Drought boosts risk of nitrate leaching from grassland fertilisation

Valentin H Klaus; Lennart Friedritz; Ute Hamer; Till Kleinebecker

doi:10.1016/j.scitotenv.2020.137877

Drought boosts risk of nitrate leaching from grassland fertilisation

Sci Total Environ. 2020 Jul 15:726:137877. doi: 10.1016/j.scitotenv.2020.137877. Epub 2020 Mar 19.

Authors

Valentin H Klaus¹, Lennart Friedritz², Ute Hamer², Till Kleinebecker³

Affiliations

¹ Institute of Agricultural Sciences, ETH Zürich, Universitätstr, 2, 8092 Zürich, Switzerland; Institute of Landscape Ecology, University of Münster, Heisenbergstr, 2, 48149 Münster, Germany. Electronic address: valentin.klaus@usys.ethz.ch.
² Institute of Landscape Ecology, University of Münster, Heisenbergstr, 2, 48149 Münster, Germany.
³ Institute of Landscape Ecology, University of Münster, Heisenbergstr, 2, 48149 Münster, Germany; Institute of Landscape Ecology and Resource Management, University of Gießen, Heinrich-Buff-Ring 26-32, 35392 Gießen, Germany.

PMID: 32481225
DOI: 10.1016/j.scitotenv.2020.137877

Abstract

Both climate change and agricultural intensification are drivers of global nutrient cycles and biodiversity loss. A potentially great environmental threat can arise when these two drivers interact, for example, when farmers try to compensate reduced soil nutrient availability due to drought by the application of liquid organic fertiliser. As dry soils don't hold back nutrients very well, this approach can lead to nitrate leaching and potentially also to the pollution of drinking water. However, little is known about leaching from dry but fertilised grassland soil, and how this is affected by land use intensity and plant diversity. In this mesocosm study, we transferred 60 grassland sods differing in past land use intensity to a greenhouse and treated them with severe drought, fertilisation and both together. Drought was induced by almost entirely stopping irrigation for seven weeks. Fertilisation was done by three applications of slurry summing up to 168 kg total nitrogen per hectare (111 kg NH₄-N). We assessed nutrient leaching risk with ion-exchange resin (IER) bags installed in the soil of all mesocosms. IER bags were retrieved after drought and extracts were analysed for concentrations of nitrate, ammonium, phosphate and potassium. Fertilisation partially buffered drought-induced losses in yield. However, the interaction of fertilisation and drought resulted in a drastic increase in nitrate leaching risk when soils are rewetted (>300%), while neither drought nor fertilisation alone were significant. Ammonium concentrations followed the same trend as nitrate, but less pronounced. Phosphate and potassium concentrations were not affected by the treatments. Past land use was hardly related to soil nutrient concentrations, rather was plant diversity. However, results indicate that plant diversity was not driving nitrate and ammonium concentrations under drought and/or fertilisation. This study reveals grassland fertilisation during drought to be a severe environmental problem due to significantly increased nitrate leaching risk.

Keywords: Climate change; Grassland management; Ion-exchange resin bags; Land use history; Land use intensity; Nitrate.