Quantifying risk for water harvesting under semi-arid conditions: Part II. Crop yield simulation

Risk assessment of maize yield was carried out using a crop growth model combined with a deterministic runoff model and a stochastic rainfall intensity model. These were compared with empirical models of daily rainfall–runoff processes. The combination of the deterministic runoff model and the stochastic rainfall intensity model gave more flexible performance than the empirical runoff model. Scenarios of crop simulation included production techniques (water harvesting, WH, and conventional total soil tillage, CT) and initial soil water content at planting (empty, half and full). The in-field water harvesting technique used in the simulation was a no-till type of mini-catchment with basin tillage and mulching. The lower the initial soil water content at planting, the greater the yield difference between the WH and CT production techniques. With the low initial soil water content at planting, the WH production technique had up to 50% higher yield compared to the CT production technique, clearly thus demonstrating the superiority of the WH production technique. Under all the variations in agronomic practices (planting date, plant population, cultivar type) tested, the WH had a lower risk than CT under these semi-arid climatic conditions (i.e., WH increased the probability of higher crop yields).     

基于LiDAR的亚热带次生林林窗对幼树更新影响分析

以湖南亚热带次生林为研究对象,利用多时相机载激光雷达(Light detection and ranging,Li DAR)和野外调查数据对林窗及幼树进行监测,分析比较林窗对幼树密度分布和树高生长变化的影响。结果表明,林窗大小和位置对幼树密度分布都有显著影响,喜光树种幼树主要集中在小林窗的中心区或大林窗的过渡区,在大林窗中密度最大(647株/hm2),耐荫树种幼树主要集中在林窗的边缘区,在中等林窗中密度最大(941株/hm~2)。林窗大小对幼树树高生长有显著影响,喜光树种和耐荫树种幼树分别在大林窗和中等林窗中树高生长量最大(69.3 cm/a、57.7 cm/a),喜光树种幼树在中心区的树高生长量明显大于其他位置,耐荫树种幼树的树高生长量在位置上的差异不显著。线性混合模型分析显示林窗大小是促进幼树树高生长的最主要因素,幼树树高生长变化在不同林窗中呈聚集性。从幼树密度树高生长情况来看,50~150 m~2林窗较适合促进亚热带次生林的群落演替。     

Adapting the CROPGRO model for saline soils: the case for a common bean crop

Water scarcity and severe environmental degradation are causing water managers in the Fergana Valley, Uzbekistan to re-evaluate irrigation water use. Crop models could play an important role in helping farmers decide which systems (crops and irrigation technologies) are feasible. CROPGRO is a physiologically robust agronomic model, although the current version does not consider the effects of soil salinity on crop water use or growth. CROPGRO was modified to include a salinity response function and was tested for gypsiferous soils. A qualitative analysis of the model indicated the model performed as expected under a range of atmospheric, irrigation and crop tolerance scenarios. Model simulations compared very favourably for common bean (Phaseolus vulgaris) to results obtained in the greenhouse for yield and seasonal crop evapotranspiration with values of the Willmott agreement index (i) of 0.98 for both variables evaluated at different levels of salinity and deficit irrigation. Final biomass predictions were less satisfactory, although the modified model performed as well as the original model. The modified model was successfully tested with field data on common bean from an experiment in the Fergana Valley (i of 0.75 for ET and 0.74 for final yield), although the sensitivity of the model to a soil fertility function and relative nodule number made it difficult to assess the model performance.     

不同叶菜越夏种植模式对比试验

针对夏季高温对日光温室叶菜生长的影响，分别对土壤+遮阳网、基质+遮阳网、基质+遮阳网+湿帘3种越夏种植模式进行对比试验，分析其对温室温湿度、叶菜生长及经济效益的影响。研究结果初步表明:一年中最热的一天，室外白天（早8:00～15:30）平均温度为32.5 ℃时，土壤+遮阳网、基质+遮阳网种植模式室内白天平均温度分别比基质+遮阳网+湿帘种植模式温度高7.1 ℃、6.4 ℃。同时，室内白天平均相对湿度，基质+遮阳网比土壤+遮阳网种植模式低，基质+遮阳网+湿帘种植模式平均相对湿度最高。结合产量及效益可知，京研快菜、京水菜在基质+遮阳网+湿帘模式下产量最高，春油1号在基质+遮阳网模式下种植产量最高，3种叶菜在基质+遮阳网+湿帘种植方式下种植效益最好。      

