Retrieval of irrigated and rainfed crop data using a general maximum entropy approach

This paper presents a method to separate harvested area and yield for irrigated crops from rainfed crops in a region, given gross harvested area and yield, and climatic, agronomic and economic data for crops. The method is based on the principle of general maximum entropy, which combines incomplete data, empirical knowledge and a priori information to derive desired information. The model is applied to three large basins with aggregated climatic and agricultural conditions, and to five counties in Texas and California. The modeled results and assessed values in these study areas are compared. While the dependability of model outputs relies on empirical knowledge and judicious parameter estimation, the model remains reliable even for the significant level of uncertainty produced by subjectively predetermined major parameters. The model can be applied to retriving historical data for irrigated and rainfed crops; it can also be used for irrigated and rainfed agriculture planning based on climatic and technological projections. Moreover, the model provides other useful information, including water allocation by crop, water use efficiency and the impact of other agricultural inputs.     

Managing water in rainfed agriculture—The need for a paradigm shift

Rainfed agriculture plays and will continue to play a dominant role in providing food and livelihoods for an increasing world population. We describe the world's semi-arid and dry sub-humid savannah and steppe regions as global hotspots, in terms of water related constraints to food production, high prevalence of malnourishment and poverty, and rapidly increasing food demands. We argue that major water investments in agriculture are required. In these regions yield gaps are large, not due to lack of water per se, but rather due to inefficient management of water, soils, and crops. An assessment of management options indicates that knowledge exists regarding technologies, management systems, and planning methods. A key strategy is to minimise risk for dry spell induced crop failures, which requires an emphasis on water harvesting systems for supplemental irrigation. Large-scale adoption of water harvesting systems will require a paradigm shift in Integrated Water Resource Management (IWRM), in which rainfall is regarded as the entry point for the governance of freshwater, thus incorporating green water resources (sustaining rainfed agriculture and terrestrial ecosystems) and blue water resources (local runoff). The divide between rainfed and irrigated agriculture needs to be reconsidered in favor of a governance, investment, and management paradigm, which considers all water options in agricultural systems. A new focus is needed on the meso-catchment scale, as opposed to the current focus of IWRM on the basin level and the primary focus of agricultural improvements on the farmer's field. We argue that the catchment scale offers the best opportunities for water investments to build resilience in small-scale agricultural systems and to address trade-offs between water for food and other ecosystem functions and services.     

Water productivity in rainfed systems: overview of challenges and analysis of opportunities in water scarcity prone savannahs

Addressing the Millennium Development Goals on food and poverty over the coming decade puts enormous pressure on the world’s finite freshwater resources. Without water productivity (WP) gains, the additional freshwater in agriculture will amount to 5,600 km³ year⁻¹ in 2050. This is three times the current global irrigation use. This paper focuses on the underlying processes and future opportunities of WP gains in water scarcity prone and poverty stricken savannah regions of the world. The paper studies the consumptive (green) WP dynamics rainfed farming systems, and shows that the often assumed linear relationship between evapotranspiration (ET) and yield (Y) does not translate into constant WP over a wide range of yields. Similarly, crop transpiration (T) and Y show non-linearity under on-farm and low yield conditions. This non-linearity is validated against several on-farm research experiments in semi-arid rainfed farming systems. With integrated soil and water management, focusing on dry spell mitigation and soil fertility can potentially more than double on-farm yields, while simultaneously improve green (ET) WP and productive green (T) WP. Through the adoption of appropriate soil and water management in semi-arid smallholder farming systems, crop yields improve and result in improved livelihoods and WP gains.     

Yield and water productivity of five chickpea varieties under supplemental irrigation in contrasting years

Chickpea (Cicer arietinum L.) is one of the most important pulse crops in the world, cultivated on a wide range of environments. In Mediterranean regions, it is traditionally grown as a spring-sown rainfed crop, very dependent on rainfall. In this situation, supplemental irrigation can improve significantly the crop yield. The objective of this study was to evaluate the improvement on chickpea crop yield and water productivity (WP) of five chickpea varieties with supplemental irrigation, in the Mediterranean conditions, with both dry and wet years. Field tests were carried out over two cropping seasons, in Southern Portugal, using three kabuli-type and two desi-type chickpea varieties and four irrigation treatments, corresponding to 100, 50, 25 % of crop irrigation requirements (IR) and rainfed. The results show that all chickpea varieties responded to supplemental irrigation with the increase in grain and biomass yield. However, the magnitude of individual chickpea response depends on the year and the genotype. In 2009, a dry year, the highest WP values were attained at the 50 % IR treatment, whereas in 2010, a wet year, it was the rainfed treatment that showed the highest WP values. The Elixir variety showed the best grain yields and water productivity.     

