Stubble retention and tillage in a semi-arid environment: 1. Soil water accumulation during fallow

A study was carried out over 4 years at two sites in semi-arid, north-west Victoria, Australia, to examine the effect of soil surface management during fallow on water and nitrogen accumulation and their effect on the growth and yield of the subsequent wheat crop. The fallow treatments comprised four combinations of stubble management and tillage in 18-month-long fallows of a fallow-wheat rotation together with a pea-wheat rotation which included an annual short (6 month) tilled summer fallow. The two sites are representative of the major soil types of the region; a chromic vertisol at Dooen and a calcic xerosol at Walpeup. This paper reports observations and analyses of soil water accumulation during the fallow phase. At Dooen, tillage without stubble increased soil water storage, at sowing, on average by 76 mm (range 24–122 mm) above the summer fallow. Stubble retention added a further 52 mm (range 36–65 mm). Zero tillage was beneficial in one year, and was enhanced by the presence of stubble. In contrast, at Walpeup, tillage without stubble provided an average of 37 mm more water at sowing than the summer fallow. Stubble retention without tillage increased water storage by 27 mm in only one year. At both sites the additional water stored due to stubble retention was located deep in the profile to 2.0 m. In general, zero tillage, primarily with stubble retention, offered large and consistent increases in soil water storage on heavy-textured clay soils in a 420-mm rainfall zone. On the lighter, sandy loam soil under the lower rainfall regime (343 mm), the advantage in soil water storage, through both stubble retention and zero tillage, was less frequent.     

Productivity and sustainability of a spring wheat–field pea rotation in a semi-arid environment under conventional and conservation tillage systems

A long-term rotation experiment was established in 2001 to compare conservation tillage techniques with conventional tillage in a semi-arid environment in the western Loess Plateau of China. We examined resource use efficiencies and crop productivity in a spring wheat (Triticum aestivum L.)–field pea (Pisum arvense L.) rotation. The experimental design included a factorial combination of tillage with different ground covers (complete stubble removal, stubble retained and plastic film mulch). Results showed that there was more soil water in 0–30 cm at sowing under the no-till with stubble retained treatment than the conventional tillage with stubble removed treatment for both field pea (60 mm vs. 55 mm) and spring wheat (60 mm vs. 53 mm). The fallow rainfall efficiency was up to 18% on the no-till with stubble retained treatment compared to only 8% for the conventional tillage with stubble removed treatment. The water use efficiency was the highest in the no-till with stubble retained treatment for both field pea (10.2 kg/ha mm) and spring wheat (8.0 kg/ha mm), but the lowest on the no-till with stubble removed treatment for both crops (8.4 kg/ha mm vs. 6.9 kg/ha mm). Spring wheat also had the highest nitrogen use efficiency on the no-till with stubble retained treatment (24.5%) and the lowest on the no-till with stubble removed treatment (15.5%). As a result, grain yields were the highest under no-till with stubble retained treatment, but the lowest under no-till with no ground cover treatment for both spring wheat (2.4 t/ha vs. 1.9 t/ha) and field pea (1.8 t/ha vs. 1.4 t/ha). The important finding from this study is that conservation tillage has to be adopted as a system, combining both no-tillage and retention of crop residues. Adoption of a no-till system with stubble removal will result in reductions in grain yields and a combination of soil degradation and erosion. Plastic film mulch increased crop yields in the short-term compared with the conventional tillage practice. However, use of non-biodegradable plastic film creates a disposal problem and contamination risk for soil and water resources. It was concluded that no-till with stubble retained treatment was the best option in terms of higher and more efficient use of water and nutrient resources and would result in increased crop productivity and sustainability for the semi-arid region in the Loess Plateau. The prospects for adoption of conservation tillage under local conditions were also discussed.     

Stable high yields with zero tillage and permanent bed planting?

Subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. This article considers practices that would sustain higher and stable yields for wheat and maize in such region. A long-term field experiment under rainfed conditions was started at El Batán, Mexico (2240 m a.s.l.; 19.31°N, 98.50°W; fine, mixed, thermic, Cumulic Haplustoll) in 1991. It included treatments varying in: (1) rotation (continuous maize (Zea mays) or wheat (Triticum aestivum) and the rotation of both); (2) tillage (conventional, zero and permanent beds); (3) crop residue management (full, partial or no retention). Small-scale maize and wheat farmers may expect yield improvements through zero tillage, appropriate rotations and retention of sufficient residues (average maize and wheat yield of 5285 and 5591 kg ha⁻¹), compared to the common practices of heavy tillage before seeding, monocropping and crop residue removal (average maize and wheat yield of 3570 and 4414 kg ha⁻¹). Leaving residue on the field is critical for zero tillage practices. However, it can take some time—roughly 5 years—before the benefits are evident. After that, zero tillage with residue retention resulted in higher and more stable yields than alternative management. Conventional tillage with or without residue incorporation resulted in intermediate yields. Zero tillage without residue drastically reduced yields, except in the case of continuous wheat which, although not high yielding, still performed better than the other treatments with zero tillage and residue removal. Zero tillage treatments with partial residue removal gave yields equivalent to treatments with full residue retention (average maize and wheat yield of 5868 and 5250 kg ha⁻¹). There may be scope to remove part of the residues for fodder and still retain adequate amounts to provide the necessary ground cover. This could make the adoption of zero tillage more acceptable for the small-scale, subsistence farmer whose livelihood strategies include livestock as a key component. Raised-bed cultivation systems allow both dramatic reductions in tillage and opportunities to retain crop residues on the soil surface. Permanent bed treatments combined with rotation and residue retention yielded the same as the zero tillage treatments, with the advantage that more varied weeding and fertilizer application practices are possible. It is important small-scale farmers have access to, and are trained in the use of these technologies.     

Cropping sequence and tillage system influences annual crop production and water use in semiarid Montana,USA

Available water is typically the biggest constraint to spring wheat production in the northern Great Plains of the USA. The most common rotation for spring wheat is with summer fallow, which is used to accrue additional soil moisture. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, allowing for increased cropping intensity. We conducted a field trial from 1998 through 2003 comparing productivity and water use of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average most years, resulting in substantial drought stress to crops not following fallow. Preplant soil water, water use, and spring wheat yields were generally greater following summer fallow than wheat recropped after wheat or alternate crops. Water use and yield of wheat following summer fallow was greater than for chickpea or yellow mustard, the only other crops in the trial that followed summer fallow. Field pea performed best of all alternate crops, providing yields comparable to those of recropped spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region, at least during periods of below average precipitation. Following summer fallow, and despite drought conditions, zero tillage often provided greater amounts of soil water at planting compared to conventional tillage.     

Using legumes to enhance nitrogen fertility and improve soil condition in cotton cropping systems

Many Australian cotton growers now include legumes in their cropping system. Three experiments were conducted between 1994 and 1997 to evaluate the rotational effects of winter or summer legume crops grown either for grain or green manuring on following cotton (Gossypium hirsutum L.). Non-legume rotation crops, wheat (Triticum aestivum) and cotton, were included for comparison. Net nitrogen (N) balances, which included estimates of N associated with the nodulated roots, were calculated for the legume phase of each cropping sequence. Faba bean (Vicia faba — winter) fixed 135–244 kg N ha⁻¹ and soybean (Glycine max — summer) fixed 453–488 kg N ha⁻¹ and contributed up to 155 and 280 kg fixed N ha⁻¹, respectively, to the soil after seed harvest. Green-manured field pea (Pisum sativum — winter) and lablab (Lablab purpureus — summer) fixed 123–209 and 181–240 kg N ha⁻¹, respectively, before the crops were slashed and incorporated into the topsoil.In a separate experiment, the loss of N from ¹⁵N-labelled legume residues during the fallow between legume cropping and cotton sowing (5–6 months following summer crops and 9 months after winter crops) was between 9 and 40% of ¹⁵N added; in comparison, the loss of ¹⁵N fertilizer (urea) applied to the non-legume plots averaged 85% of ¹⁵N added. Little legume-derived ¹⁵N was lost from the system during the growth of the subsequent cotton crop.The improved N fertility of the legume-based systems was demonstrated by enhanced N uptake and lint yield of cotton. The economic optimum N fertilizer application rate was determined from the fitted N response curve observed following the application of N fertilizer at rates between 0 and 200 kg N ha⁻¹ (as anhydrous ammonia). Averaged over the three experiments, cotton following non-legume rotation crops required the application of 179 kg N ha⁻¹, whilst following the grain- and green-manured legume systems required only 90 and 52 kg N ha⁻¹, respectively.In addition to improvements in N availability, soil strength was generally lower following most legume crops than non-legume rotation crops. Penetrometer resistance during the growth of the subsequent cotton crop increased in the order faba bean, lablab, field pea, wheat, cotton, and soybean. It is speculated that reduced soil strength contributed to improvement in lint yields of the following cotton crops by facilitating the development of better root systems.     

