Abstract
High input dairy farms that are located on sandy soils in northwest Europe are predisposed to substantial nitrate leaching during a surplus of winter precipitation. Leys within integrated crop-livestock systems play an important role in soil fertility, soil C sequestration and soil N mineralization potentials. Therefore, leys are a feasible option that can be utilized to reduce local N losses to the environment, especially following maize grown for silage. We hypothesize that grass-clover leys ensure low nitrate leaching losses even when grazed intensively. The extent to which NO3-leaching occurred across seven different pasture management systems in terms of their sward composition, cutting, grazing, fertilization and combinations thereof was investigated in integrated animal-crop grazing systems over three winter periods (2017/2018, 2018/2019 and 2019/2020). The observed grazed systems were comprised of cut-used- and grazed grass-clover swards (0, 1 and 2 years after establishment following cereals), a catch crop grazed late in the year as well as a cut-used permanent grassland for comparison. Overall, all treatments resulted in nitrate leaching losses that did not exceed the WHO-threshold (25 mg nitrate/L). The highest level of NO3-leaching was observed in the catch crop system and the lowest in cut-used permanent grassland, with NO3-N losses of 19.6 ± 5.3 and 2.1 ± 0.3 kg NO3-N ha−1 year−1. Annual herbage yields were in the range of 0.9 to 12.4 t DM ha−1 and nitrogen yields varied between 181 ± 51 and 228 ± 66 kg N ha−1 during the study period. The highest herbage-N-yields were observed from the 1- and 2-year-old grass-clover leys. The highest N-field-balance was observed for the grazed leys and the lowest for the cut-used permanent grassland. However, no correlation was found between the highly positive field-N-balance and the amount of NO3-leached. This indicates a high N carry-over from grass-clover swards to the subsequent cash crop unit instead of increasing the risk of groundwater contamination from grazed leys in integrated animal crop-systems and underlines the eco-efficiency of dairy farming based on grazed ley systems.
Highlights
Dairy systems in northwest Europe strive to increase milk productivity, the amount of forage land available remains the same
Afterwards, it was converted to an organic farming system according to stipulations of the association “Bio-land” and some arable fields were converted to permanent grassland concurrently
Nitrate leaching following the swards in the current study may be generally divided into two groups: (1) low leaching (
Summary
Dairy systems in northwest Europe strive to increase milk productivity, the amount of forage land available remains the same. This has led to a land-use intensification in forage production and an increased level of supplementary feed imports at farm-gate, which is often associated with negative environmental effects. This makes the sustainability of confined systems, which are often used, questionable. The farm-nitrogen-balance of dairy systems increased and resulted in the N leaching to groundwater, which often reaches the critical limit of nitrate (NO3) per litre [1]. The majority of N leached from soils consist of NO3, whilst NH4 is considered to be less important
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