| Abstract: | Abstract Corn (Zea mays L.) was grown in the greenhouse in a Laughlin (Ultic Haploxeroll) loam soil, with various amounts of N and S added in order to determine possible interactions of these nutrients with the relationship between plant composition and grain yields. Previous field experience and preliminary experiments had shown that this soil gave yield responses to N and S additions. Regression equations were used to describe the relationship between composition of various plant parts and grain yields. The best correlation (R2 = 0.943) was obtained using the total N concentration in leaf samples taken at the silking stage, but excluding data from plants which, based on their amide N concentrations (greater than 500 ppm), were considered S deficient. Calculations using the first derivative of the cubic polynomial indicated that a concentration of 2.5% N in the lower leaves was necessary in order to obtain maximum grain yields. The concentrations of total N in the upper leaves and the stalks at the silking stage also correlated well with the grain yields. The relationship of NO3‐N in the stalks at silking to grain yields could be better described mathematically with an exponential function, but the correlation coefficient was low (R2 = 0.58). The responses of two genotypes, one containing the opaque ‐ 2 gene, the other its normal counterpart, were similar. The total N concentration in the leaves collected at the tassel stage did not correlate quite as well with grain yield as those collected later, but using the exponential model NO3‐N concentrations in the stalks at the earlier stage showed a closer relationship to grain yield than for samples collected at silking. Excluding data for the plants showing S deficiency, a correlation coefficient of 0.90 was obtained. At both tasseling and silking stages, the S deficient plants were characterized by high N:S ratios, with values of 18 to 50 for the stalks, compared to values of less than 10 for the S adequate plants. The marked effect of inadequate S on grain formation was not evident in the amounts of leaves and stalks produced. Field studies will be necessary to evaluate further the merit of the diagnostic procedure indicated by these experiments. |
