Browsing by Author "Labuschagne, Johan"

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    Canola is injured by in‐row nitrogen placement associated with disc openers, but not by tine openers
    (Crop Science Society of America, 2020) Swanepoela, Pieter A.; Labuschagne, Johan
    Seed drills are used in no‐tillage systems to place seed directly in soil. Various furrow openers exist, each with unique seed and fertilizer placement characteristics, particularly positioning of fertilizer in relation to the position of the seed. Seedling damage may occur if seed and fertilizer placement is not appropriate for the particular crop. Canola (Brassica napus L.) seed is small, resulting in seedlings susceptible to injury by fertilizers. A study was conducted to evaluate the effect of in‐row N placement with a seed drill fitted with single‐ and double‐chute tine openers, and disc openers. The study was performed in a Mediterranean‐type climate region in South Africa over 2 yr. Plant establishment was reduced by 48% when canola was established with disc openers with no separation between N and the seed (P < .05). Tine openers were most successful in establishing an acceptable plant population, as well as ensuring high biomass production throughout the season, leading to a high leaf area index. Although no yield differences (P > .05) were observed between openers, it was concluded that the application of N in the band at the same position as the seed is a risk. Tine openers, either with a single or double seed chute, that separate seed and fertilizer resulted in the best canola performance.
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    Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system
    (Elsevier, 2021) Tshuma, Flackson; Rayns, Francis; Labuschagne, Johan; Bennett, James; Swanepoel, Pieter Andreas
    No-tillage can improve soil quality but can also increase the stratification of soil chemical parameters. Nutrient uptake by crops might be limited when nutrients are stratified, especially in semi-arid or Mediterranean regions. To reduce stratification, infrequent tillage could be considered. However, there is a paucity of information on the effects of long-term infrequent tillage on the stratification of soil chemical parameters. This study aimed to assess the effects of long-term infrequent tillage on the stratification of selected soil chemical parameters to a depth of 300 mm. The research was conducted on a long-term (42 years) research site at Langgewens Research Farm in South Africa. Seven tillage treatments were investigated: continuous mouldboard ploughing to a depth of 200 mm, tine-tillage to 150 mm, shallow tine-tillage to 75 mm, no-tillage, shallow tine-tillage every second year in rotation with no-tillage, shallow tine-tillage every third year in rotation with no-tillage and shallow tine-tillage every fourth year in rotation with no-tillage. Tillage treatments had differential effects on the distribution of soil chemical parameters. The mouldboard plough prevented stratification of most soil chemical parameters, such as soil acidity, soil organic carbon (SOC), extractable P, exchangeable Ca and Mg and cation exchange capacity (CEC). However, mouldboard ploughing also led to significantly lower SOC stocks and extractable P stocks. The SOC stocks and extractable P stocks of the no-tillage treatment were not significantly different from those of the infrequent tillage treatments. Overall, the infrequent tillage treatments were no better (P > 0.05) than the no-tillage treatment as infrequent tillage could not effectively ameliorate the stratification of most soil chemical parameters and did not increase the stocks and stratification ratios of SOC and extractable P.
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    Extent of soil acidity in no-tillage systems in the Western Cape Province of South Africa
    (MDPI, 2020) Liebenberg, Adriaan Louwrens; Van Der Nest, John Richard (Ruan); Hardie, Ailsa G.; Labuschagne, Johan; Swanepoel, Pieter Andreas
    Roughly 90% of farmers in the Western Cape Province of South Africa have converted to no-tillage systems to improve the efficiency of crop production. Implementation of no-tillage restricts the mixing of soil amendments, such as limestone, into soil. Stratification of nutrients and pH is expected. A soil survey was conducted to determine the extent and geographical spread of acid soils and pH stratification throughout the Western Cape. Soil samples (n = 653) were taken at three depths (0–5, 5–15, 15–30 cm) from no-tillage fields. Differential responses (p ≤ 0.05) between the two regions (Swartland and southern Cape), as well as soil depth, and annual rainfall influenced (p ≤ 0.05) exchangeable acidity, Ca and Mg, pH(KCl), and acid saturation. A large portion (19.3%) of soils (specifically in the Swartland region) had at least one depth increment with pH(KCl) ≤ 5.0, which is suboptimal for wheat (Triticum aestivum), barley (Hordeum vulgare), and canola (Brassica napus). Acid saturation in the 5–15 cm depth increment in the Swartland was above the 8% threshold for production of most crops. Acid soils are a significant threat to crop production in the region and needs tactical agronomic intervention (e.g. strategic tillage) to ensure sustainability.