Potential benefits of early vigor and changes in phenology in wheat to adapt to warmer and drier climates

Developing crop cultivars with novel traits could help agriculture adapt to climate change. As introducing new traits into crops is expensive and time consuming, it is helpful to develop methods which can test whether a potential new plant trait increases or maintains production in future climates. We used a crop-soil simulation model (APSIM-Nwheat) to test whether changes in physiological traits, related to early vigor and flowering time, would result in increased yield when compared to traditional cultivars of wheat grown at higher temperatures, elevated atmospheric CO₂ and lower rainfall in a Mediterranean climate. Early vigor was simulated by changing four different plant traits. The impact of each trait on grain yield varied with climate scenario and soil type. Higher specific leaf area had minimal effect on yield for the historical climate, but it could increase production in future warmer climates. Increased rooting depth generally had a positive impact on yield, while lower radiation use efficiency and earlier flowering tended to reduce yield. The interaction between these traits was generally positive, and our results indicate that early vigor may improve yield for a range of future climate scenarios. However, in the low rainfall regions, early vigor is unlikely to compensate for rainfall reductions of ?30%. Yield gains for early vigor are likely to be larger on sandy loam than on heavier clay soil.The simulation of cultivars differing in flowering time showed that in drier climates earlier flowering cultivars increase potential yield while in warming climates later cultivars increase yield.In conclusion, our analyses suggest that there is great potential for adapting wheat systems to climate change by introducing cultivars with new traits. Our results also show how simulation analyses can assist plant breeders in determining which traits could be important for crop production in future climates.     

Profitability analysis of a farming system in Africa

This analysis questions the assumptions that in a traditional farming system food production is primarily for home consumption and is not competitive with export crop (cocoa) production. Government planners and policy makers must look at the total operation of a farmer to understand the role of food crop production. In the case of Ghana in 1981 they needed to seek ways to make cocoa production relatively more profitable if the goal of increased cocoa production from small farms were to succeed.The analysis indicates why farmers were devoting scarce resources, particularly labor, to producing food crops in Ghana in 1981. Food crops were the most profitable both (1) in 1981 and (2) when the flow of income from the life of the trees was considered. Clearly, the farmers were demonstrating that they were rational economic men.In order to get an idea of what price cocoa must bring for it to be as profitable as the food crop systems, the price of cocoa was varied with all other prices held constant. The price of cocoa would have had to be approximately ¢400 per load of 30 kilograms in 1981. The government purchase price was ¢120 per load. Nor surprisingly, cocoa production in Ghana was declining steadily.     

林下种植粮食作物模式研究与示范

为开展林（幼林）下种植粮、油农作物的课题研究与示范，对比试验了林下种植甘薯和林下种植绿豆的不同模式，并对试验结果进行分析，给出了优选方案。试验及研究结果可为确定高效林粮生产模式提供参考，从而达到既促进林木生长，又促进粮食增产增效的目的。      

Soil random roughness and depression storage on coffee farms of varying shade levels

Water availability in rainfed coffee agroecosystems is an important factor in determining the production success of the crop. In this study, an estimate of soil water capture and storage was conducted in order to understand the differences of soil water availability among coffee farms or various management intensities, distinguished here by differences in shade cover level. Measurements of effective soil depression storage, leaf litter and soil moisture were taken in each of the sites. These measurements were taken to better understand how different shade coffee systems may gain or lose opportunities to keep water within the system due to contributions of shade. Three sites of varying shade were chosen in the Soconusco region of Chiapas, Mexico. The medium (30-50% cover) shade site was found to be more effective for precipitation capture when compared to the low (10-30% cover) shade site because of a larger value of effective depression storage (t-test, p = 0.05) due to increased soil roughness. This conclusion was supported by significantly higher soil moisture measurements in the medium shade site when compared to the low shade site in the dry season (repeated measure GLM, p = 0.001). The high shade (60-80% cover) site was found to have a greater slope than the other two sites, yielding smaller effective storage capacities; yet the high shade site was able to retain 15% of the available rainfall during the dry season through surface storage, possibly because of greater leaf litter and other shade contributions. Farmers may consider the use of shade trees within coffee farms as a practical method toward preserving water within the agroecosystem.     

