Abstract
Monitoring wheat grain maturity and harvesting immediately after maturity are important to avoid damage in grain quality by rainfall. Grain drying and wetting rate were measured to develop a model for estimating the water content of kernel in wheat (cv. ‘Norin61’) using meteorological data. Drying rate (change in % per hour) was most heavily influenced by vapor pressure deficit. The initial water content of kernel also had a significant effect on the drying rate and it was incorporated into the equation as a coefficient of resistance. Water absorption of kernels measured by soaking ears in water was equivalent to that measured by exposing to natural rain. Based on these data an equation was derived for estimating water content of kernels under rainfall which was determined by initial water content and time of the rain duration. Using these equations, we could estimate the drying and rewetting process of kernel after physiological maturity under field conditions. Before physiological maturity, i.e., from flowering to physiological maturity, the water content of kernels could be estimated using the temperature-dependent model that we previously reported. Differences between calculated and measured values reached the minimum (RMSE=3.68%) when the model for before physiological maturity was switched gradually over three days prior to and after physiological maturity. Water contents of kernels used in this study were in good agreement with the spike water contents obtained by the commonly used method for estimation of harvest time. These results suggest that this model is useful for monitoring the progress of maturity of wheat and for making decisions on harvest.
