Using AquaCrop to derive deficit irrigation schedules

Straightforward guidelines for deficit irrigation (DI) can help in increasing crop water productivity in agriculture. To elaborate such guidelines, crop models assist in assessing the conjunctive effect of different environmental stresses on crop yield. We use the AquaCrop model to simulate crop development for long series of historical climate data. Subsequently we carry out a frequency analysis on the simulated intermediate biomass levels at the start of the critical growth stage, during which irrigation will be applied. From the start of the critical growth stage onwards, we simulate dry weather conditions and derive optimal frequencies (time interval of a fixed net application depth) of irrigation to avoid drought stress during the sensitive growth stages and to guarantee maximum water productivity. By summarizing these results in easy readable charts, they become appropriate for policy, extension and farmer level use. We illustrate the procedure to derive DI schedules with an example of quinoa in Bolivia. If applied to other crops and regions, the presented methodology can be an illustrative decision support tool for sustainable agriculture based on DI.     

A global benchmark map of water productivity for rainfed and irrigated wheat

The growing pressure on fresh water resources demands that agriculture becomes more productive with its current water use. Increasing water productivity is an often cited solution, though the current levels of water productivity are not systematically mapped. A global map of water productivity helps to identify where water resources are productively used, and identifies places where improvements are possible. The WATPRO water productivity model for wheat, using remote sensing data products as input, was applied at a global scale with global data sets of the NDVI and surface albedo to benchmark water productivity of wheat for the beginning of this millennium. Time profiles of the NDVI were used to determine the time frame from crop establishment to harvest on a pixel basis, which was considered the modelling period. It was found that water productivity varies from approximately 0.2 to 1.8 kg of harvestable wheat per cubic metre of water consumed. From the 10 largest producers of wheat, France and Germany score the highest country average water productivity of 1.42 and 1.35 kg m⁻³, respectively. The results were compared with modelling information by Liu et al. (2007) who applied the GEPIC model at a global scale to map water productivity, and by Chapagain and Hoekstra (2004) who used FAO statistics to determine water productivity per country. A comparison with Liu et al. showed a good correlation for most countries, but the correlation with the results by Chapagain and Hoekstra was less obvious. The global patterns of the water productivity map were compared with global data sets of precipitation and reference evapotranspiration to determine the impact of climate and of water availability reflected by precipitation. It appears that the highest levels of water productivity are to be expected in temperate climates with high precipitation. Due to its non-linear relationship with precipitation, it is expected that large gains in water productivity can be made with in situ rain water harvesting or supplemental irrigation in dry areas with low seasonal precipitation. A full understanding of the spatial patterns by country or river basin will support decisions on where to invest and what measures to take to make agriculture more water productive.     

Agricultural water productivity assessment for the Yellow River Basin

Agricultural water productivity (WP) has been recognized as an important indicator of agricultural water management. This study assesses the WP for irrigated (WPI) and rainfed (WPR) crops in the Yellow River Basin (YRB) in China. WPI and WPR are calculated for major crops (corn, wheat, rice, and soybean) using experimental, statistical and empirically estimated data. The spatial variability of WPI and WRR is analyzed with regard to water and energy factors. Results show that although irrigated corn and soybean yields are significantly higher than rainfed yields in different regions of the YRB, WPI is slightly lower than WPR for these two crops. This can be explained by the seasonal coincidence of precipitation and solar energy patterns in the YRB. However, as expected, irrigation stabilizes crop production per unit of water consumption over space. WPI and WPR vary spatially from upstream to downstream in the YRB as a result of varying climate and water supply conditions. The water factor has stronger effects on both crop yield and WP than the energy factor in the upper and middle basin, whereas energy matters more in the lower basin. Moreover, WP in terms of crop yield is compared to that in terms of agricultural GDP and the results are not consistent. This paper contributes to the WP studies by a basin context, a comparison between WPI and WPR, a comparison of WP in terms of crop yield and economic value, and insights on the water and energy factors on WP. Moreover, policy implications based on the WP analysis are provided.     

The downstream externalities of harvesting rainwater in semi-arid watersheds: An Indian case study

Water-related investment projects affect downstream water availability, and therefore should account for these externalities. Few projects do, however, owing to lack of awareness, lack of data and difficulty in linking upstream investments to downstream effects. This article assesses the downstream impacts of rainwater harvesting in a semi-arid basin in Southern India, focusing on the trade-offs that arise when crop water use is re-allocated from a downstream surface water irrigation system to groundwater irrigated agriculture upstream. The results indicate that the downstream impacts are considerable and that net benefits are insufficient to pay back investment costs. Further research is required to reduce the uncertainties in the water balance of irrigation systems at basin level, to account for the inter-annual variability of crop water availability and to elaborate the wider welfare effects.     

