The evolution of soil fertility under longterm experiments in the Moldavian Plateau

The paper presented the results of investigations concerning the influence of long-term fertilization (43 years) on some chemical characteristics of soil from the Moldavian Plateau, of wheatmaize rotation. The studies were performed on a typical cambic chernozem soil, prevailing in the Moldavian Plateau, and followed the dosing of fertilizers which ensures an efficient production increases and determines maintain or increase soil organic carbon content. Soil that has been placed experiences-clay loam, neutral to slightly acid reaction and a medium nutrient supply. On lands from the Moldavian Plateau, maintaining a good supply in mobile phosphorus for field crops (37-72 mg/kg) was done in case of the annual application of a rate of N100P100, and a very good supply in mobile phosphorus (69-78) and mobile potassium (over 200 mg/kg) was found at a rate of N100P100+60 t/ha manure. In wheat-maize rotation, applying a rate of N100P100 , for 43 years, has determined the pH decrease until the limit of moderately acid interval (5.1-5.8) and was maintained within the weakly acid interval (5.9-6.8) in case of the annual application of a rate of N50P50 + 60 t/ha manure. Soil organic carbon content, in wheat - maize rotation, decreased after 43 years of experiences from 19.8 to 16.3 g/kg in unfertilized variant and until 18.1 g/kg in case of the annual application of a rate of N100P100. In wheat - maize rotation, the significant increase in organic carbon content from soil has been registered at higher than N50P50 + 40 t/ha manure and at N100P100 + 60 t/ha manure. The determinations of mean annual amounts of nitrogen exported from soil by wheat (grains + straw) have shown that in wheat crop, its values varied according to fertilizers system, between 71.5 and 128.4 kg/ha. In maize crop, of the mean annual amounts of nitrogen exported from soil varied according to applied fertilizers, between 64.6 and 178.9 kg/ha