In-season estimation of grain sorghum yield potential using a hand-held optical sensor

Sensor based nitrogen (N) management technology has helped to improve fertilizer recommendations for various crops. The objective of this study was to estimate the in-season yield potential (YP0) of grain sorghum (Sorghum bicolor L. Moench) using a hand held optical sensor. This experiment was conducted with four levels of N (50, 100, 150 and 200 kg ha−1) and three application timing (Preplant, topdress and split) arranged in a randomized complete block design with three replications at three locations, in Oklahoma in 2004 and 2005. Sensor readings were taken using red (650 ± 10 nm) and green (550 ± 12.5 nm) sensors at sorghum growth stages 2, 3, 5, 6 and 7. Results from statistical analysis have shown that 75 and 77% of the variation in sorghum grain yield was explained by red and green Normalized Difference Vegetation Index (NDVI), respectively at growth stage 3. Similarly, grain N content was correlated to both green and red (coefficient of determination, r2 = 0.61) NDVI readings at growth stage 3. In-season estimated yield (INSEY) derived from green NDVI was also found correlated with final grain yield (r2 = 0.71). The results of this experiment suggest that INSEY can be used as a tool to predict mid-season sorghum grain yield potential at sorghum growth stage 3.