Integrating remote sensing and a process-based hydrological model to evaluate water use and productivity in a south Indian catchment

The combined use of remote sensing and a distributed hydrological model have demonstrated the improved understanding of the entire water balance in an area where data are scarcely available. Water use and crop water productivity were assessed in the Upper Bhima catchment in southern India using an innovative integration of remotely sensed evapotranspiration and a process-based hydrological model. The remote sensing based Surface Energy Balance Algorithm for Land (SEBAL) was used to derive an 8 month time series of observed actual evapotranspiration from October 2004 to May 2005. This dataset was then used in the calibration of the Soil and Water Assessment Tool (SWAT). This hydrological model was calibrated by changing 34 parameters to minimize the difference between simulated and observed actual evapotranspiration. The calibration efficiency was assessed with four different performance indicators. The calibrated model was used to derive a monthly basin water balance and to assess crop water productivity and crop water use for the irrigation year 2004-2005. It was found that evapotranspiration is the largest water loss in the catchment and total evaporative depletion was 38,172 Mm³ (835 mm). Of the total evaporative depletion 42% can be considered as non-beneficial and could be diverted to other beneficial utilization. Simulated crop water productivities for sugarcane, sorghum and winter wheat are relatively high at 2.9 kg/m³, 1.3 kg/m³ and 1.3 kg/m³, respectively. The frequency distributions of crop water productivity are characterised by low coefficient of variation, yielding limited scope for improvement in the agricultural areas under the current cropping systems. Further improvements in water productivity may however be achieved by shifting the crop base from sugarcane to a dual crop and introducing a fallow period from March to May or by converting non-productive rangelands to bio fuel production or other agricultural land uses.     

Livestock water productivity in mixed crop–livestock farming systems of the Blue Nile basin: Assessing variability and prospects for improvement

Water scarcity is a major factor limiting food production. Improving Livestock Water Productivity (LWP) is one of the approaches to address those problems. LWP is defined as the ratio of livestock’s beneficial outputs and services to water depleted in their production. Increasing LWP can help achieve more production per unit of water depleted. In this study we assess the spatial variability of LWP in three farming systems (rice-based, millet-based and barley-based) of the Gumera watershed in the highlands of the Blue Nile basin, Ethiopia. We collected data on land use, livestock management and climatic variables using focused group discussions, field observation and secondary data. We estimated the water depleted by evapotranspiration (ET) and beneficial animal products and services and then calculated LWP. Our results suggest that LWP is comparable with crop water productivity at watershed scales. Variability of LWP across farming systems of the Gumera watershed was apparent and this can be explained by farmers’ livelihood strategies and prevailing biophysical conditions. In view of the results there are opportunities to improve LWP: improved feed sourcing, enhancing livestock productivity and multiple livestock use strategies can help make animal production more water productive. Attempts to improve agricultural water productivity, at system scale, must recognize differences among systems and optimize resources use by system components.     

In situ use of groundwater by alfalfa

Disposal of saline drainage water is a significant problem for irrigated agriculture. One proposal is to recycle drainage water to irrigate salt tolerant crops until the volume has been reduced sufficiently to enable final disposal by evaporation. Part of this concept requires in situ crop water reuse from shallow groundwater; and data is needed to quantify the potential use of groundwater by alternative crops. A column lysimeter study was initiated to determine the potential crop water use from shallow groundwater by alfalfa as a function of groundwater quality and depth to groundwater. The results demonstrated that up to 50% of the crop water use could be met from shallow groundwater (<1.2 m) with an electrical conductivity less than 4 dS/m, and that the potential crop water use from deeper groundwater (2 m) increased over the years. The columns with high salinity (>4 dS/m) in the shallow groundwater experienced increased salinity in the soil profile with time, which resulted in reduced crop water use from shallow groundwater. Yields decreased with time as the groundwater salinity increased and periodic leaching will be required for in situ use to be a sustainable practice. Statistical analysis of crop yield demonstrated that there was significant use of groundwater with an EC of 6 dS/m for a few years.     