玉米秸秆还田对土壤呼吸速率的影响

对传统耕法、宽窄行立茬交替休闲+条带深松、宽窄行立茬+秸秆粉碎还田+条带深松、宽窄行立茬+秸秆条带覆盖+条带深松、宽窄行立茬+全方位深松5个耕作模式下土壤呼吸速率进行研究。结果表明,少免耕模式与传统耕法相比土壤呼吸速率降低,宽窄行立高茬+秸秆粉碎还田+条带深松降低最为明显,降低了42.63%。相关分析表明,土壤呼吸速率与土壤温度存在显著线性关系。     

Long-term effects of mulch,fertilization and tillage on cassava grown in sandy soils in northern Colombia

Cassava (Manihot esculenta Crantz) is often cultivated in sandy soils that are very low in nutrients and organic matter. Under such conditions, yields often decline when the crop is grown successively without fertilizer application. An 8-year on-farm trial was conducted on sandy soils in northern Colombia to study effects of (1) surface mulching with residues of the grass Panicum maximum, (2) moderate applications of N, P and K fertilizer and (3) tillage on crop productivity, root quality and soil properties. Mulch applications significantly increased root and top biomass, increased root dry matter content while reducing its yearly variation, and decreased root HCN, particularly in the absence of fertilizer. Mulch applications also significantly reduced soil temperatures within the top 20 cm and increased soil organic carbon, K, P, Ca and Mg. Without mulch, soil pH decreased over the years. Annual applications of 21 kg ha⁻¹ P resulted in a build-up of soil P, whereas no build-up of soil K was observed with applications of 41 kg K ha⁻¹. The application of N, P and K fertilizer significantly increased root and top biomass and reduced root HCN, especially if no mulch was applied. Where both mulch and fertilizer applications were absent, root yield and top biomass declined over the years. Tillage, except when combined with fertilizer application, had no effect on root yield, top biomass, root dry matter or HCN contents. Neither were effects of tillage observed in any of the studied soil parameters. The trial indicated that, to sustain cassava productivity in poor sandy soils, applications of plant mulch and/or chemical fertilizer are highly desirable.     

Orchardgrass response to different types,rates and application patterns of dairy manure

Manure management is a difficult task on many intensive dairy farms. Crops that can utilize large quantities of manure N, yield quality forage with larger rates of manure application, and allow manure spreading at different times in a year can simplify that task. A study was conducted in 1990 and 1991 on a Copake sandy loam soil (mixed mesic) in New Milford, Connecticut. The objectives were: (1) to measure and compare dry matter (DM) response of orchardgrass (Dactylis glomerata L.) to different amounts and application times of N fertilizer and liquid and solid cattle manure; and (2) to determine crop uptake of fertilizer and manure N. Fertilizer and liquid and solid manure were applied to the soil surface annually in amounts of 150, 300 or 450 kg N ha⁻¹ in one, two or four equal applications. Orchardgrass dry matter production increased over the entire range of N amounts from all sources. Yields varied from approximately 2500 kg DM ha⁻¹ for control plots (0 kg N) to 10600 kg for plots receiving 450 kg N ha⁻¹ either as fertilizer or liquid manure. Crop response to liquid manure application was greater in year one with abundant rainfall than in year two with dry conditions during most of the growing season, whereas crop response to solid manure application improved in the second year, due to the availability of residual organic N. Orchardgrass was more sensitive to the timing of fertilizer N application than to manure N application. Despite the large differences in weather patterns experienced during this study, analysis of application patterns indicated that manure could be applied throughout the growing season to crop stubble (post-harvest) with comparable rates of uptake overall. N uptake in control plots averaged 56 kg N ha⁻¹ for both years, compared to 340 kg N ha ⁻¹ for fertilizer plots, 250 kg N ha ⁻¹ for liquid manure plots and 190 kg N ha⁻¹ for solid manure plots receiving 450 kg total N ha ⁻¹.     

