Will nutrient-efficient genotypes mine the soil? Effects of genetic differences in root architecture in common bean (Phaseolus vulgaris L.) on soil phosphorus depletion in a low-input agro-ecosystem in Central America

Crop genotypes with root traits permitting increased nutrient acquisition would increase yields in low fertility soils but have uncertain effects on soil fertility in the long term because of competing effects on nutrient removal vs. the soil conserving effects of greater crop biomass. This study evaluated the relative importance of phosphorus loss in crop extraction vs. phosphorus loss in soil erosion as influenced by genetic differences in root shallowness and therefore phosphorus uptake in common bean (Phaseolus vulgaris L.). Six recombinant inbred lines of varying root architecture and two commercial genotypes of bean were grown in unfertilized, steeply sloped (32%), low phosphorus (5.8 mg kg^?1, Fe-strip) Udults in Costa Rica. Fertilized (60 kg total phosphorus ha^?1) plots of commercial genotypes were also included in the study. Runoff was monitored throughout the bean growing season in 2005 and 2006, and in 2006, monitoring continued through the maize growing season. Phosphorus removed in plant biomass at harvest through the 2006 bean–maize crop cycle averaged 7.3 kg ha^?1 year^?1, greatly exceeding phosphorus loss due to erosion (0.15–0.53 kg ha^?1 year^?1) in unfertilized plots. In fertilized bean plots, total biomass phosphorus averaged 6.32 kg ha^?1 year^?1 and total eroded phosphorus averaged 0.038 kg ha^?1 year^?1, indicating rapid sorption of fertilizer phosphorus. Shoot growth of several recombinant inbred lines under low phosphorus was comparable to that of fertilized commercial genotypes, illustrating the effectiveness of selection for root traits for improving plant growth in low-phosphorus soils. Genotypic differences in root architecture of recombinant inbred lines led to 20–50% variation in groundcover by shoots, which was associated with 50–80% reduction in sediment loss. This study demonstrates that root architecture traits can affect nutrient cycling at the agro-ecosystem level, and that integrated nutrient management strategies are necessary to avoid soil nutrient depletion.     

Emissions of ammonia,nitrous oxide and carbon dioxide from urban gardens in Niamey,Niger

Urban and peri-urban agriculture (UPA) contributes significantly to meet increasing food demands of the rapidly growing urban population in West Africa. The intensive vegetable cultivation in UPA gardens with its high nutrient inputs is often reported to operate at large surpluses of nutrients and presumably high turnover rates of organic matter (OM) and nitrogen (N) losses via emanation and leaching. Many of these claims are lacking solid data which would allow suggesting mitigation strategies. Therefore, this study aimed at quantifying gaseous emissions of ammonia (NH₃), nitrous oxide (N₂O), and carbon dioxide (CO₂) in three representative urban gardens of Niamey, Niger using a closed chamber gas monitoring system. Mean annual N emissions (NH₃-N and N₂O-N) in two gardens using river water for irrigation reached 53 and 48 kg N ha^?1 yr^?1, respectively, while 25 and 20 Mg C ha^?1 yr^?1 was lost as CO₂-C. In the garden irrigated with sewage water from the city's main wadi, N₂O was the main contributor to N losses (68%) which together with NH₃ reached 92 kg N ha^?1 yr^?1, while CO₂-C emissions amounted to 26 Mg ha^?1 yr^?1. Our data indicate that 28% of the total gaseous C emissions and 30–40% of the N emissions occur during the hot dry season from March to May and another 20–25% and 10–20% during the early rainy season from June to July. Especially during these periods more effective nutrient management strategies in UPA vegetable gardens should be applied to increase the nutrient use efficiency in UPA vegetable gardens.     

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.     

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.     

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.     

Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Deceleration in rice (Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T₁), one-third of recommended fertilizer doses (T₂), two-thirds of recommended fertilizer doses (T₃), full doses of recommended fertilizers (T₄), T₂+5 t CD and 2.5 t ash ha⁻¹ (T₅) and T₃+5 t CD and 2.5 t ash ha⁻¹ (T₆) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T₁ was 5.33 t ha⁻¹ per year, while the yield with T₂ was 6.86 t ha⁻¹ per year. Increased fertilizer doses with T₃ increased the grain yield to 8.07 t ha⁻¹ per year, while the application of recommended chemical fertilizer doses (T₄) gave 8.87 t ha⁻¹ per year. The application of CD and ash (T₅ and T₆) increased rice yield by about 1 t ha⁻¹ per year over that obtained with chemical fertilizer alone (T₂ and T₃, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T₃ through T₆, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.     

Simulation of seasonal stalk water content and fresh weight yield of sugarcane

Stalk water content is an important variable for a sugarcane simulation model as sugar industries in many countries use cane yield and sucrose content on a wet mass basis for payment and yield reports. The prime objective was to develop a stalk water content module (SWCM) that can be incorporated into a sugarcane simulation model. SWCM starts from consideration of the dynamics of water concentration (ρ, g water g⁻¹ dry matter) along stalks and through seasons. The quantities of stalk water were modelled separately for the top and basal sections of the millable stalks. Field observations showed that the stalk water concentration (ρ) declined from 7.8 to 11.8 in the top internodes to 1.6–2.9 g water g⁻¹ dry matter in bottom internodes. In the basal section, ρ ranged from 1.98 in winter to 2.83 g water g⁻¹ stalk dry matter in summer. A two-parameter equation was used to model ρ and resulted in a range of coefficients of determination from 0.8 to 0.97 for six varieties. The SWCM was developed to simulate both the effects of seasonal variation and the age of internodes on the quantity of stalk water. The module was incorporated into a process oriented model of sugarcane growth for validation against field observations in tropical and subtropical areas of Australia and Hawaii, USA. Comparison of observed yields with cane yield simulated by the model that included the SWCM, gave an average of R² of 0.95, compared with the average of R² of 0.97 for simulation of stalk dry matter. The average relative root mean squared error (RMSE) was 15.2% in simulation of cane yield and 15.1% for simulation of cane dry weight. The module can be readily incorporated into a model that simulates sugarcane dry matter so that commercial crop yield can be estimated.     

Pig slurry applications to alfalfa: Productivity,solar radiation utilization,N and P removal

A field study was carried out over 4 years at one site in the Low Po Valley, Northern Italy, to examine the effect of various levels of pig slurry applications on alfalfa (Medicago sativa L.) productivity, solar radiation utilization, and nutrient removal. Treatments consisted of three liquid pig manure rates, estimated to provide in total 300, 450 and 600 kg N ha⁻¹ year⁻¹ (PS300, PS450, PS600, respectively), and one unfertilized control (named as Control). Treatments were applied on the second and third year of crop stand (1994 and 1995), whilst during the subsequent fourth and fifth years of crop stand (1996 and 1997) the residual effects of previous treatments were investigated. Regardless of crop age and year-to-year variability, pig slurry tended to increase annual forage production during the 2 years of fertilization and the subsequent biennium of stand duration. Overall, the forage dry matter production, accumulated over four growing seasons and 17 cuts, was 39 000 kg ha⁻¹ for the Control, 44 500 kg ha⁻¹ (+14%) for PS300, to 49 800 kg ha⁻¹ (+28%) for PS450 and 45 800 kg ha⁻¹ (+17%) for PS600. Nitrogen concentration in shoot dry matter was not influenced by the treatment applied. P concentration, on the other hand, was substantially increased by all three rates of pig slurry application, with an evident residual effect observed during the last 2 years of crop stand. However, the evident increase of P availability, assured by pig slurry fertilization, resulted in most of cases in luxury consumption of P by the crop plant. A strong linear relationship was found between cumulative forage dry matter and accumulated incident global solar radiation. Pig slurry fertilization increased significantly the slope of the regressions with respect to the Control. Since enhanced N and P availability may reduce the carbon costs for sustaining root nodules and symbiotic organisms, it seems likely that the crop plant must gain advantage in terms of dry matter produced per unit of radiation intercepted. However, further research is needed to clarify whether the effect of manure is attributable to improved alfalfa efficiency in converting intercepted solar energy into forage dry matter, to enhanced canopy cover thus higher radiation capture per unit of soil area, or to a combination of both mechanisms.     

