Residual benefits of promiscuous soybean to maize (Zea mays L.) grown on farmers’ fields around Minna in the southern Guinea savanna zone of Nigeria

Biological nitrogen fixation (BNF) by promiscuous cultivars of soybeans (Glycine max (L.) Merr.) in cereal-based cropping systems of Nigeria’s moist savanna zone offers a potential for minimizing the investment made by resource-poor farmers on nitrogen fertilizers. A 3-year trial was conducted on five farmers’ fields in the southern Guinea savanna zone of Nigeria to assess the residual effects of two successive crops of promiscuous soybean cultivars on the yield of a following maize (Zea mays L.) crop. The soybean cultivars, TGX1456-2E (medium maturity) and TGX1660-19F (late maturity), were grown in 1996 and 1997. Treatments, imposed only in the first year of the trial, were: (i) uninoculated, (ii) inoculated with a mixture of two Bradyrhizobium strains, and (iii) fertilized with 60 kg N ha⁻¹. A fourth treatment was a plot left to fallow. In 1998, all the previous soybean and fallow plots were sown to maize without any fertilizer application. Results in 1996 and 1997 showed a soybean response to inoculation in the first year, but differences due to the residual effect of inoculation in the second year were not significant. Both cultivars showed a similar response to inoculation but responses at the five sites were varied. Soybean cultivar 1456-2E fixed 43–52% of its N amounting to 56–70 kg N ha⁻¹ and cultivar 1660-19F derived 39–54% of its N from N₂-fixation which amounted to 51–78 kg N ha⁻¹. Both cultivars had a high N harvest index resulting in a net removal of 52–95 kg N ha⁻¹ when both grain and stover were exported. Even when the stover was returned, there was a depletion of 23–65 kg N ha⁻¹, with 1456-2E removing more N than 1660-19F. Arbuscular-mycorrhizal infection on maize roots was 11–27% and dependent on previous soybean treatments and farmers’ fields. Plant height, shoot biomass, grain yield, and N uptake of maize were significantly greater in plots previously sown to soybean than in the fallow plots. In general, plots sown to the late maturing cultivar 1660-19F exhibited better residual effect, producing larger yield parameters than the plots planted with medium maturing 1456-2E.     

Modelling nitrogen cycles of farming systems as basis of site- and farm-specific nitrogen management

The paper describes a model designed for analysing interrelated nitrogen (N) fluxes in farming systems. It combines the partial N balance, farm gate balance, barn balance and soil surface balance, in order to analyse all relevant N fluxes between the subsystems soil–plant–animal–environment and to reflect conclusive and consistent management systems. Such a system approach allows identifying the causes of varying N surplus and N utilisation.The REPRO model has been applied in the experimental farm Scheyern in southern Germany, which had been subdivided into an organic (org) and a conventional (con) farming system in 1992. Detailed series of long-term measuring data are available for the experimental farm, which have been used for evaluating the software for its efficiency and applicability under very different management, yet nearly equal site conditions.The organic farm is multi-structured with a legume-based crop rotation (N₂ fixation: 83 kg ha⁻¹ yr⁻¹). The livestock density is 1.4 LSU ha⁻¹. The farm is oriented on closed mass cycles.The conventional farm is a simple-structured cash crop system based on mineral N (N input 145 kg ha⁻¹ yr⁻¹). Averaging the years 1999–2002, the organic crop rotation reached, with regard to the harvested products, about 81% (6.9 Mg ha⁻¹ yr⁻¹) of the DM yield and about 93% (140 kg ha⁻¹ yr⁻¹) of the N removal of the conventional rotation. Related to the cropped area, the N surplus calculated for the organic rotation was 38 kg ha⁻¹ yr⁻¹ versus 44 kg ha⁻¹ yr⁻¹ for the conventional rotation. The N utilisation reached 0.77 (org) and 0.79 (con), respectively. The different structure of the farms favoured an enhancement of the soil organic nitrogen stock (35 kg ha⁻¹ yr⁻¹) in the organic crop rotation and caused a decline in the conventional system (−24 kg ha⁻¹ yr⁻¹). Taking account of these changes, which were substantiated by measurements, N surplus in the organic rotation decreased to 3 kg ha⁻¹ yr⁻¹, while it increased to 68 kg ha⁻¹ yr⁻¹ in the conventional system. The adjusted N utilisation value amounted to 0.98 (org) and 0.69 (con), respectively.     

