Concentration of pecan roots in the 15-45 cm layer of soil and lower soil pH, P, and K in the 15-30 cm layer than in adjacent layers indicate that pecan trees are feeding primarily in this zone. Fertilization with N-containing complete fertilizers or NH4NO3 reduced soil pH gradually, and continued annual application gradually affected deeper soil layers. Phosphorus and K applications affected soil pH very little.
Continued annual applications of P gradually built up residual soil P (measured one year later) to high levels at all layers sampled for old trees over a 10-year period. When P applications were based on topsoil P levels, subsoil P level was not affected over a 5-year period.
Applications of K usually increased residual soil K, but rate effects were slow to appear in old trees and were often erratic. Rates of K were readily reflected in residual soil K levels at depths to 70 cm when rates were based on topsoil K level.
Zinc uptake by pecan leaves as affected by Zn sources and methods of application was compared for young and old pecan trees. Sources of Zn used were ZnSO4, ZnO, ZnHEDTA, and ZnEDTA. Methods of application were broadcast, in holes, and foliar sprays. Chelates were applied at 1/5 - 1/10 the rate of Zn used for ZnSO4 or ZnO. Leaf Zn from trees treated with ZnO broadcast was either equal to or greater than that from trees treated with ZnSO4 broadcast when both were applied every year. On young Zn deficient trees, ZnEDTA entered the tree earlier than the other sources when broadcast. Zinc deficiency symptoms appeared when leaf Zn was 40 ppm or less. Foliar sprays of ZnSO4 caused erratic and temporary increases in leaf Zn.
Correlations between pecan yield, quality, tree growth, and various nutritional variables were studied over an 8-year period. Yield was negatively correlated with yield the previous year, but yield was positively correlated with yield accumulated over several years. Terminal shoot growth and nuts/lb. varied in a pattern similar to yield. Soil and leaf analysis was not often correlated with yield, nut quality, or tree growth. Degree of leaf retention in a heavy crop year was positively correlated with yield the following season.
Although variation between years was large, yield responses were obtained from N in 3 years, P in 2 years, and K in 1 year of the 4 year test. Results indicated that application levels should be 25-50 lb of N/A, 11-22 lb of P/A, and not over 42 lb of K/A. A complete fertilizer supplying 50-22-42 lb of N-P-K/A gave the highest average yield. Fertilizer treatments had little effect on leaf analysis at harvest in 1963, and correlation coefficients were not significant for leaf mineral concentration of N, P, K, Ca, Mg, Na, Mn, Fe, B, Zn, Al, Mo, Ni, Sr, Ba, and Ti with yield. Significant negative correlation coefficients were found for yield with leaf Cu, Zn, Al, and Ti, but they were all -.36 or less.
Magnesium sulfate applied as a soil amendment (34 kg Mg/ha annually for 3 years or a single application of 224 kg Mg/ha) increased leaf Mg 5 years after initial application. Dolomite increased soil pH and soil test Mg but not leaf Mg. Sulfate of potash magnesia and MgO increased soil test Mg and slightly, though insignificantly, increased leaf Mg. Single foliar sprays of MgSO4 and Mg(NO3)2 did not affect leaf Mg.