Estimation of the impact of precrops and climate variability on soil depth differentiated spring wheat growth and water, nitrogen and phosphorus uptake

Water and nutrients in the subsoil are valuable resources in crop production but the availability varies with weather conditions and management, in particular the crop rotation. Moreover, constraints such as mechanical resistance or water stress may impede root growth into deeper soil layers. This study presents a simulation-based stochastic approach to investigate the impact of precrops on spring wheat growth and water and nutrient uptake under varying weather conditions. The effect of the three precrops lucerne, chicory and tall fescue on spring wheat growth was investigated extensively in a field trial. For model calibration and evaluation, we selected a year with a dry spell (2010) and one with abundant precipitation (2012) and used field data on biopore densities in the subsoil, crop development, leaf area index, shoot biomass, grain and straw yield, nitrogen (N) and phosphorus in shoot, grain and straw, root length densities, as well as soil moisture and soil N and P concentrations for several soil depths. The modeling framework consisted of the modeling platform SIMPLACE and the stochastic weather generator LARS-WG to consider climate variability. The weather generator was used to generate a synthetic time-series of daily weather data (100 years) based on observed weather data of the experimental site in order to simulate 100 spring wheat growth periods under recent climate conditions for each precrop. Moreover, a 100 year long time-series with annual dry spells in June was generated to analyze the effect of drought during flowering on crop water and nutrient uptake. During the scenario runs, the model was annually reinitialized at sowing to provide identical initial conditions. The experimental data over two years showed that spring wheat growth as well as total N and P uptake were clearly enhanced after precrop lucerne. This was comfirmed by the simulations over 100 years. The simulation runs also prompt that precrop fescue led to higher spring wheat biomass and enhanced subsoil and total water and N uptake in years with normal precipitation pattern compared to precrop chicory, but in drier years, it was vice versa. Because plants compensate for moderate nutrient or water deficiencies, small differences in grain yield may hide significant differences in total and in subsoil N and P uptake.