Pieter A Swanepoel

Assessment of tillage effects on soil quality of pastures in South Africa with indexing methods

Soil quality of pastures changes through time because of management practices. Excessive soil disturbance usually leads to the decline in soil quality, and this has resulted in concerns about kikuyu (Pennisetum clandestinum)–ryegrass (Lolium spp.) pasture systems in the southern Cape region of South Africa. This study aimed to understand the effects of tillage on soil quality. The soil management assessment framework (SMAF) and the locally developed soil quality index for pastures (SQIP) were used to assess five tillage systems and were evaluated at a scale inclusive of variation in topography, pedogenic characteristics and local anthropogenic influences. Along with assessment of overall soil quality, the quality of the physical, chemical and biological components of soil were considered individually. Soil physical quality was largely a function of inherent pedogenic characteristics but tillage affected physical quality adversely. Elevated levels of certain nutrients may be warning signs to soil chemical degradation; however, tillage practice did not affect soil chemical quality. Soil disturbance and the use of herbicides to establish annual pastures has lowered soil biological quality. The SQIP was a more suitable tool than SMAF for assessing soil quality of high-input, dairy-pasture systems. SQIP could facilitate adaptive management by land managers, environmentalists, extension officers and policy makers to assess soil quality and enhance understanding of processes affecting soil quality.

A critical view on the soil fertility status of minimum-till kikuyu–ryegrass pastures in South Africa

Cultivated pastures provide increased productivity and contribute inter alia to food security. Rangelands in the southern Cape region of South Africa have had a low animal production potential and were therefore improved through time as cultivated pastures. Initially, annual pastures were established by conventional tillage methods, but from the 1990s permanent pastures were established on a minimum-tillage regime. Lime and fertiliser guidelines, which were developed for annual pastures established by conventional tillage methods, were followed on minimumtillage systems, despite changes in the soil physical properties and stratification of biological parameters. The study aim was to survey the soil fertility of irrigated minimum-till kikuyu–ryegrass pastures in the southern Cape region. This study highlights changes in soil fertility and identified potential detrimental effects of elevated levels of extractable phosphorus and zinc, which were drastically increased in the topsoil layer. The necessity for remedial and preventative strategies to mitigate nutrient loading in cultivated pasture soil are stressed. Fertiliser guidelines should be applied strictly and should fit the farming system. In doing so, the dual goals of economic and ecological sustainability should be achieved.

Impact of cultivation method on productivity and botanical composition of a kikuyu–ryegrass pasture

Kikuyu (Pennisetum clandestinum)–ryegrass (Lolium spp.) cultivated pastures form the base for dairy production in the southern Cape region of South Africa. The impact of various methods and implements used to over-sow ryegrass on the productivity and botanical composition of the pasture is unknown. The study aimed to assess the impact of cultivation along a soil disturbance gradient on the productivity and botanical composition of kikuyu-based pastures. Five tillage treatments were assessed, namely kikuyu over-sown with ryegrass using a minimum till planter, eradication of kikuyu with herbicide and ryegrass sown with a minimum-till planter, shallow (<150 mm) and deep (>150 mm) disturbance with a rotavator or conventional tillage, respectively, and a control. The autumn, spring, summer and annual productions of treatments with the least soil disturbance were the highest (P ≤ 0.05). Shallow or deep tillage resulted in intermediate annual productions and the lowest (P ≤ 0.05) was recorded for the herbicide treatment. Differences in production caused by different tillage methods were significant (P ≤ 0.05) and changed the botanical composition. Kikuyu over-sown with ryegrass using a mulcher and minimum-till planter was the most viable option to manage cultivated pastures.

Managing cultivated pastures for improving soil quality in South Africa: challenges and opportunities

Loss of productive agricultural land due to soil degradation poses a serious threat to agricultural output and sustainability. Soil degradation of cultivated pastures manifests as a long-term decline in production potential. There are concerns that soils under pastures in certain regions of South Africa are degrading as a result of mismanagement, which include practising continuous tillage, improper grazing management, injudicious application of fertilisers and poor irrigation management. Soil quality indicators, which include physical, chemical and biological parameters in soil, are science-based methods to monitor sustainability and protect soil. Soil quality data informs the land manager in the decision-making process to address practices that degrade agro-ecological systems and mitigate any loss of function. The aim of this paper is to provide a synthesis of the challenges and opportunities in soil management of pastures. The value of assessing soil chemical, physical and biological indicators to monitor soil quality is stressed.