Evaluating irrigation performance in a Mediterranean environment

Assessment of irrigation performance is a prerequisite for improving water use in the agricultural sector to respond to perceived water scarcity. Between 1996 and 2000, we conducted a comprehensive assessment of the performance of the Genil–Cabra irrigation scheme (GCIS) located in Andalusia, southern Spain. The area has about 7,000 ha of irrigated lands distributed in 843 parcels and devoted to a diverse crop mix, with cereals, sunflower, cotton, garlic and olive trees as principal crops. Irrigation is on demand from a pressurized system and hand-moved sprinkler irrigation is the most popular application method. Six performance indicators were used to assess the physical and economic performance of irrigation water use and management in the GCIS, using parcel water-use records and a simulation model. The model simulates the water-balance processes on every field and computes an optimal irrigation schedule, which is then checked against actual schedules. Among the performance indicators, the average irrigation water supply:demand ratio (the ratio of measured irrigation supply to the simulated optimum demand) varied among years from 0.45 to 0.64, indicating that the area is under deficit irrigation. When rainfall was included, the supply:demand ratio increased up to 0.87 in one year, although it was only 0.72 in the driest year, showing that farmers did not fully compensate for the low rainfall with sufficient irrigation water. Nevertheless, farmers in the area made an efficient use of rainfall, as indicated by the relatively high values (0.72–0.83) for the ratio of actual:attainable crop yields. Water productivity (WP) in the GCIS oscillated between 0.72 €/m³ and 1.99 €/m³ during the 4 years and averaged 1.42 €/m³ of water supplied for irrigation, while the irrigation water productivity (IWP) averaged 0.63 €/m³ for the period studied. WP is higher than IWP because WP includes production generated by rainfall, while IWP includes only the production generated by irrigation.Communicated by A. Kassam     

Sustainability of bean production systems on steep lands in Costa Rica

Responding to changes in rural-urban linkages and government policies, bean (Phaseolus vulgaris L.) production systems in Costa Rica are undergoing transitions. Impacts of changes in bean production systems on environmental and economic sustainability were analysed at the field, farm and policy levels. A combination of interviews, agronomic surveys, on-farm experiments, and secondary information was used. Changes in agronomic and economic conditions over time were assessed by conducting agronomic surveys and experiments on farms representing a range of land-use intensities. Trade-offs between productivity and stability were quantified using Modified Stability Analysis. The adoption of land and agrochemical-intensive methods by resource-poor farmers cultivating steep lands resulted in decreased environmented and economic sustainability. Farmers with adequate resources were able to maintain economic viability by transferring land out of beans and into other commodities, particularly cattle. However, this shift in resource use decreased social equity by decreasing farm labour opportunities for smallholders and landless farmers and diminishing land available for tenants. These studies indicate that the impact of technology introduction on farming system sustainability can be assessed effectively by conducting integrated socioeconomic and agronomic analyses across farms representing various land-use practices and intensities.     

