservation. Such management regimes may also change the species composition of soil seed banks, which may themselves affect future vegetation change. We compared soil seed banks and vegetation from a long-term meadow management trial and from a series of traditionally managed species-rich meadows in northern England, UK. 2 The management trial used three hay-cut date treatments (14 June, 21 July and 1 September), two fertilizer treatments [no fertilizer or 25 kg nitrogen ha−1 plus 12·5 kg ha−1 phosphate (P2O5) and potash (K2O)] and two seed-addition treatments (no seed, seed of many species sown 1990–92). Soil seed banks were assessed in 1998. Subsequent vegetation development under these treatments, and under an additional farmyard manure treatment, was assessed in 2000. 3 Most seed was in the 0–5-cm soil layer and most of the frequent species germinated in the autumn. Short- and long-term persistent seed banks were most abundant. The species composition of the seed banks and the vegetation in the trial, and in the traditionally managed meadows used as a control, were distinctly different, the meadow trial seed bank being the most uniform. 4 An ordination of simulated plant communities based on the UK National Vegetation Classification provided a wider framework for comparing vegetation and seed banks with the species composition of British meadow communities, some of which are also found in Europe. The soil seed banks throughout the meadow trial plots and the control fields were very similar in species composition to that of the vegetation in agriculturally improved meadows. However, there were many more species in the soil seed bank of the traditionally managed control meadows. 5 In 2000, only the seed-addition treatment increased the species richness of the vegetation. Farmyard manure and mineral fertilizer had similar effects, increasing the cover of Poa trivialis and Rumex acetosa and decreasing the cover of Rhinanthus minor and Anthoxanthum odoratum. 6 It was concluded that the development of the soil seed bank probably lags behind increases in vegetation diversity initiated by seed sowing. This emphasizes the need to introduce additional species as seed when increased diversity is a target for the restoration management of previously intensively managed grasslands.

The importance of the farmers' seed systems in a functional national seed sector

Abstract: The farmers' systems of seed supply and crop development form by far the most important source of seed in most farming systems of the world. Despite the efforts of large seed programmes to replace the farmers' seed systems for a system in which farmers use seed as an external input, the major part of agricultural land in the world is still sown with seed that is informally produced by farmers. Aiming for a formal seed sector that supplies 100% of the seed for planting is only realistic for a small number of crops and in few countries. The importance of farmers' seed systems merits that closer attention be paid to farmers' seed production and seed exchange at the policy level and in technical assistance projects. Linking formal and farmers' seed systems and improving the latter may in many cases be a more effective strategy to improve national and local seed supply than aiming only at improving the infrastructure and investment climate for the formal (private and public) seed sector. In fact, anal...

Effects of Planting Date, Genotype, and Their Interactions on Sunflower Yield

Abstract: Sunflower (Helianthus annuus L.) yields are strongly reduced when normal sowing dates are delayed. The objectives of this study were to investigate the physiological bases of the sowing date (S), genotype (G), and G x S interaction effects on sunflower yield, and to contribute to the formulation of ideotype-based selection strategies for improving yield at late plantings. Nine hybrids differentially adapted to northern and central Argentina were evaluated during two seasons in October (normal) and December (late) planting dates at Venado Tuerto, Argentina. Yield was defined as the product of total biomass and harvest index. Sowing date accounted for most of the yield variation. The G × S interaction, in turn, accounted for a portion of the total variability three times higher than the contribution of G. Both S and G x S interaction effects on yield mostly involved the variation of attributes and processes expressed postanthesis. Biomass differences between planting dates were the dominant determinant of the S effect on yield. The genotype-specific responses for harvest index were the dominant determinant of the G x S interaction, and were mostly associated with changes in the rate of harvest index increase. Variations in biomass and harvest index were strongly associated with the amount of intercepted radiation during grain filling which, in turn, was associated to duration of grain filling and green leaf area. Canopy stay green proved to be associated with adaptation to late planting dates. This indirect selection criterion appears to be a more reliable attribute for use in breeding for adaptation to late plantings than some other genotype characteristics linked to yield.