Soybean–chickpea rotation on Vertic Inceptisols II. Long-term simulation of water balance and crop yields

In rainfed agriculture, climatic variability has profound effects on the performance of management systems in improvements of productivity and use of natural resources. A field study was conducted on a Vertic Inceptisol during 1995–1997 seasons at the ICRISAT Center, Patancheru, India, to study the effect of two landforms, i.e., broadbed-and-furrow (BBF) and flat, and two soil depths (shallow and medium-deep) on crop yield and water balance of a soybean–chickpea rotation. Using two seasons experimental data, a soybean–chickpea sequencing model was evaluated and used to extrapolate the results over 22 years of historical weather records. The simulation results showed that in 70% of years total runoff for BBF was greater than 35 mm (range 35–190 mm) compared to greater than 60 mm (range 60–260 mm) for flat on the shallow soil. In contrast on the medium-deep soil it was greater than 70 mm (range 70–280 mm) for BBF compared to greater than 80 mm (range 80–320 mm) for the flat landform. The decrease in runoff on BBF resulted in a concomitant increase in deep drainage for both soils. In 70% of years, deep drainage was greater than 60 mm (range 60–390 mm) for the shallow soil and ranged from 10 to 280 mm for the medium-deep soil. In 70% of years, the simulated soybean yields were greater than 2200 kg ha⁻¹ (range 2200–3000 kg ha⁻¹) and were not influenced by landform or soil depth. In the low rainfall years, yields were marginally higher for the BBF than for the flat landform, especially on the shallow soil. Simulated chickpea yields were higher for the medium-deep soil than for the shallow soil. In most years, marginally higher chickpea yields were simulated for the BBF than for the flat landform on both soil types. In 70% of years, the chickpea yields were greater than 500 kg ha⁻¹ (range 500–1500 kg ha⁻¹) for the shallow soil, and greater than 800 kg ha⁻¹ (range 800–1960 kg ha⁻¹) for the medium-deep soil. Total productivity of soybean–chickpea rotation was greater than 3000 kg ha⁻¹ (range 3000–4150 kg ha⁻¹) for the shallow soil and greater than 3450 kg ha⁻¹ (range 3450–4700 kg ha⁻¹) for the medium-deep soil in 70% of years. These results showed that in most years BBF, landform increased rainfall infiltration into the soil and had marginal effect on yields of soybean and chickpea. Crop yields on Vertic Inceptisols can be further increased and sustained by adopting appropriate rain water management practices for exploiting surface runoff and deep drainage water as supplemental irrigation to crops in a watershed setting.     

Effect of N rate,timing and splitting and N type on bread-making quality in hard red spring wheat under rainfed Mediterranean conditions

