Substantially increasing the productivity of water used in agriculture is essential to meet goals of food and environmental security. Achieving these increases requires research that spans scales of analysis and disciplines. In spite of its importance, we do not have a common conceptual framework and language to facilitate research and communication among stakeholders. The objective of this chapter is to propose a common conceptual framework for water productivity. In a broad sense, productivity of water is related to the value or benefit derived from the use of water. Definitions of water productivity differ based on the background of the researcher or stakeholder. For example, obtaining more kilograms per unit of transpiration is an important means of expressing productivity of water when the interest of analysis is crops. At the basin scale, obtaining more value from water used from irrigated and rain-fed crops, forests, fisheries, ecosystems and other uses is of importance. There are several interrelated definitions of water productivity that are important across scales and domains of analyses. We propose in this chapter a set of definitions for water productivity and show how these are related across scales.As the analysis moves from individual plants to fields, farms, irrigation systems and water basins, different processes and means of analysis are important. Understanding how measures of water productivity scale up and scale down provides the key to how a group of people of diverse disciplines can work together on this topic. For example, crop scientists and breeders may focus on obtaining more mass per unit of transpiration, while planners and economists may consider policies to allocate water and land resources between different uses. To capture the full benefits of improved water productivity at farm level, it is necessary to integrate these with system-and basin-level changes. We provide a framework to show the interrelationship of the work of various disciplines.
Considering the persistently growing pressure on finite freshwater and soil resources, it becomes increasingly clear that the challenge of feeding tomorrow's world population is, to a large extent, about improved water productivity within present land use. Rainfed agriculture plays a critical role in this respect. Eighty percent of the agricultural land worldwide is under rainfed agriculture, with generally low yield levels and high on-farm water losses. Ninety-five percent of current population growth occurs in developing countries and a significant proportion of these people still depend on a predominantly rainfed-based rural economy. This chapter presents the agrohydrological rationale for focusing on water productivity in rainfed agriculture, identifies key management challenges in attempts to upgrade rainfed agriculture and presents a set of field experiences on system options for increased water productivity in smallholder farming in drought-prone environments. Implications for watershed management are discussed, and the links between water productivity for food and securing an adequate flow of water to sustain ecosystem services are briefly analysed. The focus is on sub-Saharan Africa, which faces the largest food-deficit and water-scarcity challenges. The chapter shows that there are no agrohydrological limitations to doubling or even quadrupling on-farm staple-food yields, even in drought-prone environments, by producing more 'crop per drop' of rain. Field evidence is presented suggesting that meteorological dry spells are an important cause of low yield levels. It is hypothesized that these dry spells constitute a core driving force behind farmers' risk-aversion strategies. Risk aversion also contributes to the urgent soil-fertility deficits resulting from insignificant investments in fertilizers. For many smallholder farmers in the semiarid tropics, it is simply not worth investing in fertilizers (and other external inputs) so long as the risk for crop failure remains a reality every fifth year and the risk of yield reductions every second year. These high risks are associated with periodic water scarcity during the growing season (i.e. not necessarily cumulative water scarcity). Results are presented from on-farm agrohydrological field research with innovations in water harvesting and conservation tillage among smallholder farmers in semiarid rainfed farming systems in Burkina Faso, Kenya and Tanzania. These results indicate that upgrading rainfed production systems through supplemental irrigation during short dry spells can lead to large increases in water productivity. Downstream implications of increased upstream withdrawals of water for upgrading of rainfed food production are discussed. Finally, it is argued that some of the most exciting opportunities for water-productivity enhancements in rainfed agriculture are found in the realm of integrating components of irrigation management within the context of rainfed farming, e.g. supplemental or microirrigation for mitigating the effects of dry spells. Combining such practices with management strategies that enhance soil infiltration and improving water-holding capacity and the potential of water uptake of plants can have a strong impact on agricultural water productivity. This suggests that it is probably time to abandon the largely obsolete distinction between irrigated and rainfed agriculture, and instead focus on integrated rainwater management.
In the dry areas, water, not land, is the limiting factor in improving agricultural production. Maximizing water productivity, and not yield per unit of land, is therefore a better strategy for on-farm water management under such conditions. This chapter highlights the major research findings at the International Center for Agricultural Research in the Dry Areas (ICARDA) regarding improving the water productivity of its mandate crops of wheat, barley, lentils, chickpea and faba bean. It is shown 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, designed to maximize yield per unit area, need to be revised for achieving maximum water productivity instead. A case study from Syria shows the applicability of this option. It illustrates that, when water is scarce, higher farm incomes may be obtained by maximizing water productivity than by maximizing land productivity.
Rainwater is the main source of water for agriculture but its current use efficiency for crop production ranges between only 30 and 45%. Annually, 300-800 mm of seasonal rainfall are not used productively, as the rainfall becomes surface runoff or deep drainage. The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)'s long experience, in partnership with national agricultural research systems, in integrated watershed management has clearly demonstrated that areas with good soils in the semi-arid tropics (SAT) in Asia can support double-cropping, while surplus rainwater could recharge the groundwater. In the integrated watershed approach, the emphasis is on in situ conservation of rainwater at farm level, with the excess water being taken out of the fields safely through community drainage channels and stored in suitable low-cost structures. The stored water is used as surface irrigation or for recharging groundwater. Following conservation of the rainwater, its efficient use is achieved through choosing appropriate crops, improved varieties, cropping systems and nutrient and pest-management options for increasing productivity and conserving natural resources. Longterm, on-station watershed experiments have demonstrated that Vertisols with a rainfall of 800 mm have the capacity to feed 18 persons ha Ϫ1 (4.7 t of food grains ha Ϫ1) compared with their current productivity of 0.9 t ha Ϫ1 supporting four persons ha Ϫ1. This increased productivity can be achieved if the productivity of rainwater is doubled (from 30% to 67%) and the soil loss is reduced by 75% compared with the loss under traditional methods of cultivation. By adopting such a holistic approach to the management of rainwater in partnership with the communities, crop productivity in the watersheds is substantially increased (up to 250%), groundwater levels improved and soil loss minimized. Results from such on-farm integrated watersheds are discussed. Conditions for success in the improved management of rainwater are: community participation, capacity building at local level through appropriate technical guidance and the use of new scientific tools to manage the watersheds efficiently. To sustain agricultural productivity in the SAT, this holistic approach of watershed management needs to be scaled up through appropriate policy and institutional support and its on-site and off-site impacts need to be studied.
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