Factors contributing to yield variation among unfertilized paddy fields in northern Japan
2016
Hosoya, K. (Iwate Univ., Iwate (Japan). The United Graduate School of Agricultural Science) | Sugiyama, S.
Unfertilized crop cultivation system (unfertilized cultivation) is believed to reduce the yield markedly. However, some rice farmers using unfertilized cultivation attain high yields, which are comparable with those obtained in conventional farming. In the present study, we surveyed 16 rice farmers employing unfertilized cultivation in Aomori, Iwate, Miyagi, and Niigata prefectures. Our objective was to identify factors contributing to yield variation. During 2011-2013, the mean annual rice yield obtained by these farmers was 300 kg per 10a; however, some farmers consistently achieved annual yields of 420-480 kg per 10a. The yield was highly correlated with the grain number per square m, especially with the panicle number (r=0.92***). In addition, the panicle number showed a strong correlation with the average air temperature from transplanting to 43 days before heading (r=0.66**). We conducted a rice growth experiment in pots using unfertilized paddy soil and transplanting at four different days. The tillering rate was highly correlated with the average air temperature during the growing period (r=0.92***). The results of path analysis based on multiple linear regression revealed that the effects of air temperature on the tillering rate were derived from a direct effect on rice growth (57%) and from increased nitrogen mineralization in the soil (43%). Our findings indicate that ensuring an adequate accumulated temperature during the early vegetative growth period is crucial in unfertilized rice cultivation in northern Japan.
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