Modeling the potential for closing quinoa yield gaps under varying water availability in the Bolivian Altiplano

In the Bolivian Altiplano, the yields of rainfed quinoa are relatively low and highly unstable. We use a validated crop water productivity model to examine the potential of closing quinoa yield gaps in this region. We simulate the expectable yields under rainfed cultivation and under different deficit irrigation (DI) strategies using the AquaCrop model for the Northern, Central and Southern Bolivian Altiplano. Simulated DI scenarios include a reference strategy avoiding stomatal closure during all sensitive growth stages and allowing drought stress during the tolerant growth stages (DI₀) and various restrictive deficit irrigation strategies (DI_i) representing cases when water resources are limited. We obtain a logistic crop water production function for quinoa by plotting the seasonal actual evapotranspiration versus total grain yield. Due to the large scatter, this function only indicatively provides expectable yields. From the scenario analysis, we derive yield probability curves for the 3 agro-climatic regions. DI, without restriction in irrigation water during the drought sensitive growth stages, is able to close the yield gaps in the Northern, Central and Southern Bolivian Altiplano, and would guarantee a high and stable level of water productivity (WP). The yields of quinoa under rainfed cultivation during dry years are only 1.1, 0.5 and 0.2 Mg ha⁻¹ in the Northern, Central and Southern Bolivian Altiplano, whereas under DI₀ they are 2.2, 1.6 and 1.5 Mg ha⁻¹, respectively. Under limited water availability for irrigation, these stable yield levels decrease, most drastically in the Southern Bolivian Altiplano. Below a minimum water availability of 600 m³ per ha and 700 m³ per ha in the Central and Southern Bolivian Altiplano, respectively, the application of DI for quinoa is not significantly effective and should be avoided to save valuable resources. The yield probability curves we derive can serve as input for stochastic economic analysis of DI of quinoa in the Bolivian Altiplano.     

Conjunctive use of saline and non-saline irrigation waters in semi-arid regions

In arid and semi-arid regions, effluent from sub-surface drainage systems is often saline and during the dry season its disposal poses an environmental problem. A field experiment was conducted from 1989 to 1992 using saline drainage water (EC=10.5–15.0 dS/m) together with fresh canal water (EC=0.4 dS/m) for irrigation during the dry winter season. The aim was to find if crop production would still be feasible and soil salinity would not be increased unacceptably by this practice. The experimental crops were a winter crop, wheat, and pearl-millet and sorghum, the rainy season crops, grown on a sandy loam soil. All crops were given a pre-plant irrigation with fresh canal water. Subsequently, the wheat crop was irrigated four times with different sequences of saline drainage water and canal water. The rainy season crops received no further irrigation as they were rainfed. Taking the wheat yield obtained with fresh canal water as the potential value (100%), the mean relative yield of wheat irrigated with only saline drainage water was 74%. Substitution of canal water at first post-plant irrigation and applying thereafter only saline drainage water, increased the yield to 84%. Cyclic irrigations with canal and drainage water in different treatments resulted in yields of 88% to 94% of the potential. Pearl-millet and sorghum yields decreased significantly where 3 or 4 post-plant irrigations were applied with saline drainage water to previous wheat crop, but cyclic irrigations did not cause yield reduction. The high salinity and sodicity of the drainage water increased the soil salinity and sodicity in the soil profile during the winter season, but these hazards were eliminated by the sub-surface drainage system during the ensuing monsoon periods. The results obtained provide a promising option for the use of poor quality drainage water in conjunction with fresh canal water without undue yield reduction and soil degradation. This will save the scarce canal water, reduce the drainage water disposal needs and associated environmental problems.     

