Root length of winter wheat and the content of mineral nitrogen in soil profile

Winter wheat (cv. Regina) root length (RL) distribution and the content of mineral N (N-anorg, NO3-N + NH4-N) in soil profile during spring were determined in two year field experiment on sandy loam soil (Eutric Cambisol) in Pernolec (elev. 530 m, precipitation per year 624 mm, average temperature 6.4 degrees C). The soil was sampled every 10 cm with steel cylinder (8.5 cm diam.), on a row and between rows; roots were washed on sieves. Two treatments, unfertilized with N (NO) and fertilized with 40 kg N/ha in early spring (N1). The content of N-anorg in the soil was determined in layers 0-30 cm, 30-60 cm and 60-90 cm following standard sampling scheme and analytical procedure. Total root length at the start of tillering (early spring), at the end of tillering and at heading reached on average 0.47 km.m(-2), 4.9 km.m(-2), 7.8 km.m(-2), resp., in. 1993, and 0.3 km.m(-2), 5.4 km.m(-2) and 14.9 km.m(-2), resp., in 1994. The difference of the total root length in heading between 1993 and 1994 might be the result of impaired wheat growth in 1993 due to extremely cold and dry winter and spring. The grain yield reached 1.8 t.ha(-1) (N0) and 3.04 t.ha(-1) (N1) in 1993, and 4.13 t.ha(-1) (N0) and 6.41 t.ha(-1) (N1) in 1994. These inter-year differences were reflected in depletion of N-anorg between tillering and heading (Figs 1B and 1C). Root length density decreased exponentially from surface layers to subsoil (Figs 1A to 1C). We observed lower root density between rows in surface layer in comparison with rows. There was a tendency to higher root density in surface layer in N-fertilized treatment (N1). At the time of plant regeneration (early spring), rooting depth and density gave no access to supply of mineral N under depth of 20-25 cm, where only scarce unbranched primary roots could be observed. Wheat plants reached only the start of tillering stage in the time. In the course of tillering and stem elongation the rooted volume of soil and thus the potentially available supply of N increased with increased root depth and density in subarable layers. However, even in the period of heading, the substantial amount of N washed to layers under 60-80 cm depth, was not readily available for wheat crop. Root density in the layer 50-60 cm reached 0.05 cm.cm(-3) and 0.15 cm.cm(-3), in 1993 and 1994, resp. Sporadic unbranched root axes penetrating to deeper layer were mostly concentrated in biopores without tight contact with soil particles.