Effects of harvest and sowing time on the performance of the rotation of winter wheat–summer maize in the North China Plain

Rotation of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) is the prevailing double-cropping system in the North China Plain. Typically, winter wheat is planted at the beginning of October and harvested during early June. Maize is planted immediately after wheat and harvested around 25th of September. The growing season of maize is limited to about 100–110 days. How to rectify the sowing date of winter wheat and the harvest time of summer maize are two factors to achieve higher grain yield of the two crops. Three-year field experiments were carried out to compare the grain yield, evapotranspiration (ET), water use efficiency (WUE) and economic return under six combinations of the harvest time of summer maize and sowing date of winter wheat from 2002 to 2005. Yield of winter wheat was similar for treatments of sowing before 10th of October. Afterwards, yield of winter wheat was significantly reduced (P < 0.05) by 0.5% each day delayed in sowing. The kernel weight of maize was significantly increased (P < 0.05) by about 0.6% each day delayed from harvest before 5th of October. After 10th of October, kernel weight of maize was not significantly increased with the delay in harvest because of the lower temperature. The kernel weight of maize with thermal time was in a quadratic relationship. Total seasonal ET of winter wheat was reduced by 2.5 mm/day delayed in sowing and ET of maize was averagely increased by 2.0 mm/day delayed in harvest. The net income, benefit–cost and net profit per millimetre of water used of harvest maize at the beginning of October and sowing winter wheat around 10th of October were greater compared with other treatments. Then the common practice of harvest maize and sowing winter wheat in the region could be delayed by 5 days correspondingly.     

Rice straw mulching and nitrogen response of no-till wheat following rice in Bangladesh

Wheat (Triticum aestivum L.) cultivation in no-till soil of a postrice harvest field utilizes residual soil moisture and reduces the time period from rice harvest to wheat seeding in intensive rice-wheat cropping systems. Some of the major constraints in no-till wheat production are high weed infestation, poor stand establishment due to rapid drying of topsoil and low nitrogen use efficiency (NUE). A field experiment was conducted at the research farm of the Wheat Research Centre, Dinajpur, Bangladesh, for two consecutive years to overcome those constraints, to evaluate rice straw as mulch, and to determine the optimum application rate of nitrogen (N) for no-till wheat. The treatments included 12 factorial combinations of three levels of mulching: no mulch (M₀), surface application of rice straw mulch at 4.0 Mg ha⁻¹ that was withdrawn at 20 days after sowing (M₁), the same level of mulch as M₁ but allowed to be retained on the soil surface (M₂), and four nitrogen levels (control 80, 120 and 160 kg ha⁻¹). Rice straw mulching had a significant effect on conserving initial soil moisture and reducing weed growth. Root length density and root weight density of wheat were positively influenced both by straw mulching and N levels. N uptake and apparent nitrogen recovery of applied N fertilizer were higher in mulch treatments M₁ and M₂ as compared to M₀. Also mulch treatment of M₁ and M₂ were equally effective at conserving soil moisture, suppressing growth of weed flora, promoting root development and thereby improved grain yield of no-till wheat. N application of 120 kg ha⁻¹ with straw mulch was found to be suitable for no-till wheat in experimental field condition.     