Irrigation modernization and water conservation in Spain: The case of Riegos del Alto Aragón

This study analyzes the effects of irrigation modernization on water conservation, using the Riegos del Alto Aragón (RAA) irrigation project (NE Spain, 123354 ha) as a case study. A conceptual approach, based on water accounting and water productivity, has been used. Traditional surface irrigation systems and modern sprinkler systems currently occupy 73% and 27% of the irrigated area, respectively. Virtually all the irrigated area is devoted to field crops. Nowadays, farmers are investing on irrigation modernization by switching from surface to sprinkler irrigation because of the lack of labour and the reduction of net incomes as a consequence of reduction in European subsidies, among other factors. At the RAA project, modern sprinkler systems present higher crop yields and more intense cropping patterns than traditional surface irrigation systems. Crop evapotranspiration and non-beneficial evapotranspiration (mainly wind drift and evaporation loses, WDEL) per unit area are higher in sprinkler irrigated than in surface irrigated areas. Our results indicate that irrigation modernization will increase water depletion and water use. Farmers will achieve higher productivity and better working conditions. Likewise, the expected decreases in RAA irrigation return flows will lead to improvements in the quality of the receiving water bodies. However, water productivity computed over water depletion will not vary with irrigation modernization due to the typical linear relationship between yield and evapotranspiration and to the effect of WDEL on the regional water balance. Future variations in crop and energy prices might change the conclusions on economic productivity.     

漳河灌区灌溉用水量及水分生产率变化分析

根据湖北省漳河灌区长系列灌溉用水量、作物产量及灌溉面积等资料 ,从田间、灌溉系统及整个灌区3个不同尺度分析了漳河灌区历年来灌溉用水量及灌溉水分生产率变化情况。结果表明 ,漳河水库农业灌溉供水从第一阶段的 8.5亿 m3减少到第三阶段的 3.94亿 m3 ,单位面积灌溉供水量从第一阶段的 5 94 6m3 /hm2减少到第三阶段的 30 91 m3 /hm2 ,灌溉水分生产率从第一阶段的 0 .6 5 kg/m3提高到第三阶段的 2 .37kg/m3。相应的在灌溉系统和田间尺度 ,单位面积灌溉供水量及灌溉水分生产率呈现同样变化规律。由于灌溉系统和灌区尺度水的重复利用程度逐渐提高 ,使从田间、灌溉系统到灌区灌溉水分生产率逐渐提高。分析灌溉水利用率及水分生产率提高的原因表明 ,节水灌溉技术的推广应用以及通过各类调蓄设施提高水的重复利用率等占一半 ,农业结构的调整及作物品种改进使粮食单产提高等占另一半。     

Integrating remote sensing, census and weather data for an assessment of rice yield, water consumption and water productivity in the Indo-Gangetic river basin

Crop consumptive water use and productivity are key elements to understand basin water management performance. This article presents a simplified approach to map rice (Oryza sativa L.) water consumption, yield, and water productivity (WP) in the Indo-Gangetic Basin (IGB) by combining remotely sensed imagery, national census and meteorological data. The statistical rice cropped area and production data were synthesized to calculate district-level land productivity, which is then further extrapolated to pixel-level values using MODIS NDVI product based on a crop dominance map. The water consumption by actual evapotranspiration is estimated with Simplified Surface Energy Balance (SSEB) model taking meteorological data and MODIS land surface temperature products as inputs. WP maps are then generated by dividing the rice productivity map with the seasonal actual evapotranspiration (ET) map. The average rice yields for Pakistan, India, Nepal and Bangladesh in the basin are 2.60, 2.53, 3.54 and 2.75 tons/ha, respectively. The average rice ET is 416 mm, accounting for only 68.2% of potential ET. The average WP of rice is 0.74 kg/m³. The WP generally varies with the trends of yield variation. A comparative analysis of ET, yield, rainfall and WP maps indicates greater scope for improvement of the downstream areas of the Ganges basin. The method proposed is simple, with satisfactory accuracy, and can be easily applied elsewhere.     

