The System of Rice Intensification (SRI) is a resource-conserving rice productionsystem that uses intermittent flooding and organic fertilization. The SRI isemerging as an alternative to conventional rice production systems that usecontinuous flooding and mineral fertilizer only, however yield improvements withSRI have been highly variable. The objective of this research was to determine ifsoil properties control the yield improvements with SRI and, if so, the underlyingchemical and biological mechanisms. A meta-analysis of 72 SRI vs. conventionalsystem trials from 16 countries found a significant yield response to SRI in lowfertility soils (P<0.0001), but no difference between SRI and the conventionalsystem in moderate and high fertility soils. These results were validated in agreenhouse study. Soils with low P availability (≤7.1 mg P kg-1) respondedpositively to intermittent flooding and organic fertilizer by increasing plantbiomass, plant P uptake, available soil P and microbial P concentrations,compared to soils under continuous flooding and amended with mineral NPKfertilizer only. A field study investigating the interactive effects of water regimeand fertilizer source found that, under conditions of P limitation, yields weregreater with NPK + composted cow manure (compost) than NPK fertilizer alonein 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 significantlyincreased by compost and was correlated with yield (P=0.007). When N was themost limiting nutrient, according to the Diagnostic and RecommendationIntegrated System (DRIS) analysis, yields were greater in the continuouslyflooded (5.2 t ha-1) than intermittently flooded (2.7 t ha-1) soils receiving NPKfertilizer only, but showed no difference when compost was applied. Compost hada 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 averageyield increase of 47% and 86% less water use. SRI is recommended as a riceproduction system to conserve water and improve rice yields under conditions ofP limitation. Organic fertilization is recommended to improve crop nutrientbalance and yield under intermittently flooded soil conditions.
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