Weed control in a pigeon pea–wheat cropping system

Pigeon pea (Cajanus cajan (L.) Millsp.) seedlings compete poorly against the rapid growth of warm-season annual weeds. Weed control is required before this heat and drought-tolerant legume can be reliably grown in the U.S. southern Great Plains as a potential source of livestock hay between annual plantings of winter wheat (Triticum aestivum L.). Currently, no herbicides are labeled for use on pigeon pea grown in the U.S. Three years of replicated field experiments were conducted to determine the effects of applications (1× and 2× rates) of herbicides (pre-emergence, sulfentrazone + chlorimuron and metribuzin; post-emergence, imazapic and sethoxydim) on weed suppression, pigeon pea dry matter, and carry-over effects on a winter wheat crop. The most abundant summer weeds were broadleaf, and all herbicide treatments, except sethoxydim (grass herbicide), reduced weed densities compared to untreated plots without adversely affecting pigeon pea stands. Imazapic treatments provided the most effective weed control. Overall average pigeon pea dry matter ranged from 75 to 256 g m⁻² with sethoxydim and the untreated control ≤ metribuzin ≤ sulfentrazone + chlorimuron ≤ hand weeded control ≤ imazapic. Compared to the hand-weeded control, imazapic treatments greatly reduced wheat dry matter (1×, 65% and 2×, 91%) and grain yield (1×, 59% and 2×, 93%). Imazapic should not be used unless nontransgenic imidazolinone herbicide tolerant wheat cultivars are planted. While the other herbicides decreased negative effects of weeds on pigeon pea dry matter without greatly affecting productivity of a following wheat crop, appropriate labels for each of these herbicides will be required prior to their use by southern Great Plains pigeon pea producers.     

Rates of nitrogen application required to achieve maximum energy efficiency for various crops: results of a long-term experiment

A long-term experiment with four rates of mineral nitrogen (N) application (averaged across all the crops in a crop rotation: 0, 50, 100, 150 kg ha⁻¹ per year) was conducted on a fertile loess-derived soil in central Germany. The objectives of this study were to (i) determine the rates of mineral nitrogen N application required for maximum net energy output (energy output minus energy input), maximum energy output/input ratio, and minimum energy intensity (energy input per unit grain equivalent) for various crops in a realistic crop rotation (potatoes [Solanum tuberosum L.], winter wheat [Triticum aestivum L.], winter barley [Hordeum vulgare L.], sugar beets [Beta vulgaris L.], spring barley [Hordeum vulgare L.]): (ii) identify long-term trends (from 1968 to 2000) in the rates of mineral N application necessary to achieve the most efficient use of energy in the production of winter wheat and (iii) assess the effects of changing the system boundaries and the energy equivalents assigned to selected inputs on the energy balance by means of a sensitivity analysis. In the last two crop rotations (1989–1993 and 1994–1999), the amount of N fertilizer required to maximize net energy output of the main products (cereal grains, beet roots) increased in the order sugar beets–winter wheat–winter barley. At optimum N fertilization, the net energy output increased in the order winter barley–winter wheat–sugar beets. Averaged across the two rotations, the N fertilizer demand for a maximum output/input ratio and minimum energy intensity increased in the order sugar beets–winter wheat–winter barley. There was no clear-cut time trend in the rate of N application required to maximize grain yield and net energy output of wheat; maximum grain yield, maximum net energy output, and output/input ratio increased significantly with time, whereas the minimum energy intensity decreased over the experimental period. For all the crops, the rate of N application required for the maximum net energy output was much higher than that required for the maximum output/input ratio and minimum energy intensity.     

Foliar sprays of concentrated urea at maturity of pigeonpea to induce defoliation and increase its residual benefit to wheat

