WHEAT ROOT BIOMASS AND NITROGEN DYNAMICS - EFFECTS OF DAILY IRRIGATION AND FERTILIZATION

Root biomass, root nitrogen content, and root distribution down to 50 cm depth in winter wheat were determined by soil coring on five dates in four different treatments: control (C), drought (D), daily irrigation (1), and daily irrigation and fertilization (IF). The first three treatments received the N fertilizer application as a single dose in spring, whereas in IF daily doses of N were supplied in the irrigation water using a drip-tube system, according to the estimated nutrient demand of the crop. All treatments received 20 g N m-2 year-1. The maximum root biomass (104 g m-2) was reached earliest in IF. On 6 June, root samples were taken down to a depth of 100 cm, and the proportion of deep roots (50-100 cm) was least in I, indicating that it had the shallowest root system. The root biomass as a fraction of the total plant mass decreased during crop development in all treatments down to about 4% at harvest. The decrease was more rapid in I and C than in D and IF. The higher proportion of roots during spring in D and IF coincided with a low nitrogen concentration in the roots, which was attributed to the restricted water supply and to the relative shortage of nitrogen during early crop development in D and IF, respectively. The dynamics of mass and nitrogen in macroscopic organic debris in the soil suggested that root turnover rates were high.