Dry-matter yield and herbage quality of a perennial ryegrass/white clover sward in a rotational grazing and cutting system

The expected reduction in the use of fertilizer nitrogen (N) on grassland in the Netherlands has led to renewed interest in white clover. Therefore, the performance of a newly sown perennial ryegrass/white clover sward on clay soil was assessed during 4 consecutive years. The experiment consisted of all combinations of two defoliation systems, i.e. one or two silage cuts per year (S1, S2), spring N application rate, i.e. 0 or 50 kg ha⁻¹ year⁻¹ (N₀, N₅₀), and the management system, i.e. rotational grazing and cutting, or cutting only (RGC, CO). The overall mean white clover cover was 30%. All treatments affected white clover cover, which was 8% higher with S2 than with S1, 6% higher with N₀ than with N₅₀ and 12% higher with CO than with RGC. The overall mean annual dry-matter (DM) yield (13·1 t ha⁻¹ year⁻¹) was significantly affected only by the management system: in two relatively wetter years, the annual DM yield was 1·19 t ha⁻¹ higher with RGC than with CO, whereas there was no difference in two relatively drier years. Nitrogen application increased the DM yield in the first cut by 7·0 kg kg⁻¹ N applied, but had no significant effect on the annual DM yield. Herbage quality was not affected by the experimental treatments. The average in vitro organic matter digestibility was 0.801, and the average crude protein content was 193 g kg⁻¹ DM. With the expected reduction in the use of fertilizer N, perennial ryegrass/white clover swards should be seriously considered as an alternative option to perennial ryegrass swards on these clay soils.     

A review of farm level modelling approaches for mitigating greenhouse gas emissions from ruminant livestock systems

Ruminant livestock systems contribute to global warming through the emission of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). This paper discusses a general framework for a whole-farm approach to develop cost-effective GHG mitigation strategies. A dairy farm is a complex system with different interacting components. Generally, whole-farm approaches distinguish at least an animal component and a soil–crop component. Whole-farm models should be able to give an accurate representation of the internal cycling of materials and its constituents as well as the exchange between the farming system and its environment. The paper gives an overview of current whole-farm models that are able to simulate GHG emissions for dairy farms. These models are DairySim, FarmGHG, SIMS_DAIRY and FarmSim. All models are able to calculate CH₄ and N₂O emissions, but differences appear in the ability to calculate CO₂ emissions, economics and other parameters. The effects of selected mitigation strategies are demonstrated with some of the models. It is concluded that a whole-farm approach is a powerful tool for the development of cost-effective GHG mitigation options as it reveals relevant interactions between farm components. Model calculations underlined the relationship between farm gate N surplus and GHG emissions, and thus the possibility to use N surpluses as an indicator for GHG emissions.