Soil quality and crop yields, after utilization of sewage sludge on agricultural land, in the Moldavian plain, Romania

Abstract

Investigations conducted at the Podu-Iloaiei Agricultural Research Station, Iaşi County, have studied the influence of different sewage sludge rates on yield quality and quantity and soil agrochemical characteristics. Trials were set up in a five year-crop rotation, winter rapewheat- maize-sunflower-wheat. Sewage sludge was applied every 2 years at rates of 20, 30, 40 and 60 t/ha, with different mineral fertilizer rates, differentiated according to the growing plant. The Cambic Chernozem used for experiments had a clayey-loam texture (410 g clay, 310 g loam and 280 g sand), a weakly acid reaction and a mean supply with mobile phosphorus and a very good one with mobile potassium. Applying rates of 30 t/ha sewage sludge has resulted in the accumulation of mobile phosphate stock in soil of 57 mg/kg and the microelement content, mobile forms from soil, was of 7.9 mg/kg at Cu, 1.4 mg/kg at B, 6.8 mg/kg at Zn and 186 mg/kg at manganese. The combined use of mean rates of mineral fertilizers (N100P80), together with 40 t/ha sewage sludge has resulted in improving soil chemical characteristics and getting yield increases in winter rape of 1854 kg/ha (108 %). After 8 years since the application of a rate of 30 t/ha sewage sludge, soil pH has increased 0.4 units, while phosphorus and potassium content from soil has increased by 30 and 52 mg/ kg soil, respectively. Sewage sludge from the Iaşi Water Treatment Station, which was applied every two years at rates of 20 and 30 t/ha, has determined the increase in the organic carbon content from soil by 2.9 g/kg (18%) and 4.4 g/kg (28%), respectively, compared to the unfertilized variant. The copper and zinc content from grains in wheat and maize crops, fertilized with 30 t/ha sewage sludge, was by two-four times higher, compared to the unfertilized control.