Soil loss due to harvesting of various crop types in contrasting agro-ecological environments

Soil erosion studies on cropland usually only consider water, wind and tillage erosion. However, significant amounts of soil are also lost from the field during the harvest of crops such as sugar beet (Beta vulgaris L.), potato (Solanum tuberosum L.), chicory roots (Cichorium intybus L.), cassava (Manihot spp.) and sweet potato (Ipomoea batatas (L.) Lam). During the harvest soil adhering to the crop, loose soil or soil clods and rock fragments are exported from the field together with these crops.This soil erosion process is referred to as ‘soil losses due to crop harvesting’ (SLCH). Most of the studies investigated SLCH variability and its controlling factors for one crop type in similar agro-ecological environments and for comparable harvesting techniques. In this study, a compilation of SLCH studies was made in order to investigate the effect of crop type, agricultural systems, ecological conditions and harvesting technique on SLCH variability. SLCH rates ranged from few to tens of Mg ha⁻¹ harvest⁻¹ and SLCH was highly variable both in space and time. Comparison of four studies on SLCH for sugar beet revealed that harvesting technique and soil moisture content at harvesting time can be equally important for SLCH variability. The occurrence of soil clods harvested with the crop explained why SLCH was significantly larger for mechanically harvested potato in Belgium compared to manually harvested potato in China. SLCH values for manually harvested sugar beet, potato, cassava and sweet potato in China and Uganda were in general smaller than SLCH values for mechanically harvested sugar beet, potato and witloof chicory roots measured in Belgium and France. However, SLCH may also vary significantly within Europe due to differences in harvesting techniques. Soil moisture content at harvesting time was besides harvesting technique one of the key factors controlling SLCH variability. There were no systematic differences in SLCH between crop types, although the soil–crop contact area–crop mass ratio could explain more than 40% of the means from several SLCH studies.     

Simulating dairy liquid waste management options as a nitrogen source for crops

Large scale dairy operations are common. In many cases the manure is deposited on a paved surface and then removed with a flushing system, after which the solids are separated, the liquid stored in ponds, and eventually the liquid applied on adjacent crop land. Management of liquid manure to maximize the fertilizer value and minimize water quality degradation requires knowledge of the interactive effects of mineralization of organic N (ON) to NH₄⁺, crop uptake of mineral N, and leaching of NO₃⁻ on a temporal basis. The purpose of the research was to use the ENVIRO-GRO model to simulate how the amount of applied N, timing of N application, ON mineralization rates, chemical form of N applied, and irrigation uniformity affected (1) yields of corn (Zea mays) in summer and a forage grass in winter in a Mediterranean climate and (2) the amount of NO₃⁻ leached below the root zone. This management practice is typical for dairies in the San Joaquin Valley of California. The simulations were conducted for a 10-year period. Steady state conditions, whereby an equivalent amount of N applied in the organic form will be mineralized in a given year, are achieved more rapidly for materials with high mineralization rates. Both timing and total quantity of N application are important in affecting crop yield and potential N leaching. Major conclusions from the simulations are as follows. Frequent low applications are preferred to less frequent higher applications. Increasing the amount of N application increased both the crop yield and the amount of NO₃⁻ leached. Increasing irrigation uniformity increased crop yields but had variable effects on the amount of NO₃⁻ leached. A winter forage crop following a summer corn crop effectively reduced the leaching of residual soil N following the corn crop.     

控释掺混肥对麦玉轮作体系作物产量和温室气体排放的影响

为探究控释掺混肥一次性施肥对华北平原麦玉（冬小麦和夏玉米）轮作体系作物产量和温室气体排放的影响,于2020~2022年在德州市现代农业科技园区开展田间试验.冬小麦和夏玉米均设不施氮对照（CK）、农户习惯施氮（FFP）、优化施氮（OPT）、CRU1（包膜尿素与普通尿素在冬小麦和夏玉米上的掺混比例分别为5∶5和3∶7）、CRU2（包膜尿素与普通尿素在冬小麦和夏玉米上的掺混比例分别为7∶3和5∶5）共5个处理.对比分析了不同处理的作物产量、氮肥利用效率、施肥经济效益和温室气体排放的差异.结果表明,施氮可显著提高麦玉轮作系统单季和周年作物产量（P<0.05）.与FFP相比,CRU1和CRU2处理的夏玉米、冬小麦和周年产量分别提高了0.4%~5.6%、-5.4%~4.1%和-1.1%~3.9%（P>0.05）;氮肥吸收利用率、氮肥农学利用率和氮肥偏生产力分别提高了-8.6%~43.4%、2.05~6.24 kg·kg^-1和4.24~10.13 kg·kg^-1;周年净收益提高了0.2%~6.3%.施氮显著增加了麦玉轮作体系的土壤N₂O和CO₂的周年排放（P<0.05）,但对CH₄周年排放没有影响（第1年FFP处理除外）.CRU1和CRU2处理的土壤N₂O周年排放总量较FFP处理显著降低了23.4%~30.2%（P<0.05）.施氮显著增加了麦玉轮作体系的周年全球增温潜势（GWP）（P<0.05）,但各施氮处理通过提高作物产量降低了温室气体排放强度.与FFP相比,CRU1和CRU2处理的周年GWP降低了9.6%~11.5%（P<0.05）,周年温室气体排放强度（GHGI）降低了11.2%~13.8%（P>0.05）.综上所述,一次性减量施用控释掺混肥在减少氮肥和人工投入、提高作物产量、经济效益和降低温室气体排放方面具有积极作用,是促进华北平原粮食作物清洁生产的有效氮肥管理措施.     