Simulating phenology and yield response of canola to sowing date in Western Australia using the APSIM model

Abstract: Canola is a relatively new crop in the Mediterranean environment of Western Australia and growers need information on crop management to maximise profitability. However, local information from field experiments is limited to a few seasons and its interpretation is hampered by seasonal rainfall variability. Under these circumstances, a simulation model can be a useful tool. The APSIM-Canola model was tested using data from Western Australian field experiments. These experiments included different locations, cultivars, and sowing dates. Flowering date was predicted by the model with a root mean squared deviation (RMSD) of 4.7 days. The reduction in the period from sowing to flowering with delay in sowing date was accurately reproduced by the model. Observed yields ranged from 0.1 to 3.2 t/ha and simulated yields from 0.4 to 3.0 t/ha. Yields were predicted with a RMSD of 0.3–0.4 t/ha. The yield reduction with delayed sowing date in the high, medium, and low rainfall region (3.2, 6.1, and 8.6% per week, respectively) was accurately simulated by the model (1.1, 6.7, and 10.3% per week, respectively). It is concluded that the APSIM-Canola model, together with long-term weather data, can be reliably used to quantify yield expectation for different cultivars, sowing dates, and locations in the grainbelt of Western Australia.

Woody invasion of grasslands: evidence that CO 2 enrichment indirectly promotes establishment of Prosopis glandulosa

Abstract: Grasslands worldwide have been invaded by woody species during the last 200 years. Atmospheric CO2 enrichment may indirectly have facilitated invasion by reducing soil water depletion by grasses. We used a two-step correlative approach to test this hypothesis with the invasive and native shrub honey mesquite (Prosopis glandulosa Torr. var. glandulosa). 1) Water content to 0.15 m depth was measured in grassland exposed to a CO2 gradient from 200 to 550 mol/mol to evaluate the prediction that CO2 enrichment lessens soil water depletion by grasses. 2) Soil water content and emergence and survival of mesquite seedlings were measured in adjacent grassland plots from which grass roots were excluded to 0.15 m depth to reduce water depletion or that were irrigated to increase soil water levels. With these measurements, we tested the hypothesis that mesquite establishment is limited by water. Excluding grass roots doubled emergence of mesquite and almost tripled the fraction of emergent seedlings that survived for 12 weeks following the first of two plantings. Seedlings were taller, heavier, and had greater leaf area when grown without grass roots. Root exclusion did not measurably affect soil water during the 3-week period of seedling emergence, but soil water content over the 12 weeks that seedling survival was studied was higher in plots from which grass roots were excluded and following an April than May planting. Survivorship of mesquite seedlings correlated positively with soil water content. Percentage survival of seedlings increased from 1.5% to 15% and 28% at the soil water content measured in grassland exposed to CO 2 concentrations of 270 (preindustrial), 360 (current), and 550 mol/mol (future), respectively. We infer that recent and projected increases in atmospheric CO 2 concentration may be large enough to increase establishment of invading mesquite seedlings in grasslands that are severely water-limited.

On-farm assessment of environmental and management constraints to wheat yield and efficiency in the use of rainfall in the Mallee