Influence of crop rotation on selected chemical and physical soil properties in potato cropping systems

Crop yields are often increased through crop rotation. This study examined selected soil chemical and physical properties that may constitute the N and non-N related effects of crop rotation in potato cropping systems. Potato (Solanum tuberosum L. Norwis) was grown continuously and in two-year rotations with annual alfalfa (Medicago sativa L. Nitro), hairy vetch (Vicia villosa Roth), white lupin (Lupinus albus L. Ultra), and oat (Avena sativa Astro). Hairy vetch contributed more residue N than any other crop rotation, ranging from 110 to 119 kg N ha^?1. Inorganic N concentrations in potato soils were related to the previous crop’s residue N contents, and were highest following vetch and alfalfa and lowest following oat and potato. The highest mineralizable N concentration was found following vetch (46.6 mg N kg^?1). Saturated soil hydraulic conductivity in potato following all rotations ranged from 9.88 to 11.28 cm h^?1 compared to 5.71 cm h^?1 for continuous potato. Higher soil water contents were maintained in the 30 to 45 cm depth for all rotations compared to continuous potato. Thus several parameters indicate substantial N effects associated with particular crop rotations. Soil hydraulic conductivity and soil water status may also represent significant components of the rotation effect not directly related to N for these cropping systems.     

Root growth,soil water content and yield of barley under different tillage systems on two soils in semiarid conditions

An experiment was conducted on two soils in a semiarid area in the Spain’s Ebro valley. Soil A was a Fluventic Xerochrept of 120 cm depth and Soil B was a Lithic Xeric Torriorthent of 30 cm depth. Three tillage systems were compared in Soil A: subsoiler tillage, minimum tillage and no-tillage, and two (minimum tillage and no-tillage) in Soil B. The experiment was repeated for 5 years on Soil A and 3 years on Soil B. Root length density, volumetric water content and dry matter were measured at important developmental stages. Yield was determined at harvest. In Soil A, root length density and volumetric water content were significantly greater for no-tillage than for subsoiler or minimum tillage (up to 1.4 cm cm⁻³ and 5%, respectively), mainly in the upper part of the soil profile. At lower depths, differences as great as 0.8 cm cm⁻³ and 6% were also found. Mean yield (4 years) was similar between no-tillage (3608 kg ha⁻¹) and minimum tillage (3508 kg ha⁻¹), and significantly smaller for subsoiler tillage (3371 kg ha⁻¹). In Soil B, no differences were observed between tillage systems for volumetric water content. Significant interactions between tillage and year were found for root length density, dry matter and yield. Mean yield (3 years) was not significantly different for minimum tillage (1806 kg ha⁻¹) and no-tillage (1867 kg ha⁻¹). The results in Soil A showed that surface conditions are of major importance in the water content of the soil and determined the differences among tillage systems. No-tillage favoured greater and deeper water accumulation in the soil profile and greater root growth. This makes this system potentially better for years of low rainfall. In Soil B no tillage system proved to be better because of the low water-holding capacity of this soil (56 mm).     

Long-term effect of tillage systems on soil microbiological,chemical and physical parameters and the incidence of charcoal rot by Macrophomina phaseolina (Tassi) Goid in soybean

A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot (Macrophomina phaseolina) of soybean and crop yield. The tillage systems evaluated were direct seeding (DS), DS + scarifier (DS + S), minimum tillage (MT) and conventional tillage (CT). DS presented higher values than CT in culturable total fungi (26.33 × 10⁵ vs. 2.33 × 10⁵ CFU g⁻¹ dry soil), total bacteria (182 × 10⁷ vs. 64 × 10⁷ CFU g⁻¹ dry soil), microbial respiration (0.77 mg CO₂ g⁻¹ week⁻¹ vs. 0.45 mg CO₂ g⁻¹ week⁻¹) and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g⁻¹ h⁻¹ vs. 1.70 ug fluorescein g⁻¹ h⁻¹ in CT. Fungal and bacterial community fingerprints, by terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intergenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME (fatty acid methyl ester) profiles showed that microbial community structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results showed that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS. Soybean grown in high-quality soil was not affected by charcoal rot, however, under CT, disease incidence in soybean was 54%. These differences were correlated to the higher microbial abundance and activity under DS, the biological component being a key factor determining soil capacity to suppress the soilborne pathogen.     

