Comparisons of growth analysis functions within and among experiments are often confounded by sources of variation other than those imposed by treatment. We suggest use of a temperature index, such as modified growing degree days, as the divisor in growth functions to facilitate treatment comparisons within certain experiments and to reduce the effects of differing temperature regimes among experiments on these comparisons. Three experiments were identified to provide data to analyze this new approach. Mean absolute growth rate () and mean relative growth rate () were compared in two experiments with maize (Zea mays L.) conducted in eastern Nebraska. Previously published values of and mean net assimilation rate () of barley (Hordeura vulgare L.) grown under controlled environments in a soil temperature and P fertility study were also evaluated. Use of modified growing degree days, rather than days, as the divisor in these growth functions led to the recognition of physiological differences due to or associated with treatment, which were previously masked by normal crop response to temperature, and clarified other treatment differences by reducing the effect of temperature.

Highly significant inverse yield‐protein relationships in wheat grain were found at each level of applied N in an irrigation‐N rate experiment on hard red winter wheat over a 3‐year period at North Platte, Nebraska. The chief effect of applied N with adequate water was to increase yields, while the chief or entire effect with severe water deficits was to increase protein content. In intermediate situations, N increased both yield and protein content. In dryland experiments in 1966 and 1967 showing significant grain yield response to applied N, protein content also increased. Where little or no yield response occurred, N mainly increased protein content. Content of NO3−N in the soil to a depth of 180 cm was also important in yield‐protein relationships. Average protein contents of about 20 hard red winter wheat varieties at different locations in Nebraska in 1966 and 1967 were also negatively related to grain yields. Protein contents varied more widely among locations than among varieties at each location.

The objective of this experiment was to evaluate the effects of irrigation sequence and of time and rate of nitrogen application on the dry matter production and fertilizer use efficiency of irrigated corn (Zea mays L.), grown on a representative fine‐textured soil of eastern Nebraska, and to monitor the movement of fertilizer N in this soil. During 1974–1976, 15N‐depleted ammonium sulfate was banded at rates of 112, 168, or 224 kg N/ha at planting or sidedressed at the eight‐leaf growth stage. No N was applied in 1977–1979. In 1974–1977, irrigation applications of 5, 7.5, or 10 cm of water were made at 2‐, 3‐, or 4‐week intervals, respectively, until a total of 30 cm had been applied. The plots were uniformly irrigated in 1978–1979.Grain yield and N uptake in 1974–1976 were not influenced by time of N application, and were highest with light, frequent irrigation. From 1977–1978, yield increased with previous N rate in response to residual mineral N in the soil. During both treatment and residual years, fertilizer N recovery in the grain was greater with sidedressing and increased with N rate. Heavier, infrequent irrigation decreased tracer N recovery in 1974–1976. Maximum fertilizer use efficiency was obtained with the low N rate, applied as a sidedressing, and with light, frequent irrigation.