Factors affecting irrigation water savings in raised beds in rice and wheat

Raised beds have been proposed for rice-wheat (RW) cropping systems in the Indo-Gangetic Plains as a means of increasing irrigation water productivity, among many other potential benefits. Field experiments were carried out in Punjab, India, during 2002-2006 to compare irrigation water use and productivity of transplanted rice and drill-sown wheat on fresh and permanent beds and conventionally tilled flats. Total irrigation applications to conventionally tilled wheat (CTW) and wheat on beds were similar on both soils, in both small plots and in a farmers' field, with one exception irrigation amount on fresh beds was 10% lower than on permanent beds in the farmers' field. Yields on beds and CTW were similar on the loam, but were sometimes lower on beds on the sandy loam. In the small plots, irrigation water productivity (WPIW) on beds and in CTW was similar (mean 2 g kg(-1)) on the loam, but about 20% on the sandy loam, mainly due to lower yields. In the farmers' field, WPIW (1.5 g kg(-1)) was 15% higher on the fresh beds than on the permanent beds due to lower irrigation amount. The amount of irrigation water applied to rice on permanent beds and puddled transplanted rice (PTR) was similar in the small plots on the sandy loam. However, on the loam, irrigation application to the permanent beds was significantly higher, by about 18%. There was a significant decline in grain yield on the permanent beds relative to that in PTR over the 4 years, on both soils. WPIW on the permanent beds decreased with time on both soils, mainly due to declining grain yield. Irrigation applications to rice on fresh beds were lower than applications to the puddled flats (by 11% on the sandy loam, and by 20-24% on the loam) while yields were 7 and 15% lower, resulting in similar WPIW on fresh beds and PTR. Reducing irrigation application from full-furrow to half-furrow depth in the farmers' field reduced the irrigation amount on both permanent and fresh beds by 40-50%, but yield was also reduced by about 20%. The results show that beds do not always save irrigation water or increase WPIW in comparison with conventionally tilled flat fields, for both rice and wheat under our soil and environmental conditions. The effects of the beds depend on irrigation/water management (of both beds and flats), age of the beds and soil type. The effect of beds on irrigation amount is also likely to depend on factors such as depth to the water table, levelness of the soil surface, and size and shape of fields relative to irrigation flow rate. (C) 2010 Elsevier B.V. All rights reserved.