POSTHARVEST EVALUATION OF NITROGEN SUFFICIENCY FOR SMALL-GRAIN CEREALS BY MEASURING GRAIN PROTEIN-CONCENTRATION

Nitrogen (N) fertilizer is an important and expensive input in small-g rain cereal production, and growers therefore should aim to optimize i ts use. Possibilities for using grain protein concentration for post-h arvest evaluation of N sufficiency were determined in this study. Fiel d experiments including spring wheat (Triticum aestivum L), spring bar ley (Hordeum vulgare L.) and spring oats (Avena sativa L.), and variou s rates of N fertilizer application were conducted in southern and wes tern-Finland over 2 years. Grain yield and grain protein were positive ly correlated and fitted quadratic regression models. Both critical an d optimum levels for grain protein concentration were determined by Ca te-Nelson analysis. Critical values were 12.2 for wheat, 10.2 for barl ey and 10.9 for oats, and corresponding optimum values were 13.3, 11.1 and 12.7, respectively. The accuracy of the method was tested using r esults from on-farm spring wheat trials. The results indicated that N fertilizer uptake and grain yield were best in fields where grain prot ein concentration exceeded the critical values but not the optimum. Gr owers should use more intensive N fertilization management if grain pr otein concentration does not exceed critical values. Grain protein con centrations above optimum values indicate over-fertilization for maxim um grain yield. Analysing previous research data to identify the ''cri tical level'' of grain protein concentration is not difficult, and wil l provide growers, extension personnel, and fertilizer dealers with a cost effective means of evaluating the efficiency of N use by the crop and for developing N fertilization recommendations.