NITROGEN AND PHOSPHORUS MANAGEMENT UNDER LONG-TERM EXPERIMENTS

The investigations conducted at the Podu-Iloaiei Agricultural Research Station, Ia?i County, Romania, have studied the influence of different mineral fertilizers rates on wheat and maize yield and soil agrochemical characteristics. In bean-wheatmaize- sunflower-wheat crop rotation, the mean yield increases, obtained for each kg of a.i. of applied fertilizer, were comprised between 8.3 and 10.1 kg in wheat (N120P80- N160P80) and between 10.8 and 11.0 kg in maize (N150P80-N200P100). Generally, nitrogen use efficiency is low and, to achieve maximum yields, need for high doses of nitrogen which can increase the risk of environmental pollution. The N agronomic efficiencies and physiological efficiencies in wheat and maize declined with the increase of nitrogen rate. Wheat placed in rotation for five years, after sunflower at recommended dose (N160P80), physiological efficiency of nitrogen utilization was 43.4 kg grain per kilogram of nitrogen exported from soil, from fertilizer applied. Mean annual amounts of nutrients exported from soil by wheat in dry (14 yr.) and favourable (11 yr.) years in five year crop rotation have varied according to rates,between 34.5 and 100.7 kg at nitrogen and between 6.5 and 18.4 kg at phosphorus. The long-term use of bean - wheat - maize - sunflower - wheat rotation determined the diminution by 43.4% (2,772 t/ha) in the mean annual losses of eroded soil and by 38.5% (5.61 kg/ha) in nitrogen leakages by erosion, compared with maize continuous cropping.