Browsing by Author "Viljoen, Charne"

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    Benefits are limited with high nitrogen fertiliser rates in kikuyu-ryegrass pasture systems
    (MDPI, 2020) Viljoen, Charne; Van der Colf, Janke; Swanepoel, Pieter Andreas
    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conditions different to current management practices, yet dairy producers still base fertiliser programmes on these outdated guidelines.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. View Full-Text
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    Optimising nitrogen fertilisation of kikuyu and kikuyu-ryegrass pastures
    (Stellenbosch : Stellenbosch University, 2018-12) Viljoen, Charne; Swanepoel, Pieter Andreas; Van der Colf, Janke; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Dairy production in the southern Cape is mostly based on irrigated planted pastures. Pure grass pastures [kikuyu (Pennisetum clandestinum) and ryegrass (Lolium spp.)] are often established by using minimum-tillage methods. One of the most important management practices of kikuyu-ryegrass pastures is nitrogen (N) fertilisation. The current N fertilisation guidelines often recommend more than 500 kg N ha-1 yr-1, which is possibly too high. The guidelines need to be re-evaluated, since it was developed under cutting conditions using conventional-tillage, and may not be accurate for the minimum-tilled and grazed systems. The aim of this study was to determine an optimum rate of N application of kikuyu and kikuyu-ryegrass pastures, either by a fixed N fertilisation rate or a variable rate according to the demand of the plant in a specific season. Six N fertilisation treatments, one variable rate (Nvar) and five fixed rates (0, 20, 40, 60 and 80 kg N ha-1 grazing cycle-1) were used in the current study. Treatment Nvar was based on the soil water nitrate concentration obtained from using wetting front detectors (WFD). The nitrate concentrations and total soil mineral N indicated that a major pool of N is vulnerable to potential leaching losses. In both kikuyu and kikuyu-ryegrass systems, applications above 40 kg N ha-1 grazing cycle-1 indicated a build-up of total mineral N in soil. No difference between the lower N treatments (≤ 40 kg N ha-1) was found in terms of total mineral N. Mineral N and urease enzyme activity were the only soil parameters that were affected by treatments. Urease activity of the control treatment (no N) was mostly higher (P≤0.05) compared to the 80 kg N ha-1 treatment. Total soil N resulted in seasonal differences and was considered to be related to variation in seasonal herbage production. For example, during periods of high pasture production total soil N in soil was low, but increased during periods of low pasture production. For both kikuyu and kikuyu-ryegrass pastures, the highest herbage production was during spring and summer, while the lowest total soil N was found during summer and autumn. On the kikuyu site, N treatments had an effect on the herbage production during all the seasons of year one, but not during year two. On the kikuyu-ryegrass site, N treatment affected the production during winter, spring and summer of year one, and during the summer of year two. As N treatments increased on both the study sites, the self-sown clover component decreased. Agronomic N use efficiency was similar across treatments and seasons on the kikuyu and kikuyu-ryegrass site, with the exception of winter in the first year in the kikuyu-ryegrass site. This supports the notion that the soil is saturated with N. Crude protein (CP) content of herbage increased with an increase in N, to a point where CP was too high for milk production for some treatments. It is concluded that the current N guidelines needs to be revisited as they pose a risk to the environment and farm economics.