More from Less: Policy Options and Farmer Choice under Water Scarcity

In much of the world, fresh water isscarce and getting scarcer. Growing populations, increasing industrialisation, and environmentalconcerns have all put pressure on the water consumedby agriculture. This paper addresses the economicconsequences of a permanent reduction in canal waterfor irrigation. Using detailed cost-of-cultivationdata from the Gediz Basin, Turkey, the key questionsare: How can farmers best respond to reduced surfacewater supplies? How can the canal managementauthorities best distribute this limited water? And,can the demand for water be reduced through input andoutput price policy? These questions are answered withscenario comparisons under several water availability,crop pattern, price and investment assumptions, forthe short and medium time horizons. Keeping productivity high and water use low requirescoordination between farmers and the water managementauthorities. The analysis shows that, in this region,farmers should keep all their land irrigated at loweryield levels, rather than reduce their cropped areas.The canal managers should opt for a short irrigationseason, rather than an extended season with long dryintervals. Sensitivity analysis on a range of pricesindicates that crop, rather than water prices, affectthe efficiency of water use. The scenarios areevaluated using AGWAT, a spreadsheet-based farm-budgetprogram which is simple and widely applicable. Therange of policy choices considered establishes aframework of analysis for other, potentiallywater-short basins, beyond the Gediz or Turkey.     

Determining the disaggregated economic value of irrigation water in the Musi sub-basin in India

In this paper the residual method is used to determine the disaggregated economic value of irrigation water used in agriculture across crops, zones and seasons. This method relies on the belief that the value of a good (its price by its quantity) is equal to the summation of the quantity of each input multiplied by its average value. By applying this method to the Musi sub-basin; a subdivision of the Krishna basin in India, it was found that the value of irrigation water use is not equated across the crops, zones and seasons. The reasons why there is no sinlge value of irrigation water use are suggested. As farmers do not have perfect knowledge, do not all possess the same resource base, plant different crops for a variety of reasons (some for a financial return on land instead of water and others for sustenance), possess different crop rotation practices and are possibly riks adverse, they all value water differently. However, the results need to be interpreted with care as the crop with the lowest return to water is probably not the one to be sacrificed if water is restricted, since farmers plant crops for a variety of reasons (and sometimes not for the highest return to water that they can achieve).     

灌区尺度作物水分利用效率指标研究

在对灌区来水、作物产量和作物需水量尺度分析的基础上,研究了灌区尺度作物水分利用效率指标,结果表明,冬小麦、夏玉米、棉花不同的生育期对采用哪种水分利用效率指标有直接影响;灌溉、降雨、地下水补给等资料较全时,3种作物都采用WUEET;无降雨资料时,冬小麦可选用WUEi近似代替WUEET;正常年份,夏玉米的WUEP0就是WUEET,干旱年份且需夏灌时,夏玉米WUEET由有效降雨量与灌溉量共同产生;棉花不能用WUEi或WUEP0中的任何一种指标反映其真实的水分利用效率,而只能用WUEET确定。     

Crop water use efficiency at multiple scales

Food security is an issue of global concern, which is tightly linked with water supply issues as regional demands for water are dominated by agricultural water use. This special issue of Agricultural Water Management focuses on crop-water use in China, especially in the North China Plain (NCP) and Loess Plateau and surrounding areas, where intensive agriculture (e.g., wheat-maize double cropping) with limited water is practiced to meet the large demand for grains. Such intensive agriculture raises concerns for agricultural sustainability due to limited water supply and effects on water quality, which may be aggravated by projected climate change and its variability across the region and over time. Addressing these issues requires basic understanding of crop-water relationships in water-limited agricultural systems, methods to quantify water demand and actual crop-water use over multiple scales, and strategies to improve water use efficiency (WUE, or water productivity). Advances in crop breeding (selection) and agronomic management, such as irrigation and nutrient management, and tools to assess and improve WUE at multiple scales are addressed for a range of cropping systems in China. Water supplies within a basin (regional scale) must be managed in view of the patterns of water demand in space and time determined by soil and climatic conditions.     

Economic analysis of water harvesting in a mountainous watershed in India

Water management is an essential feature of any project related with overall development of agriculture. The Soan river catchment in the northwest Himalayas, is fed only by rainwater. Hence, a strategy of rainfed agriculture needs to be developed through water conservation and storage techniques. The Soan is an important river from a soil erosion and water management point of view and detailed economic analysis is needed for any proposal to be implemented in the field. The present study was undertaken to propose an economic analysis of water harvesting structures for the Soan catchment. The purpose of the investigation is to control erosion and conserve water to meet the requirements of supplemental and pre-sowing irrigation for major cereal crops in the area and to maximise agricultural productivity. Benefit/cost ratios ranging from 0.41 to 1.33 are obtained for water harvesting structures of different sizes with estimated life of 25 and 40 years respectively, by taking into account different crop return from maize and wheat.     

