Mineral nitrogen content in a soil profile and nitrogen accumulation in winter wheat crop

Winter wheat (cv. Samanta) growth, N accumulation in shoots, and the content of mineral N (N-min = NO3-N + NH4-N) and water in a soil profile were studied in a two year field experiment. It was carried out on a degraded chernozem soil at Prague-Ruzyne (elev. 340 m, long-term average precipitation and temperature: 450 mm per year and 7.8 degrees C, resp.). Two treatments were observed, unfertilized with N (NO) and fertilized with 100 kg.ha(-1) (1995) and 85 kg.ha(-1) (1996) as ammonium nitrate (treatment N1) split-applied at the beginning of vegetative growth in spring and during full tillering. Soil was sampled in 10 to 30 cm layer increments to the depth of 120 or 150 cm. The content of N-min in freshly taken soil samples was determined by a standard sampling scheme and analytical procedure (Ruzek, 1993). At harvest the wheat crop had accumulated in the above-ground parts 91.3 kg.ha(-1) (treatment NO) and 125.2 kg.ha(-1) (N1) in 1995 and 149 kg.ha(-1) (NO) and 177 kg.ha(-1) (N1) in 1996 (Fig. 1). The degree of water and N-min depletion decreased with the depth of the soil layer (Fig. 2, 3). The results suggest that under the given conditions the wheat crop used effectively the supply of N and water from the arable layer and subsoil down to a 70 cm depth. The depletion of the sources was less in the 70 to 120 cm zone, and low or none in 120 to 150 cm (Fig. 2, 3). The decrease in N-min, from the soil profile during the period of rapid linear growth corresponded with accumulation of N in shoots in 1996, while during ripening the accumulation of N was higher than the decrease in soil N-min (Fig. 4). In 1995 the total N-min content at harvest was higher than at shooting. Determination of the distribution of N uptake from a soil profile demands a description of root system and functions and reliable quantification of water and N redistribution, mineralization, immobilization and denitrification processess.