Modeling wheat yield and crop water productivity in Iran: Implications of agricultural water management for wheat production

In most parts of Iran, water scarcity has been intensifying and posing a threat to the sustainability of agricultural production. Wheat is the dominant crop and the largest irrigation water user in Iran; hence, understanding of the crop yield-water relations in wheat across the country is essential for a sustainable production. Based on a previously calibrated hydrologic model, we modeled irrigated and rainfed wheat yield (Y) and consumptive water use (ET) with uncertainty analysis at a subbasin level in Iran. Simulated Y and ET were used to calculate crop water productivity (CWP). The model was then used to analyze the impact of several stated policies to improve the agricultural system in Iran. These included: increasing the quantity of cereal production through more efficient use of land and water resources, improving activities related to soil moisture conservation and retention, and optimizing fertilizer application. Our analysis of the ratio of water use to internal renewable water resources revealed that 23 out of 30 provinces were using more than 40% of their water resources for agriculture. Twelve provinces reached a ratio of 100% and even greater, indicating severe water scarcity and groundwater resource depletion. An analysis of Y-CWP relationship showed that one unit increase in rainfed wheat yield resulted in a lesser additional water requirement than irrigated wheat, leading to a larger improvement in CWP. The inference is that a better water management in rainfed wheat, where yield is currently small, will lead to a larger marginal return in the consumed water. An assessment of improvement in soil available water capacity (AWC) showed that 18 out of 30 provinces are more certain to save water while increasing AWC through proper soil management practices. As wheat self-sufficiency is a desired national objective, we estimated the water requirement of the year 2020 (keeping all factors except population constant) to fulfill the wheat demand. The results showed that 88% of the additional wheat production would need to be produced in the water scarce provinces. Therefore, a strategic planning in the national agricultural production and food trade to ensure sustainable water use is needed. This study lays the basis for a systematic analysis of the potentials for improving regional and national water use efficiency. The methodology used in this research, could be applied to other water scarce countries for policy impact analysis and the adoption of a sustainable agricultural strategy.     

Crop water deficit estimation and irrigation scheduling in western Jilin province,Northeast China

Jilin province is one of the main dryland grain production areas in China. Recently, limited supplemental irrigation, using groundwater in the semi-arid western area of the province, has developed rapidly to improve the low grain productivity caused by rainfall variability. Research was conducted to estimate the actual crop water requirements and identify the timing and magnitude of water deficits of the main crops such as corn (Zea mays L.), soybean (Glycine max L.) and sorghum (Sorghum bicolor L.). Using the guidelines for computing crop water requirements in FAO Irrigation and Drainage paper 56 and historical rainfall distributions, the crop water requirements, ETc and the crop water deficits of corn, soybean and sorghum were calculated. Based on the water deficit analysis, a recommended average supplemental irrigation schedule was developed. Crop production was compared to full irrigation and to a rainfed control in a field experiment.On average, compared to the rainfed control, the full irrigation and the average supplemental irrigation treatments of corn, increased yields 49.0 and 43.9%, respectively; soybean yields of those treatments increased by 41.0 and 34.7%, and sorghum yields of those treatments increased by 55.5 and 46.3%. A supplemental irrigation schedule can be used in the semi-arid western Jilin province to improve crop yields.     

Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

A rule-based method for the development of crop management systems applied to grain sorghum in south-western France

A generic approach is proposed for the development and testing of crop management systems in contrasting situations of water availability. Ecophysiological knowledge, expertise, regional references and simulation models are combined to devise management strategies adapted to production targets and constraints. The next stage consists of converting these crop management strategies into logical and consistent sets of decision rules. Each rule describes the reasoning which is used to apply a technical decision by taking account of observed or simulated environmental conditions or predicted agronomic risks.

This approach was applied to design crop management systems for grain sorghum (Sorghum bicolor L. Moench.) in south-western France. For spring-sown crops, management (sowing date, plant density, varietal choice, N fertilizer rate and timing) was based on water availability, both for economic and environmental reasons. Specific sets of decision rules were written for irrigated and rainfed conditions. The establishment of rules was based on agronomic principles (e.g. for plant density) or on the application of a simulation model (e.g. for sowing date, variety). N fertilization and irrigation were applied using combined N and water dynamic models.

A novel methodology combining crop diagnosis, analytical trials and crop simulation was developed to evaluate the management systems. An irrigated and a rainfed rule-based management system were compared near Toulouse (S.W. France) from 1995 to 2002. The profitability of rainfed low-input management was confirmed for sorghum in spite of high yields under irrigation (up to 10 t ha⁻¹). The adaptation of sorghum management in rainfed conditions was mainly achieved through early maturing cultivars and by reducing N applications by 65%.     

