Intercepted radiation at flowering and kernel number in maize

When water and nutrients are not limiting growth, kernel number per plant (KNP) can be calculated for maize (Zea mays L.) using linear models based on intercepted photosynthetically active radiation per plant (IPARP). These models do not include the concept of a threshold IPARP for KNP. Our objective was to study the response of KNP to IPARP in order to improve current models. Published information from several field experiments, performed with two maize hybrids in the temperate region of Argentina, was used for the analysis. Both linear and curvilinear (inverse linear and exponential) models based on IPARP explained more than 75% of the variability in I(NP and kernel number per apical ear (KNA). Curvilinear models gave a better fit at low (<0.5 MJ plant(-1) d(-1)) and intermediate (1.3-2 MJ plant(-1) d(-1)) values of IPARP than a simple two-line linear model. Models allowed the estimation of maximum KNA and maximum KNP, and the minimum IPARP to reach them, but only curvilinear models allowed the estimation of a threshold IPARP (0.31-0.37 MJ plant(-1) d(-1)) to avoid plant barrenness. The inverse linear model gave a better prediction of maximum kernel number than the other two models. The exponential model allowed a better estimation of the initial value (2.16 MJ plant(-1) d(-1)) for expressing prolificacy tears plant(-1)) > 1. The relationship between KNP and IPARP did not improve when IPARP was expressed on a thermal time basis (photothermal quotient), probably because air temperature did not vary much among the situations explored in this work.