Submitted to: Peanut Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/25/2007
Publication Date: 6/1/2008
Citation: Rowland, D., Sorensen, R.B., Butts, C.L., Faircloth, W.H., Sullivan, D.G. 2008. Canopy Characteristics and their Ability to Predict Peanut Maturity. Peanut Science (35):86-91. Interpretive Summary: Determining when to dig peanuts is one of the most important decisions a peanut grower has to make because the maturity of the crop must be optimum to make the most profit. This study developed a new maturity prediction method based on nutrient analyses of the canopy portion of the peanut. Therefore, no destructive harvesting was necessary for this method – something previous methods have all required. It was determined that there were seven important nutrients in the leaf: nitrogen, phosphorus, potassium, magnesium, calcium, manganese, and iron, which could be followed over the last part of the season and had the ability to predict when the crop was mature. These nutrients followed a quadratic pattern during the last 30-40 days of the season such that levels at 100 days after planting were high, then dipped over the next 14-20 days and eventually increased again back to their original levels. It was recommended that for growers that wanted to use an alternative, non-destructive method of predicting peanut maturity, degree days should be calculated and nutrient levels in leaves followed starting at 100 days after planting. When 2400 degree days had been accumulated and nutrient levels had returned to their original levels, digging was recommended.
Technical Abstract: To ensure maximum economic return, a peanut producer must accurately predict harvest time when the crop has reached optimal maturity without risking losses through mechanical damage due to deteriorating peg attachments. Currently utilized methods for predicting peanut maturity are based on hull color determination and are somewhat labor-intensive and subject to the observer’s ability to finely discriminate color classes. This study sought to test and evaluate canopy traits that may be correlated with crop maturity. Specifically, the objective of this study was to determine if plant canopy characteristics could be used successfully to predict peanut maturity, through the correlation of solute concentrations, chlorophyll content, nutrient analysis, and reflectance with crop maturity. Using sequential harvest dates in 2003 and 2004 at two sites (Sasser and Dawson, GA), canopy characteristics including: Brix, osmolality, chlorophyll content, and macro- and micro-nutrients, were correlated with the maturity of the crop represented by Maturity Index 1 (the percentage of brown and black pods). Canopy reflectance in the 830 and 850 nm bands also showed strong correlation with crop maturity. Stepwise regression of these canopy characteristics with Maturity Index 1 indicated seven leaf characteristics were important in predicting the maturity of the crop: nitrogen, phosphorus, potassium, magnesium, calcium, manganese, and iron. By calculating and summing the relative change of these leaf nutrients from the first to the last harvest, it was determined this Change Index showed a quadratic relationship across harvests. Therefore, it appears that crop maturity can be accurately and objectively predicted through the use of degree day methods in combination with late season canopy nutrient analysis. Spectral indices also showed promise in predicting maturity and further development of this method is needed.