The purpose of this study was to determine the effect of fertilizer application on corn yields and the composition of certain leaves, and the relationships between leaf composition and yields. Three experiments differing in details were conducted under irrigation with hybrid Iowa 939 corn in central Washington.
Leaves were selected at several growth stages, but the second leaf below the ear collected at silking was studied most intensively. Analyses were made for total N, P, Ca, Mg, K, and Mn and for P soluble in 2% acetic acid. Only N increased yields significantly; K and P applications did not. Calcium nitrate was least effective of the five N sources used. Total N content of leaves selected prior to silking gave lower correlations with yield than those selected at silking. Yields were highly positively correlated with both N and total P contents of leaves selected at silking, and total P and N contents of leaves were also highly correlated. Partial regression analysis showed that leaf N was probably the dominant determinant of yield, but that the leaf P content was sometimes important.
For the three experiments the regression coefficients of yield on leaf N content were not significantly different, but the intercepts were markedly different.
In one experiment, yields declined 15 bushels per acre for each leaf per plant showing N deficiency symptoms at silking. The minimum leaf N percentage associated with no evidence of the characteristic tip firing of N deficiency appears to be far below the reported critical N concentrations for maximum yield.
Ammonium sulfate produced the highest leaf P and K contents and the lowest Ca and Mg contents in comparison with Ca(NO3)2 and NH4NO3 as N sources. The sum of the determined cations Ca, Mg and K in leaves selected at silking tends to be a constant at about 100 m.c. per 100 gm.
Phosphorus soluble in 2% acetic acid was a linear function of and equal to about two-thirds of the total P over a wide range of total P in the leaves.