Soil N balance as affected by soybean maturity class in the Guinea savanna of Nigeria

Legume–cereal rotation may reduce the fertilizer requirement of the cereal crop and we hypothesize that the benefit depends on the maturity class of the soybean. Field trials were therefore conducted in 1995 in four Guinea savanna sites to monitor the effect of soybean (Glycine max (L.) Merrill) cultivation on the N balance of the soil. In trial 1, an early (TGx1485-1D) and a late (TGx1670-1F) soybean were grown to maturity along with a maize (Zea mays L.) reference plot. In trial 2, six varieties of soybean (early: TGx1485-1D, TGx1805-2E and TGx1681-3F; medium: TGx1809-12E and TGx923-2E; late: TGx1670-1F) were grown to maturity along with a reference maize plot. The total nitrogen (N) content, aboveground N₂ fixed, and N remaining in the stover were higher in the medium and the late varieties than in early varieties. Also, the early varieties had higher nitrogen harvest indices (81–84%) than medium and late varieties (74–79%). From the N balance calculation, it was found that medium and late maturing soybean resulted in an addition of 4.2 kg N ha⁻¹ to the soil, whereas the early maturing varieties resulted in depletion of the soil N reserve by 5.6 kg N ha⁻¹ (P<0.05). On average, among the medium and late varieties, late maturing TGx923-2E resulted in an addition of 9.5 kg N ha⁻¹ to the soil. When the stover was not returned to the field, early soybean resulted in more negative N balance than the medium and late soybean (P<0.05). Therefore, planting an early variety of soybean for one season resulted in net depletion of soil N, even when the soybean residues were returned to the soil and N₂ fixed in the roots and N in the fallen leaf litter were included in the N balance calculations. Contrary to this, planting medium and late soybean for one season resulted in an addition of N to the soil. Therefore, medium and late soybean should be used as a preceding crop in legume–cereal rotation, if possible, to minimize or avoid depletion of soil N by early varieties of soybean.     

Effect of fertilization and irrigation schedule on water and fertilizer solute transport for wheat crop in a sub-humid sub-tropical region

In order to increase the water and fertilizer use efficiency and decrease the losses of water and fertilizer solutes (N and P), it is necessary to assess the influence of level of fertilization and irrigation schedule on movement and balance of water and fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization and irrigation schedule on water movement and fertilizer solute transport in wheat crop field in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop of cultivar Sonalika (Triticum aestivum L.) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment consisted of four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments were: I₁ = 10% maximum allowable depletion (MAD) of available soil water (ASW); I₂ = 40% MAD of ASW; I₃ = 60% MAD of ASW. The fertilizer treatments during the experiment were: F₁ = control treatment with N:P₂O₅:K₂O as 0:0:0 kg ha⁻¹; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha⁻¹ and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha⁻¹. The results of the investigation revealed that low volume high frequency irrigation results in higher deep percolation losses than the low frequency high volume irrigation with different levels of fertilization for wheat crop in coarse lateritic soil, whereas different levels of fertilization did not significantly affect soil water balance of the wheat crop root zone during all the irrigation schedules. Level of fertilization and irrigation schedule had significant effect on nitrogen leaching loss whereas irrigation schedules had no significant effect on nitrogen uptake under different levels of fertilization. On the other hand, the leaching loss of phosphorus was not significantly influenced by the irrigation schedule and level of fertilization of wheat crop. This indicated that PO₄–P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. From the observed data of nitrogen and phosphorus use efficiency, it was revealed that irrigation schedule with 40% maximum allowable depletion of available soil water with F₂ fertilizer treatment (N:P₂O₅:K₂O as 80:40:40 kg ha⁻¹) was the threshold limit for wheat crop with respect to nitrogen and phosphorus use, crop yield and environmental pollution.     