Three different experiments were designed to study the effects of N fertilizer rate, timing and splitting, and the response to combined application of N and S fertilizer on the bread-making quality of hard red spring wheat (Triticum aestivum L.) over a 3-year period in Vertisols under rainfed Mediterranean conditions. The following parameters were analyzed: grain yield, test weight, grain protein content, gluten index and alveograph parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio). The N rate experiment included rates of 0, 100, 150 and 200 kg N ha⁻¹ applied on four different sites. The experiment was designed as a randomized complete block with four blocks. For the experiment on N timing and splitting, a single rate of 150 kg N ha⁻¹ was used, different fractions being applied at sowing, tillering and stem elongation, at a single site; again, experimental design was a randomized complete block with four blocks. Finally, for the experiment on the response to combined application of N and S fertilizer, a single fertilizer dose of 150 kg N ha⁻¹ was applied in two forms (urea+ammonium nitrate and urea+ammonium nitrosulfate) with one leaf application at ear emergence (zero, 25 kg S ha⁻¹, 25 kg N ha⁻¹, $\text{25}\text{kg}\text{S}\text{ha}{}^{\mathrm{-1}}\text{+25}$ kg N ha⁻¹ and 50 kg N ha⁻¹), also at a single site, using a split-plot design with four replications. Year-on-year variation in rainfall led to marked variations in wheat yield, grain protein content and bread-making quality indices. A close correlation was observed between rainfall over the September–May period and both grain yield and grain protein content (optimum values for both being recorded in the rainfall range 500–550 mm) as well as the alveogram index. A negative correlation was observed between mean maximum temperatures in May and both test weight and alveogram index (W). N fertilizer rate had a more consistent effect on bread-making quality than on grain yield. The highest values for grain yield were recorded at an N rate of 100 kg ha⁻¹, while maximum grain protein content values were recorded at 150 kg ha⁻¹. Application of half or one-third of total fertilizer N at stem elongation improved grain yield and grain protein content with respect to applications at sowing alone or at both sowing and tillering. Increased N rates led to a considerable increase in W values and to a reduction in the P/L ratio, thus improving dough balance, with a negative effect on the gluten index. Leaf application of N at ear emergence only affected grain protein content and the W index. Soil or leaf application of S had no effect on protein quality indices. The response of grain yield and grain protein content to fertilizer N differed from that reported for temperate climates.     

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.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

The efficiency of nitrogen fertiliser for rice in Bangladeshi farmers’ fields

Bangladesh is currently self sufficient in rice (Oryza sativa L.), which accounts for approximately 80% of the total cropped area, and 70% of the cost of crop production. However, farmers are increasingly concerned about the perceived decline in productivity, expressed as the return on fertiliser inputs. Agronomic efficiency is a measure of the increase in grain yield achieved per unit of fertiliser input that can provide a way to quantify the observation of farmers. This study indicates that the yields achieved where only P and K fertiliser were applied ranged from 3–5 t ha⁻¹, indicating good soil fertility, particular in terms of soil N supply (37–112 kg N ha⁻¹). However, at recommended rates and at rates used by farmers, the yield response to application of fertiliser N was low. Data shows that grain yields were significantly correlated in both years (R² = 0.77 and R² = 0.67) with plant uptake in nitrogen. The internal nitrogen use efficiency seems to confirm that sink formation was limited by factors other than nitrogen. Low agronomic efficiency (5–19 kg grain kg⁻¹ N) was caused by poor internal efficiency (45–73 kg grain kg⁻¹ N), rather than low supply of soil N or loss of fertiliser N. Thus, often the applications of large amounts of N fertiliser (39–175 kg N ha⁻¹) by farmers to increase yields of high yielding variety Boro rice were not justified agronomically and ecologically. A rate of 39 kg N ha⁻¹ is very low, hardly an environmental threat. No one single factor could be identified to explain the low internal efficiency. Therefore, it is concluded that the data presented tend to confirm the indication that yields are limited by a factor other than nitrogen, which could be crop establishment, plant density, water or pest management, micro-nutrients deficiency, poor seed and transplanted seedling quality, varieties and low radiation.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Interannual variation in soybean yield: interaction among rainfall,soil depth and crop management

Using data from large, grower-managed fields we investigated the variation in yield of dryland soybean in an area with low and variable summer rainfall, and soils that are variable in depth and poor in phosphorus (P). First, using data from unfertilised, wide-row (0.7 m) crops grown under standard management between 1989 and 1992 (Series 1), we quantified the relationship between yield and W, a rainfall-based estimate of water availability during the period of pod and grain set. Separate functions were established for deep (depth ≥ 1 m) and shallow soils (0.75 m ≥ depth ≥ 0.5 m). Second, we partially tested these functions using two independent data sets (Series 2 and 3). Third, we evaluated the effects on yield of large (18 kg P ha⁻¹, Series 4) or moderate doses of P fertiliser (8–12 kg P ha⁻¹) in narrow-row crops (0.35 m, Series 5). To investigate water × management interaction we (i) calculated ΔY, the difference between actual yield in Series 4 and 5 and yield calculated with the functions derived from Series 1, and (ii) tested the association between ΔY and actual W. In a set of 24 crops (Series 1), yield varied between 2.1 and 3.1 t ha⁻¹ in deep soils and between 1.3 and 2.6 t ha⁻¹ in shallow soils; non-linear functions described fairly well, the response of yield to W. Fertilisation with 18 kg P ha⁻¹ increased yield by 0.6 t ha⁻¹ irrespective of water availability. The combination of narrow rows and a moderate dose of fertiliser increased yield in 73% of crops in deep soil but only in 53% of crops in shallow soil. There was a positive association between ΔY and W in deep soil but no relationship between these variables in shallow soil. Yield responses to management were thus differentially affected by rainfall in deep and shallow soils.     

