EVALUATION OF THE LONG-TERM EFFECT OF CROP ROTATION ON WATER RUNOFF, SOIL AND NUTRIENT LOSSES IN THE MOLDAVIAN PLATEAU

ABSTRACT- The goal of the experiments carried out during 1981-2008, at the Podu-Iloaiei Agricultural Research Station, Iaşi County, was the study of water runoff and soil losses, caused by erosion, in different crops, the annual rate of erosion processes under the influence of anti-erosion protection of different crops, the influence of water and soil erosion on the losses of organic matter and mineral elements from soil. On 16 % slope fields, the use of peas-wheat – maize rotation + two outside fields, cultivated with perennial grasses, determined the diminution by 40.2 % (1.291 t/ha) in the mean annual losses of eroded soil and by 36.7 % (2.8 kg/ha) in nitrogen leakages, compared with wheat-maize rotation. The introduction of some rotations, which include in the crop structure 20 % maize and plants for the protection against erosion (peas- wheat – maize rotation + two outside fields cultivated with perennial grasses) determined the diminution by 39.8 % (24.7 kg/ha) in mean annual losses of organic carbon and by 37.5 % (3.2 kg/ha) in losses of mineral elements. During 1981-2008, on 16 % slope fields, the increase from 20 to 40 % of the percent of row crops (maize and sunflower) used in rotations determined the increase in mean annual losses of eroded soil by 16.9 % (0.325 t/ha) and the use of crop rotations with 60 % row crops resulted in the increase by 78.9 % (1.514 t/ha) of the mean annual quantities of eroded soil. Key words: slope land, cropping systems, water erosion, organic carbon, nutrient losses