Spatial and Temporal Distribution of Soil Water Availability in the Indo-Gangetic Plains of India, Bangladesh, Pakistan, and in Sri Lanka: Natural Resource Management Program Report No. 3

Abstract

Cultivation of legumes, which used to be an important component of the cropping systems in South Asia, has been ignored by farmers growing rice and/or wheat crops, or relegated to marginal lands in recent years. This bulletin contends that greater cultivation of legumes for grain, forage or as green manure in rice and wheat systems can help maintain sustainability of these systems and achieve a required level of crop diversification. As legumes are normally grown rainfed, soil water availability will be a major determinant of their success or otherwise. This bulletin presents temporal and spatial soil water availability scenarios in order to assess the scope for greater inclusion of legumes in the predominantly rice or wheat-based cropping systems of the Indo-Gangetic Plains of India, Bangladesh, and Pakistan and for rice-based cropping systems in Sri Lanka. This has been achieved through the application of a water balance model ‘WATBAL’ and making use of geographic information systems (GIS) to display and analyze month-wise maps of various indices of soil water availability, and determine length of growing season. The scenarios indicate considerable spatial and temporal variability with respect to rainfall and moisture indices varying from more favorable to less favorable. The water availability scenarios presented in this bulletin are generic in nature and can also be used to assess other rainfed crops besides legumes and refine irrigation scheduling for irrigated crops. These scenarios are based on monthly input of climatic data and therefore could be improved further using daily or weekly climatic data for the target regions