Effects of tillage,crop rotation and nitrogen fertilization on wheat-grain quality grown under rainfed Mediterranean conditions

The grain quality of wheat is influenced by the protein content, which in turn depends on environmental conditions and cropping practices. We carried out a 3-year field study in a rainfed Mediterranean region on the effects of tillage, crop rotation and nitrogen fertilization on the grain quality of hard red spring wheat (Triticum aestivum) in terms of protein content, test weight and alveogram indices. Tillage treatments were no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–fababean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Fertilizer nitrogen was used at three different rates: 50, 100 and 150 kg N ha⁻¹. A split–split plot design with four replicates was used. Grain protein content was found to be inversely proportional to rainfall during the growing season. The tillage method was also found to affect grain protein content, test weight and some grain quality indices. Through its effect on moisture and nitrate in the soil. The crop rotations that included a legume (WCP and WFB) had marked effects on wheat quality. The increased grain protein content and resulted in improved rheological properties of the dough (viz. a higher alveogram index and a more balanced tenacity/extensibility ratio). However, no differences due to N dilution in the plant were observed in the wettest year studied, which was also the highest yielding. Increasing the fertilizer N rate increased the grain protein content; this variable had the most marked influence on grain quality indices, though in the year that gave the highest yield the N dilution effect was observed. The many significant interactions among experimental variables reveal a close relationship among grain yield, protein content, grain quality and the wheat growth conditions. Specifically, the amount of rainfall and its distribution in the growing season strongly influenced N availability and uptake by the crop, as well as wheat-grain quality indices.     

Effects of crop density and tillage system on grain yield and N uptake from soil and atmosphere of sole and intercropped pea and oat

Pea (Pisum sativum L.) and oat (Avena sativa L.) were grown as sole and mixed crops in various densities under two different tillage systems on a loess soil near Göttingen/Germany in a 2-year field experiment (2002/2003). In the conventional tillage system a mouldboard plough (CT) was used and in the minimum tillage system a rotary harrow (MT) was employed. The effect of crop density and tillage system on the grain dry matter and grain N yields, N₂ fixation and soil N uptake were determined to address the following questions: (i) which mixture compositions exhibit the highest grain yields compared to the sole crops, (ii) which mixture compositions also fix a high level of N₂ and leave low levels of residual inorganic soil N after harvest, and (iii) whether the intercrop advantage is influenced by the tillage system. For (i) the result in 2002 showed that the highest grain yields of both sole cropped pea and oat and intercropped pea and oat were achieved at the highest densities. In 2003, when the inorganic soil N content was higher and weather conditions were warmer and drier, grain yields were significantly higher than in 2002, but sole as well as intercropped pea and oat gave their highest grain yields at lower densities. For both years and tillage systems, the highest intercrop advantages were achieved in mixtures with densities above the optimal sole crop densities. The result for (ii) was that a distinctly higher proportion of nitrogen was derived from the atmosphere (Ndfa) by intercropped pea than by sole cropped pea. However, the uptake of soil N by intercropped pea and oat was not reduced in comparison with that of sole cropped oat as the decrease in the uptake of N from the soil by oat at lower oat densities in the mixture was compensated for by the soil N uptake of pea. Additionally, the N_min-N content of the soil following the mixtures and sole cropped oat did not differ, especially in the deeper soil layers because oat in mixture was forced to take up more soil N from deeper layers. Therefore, the risk of soil N losses through leaching after mixtures was lower compared to sole cropped pea. The tillage system (iii) had no significant influence on grain yield and soil N uptake, but N₂ fixation and the competitive ability of intercropped pea were higher under CT than with MT. An additional result was that intercropping led to a significantly increased grain N content of both pea and oat compared to the sole crops. The increase in grain N content from sole to intercrop was from 3.30 to 3.42% for pea and from 1.73 to 1.96% for oat as a mean for both years and tillage systems. The present study confirms that growing pea and oat as intercrops highlights potential economic and environmental benefits which still need to be understood in more detail in order to exploit intercropping to a greater extent.     

