EVALUATION OF INTERACTIONS IN A FACTORIAL GREENHOUSE EXPERIMENT WITH CORN GROWN WITH COMBINATIONS OF N-FERTILIZER, P-FERTILIZER, K-FERTILIZER AND S-FERTILIZER

In an experiment reported in the literature, factorial combinations of N, P, K and S were applied at one level of each to corn plants (Zea mays L.) grown in a greenhouse in pots of soil. The relative yields for 0, 1, 2, 3 and 4 of the inputs simultaneously as averages were 1.00, 1.36, 1.54, 1.87 and 3.04. The predicted relative yields according to sequential additivity were 1,00, 1.36, 1.83, 2.48 and 3.31. Various interactions contributed to the differences between observed and calculated yields. Antagonisms were indicated because additions of one or more of the nutrients decreased plant concentrations of nutrients not added. There is little indication of sequentially additive responses because of the antagonisms and the fact that all four nutrients involved were well below respective critical levels in the control which would lead to synergism for their correction. The last incremental addition whether it was N, P, K or S each resulted in the major portion of the total yield increase when all four nutrients were supplied: 56% for S, 58% for P, 60% for K, and 55% for N. The portion for the first addition is calculated at 14% for S, 24% for P, 27% for K and 5% for N. Each of the four nutrients were Liebig-type limiting factors and the order of addition of each was of much less importance than the fact that all four needed to be applied for yield improvement. Copyright © 1990 by Marcel Dekker, Inc.