Browsing by Author "Swanepoel, Pieter A."

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    Aligning conservation agriculture among various disciplines in South Africa
    (Taylor & Francis, 2021-10-01) Swanepoel, Pieter A.
    n South Africa, the term Conservation Agriculture (CA) is often used to describe any soil conservation action rather than a combination of the three management principles that CA encompasses, namely minimum soil disturbance, using a diversity of crops in rotation or association, and protecting the soil with an organic soil cover. A workshop was held with delegates from tertiary institutions, research institutions, government and private companies, in January 2019, to share and exchange CA research experiences and lessons, and to identify research gaps in the field of CA in South Africa. By collating the information from the workshop, this article aims to align CA approaches among various disciplines in South Africa and to identify the inevitable challenges with CA and (mis-)perceptions of CA in South Africa. It was clear that CA is applicable to most farming systems, but is context specific. No specific CA practice can be recommended as a panacea to solve issues experienced in all systems. Adaptation and application of CA within different South African farming systems needs to be dealt with sensibly and realistically, in ways that are based on practical rather than purely theoretical considerations. It is important that CA is not advocated without taking sustainable intensification into account. Dealing with CA sensibly requires a multidisciplinary approach.
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    Excessive nitrogen fertilization is a limitation to herbage yield and nitrogen use efficiency of dairy pastures in South Africa
    (MDPI, 2022-04-06) Phohlo, Motsedisi P.; Swanepoel, Pieter A.; Hinck, Stefan
    The response of crop yields to fertilizers is a long-standing topic of agricultural production. Currently, in dairy-pasture systems, nitrogen (N) fertilizer is used as a management tool that is said to be directly proportional to pasture yield. We evaluated a large dataset consisting of data from 153 fields over five years to examine the effects of N fertilization on pasture yield and nitrogen use efficiency in the Eastern Cape province of South Africa. Fertilizer application rates were grouped into three treatments viz., <200, 200–350, and >350 kg N ha−1 , and herbage yield response over the years was analyzed with mixed models. There were no differences found between treatments for total annual herbage yield over the years. High N fertilizer rates did not translate to a higher herbage yield of pastures. The N rate had a weak but significant negative correlation with the total annual yield and only accounted for 6% of the yield variation. The N use efficiency of pastures improved with reduced N application rates. Pasture yield varies through different seasons. Spring and summer account for the highest yield, coinciding with warm and moist conditions favorable for N mineralization in the soil. Farmers need to consider the time of the year and plan their monthly or seasonal fertilizer application accordingly to account for peak N mineralization rates.
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    Grazing under irrigation affects N2O-emissions substantially in South Africa
    (MDPI, 2020-08-29) Smit, Hendrik P. J.; Reinsch, Thorsten; Swanepoel, Pieter A.; Kluss, Christof; Taube, Friedhelm
    Fertilized agricultural soils serve as a primary source of anthropogenic N2O emissions. In South Africa, there is a paucity of data on N2O emissions from fertilized, irrigated dairy-pasture systems and emission factors (EF) associated with the amount of N applied. A first study aiming to quantify direct N2O emissions and associated EFs of intensive pasture-based dairy systems in sub-Sahara Africa was conducted in South Africa. Field trials were conducted to evaluate fertilizer rates (0, 220, 440, 660, and 880 kg N ha−1 year−1) on N2O emissions from irrigated kikuyu–perennial ryegrass (Pennisetum clandestinum–Lolium perenne) pastures. The static chamber method was used to collect weekly N2O samples for one year. The highest daily N2O fluxes occurred in spring (0.99 kg ha−1 day−1) and summer (1.52 kg ha−1 day−1). Accumulated N2O emissions ranged between 2.45 and 15.5 kg N2O-N ha−1 year−1 and EFs for mineral fertilizers applied had an average of 0.9%. Nitrogen in yielded herbage varied between 582 and 900 kg N ha−1. There was no positive effect on growth of pasture herbage from adding N at high rates. The relationship between N balance and annual N2O emissions was exponential, which indicated that excessive fertilization of N will add directly to N2O emissions from the pastures. Results from this study could update South Africa’s greenhouse gas inventory more accurately to facilitate Tier 3 estimates.
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    Narrow rows and high maize plant population improve water use and grain yield under conservation agriculture
    (American Society of Agronomy, 2020-03-11) Haarhoff, Stephanus Johannes; Swanepoel, Pieter A.
    The relationship between maize (Zea mays L.) population density and grain yield is influenced by soil and crop management strategies, including Conservation Agriculture (CA). Yet little is known about the response of maize grain yield to varying plant population and/or row spacing under CA. A three‐year study was conducted under CA to evaluate the effects of plant population and row spacing on maize grain yield, plant available soil water and soil temperature. Plant populations ranging from 40 000 to 80 000 plants ha−1 were evaluated at three row spacings (0.5, 0.76 and 1.0 m). The response of maize grain yield to plant population was highly variable between seasons: it was not affected by plant population in the season with the highest early‐season rainfall but increased with increasing plant population in the driest season and in the season with well‐distributed near average rainfall. Higher plant populations resulted in lower soil water levels, presumably due to greater water extraction. Plant population affected soil water availability in the 20–80 cm soil layer in Season 2, while plant population affected soil water availability at all soil layers except the 10–20 and 60–80 cm soil layers in Season 3. Rapid maize leaf‐canopy closure provided by increased plant population and narrower row spacing is critical to adequately utilize the benefits associated with CA.
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    Vulnerability, institutional arrangements and the adaptation choices made by farmers in the Western Cape of South Africa
    (Taylor & Francis, 2019) Raaijmakers, Sanne; Swanepoel, Pieter A.
    From 2015 to 2018, South Africa suffered from the worst drought since 1904. Climate change is predicted to increase both the frequency and intensity of droughts in parts of South Africa. In this light it is evident that agricultural systems must adapt in order to sustain income and food security of rural populations. One set of adaptation measures offered to farmers centred on Conservation Agriculture (CA). Variation in the form and extent to which farmers embrace adaptation measures in response to drought has been observed. A study was set out to explain variation in the adoption of adaptation measures by testing the particular impact of vulnerability attributes, the effects of which – we hypothesise – are mediated by institutional arrangements. Our sample frame consisted of 30 farmers in two drought-stricken regions: the Swartland (n = 15) and southern Cape (n = 15). Variation on vulnerability attributes was guaranteed by the selection of commercial (n = 16) and emerging (n = 14) farmers. Our results showed that vulnerability attributes, especially the lack of financial, natural, human and physical capital, account for variation in form and extent of adopting CA adaptation measures. In order to ensure inclusive agricultural adaptation, efforts are needed to further facilitate equal adaptation opportunities, especially for marginalised farmers.