Influence of different tillage methods and pre-emergence herbicides on weed control in cowpea (Vigna unguiculata (L.) Walp.)

In the early and late cropping seasons of 1983, three different methods of tillage (minimum tillage, conventional tillage, and tilled and ridged) were evaluated for their influence on the performance of some pre-emergence herbicides used during the production of cowpea. Four varieties of cowpea (Ife Brown, H 144-1, TVx 3236, and Black-eyed bean) were planted in the early season while five varieties (Ife Brown, H 144-1, TVx 3236, H64/3 and Vita-5) were planted in the late season. A single spray application of 3·0 kg/ha alachlor, 3·0 kg/ha metobromuron + metolachlor and 3·5 kg/ha metolachlor was carried out one day before planting. Cyanazine at 3·0 kg/ha was included in the late season trial. The plots were either minimally tilled, conventionally tilled or tilled and ridged at the Teaching and Research Farm of the University of Ife. Results showed that the performance of all three herbicides used in the early season, as measured by weed control and grain yields, was best on the conventionally tilled, while the performance of the four herbicides in the late season was best on tilled and ridged plots. Metobromuron + metolachlor performed consistently better than each of the other herbicides irrespective of the method of tillage during both seasons. Conventional tillage enhanced the performance of metobromuron + metolachlor over minimum tillage plots and tilled and ridged plots in the early season; however, in the late season, the performance of metobromuron + metolachlor was best on tilled and ridged plots. Alachlor did not effectively control competing weeds in both seasons but did not injure any cowpea line. On the other hand, cyanazine did not control weeds effectively but was phytotoxic to Ife Brown variety of cowpea. In both seasons, the control of the broad-leaved weeds Ageratum conyzoides, Amaranthus spp., Euphorbia heterophylla, Ipomoea spp., Spigelia anthelmia, Synedrella nodiflora and Talinum triangulare was not adequate. The control of the grassy weeds Brachiaria deflexa, Cynodon dactylon, Imperata cylindrica and Eleusine indica was, however, effective.     

A framework for determining the efficient combination of organic materials and mineral fertilizer applied in maize cropping

Application of organic manures and composts in crop production has been strongly encouraged in many places but often without due consideration to their quality and price. Since organic amendments can vary greatly in composition and mineralization rate, a framework is needed to make rational choices on their use as replacements of inorganic fertilizer, especially when considering poor quality organic materials. A field experiment was carried out with maize grown annually for 5 years on a Rhodic Kandiustox in Thailand to test response to mineral fertilizer (at 0-0 to 125-55 kg N-P ha⁻¹ yr⁻¹), compost (0.59% N, 0.31% P and 0.55% K at 0-7500 kg ha⁻¹ yr⁻¹) and stubble removal. The DSSAT model was calibrated to predict yields using the first year's trial data and then used to predict treatment yields for the following 4 years. The Seasonal Analysis module of DSSAT using Dominance Analysis showed that mineral fertilizer (125-55 kg N-P ha⁻¹ yr⁻¹) with stubble return gave the highest net profit whereas the highest rate of compost without mineral fertilizer gave the biggest loss. The yield response was attributed primarily to N supply rather than P. Effects of compost, mineral fertilizer, stubble management, and their interactions on yield and profit were not related to bulk density or soil available water capacity even though soil organic matter (SOM) levels increased. With stubble return, the highest rate of mineral fertilizer increased SOM whereas with compost application or stubble removal it did not. The DSSAT simulation of yield indicated that the low quality compost would only be as profitable as mineral fertilizer if the N concentrations are 3-4 times higher than the present compost (1.8-2.4% N) or if the compost price is greatly reduced. The DSSAT yield simulation and Seasonal Analysis provided a framework whereby the suitability of compost as a N fertilizer replacement for maize could be determined based on its composition, rate of application and price. Further validation of this approach is needed where the organic amendments have significant effects on soil physical properties and where other nutrients besides N are a significant factor in the crop yield response.     

