Impact of field-scale nighttime air temperatures during kernel development on rice milling quality

Recent research has shown that elevated nighttime air temperatures (NTATs) may contribute to increased chalk and reduced milling quality. The objective of this study was to develop a method to quantify the effects of elevated NTATs on chalk formation and peak head rice yield (pHRY) in field-grown rice cultivars. To do so, 95th percentiles of NTAT frequencies (NT₉₅) occurring during reproductive (R) stages of Bengal, Jupiter, Cypress, LaGrue, Wells, and XL723 cultivars were correlated with chalk levels and pHRYs observed during the 2007 through 2009 harvest seasons. Chalk levels were strongly correlated with NT₉₅ during the R7 and R8 stages for all cultivars, except Bengal. Peak HRYs of Cypress, LaGrue, Wells, and XL723 were linearly and inversely related to NT₉₅ occurring during the R8 stage, while pHRYs of Bengal and Jupiter showed no significant correlations with this percentile at any R-stage. Although strong correlations of chalk levels and pHRYs with NT₉₅ were observed during the R8 stage of cultivar development, it is speculated that rice plants classified in this stage actually exhibit many kernels that lag in development and exist in the R6 and R7 grain-filling stages, where elevated NTATs are thought to have deleterious effects on chalk levels and milling quality.