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    Nitrogen management strategies on perennial ryegrass-white clover pastures in the Western Cape Province
    (Stellenbosch : University of Stellenbosch, 2005-03) Labuschagne, Johan; Agenbag, G. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Agronomy.
    The response of perennial ryegrass and white clover, grown under controlled conditions, to fertiliser N rates applied under variable soil temperature (6, 12 and 18 °C), soil water potential (-10, -20, -25 and -35 kPa) and seasonal growing (June/July and October/November) conditions as well as field conditions, were evaluated. Primary- (PDM), residual- (RDM) and total dry matter (TDM) production (g pot-1) were recorded over the first- and second regrowth cycles as well as the accumulative DM production over the two regrowth cycles, respectively. Leaf N content (%) was recorded at the end of first and second regrowth cycles. Tiller/stolon numbers and root dry mass (g pot-1) were recorded at the end of the second regrowth cycle. Soil ammonium-N and nitrate-N (mg kg-1) content was monitored after fertiliser N application. Decreasing soil temperatures resulted in decreased TDM production in both crops. Only perennial ryegrass was influenced by fertiliser N rate, with a general increase in dry matter production as fertiliser N rate was increased. Ryegrass TDM production did not differ between the 100 and 150 kg N ha-1 rates but were both higher (P=0.05) if compared to the 0 and 50 kg N ha-1 treatments. Soil nitrate levels 31 days after application of 150 kg N ha–1 were still sufficient to stimulate ryegrass RDM production. The 173.8% increase in ryegrass TDM production measured at 6 °C where 150 kg N ha-1 was applied compared to the 0 kg N ha-1 treatment illustrated the ability of ryegrass to respond to fertiliser N at low soil temperatures. Soil water potential of -20 kPa resulted in higher ryegrass PDM and TDM production compared to the -25 and -35 kPa levels. White clover PDM and TDM production were however not influenced by soil water potential or fertiliser N rate. Ryegrass TDM production increased (P=0.05) as fertiliser N rates were increased. The most favourable soil water level for both ryegrass and clover root development was found to be -35 kPa. Perennial ryegrass and white clover PDM, RDM and TDM production were higher during the October/November season compared to the June/July season. Increased fertiliser N rates resulted in increased (P=0.05) ryegrass PDM and TDM production. White clover dry matter production was not influenced by fertiliser N rates. In the field study the effect of 0, 50, 100 and 150 kg N ha-1 applied as a single application either in autumn, early winter, late winter, early spring or late spring on pasture dry matter production, clover content and selected quality parameters of a perennial ryegrass-white clover pasture were investigated. Soil nitrogen dynamics in the 0-100, 200-300 and 400-500 mm soil layers were studied for 49 days following fertiliser N application. The effect of 50 kg N ha-1 on soil N dynamics was generally the same as found at the 0 kg N ha-1 applications and may therefore be regarded as a low risk treatment. The application of 150 kg N ha-1 especially in autumn and early winter showed a tendency to exceed the absorption capacity of the pasture and thereby expose fertiliser N to possible leaching and contamination of natural resources. Increased fertiliser N rate resulted in a general increase in pasture dry matter production with the highest yields recorded where N was applied in early and late spring and the lowest in early winter. The application of 150 kg N ha-1 in early and late spring resulted in the highest TDM production, however, the 50 kg N ha-1 resulted in a more efficient conversion of N applied to additional DM produced. In contrast to DM production, the clover percentage generally decreased as fertiliser N rate was increased. The effect of season of application was inconsistent. Annual trends show that the clover percentage eventually recovered to the same levels as the 0 kg N ha-1 treatments. Due to the above minimum levels recorded for most mineral and quality parameters tested it is envisaged that treatment combinations as used in this study will not be at any disadvantage to pasture and animal productivity. The study has shown that the use of fertiliser N to boost perennial ryegrass-white clover productivity and thereby minimising the negative effect of the winter gap on fodder flow management during the cool season in the Western Cape Province, may be an important management tool. Except for late spring applications, all seasons of application reduced the negative impact of the winter gap on fodder availability. It is concluded that regression lines as summarised in Tables 7.2 and 8.2 show great potential to be instrumental in developing regression models, accurately predicting the effect of fertiliser N rate on pasture performance. Other factors to be considered includes the productivity of the pasture, initial clover content, expected clover content at the end of the first regrowth cycle after fertiliser N application and the quantity of additional fodder required. Additional requirements will be to maintain and 150 kg N ha-1) in winter, as the N uptake capacity of the pasture could be exceeded and thereby increasing the risk of N leaching, resulting in environmental pollution. The N response efficiency of the pasture is also the lowest at the 150 kg N ha-1 rates, thereby reducing the profitability of these treatments.