Enhancing Green Water in Soils of South Asia

Abstract

Enhancing green water (GW) in soils has vast significance with respect to depleting water resources, especially in South Asia (SA). The water stored in soil that's productively used for transpiration is called GW. The enhancement of GW includes all those techniques and approaches that lead to increased soil-water storage and infiltration, reduced runoff, and decreased evaporation, such as minimum tillage, mulching, terracing, small-scale water harvesting and recycling, contouring, and strip cultivation. Because rice (Oryza sativa) is a dominant crop in SA and it requires four to five times more water than other cereals, adoption of new techniques like direct dry seeding, wet seeding, system of rice intensification (SRI), intermittent irrigation, soil matric potential-based irrigation, laser land leveling, and raised-bed planting can save 20–87% of irrigation water. Enhancing GW in soils is important to achieving a much-needed new Green Revolution in countries faced with the dire issue of food insecurity. Many water-stressed countries can produce enough food for their populations provided that the GW is enhanced and managed well. More food means more consumptive use of the so-called GW flow (vapor flow sustaining crop growth). The present level of food production requires some 7,000 km3/yr of consumptive freshwater (i.e., GW as evapotranspiration), of which 1,800 km3/yr originates from blue water use (i.e., runoff water in irrigation) and the remaining 5,200 km3/yr from direct GW use. Identification and use of efficient GW-management techniques necessitate a thorough knowledge of social, biophysical, economic, and practical aspects, and these must be in accord with the existing farming systems. A new approach to water management, integrated water-resource management (IWRM), is widely recognized as a pathway toward sustainability. The IWRM in SA countries can increase productivity by 28% to 120%, while also reducing runoff by 26% to 66% and soil loss by 20% to 43%, and raising the groundwater level by 4 to 5 meters. A policy shift is needed and incentives through GW credits must be given to the farmers for adopting and maintaining best practices for enhancing GW in soil.