Soil Quality and Crop Yields, After Utilization of Sewage Sludge on Agricultural Land, in the Moldavian Plain, Romania

Abstract

Soil Quality and Crop Yields, After Utilization of Sewage Sludge on Agricultural Land, in the Moldavian Plain, Romania 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 rape-wheat-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.