Quality characteristics of Burley tobacco irrigated with saline water

The effect of irrigation with saline water on quality of Burley tobacco (cv. C 104) was investigated in Southern Italy over four consecutive years. A rainfed control (RC) was compared with treatments irrigated with volumes equal to crop evapotranspiration of saline waters at 0.5 (NW), 2.5 (SW₁), 5 (SW₂) and 10 (SW₃) dS m⁻¹ electrical conductivity (EC_w). In 2000 and 2001 an additional salinity treatment (15 dS m⁻¹ EC_w) was included (SW₄). The amounts of Cl⁻ added to the soil by irrigation ranged from 36.3 kg ha⁻¹ (good quality water in 1999) to 16.2 Mg ha⁻¹ (saline water at 15 dS m⁻¹ EC_w in 2000). Saline irrigation did not affect yield and yield components of cured leaves. In 1998 and 1999 the filling power of Burley tobacco did not change significantly with increasing salinity of the irrigation water. In 2000 and 2001 the filling power of SW₂, SW₃ and SW₄ treatments was significantly less than that of NW. The Cl⁻ content of tobacco grown with SW₂ was significantly greater than that grown with NW and there were no differences between SW₁ through SW₄ treatments. The filling power and the leaf Cl⁻ content were inversely related to the amount of Cl⁻ applied in the range between 40.3 kg ha⁻¹ and 5.1 Mg ha⁻¹. The filling power decreased and Cl⁻ increased up to the SW₂ treatment; beyond that level neither Cl⁻ nor filling power changed in response to increasing amounts of Cl⁻ applied. The leaf alkaloid content was unaffected by salinity. Total N was unaffected by either the growing season or the saline treatments. Cigarettes obtained from saline treatments did not burn during the smoking test in 1998. In 1999 cigarettes made from SW₁ and SW₂ did burn, but those from SW₃ did not. In 2000 and 2001 the smoking test was performed only on commercial blends containing 10 or 30% of cut tobacco from saline treatments and both blends burned similarly to cigarettes made entirely from tobacco grown under non-saline conditions. In conclusion, quality of Burley tobacco was unaffected by irrigation with saline water at 2.5 dS m⁻¹ and the inhibitory effect of salinity on burning properties could be overcome by appropriate mixture in commercial blends.     

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.     

Effect of nitrogen supply on crop conductance,water- and radiation-use efficiency of wheat

Water-use efficiency (WUE_DM) is directly related to radiation-use efficiency (RUE) and inversely related to crop conductance (g_c). We propose that reduced WUE_DM caused by shortage of nitrogen results from a reduction in RUE proportionally greater than the fall in conductance. This hypothesis was tested in irrigated wheat crops grown with contrasting nitrogen supply; treatments were 0, 80 and 120 kg N ha⁻¹ in 1998 and 0, 80, 120 and 160 kg N ha⁻¹ in 1999. We measured shoot dry matter, yield, intercepted solar radiation and soil water balance components. From these measurements, we derived actual evapotranspiration (ET), soil evaporation and transpiration, WUE_DM (slope of the regression between dry matter and ET), WUE_Y (ratio between grain yield and ET), RUE (slope of the regression between dry matter and intercepted radiation), and g_c (slope of the regression between transpiration and intercepted radiation). Yield increased from 2.3 in unfertilised to an average 4.7 t ha⁻¹ in fertilised crops, seasonal ET from 311 to 387 mm, WUE_DM from 23 to 37 kg ha⁻¹ mm⁻¹, WUE_Y from 7.6 to 12.4 kg ha⁻¹ mm⁻¹, RUE from 0.85 to 1.07 g MJ⁻¹, while the fraction of ET accounted for soil evaporation decreased from 0.20 to 0.11. In agreement with our hypothesis, RUE accounted for 60% of the variation in WUE_DM, whereas crop conductance was largely unaffected by nitrogen supply. A greater fraction of evapotranspiration lost as soil evaporation also contributed to the lower WUE_DM of unfertilised crops.     

