Long-Term Effect of Fertilizer and Crop Residue on Soil Fertility in the Moldavian Plateau
Since 1965, at the Agricultural Research Station of Podu-Iloaiei, Iaşi County, Romania (47°12' N latitude, 27°16' E longitude), investigations were conducted on the influence of different fertilizer systems on production and soil fertility. For wheat and maize crops, placed in a three-year rotation (pea - wheat - maize), three fertilization systems were experienced: (1) mineral fertilization with nitrogen and phosphorus rates until N140P100; (2) manure fertilization (20, 40, and 60 t/ha), with and without mineral fertilization and (3) mineral fertilizers + hashed residue applied in autumn under the base ploughing. The paper presented the results of investigations concerning the influence of long-term fertilization (46 years) on some chemical characteristics of Cambic Chernozem from the Moldavian Plateau. The climatic conditions in the Moldavian Plain were characterized by annual mean temperature of 9.6°C and a mean rainfall amount, on 50 years, of 553.5 mm, of which 141.5 mm during September-December and 412.0 mm during January-August. After 46 years of experiences, in pea-wheat-maize crop rotation, the content of organic carbon from soil has decreased by 22.3% (4.2 g/kg soil) at the unfertilized control and by 14.4% (2.7 g/kg soil) at the rate of N120P80. In wheat and maize, nitrogen uptake by weeds was between 7 and 9.5 kg/ha from all the plots. Applying moderate rates of mineral fertilizers (N80P60), together with 6 t/ha wheat straw or 40 t/ha manure, has determined the increase in organic carbon content from soil by 0.5 and, respectively, 2.8 g/kg.
Long term effect of tillage system and crop residue management on soil carbon content of a luvisol under rainfed Mediterranean conditions