The pigeonpea (Cajanus cajan (L.) Millsp.) crop retains appreciable amounts of green foliage even after reaching physiological maturity, which if allowed to defoliate, could augment the residual benefit of pigeonpea to the following wheat (Triticum aestivum L.) in a pigeonpea–wheat rotation. The effect of addition of leaves present on mature pigeonpea crop to the soil was examined on the following wheat during the 1999/2000 growing season at Patancheru (17°4′N, 78°2′E) and during the 2001–2003 growing seasons at Modipuram (29°4′N, 77°8′E). At Patancheru, an extra-short-duration pigeonpea cultivar ICPL 88039 was defoliated manually and using foliar sprays of 10% urea (30 kg/ha) and compared with a millet (Pennisetum glaucum (L.) R.Br.) crop, naturally senesced leaf residue and no-leaf residue controls. At Modipuram, the effect of 10% urea spray treatment on mature ICPL 88039 was compared with the unsprayed control. At both locations, the rainy season crops were followed by a wheat cultivar UP 2338 at four nitrogen levels applied in a split plot design, which at Patancheru were 0, 30, 90 and 120 kg N ha⁻¹ and at Modipuram 0, 60, 120 and 180 kg N ha⁻¹. At Patancheru, urea spray added 0.5 t ha⁻¹ of extra leaf litter to the soil within a week without significantly affecting pigeonpea yield. This treatment, however, increased mean wheat yield by 29% from 2.4 t ha⁻¹ in the no-leaf residue pigeonpea or pearl millet plots to 3.1 t ha⁻¹. At Modipuram, the foliar sprays of urea added more leaf litter to the soil than at Patancheru. Here, increase in subsequent wheat yield due to additional pigeonpea leaf litter was 7–8% and net profit 21% more than in the unsprayed control. The addition of pigeonpea leaf litter to the soil resulted in a saving of 40–60 kg N for the following wheat crops in both the environments. The results demonstrated that pigeonpea leaf litter could play an important role in the fertilizer N economy in wheat. The urea spray at maturity of the standing pigeonpea crop significantly improved this contribution in increasing wheat yield, the effect of which was additional to the amount of urea used for inducing defoliation. The practice, if adopted by farmers, may enhance sustainability of wheat production system in an environmentally friendly way, as it could reduce the amount of fertilizer N application to soil and enhance wheat yield.     

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.     

Efficient phosphorus application strategies for increased crop production in sub-Saharan West Africa

Comparable data are lacking from the range of environments found in sub-Saharan West Africa to draw more general conclusions about the relative merits of locally available rockphosphate (RockP) in alleviating phosphorus (P) constraints to crop growth. To fill this gap, a multi-factorial field experiment was conducted over 4 years at eight locations in Niger, Burkina Faso and Togo. These ranged in annual rainfall from 510 to 1300 mm. Crops grown were pearl millet (Pennisetum glaucum L.), sorghum (Sorghum bicolor (L.) Moench) and maize (Zea mays L.) either continuously or in rotation with cowpea (Vigna unguiculata Walp.) and groundnut (Arachis hypogaea L.). Crops were subjected to six P fertiliser treatments comprising RockP and soluble P at different rates and combined with 0 and 60 kg N ha⁻¹. For legumes, time trend analyses showed P-induced total dry matter (TDM) increases between 28 and 72% only with groundnut. Similarly, rotation-induced raises in cereal TDM compared to cereal monoculture were only observed with groundnut. For cereals, at the same rate of application, RockP was comparable to single superphosphate (SSP) only at two millet sites with topsoil pH-KCl<4.2 and annual average rainfall>600 mm. Across the eight sites NPK placement at 0.4 g P per hill raised average cereal yields between 26 and 220%. This was confirmed in 119 on-farm trials revealing P placement as a promising strategy to overcome P deficiency as the regionally most growth limiting nutrient constraint to cereals.     

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha⁻¹ in 2002, 310 kg ha⁻¹ in 2003, and 360 kg ha⁻¹ in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha⁻¹ of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.     

Model predictions of winter rainfall effects on N dynamics of winter wheat rotation following legume cover crop or fallow