Planning and management modeling for treated wastewater usage

Due to urban growth, some agricultural lands have been replaced by residential, municipal, and industrial areas. In some cases the remaining agricultural land will not have enough water because of transfers from agriculture to M&I (municipal and industrial) users. Therefore, in many places, especially in arid and semi-arid regions, the use of treated wastewater as a reliable source of irrigation water has already been, or will be, considered in the future. Due to its unique characteristics, this new resource has many challenges that cannot be ignored, such as health issues, water quality, and long- and short-term effects on soils and crops. The study described herein considered the development of a new GIS-based model for planning and managing the reuse of treated wastewater for the irrigation of agricultural and green lands, considering various factors such as population and urban growth. The model is composed of several different modules, including an urban growth model. These modules are designed to help in the decision-making process for allocations of water resources to agricultural areas, considering factors such as crop types, crop pattern, water salinity, soil characteristics, pumping and conveyance costs, and also by comparing different management scenarios. Appropriate crops that can be grown with a specific water salinity and soil characteristics, proper water resources for each farm (according to pumping and conveyance costs, and analysis of water demand, and water supply) can be determined through the application of this model. The model can also rank agricultural areas and open spaces in and near an urban area according to their suitability for irrigated agriculture.     

Spatial and temporal trends of water productivity in the lower Mekong River Basin

We estimate the physical and economic water productivities of rice and upland crops grown in the Lower Mekong River Basin and we examine their spatial and temporal trends. We discuss the constraints to low productivity, suggest measures for improvement and show the future productivity requirements for food security for increased population. Both the physical and economic water productivities of rice are higher in Vietnam, moderate in Laos, and lower in Thailand and Cambodia. In contrast, the physical water productivities of upland crops such as sugarcane and maize are highest in Thailand. The economic water productivity of upland crops is higher in Laos followed by Vietnam, Cambodia and Thailand, and is much higher than that of rice. However, the economic productivity of all crops is dominated by the productivity of rice, particularly lowland rainfed rice, which is the dominant crop in the Lower Basin. The intra-regional variation (among the provinces within a country) of productivity is not substantial. There is an increasing trend of both physical and economic water productivity in all four riparian countries; however, the increase is more prominent in Laos and Vietnam. The economic productivity of upland crops is much higher than that of rice and therefore cultivation of more upland crops can significantly increase farm-level incomes, with positive impacts on reducing poverty. Increasing upland crops areas is unlikely to have any impact on the food security of the basin. The current rate of increase of both production and productivity of rice is considerably greater than the rate required to feed the expected extra population by 2050, suggesting that food security is not threatened by the population increase. There appears to be considerable scope to increase productivity and maintain the export potential of the basin.     

Decision models for optimal cropping patterns in irrigations based on crop water production functions

A study was conducted to demonstrate the usefulness of alternative levels of water use over the fixed yield approach when there is a constraint on water. In the multi-crop farm models used, a water production function for each crop could be included so that one has the choice of selecting alternative levels of water use depending upon water availability. Water production functions (square root and quadratic type) for seven crops, viz. wheat, gram, mustard, berseem, sugarcane, paddy and cotton, based on experimental data from irrigated crops were used.The fixed yield model was modified incorporating the stepwise water production functions using a separable programming technique. The models were applied on a selected canal command area and optimal cropping patterns determined. Sensitivity analysis for land and water resources was also conducted. The water production function approach gives better possibilities of deciding upon land and water resources.     

Increasing water productivity in crop production—A synthesis

Scarcity of water resources and growing competition for water in many sectors reduce its availability for irrigation. Effective management of water for crop production in water scarce areas requires efficient approaches. Increasing crop water productivity (WP) and drought tolerance by genetic improvement and physiological regulation may be the means to achieve efficient and effective use of water. But only high water productivity values carry little or no interest if they are not associated with high or acceptable yields. Such association of high (or moderate) productivity values with high (or moderate) yields has important implications on the effective use of water. In this paper we discussed the factors affecting water productivity, and the possible techniques to improve water productivity. A single approach would not be able to tackle the forthcoming challenge of producing more food and fiber with limited or even reduced available water. Combining biological water-saving measures with engineering solutions (water saving irrigation method, deficit irrigation, proper deficit sequencing, modernization of irrigation system, etc.), and agronomic and soil manipulation (seed priming, seedling age manipulation, direct- or wet-seeded rice, proper crop choice, integrating agriculture and aquaculture, increasing soil fertility, addition of organic matter, tillage and soil mulching, etc.) may solve the problem to a certain extent. New scientific information is needed to improve the economic gains of WP because the future improvements in WP seem to be limited by economic rather than a lack of technological means.     

