PRODUCTIVITY OF COTTON CULTIVAR DARMI UNDER THE INFLUENCE OF FERTILIZATION AT LONG-TERM FIELD TRIAL

Abstract

The aim of this study was to evaluate the effects of different application rates of nitrogen and phosphorus on growth, yield, earliness and quality of cotton (Gossypium hirsutum L.) cultivar Darmi, grown in Chirpan, Bulgaria. The cotton was grown during 2007-2010 in crop-rotation with durum wheat under non-irrigated conditions. The experimental design was a randomized complete block with four replications. Single and combined nitrogen and phosphorus fertilizers in rates 0; 40; 80; 120 and 160 kg.ha-1 were tested. Values were established for the September and total seedcotton yield, earliness, lint percentage, number of bolls per plant, boll size, plant height, 1000 seeds weight, fibre length. Under the influence of N fertilization the total yield increased with 10.0- 23.1% compared to the control and under phosphorous fertilization - with 1.4- 6.6% (P120). Productivity increased most under combined fertilization N120-160 P40-80 - 27.7-36.3% more than the unfertilised with a very good share of the September yield. The increase of nitrogen rates decreased earliness with 4.2% (N120) to the check. Average for the 20-year period a high effective yield was formed under moderate N rates combined with low to moderate P levels, whereat the cotton yield increased with 17.8- 24.4%. The fertilization significantly increased the height of the plant, boll number (55.6% over control) and boll weight (21.8% more). There was a tendency for decrease in lint percentage with the increase of fertilization rate. No significant changes were found in terms of fiber length and it ranged within 23.76-25.05 mm.