Effects of N application on agronomic and environmental parameters in silage maize production on sandy soils

The current nitrogen (N) use in silage maize production can lead to considerable N losses to the environment. Maize growers fear that a reduction of N inputs needed to minimize N losses might depress yields. The objective of this study was therefore to quantify: (1) the response of silage maize dry matter (DM) yields to N, (2) the economically optimal N reserve, and (3) the trade-off between silage maize DM yield and N losses. The indicators of N losses used in this study were the difference between N input and N uptake and the post-harvest residual soil mineral N. Regression models were used to fit DM yields and N uptakes of silage maize measured in 25 experiments on sandy soils in the Netherlands to the sum (SUMN) of the soil mineral N reserve (SMN_early) in March–April, plus mineral N in fertilizer, plus ammonium N in spring-applied slurry. The values obtained for the economically optimal SUMN in the upper 30 and 60 cm of soil were, respectively, 173 and 195 kg N ha⁻¹, when we assumed that the value of 1 kg fertilizer N equals the value of 5 kg silage DM. The economically optimal SUMN was not significantly related to the attainable DM yield. The apparent N recovery (ANR) of maize averaged 53% at the economically optimal SUMN. The ANR rose considerably, however, when N was applied at lower rates, indicating that N losses may be considerably smaller in less intensive maize cropping. When maize was fertilized at 100 kg N ha⁻¹ below the economic optimum, the ANR was 73%, the difference between the mineral N input and the N crop uptake decreased by 57 kg N ha⁻¹ and the soil mineral N residue at the end of the growing season (0–60 cm) decreased by 24 kg N ha⁻¹. The associated reduction in DM yield averaged 16%. Fertilizer prices would have to be as much as four times higher to make maize growers spontaneously reduce the application rates by a 100 kg N ha⁻¹, however. It is concluded that adjusting the N input to a level below the economically optimal rate can reduce the risks for N losses to the environment associated with conventional maize production, with a limited effect on silage yields.     

Effect of irrigation and nitrogen fertilization on biomass yield and efficiency of energy use in crop production of Miscanthus

The perennial C₄ grass Miscanthus has been proposed as a biomass energy crop in Europe. Effects of crop age, irrigation and nitrogen fertilization on biomass and energy yields and N content of Miscanthus were investigated and the energy costs of production determined. After an establishment period of 1 year, cultivation of Miscanthus resulted in a dry matter production of over 37 t ha⁻¹ year⁻¹ over a period of 4 years. Irrigation and nitrogen level greatly affected Miscanthus biomass yield. In absence of N fertilization, irrigation did not modify biomass yield and the effect of irrigation increased with the increase in N level. The average N response ranged from 37 to 50 kg biomass kg⁻¹ N applied. Because the calorific value of Miscanthus biomass (16.5 MJ kg⁻¹) was not affected by irrigation and N fertilization, energy production depended exclusively on biomass yield. Maximum energy yield was 564 GJ ha⁻¹ year⁻¹. Without N supply and irrigation, energy yield was 291 GJ h⁻¹. Net energy yield, calculated as the difference between energy output and input, but without inclusion of drying costs, was 543 GJ ha⁻¹ with N fertilization and irrigation and 284 GJ ha⁻¹ without; the ratios of energy output to input in crop production were 22 and 47, respectively.