Integrated assessment of promising measures to decrease nitrogen losses from agriculture in EU-27

Following the recognition of the detrimental effects of nitrogen (N) losses from agriculture in the European Union (EU) on human health and environment, series of environmental policy measures have been implemented from the early 1990s onwards. However, these measures have only been partially successful. Clearly, there is lack of integration of available measures and there is lack of enforcement and hierarchy; which measures should be implemented first? We identified and assessed three ‘most promising measures’ to decrease N losses from agriculture, i.e., (i) balanced fertilization, (ii) low-protein animal feeding, and (iii) ammonia (NH₃) emissions abatement measures. Environmental-economic assessments were made using scenario analyses and the modeling tools MITERRA-EUROPE and CAPRI.In the baseline scenario (business as usual), N use efficiency (NUE) in crop production increases from 44% in 2000 to 48% in 2020, while total N losses decrease by 10%. Implementation of promising measures increases NUE further to 51–55%, and decreases NH₃ emissions (by up to 23%), nitrous oxide (N₂O) emissions (by up to 10%) and N leaching losses (by up to 35%). Differences in responsiveness to promising measures varied between and within Member States. Strict implementation of balanced fertilization in nitrate vulnerable zones, as defined in the Nitrates Directive, decreases total farmers’ income in EU-27 by 1.7 billion euros per year. Implementation of all three measures decreases farmers income by 10.8 and total welfare by 17 billion euros per year, without valuing the environmental benefits.The study presented here is one of the first EU-wide integrated assessments of the effects of policy measures on all major N losses from agriculture and their economic costs. Our results show that the most promising measures are effective in enhancing NUE and decreasing NH₃ and N₂O emissions to the atmosphere and N leaching to groundwater and surface waters, but that income effects are significant. The order of implementation of the measures is important; NH₃ emissions abatement measures must be implemented together with balanced N fertilization.     

Climate change impact and potential adaptation strategies under alternate climate scenarios for yam production in the sub-humid savannah zone of West Africa

Globally, yam (Dioscorea spp.) is the fifth most important root crop after sweet potatoes (Ipomoea batatas L.) and the second most important crop in Africa in terms of production after cassava (Manihot esculenta L.) and has long been vital to food security in sub-Saharan Africa (SSA). Climate change is expected to have its most severe impact on crops in food insecure regions, yet very little is known about impact of climate change on yam productivity. Therefore, we try estimating the effect of climate change on the yam (variety: Florido) yield and evaluating different adaptation strategies to mitigate its effect. Three regional climate models REgional MOdel (REMO), Swedish Meteorological and Hydrological Institute Regional Climate Model (SMHIRCA), and Hadley Regional Model (HADRM3P) were coupled to a crop growth simulation model namely Environmental Policy Integrated Climate (EPIC) version 3060 to simulate current and future yam yields in the Upper Ouémé basin (Benin Republic). For the future, substantial yield decreases were estimated varying according to the climate scenario. We explored the advantages of specific adaptation strategies suggesting that changing sowing date may be ineffective in counteracting adverse climatic effects. Late maturing cultivars could be effective in offsetting the adverse impacts. Whereas, by coupling irrigation and fertilizer application with late maturing cultivars, highest increase in the yam productivity could be realized which accounted up to 49 % depending upon the projection of the scenarios analyzed.     

Yield response of potato to spatially patterned nitrogen application

Although crop response to nitrogen fertilization has long been studied, classical experimental designs have led to inadequate accounting of spatial variability in field properties and yield response. Analytical methods to explicitly account for spatial variability now exist but the complementary modification of experimental design is still developing. There is a need to combine these analytical methods with non-traditional experimental design. A 2-year study was implemented to assess the response of potato (Solanum tuberosum cv. Kennebec) yield to nitrogen fertilizer rate. We used a transect-type plot design where four nitrogen treatments (0, 56, 112, and 280 kg N ha^?1) were applied systematically in a continuous sinusoidal pattern along longitudinal transects. Measured field properties included topography, soil texture, pre-application soil nitrate levels, and plant available soil water content. A random field linear model was used to simultaneously account for treatment effects and soil properties. The results showed that treatment effects were significantly different from each other; however, if spatially correlated errors were accounted for, these differences were smaller and significance levels lower. Nitrogen response functions varied widely throughout the field. Of the covariates, only clay content proved important in explaining spatial differences in response to N. The sinusoidal response pattern of N was similar over the 2 years but the amplitudes varied due to differences in weather. Interactions between uncharacteristically high rainfall and a sandy field soil may have minimized discernable effects of the other covariates. The results demonstrated how the statistical analysis of potato response to a patterned application of nitrogen fertilizer can take advantage of spatial correlations to understand the response of potato to nitrogen application over larger areas.     

