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Grain Yield of Maize (Zea mays L.) in Relation to Nitrogen, Phosphorus, Sulfate, Chloride, Zinc, Boron, Manganese, and Plant Population¹

ABSTRACT

Excellent climatic conditions for maize (Zea mays L.) production in the Beqa'a Plain of Lebanon led to a series of eight multivariate irrigated field experiments on a calcareous clay soil typical of much of the Middle East. The objective was to determine which factors, in addition to N and P deficiencies, may become important as grain yields are increased to levels in the range of 12 to 18 tons/ha or more. Central composite, rotatable, experimental designs and regression analysis were used.

Applied N was the only variable having an appreciable first order effect and most of the yield variation was attributed to the various two and three-factor interactions involved. Although the soil was well-drained and the quality of the irrigation water good, amounts of applied chloride and sulfate needed to be minimized due to negative P-Cl, P-S, and N-P-S interactions when N and P were applied at necessary levels of about 300 kg/ha. Positive interactions of applied Zn with plant population and applied P with population along with the positive Zn-B-population and P-B-population interactions indicated a requirement for relatively high levels of applied P, Zn, B, and plant population. Positive response to applied Zn and B occurred up to the 90 to 180 kg/ha level indicating the need for these elements at high yield levels. However the efficiency of use was low for the application method used (somewhat dispersed band about 5 cm below the seed) and further work is needed.

The experiments were exploratory pointing the way to further investigation of nutrient balance and plant population. The micronutrient requirements of maize appear to be especially critical at very high yield levels and the detrimental effect of applied sulfate on grain yield requires further work in relation to anion balance.

¹ Authorized for publication on Sept. 8, 1967 as Journal no. 206 by the Faculty of Agricultural Sciences of the American University of Beirut, Lebanon.

² Professor of Soils, Research Assistant, Graduate Fellow, and Graduate Assistant, respectively.

Received for publication September 27, 1967. Accepted for publication May 29, 1969.