Management trends and responses to water scarcity in an irrigation scheme of Southern Spain

Improvement of irrigation management in areas subjected to periods of water scarcity requires good knowledge of system performance over long time periods. We have conducted a study aimed at characterizing the behaviour of an irrigated area encompassing over 7000 ha in Southern Spain, since its inception in 1991. Detailed cropping pattern and plot water use records allowed the assessment of irrigation scheme performance using a simulation model that computed maximum irrigation requirements for every plot during the first 15 years of system operations. The ratio of irrigation water used to maximum irrigation requirements (Annual Relative Irrigation Supply, ARIS) was well below 1 and oscillated around 0.6 in the 12 years that there were no water supply restrictions in the district. The ARIS values varied among crops, however, from values between 0.2 and 0.3 for sunflower and wheat, to values approaching 1 for cotton and sugar beet. Farmer interviews revealed some of the causes for the low irrigation water usage which were mainly associated with the attempt to balance profitability and stability, and with the lack of incentives to achieve maximum yields in crops subsidized by the Common Agricultural Policy (CAP) of the European Union. The response to water scarcity was also documented through interviews and demonstrated that the change in crop choice is the primary reaction to an anticipated constraint in water supply. Water productivity (value of production divided by the volume of irrigation water delivered; WP) in the district was moderate and highly variable (around 2€ m⁻³) and did not increase with time. Irrigation water productivity (increase in production value due to irrigation divided by irrigation water delivered) was much lower (0.65€ m⁻³) and also, it did not increase with time. The lack of improvement in WP, the low irrigation water usage, and the changes in cropping patterns over the first 15 years of operation indicate that performance trends in irrigated agriculture are determined by a complex mix of technical, economic, and socio-cultural factors, as those that characterized the behaviour of the Genil-Cabra irrigation scheme.     

Nitrogen balance and irrigation water productivity for corn, sorghum and durum wheat under direct seeding into mulch when compared with conventional tillage in the southeastern France

Direct seeding into mulch (DSM) reduces soil evaporation. Therefore, DSM can decrease the crop water demand. Furthermore, DSM provides a favorable food source for soil microorganisms that can enhance the degradation of organic matter and improve nitrogen (N) availability for crops. Nowadays, a major challenge in irrigation is to increase irrigation water productivity (WP). This study assessed the impact of DSM on the N balance and WP according to experimental results compared with conventional tillage (CT). The results showed that DSM could mitigate N losses and improve WP for corn and sorghum. Because of field experimental limitations, PILOTE, an operational model, was employed to test the hypothesis that DSM can be more efficient in water use. PILOTE was adapted and then calibrated and validated in the same experimental station. Taking into account the cover crop season, the model simulated the irrigation amount for a corn crop with a target yield of 14 t/ha during the long climatic series of 1991–2007. The results showed a WP increase from 77 with CT to 102 kg/mm with DSM. DSM can improve WP and save a water application depth of 40 mm compared to CT, which is interesting in a context with water scarcity.     

Improving agricultural water productivity: Between optimism and caution

In its broadest sense, water productivity (WP) is the net return for a unit of water used. Improvement of water productivity aims at producing more food, income, better livelihoods and ecosystem services with less water. There is considerable scope for improving water productivity of crop, livestock and fisheries at field through to basin scale. Practices used to achieve this include water harvesting, supplemental irrigation, deficit irrigation, precision irrigation techniques and soil-water conservation practices. Practices not directly related to water management impact water productivity because of interactive effects such as those derived from improvements in soil fertility, pest and disease control, crop selection or access to better markets.However, there are several reasons to be cautious about the scope and ease of achieving water productivity gains. Crop water productivity is already quite high in highly productive regions, and gains in yield (per unit of land area) do not necessarily translate into gains in water productivity. Reuse of water that takes place within an irrigated area or a basin can compensate for the perceived losses at the field-scale in terms of water quantity, though the water quality is likely to be affected. While crop breeding has played an important role in increasing water productivity in the past, especially by improving the harvest index, such large gains are not easily foreseen in the future. More importantly, enabling conditions for farmers and water managers are not in place to enhance water productivity. Improving water productivity will thus require an understanding of the biophysical as well as the socioeconomic environments crossing scales between field, farm and basin.Priority areas where substantive increases in water productivity are possible include: (i) areas where poverty is high and water productivity is low, (ii) areas of physical water scarcity where competition for water is high, (iii) areas with little water resources development where high returns from a little extra water use can make a big difference, and (iv) areas of water-driven ecosystem degradation, such as falling groundwater tables, and river desiccation. However, achieving these gains will be challenging at least, and will require strategies that consider complex biophysical and socioeconomic factors.     

