The relationship of Trifolium repens and T. ambiguum with host-specific Rhizobium bacteria for potential incorporation into sustainable, low N input pastures

Research on efficient management systems to optimise Trifolium repens-Rhizobium symbiosis, is lacking in South Africa. The amount of nitrogen (N) fixed by symbiotic rhizobia in root nodules of T. repens is ultimately determined by health of the soil environment. Soil organic matter (SOM) is the main attribute that will sustain soil health as it affects the chemical, physical and biological aspects of soil. The aim of this study was to determine the potential of T. repens and T. ambiguum to sustain low N input pastures. The hypotheses of this study is that SOM can play an important role in ensuring good soil health, which supports the optimum growth and production of Trifolium spp. in low N input pastures. Four Trifolium repens cultivars were evaluated in field conditions to determine the effect of Rhizobium bacteria on the potential of the cultivars to nodulate. The cultivars Grasslands Huia, Haifa, Ladino and Regal were selected for assessment. The thousand-seed-mass (TSM) of each cultivar was measured to determine the quality and viability of the seed; and to determine the interaction between seed mass and nodulation. Mean TSM values of T. repens cultivars differed significantly, with Huia having the highest TSM followed by Haifa, Ladino and Regal. Biomass production was also measured as an indicator of efficiency of nitrogen fixation. The cultivar Huia, with the heaviest seed, showed the highest biomass production. After eight weeks of growth, the nodulation index was determined from the size, number and colour of the bacterially associated root nodules. All plants, regardless of cultivar, formed nodules within eight weeks. It was concluded that TSM had no notable effect on nodulation. Planting date with associated temperature effects and the intrinsic cultivar effect also had no influence on nodulation. It was therefore concluded that nodulation potential of the four cultivars tested was similar in the specific environmental conditions. The total number of symbiotic rhizobial cells per gram of soil as affected by soil C content and the host plant was also determined. Inoculated and un-inoculated seeds were planted on five soil treatments, each with a different level of soil C. The plant infection technique (most-probable-number/MPN technique) was used to quantify the rhizobial numbers in soil as affected by soil C content and the host plant. The mean MPN-value ranged from 8907 to 78 Rhizobium cells per gram of soil for T. repens treatments, and 0 to 436 for T. ambiguum treatment. Soil C had no effect on the number of Rhizobium bacteria present in the soil. Inoculation however, had a significant effect on the MPN value of T. ambiguum, but not for T. repens. Most symbiotic Rhizobium was detected between a soil C content of 2.03% to 3.80% in both inoculated and non-inoculated soils. The spread plate count was used to determine the total number of symbiotic and saprophytic rhizobia. This method was used to quantify both symbiotic and free-living rhizobia. The effect of different levels of soil C on the amount of atmospheric N fixed was assessed by the N difference technique. Arctotheca calendula (cape weed) served as the reference plant in this study, to determine what percentage of N is derived from the atmosphere (%Ndfa). Biomass production was determined and served as the parameter to establish the efficiency of the Rhizobium bacteria in the soil. Inoculating seed with host specific rhizobia had no effect on the amount of N fixed. The mean %Ndfa differed significantly between soil organic C treatments with the species T. repens but did not differ significantly between soil organic C treatments with T. ambiguum. It was concluded from this study that symbiotic rhizobia introduced by inoculant was much more efficient in higher C content soils than free-living rhizobia, which highlights the importance of inoculation in improving the sustainable production of T. repens pastures. Although the amount of N fixed increased as the level of soil organic matter decreased, the efficiency of N fixation decreased proportionally. This explains the bigger change in soil N content on soil with a high C content. This study has thus highlighted the importance of soil organic carbon in the host specific Rhizobium inoculation sucsess, of T. repens low N input pasture systems.Dissertation (MSc(Agric))--University of Pretoria, 2010.Plant Production and Soil Scienceunrestricte

A prospectus for sustainability of rainfed maize production systems in South Africa

CITATION: Haarhoff, S. J., Kotze, T. N. & Swanepoel, P. A. 2020. A prospectus for sustainability of rainfed maize production systems in South Africa. Crop Science, 60(1):14-28, doi:10.1002/csc2.20103.The original publication is available at https://acsess.onlinelibrary.wiley.comThe rainfed maize (Zea mays L.) production systems of South Africa require an integrated approach to use the limited soil available water more efficiently, and to increase system productivity and sustainability. The soils across the major maize production regions are highly susceptible to wind and water erosion. Rigorous soil tillage, maize monoculture, and fallow periods are common, which depletes the soil from organic matter and nutrients. Despite the pressing need for transforming the highly degraded rainfed maize production systems, adoption of more sustainable management approaches has been limited, likely due to a shortage of local scientific field trials to evaluate current and alternative maize agronomic management practices. Erratic interseasonal rainfall patterns cause high variability in maize grain yields. Major challenges associated with no‐tillage are poor crop establishment, subsoil compaction, and high maize grain yield variability. The use of fallow in the maize–fallow production system leads to excessive runoff and soil erosion losses despite increased maize grain yields. Crop intensification and alternative crops are needed to increase rainfall water use efficiency and lower fallow frequency. The use of cover and forage crops may provide the opportunity to diversify and intensify maize production systems. Cover crop biomass could be beneficial in livestock‐integrated production systems providing livestock feed in either winter or summer. Research is drastically required to improve the understanding of current South African rainfed maize production systems and to facilitate the development of fitting sustainable agronomic management practices.https://acsess.onlinelibrary.wiley.com/doi/10.1002/csc2.20103Publisher's versio