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.     

作物干旱胁迫补偿效应研究进展

干旱是作物生长环境中普遍存在的逆境胁迫之一,在一定范围的干旱胁迫后复水短期内,作物在生理生化代谢和生长发育等方面产生补偿或超补偿效应的正面效应,以弥补干旱胁迫期间对作物造成的伤害和损失.补偿效应是作物抵御逆境胁迫的重要调节机制,也是对作物进行有效水分调控,实现节水高效农业的主要生理依据.文中从生长、生理生化、代谢及产量补偿效应及其影响因素等进行了综述.在此基础上,提出今后可从胁迫-复水条件下作物农艺及生理指标的补偿机制,光合作用的补偿规律及反馈机制,水分胁迫后补偿效应的效益评价3个方面进行研究.对于完善和丰富生物性节水理论和指导农业高效用水管理,发展节水灌溉和提供作物水分生产力具有重要的理论意义和实用价值.     

Water use efficiency and economic feasibility of growing rice and wheat with sprinkler irrigation in the Indus Basin of Pakistan

With a population of more than 150 million, Pakistan cannot meet its need for food, if adequate water is not available for crop production. Per capita water availability has decreased from 5600 m³ in 1947 to 1000 m³ in 2004. Water table has gone down by more than 7 m in most parts of the country. Present need is to identify and adopt measures, that will reduce water use and increase crop production. This study was conducted in farmers’ fields during 2002–2004 to evaluate the water use efficiency and economic viability of sprinkler irrigation system for growing rice and wheat crops. Yields and water use were also measured on adjacent fields irrigated by basin flooding, which were planted with the same crop varieties. Sprinkler irrigation of rice produced 18% more yield, while reducing consumption of water to 35% of that used in the traditional irrigation system. Sprinkler irrigation of wheat resulted in a water use efficiency of 5.21 kg of grain per cubic meter of water used compared to 1.38 kg/m³ in the adjacent flooded basins. Benefit–cost analysis showed that adoption of rain-gun sprinkler irrigation for rice and wheat is a financially viable option for farmers. While these findings show large potentials for improving water use efficiency in crop production they also indicate that a large portion of the water applied in traditional flooded basin irrigation is going to groundwater recharge, which has high value near large cities which draw their water from the aquifer.     

Hydrological impact of biofuel production: A case study of the Khlong Phlo Watershed in Thailand

This study evaluates the potential impact of increased biofuel production on the hydrology of a small watershed, Khlong Phlo, in the eastern part of Thailand. The water footprint of biofuel energy was estimated for three crops in order to identify the most water-efficient crop. The Soil and Water Assessment Tool (SWAT) model was used to evaluate the impact of land use change (LUC) caused by the expansion of biofuel crops on the components of water balance and water quality in the studied watershed. Several LUC scenarios consisting of oil palm (biodiesel), cassava and sugarcane (bio-ethanol) expansion were evaluated. The water footprint results indicated that cassava is more water-efficient than the other two crops considered. Simulation results revealed that although oil palm expansion would have negligible alteration in evapotranspiration (0.5 to 1.6%) and water yield (−0.5 to −1.1%), there would be an increased nitrate loading (1.3 to 51.7%) to the surface water. On the contrary, expansion of cassava and sugarcane would decrease evapotranspiration (0.8 to 11.8%) and increase water yield (1.6 to 18.0%), which would lead to increased sediment (10.9 to 91.5%), nitrate (1.9 to 44.5%) and total phosphorus (15.0 to 165.0%) loading to surface water. Based on the results, it can be concluded that land use change for biodiesel production would affect water quality, while both the water balance components and water quality would be affected by the expansion of bio-ethanol crops. Overall, the study indicates that biofuel production would have a negative impact on the water quality of the studied watershed. Further research at large scale (e.g. basin level) and on the economic aspect is recommended, in order to contribute to developing suitable land use and energy policies.