Results of previous studies on the chemical composition of pecan leaves indicated a significant relationship between the level of phosphorus and potassium in the leaves and quality of nuts. The objective of the present study was to apply phosphate and potash fertilizers under two systems of culture with the view of increasing the uptake of these fertilizers. A block of trees was selected and the entire block was seeded to blue lupine for the purpose of supplying nitrogen to the trees. The block was divided into plots to accommodate a split-plot experiment using phosphate and potash singly and in combination. The plots were then divided into two series, one to be cultivated during the summer and the other to have the lupine mowed and left as a mulch. Leaf samples were taken in September of each year and analyzed for N, P, K, Ca, and Mg. Yield records were taken and samples of nuts were examined for quality.
The percentages of nitrogen, potassium, and calcium found in the leaves were not significantly influenced by either cultivation, mulching, or fertilizer. In 1950, the fourth year of treatment, the leaf phosphorus was increased significantly by the application of phosphate and by the summer mulching of the lupine. Leaf magnesium was not significantly influenced by the application of fertilizers, but it was increased significantly by the summer mulching. The mean percentages of leaf N, P, and K were less in 1950 than in 1946 despite the fact that relatively large quantities of these elements were returned to the soil by the cover crop growth and the fertilizer applications. This may have been due to the high utilization of these elements in production of nuts and growth of trees.
Nuts of good quality were produced with a relatively wide range of total nutrients in the leaves. Yield of nuts and quality of the kernels were not highly correlated with the level of any one particular element found in the leaves, but there is evidence that the balance of elements in the leaves was the determining factor in influencing quality.