Modifying traditional and high-input agroecosystems for optimization of microbial symbioses: a case study of dry beans in Costa Rica

Optimization of symbioses between plants and microbes has been suggested as method for enhancing nutrient uptake in low-input agroecosystems. In generall symbioses may be maximized through: (1) the selection of plant cultivars responsive to symbiontss; (2) ionoculation with highly efficient strains of symbionts; (3) habitat modification to encourage symbioses. These methods were tested under a traditional, slash mulch, ‘frijol tapado’ en agroecosystem and/or a high-input (‘espequeado’) system to increase nodulation and vesicular-arbuscular mycorrbizae (VAM) of beans with the following results: (1) Under the espequeado system (modified by the exclusion of fertilizer application), four cultivars of indeterminate, vining dry beans (Phaseolus vulgaris) nodulated more than two determinate, bush varieties, especially under low available soil phosphorus (P). VAM levels were not statistically different under these conditions. (2) Under the tapado system, pelletization with rock phosphate and Rhizobium inoculum did not significantly change nodule biomass, dinitrogen (N₂)-fixation or yield. (3) Without P application, neither nodulation nor % VAM were significantly different between the two systems of bean production. However, as applied P increased, differences in %VAM of the two systems became significant, decreasing more sharply with increasing P in the tapado system.The tripartite symbiosis of beans can be influenced by various factors such as cultivar, nutrient application and production system. Although traditional varieties and systems may optimize certain microbial symbioses, the quantity of the symbiosis appears to depend on a number of complex factors. An intermediate agricultural technology, the mixing of traditional and modern, is exemplified here by the application of moderate levels of fertilizer to the tradional, tapado systems. This intermediate approach promises to decrease inputs in comparison to the espequedo system, as well as the need for shift cultivation, but long-term testing is needed.     

Assessment of the nitrogen and carbon budget of two managed temperate grassland fields

Greenhouse gas budgets as well as the productivity of grassland systems are closely related to the carbon (C) and nitrogen (N) cycles. Within the framework of the CarboEurope and NitroEurope projects we have measured C and N exchange on the field scale at the grassland site Oensingen previously converted from arable rotation. The site is located on the Swiss Central Plateau and consists of two parallel fields of equal size. One field was subjected to intensive management with average nitrogen input of 230 kg-N ha⁻¹ year⁻¹ and 4–5 cuts per year, and the other to an extensive management with no fertilisation and less frequent cutting. The total C budget of the fields was assessed by measuring the CO₂ exchange by eddy covariance and analysing the carbon import by manure application and export by harvest. The N budget of the managed grassland is more complex. Besides the management related import and export, it includes gaseous exchange in many different forms (NO, NO₂, HNO₃, N₂O, NH₃, N₂) needing different analytical techniques, as well as input by rain and leaching of N-compounds with the soil water. The main (“level-3”) field sites in the NitroEurope project are supposed to measure 95% of the N fluxes at the field scale. For several of the N fluxes specific measurements have been performed for 1 year or longer at the site. Some of the remaining N budget components (dry and wet deposition) could be estimated from results of a national deposition network, while other components (NH₃ and N₂ emission) were estimated based on literature parameterisations. However, we found indications that the (systematic) uncertainties of these estimated N-fluxes are large and that it is important to make site-specific measurement for all relevant budget components. The suitability of corresponding experimental methods is discussed.Analysis of the C budget over a 6-year period (2002–2007) showed a significant mean difference between the two newly established grassland fields with a likely net carbon loss for the extensive management and a net sequestration for the intensive management. Since the C/N ratio of the soil organic matter of the grassland is constrained in a rather narrow range around 9.3, the change in the soil carbon pool is supposed to be accompanied by a corresponding change in the N storage. This approach provided an alternative method to check the N budget of the two grassland fields derived from the individual N fluxes.     

