Abstract
Nitrogen (N) fertiliser is applied to pastures in dairy farming systems to ensure productivity, but it is an expensive input that could be damaging to the environment if used excessively. In the southern Cape region of South Africa, N fertilisation guidelines for pastures were developed under conditions different to current management practices, yet dairy producers still base fertiliser programmes on these outdated guidelines. This study aimed to determine the efficiencies of N fertilisation. Various N fertiliser rates (0, 20, 40, 60 and 80 kg ha−1 applied after grazing), as well as a variable rate according to the nitrate concentration in the soil water solution, were assessed on a grazed pasture. Dairy cows returned to a pasture approximately 11 times per year. Pasture production showed a minimal response to fertilisation within each season. The most responsive parameters to fertilisation were the herbage crude protein content, soil mineral N content and urease activity. Reduced microbial activity was observed when more than 40 kg N ha−1 was applied. When considering the soil total mineral N content, N is used inefficiently at rates above 40 kg N ha−1. The results are indicative of an N saturated system that provides a rationale for reducing N fertiliser rates.
Highlights
Kikuyu grass (Pennisetum clandestinum) is utilised as a pasture base for dairy production [1].kikuyu becomes dormant when temperatures decrease during winter and spring [2] and the strategic incorporation of cool-season forage species is used to improve fodder availability throughout the year [3]
The current study investigated the efficiency related to the N fertilisation of a no-tillage, grazed kikuyu-ryegrass pasture in the southern Cape of South Africa
The response of the botanical composition, agronomic N use efficiency (ANUE) and crude protein content of the pasture were evaluated in response to season and N fertilisation
Summary
Kikuyu grass (Pennisetum clandestinum) is utilised as a pasture base for dairy production [1].kikuyu becomes dormant when temperatures decrease during winter and spring [2] and the strategic incorporation of cool-season forage species is used to improve fodder availability throughout the year [3]. Kikuyu grass (Pennisetum clandestinum) is utilised as a pasture base for dairy production [1]. Ryegrass (Lolium spp.) is a productive grass species commonly sown into kikuyu to contribute to herbage production [1,3,4] and pasture quality [5]. It is often suggested that legumes, such as clovers (Trifolium spp.), should be incorporated into grass pastures to reduce nitrogen (N) fertiliser requirements. Oversowing clovers into grass pastures is often unreliable. This is because clovers exhibit lower herbage production than grasses [5], present poor establishment abilities [6,7] and often display poor persistence as a result of the competitive nature of grasses, kikuyu [5,8]
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