Post-Harvest Residues of Winter Wheat and Corn and Their Incorporation Depending on Nitrogen Fertilization
I. Amount of Post-Harvest Residues

1 Regional Center for Extension Service, BG - 7700 Targovishte, Bulgaria,
2 Dobroudja Agricultural Institute, BG - 9520 General Toshevo, Bulgaria


DONKOVA, D. and T. TONEV, 2005. Post-harvest residues of winter wheat and corn and their incorporation depending on nitrogen fertilization. I. Amount of post-harvest residue. Bulg. J. Agric. Sci., 11: 11-21

The investigation was carried out at the trial field of the Regional Center for Extension Service in Targovishte during 1999-2003 and was representative for the conditions of dark gray forest soils in this region.Winter wheat and corn were grown in two-field crop rotation with the final aim to determine the effect from the way the post harvest residue of the previous crop is used on the yield from the next crop, as well as the effect of nitrogen fertilization. Three ways for using post harvest residue were studied: (1) clearing the field (removing the plant residue) after harvesting and burning the stubble - control variant; (2) clearing the field (removing the plant residue) after harvesting and ploughing/disking of the stubble; (3) chopping, uniform spreading and incorporation of the whole post harvest residue of the previous crop. The aim of this study was the third way of using the post-harvest residue. Four nitrogen fertilization rates were tested - 0, 60, 80 and 120 kg/ha, against background P80K80. It was established that the amount of wheat post harvest residue varied between 1.04 and 9.14 t/ha according to the year conditions and the nitrogen fertilization applied. The mean relative effect of nitrogen fertilization was highest between the rates 0 and 60 kg/ha (98.1%), and decreased between 120 and 180 kg/ha N (to 4.9 %). The mean amount of corn post harvest plant residues changed from 3.75 t/ha in 2000 to 7.87 t/ha in 2001, and the mean share of cornstalks from the total biological yield at stage maturity varied from 74.6 to 39.6 %. Averaged for the period of investigation, 4.95 t/ha of corn post harvest residue was incorporated, which respectively amounted to 56.9 % of the biological yield obtained. The optimization of nitrogen fertilization during the years of study changed corn post harvest residue amount with averagely up to 18.5 %, although the effect reached 81.9 % during some individual years (2003). The agrometeorological conditions had different influence on the total biological productivity of the crops, and on the effect of applied nitrogen fertilization; therefore the amount of incorporated post harvest residues in both crop rotation fields, as well as the share of both crops in the total amount varied as follows: in the first field the total amount was between 13.34 t/ha (N0) and 23.61 t/ha (N180), i.e. the mean relative effect of nitrogen fertilization was 77.0 %, andthe mean share of wheat - 30.7%; in the second field the amount reached 19.6 t/ha, the effect of nitrogen fertilization being lower - 46.5 %, and the relative share of wheat post harvest residue was averagely 51.4 %.

Key words: post harvest residues, wheat, corn, nitrogen fertilization, dark gray forest soil