The influence of long-term fertilization and irrigation on wheat and maize yield and soil fertility was studied at the Agricultural Research and Development Station of Podu-Iloaiei since 1980. These experiments were carried out on a 10% slope field, on a Cambic Chernozem with clayey loam texture (423 g clay, 315 g loam and 262 g sand), a neuter to weakly acid reaction and a mean nutrient supply. The mean annual rainfall amounts, recorded in the last 28 years, were higher, with values comprised between 12.7 and 279.2 mm, compared to the multiannual mean on 80 years (542 mm) in 16 years, and lower by 25.3-236.7 mm in 10 years. Annual application of rates of N 160 P 80, in a four-year crop rotation (soybean-wheat-sugar beet-maize)+a reserve field, cultivated with legumes and perennial grasses, determined the accumulation of a reserve of mobile phosphates of 78 mg/kg soil. Under irrigated, a good plant supply with mineral elements and the increase in the content of organic carbon from soil were done by applying the rate of N 80P 70+30 t/ha manure. Nitrogen and phosphorus fertilizers, although applied at high rates (N 130+100 P 2O 5), could not prevent the decrease in organic carbon content from soil.
