Impact of fertiliser, water table, and warming on celery yield and CO2 and CH4 emissions from fenland agricultural peat

Highlights: • Cultivation of peat soil requires drainage as most crops are intolerant of root-zone anoxia. • This study attempts to find a water table level that would balance peat preservation and crop yield. • We used two water table levels and two temperatures to examine the effects on celery yield and GHG emissions. • Raising the water table from −50 cm to −30 cm lowered CO2 emissions, but depressed celery yield. • CH4 emissions were very low and for the most part not different from zero across all treatments. -- Abstract: Peatlands are globally important areas for carbon preservation; although covering only 3% of global land area, they store 30% of total soil carbon. Lowland peat soils can also be very productive for agriculture, but their cultivation requires drainage as most crops are intolerant of root-zone anoxia. This leads to the creation of oxic conditions in which organic matter becomes vulnerable to mineralisation. Given the demand for high quality agricultural land, 40% of the UK's peatlands have been drained for agricultural use. In this study we present the outcomes of a controlled environment experiment conducted on agricultural fen peat to examine possible trade-offs between celery growth (an economically important crop on the agricultural peatlands of eastern England) and emissions of greenhouse gases (carbon dioxide (CO₂) and methane (CH₄)) at different temperatures (ambient and ambient +5 °C), water table levels (−30 cm, and −50 cm below the surface), and fertiliser use. Raising the water table from −50 cm to −30 cm depressed yields of celery, and at the same time decreased the entire ecosystem CO₂ loss by 31%. A 5 °C temperature increase enhanced ecosystem emissions of CO₂ by 25% and increased celery dry shoot weight by 23% while not affecting the shoot fresh weight. Fertiliser addition increased both celery yields and soil respiration by 22%. Methane emissions were generally very low and not significantly different from zero. Our results suggest that increasing the water table can lower emissions of greenhouse gases and reduce the rate of peat wastage, but reduces the productivity of celery. If possible, the water table should be raised to −30 cm before and after cultivation, and only decreased during the growing season, as this would reduce the overall greenhouse gas emissions and peat loss, potentially not affecting the production of vegetable crops.