ROOT LENGTH OF WINTER-WHEAT AND THE CONTE NT OF MINERAL NITROGEN IN SOIL-PROFILE

Winter wheat (cv. Regina) root length (RL) distribution and the conten t 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 (Eutri c Cambisol) in Pernolec (elev. 530 m, precipitation per year 624 mm, a verage temperature 6.4 degrees C). The soil was sampled every 10 cm wi th steel cylinder (8.5 cm diam.), on a row and between rows; roots wer e washed on sieves. Two treatments, unfertilized with N (NO) and ferti lized 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 follo wing standard sampling scheme and analytical procedure. Total root len gth 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 differenc es were reflected in depletion of N-anorg between tillering and headin g (Figs 1B and 1C). Root length density decreased exponentially from s urface layers to subsoil (Figs 1A to 1C). We observed lower root densi ty between rows in surface layer in comparison with rows. There was a tendency to higher root density in surface layer in N-fertilized treat ment (N1). At the time of plant regeneration (early spring), rooting d epth 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 so il and thus the potentially available supply of N increased with incre ased 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 1 993 and 1994, resp. Sporadic unbranched root axes penetrating to deepe r layer were mostly concentrated in biopores without tight contact wit h soil particles.