Browsing by Author "Swanepoel, P. A."

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    A comparison of experimental designs for cultivar evaluations
    (Taylor and Francis, 2020) Saul, Hae; Booyse, M.; Swanepoel, P. A.
    Spatial heterogeneity and the lack of clear or significant treatment responses in agricultural field experiments complicates recommending the most suitable cultivar(s) to producers for a specific area. Increased attention should be given to the experimental design of cultivar trials, as failure to capture spatial heterogeneity may increase the unexplained variance and thus might influence the accuracy of results. A randomised complete block design (RCBD) is the most popular design in variety trials in South Africa. However, latinised row-column designs (LRCD) is widely recommended in literature for field experimentation, because of the efficiency to control heterogeneity in two dimensions. The aim of this study was to compare the efficiency of RBCD with LRCD and recommend the more appropriate design for use by practitioners in cultivar trials. Wheat (Triticum aestivum) was used as a test crop. An analysis of variance was performed on the data produced from both designs conducted on wheat in the Swartland region of South Africa over a two-year period. An LRCD provided better accuracy and model or design estimations than RCBD. The results demonstrated the value of eliminating variance in two directions rather than one direction. We therefore recommend the use of LRCD in preference to RCBD in variety trials.
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    Seed-drill opener type and crop residue load affect canola establishment, but only residue load affects yield
    (American Society of Agronomy, 2019) Swanepoel, P. A.; Le Roux, P. J. G.; Agenbag, G. A.; Strauss, J. A.; MacLaren, C.
    Core Ideas Canola establishment can be affected by the residues of the previous crop. Different planting tools may handle crop residue differently. Tine and disc furrow openers at different residue loads were tested. Canola performed best when established with tine openers and when residue load is low. Handling crop residue during planting operations is a challenge to conservation agriculture (CA) farmers worldwide. It remains unclear which tools are most effective in which conditions. Canola (Brassica napus L.), an oilseed crop widely used in rotation with cereals, is particularly sensitive to seedbed conditions, and thus may be influenced by residue loads and the choice of seed-drill openers. To identify optimal planting practices, this study compared the performance of disc and tine openers on canola establishment, growth, and yield under differing residue loads in a Mediterranean-type climate region. First, soil disturbance caused by disc and tine openers was evaluated to assess their effect on seedbed conditions; and second, the interacting effects of the openers with different residue loads was investigated. Tine openers and low crop residue loads resulted in the best (P < 0.05) canola establishment. However, canola at reduced plant populations compensated in both biomass and grain yield, so that no yield differences resulted from different opener types, and only small yield differences occurred between residue loads (P > 0.05).