In March 2020 two field experiments are laid out for the third and last year within the Netherlands (see pictures). The objective of the field experiments is to explore the effects of differences in organic matter input with animal manure, household waste compost (a recycling-derived fertilizer) and/or verge grass on soil quality (e.g. organic matter content and quality, water holding capacity, etc.), crop yield and N uptake of maize and on the risk of nitrate leaching (determined with nitrate in soil profile after harvest). The field experiments are located on sandy soils in the Province of Gelderland, near Wageningen. One field experiment was located on a sandy soil with a deep groundwater table (> 5 m; no irrigation) and the other one on a sandy soil with shallow groundwater table (> 1 m; with irrigation).
Because of the hot and dry summers of 2018 and 2019, the yields of the silage maize on the location with the deep groundwater table and no irrigation was low (25-35 tonnes per ha), while it was significantly higher on the location with the shallow groundwater table and irrigation (35-55 tonnes per ha). Yield and nitrogen uptake by the crop were not significantly different between treatments in 2018 and 2019. The amount of nitrate in the soil profile after harvest was high in both years and both locations (80-120 kg NO3-N/ha), which means a high risk for nitrate leaching. However, catch crops were sown after harvest of the maize according to national legislation, by which nitrate leaching will be largely prevented. Nitrate in the soil profile did not significantly differ between treatments.
So, our provisional conclusion after two years is that it is possible to supply additional organic matter to a maize crop within legal boundaries, with no significant effects on crop yield and nitrate leaching. We are curious if this conclusion will be confirmed at the basis of the results we will obtain in 2020 and what the effect on soil quality will be.