Catch Crops in Lower Saxony-More Than 30 Years of Action against Water Pollution with Nitrates: All in Vain?

Intensive animal production, vast amounts of biogas plants, and the spreading of manure and digestates, exerts strong pressure on water quality in the German federal state of Lower Saxony. Catch and cover crop (c&c) cultivation is seen as one measure to inhibit nitrate leaching into soils, and to prevent water pollution with nitrates. A document analysis was carried out, covering the time span of 1992 to 2020, and the findings were combined with available quantitative data of the same period, and with GIS analysis. From 1994 to the year 2020, the acreage of subsidized c&cs increased from ca. 10,000 ha to ca. 380,000 ha. In addition, there was an acreage of unsubsidized c&cs of about 100,000 ha declining to 50,000 ha. In comparison, the acreage of arable land remained at approximately 1,880,000 ha. We found that c&cs did not contribute substantially to water protection for the following reasons: the design of the measure, control of farmer's actions, and the antagonistic trend due to the increase in animal numbers and biogas plants. The development of c&cs over time and space reveals that frame conditions and management requirements of cultivating c&cs need to be well designed to be effective and efficient (with regard to N reduction and reduction of costs). It is vital to coordinate all programs and schemes in one region. From our evaluation, we conclude that a measure such as c&c cultivation, which is simple to introduce and easy to control, should be implemented over winter as a mandatory measure in order to achieve a greater uptake. Additionally, result-based measures could complement this scheme, as there is a strong link between subsidy level and the success of the measure.

Automated summary

Intensive animal production, biogas plants, and spreading of manure in Lower Saxony have put pressure on water quality. Catch and cover crop cultivation is considered to inhibit nitrate leaching and prevent water pollution, but its contribution to water protection is limited due to design, control, and increasing animal numbers and biogas plants. Well-designed and coordinated measures are needed for effective and efficient N reduction.