Changes in nitrogen budget and potential risk to the environment over 20 years (1990-2010) in the agroecosystems of the Haihe Basin, China

The nitrogen balance can serve as an indicator of the risk to the environment of nitrogen loss from agricultural land. To investigate the temporal and spatial changes in agricultural nitrogen application and its potential threat to the environment of the Haihe Basin in China, we used a database of county-level agricultural statistics to calculate agricultural nitrogen input, output, surplus intensity, and use efficiency. Chemical fertilizer nitrogen input increased by 51.7% from 1990 to 2000 and by 37.2% from 2000 to 2010, concomitant with increasing crop yields. Simultaneously, the nitrogen surplus intensity increased by 53.5% from 1990 to 2000 and by 16.5% from 2000 to 2010, presenting a continuously increased environmental risk. Nitrogen use efficiency decreased from 0.46 in 1990 to 0.42 in 2000 and remained constant at 0.42 in 2010, partly due to fertilizer composition and type improvement. This level indicates that more than half of nitrogen inputs are lost in agroecosystems. Our results suggest that although the improvement in fertilizer composition and types has partially offset the decrease in nitrogen use efficiency, the environmental risk has still increased gradually over the past 20 years, along with the increase in crop yields and nitrogen application. It is important to achieve a better nitrogen balance through more effective management to significantly reduce the environmental risk, decrease nitrogen surplus intensity, and increase nitrogen use efficiency without sacrificing crop yields.     

Changes in nitrogen budget and potential risk to the environment over 20 years(1990–2010) in the agroecosystems of the Haihe Basin,China

The nitrogen balance can serve as an indicator of the risk to the environment of nitrogen loss from agricultural land. To investigate the temporal and spatial changes in agricultural nitrogen application and its potential threat to the environment of the Haihe Basin in China, we used a database of county-level agricultural statistics to calculate agricultural nitrogen input, output,surplus intensity, and use efficiency. Chemical fertilizer nitrogen input increased by 51.7% from1990 to 2000 and by 37.2% from 2000 to 2010, concomitant with increasing crop yields.Simultaneously, the nitrogen surplus intensity increased by 53.5% from 1990 to 2000 and by16.5% from 2000 to 2010, presenting a continuously increased environmental risk. Nitrogen use efficiency decreased from 0.46 in 1990 to 0.42 in 2000 and remained constant at 0.42 in 2010,partly due to fertilizer composition and type improvement. This level indicates that more than half of nitrogen inputs are lost in agroecosystems. Our results suggest that although the improvement in fertilizer composition and types has partially offset the decrease in nitrogen use efficiency, the environmental risk has still increased gradually over the past 20 years, along with the increase in crop yields and nitrogen application. It is important to achieve a better nitrogen balance through more effective management to significantly reduce the environmental risk,decrease nitrogen surplus intensity, and increase nitrogen use efficiency without sacrificing crop yields.     

Occurrence of phytophagous insects on wild Vigna sp. and cultivated cowpea: comparing the relative importance of host-plant resistance and millet intercropping

The effects of host-plant resistance on cowpea phytophagous insects and their natural enemies under pure and mixed crop conditions was evaluated at Minjibir, Kano State, Nigeria, in 1992–1994 crop seasons. Cowpea Vigna unguiculata cv ‘IT86D-715' (susceptible to insect pests) and a wild Vigna line Vigna vexillata ‘TVnu 72' (resistant to most insect species) were planted alone and in mixtures with millet (Pennisetum glaucum) in plots of 25×25 m.Mixed cropping had limited effect on major insects and natural enemies. Colonies of Aphis craccivora were significantly smaller and there were more adults of Maruca vitrata in crop mixtures than in monocultures. However, flower and raceme infestation by larval M. vitrata, Megalurothrips sjostedti, and Sericothrips sp. were similar in crop mixtures and monocultures. Empoasca sp. populations and seedling infestation by beanfly Ophiomyia phaseoli were also similar in mixtures and monocultures as well as pod damage by M. vitrata and populations of Clavigralla tomentosicollis. Parasitization rates of M. vitrata, C. tomentosicollis and O. phaseoli and predator–prey ratios of spiders and Orius sp. were similar across cropping systems. Host-plant resistance in TVnu 72 drastically reduced insect populations and damage. Grain yield per hill was high in cowpea IT86D-715 and was not affected by intercropping with millet. Grain yield of TVnu 72 was poor and reflected the low yield potential of this accession.Host-plant resistance is an effective means of controlling insect pest damage in cowpea and there is no evidence that high levels of resistance reduced natural biological control.     