Designing crop technology for a future climate: An example using response surface methodology and the CERES-Wheat model

Future crop production will be adapted to climate change by implementing alternative management practices and developing new genotypes that are adapted to future climatic conditions. It is difficult to predict what new agronomic technologies will be necessary for crop production under future climatic conditions. The purpose of this work was to develop an approach useful in identifying crop technologies for future climatic conditions. As an example of the approach, we used response surface methodology (RSM) in connection with the CERES-Wheat model and the HADCM2 climate simulation model to identify optimal configurations of plant traits and management practices that maximize yield of winter wheat in high CO₂ environments. The simulations were conducted for three Nebraska locations differing in altitude and rainfall (Lincoln, Dickens and Alliance), which were considered representative of winter wheat growing areas in the central Great Plains. At all locations, the identified optimal winter wheat cultivar under high CO₂ conditions had a larger number of tillers, larger kernel size, fewer days to flower, grew faster and had more kernels m⁻² than the check cultivar under normal CO₂ conditions. In addition, optimal sowing dates were later and optimal plant densities were smaller than under normal conditions. We concluded that RSM used in conjunction with crop and climate simulation models was useful in understanding the complex relationship between wheat genotypes, climate and management practices.     

降雨年型对南通棉花生产的影响

通过对南通棉区降雨量和棉花产量的长系列资料的整理分析，揭示棉花生育期各时段的雨量与产量的关系，运用统计学的聚类分析方法，将生育期的雨量划分为特征鲜明的若干年型．用水量平衡方法进一步分析降雨年型对棉花生产的影响，最后建立统计模型，进行降雨（丰、歉）年型的预测。     

基于神经网络和粒子群算法产流量模型构建

为了研究坡面产流量与各影响因子间定量关系,分析野外多尺度人工径流小区实测数据,采用人工神经网络及粒子群算法,建立了坡面产流量预测模型,产流量与坡长、坡宽、坡度、前期土壤含水量间可采用二次抛物线关系进行描述,与植被覆盖度、降雨量间分别采用幂函数和线性函数进行描述.另外采用加权相对差距和法确定了产流量BP神经网络模型最优拓扑结构及网络参数,建立了产流量BP神经网络模型,该模型模拟值与实测相对误差在±20%以内,预测精度较高.同时基于产流量与各单因子定量关系,建立了产流量经验模型,采用粒子群算法推求了模型未知参数,该经验模型相对误差主要在±30%以内,其精度略逊于BP神经网络模型.     

InfoCrop: A dynamic simulation model for the assessment of crop yields,losses due to pests,and environmental impact of agro-ecosystems in tropical environments. II. Performance of the model

InfoCrop, a generic crop model, simulates the effects of weather, soils, agronomic management (planting, nitrogen, residues and irrigation) and major pests on crop growth, yield, soil carbon, nitrogen and water, and greenhouse gas emissions. This paper presents results of its evaluation in terms of its validation for rice and wheat crops in contrasting agro-environments of tropics, sensitivity to the key inputs, and also illustrates two typical applications of the model. Eleven diverse field experiments, having treatments of location, seasons, varieties, nitrogen management, organic matter, irrigation, and multiple pest incidences were used for validation. Grain yields in these experiments varied from 2.8 to 7.2 ton ha⁻¹ in rice and from 3.6 to 5.5 ton ha⁻¹ in wheat. The results indicated that the model was generally able to explain the differences in biomass, grain yield, emissions of carbon dioxide, methane and nitrous oxides, and long-term trends in soil organic carbon, in diverse agro-environments. The losses in dry matter and grain yield due to different pests and their populations were also explained satisfactorily. There were some discrepancies in the simulated emission of these gases during first few days after sowing/transplanting possibly because of the absence of tillage effects in the model. The sensitivity of the model to change in ambient temperature, crop duration and pest incidence was similar to the available field knowledge. The application of the model to quantify multiple pests damage through iso-loss curves is demonstrated. Another application illustrated is the use of InfoCrop for analyzing the trade-offs between increasing crop production, agronomic management strategies, and their global warming potential.     

Impact of global warming on cowpea bean cultivation in northeastern Brazil

This study evaluated the effects of climate change on cowpea bean crop grown in northeastern Brazil based on the reports of the Intergovernmental Panel on Climate Change (IPCC). The water balance model combined with Geographic Information System techniques was used to identify regional areas where the cowpea bean crop will suffer yield reduction due to climate changes. Model input variables were: rainfall, crop coefficients, potential evapotranspiration and duration of the crop cycle. A limit value of 0.5 was adopted for the water requirement satisfaction index (WRSI), being the ratio of actual to maximum evapotranspiration. The acceptable seeding date was defined as the date at which the water balance simulation presented a WRSI value greater than the limit value, with a frequency of at least 80%. An increase in air temperature will cause a significant reduction in the areas currently favorable to cowpea bean crop growth in northeastern Brazil, and it is recommended that bean varieties better suited to high-temperature conditions should be planted.     

