Potential of boreholes combined with deep-rooted cover crops to ameliorate subsoil compaction: year 2022: results from the final year of the experiments; 2022

This document summarises the results from the year 2022 of the experiments on amelioration of subsoil compaction in Lelystad and Vredepeel as part of the PPS Climate Adaptation. The results of the experiments are briefly described and interpreted. Potatoes were grown at both trial sites in 2022 and it has been about two years since the experimental treatments were applied (both mechanical treatments and green manures). In Lelystad in 2022 there were no significant effects from the 2019-2020 cover crop treatments on potato yields, bulk density or soil moisture. There were minor but statistically significant differences in penetration resistance between the cover treatments. There were no major differences between the mechanical treatments that can be interpreted using only 2022 data, due to lack of repetitions. In Vredepeel we saw an effect from the experimental treatments on the penetration resistance in the subsoil and nitrate leaching, but not on crop growth, bulk density and soil moisture. Large boreholes appear to have the largest decreasing effect on the penetration resistance in the subsoil in combination with the black oats and tall fescue + English ryegrass cover crops. The choice of cover crop seems to influence the effect of the mechanical treatment, and vice versa. In order to substantiate effects on penetration resistance and nitrate leaching, data from previous years need to be taken into account. Additionally, in 2022 the soil was not compacted, hence in order to be able to conclude whether the measures can ameliorate subsoil compaction, we need to look at the level of compaction in previous years. Across both experiments the preliminary conclusion is that effects from previous years’ treatments are not apparent and that differences between the treatments are either too small to be interesting or too variable in order to be able establish clear and meaningful relation with our hypothesized effects from the treatments. It is advisable to look at the effects seen in previous years to be able to draw final conclusions on where observed effects are coming from and what the developments over time were. The full analysis and conclusions from the experiments over the full duration (2019-2022) will follow in the final report later in 2023.