Peanut response to planting date and potential of canopy reflectance as an indicator of pod maturation
Determining when to dig peanut (Arachis hypogea L.) is complicated because of its indeterminate growth habit. Pod mesocarp color is often used an indicator of pod maturation. However, this process is time consuming and is usually based on a relatively small subsample of pods from peanut fields. Research was conducted during 2003–2005 to determine if reflectance of the peanut canopy, using multispectral imaging (350–2500 nm), could be used as an indicator of pod maturation. The cultivars VA 98R and NC-V 11 were planted beginning in early May through early June during each year with reflectance and the percentage of pods at optimum maturity (percentage of pods with brown or black mesocarp color) determined in mid-September. The highest yield observed for VA 98R across the 3 yr of the experiment was noted when peanut was planted in mid-May rather than early or late May or when planted in early June when peanut was dug based on optimum pod maturity using pod mesocarp color. Pod yield for the cultivar NC-V 11 did not differ when comparing planting dates. For cultivar VA 98R, Pearson's correlations were significant for all bandwidth categories except the normalized difference vegetation index (NDVI) when reflectance was compared with percentage of mature pods. Reflectance for NC-V 11 was not significant for any of the correlations even though significant differences in the percentage of mature pods were noted in mid September when comparing planting dates. These data suggest that canopy reflectance could potentially aid in predicting pod maturation, but more research is needed to determine feasibility of this approach.