A growth-irrigation scheduling model for wastewater use in forest production

Applying wastewater and sludge to land for remediation has been recommended by the Environmental Protection Agency (EPA) as a method to recycle nutrient and organic matter and conserve water resources. The level of sewage treatment can range from simple primary treatment using a lagoon to tertiary treatment using a standard wastewater treatment plant. Small communities are selecting primary treatment and land application as the most cost-effective way of treating municipal wastewater.Wastewater was used to irrigate an Eucalyptus camaldulensis plantation in Ojinaga, Chihuahua, Mexico. The overall objective of the research was to develop a daily growth-irrigation scheduling model (GISM) for Eucalyptus tree plantations based on the trees’ water needs with the source of irrigation water being wastewater from a lagoon sewage treatment system. A second objective was to check this model against measured growth data to determine the limitations of using a simple irrigation-scheduling model to manage the irrigation system to maximize tree growth and wood production.The GISM calculated the evapotranspiration (Et) from the volume balance soil water model and a tree biomass sub-model, based on a water use efficiency (WUE) (biomass/Et) that partitions biomass determined from Et into the component parts of leaves and stems plus branches. The water balance portion of the model computes the Et for grass growing between the trees until a closed canopy system is reached. Weather data and a soil water stress function were used to calculate Et based on calculated reference Et and crop coefficients (K_cs) for both the trees and grass scaled to nonstressed Et.The GISM model accurately modeled height and diameter growth, although, it slightly overestimated the height growth of Eucalyptus for the high irrigation treatment in the second and the third years. The GISM model was successful in predicting height and diameter growth within a 95% confidence level of the measured height and diameter of the trees under all irrigation treatments.Based on the modeled and measured data analysis, the GISM model can be a useful tool to predict tree growth and schedule irrigations for Eucalyptus tree plantations, understand the trees response to environmental and water stress, and to provide better analyses for future research efforts. The climate-driving variables (temperature and rainfall) needed by the model are readily available for any location in the world from the National Climatic Data Center (NCDC).     

Agronomic and economic response to furrow diking tillage in irrigated and non-irrigated cotton (Gossypium hirsutum L.)

The Southeast U.S. receives an average of 1300 mm annual rainfall, however poor seasonal distribution of rainfall often limits production. Irrigation is used during the growing season to supplement rainfall to sustain profitable crop production. Increased water capture would improve water use efficiency and reduce irrigation requirements. Furrow diking has been proposed as a cost effective management practice that is designed to create a series of storage basins in the furrow between crop rows to catch and retain rainfall and irrigation water. Furrow diking has received much attention in arid and semi-arid regions with mixed results, yet has not been adapted for cotton production in the Southeast U.S. Our objectives were to evaluate the agronomic response and economic feasibility of producing cotton with and without furrow diking in conventional tillage over a range of irrigation rates including no irrigation. Studies were conducted at two research sites each year from 2005 to 2007. Irrigation scheduling was based on Irrigator Pro for Cotton software. The use of furrow diking in these studies periodically reduced water consumption and improved yield and net returns. In 2006 and 2007, when irrigation scheduling was based on soil water status, an average of 76 mm ha⁻¹ of irrigation water was saved by furrow diking, producing similar cotton yield and net returns. Furrow diking improved cotton yield an average of 171 kg ha⁻¹ and net return by $245 ha⁻¹ over multiple irrigation rates, in 1 of 3 years. We conclude that furrow diking has the capability to reduce irrigation requirements and the costs associated with irrigation when rainfall is periodic and drought is not severe.     