Trends in maize grain yields in a long-term fertilizer trial

Maize (Zea mays L.) (summer) was rotated with field pea (Pisum arvense Poir.) (winter) on soil of the Hutton form (loamy, mixed, thermic Rhodic Kandiudalf) over a 50-year period. Water (W), nitrogen (N), phosphorus (P), potassium (K) and farm yard manure (M) were each applied at two levels in a 2⁵ factorial experiment. The lower levels of N, P, K and M were zero applications. Simple effects for N, P and K and the main effect for M were positively correlated with yield level. Over time, the simple effect of N exhibited an increased positive trend only when pea straw was removed rather than incorporated, while simple effects of P and K increased sharply during later years. The zero fertilizer treatment yielded in excess of 2 t maize grain ha⁻¹ during the last decade of the trial. Manure provided consistently high yields without addition of inorganic fertilizer. This was ascribed mainly to an ample nutrient supply, as soil organic matter levels were only marginally higher than in the balanced NPK treatment, which received inorganic fertilizers. The greatest depletion of soil organic matter occurred in imbalanced treatments and the control. Threshold P and K levels in topsoil for attaining yields of 4–6 t ha⁻¹ were ca. 5 mg kg⁻¹ P and 35–40 mg kg⁻¹ K, respectively, in P- and K-deficient treatments. Fertilizer N, P and K were utilised more efficiently in fully balanced than in imbalanced fertilizer treatments. In treatments receiving abundant P, about 60% of potential plant-available P could not be accounted for. The legume crop apparently played a major role in the more efficient utilisation of nitrogen and phosphorus by crops in treatments where these elements were not applied.     

The effect of sowing date and nitrogen on the dry‐matter yield and nitrogen content of forage rape (Brassica napus L.) and stubble turnips (Brassica rapa L.) in Ireland

Two field experiments were conducted at Teagasc, Moorepark, Ireland, to determine the effect of sowing date and nitrogen application on the dry‐matter (DM) yield and crude protein (CP) content of forage rape and stubble turnips. The first experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) on forage rape DM yields. The second experiment consisted of three sowing dates (1 August, 15 August and 31 August) with four rates of fertilizer N (0, 40, 80 and 120 kg N ha^?1) over two soil sites (fertile or nitrogen depleted) on forage rape and stubble turnip DM yields. A delay in sowing from 1 to 31 August characterized a 74·5% decrease in forage rape DM yield, while stubble turnip DM yield decreased by 55·5%. Forage rape DM yields increased positively up to 120 kg N ha^?1 at the first two sowing dates over both sites. In contrast, stubble turnips showed less response beyond 40 kg N ha^?1 on site 1 in the first two sowing dates, while DM yield increased positively up to 120 kg N ha^?1 on the less fertile site. The results indicate that the optimal sowing time for forage rape and a stubble turnip in Ireland was early August.     

休闲期覆膜与施氮量对旱地小麦水氮利用效率和籽粒产量的影响

为探寻旱地小麦休闲期覆盖下的适宜施氮量,在旱地小麦休闲期覆盖与不覆盖条件下,分别设置75、150和225kg·hm-2三个施氮量,分析了休闲期覆盖配施氮肥对旱地小麦水氮利用效率和籽粒产量的影响。结果表明,休闲期覆盖显著提高播种至孕穗期0~300cm土壤蓄水量,其中播种期土壤水分增加70~81mm,其蓄水保墒效果可延续至孕穗期,进而提高了小麦产量和水分利用效率。休闲期覆盖促进了小麦植株对氮素的吸收和积累,增加了植株花前氮素转运量、花后氮素积累量以及籽粒氮素积累量,提高了氮素收获指数和氮素生产效率。休闲期覆盖配施氮素150kg·hm-2时,蓄水、增产和水分高效利用、氮素积累与转运的效果最好。     

Cover Crops as Affecting Soil Chemical and Physical Properties and Development of Upland Rice and Soybean Cultivated in Rotation

