SOIL-NITROGEN MINERALIZATION INDEXES AND CORN RESPONSE IN CROP ROTATIONS

Predicting N availability from legumes to a subsequent crop has been p roblematic. We tested the hypothesis that corn (Zea mays L.) grain yie ld and whole plant N accumulation could be predicted from N mineraliza tion indexes of soil samples containing representative amounts of inco rporated residues from the previous crop. Soil samples were taken from a crop rotation study conducted at four locations in Minnesota, in wh ich corn was grown following eight crop treatments, including fallow, alfalfa (Medicago sativa L.), soybeans [Glycine max L. (Merr.)], corn, and wheat (Triticum aestivum L.). Corn received from 0 to 224 kg of f ertilizer N/ha. Soil was procured from the plow layer during the 2 wee ks before planting and to 1.5 m (for inorganic N) within 1 week after planting. Subsamples were subjected to acid permanganate, autoclave, a nd glucose extractions, inorganic N determination, and aerobic and ana erobic incubations. With stepwise multiple regression, 1 week of aerob ic incubation contributed as much as did incubation times up to 12 wee ks to models of grain yield and total N uptake at physiological maturi ty. Results of acid permanganate, autoclave, and glucose extractions, and of anaerobic incubation did not consistently contribute to the mod els. Over all locations, topsoil inorganic N and 1 week of aerobic inc ubation explained between 65 and 81% of the variability in grain yield and total N accumulation of nonfertilized corn. For fertilized corn, N application rate alone accounted for the majority of variability in grain yield and total N uptake. Two independent crop rotation experime nts provided data used to validate the predictive capability of the re gression models. Despite promising relationships derived from the init ial experiment, results from validation experiments were not reliably predicted by these equations. Although analyses of soil samples contai ning crop residues for inorganic soil N and a particular N mineralizat ion index may relate well to yield and N uptake by corn in a given yea r, variability among years may preclude general use of these models fo r predictive purposes.