Several methods have been proposed to simulate yield in crop simulation models. In this work, we present a simple method to estimate harvest index (HI) of grain crops based on fractional post-anthesis phase growth (fG = fraction of biomass accumulation that occurred in the post-anthesis phase). We propose that HI increases in a linear or curvilinear fashion in response to fG. The linear model has two parameters, the intercept (HIo) and the slope (s). The curvilinear model was assumed to be monotonic: HI = HIx - (HIx - HIo) · exp(-k·fG); where HIx is the asymptote, HIo is the intercept and k is a constant modulating the rate of HI increase. The models were tested for barley (Pullman, WA and Uruguay), wheat (Pullman, WA) and sorghum (Australia). A positive relationship between HI and fG was in general evident. For barley, the linear model appropriately represented the response of HI to fG, with both HIo and s in the vicinity of 0.3. For wheat HIo and s were 0.34 and 0.21, respectively, but the curvilinear model yielded a slightly better fitting than the linear model. For sorghum, both linear and linear-plateau models fitted data reasonably well. It is shown that the models work well in crops source-limited or source-sink co-limited during grain filling, but in sink-limited conditions the magnitude of the limitation needs to be characterized to compute HI. A major advantage of this method is that the parameters of the linear or curvilinear model are readily calibrated from yield data and biomass measurements at anthesis and harvest.
All Science Journal Classification (ASJC) codes
- Agronomy and Crop Science
- Soil Science