Winter rainfall in a Mediterranean region varies from year to year. Both release of inorganic N from soil organic matter (SOM) or a legume cover crop (LCC) and subsequent nitrate movement in the soil profile are strongly affected by winter rainfall, through its effects on soil water status and on vertical flux. N accumulation of a LCC also varies over years due to weather effects on growth. Thus, these two factors need to be taken into account for efficient use of SOM-N and LCC-N in a wheat (Triticum aestivum L.) rotation. To determine how winter weather might affect the performance of wheat-fallow rotations that include an LCC grown and incorporated during the fallow year, we used the CERES-wheat model and a 46-season weather record to simulate N dynamics of 2-year unfertilized and irrigated winter-LCC wheat systems with high LCC (236 kg N ha⁻¹) or low LCC (118 kg N ha⁻¹) inputs. Unfertilized and fertilized fallow-wheat controls were also simulated. Within a given LCC input value, coefficients of variation for total seasonal N supply (the sum of predicted wheat N uptake, N leaching and inorganic soil N at wheat maturity) over years were <15%, despite the fluctuating winter rainfall (CV 48%). Average N leaching was predicted to be highest in the high LCC input system (108 kg N ha⁻¹), followed by the low LCC input system (86 kg N ha⁻¹) and midseason-intensive and planting-intensive fertilized wheat-fallow systems (82 and 72 kg N ha⁻¹, respectively), and least in the unfertilized wheat-fallow system (54 kg N ha⁻¹). N leaching exceeded 100 kg N ha⁻¹ in 4, 20, 16, 18, and 29 seasons out of 46 seasons, respectively, in the unfertilized and planting-intensive and midseason-intensive fertilized wheat-fallow rotations and in wheat rotations with low and high LCC inputs. There was no difference in predicted wheat yield among the four systems with N inputs from fertilizer or LCC, but yield was lower in the unfertilized wheat-fallow rotation. If the goal of use of LCC was to attain the same yield level as high LCC input or fertilized wheat system while diminishing the risk of N leaching, the low LCC input case met this goal in the short term. However, a simple balance sheet using the model showed that the N balance of the low LCC input system was −147 kg N ha⁻¹ season⁻¹, if we assumed 50% of LCC-N was derived from atmospheric fixation. The low-LCC-input system could therefore fail to maintain inherent soil N fertility in the long term unless nearly 100% LCC-N was derived from fixation.     

The effect of increasing NaCl in irrigation water on growth,gas exchange and yield of tobacco Burley type

Despite the economic importance of tobacco, there is limited field study on the quantitative response of growth and yield to increasing soil salinity. The effects of irrigation with saline water on yield components of field-grown tobacco (Nicotiana tabacum L.) “Burley” type plants were studied over two growing seasons. Growth, dry matter partitioning and gas exchange were measured either in rainfed or fully irrigated plants growing in a clayey–sandy–loam soil. The four fully irrigated treatments received amounts of saline waters at 0.54, 2.5, 5.0 or 10 dS m⁻¹ electrical conductivity (EC_w) equal to crop evapotranspiration. In both years, the electrical conductivity of the saturation phase (EC_e) across the 0.6 m topsoil profile increased with increasing salinity of the irrigation water. Soil moisture was markedly lower in the rainfed treatment than in fully irrigated treatments. Different saline concentrations of irrigation water had virtually no effect on soil moisture. Carbon assimilation rate, stomatal conductance and water use efficiency of the saline treatments were lower than the fully irrigated plants at 0.54 dS m⁻¹ (NW treatment) in 1996, but not in 1997. Transpiration rates were unaffected by salinity in both years. The highest yield was produced by plants irrigated with good quality water. The number of leaves per unit land area was greater for the NW plants, whereas there were no differences between the other four treatments. Salinity decreased plant dry matter and height at harvest, increased dry matter partitioning into leaves and decreased that into stems in both years. Dry matter partitioning to leaves was also greater for the rainfed plants than for the NW plants. Tobacco plants grown under field conditions showed a maximum reduction of relative yield at the highest salinity level of only 31%. The threshold values (0.56 and 0.96 dS m⁻¹) and the EC_e at which a 10% yield reduction was obtained (3.12 and 2.55 dS m⁻¹) calculated from the linear model of response of relative yield to increasing EC_e were typical of moderately sensitive crops. The EC_e values at which 50% yield was reduced (13.34 and 8.91 dS m⁻¹) were indicative of moderate tolerance to salinity.     

