The system of rice intensification (SRI) has been proposed as a way of transitioning towards more sustainable rice farming. In rainfed rice farming, however, various environmental constraints often make SRI practices challenging to adopt. We conducted an on-farm experiment in 30 rainfed lowland fields to examine the technical efficacy of SRI in southern Cambodia during the wet seasons of over three years of 2012, 2013, and 2015. Across the three years, the SRI practices produced significantly greater plant biomass and grain yield than non-SRI. We ascribed the yield increase to the increased number of grains per land area as the increased number of spikelets per panicle rather than the number of panicles per land area. With no significant difference in seedling age between the SRI and the non-SRI, we attributed the more substantial number of grains per panicle to the reduced planting density, increased manure application, and reduced amount of inorganic fertilizers in SRI fields. Our results suggest that the advantage of the SRI lies in the efficient use of internally available soil nutrients, whose mechanisms need quantitative understanding through future studies.

1. 본 연구는 저지대 천수답지역인 캄보디아 남부 따게오주에서2012~2013년에 2년간 벼 집약재배관리 시스템(System of Rice Intensification: SRI)에 대한 현장 연구 결과이다. 2. 천수답 지역에서 2년간 SRI는 FP 보다 화학비료 사용 없이 쌀 수량이 증가 되었다. 캄보디아 천수답 농가의 SRI 은 어린모로 조기 이앙과 넓은 재식 밀도로 인해 이삭수 확보와 함께 지형에 따른 물 보유 능력과 오랜 기간 유기물 사용으로 수량이 증가된 것으로 판단된다. 3. 쌀 수량에 미치는 영향으로 총 질소 흡수량과 단위면적당 총 영화수는 (r2=0.95) 정의 상관관계를 보였으며, 천수답 지역에서 물 관리 방법은 어렵지만 유기물을 장기간 사용한 지역 농가의 쌀 생산은 증가 되었다. 4. 최근 국내에서 일부 지역에서 소식재배가 확대되고 있는데SRI원리를 소식재배와 연계한다면 보다 좋은 재배방법이 될것으로 기대된다.

New QTLs were identified for high grain yield with long panicle in rice. A total of 137 F15 recombinant inbred lines (RILs) derived from a cross between Dasanbyeo (Tongil) and TR22183 (japonica), together with the parents were evaluated for 16 agronomic traits at IRRI in dry and wet seasons under different phosphorus (P) and irrigation conditions. A linkage map was constructed using 236 polymorphic markers in 384-plex Bead Xpress indica-japonica single nucleotide polymorphism (SNP) platform. P and water effects were significant in both wet and dry seasons. Both parents and RILs showed varying degree of sensitivities to scarcities in water and phosphorus in terms of panicle length. Collocating with 20 yield-related QTLs, the panicle QTLs on chromosomes 1 (pl01) ,2 (pl02), 9 (pl09), and 11 (pl11) under low P and rainfed conditions were identified. RILs with TR22183 allele at pl11 showed longer panicle length under low P input rainfed condition in dry and wet seasons. The whole-genome sequences of the two varieties are being compared to design the molecular markers for fine-mapping and candidate gene identification. Based on Nipponbare MSU 7.0 annotation, a total of 1464 genes with predicted function were identified within the four QTL regions. Candidate genes identified in other studies for QTLs under low P and water conditions, such as calmodulin and dehydrin genes, were targeted for designing molecular markers for fine-mapping and expression analysis. Pyramiding the panicle length QTLs correlating with yield QTLs will provide an opportunity of improving yield traits.