The effects of repeated soil wetting and drying on lowland rice yield with system of Rice Intensification (SRI) methods

Abstract

In lowland rice farming, water management is the most important practice that determines the productivity of other inputs, e.g. nutrients, herbicides, pesticides, farm machinery, microbial activity, mineralization rates. Deliberate flooding or poor drainage that keeps soil saturated is detrimental to crops and degrades soil quality. This study evaluated whether rice grain yield could be increased relative to continuous flooding by using the management practices of the System of Rice Intensification (SRI). The effects of SRI's repeated wetting and drying cycles plus different plant populations were investigated at Sapu Research Station in The Gambia, on an alluvial soil between 2000 and 2002. The water management practices proposed for SRI were found to be beneficial to rice growth. At 20 cm spacing, average grain yield with SRI practice was 7.3 t ha⁻¹ compared with 2.5 t ha⁻¹ under continuous flooding. At 30 cm spacing SRI practice yielded 6.6 t ha⁻¹, while under continuous flooding, grain yield was only 1.7 t ha⁻¹. Even wider spacing did not produce higher yield. At 40 cm spacing, SRI management gave 4.7 t ha⁻¹, while continuous flooding yielded 1.3 t ha⁻¹. Thus overall, SRI practices gave better results than continuous flooding. This was probably as a result of increased nutrient availability and superior growing conditions which enhanced physiological development and grain yield. Rewetting dry soil reportedly facilitates nitrogen mineralization. The phenomenon of having a flush of nitrogen mineralization occurring after rewetting dry soil was first reported by Birch in 1958. This intensive pathway of nitrogen mineralization and nitrogen availability has potential to increase lowland rice yields in ways consistent with sustainable agricultural production.

Keywords:

• SRI
• lowland rice
• intermittent flooding
• water management
• water productivity