Cyclic and blending strategies for using nonsaline and saline waters for irrigation

Summary Large quantities of saline water frequently exist in irrigated areas of the world. Various strategies have been proposed to use these saline waters. Blending involves mixing saline water with good quality water to an acceptable salinity and then using this water to irrigate crops. The cyclic strategy uses waters of various salinities separately either during one season or in a crop rotation as a function of the crop's salt tolerance. A multi-seasonal transient state model, known as the modified van Genuchten-Hanks model, was used to investigate the effects of cyclic or blending application of irrigation waters of two salinity levels on alfalfa (Medicago sativa L.), and on a corn (Zea mays L.) and cotton (Gossypium hirsutum L.) crop rotation. Simulated alfalfa yields were similar for the cyclic and blending strategies that applied the same amount of salt and water. The cyclic strategy produced higher simulated yields of salt-sensitive corn than the blending strategy, whereas the simulated salt-tolerant cotton yield was not affected by the two strategies. The beneficial effects of the cyclic strategy on corn production decreased under deficit irrigation.     

Efficient use of water in the southern region of Portugal: agronomic aspects

The present paper analyses several aspects of agricultural production techniques and their relationship with an efficient water use paying special attention to the conditions prevailing in the Mediterranean environment. The agronomic aspects discussed are the following: crop rotation, seeding date and nitrogen fertilisation. With regard to the crop rotation in the effect of the preceding crop on the yield of the following wheat crop is analysed for different precipitation regimes as they frequently occur under Mediterranean conditions. What the concerned seeding date is and its effect on the water availability is studied for both the autumn and spring sown annual crops. Finally the importance of the quantity and distribution of the nitrogen fertilisation for reasonable crop yields in wet years is discussed.     

宁夏南部雨养农业区玉米生育期土壤含水率控制阈值研究

在宁夏南部雨养农业区,设置玉米不同生育期土壤含水率控制下限指标,开展以土壤含水率为灌溉控制指标的精量灌溉技术试验研究。在分析玉米各生育期灌水量、土壤含水率、作物产量、水分利用效率的基础上,推荐在丰水条件下,玉米生育期土壤含水率控制阈值为:种植期80%θf、苗期—拔节期55%θf、拔节期—抽雄期85%θf、抽雄期—灌浆期80%θf,水分生产效率可达3.35kg/m3。宁夏南部雨养农业区推荐土壤含水率控制阈值为:种植期60%θf、苗期45%θf、拔节期50%θf、抽雄前期60%θf,水分生产效率可达3.7kg/m3。     

Water harvesting and supplemental irrigation for improved water productivity of dry farming systems in West Asia and North Africa

In the dry areas, water, not land, is the most limiting resource for improved agricultural production. Maximizing water productivity, and not yield per unit of land, is therefore a better strategy for dry farming systems. Under such conditions, more efficient water management techniques must be adopted. Supplemental irrigation (SI) is a highly efficient practice with great potential for increasing agricultural production and improving livelihoods in the dry rainfed areas. In the drier environments, most of the rainwater is lost by evaporation; therefore the rainwater productivity is extremely low. Water harvesting can improve agriculture by directing and concentrating rainwater through runoff to the plants and other beneficial uses. It was found that over 50% of lost water can be recovered at a very little cost. However, socioeconomic and environmental benefits of this practice are far more important than increasing agricultural water productivity. This paper highlights the major research findings regarding improving water productivity in the dry rainfed region of West Asia and North Africa. It shows that substantial and sustainable improvements in water productivity can only be achieved through integrated farm resources management. On-farm water-productive techniques if coupled with improved irrigation management options, better crop selection and appropriate cultural practices, improved genetic make-up, and timely socioeconomic interventions will help to achieve this objective. Conventional water management guidelines should be revised to ensure maximum water productivity instead of land productivity.