Use of Normalized Difference Vegetation Index to Assess N Status and Predict Grain Yield in Rice

Fine tuning N recommendations requires an understanding of crop N status and yield potential early enough in the growing season when changes to N management can influence yields. Recent studies have demonstrated the ability of Normalized Difference Vegetation Index (NDVI) to assess crop N status and predict yield in wheat ( Tricticum aestivum L.) and maize ( Zea mays L.); however, there has been relatively little such research on rice ( Oryza sativa L.). The objectives of this study were to determine how well NDVI measured at the panicle initiation (PI) rice growth stage assesses crop N status and predicts final grain yield. Nitrogen response trials were established over a 4‐yr period (10 site‐years) at various locations throughout the Sacramento Valley rice growing region of California. Additionally, the relationship between NDVI and crop N status was characterized across 28 on‐farm plots representing a range of environmental conditions and management practices. The NDVI at PI was best correlated with total N uptake (N UP , r 2 = 0.66), followed by N concentration (N CONC , r 2 = 0.54), and aboveground biomass (AGB, r 2 = 0.51). The utility of NDVI was greatest at lower values of crop N status, whereas at higher values, NDVI saturated. The NDVI at PI was positively correlated with final grain yield ( r 2 = 0.58) indicating utility for developing in‐season yield predictions. While NDVI is a potentially useful tool to improve N fertilizer management and develop in‐season yield predictions in rice, alternative indices that do not saturate would likely provide a basis for a better tool. Core Ideas The ability of NDVI to assess rice N status and predict final grain yield was evaluated across 38 sites and four years. NDVI at panicle initiation was most closely related to crop N uptake. At high values of crop N status NDVI had limited utility due to saturation. NDVI at panicle initiation was positively correlated (r 2 = 0.58) with final grain yield. NDVI of 0.66 at panicle initiation indicated sufficient crop N uptake to achieve average maximum grain yield.