An analysis of factors determining spatial variable grain yield of winter wheat

• We analyzed causes for spatial variable yields of winter wheat.
• Soil texture, leaf area index measurements and simulation modelling were used in a 3 year study.
• The drought stress corrected amounts of intercepted radiation or the ratio of the sum of actual transpiration to potential evapotranspiration explained grain yield ex post but also when evaluated about 6 weeks before end of grain growth.
• Maximum leaf area index and plant available soil water did not correlate significantly with grain yield when evaluated for all experimental years simultaneously.
• Simulation modelling in combination with remote sensing seems an appropriate approach for delineating site specific N supply in wheat.

We analyzed under the temperate weather conditions of northwest Germany the relationships between soil water supply, crop canopy dynamics, radiation interception, components of the soil water balance and grain yield of winter wheat using data obtained from field experiments during three years. A dynamic model of the soil water budget in combination with frequent measurements of canopy parameters thereby was used to estimate the components of the water balance and radiation interception site specifically. Differences in soil texture and soil water supply characteristics in combination with variable canopy dynamics lead to substantial differences in radiation interception, components of the soil water budget and yield. The sum of intercepted photosynthetic active radiation corrected for drought stress by the ratio of actual to potential transpiration showed a unique positive correlation to grain yield over the three experimental years. Positive correlations between grain yield and actual transpiration normalized by saturation deficit were also found, however, the slopes differed between years. The best predictor of grain yield was the ratio of the sum actual transpiration to the sum of potential evapotranspiration. We could also show that drought stress corrected radiation interception and the ratio ΣTa/ΣETp evaluated at end of May already correlated significantly with final grain yield. This may offer options for improved site specific crop management.