Drought-resistant soils Optimization of soil moisture for sustainable plant production FAO Land and Water bulletin Series, Vol. 11

Water is the “lifeblood” of agricultural practice worldwide. However, water scarcity is a major constraint on rainfed agriculture. As well as being a consequence of low or erratic rainfall, the perceived water scarcity may be caused by choices made by the farmer, e.g. of a crop or variety sensitive to water stress, or by inadequate management of available water from rainfall. Inappropriate practices in a particular context can have a dramatic affect on water resources management and soil moisture availability. In order to minimize the impact of drought, soil needs to capture the rainwater that falls on it, store as much of that water as possible for future plant use, and allow plant roots to penetrate and proliferate. Problems with or constraints on one or several of these conditions cause soil moisture to be a major limiting factor for crop growth. Where natural rainfall patterns or quantities do not allow reasonably secure satisfaction of crop water requirements, the conventional answer to water deficit has often been to increase water availability through irrigation systems. However, irrigation may not be feasible or even desirable. On the other hand, building on local experiences over generations, farmers worldwide have developed management options that can increase the capacity of soil to store water for plant use and reduce vulnerability to drought. Soil can be managed in ways that reduce the need for supplemental watering and increase the sustainability of the farm. However, market forces and rural–urban migration in many regions have introduced changes in farming systems and practices that have negative impacts on resources management and increase the risk of drought, as well as inducing other related negative environmental effects. In the world today, about 40 percent of food production comes from irrigated agriculture. However, most smallholder farmers in developing countries are reliant on rainfed agriculture; a practice that will continue for several reasons. Irrigation water and infrastructure is often not accessible or viable depending on the resource endowment and agricultural infrastructure. Moreover, irrigation development is usually expensive, and sometimes economically and environmentally hazardous. As a result, investment support for irrigation has declined considerably in the last 20 years. The potential for expansion of irrigation schemes in the arid and semi-arid areas is limited, hampered by land suitability, water availability, and conflicts over water ownership among farmers (and between farmers and non-farmers). In this context, a significant contribution to food security would be made by the development of improved rainfed agriculture systems that are affordable and sustainable and that increase water availability to crops in dry areas where other water resources are not available or are uneconomic to develop. Recognizing the importance of rainfed agriculture in food security and in particular to the majority of smallholder farmers worldwide, improved rainfed management strategies have to be developed in order to improve water productivity within present farming systems. Under low and variable rainfall conditions, efficient soil moisture management is a good way of improving water-use efficiency. Specific runoff farming and water-harvesting techniques may also be considered. The question is how to optimize soil moisture, which is a key parameter for drought- proofing the soil and increasing productivity in rainfed or irrigated agriculture, while protecting water resources.