Erosión y desertificación.-Effects of cropping systems on water runoff, soil erosion and nutrient loss in the Moldavian Plateau, Romania

Abstract

ABSTRACT The experiments carried out at the Podu-Iloaiei Agricultural Research Station, during 19862008, had the following objectives: the study of water runoff and soil losses, 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 runoff and soil erosion on losses of organic matter and mineral elements from soil. The determination, in different crops, of water runoff, soil, humus and nutritive element losses by erosion was done by the help of plots for loss control, which are isolated from the rest of the area by metallic walls and have basins and devices for division; we took water and soil samples from plots for determining the partial turbidity and for chemical elements analyses. The determination of water runoff, soil, humus and nutritive element losses on fields arranged by anti-erosion was done on the whole area of the retention basin (159 ha), where experiments were conducted, since 1982, bands with grasses and field strips were set up. The erosion control was done by the help of hydrological station with triangular waste weir, rain gauge, recording rain gauge, limnigraph and devices for water and soil samples uptake during rainfalls. Mean annual losses of soil by erosion, registered during 1986-2008 were of 0.298 t·ha-1 in perennial grasses on the second growth year, 4.618 t·ha-1 in beans, 9.176 t·ha-1 in maize and 9.650 t·ha-1 in sunflower. Erosion has affected soil fertility by removing once with eroded soil, high amounts of humus and mineral elements, which reached 17.4-17.7 kg·ha-1 nitrogen, 1.1 kg·ha-1 phosphorus and 2.3 kg·ha-1 potassium, in maize and sunflower crops. From the investigations carried out on effective erosion, based on direct determinations, we found out that the effective erosion in the Moldavian Plateau, in peas-wheat-maize rotation, had a mean value of 4.502 t·ha-1·year-1. From the results obtained on erosion in different crop rotations, we have found out that in 16 % slope fields from the Moldavian Plateau, soil losses by erosion were diminished below the allowable limit of 3-5 t·ha-1·year-1 only in case of 4 year-crop rotations with one or two reserve fields, cultivated with legumes and perennial grasses, which protect soil. These elements were necessary for establishing the crop structure and dimensioning the ant erosion works, which determine the decrease of soil erosion and water runoff, soil and nutrients losses below the limit corresponding to the natural capacity of annual soil recovering, of 3-5 t·ha1·year-1 of eroded soil.