EFFECTS OF NITROGEN ON PRODUCTIVITY, GRAIN QUALITY, AND OPTIMAL NITROGEN RATES IN WINTER WHEAT CV. KUMPA-INIA IN ANDISOLS OF SOUTHERN CHILE

Nitrogen is one of the main inputs of the winter wheat crop (Triticum aestivum L.) in southern Chile. Nitrogen efficient management is basic to optimizing its utilization while decreasing pollution risks and operational costs. Crop response and N use efficiency (NUE, defined as the ratio of yield to mineral N supply, regardless of source) are important for evaluating N requirements of winter wheat, and reaching maximum and economic yields. The objective of this study was to determine the effect of N rate on grain yield, calculate the N rate that maximizes yield, and estimate the optimal grain yield rate and quality of high-yielding winter wheat cv. Kumpa-INIA. Five annual N rates were evaluated in a randomized complete block design during two successive winter wheat cropping seasons on a Vilcun series soil of the Pachic Melanudands family (Andisol) in La Araucania Region, Chile, and subjected to intensive annual crop rotation. Significant effects (P <= 0.01) of N rate on grain yield and quality were found. The optimal physical N rate (OPR) in both seasons ranged from 290 to 339 kg ha(-1), whereas optimal economic N rate (OER) ranged from 248 to 274 kg ha(-1), with yields between 10.2 and 10.1 t ha(-1). Nitrogen use efficiency associated to OER was high in both seasons (36.9 and 41.2 kg grain kg(-1) N) and fluctuated in similar ranges. Nitrogen rate increased hectoliter weight and grain protein, but decreased NUE.