ARS | Publication request: Determination of peanut pod maturity by near-infrared reflectance spectroscopy

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 5, 2010
Publication Date: April 12, 2010
Citation: Windham, W.R., Kandala, C.V.K., Sundaram, J., Nuti, R.C. 2010. Determination of peanut pod maturity by near-infrared reflectance spectroscopy. Transactions of the ASABE. 53(2) 491-495.

Interpretive Summary: Deciding when to dig peanuts is perhaps the most stressful decision a grower makes because the crop has a wide distribution of pod maturities. Early harvest will result in yield loss and premature peanuts that are at a higher risk of aflatoxin contamination. Even greater losses may occur if the harvest is delayed past optimum maturity due to over mature pod loss and the lack of expected flavor. Peanut pod maturity is currently determined by the hull scrape method which is based on the visual and subjective assessment of pod color. A method to predict pod maturity distribution and the estimate of “days until digging” was developed. Using light, from the visible region of the spectrum a model was developed to predicted maturity on a pod-by-pod basis. The method was able to estimate the days until digging equal to and/or 3 days longer than the hull scrape method. Future experiments must include testing the method on different runner-type peanuts grown in the southeastern U.S. and the methods utility over multiple growing seasons.

Technical Abstract: Peanuts are indeterminate crops and do not mature evenly. Thus it is difficult to decide the optimal time of harvest. Pod maturity is currently determined by the hull scrape method in conjunction with the maturity profile board (MPB) for estimating “days until digging”. The method is based on the known correlation between maturity level and pod mesocarp color, which is a subjective assessment. The objective of this research was to develop visible (Vis – 400 to 750 nm) and/or visible plus short wave near- infrared (Vis/NIR – 400 to 1100 nm) reflectance models to predict maturity classes on a pod-by-pod basis. This would allow the estimation of the optimum days to dig the crop. Peanuts (Georgia Green) were harvested on 5 dates in 2008 and analyzed by the hull scrape method and Vis/NIR reflectance spectroscopy. Spectra from the side of the pod basal segment (N=754) and from the saddle of the dorsal segment (N=625) of each pod were analyzed in the Vis and Vis/NIR regions. Partial least squares regression was used to regress MPB maturity column number on spectra of pods from three sampling dates. Calibration regression error for MPB class column number was higher for saddle spectra. Based on the calibrations, placement of the pods on the profile board could differ by 1.5 columns which could alter the estimate of days until digging by ± 3 days. Validation of all spectroscopic models were equal to and/or 3 to 7 days longer than the corresponding MPB estimates of days until digging. Separation of the maturity classes was primarily due to the broad and increasing absorbance at 640 nm as the pod matures.