Precipitation-optimised nitrogen fertilisation application

McKay Fletcher, Daniel, Ruiz, Siul Aljadi, Williams, Katherine, Petroselli, Chiara, Walker, Nancy, Catherine and Roose, Tiina (2020) Precipitation-optimised nitrogen fertilisation application. EGU General Assembly 2020, Online. 04 - 08 May 2020.

Abstract

Sufficient nitrogen fertilisation is essential for obtaining the crop yields required to feed the growing population. Often, nitrogen applied to fields is lost to a number of processes including denitrification, surface run-off and leaching. These processes can damage the local ecology and contaminate water supplies. Additionally, nitrogen lost as ammonia gas and the large energy input required to synthesize ammonia are both large contributors to global greenhouse gas emissions. Choosing fertilisation strategies to optimise the proportion of nitrogen taken up by crops (nitrogen use efficiency) can reduce the production of ammonia and the pollution of water supplies.
A mathematical model that describes the movement of water and multiple nitrogen species in soil at the plant scale over a growing season was used to assess the nitrogen use efficiency of varying fertilisation strategies. We carefully consider the effects of a number of physical processes including: root growth, root uptake, the transfer of nitrogen between different nitrogen species and the effect of soil saturation on nitrogen transport. The resulting model comprises of a coupled system of partial and ordinary differential equations that describe the mathematical interplay between nitrogen transport, water movement and root uptake. The system of equations is solved numerically using a finite element approach. Numerical experiments were conducted to determine how nitrogen uptake efficiency was affected by different fertilisation strategies. We examine numerous cases by varying the quantity of fertiliser applied to the soil and the fertiliser application times.
The numerical experiments suggest that, under uniform rainfall rates, the optimal fertilisation times (within the bounds of typical times found in agriculture) can result in 25% more nitrogen uptake than the worst strategies. However, there were large time periods, 28 days for the first application and 10 days for the second, which resulted in close-to-optimal nitrogen use efficiency. This result suggests farmers have large time-windows in which they can choose fertilisation times based on additional factors, such as past and predicted rainfall and crop health, without worrying about expected nitrogen use efficiency.

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Contributors

Author: Katherine Williams

Author: Nancy, Catherine Walker

Author: Tiina Roose

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