WINTER-WHEAT BIOMASS AND NITROGEN DYNAMICS UNDER DIFFERENT FERTILIZATION AND WATER REGIMES - APPLICATION OF A CROP GROWTH-MODEL

Growth, nitrogen uptake and nitrogen allocation between roots, stems, leaves and grains were measured and simulated in winter wheat on a cla y soil in three treatments including daily irrigation and fertilizatio n. Special emphasis was placed on biomass and nitrogen allocation with in the crop and on the availability of soil nitrogen for crop growth. The model used for the simulations of growth (SOILN-CROP), which was d riven by a hydrological model, is based on the light interception conc ept and empirical allometric functions. Growth is the driving force fo r nitrogen uptake, which is limited by the availability of mineral N i n the soil. The model was calibrated for one treatment. Thereafter, th e same parameter set was used to simulate the other two treatments. Fr equent irrigation in combination with single-dose fertilization increa sed crop growth and N leaching compared with the non-irrigated but sin gle-dose fertilized control, whereas irrigation together with daily fe rtilization increased crop growth and N uptake but not N leaching. Sim ulated soil mineral N levels agreed well with measurements on a 1-year time scale. Assimilate allocation to roots decreased logarithmically with total crop biomass in all treatments. Allocation to leaves decrea sed linearly with total above-ground crop mass. The crop availability of mineral N differed considerably between treatments. The model param eter defining the proportion of soil mineral N available for plant upt ake had a strong influence on model behaviour. This proportion is indi cated to depend on soil water content and the mechanisms of this relat ion need to be considered in future work to improve our predictions of N uptake. (C) 1997 Elsevier Science B.V.