Cover crops can provide changes in soil chemical and physical properties, which could allow a sustainable development of soybean and upland rice rotation in Brazilian Cerrado. The objective of this study was to determine the effects of cover crops(cultivated in the offseason) in the soybean-upland rice rotation(cultivated in the summer season) on the soil chemical and physical properties, yield components and grain yield of the cash crops. The experimental design was a randomized block design in factorial scheme 4 × 2 with six replications. Treatments were composed by four cover crops: fallow, millet(Pennisetum glaucum) + Crotalaria ochroleuca, millet + pigeon pea(Cajanus cajans), and millet + pigeon pea + Urochola ruziziensis in the offseason with one or two cycles of cover crops, with rice(Oryza sativa)or soybean(Glycine max) in the summer season. Cover crops alone provided no changes in soil chemical properties. However, the rotation cover crops/cash crops/cover crops/cash crops reduced p H, Al and H + Al and increased Ca, Mg, K and Fe contents in the soil. The cover crops millet + pigeon pea and millet + pigeon pea + U. ruziziensis improved soil physical properties in relation to fallow,especially in the 0–0.10 m soil layer. In spite of the improvement of the soil physical properties after two years of rotation with cover crops and cash crops, the soil physical quality was still below the recommended level, showing values of macroporosity, S index and soil aeration capacity lower than 0.10 m3/m3, 0.035 and 0.34, respectively. Upland rice production was higher under mixtures of cover crops than under fallow, mainly because of soil physical changes done by these mixtures of cover crops.Soybean grain yield was similar under all cover crops tested, but was higher after the rotation cover crops/upland rice/cover crops than after only one cycle of cover crops.     

The implications of land preparation, crop establishment method and weed management on rice yield variation in the rice-wheat system in the Indo-Gangetic plains

The implications of adopting alternative seeding methods for rice and wheat establishment were examined at three geographically separate sites in the rice-wheat system of the Indo-Gangetic plains, across northern India. Rice yields in cultivated plots, established by either wet or dry seeding methods, were evaluated in comparison to yields from zero-tillage plots and under conventional transplanting methods. In the same trials, the effects of crop establishment methods in wheat were assessed both on wheat yields and rice yields. Rice crop establishment methods markedly influenced the emerging weed flora and attainable yields were measured in relation to intensity of weed management. Over four years, average rice grain yields in the absence of weed competition were greatest (6.56 t ha⁻¹) under wet seeding (sowing pre-germinated rice seed on puddled soil), and similar to those from transplanted rice (6.17 t ha⁻¹) into puddled soil, and dry seeded rice after dry soil tillage (6.15 t ha⁻¹). Lowest yields were observed from dry seeded rice sown without tillage (5.44 t ha⁻¹). Rice yield losses due to uncontrolled weed growth were least in transplanted rice (12%) but otherwise large (c. 85%) where rice had been sown to dry cultivated fields or to puddled soil, rising to 98% in dry seeded rice sown without soil tillage. Weed competition reduced multiple rice yield components, and weed biomass in wet seeded rice was six-fold greater that in rice transplanted into puddled soil and twice as much again in dry seeded rice sown either after dry tillage or without tillage. Wheat grain yields were significantly higher from crops sown into tilled soil (3.89 t ha⁻¹) than those sown without tillage (3.51 t ha⁻¹), and also were elevated (5% on average) where the soil had been dry cultivated in preparation for the previous rice crops rather than puddled. The method of wheat cultivation did not influence rice yield. Soil infiltration rates in the wheat season were least where the land had been puddled for rice (1.52 mm h⁻¹), and greater where the soil had been dry-tilled (2.63 mm h⁻¹) and greatest after zero-tillage (3.54 mm h⁻¹).These studies demonstrated at research managed sites across a wide geographic area, and on farmers’ fields, that yields of dry seeded rice sown after dry cultivation of soil were broadly comparable with those of transplanted rice, providing weed competition was absent. These results support the proposition that direct seeding of rice could provide an alternative to the conventional practice of transplanting, and help address rising costs and threats to sustainability in the rice-wheat rotation. Further, analysis of patterns of long-term rainfall data indicated that farmers reliant on monsoon rainfall could prepare fields for dry direct seeded rice some 30 days before they could prepare fields for either transplanting or seeding with pre-germinated seed. Dry, direct seeding of rice contributes a valuable component of an adaptive strategy to address monsoonal variability that also may advance the time of wheat establishment and yield. Whilst the results illustrate the robustness, feasibility and significant potential of direct seeded rice, they also highlight the critical nature of effective weed control in successful implementation of direct seeding systems for rice.