Abstract
The objective of this study was to propose a model for explaining rice responses to a wide range of N application rates in various growth attributes associated with the occurrence of chalky grains. We improved the sub-model for N uptake process of a previous rice model which was originally developed for explaining genotypic and environmental variations in the whole growth processes, considering the difference in the rate of N loss from the plant-soil system between indigenously supplied soil mineral N and fertilizer N. A total of 80 growth datasets of cultivar ‘Koshihikari’ grown at Shiga prefecture, Japan, in 2010 was utilized for the calibration and validation of the model. The rice growth model well explained the above-ground biomass growth (RMSD = 78.7 g m−2) and rough dry grain yield (RMSD = 83.2 g m−2) for the validation data-set, simultaneously. The simulated carbohydrate content available per single spikelet was negatively correlated with the observed percentage of the milky-white grain which includes white-cored grain (r = −.77, p < .001) for all the data-sets of calibration and validation. On the other hand, the observed percentage of the sum of white-back and white-base grains was closely correlated with the simulated plant N content available per single spikelet (r = −.59, p < .001). It was suggested that the present rice growth model would rationally explain the effects of N application on the occurrence of the chalky grains through the dynamic change of the carbohydrate content and plant N content available per single spikelet.
Highlights
The current global warming tendency (IPCC 2007) poses new challenges in rice production
Recent studies clearly showed that the percentages of white-back and white-base grains were more related to the plant N status than the spikelet number or the amount of carbohydrate available for filling grains; the decline in plant N concentration during the early stage of grain filling resulted in the enhanced occurrence of the white-back and white-base grains (Kusuda et al, 2004; Morita et al, 2005; Nakagawa et al, 2006; Tanaka et al, 2010)
This paper shows the relationships between the observed occurrences of chalky grains and simulated variables associated with the occurrence of chalky grains for those rice plants grown at Shiga prefecture in 2010 under various N application rates
Summary
The current global warming tendency (IPCC 2007) poses new challenges in rice production. The amount of carbohydrate available per single spikelet, defined as the sum of non-structural carbohydrate content accumulated up to the heading stage and biomass production during the period from heading to maturity divided by the number of spikelet (Kobata et al, 2004), is the final outcome of the dynamics in the balance. A crop growth model which explains the effects of N application rate and timing on growth, yield and plant properties associated with the occurrence of chalky grains in rice will be a useful tool to assess the adaptive rice production technology to a given environmental condition. The primary objective of this study is to propose a rice model for explaining rice responses to a wide range of fertilizer N application rate in various growth attributes associated with the occurrence of chalky grains. We discuss the possibility of predicting the occurrence of chalky grains based on a dynamic rice growth model
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