Peer review

Soil-water availability is the major yield determinant of rice (Oryza sativa L.). The objective of this investigation was to study the effects of organic manures vs. inorganic fertilizers on phenological, physiological and yield parameters under drought imposed at various reproductive stages of hybrid rice cv. NDRH-2. The vulnerability of various reproductive stages to drought was ranked as: gametogenesis>anthesis>grain-filling>dough formation>post-dough formation>whole grain. Drought-caused spikelet sterility was related more to injury to palea than to lemma, though the grain growth continued even after the death of palea and/or lemma. Organic manures enhanced the survival of flag leaf (55%) and second leaf (40%) against 31% in plants inorganically fertilized; and increased the number of filled grains by reducing spikelet sterility. Drought at 10 days before anthesis up to 5 days after it proved most harmful in the inorganically fertilized soil (IFS, i.e., control) than in the organically fertilized soil (OFS, i.e., green manure, compost). The net assimilation rate (NAR) varied from 925 (green manure) to 900 mg m−2 day−1(compost) against 888 mg m−2 day−1 in the control. The relative growth rate (RGR) was 4.6 for green manure and 4.4 mg g−1 day−1 for compost, which were higher than the RGR for the control (4.1 mg g−1 day−1). Grain yields [15.9 g (green manure) to 15.4 g (compost) hill−1 in OFS] were higher than the IFS grain yield (13.5 g hill−1), with the harvest indices in OFS [34.4% (green manure) to 34% (compost)] being higher than that in IFS (32.2%) at 10 days before heading. Thus, the use of organic manures enhanced drought tolerance, which minimized the reduction in NAR, RGR, and spikelet sterility, thereby stabilized grain yield under drought.

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