Adapting to climate change: Agricultural system and household impacts in East Africa

The East African region exhibits considerable climatic and topographic variability. Much spatial and temporal variation in the response of different crops to climate change can thus be anticipated. In previous work we showed that a large part of this variation can be explained in terms of temperature and, to a lesser extent, water effects. Here, we summarise simulated yield response in two crops that are widely grown in the region, maize and beans, and investigate how the impacts of climate change might be addressed at two levels: the agricultural system and the household. Regionally, there are substantial between-country and within-system differences in maize and bean production responses projected to 2050. The arid-semiarid mixed crop-livestock systems are projected to see reductions in maize and bean production throughout most of the region to 2050. Yields of these crops in the tropical highland mixed systems are projected to increase, sometimes substantially. The humid-subhumid mixed systems show more varied yield responses through time and across space. Some within-country shifts in cropping away from the arid-semiarid systems to cooler, higher-elevation locations may be possible, but increased regional trade should be able to overcome the country-level production deficits in maize and beans caused by climate change to 2050, all other things being equal. For some places in the tropical highlands, maize and bean yield increases could have beneficial effects on household food security and income levels. In the other mixed systems, moderate yield losses can be expected to be offset by crop breeding and agronomic approaches in the coming decades, while more severe yield losses may necessitate changes in crop types, movement to more livestock-orientated production, or abandonment of cropping altogether. These production responses are indicative only, and their effects will be under-estimated because the methods used here have not accounted for increasing weather variability in the future or changes in the distribution and impacts of biotic and other abiotic stresses. These system-level shifts will take place in a context characterised by high population growth rates; the demand for food is projected to nearly triple by the middle of this century. Systems will have to intensify substantially in response, particularly in the better-endowed mixed systems in the region. For the more marginal areas, the variability in yield response, and the variability in households’ ability to adapt, suggest that, even given the limitations of this analysis, adaptation options need to be assessed at the level of the household and the local community, if research for development is to meet its poverty alleviation and food security targets in the face of global change.     

An agronomic, economic and behavioral analysis of N application to cotton and wheat in post-Soviet Uzbekistan

Cotton and winter wheat play a vital role in Uzbek agriculture: the first crop is a vital component of the national export revenues, while the latter is key in achieving independence from grain imports. Due to these strategic roles in the national economy, both crops are part of the state procurement system and, hence, are subject to strict regulations imposed to ensure budget revenues and self-sufficiency. However, many factors cause the divergence of crop yields from their technically maximum levels. We analyzed those factors, which hamper achieving the optimum response to fertilizer applications. In a stepwise procedure, we (i) reviewed the technical and financial optimum yield responses of cotton and winter wheat production to fertilizer applications and (ii) analyzed the changes of fertilizer-to-product price ratios to shed light on the agronomic and economic performance of cotton and wheat in the post-Soviet agricultural system of Uzbekistan. The analysis combined data from long-term, historical yield and fertilizer responses, agronomic N-fertilizer response experiments, and socio-economic farm surveys. Quadratic yield-response functions were used to derive economic and technical optimum rates of N-fertilizer applications. Based on the parameterized function and fertilizer-to-product price ratios observed for 1996-2003, we analyzed the difference between recommended fertilization and economic optimum application rates. Results showed that under the state procurement system, Uzbek farmers may not necessarily tend to maximize the profits from their cotton and wheat production. The level of subsidies and the differential crop support by the state induce farmers to follow the official fertilizer recommendations to ensure that they fulfill the production targets even if it implies higher production costs. The present gaps between the officially recorded yields and those technically achievable given the agro-ecological conditions in Uzbekistan cannot be narrowed by only improving N-fertilizer management. It would require additional efforts to improve cotton and wheat yields.     

山东地区小麦高产栽培农艺措施

面对山东地区小麦需求的逐年提高,自然资源有限以及农业生产条件不断变化的情况,好的栽培农艺措施的引入势在必行。从山东地区的小麦种植发展现状出发,结合高产栽培农艺措施的意义,进行山东地区小麦高产栽培农艺措施的探讨,以期能够为山东地区小麦的高产获得理论基础,对当地农业发展有指导意义。