Evaluating peat pasture performance under elevated groundwater conditions

Historically, Dutch peatlands have been drained for agriculture, particularly as pastures for dairy production. While drainage increases productivity, it degrades the peat layer, leading to high greenhouse gas emissions and soil subsidence. Raising the depth of the groundwater table (WT) to 20 cm below field level, contrasted to commonly drained peat at approximately 50 cm below field level, is considered an effective solution to limit peat degradation. However, it is unclear how raising the WT with an active water infiltration system (AWIS) would affect grass yield and quality, and whether dairy farming can be maintained. We studied the effect of raising WT on grass production, quality, and nitrogen utilization, using experimental plots with different WT and fertilization levels in 2020–2024. Raising WT from 50 to 20 cm below field level resulted in an average decrease of 9 % in herbage dry matter yield (DMY), with significant variation between years due to varying weather conditions. The reduction in DMY could partly be explained by the observed decrease in soil N supply in wetter conditions, due to a lower mineralization rate. Increased N fertilization could mediate the lower DMY but increases nutrient losses. Herbage crude protein concentration was moderately affected by WT, and more strongly by yearly variation. Although results are on plot level, which excludes losses originating from trafficking by machinery and animals, they indicate that raising WT is compatible with relatively high grass production and similar grass quality. Consequences on farm level need to be further explored. • Grass yields decreased with 9 % when raising groundwater table from 50 to 20 cm. • Fertilizer apparent N recovery and N use efficiency were unaffected by water table. • Grass had less protein at high groundwater tables, energy value was not affected. • Yearly weather conditions caused significant variations for the studied parameters. • We recommend further research on farm level implications of raising water tables.