Winter Runoff of Nitrogen and Phosphorus from a Rotational Pen Design with Suckler Cows

Abstract

Keeping beef cattle outdoors during winter reduces costs and improves animal welfare, but increases the risk of nitrogen (N) and phosphorus (P) runoff losses. This study evaluated a rotational 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 areas 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 mineral-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 corresponding vegetated sub-area without cows. The study design did not provide a sufficient distribution of excretions and a high animal density in combination with trampling resulted in unacceptable N and P run-off losses. An environmentally friendly design would need to include frequent moving of all equipment and access to larger areas.