Possibilities of significant influence on maize yields by means of irrigation, more precise nitrogen nutrition management and plant residues utilization

In autumn 2000 a field trial was established on Calcarocaltic Chernozem in south-western Slovakia intended to study the decomposition of ploughed straw and stubble enriched by different sources of nitrogen and Biostim preparation. From 2000 to 2002 a monoculture of Eveline hybrid grain maize was grown; in the first year (2000) it followed wheat and wheat straw and stubble ploughed in and in the next two years maize stalks were ploughed in. Nitrogen contents at three depths (0 - 0.3 m, 0.3 - 0.6 m a 0.6 - 0.9 m) and at three times (before sowing in April, prior to the intensive nutrients uptake in early June and just after harvest) were investigated. The determinations were carried out in samples of wet soil and extracted by 1 % solution K2SO4 using San+ Analyzer (fi Skalar HT Breda, Netherlands). Fertilization and straw management treatments: K û control treatment without any straw ploughed in; S û chopped straw ploughed in S+LAV û ammonium-calcium nitrate (LAV); S+H - pig slurry; S+DAM û ammonium nitrate/urea mixture (DAM-390); S+B û 4.2 liter of Biostim preparation containing cellulolytic bacteria was applied per one ton of chopped straw. Fertilizers and Biostim were applied on chopped straw prior its being ploughed in. Maize was grown in two moisture treatments (irrigated and non-irrigated). Soil moisture course at a one-meter depth at seven-day intervals was traced using a neutron probe. The relations of inorganic nitrogen in soil and yields of grain maize were processed by linear regression analysis, those of yields using analysis of variance, and differences were subject to the Tukey-test. A significant correlation was found between inorganic nitrogen content in soil and grain maize of yield. Results show that in the soil layer between 0.0 and 0.6 m depth the concentrations of this form of nitrogen in soil should be of 15-20 mg/kg and of 30 mg/kg prior to sowing and by early June respectively to ensure higher grain maize yields. The highest yields of maize grain (13.0-14.0 t/ha) was achieved in the irrigated treatment, in particular wherein homogeneously distributed pig slurry, with the nitrogen content equal to that of artificial fertilisers, was applied on chopped wheat straw or maize stalks. The efficacy of Biostim microbial preparation was higher in the irrigated treatment, where it produced a 2.03 t/ha yield increase as compared with the treatment where only dry straw was ploughed in.