Variability of nitrogen content in grain and nitrogen harvest index at different nitrogen fertilization of spring barley

A three-year polyfactorial experiment of spring barley (varieties Bonus, and Orbit grown after two forecrops - winter wheat and silage maize) was carried out to study the effect of intensive nitrogen fertilization on the grain yield, nitrogen content in grain, harvest indices, and quality of spring barley grain. The stand was situated in warm, medium-dry climatic area (south-western of Slovakia), with alluvial, slightly clay soil (medium stock of phosphorus and potassium, 2,31 - 3.23% of humus content, pH 5.73 - 6.70). The terms of seeding the barley were 5.4.1986 - 7.4.1987 - 8.4.1988 and sowing rate 3.5 - 4.5 - 5.5 million of germinative seeds per hectare. The experiment had three variants of the fertilization: a - control variant without fertilization, b - 60 kg of N, 37.7 kg of P, 99,6 of K per hectare, c - 170.5 kg of N, 37.4 kg of P, 99.6 kg of K per hectare. The fertilizers were used separately - P and K before the autumn tillage, N before the spring seeding, Before the harvest from all variants there were taken plant samples in the phase of full maturity for chemical analyses to set the content of nitrogen, phosphorus and potassium in grain, and straw with the aim to determine the harvest index and quality properties of grain. The results prove significant effect of nitrogen fertilization on the studied parameters. Increasing dose of nitrogen did not have marked effects - on the yield - at the optimum dose (60 kg.ha-1) the average yield during the experiment was 7.29 t.ha-1. After the heightening of the dose it raised just to 7.55 t.ha-1. The rise in the grain yield was mostly affected by the weather condition during the year (35%), fertilization (28.9%), maize as a forecrop (22.8%), and the properties of the variety (13.3%). The content nitrogen in the grain increased in both fertilized variants by 3.6 and 4.7%, which is nearly negligible in comparison with the non-fertilized control. The grain yield increase of nitrogen was mostly influenced by the forecrop (40.7%), then year (29.9%), fertilization (19.1%), and varieties (10.3%). The harvest index (HI-IN) of the non-fertilized control variant was 78.19, and HI-IN of the variant with the highest dose nitrogen 74.96. The value of this index decreases with the increase of the nitrogen dose, compared with the non-fertilized control 4.9%, compared with the optimally fertilized variant by 2.8% (whereas the dose of nitrogen was increased nearly three times). With the optimal nitrogen dose the HI-IN was only by 1.5% lower the control. Nitrogen harvest index was relatively steady, while its variance value was negligible at the different intensity of N-fertilization. This variance was influenced positively by the weather conditions during the year (73.8%), forecrop (46.4%), varieties (25.0%), but the increase of the intensive N fertilization had the adverse affect (-42.5%)