Interspecific competition,N use and interference with weeds in pea–barley intercropping

Field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) were intercropped and sole cropped to compare the effects of crop diversity on productivity and use of N sources on a soil with a high weed pressure. ¹⁵N enrichment techniques were used to determine the pea–barley–weed-N dynamics. The pea–barley intercrop yielded 4.6 t grain ha⁻¹, which was significantly greater than the yields of pea and barley in sole cropping. Calculation of land equivalent ratios showed that plant growth factors were used from 25 to 38% more efficiently by the intercrop than by the sole crops. Barley sole crops accumulated 65 kg soil N ha⁻¹ in aboveground plant parts, which was similar to 73 kg soil N ha⁻¹ in the pea–barley intercrop and significantly greater than 15 kg soil N ha⁻¹ in the pea sole crop. The weeds accumulated 57 kg soil N ha⁻¹ in aboveground plant parts during the growing season in the pea sole crops. Intercropped barley accumulated 71 kg N ha⁻¹. Pea relied on N₂ fixation with 90–95% of aboveground N accumulation derived from N₂ fixation independent of cropping system. Pea grown in intercrop with barley instead of sole crop had greater competitive ability towards weeds and soil inorganic N was consequently used for barley grain production instead of weed biomass. There was no indication of a greater inorganic N content after pea compared to barley or pea–barley. However, 46 days after emergence there was about 30 kg N ha⁻¹ inorganic N more under the pea sole crop than under the other two crops. Such greater inorganic N levels during early growth phases was assumed to induce aggressive weed populations and interspecific competition. Pea–barley intercropping seems to be a promising practice of protein production in cropping systems with high weed pressures and low levels of available N.     

Effects of long-term tillage,crop rotation and nitrogen fertilization on bread-making quality of hard red spring wheat

The effect of tillage system, crop rotation and nitrogen (N) fertilization rates on the quality of hard red spring wheat (Triticum aestivum L.) was studied over a 6-year period under rainfed Mediterranean conditions. Grain yield, test weight, protein content and alveogram parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio; G: swelling index) were analyzed. Tillage treatments included no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annuus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–faba bean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Nitrogen fertilizer rates were 50, 100 and 150 kg N ha⁻¹ on a Vertisol (Typic Haploxerert). A split–split plot design with four replications was used. Weather conditions over the study years strongly influenced wheat yield and quality. Test weights rose considerably with yield and increased rainfall during the filling period, and fell slightly as N rates increased. Grain protein content increased with rainfall in the month of May (when grain protein accumulation occurs) up to a maximum of 80 mm. Grain protein content peaked at average mean temperatures of around 26–27°C. Protein content and alveogram parameter also improved under CT, following a prior legume crop and with rising N fertilizer rates. Alveogram parameters rose with protein content, although the P/L ratio showed greater imbalance. N fertilizer proved to be a key factor in determining bread-making quality, and the best strategy available to the farmer for optimizing wheat quality. However, the influence of weather conditions and soil residual N should be borne in mind when deciding on the additional fertilizer N to be used as a top dressing with a view to increasing yield and, particularly, enhancing wheat protein content and bread-making quality.     

Does undersowing winter wheat with a cover crop increase competition for resources and is it compatible with high yield?

