Soil properties and the response of rice production to water regime and fertilizer source in low fertility soils of the Republic of Panama

The System of Rice Intensification (SRI) is a resource-conserving rice production system that uses intermittent flooding and organic fertilization. The SRI is emerging as an alternative to conventional rice production systems that use continuous flooding and mineral fertilizer only, however yield improvements with SRI have been highly variable. The objective of this research was to determine if soil properties control the yield improvements with SRI and, if so, the underlying chemical and biological mechanisms. A meta-analysis of 72 SRI vs. conventional system trials from 16 countries found a significant yield response to SRI in low fertility soils (P<0.0001), but no difference between SRI and the conventional system in moderate and high fertility soils. These results were validated in a greenhouse study. Soils with low P availability (≤7.1 mg P kg-1) responded positively to intermittent flooding and organic fertilizer by increasing plant biomass, plant P uptake, available soil P and microbial P concentrations, compared to soils under continuous flooding and amended with mineral NPK fertilizer only. A field study investigating the interactive effects of water regime and fertilizer source found that, under conditions of P limitation, yields were greater with NPK + composted cow manure (compost) than NPK fertilizer alone in the intermittently flooded (6.6 t ha-1 vs. 4.9 t ha-1) and continuously flooded (6.8 t ha-1 vs. 6.2 t ha-1) soils. The available soil P concentration was significantly increased by compost and was correlated with yield ( P=0.007). When N was the most limiting nutrient, according to the Diagnostic and Recommendation Integrated System (DRIS) analysis, yields were greater in the continuously flooded (5.2 t ha-1) than intermittently flooded (2.7 t ha-1) soils receiving NPK fertilizer only, but showed no difference when compost was applied. Compost had a positive effect on the crop nutrient balance according to DRIS analysis (P=0.0007). On-farm trials of SRI at 10 locations in Panama showed an average yield increase of 47% and 86% less water use. SRI is recommended as a rice production system to conserve water and improve rice yields under conditions of P limitation. Organic fertilization is recommended to improve crop nutrient balance and yield under intermittently flooded soil conditions.