Ecological intensification of rice production in the lowlands of Amazonia – Options for smallholder rice producers

Abstract

This study reports on two consecutive years of experimentation to evaluate ecological intensification options for smallholder irrigated rice production on an alluvial-marine soil in the eastern periphery of Amazonia. The 2007 system-comparison trial contrasts management packages of the System of Rice Intensification (SRI) with ‘conventional’ irrigated rice (CIR). In a bi-factorial layout, we compare SRI and CIR under low (10Mgcowmanureha−1) and high (10Mg manure+additional 100kgNha−1 as urea) fertilizer regimes. The 2008 factor-comparison trial investigated the relative effects of three key rice intensification management components: (i) aerobic-moist (as opposed to anaerobic-flooded) water regime, (ii) low-density transplanting (as opposed to high-density direct seeding), and (iii) organic (as opposed to synthetic) fertilization. Weed management was not investigated and therefore standardized to manual weeding. Since a full factorial scheme (3×3 treatments) was not feasible, we compare SRI and conventional management components under the conditions we deemed most relevant for irrigated rice in our region and beyond.System-comparison indicates higher grain yield of CRI than of SRI, both at low (+21%) and at high (+9%) fertilizer levels. SRI was associated with strong increases in tillering and in individual plant biomass which almost compensated for the low plant density, as well as an increased plant height and a wider root:shoot ratio. However, the conventional treatments positively affected the final grain-filling stage, with increased numbers of filled grains per panicle, weight of 1000 grains and – ultimately – grain production. Factor comparison (i) does not support the idea of beneficial effects of an aerobic water regime and (ii) dispenses the necessity of an organic fertilizer regime, but (iii) does indicate significant benefits of low-density transplanting over direct-seeding, an important management feature for Amazonian smallholder irrigated rice farming.