Abstract
Groundwater pollution with nitrate is a big challenge for drinking water abstraction in regions with intensive agricultural land-use, specifically with high livestock densities on sandy soils in humid climates. Karst aquifers with high water flow velocities are extremely vulnerable to this problem. To cope with this situation, a field trial with an installation of ceramic suction cups under a randomised block design with a typical north-German cropping sequence of silage maize–winter wheat–winter barley was established in a karst water protection zone. Over three years, reduced nitrogen (N) application rates and N type (mineral or combined organic + mineral fertilisation) were tested for their effects on crop yields and leachate water quality below the root zone. Results showed no significant reductions in crop yields with 10/20% reduced N rates for cereals/maize and only slight reductions in cereal protein content. Nitrate concentration from adapted N rates was significantly lower in treatments with an application of organic fertilisers (−7.74 mg NO3-N l−1) with greatest potential after cultivation of maize; in only mineral fertilised plots the effect was smaller (−3.80 mg NO3-N l−1). Cumulative leaching losses were positively correlated with post-harvest soil mineral nitrogen content but even in unfertilised control plots losses >50 kg N ha−1 were observed in some crop-years. Reduced N rates led to decreased leaching losses of 14% (6.3 kg N ha−1 a−1) with mineral and 29% (20.1 kg N ha−1 a−1) with organic + mineral fertilisation on average overall cops and years. The presented study revealed the general potential of adapted fertilisation strategies with moderately reduced N applications (−10/−20%) to increase leachate water quality without affecting significantly crop yields. However, regionally typical after-effects from yearlong high N surpluses in livestock intensive farming systems are a limiting factor.
Highlights
Nitrogen (N) plays an important role in global agriculture: on the one hand, more than 50% of the world’s population is nourished by N-fertilised crops [1]; on the other hand, the environmental impacts of N use is far beyond planetary boundaries [2,3], mainly caused by agriculture [4,5]
Besides social costs for drinking water purification, further environmental impacts are caused by NO3 losses, such as indirect greenhouse gas (GHG)
We investigated the effects of adapted fertilisation strategies on leachate water quality below the root zone as an indicator for groundwater quality in a drinking water abstraction area
Summary
Nitrogen (N) plays an important role in global agriculture: on the one hand, more than 50% of the world’s population is nourished by N-fertilised crops [1]; on the other hand, the environmental impacts of N use is far beyond planetary boundaries [2,3], mainly caused by agriculture [4,5]. For feeding the growing global population, concepts, such as sustainable intensification, requests balanced production systems between optimised yields and environmental impacts [6,7,8,9]. In intensive production systems with high livestock densities as typical for northwestern Germany [10], high N balance surpluses are likely to cause nitrate (NO3 ) contamination of groundwater bodies, and applications of organic N sources boost the problem [11]. Besides social costs for drinking water purification, further environmental impacts are caused by NO3 losses, such as indirect greenhouse gas (GHG)
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