Spatial and temporal variation of below-ground N transfer from a leguminous tree to an associated grass in an agroforestry system

Nitrogen (N) transfer from leguminous trees can be a major N source for the associated crop in low-input agroforestry systems. The aim of this study was to identify the main climatic and soil factors controlling N transfer from the leguminous tree Gliricidia sepium (Jacq.) Walp to the associated grass Dichanthium aristatum (Poir.) C.E. Hubb, in a 16-year-old tropical agroforestry system. Nitrogen transfer was estimated using the natural ¹⁵N abundance method. Before tree pruning, total N transfer represented 57% of the N uptake of the grass, including 31% coming from N₂ fixation. The spatial variation induced by the tree was well described by soil organic N content (ON). In this system, ON is an index of soil available N as well as of tree root density. Rainfall (R) and evapotranspiration (ETP) were the main climatic factors controlling N transfer. Multiple regression analysis indicated that R, ETP and ON explained 79% of the temporal and spatial variation of N transfer. Transferred N cannot be estimated after pruning because of the change in the isotopic signature of the soil N source. This was related to N release from root turnover. The results suggest that grass showed a preferential uptake of N coming from the tree, which could be due to a lower energy cost compared to obtaining absorbed N from the clayey soil used in this work.     

Impacts of climate change and CO2 increase on agricultural production and adaptation options for Southern Québec, Canada

This study involves the assessment of the potential impacts of greenhouse gas climate change and changing ambient carbon dioxide (CO₂) levels on crop yields in Quebec, Canada. The methodology involves coupling the transient diagnostics of two Atmosphere-Ocean General Circulation Models, namely the Canadian CGCM1 and the British HadCM3, to the Decision Support System for Agrotechnology Transfer (DSSAT) 3.5 crop models to simulate current (1961–1990) and future (2040–2069) crop yields and changes. This is done for four different crop species, namely spring wheat, maize, soybean, and potato, and for seven agricultural regions of Southern Quebec. The results of this study focus on the main causative factors influencing crop yields, namely the direct CO₂ fertilization effect, the influence of the increase in growing season temperature, including optimal thermal conditions and acceleration in crop maturation, soil moisture availability, as influenced by precipitation and evapotranspiration, and nitrogen uptake by crops. Our results show that crop yield changes may vary according to climate scenario, crop species, and agricultural region. Consistent with other similar research, it would seem that these multiple causative factors very often seem to cancel each other out and dilute the impacts of climate change on crop yields.     

Spatial and long-term variability of soil loss due to crop harvesting and the importance relative to water erosion: A case study from Belgium

The harvest of crops such as sugar beet (Beta vulgaris L.), potato (Solanum tuberosum L.), leek (Allium porrum L.) and carrot (Daucus carota L.) causes soil loss from arable land because soil adhering to the crop and soil clods that failed to be separated by the harvesting machine, are exported from the field together with these harvested crops. These soil losses can be of the same order of magnitude as soil losses caused by water erosion processes, but are often neglected in soil erosion research. In this article we developed a methodology to investigate the spatial and long-term (1846–2004) variability of soil loss due to crop harvesting (SLCH) in Belgium and the spatial distribution of the importance of SLCH relative to soil losses caused by water erosion processes in Flanders. The study is based on long-term time series of soil tare data of crop processing factories and area and crop yield statistics. Until the middle of the 20th century, potato and roots and tubers grown as second crop, had the largest share in the SLCH-crop growing area in Belgium. Sugar beet gained importance from the end of the 19th century onwards and has now, of all SLCH crops, the largest growing area. We could estimate that, partly due to increasing crop yields and the mechanisation of the harvesting process, SLCH per hectare of cropland increased from 0.4 Mg ha⁻¹ year⁻¹ in 1846 to 2.4 Mg ha⁻¹ year⁻¹ in the 1970s and early 1980s. Since then mean annual soil losses decreased again to 1.8 Mg ha⁻¹ year⁻¹ in 2004. It was assessed that total yearly SLCH in Belgium rose from more than 575,000 Mg in the middle of the 19th century to more than 1.7 × 10⁶ Mg in the 1970s and early 1980s, while current SLCH values are 1.4 × 10⁶ Mg. We estimated that since 1846, more than 163 × 10⁶ Mg soil was exported from cropland in Belgium through this erosion process, which corresponds to 109 hm³ or an average soil profile truncation of 1.15 cm. Average sediment export from cropland in Flanders was 3.7 Mg ha⁻¹ year⁻¹ in 2002, of which 46% was due to SLCH and 54% was due to water erosion processes. The relative importance of SLCH varied, depending on the agricultural region, between 38% and 94%.     

