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Spikelet sterility is one of the poorly understood complex problems in rice and rarely harvest index exceeded 50 % in crop plants. Experiments were conducted on 800 rice cultures belonging to wide range, to identify genotypes that have low spikelet sterility, and N influence on selected genotypes, adapting a split plant technique approach to reduce sterility and removal of spikelets from panicles. Genotypes belonging to IR64 background (VG lines) and Tequing (TG lines) and other groups were screened. TG lines and japonica had greater percentage of filled grains and also relatively higher chaff content compared to that of VG lines. Application of nitrogen resulted in significant increase in secondary branch number, confirming that these were controlled by fertilizer application, while filling of spikelets on primary branches seems to be under genetic control. Evidence using retransplanting splitted transplanted seedlings after four tiller stage did not show significant yield reduction and harvest index. Spikelet removal technique from apical, middle and or basal regions for 1/3rd of the panicle, resulted in an increase in percentage filled grains, which was more when apical region spikelets were removed than at the basal region. In hybrids, the increase was as high as 20 %. Regression equations for all possible six combinations were developed for deriving a quadratic equations for (%) filled grain and grain weights separately for varieties and hybrids. Based on these experiments, 5–10 % in varieties and 10–20 % in hybrids spikelets are physiologically sterile. It will be possible to increase 5 % grain yield in rice by management and by breeding for rice yield improvement.
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