Using NIWASAVE to simulate impacts of irrigation heterogeneity on yield and nitrate leaching when using a travelling rain gun system in a shallow soil context in Charente (France)

Abstract This paper deals with the impact of irrigation and fertilising practices on corn yield and nitrate leaching on a shallow soil plot in Charente (France). This impact analysis is made using NIWASAVE, a model simulating the impact of water applications depths on crop yields and nitrate leaching, in the case of a travelling rain gun system (TRGS) on a climatic series. A first type of scenario regarding the TRGS usage (lane spacing, field orientation, daily versus night irrigation) is tested and compared to a reference scenario (current farmer practices). Simulations show low deviation levels from the reference scenario with regards to nitrogen leaching and crop yields aspects under the climatic and soil context of Charente. Results can be linked to principal wind profiles (speed, direction and time-table versus irrigation time) for this region in close proximity with the Atlantic Ocean. Moreover, a lane spacing effect on the water distribution along a transect can be observed. A second type of scenarios regarding water application depths (WADs) and fertilisation is implemented. Best results are obtained on NO32− leaching and drainage by reducing both WAD and nitrate fertiliser applications (NFAs). Whatever the scenario, a substantial drainage is observed every year during the inter-cropping season what may increase the risk of nitrate leaching during this period. In addition, this study shows that fertiliser requirements do not match those proposed by the reference scenario. A NFA reduction of 20% results in an average yield reduction of 0.1 t/ha.

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