Abstract
Keeping beef cattle outdoors during winter reduces costs and improves animal welfare, but in- creases the risk of nitrogen (N) and phosphorus (P) runoff losses. This study evaluated a rota- tional pen design on grassland with two groups of suckler cows given access to an expanding staying area and a new feeding area each week (72 cattle ha −1 ), with one month's stay per pen. The spatial distribution of excreta and effects on N and P surface runoff was evaluated during six months. The total excreta loads corresponded to 500 kg·N·ha−1 and 50 kg·P·ha−1. New feeding ar- eas did not distribute excretions evenly, which resulted in the highest proportion of excretions (31%) occurring in the first week's sub-area. The topsoil had significantly higher amounts of min- eral-N, mainly as NH4-N (29 - 81 kg·ha−1), than an unaffected area (13 kg·ha−1). Mean total runoff losses were similar for both groups (1.4 kg·P·ha−1 and 9.0 kg·N·ha−1). Around 78% of N and 70% of P runoff losses occurred during the month with cattle present. During the first two weeks with heavy rain, N and P runoff losses were 50% higher from an area with suckler cows than a corre- sponding vegetated sub-area without cows. The study design did not provide a sufficient distribu- tion of excretions and a high animal density in combination with trampling resulted in unaccept- able N and P run-off losses. An environmentally friendly design would need to include frequent moving of all equipment and access to larger areas.
Highlights
Grazing by cattle is needed during the summer period to preserve about 450,000 hectares of semi-natural grassland of high biodiversity in Sweden, but declining economic margins for Swedish beef producers are making it too expensive to house these cattle in conventional winter housing.High animal density on outdoor areas has been shown to result in large net inputs of nutrients to the soil and an increased risk of nitrogen (N) leaching [1]
The proportion of excreta deposited in the shelter area was higher for the large group (17%) than the small group (11%), which resulted in higher N and P loads for the large group despite the shelter area in both pens having the same animal density
This study showed that a rotating pen and feeding area can be a promising strategy for preventing high point loads of N and P being supplied with excreta for both group sizes tested, the overall load of 500 kg·N·ha−1 was too high
Summary
Grazing by cattle is needed during the summer period to preserve about 450,000 hectares of semi-natural grassland of high biodiversity in Sweden, but declining economic margins for Swedish beef producers are making it too expensive to house these cattle in conventional winter housing.High animal density on outdoor areas has been shown to result in large net inputs of nutrients to the soil and an increased risk of nitrogen (N) leaching [1]. The limiting animal density in Sweden is based on an average manure application corresponding to 22 kg·P·ha−1 over a five-year crop rotation [3]. For suckler cows, this corresponds to 0.7 animal units per hectare [4], i.e. it is permitted to keep 3.5 suckler cows per hectare in one year out of five, but data on how beef farmers implement this regulation in outdoor rearing systems are lacking. Application of manure during autumn and winter is highly restricted under Swedish regulations, as this high-risk period is known to contribute large N leaching loads to waters [6]
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