The sustainability of cropping systems can be increased by introducing a cover crop, provided that the cover crop does not reduce the cash crop yield through competition. The cover crop may be sown at the same time as a cash crop in the crop rotation. We carried out an experiment in 1999–2000 and 2000–2001 in the Paris Basin, to analyze the effects of simultaneously sowing winter wheat (Triticum aestivum L.) and red fescue (Festuca rubra L.), a turf grass. Competition between wheat and fescue was analyzed with one variety of red fescue, Sunset, and two varieties of wheat, Isengrain and Scipion, each sown at a density of 150 plants m^?2. In this study, we evaluated the effect of undersown fescue on wheat yield and analyzed the competition between the two species in detail. The undersown red fescue decreased wheat yield by about 12% for Isengrain (8.7 t ha^?1 for undersown Isengrain versus 9.8 t ha^?1 for Isengrain alone) and 7% for Scipion (7.4 t ha^?1 for undersown Scipion versus 8.0 t ha^?1 for Scipion alone). During the early stages of wheat growth (up to the ‘1 cm ear’ stage, corresponding to stage 30 on Zadoks’ scale), undersown fescue and fescue sown alone grew similarly. However, fescue biomass levels were much lower (5.6 and 4.7 g m^?2 for fescue grown alone and undersown fescue) than wheat biomass levels on the undersown plots (120 g m^?2 for Isengrain and 111 g m^?2 for Scipion). From the e1 stage onwards, the wheat canopy rapidly extended, whereas that of red fescue remained sparse. The time lag between the beginning of the rapid increase in LAI and PAR interception by wheat grown alone and that for fescue grown alone was 590 dd in the second year. This resulted in much slower growth rates for undersown fescue than for undersown wheat. Biomass production rate was therefore low for undersown fescue (12% those of fescue grown alone, on average, at the time of wheat harvest), as were levels of water and nitrogen use. Neither the water deficit that occurred during the second experiment nor the nitrogen nutrition status of the wheat on plots with undersown fescue significantly affected wheat biomass production after anthesis.The global interception efficiency index IG?_i indicated that the fraction of the PAR_o intercepted by the wheat during its growth (255 days) was 0.35.     

On-farm soil N supply and N nutrition in the rice–wheat system of Nepal and Bangladesh

On-farm research to evaluate the productivity and nitrogen (N) nutrition of a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system was conducted with 21 farmers in the piedmont of Nepal and with 21 farmers in northwest Bangladesh. In Nepal, two levels of N-fertilizer (0–22–42 and 100–22–42 kg N–P–K ha⁻¹) and farmers’ nutrient management practices were tested in the rice season, and three levels of N (0–22–42, 70–22–42, and 100–22–42) and farmers’ practices were evaluated in the wheat season. The treatments in Bangladesh included a researchers managed minus-N plot (0–22–42) and the farmers’ practices. Rice and wheat yields were higher in all treatments than the 0–22–42 control plots, with the exception of rice with the farmers’ practices at one location in Bangladesh. The researchers’ treatment of 100–22–42 in Nepal resulted in larger yields of both rice and wheat than the farmers’ practices, indicating that farmers’ rates of N-fertilizer (mean 49 kg N ha⁻¹) were too low. Delaying wheat seeding reduced yields in the fertilized plots in both countries, especially as N-fertilizer dose increased. Soil N-supplying capacities (SNSC), measured as total N accumulation from the zero-N plots (0–22–42), and grain yields without N additions were greater for rice than for wheat in both Nepal and Bangladesh. Higher SNSC in rice was probably due to greater mineralization of soil organic N in the warm, moist conditions of the monsoon season than in the cooler, drier wheat season. However, SNSC was not correlated with total soil N, two soil N availability tests (hot KCl-extractable NH₄⁺ or 7-day anaerobic incubation), exchangeable NH₄⁺ or NO₃⁻. Wheat in Nepal had greater N-recovery efficiency, agronomic efficiency of N, and physiological efficiency of N than rice. Nitrogen internal-use efficiency of rice for all treatments in both countries was within published ranges of maximum sufficiency and maximum dilution. In wheat, the relationship between grain yield and N accumulation was linear indicating that mobilization of plant N to the grain was less affected by biotic and abiotic stresses than in rice.     