The effect of soil carbon on symboitic nitrogen fixation and symbiotic Rhizobium populations in soil with Trifolium repens as host plant

Soil organic carbon (SOC) is the main attribute of high-quality soil. The amount of nitrogen fixed by Rhizobium symbiotically with Trifolium repens (white clover) is ultimately determined by the quality of the soil environment. The effect of SOC on the total number of symbiotic and saprophytic rhizobia was determined. Subsequently, the amount of nitrogen (N) fixed was assessed by using the N difference technique. Most Rhizobium was detected between a SOC content of 2.03% to 3.80% in both inoculated and non-inoculated soils. Inoculation increased the number of rhizobia in soil. Most N was fixed in the soil with the lowest SOC content. Although the amount of N fixed increased as the level of SOC decreased, the efficiency of N fixation decreased proportionally to SOC. Subsequently, more N was rhizodeposited. It was concluded that symbiotic rhizobia introduced by the inoculant were more efficient than free-living rhizobia in soils with higher carbon content, which highlights the importance of inoculation in improving the sustainable production of T. repens pastures.http://tandfonline.com/loi/tarf20nf201

Extent of soil acidity in no-tillage systems in the Western Cape Province of South Africa

CITATION: Liebenberg, A., et al. 2020. Extent of soil acidity in no-tillage systems in the Western Cape Province of South Africa. Land, 9(10):361, doi:10.3390/land9100361.The original publication is available at https://www.mdpi.comPublication of this article was funded by the Stellenbosch University Open Access FundRoughly 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.https://www.mdpi.com/2073-445X/9/10/361Publisher's versio

The quantification of biological nitrogen fixation by Trifolium repens as affected by soil organic matter

Management of the soil environment must receive special attention. Future research will not only be on increasing soil quality, but also on rectifying problems caused by our abusive past practices. Soil organic C is the main factor that influences soil quality, which will in turn determine sustainability and profitability.http://www.elsenburg.co

Eerlik met God in die krisisuur

Verhandeling (B. Th.) -- Universiteit van Stellenbosch, 1994.Full text to be digitised and attached to bibliographic record

Benefits are limited with high nitrogen fertiliser rates in kikuyu-ryegrass pasture systems

CITATION: Viljoen, C., Van Der Colf, J. & Swanepoel, P. A. 2020. Benefits are limited with high nitrogen fertiliser rates in Kikuyu-Ryegrass pasture systems. Land, 9(6):173, doi:10.3390/land9060173.The original publication is available at https://www.mdpi.comPublication of this article was funded by the Stellenbosch University Open Access FundNitrogen (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-Texthttps://www.mdpi.com/2073-445X/9/6/173Publisher's versio

Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system

CITATION: Tshuma, F., et al. 2021. Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system. Soil and Tillage Research, 212:105064, doi:10.1016/j.still.2021.105064.The original publication is available at https://www.frontiersin.orgNo-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.https://www.sciencedirect.com/science/article/pii/S0167198721001343Post prin

Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system

CITATION: Tshuma, F., et al. 2021. Effects of long-term (42 years) tillage sequence on soil chemical characteristics in a dryland farming system. Soil and Tillage Research, 212:105064, doi:10.1016/j.still.2021.105064.The original publication is available at https://www.frontiersin.orgNo-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.https://www.sciencedirect.com/science/article/pii/S0167198721001343Post prin

Tillage rotation and biostimulants can compensate for reduced synthetic agrochemical application in a dryland cropping system.

The effects of four continuous tillage regimes; mouldboard ploughing, tine-tillage, shallow tine-tillage, no-tillage; and three tillage rotations (involving shallow tine-tillage once every two, three, and four years in rotation with no-tillage), and two rates of synthetic agrochemicals (standard: with regular application of synthetic agrochemicals; and reduced: fewer synthetic agrochemicals in combination with biostimulants) on wheat and canola yield and quality were investigated between 2018 and 2020 under typical Mediterranean climatic conditions in South Africa. It was hypothesised that a combination of tillage rotations and the application of reduced synthetic agrochemicals will improve crop yield and quality relative to mouldboard ploughing or no-tillage. Results showed that a combination of reduced application of synthetic agrochemicals and tillage rotation practices maintained but did not significantly increase crop yield and quality, relative to no-tillage and mouldboard ploughing. Results also showed that intensive ploughing is unnecessary as it did not significantly increase yields (p>0.05). In addition, it is possible to reduce the quantity of synthetic agrochemicals applied by partially replacing them with biostimulants without significant changes in grain or seed yields and quality. We, therefore, suggest that producers opt for biostimulants in combination with no-tillage or tillage rotation as a sustainable way of farming