Estimation of crop coefficients of dry-seeded irrigated rice-wheat rotation on raised beds by field water balance method in the Indo-Gangetic plains, India.

摘要

Lack of information on crop coefficient (k_c) values of bed planted rice-wheat system in the Indo Gangetic Plains (IGP) of India has become a constraint for irrigation planning to improve the crop water productivity. In this paper, we estimated k_c values from field water balance measured crop evapotranspiration (ETc) and Penman-Monteith estimated reference ET₀ for dry-seeded irrigated bed planted rice-wheat rotation and also compared with conventional dry-seeded flat system of planting. The experiment was conducted in 2001-2003 at New Delhi, India. Estimated k_c values at initial stage (4-6th weeks of sowing) on raised beds were comparable with flat conventional planting for rice but significantly higher for wheat. However, in later stages of growth, k_c values for both rice and wheat were lesser on beds than flat land. The k_c values of rice during initial, crop development, mid-season and late-season stages on beds were 0.62, 0.75, 1.16 and 0.67, respectively while in conventional flat land, corresponding k_c values were 0.61, 0.97, 1.42 and 0.91, respectively. The k_c values for wheat at four crop growth stages (initial, crop development, mid- and late-season) on raised beds were 0.98-1.06, 1.10-1.14, 1.25-1.26 and 0.46-0.47, respectively while on flat land with conventional row (20 cm) spacing, corresponding k_c values were 0.87, 1.12, 1.45 and 0.55, respectively. Flat beds similar spacing (20-47 cm) with raised beds had comparable k_c values. Bed geometry led variation in plant population density influenced strongly both crop ET_c losses as well as k_c values. The results provide estimates of ET₀, ET_c and k_c for use in irrigation scheduling in bed planted rice-wheat system in the IGP of India and elsewhere with similar environmental conditions.