Use of glufosinate-ammonium to control cruciferous weed species in glufosinate-resistant winter oilseed rape

Weed control is an important component of integrated cropping systems. However, cruciferous weeds are difficult to control in conventional winter oilseed rape (Brassica napus L.) and new herbicide options are needed. The aim of this study was to determine the potential for use of glufosinate-ammonium (2-amino-4-(hydroxymethyl-phosphinyl)-butanoic acid) as a flexible post-emergence herbicide for control of cruciferous weeds in glufosinate-resistant winter oilseed rape in the Hercynian dry region of Central Germany. The effects of glufosinate-ammonium (900 g active ingredients ha⁻¹) on chlorophyll fluorescence and dry matter in 4-week-old Sisymbrium loeselii L. (tall hedge mustard), S. officinale (L.) Scop. (hedge mustard), S. altissimum L. (tall tumble mustard), and Descurainia sophia (L.) Webb ex Prantl (flixweed) were assessed under controlled conditions in a growth room. A 2-year field trial was used to investigate the effect of glufosinate-ammonium on the dry matter of S. loeselii. Therefore, different application times (two- to four-leaf stage, five- to six-leaf stage, end of vegetative period in autumn, beginning of vegetative period in spring) and herbicide rates (450 and 900 g a.i. ha⁻¹) were tested.Under controlled growth room conditions, plants of all four cruciferous weed species showed a gradual decrease in the quantum yield of photosystem II. The quantum yield was less than 20% of the control plants measured from 0 to 34 h after application. Dry matter production of all four species was reduced to less than 3% that of the untreated control 4 weeks after application. Under field conditions, dry matter production of S. loeselii varied in dependence on the environmental conditions and was 0–88% of the control plants. Under controlled and field conditions, the results indicate that glufosinate-ammonium is effective in post-emergence control of the tested cruciferous weeds in glufosinate-resistant winter oilseed rape. Under field conditions, weather and crop growth influenced herbicide effectiveness.     

Trends in rice–wheat area in China

This paper provides new estimates of area planted to the rice (Oryza sativa L.)–wheat (Triticum aestivum L.) rotation in China by combining the results obtained from two methodologies. One methodology uses official statistics at the province-level for sown area of rice and wheat, which allows construction of annual estimates from 1979 to 2001. The other methodology uses remote sensing data and county level Agricultural Census data on sown area of 17 major crops, which allows for construction of one estimate appropriate for the middle of the 1990s. The first methodology suggests that the area planted to the rice–wheat rotation has declined sharply in recent years. A combination of the two methodologies results in an estimate of rice–wheat area in China in 2001 of 3.4 Mha. This is substantially below other figures in the literature that reach as high as 13 Mha. This estimate, and the reasons for its declining trend over time, is important for setting priorities in crop research and for understanding how farmers might react to possible new productivity-enhancing technologies.     

Variation within a bread wheat cultivar for grain yield,protein content,carbon isotope discrimination and ash content

The study was undertaken to assess the variation within a bread wheat (Triticum aestivum L.) cultivar, primarily for grain yield, and the implications for wheat breeding. During the 1998–1999 growing season, cv. Nestos was established in a non-replicated (NR-0) honeycomb experiment, in the absence of competition (11 547 plants ha⁻¹). Ten high yielding (H) and 10 low yielding (L) plants were selected, the seeds of which were used to form the respective H and L lines. The 20 lines, along with their original cultivar, were evaluated in two locations either in the absence of competition (11 547 plants ha⁻¹) during the 1999–2000 season or under competition (5 000 000 plants ha⁻¹) during the 2000–2001 season. Results showed significant differentiation between lines for grain yield, determined both in the absence of competition at the single-plant level, i.e. yield per plant (YP), and under competition at the crop yield level, i.e. yield per plot (CY). Significant differences between lines were also found for grain protein content (PC), grain carbon isotope discrimination (Δ), and grain ash content (ASH), either in the absence of competition or under competition. A positive relationship was found between YP and CY (r=0.53,P<0.02). Results showed that selection within a bread wheat cultivar, under very low density and on the basis of individual plant grain yield, could be an effective way to either upgrade or maintain the cultivar, whereas the use of Δ or ASH as indirect selection criteria instead of grain yield was not supported by the study.     

