Nitrate leaching potential from arable land in Germany: Identifying most relevant factors

Area of Science:

• Agricultural Science
• Environmental Science
• Soil Science

Background:

• Diffuse nitrogen losses from German agriculture elevate regional groundwater nitrate levels.
• Groundwater monitoring is a delayed indicator of agricultural mitigation effectiveness due to long leachate transport times.
• Soil mineral nitrogen at autumn (SMNa) is a key indicator for nitrate leaching potential at field and farm scales.

Purpose of the Study:

• To understand the key factors controlling soil mineral nitrogen content at the start of winter.
• To evaluate the significance of management and site factors on SMNa using a data-driven approach.
• To identify effective strategies for reducing nitrate loads in vulnerable agricultural regions.

Main Methods:

• An on-farm data collection approach across 48 farms in five nitrate-sensitive German regions (2017-2020).
• Evaluation of 25 management and site factors using a random forest model to determine their significance for SMNa.
• Random forest regression analysis to quantify the influence of identified factors on SMNa, achieving R² = 0.56.

Main Results:

• Cultivated crop type is the most significant factor influencing SMNa, with potatoes, oilseed rape, and maize showing the highest levels.
• Spring barley, sugar beet, and winter barley resulted in the lowest SMNa.
• Soil type, soil texture, and October precipitation were the most decisive site factors affecting SMNa.
• Nitrogen fertilization rate and timing effects were masked by site-specific factors.

Conclusions:

• Reducing the cultivation of nitrogen-intensive crops in crop sequences is a promising strategy to mitigate nitrate loads.
• Soil properties and weather conditions play a crucial role in nitrogen release and leaching risk, potentially masking the impact of cultivation practices.
• Effective nitrate load reduction requires considering both crop management and inherent soil and weather conditions.