The ReNu2Farm project partner Nutrient Management Institute from the Netherlands performed a three years field trial with biowaste compost as a recycling-derived fertiliser. The compost was compared with other organic fertilisers such as cattle slurry as well as with mineral fertiliser in a maize crop on sandy soil. The objective of the trial was to investigate to what extent the functioning of the top soil layer of leachable sandy soil can be improved by increasing the organic matter content and the related soil functions, without leading to an increase in nitrate leaching.
A three-year application of organic residues and soil improvers does not lead to significant differences in organic matter content, maize yield and Nmin stock after harvest for the same input of active nutrients. However, there were positive effects on aggregate stability, moisture retention capacity and infiltration capacity of the soil.
In the long term, the treatments with the highest organic matter supply (high dose of compost and cattle manure with grass clippings) lead to the greatest increase in organic matter content. This is shown by model calculations carried out in addition to the field trials.
Effects of hot, dry summers
Summers in the years 2018-2020 were warmer and drier than average. The effect differed between the two locations of the trial. On the dry sandy soil where no irrigation was possible, this led to very early harvests, low yields, high Nmin stocks after harvest, and well-developed green manures. In practice, on dry sandy soils, this means that if warm, dry summers lead to low maize yields and higher Nmin stocks after harvest, the timely sowing of green manures is crucial to prevent nitrate leaching. On the lower lying sandy soil, where it was possible to irrigate, the yields were higher and the N-min stocks after the harvest lowered over time. In practice this means that on sandy soils with sufficient rainfall it is important to keep the N-supply of the soil at the right level, so that sufficient nitrogen remains available for the crop. The use of organic fertilisers, such as compost, and the cultivation of a successful catch crop in the autumn can contribute to this.
More detailed ReNu2Farm reports on the field trial results as well as a handbook of best-practice fertilisation management will be published in the coming months.