Effect of diet manipulation in dairy cow N balance and nitrogen oxides emissions from grasslands in northern Spain

Dietary modifications in dairy cattle have been reported as a useful strategy to alter the composition of manure. Many reports have been published on how changes in dietary crude protein content and forage-to-concentrate ratio reduces animal nitrogen (N) excretion, but little information exists about the effect of diet modification on nitrous oxide (N₂O) and nitric oxide (NO) emission when the subsequent slurry is applied on grassland. Two diets differing in forage:concentrate ratio (high forage or HF diet, 75:25; low forage or LF diet, 55:45) were tested to detect the improvement of N use efficiency in milk and the reduction of urinary and fecal N excretion. Triticale silage and barley grain were used as the main forage and concentrate sources in the diets. The subsequent slurries were characterized for N and ammonium-N content (NH₄⁺-N) and applied on grassland in order to study total and pattern of emission of N₂O and NO.The HF diet reduced the voluntary dry matter intake of the cows, N intake and urinary and fecal N excretion. However, the reduction of N intake did not improve the N use efficiency in milk (NUE) (21.0%) and did not reduce N excretion per unit of milk produced (15 g N l⁻¹) due to the lower milk yield. Slurries were similar in N content but differed in NH₄⁺ content, being lower in HF. Therefore, different slurry amounts were needed to be applied on grassland to reach the correct fertilisation rate (120 kg NH₄⁺-N ha⁻¹). Total emissions of N₂O (5.8 and 5.0 kg N₂O-N ha⁻¹) and NO (507.2 and 568.6 g NO-N ha⁻¹), and the pattern of emissions were not affected by dietary treatments. When fertilisation management depends on the collected volume to empty the slurry pit, higher N₂O and NO emissions per kg of slurry could be expected from LF slurry. Nevertheless, if slurry is applied following recommendation rates, N₂O and NO emission per unit of milk produced might be slightly lower from LF slurry. Grass yield (1.5 t dry matter ha⁻¹) and N uptake (50 kg N ha⁻¹) did not vary due to the applications of different slurries, and was attributed to low rainfalls. The correct management of the slurries on grasslands may justify an adequate nutritional strategy of dairy herds from an environmental and productive point of view.     

Managing crop residues, fertilizers and leaf litters to improve soil C, nutrient balances, and the grain yield of rice and wheat cropping systems in Thailand and Australia

This paper reports on the influence that residue and fertilizer management have on nutrient balances, soil organic matter (SOM) dynamics, and crop yields of a flooded rice system in northeast Thailand (1992–1997) and a wheat–forage legume rotation in eastern Australia (1992–1998). Both soils had been subject to at least 18 years of cultivation and had lost up to 90% of the original labile (C_L) and 85% of the total carbon (C_T).For the rainfed rice cropping systems of northeast Thailand, a system is described in which small applications of leaf litter from locally grown trees are applied annually to rice paddy soils prior to transplanting. Annual applications of 1500 kg ha⁻¹ of leaf litter from different locally grown shrubs for five seasons resulted in increases in rice grain yield in 1997 of between 20 and 26% above the no-leaf litter control. Nutrient balances, determined by the difference between the inputs (fertilizer and added leaf litters) and outputs (grain and straw), indicated net positive balances of up to 457 kg N ha⁻¹, and 60 kg P ha⁻¹, after five seasons of leaf litter applications. Sulfur and potassium balances resulted in net deficits of up to −13 kg S ha⁻¹ and −52 kg P ha⁻¹, where no leaf litter was applied and rice straw was removed following harvest. Soil carbon (C) concentrations increased significantly only where higher fertilizer rate and rice stubble retention were combined.The poor management of fertilizers and crop residues, and excessive cultivation has also resulted in large soil fertility losses in the grain growing areas of Eastern Australia. After five wheat and two legume/fallow crops, negative N balances of up to −303 kg ha⁻¹ were calculated for the treatments where wheat stubble was not retained and bare fallow leys were used. The balance of nutrients such as K, which are contained in larger proportions in stubble, were found to be up to −362 kg ha⁻¹ on the straw-removed treatments and up to +29 kg ha⁻¹ on the straw-retained treatments. Forage legume leys resulted in short term increases in C_L and the carbon management index (CMI).Sustainable farming systems require that crop yields are stable through the maintenance of soil fertility and the balance of nutrients in the system. Increases in soil C levels require sustained periods of balanced fertilization and residue retention.