Abstract: The responses of wheat grain yield to soil properties, weather, root diseases, and management practices were investigated in 75 grower-managed crops in the Mallee region of South Australia, Victoria, and New South Wales during 3 growing seasons. Fourteen cultivars were represented in the sampled crops, with Frame being the most common (56%). The most widespread crop sequence was wheat after pasture (43% of wheat crops), followed by wheat after fallow or cereal (both about 20%); 12% of the wheat was sown after legumes. Wheat after cereal was more common in drier sites, and wheat after fallow in wetter sites. Wheat yield was proportional to Fischer's photothermal coefficient around flowering, and ranged from nil to 4.7 t/ha. On average, wheat crops sown after cereals yielded 0.4 t/ha less than their counterparts sown after fallow, and 0.7 t/ha less than those after legumes. Sowing date ranged from 24 April to 21 July; yield declined with delayed sowing at an average rate of 17 kg/ha.day. Growing season rainfall (April-October) ranged from 111 to 266 mm, and accounted for 27% of the variation in grain yield. Soil water content at sowing (0-1 m) ranged from 32 to 330 mm; yield increased with initial soil water at an average rate of 6 kg/ha.mm. Grain yield per unit growing season rainfall was generally low, with 75% of crops producing <12 kg grain/ha.mm; the maximum ratio was 21 kg/ha.mm. Soil constraints, including sodicity, alkalinity, salinity, and boron toxicity, reduced yield in part by reducing availability of stored soil water. Owing to severity of chemical constraints increasing with soil depth, grain yield and yield per unit growing season rainfall were both inversely related to the proportion of water stored deeper in the soil (0.5-1 m). Yield was unrelated to nitrogen, both initial and applied. Larger amounts of nitrogen accumulated in soils with more severe constraints partially accounted for the lack of association between yield and nitrogen. Additional keywords: participatory research, Triticum aestivum, plant-available water, dryland agriculture, water use efficiency. Aefof l V. S

Soil attributes in a furrow-irrigated bed planting system in northwest Mexico

Abstract: In the Yaqui valley, northwest Mexico, wheat ( Triticum aestivum L.) is grown as a winter crop followed by maize ( Zea mays L.) as a summer crop both planted on beds. Straw of both crops is usually burned to facilitate seedbed preparation for the succeeding crop. Soil physical and biological attributes were determined from 1996 to 2000 from a study initiated in 1992 at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station. The objective was to compare five treatments: (1) conventional tilled bed (CTB)-straw incorporated, and permanent bed (PB) with (2) straw removed, (3) straw partly removed, (4) straw retained, and (5) straw burned — on soil strength, soil structure, and soil microbial biomass carbon (SMB). Seven N treatments were applied to wheat, but for the purpose of this study we chose a subset of three N treatments (0, 150 and 300 kg N ha −1 ) for measurements. Maize received a uniform application of 150 kg N ha −1 each year. Soil strength decreased as the amount of crop residues applied for each tillage-straw treatment increased. Permanent beds-straw burned treatment had the highest soil strength and CTB-straw incorporated the lowest. The largest soil aggregate fractionation, evaluated with a fractal dimension parameter ( D ), corresponded to PB-straw burned treatment and the lowest to PB-straw retained treatment. SMB was greater at 0–7 cm than at 7–15 cm depth. As the amount of crop residues increased in each tillage PB-straw treatment, the SMB generally increased. The largest amount of SMB occurred most often on either CTB-straw incorporated or PB-straw retained and the lowest in PB-straw burned treatment. The practice of retaining crop residues as stubble should be adopted in the Yaqui valley since changes resulting from burning crop residues showed the tendency to decrease productivity and soil quality as shown by increased soil strength and soil fractionation, and reduced SMB.

Improved Yield Potential with an Early Planting Cotton Production System

Abstract: Mid-South cotton (Gossypium hirsutum L.) has reached a yield plateau in recent years. Shifting the growing season earlier in the year by planting earlier may allow the crop to develop under more favorable weather patterns and escape late season insects, The objectives were to determine the effect of early planting on growth and development, lint yield, and fiber quality of cotton. Early season dry matter partitioning, early season light interception, weekly bloom counts, lint yield, yield components, and fiber quality data were collected on genotypes planted during the first week of April (early planting) and the first week of May (normal planting). The data were collected from two experiments conducted over the years 1996 to 2000. Early June leaf area index of the early planted plants was 172% greater than plants in the normal planting, which contributed to a 55% greater canopy light interception for the early planting at that time. Early planting shifted the blooming period earlier in the growing season every year but 1997. Four out of 5 yr, the early planted cotton demonstrated a 10% yield improvement over the normal planted crop. In 1997, the early planted crop was stunted by an early season cold period, and yet its yields were equivalent to the normal planted crop. Planting earlier than normal has the potential to provide for increased lint yields for Mississippi Delta cotton producers. Techniques to mitigate early cold temperature stress could help make the yield improvements found with this early planting production system more consistent.