عنوان مقاله [English]
In this study, the effects of different levels of macroelements, phosphorus, nitrogen and their residues from previous crops were observed on the chemical characteristics of the soil, on the quality and yield of sugar beet crop, in a wheat-sugar beet rotation system. The experiments were carried out during 1989-1995 at Kamal-abad research station. The studied parameters included four levels of pure nitrogen (0,60,120,180 kg/ha) and three levels of P2O5 (0,60,120 kg/ha) using urea and triple super phosphate as sources, respectively. Wheat-sugar beet rotation was performed during the period of experiments. Soil samples from 0-30cm and 30-60cm of depth were collected in all plots, before sowing and after harvesting every year. In this article the effect of phosphorus fertilizer treatments on P2O5 availability and sugar beet yield is discussed. These treatments, pursued during the seven years of experiment, affected considerably the amount of this elements residues in the soil. The last soil sample analysed after harvesting the plots showed three different phosphorus levels among which the most and the least amounts corresponded to the higher and the lower treatment levels. In spite of the effect of the treatments on soil residue content, the yield of the crop was not affected. There was no significant difference observed between different fertilizer treatments. It can be presumed that the crop has used the already available phosphorus in the soil and that its reaction to nutrient elements especially to phosphorus is slow.