S13 - Session P1 - Modelling carbon and nitrogen dynamics to optimise the production and retention of soil organic matter and nitrogen in root vegetable production

Authors: Marcus Travers *, Athanos Paschalis

There is momentum towards de-intensifying food production in the UK by increasing the sustainability of production and reducing the area of land under crops. However, this needs to be balanced with security of supply if it is to be achieved sustainably. Retaining as much Nitrogen (N) as possible within the field for yield is key to ensuring sustainable production. This requires N to be allocated according to the needs of crops and to carry over of excess N available after harvest to the next crop. Building and retaining soil (OM) is an important part of this process and increases the added value of soil by capturing soil Carbon (C). Increasing soil OM improves the retention of N but also water and other inputs with better availability to crops and less release into catchments. Building soil OM and retention of N are a net consequence of inputs, turnover, offtakes and losses. When the relationships between turnover and offtakes are optimised then inputs and losses should be reduced. Turnover is controlled by the chemical complexity of organic inputs and the cycling of C and N through many processes in combination with the biological activity of the soil. Understanding the actions and processes that control the turnover of OM and the plant-availability of N allows farmers to adopt the best practices and monitor the resulting effects. Management practices bring about slow changes in soil OM with evaluation only possible after many years. The complexity and slow progress of changes leads to a lack of confidence in outcomes and inconclusive results from fundamental and traditional soil measurements. Modelling the processes involved in OM turnover and N cycling, allows proactive changes to working practices to be evaluated before they are put in place. Alongside monitoring, modelling outcomes highlights performance indicators that can demonstrate the benefits of management before measurable changes in OM are achieved. Optimising the production and retention of OM and N within vegetable production has two parts to it. Identifying when land produces and retains less OM and nitrogen within the rotation allows changes to rotations to be introduced whilst maintaining food output. Identifying where land is less productive for food production but potentially more appropriate for building OM with other plants helps to rationalise the process of de-intensification and can give added value to agricultural land under alternative funding schemes. This paper presents modelling and validation data that addresses five aspects of the processes that control soil OM and N losses: The timing and amounts of N inputs. Crop growth, water use and N uptake. The development of a soil moisture deficit water, recharge and the occurrence of leaching events. Soil C and N dynamics and cycling. Nitrate availability in soils and loses during leaching events. The data is from root vegetable crops within a five year rotation in Norfolk, England.