Department of Agronomy

Permanent URI for this community

https://scholar.sun.ac.za/handle/10019.1/18

Browse

Browsing Department of Agronomy by Author "Bester, Carien"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Nitrogen management strategies for mixed pastures in the Winelands sub-region of the Western Cape
    (Stellenbosch : Stellenbosch University, 2014-04) Bester, Carien; Pieterse, P. J.; Labuschagne, Johan; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Three different pasture mixtures were established under irrigation at the Elsenburg research farm with the aim of devising nitrogen (N) management strategies for pastures in the Winelands sub-region of South Africa. The pasture mixtures were as follows: i) a mixed grass pasture consisting of perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinaceae) and cocksfoot (Dactylis glomerata); ii) a grass-clover pasture consisting of perennial ryegrass, tall fescue, cocksfoot and red and white clover (Trifolium pratense and Trifolium repens); and iii) a grass-lucerne pasture consisting of perennial ryegrass, tall fescue and lucerne (Medicago sativa). The effect of fertiliser N on selected nutritive characteristics was also evaluated. The grass-legume pastures were subjected to two management strategies: the once-off application of N and the consecutive application of N over the autumn-early spring period. The reaction of the mixed grass pasture to applied N was mostly characterised by an interaction between the season of N application and N application rate. The productivity of the pasture in terms of the primary dry matter production (PDMP) and the total dry matter production (TDMP) was highest in spring and summer with the application of 60 – 80 kg N ha-1, and decreased in autumn and winter. There was a strong response of the winter residual dry matter production (RDMP) to N, which indicated that not all applied N was utilised during the first regrowth cycle, which might present a risk of nitrate being leached below the root zone. The botanical composition of the mixed grass pasture was determined by season of N application, and not N application rate. The tall fescue content was low over all seasons, presumably due to poor establishment and strong competition from accompanying species. In the cooler months perennial ryegrass and tall fescue was the dominant species, while in the warmer months cocksfoot was the main species. Nitrogen application also had a significant effect on the quality of the pasture, most notably the crude protein (CP) content. The response of the CP content was characterised by a strong interaction between season of N application and N application rate. Crude protein levels in excess of 22 % were recorded in autumn and winter with the application of 40 – 80 kg N ha-1. Other characteristics remained within the expected range. The response of the grass-clover and grass-lucerne pastures in terms of productivity and nutritive characteristics were mainly determined by the season of N application, and not N application rate. Productivity tended to be highest in autumn and early spring for both the once-off and the consecutive N application strategies, emphasizing the effect of temperature on pasture growth. The effect of season of N application and the N application rate on the botanical composition of the respective pastures were inconsistent over the two years of the study. The clover content tended to decrease in response to increasing rates of N, while the grass fraction was stimulated. Lucerne productivity decreased from autumn through winter and reached minimum levels in early spring, and was unaffected by fertiliser N rate. The legume component in both the grass-clover and grass-lucerne pastures remained above recommended levels of 20 – 40 % for optimum animal production, even when N was applied consecutively. The nutritive characteristics measured (dry matter (DM) content, CP, in vitro organic matter digestibility (IVOMD)) remained within the expected range, except the total CP content which was very high in the first year (> 30 %), although N application rate did not have a significant effect. Based on these findings, preliminary recommendations for N fertilisation (on low carbon soils) for a mixed grass pasture is 40 kg N ha-1 during autumn and winter and 60 kg N ha-1 in spring and summer. Based on the poor response of the grass-legume pastures to applied N it is doubtful whether fertilisation will lead to an economical advantage, but low rates of approximately 40 kg N ha-1 could be beneficial in a grass-clover pasture during autumn and late winter/early spring based on the relatively strong response of PDMP to N during this period.