Reduction of phytate content while preserving minerals during whole grain cereal tempe fermentation

The effects of different pretreatments on phytate and mineral contents were investigated in whole grain barley and oat tempe fermented with Rhizopus oligosporus. Different varieties of barley and oats were exposed to pretreatments such as pearling, rolling, moistening, autoclaving and soaking before fermentation. Pearling was the most effective pretreatment for reduction of phytate content for both oats and barley. Nevertheless, mineral contents were reduced, and most likely cell wall rich fractions were also reduced by this process. In the first experiments the phytate content reduction in the oats and barley samples were reduced by 74% (3.3 μmol/g, d.m.) and 89% (1.4 μmol/g, d.m.), respectively. However, to improve iron absorption the phytate levels should not exceed 0.5 μmol/g, and further phytate degradation was necessary. Therefore, in the final experiments barley samples were exposed to an optimised process with prolonged soaking at a higher temperature and the pearling residues were returned before fermentation. When the outer layers of the barley kernels were returned before fermentation the phytate content was successfully reduced by 97% to 0.4 μmol/g (d.m.) and Fe and Zn levels were well preserved.     

Residual effect of poultry litter applied to cotton in conservation tillage systems on succeeding rye and corn

The burgeoning poultry industry in the southeastern US is presenting a major environmental problem of safe disposal of poultry litter (PL). In a comprehensive study, we explored ways of PL use in conservation tillage-based cotton (Gossypium hirsutum L.) production systems on a Decatur silt loam soil in north Alabama, from 1996 to 1999. The study reported here-in presents the residual effects of PL applied to cotton in mulch-till (MT) and no-till (NT) conservation tillage systems in 1997 and 1998 cropping seasons on N uptake, growth, and yield of rye (Secale cereale, L.) cover crop and rotational corn (Zea mays L.) in 1999. Rye was grown without additional N, whereas corn was grown at three inorganic N levels (0, 100, and 200 kg N ha⁻¹). Poultry litter was applied to cotton in 1997 and 1998 at 0, 100, and 200 kg N ha⁻¹. Residual N from PL applied to cotton in 1997 and 1998 produced up to 2.0 and 17.3 Mg ha⁻¹, respectively, of rye cover crop and corn biomass (includes 7.1 Mg ha⁻¹ of corn grain yield) without additional fertilizer. Therefore, in addition to supplying crop residues which reduce soil erosion, increase soil organic matter, and conserve soil moisture, the rye cover crop was able to scavenge residual N left by the cotton crop, which would otherwise, be at risk of being leached and pollute groundwater resources. Poultry litter applied to cotton also increased corn grain quality as shown by up to 100% increase in grain N content compared to the 0N treatment. Using PL with a slower rate of N release compared to inorganic fertilizer to meet some of the N requirements of corn, will not only reduce N fertilizer costs for corn, but will also reduce the risk of nitrate N leaching into groundwater. The maximum amount of crop residues added to the cotton based cropping system by residual N from PL and inorganic N was 21.3 Mg ha⁻¹. This will lead to an increase in soil organic carbon and soil structure in the long term and a reduction in soil erosion, thereby further improving soil productivity, while at the same time, protecting the environment from nitrate pollution and soil degradation. Our study demonstrates that cotton under conservation tillage system in combination with rye cover crop and rotational corn cropping could use large quantities of PL thereby avoiding serious potential environmental hazards.     

Maximizing yields in rice–groundnut cropping sequence through integrated nutrient management

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha⁻¹ to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha⁻¹, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha⁻¹, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha⁻¹ on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm² (333 000; 444 000; 666 000 plant ha⁻¹, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm² (444 000 plants ha⁻¹) as compared to spacing of 30×10 cm² (333 000 plants ha⁻¹). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha⁻¹ in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha⁻¹ in combination with gypsum applied to groundnut crop.