Syracuse

Catch crop emergence success depends on weather and soil seedbed conditions in interaction with sowing date: A simulation study using the SIMPLE emergence model.

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Constantin, Julie | Durr, Carolyne | Tribouillois, Hélène | Justes, Eric

Edité par CCSD ; Elsevier -

Several studies have already demonstrated the usefulness and efficiency of catch crops to reduce nitrate leaching from cropping systems into groundwater. Catch crops must be sown in summer in a temperate climate, when the soil is often dry after the main crop harvest. This can lead to poor crop establish- ment. The present study uses a model to explore differences in the emergence rates of catch crops in summer for a wide range of soil and weather conditions that occur in France and identifies the main causes of failure. The SIMPLE model predicts the emergence duration and rate of crops by considering species and seed characteristics in interaction with seedbed conditions (temperature, moisture, clods and surface crust). The model was previously validated for white mustard and seems appropriate for the present work of simulating ryegrass and vetch emergence under contrasted weather and water stress conditions. Simulations were performed for a wide range of pedoclimatic conditions and sowing prac- tices (dates, depth and seedbed structures). Soil water content and temperature in the upper layers of the soil were first simulated with the STICS soil-crop model and were then validated in an initial step by comparing simulations with experimental data. These outputs were then used as input data for the SIMPLE emergence model. Results showed that, on average, the emergence rates of catch crops sown in summer were sufficient (>75%), regardless of species and sowing technique. Simulations indicated that a poor emergence rate (<50%) occurred in less than one year in ten for northern sites, and two years in ten in south-western France. In regions with a Mediterranean climate, emergence varied greatly from year to year, with failures (<25%) approximately two years in ten and low emergence (<50%) in approx- imately four years in ten. In dry summer regions, poor emergence occurred more frequently with early sowing (mid-July) due to water stress, while later sowing (around September 15) was generally more successful. Predictions indicate that sowing date is the management choice with the most impact and that it must be carefully adapted to weather to maximise the potential of catch crops to trap nitrate and thus minimise nitrate leaching. This work illustrates the application of modelling as a tool for evaluating risks and optimising the management of catch crops for a wide range of conditions, which thus increases the success of emergence and cover establishment under field conditions.

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