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Effect of Soil pH and Clay Content on the Zinc Soil Test Interpretation for Corn

CNPq Fellow, EMPAER, Campo Grande, MS, Brazil

F. R. Cox^*

Soil Science Dep., North Carolina State Univ., Raleigh, NC 27695-7619

*Corresponding author.

ABSTRACT

Soil test interpretations are usually improved by considering at least one soil property in addition to the extractable nutrient concentrations. Greenhouse and field experiments were carried out to evaluate the effects of soil pH and clay content on the Zn soil test interpretation for corn (Zea mays L.). In a greenhouse experiment, four Oxisols with 68, 63, 57 and 21% clay were adjusted to pH 5.2, 5.7 and 6.2. Five Zn levels within each soil pH were created by applying Zn at 0, 0.8, 1.6, 3.2 and 6.4 mg L^–1. Three crops of Cargill 111-S corn were grown, each for about 4 weeks. Soil Zn extracted with Mehlich-1 was not affected by changes in pH, but plant Zn decreased as soil pH was increased. Plant growth was depressed at the highest soil pH and lowest soil Zn concentration, and the prediction of dry matter as a function of soil Zn was markedly improved by including soil pH for three of the four soils. The soil-Zn critical level was calculated and was not affected by clay content, but did increase with an increase in pH. The critical levels in the greenhouse were 1.0, 1.4, and 2.0 mg L^–1 for soils of pH 5.2, 5.7, and 6.2, respectively. In the field, the same variety of corn was grown one season in a residual experiment on a Typic Haplustox. Lime and zinc levels had been established by treatments imposed 13-yr prior. Current pH ranged from 6.0 to 6.7, and the soil Zn from 0.6 to 1.6 mg L^–1. The results were similar to those obtained in the greenhouse. The effect of pH on the soil Zn critical level, however, was not as striking, perhaps because of the high average and more narrow range in soil pH.

Paper 11429 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601.

Received for publication February 16, 1988.