Production potential of Italian and Westerwolds ryegrass established at different planting dates

Fodder flow planning is essential for dairy-pasture systems because its implementation allows fodder to be available throughout the year. Italian and Westerwolds ryegrass varieties (Lolium multiflorum var. italicum and westerwoldicum, respectively) are temperate annuals often planted in the southern Cape region of South Africa. The monthly production potential of these grasses could be manipulated by planting date. The aim of this study was to determine the pasture production potential of Italian and Westerwolds ryegrass planted at different planting dates. Four cultivars of each variety were evaluated by sowing each cultivar in a factorial arrangement in a randomised complete block design every 28 days for two years. Planting date influenced the production potential of both varieties. If the requirement of a fodder flow programme is to provide fodder from May until November, which includes the critical winter months, Italian ryegrass is a better option than Westerwolds ryegrass and should be planted during February or March. If the aim is to have high production in spring and early summer, Italian ryegrass should be planted during May or June. Regardless of the variety, annual ryegrass should not be planted later than June.

Soil quality effects on regeneration of annual Medicago pastures in the Swartland of South Africa

Annual medic (Medicago spp.) pastures are widely used as the forage component of crop rotation systems in the Mediterranean region of South Africa. Reliable establishment of medics can be challenging. This may be related to poor soil quality, an inherent problem of soils in the region often aggravated by poor management. The aim of this study was to determine the underlying soil quality factors that result in classifying soils as having low, medium and high medic pasture production potential. The study was carried out on two farms that have followed crop/pasture rotation systems for the past 20 years. Two growing seasons (2015 and 2016) were evaluated on areas within fields that were identified to have poor, medium and high production potential. Soil samples were taken to evaluate soil quality and to determine the medic seed density in soil. Above-ground seed production and herbage production were monitored during the growing season. The low productivity soils had the lowest below-and above-ground seed density, medic seedlings establishment and medic herbage yield. Soil sodicity was one of the main factors decreasing pasture productivity. In a production system where medics need to regenerate effectively following good seed production, soil sodicity may be especially detrimental.

Considering soil quality when comparing disc and tine seed-drill openers for establishing wheat

Wheat (Triticum aestivum) is planted widely in the Western Cape of South Africa in conservation agriculture systems. Although most producers rely on tine openers to establish wheat, the interest in planters with disc openers is increasing. Given that the soils in the Western Cape are highly variable, it is hypothesised that soil quality may influence the choice of openers to use. The aim of this study was therefore to evaluate the effects of tine and disc openers in soils of contrasting qualities, to discern whether soil quality is a factor to consider when choosing between tine and disc openers. The study was conducted on Langgewens Research Farm. Soil disturbance was evaluated directly after sowing wheat with tine and disc openers. Tine openers disturbed the soil more (p < 0.05) than the disc openers in low quality soil, and did not differ (p > 0.05) from the disc opener effect in high quality soil. Establishment of wheat with disc openers resulted in an 11% yield increase as opposed to when established with tines. Grain yield was 24% higher in the high quality soils compared with the low quality soils. To ensure high yields, the importance of ensuring that soil quality is maintained, is stressed.

Livestock in diverse cropping systems improve weed management and sustain yields whilst reducing inputs

1. Intensive cropping systems select for a low diversity of weeds tolerant of chemical control, leading to persistent weed-crop competition and declining biodiversity. Crop rotation can mitigate this by introducing variable filters on the weed community through increasing management diversity. In this study, we investigate the effect of integrating livestock into no-till crop rotations to complement chemical weed control. 2. We analysed 12 years of weed seedbank data from a trial of eight rotation systems with different crop sequence diversities, of which four included grazed for- age phases. Linear mixed models and ordination were used to assess how weed abundance, diversity, and community composition responded to management filters, defined in terms of levels of disturbance strength and diversity (grazing and herbicides), and resource availability and diversity (inorganic fertilizers, legumes, and manure). 3. Grazed rotation systems had less herbicide applied than ungrazed rotation sys- tems, and had the lowest weed abundance and highest weed diversity. Herbicides and grazing apply contrasting selection pressures on weeds, and this combination was more effective in reducing weed pressure than increasing herbicide quantity or mode-of-action diversity. Lower resource availability and higher nitrogen source diversity in grazed systems may have further reduced weed abundance and promoted diversity. 4. Crop sequence diversity also reduced weed abundance and promoted weed diversity, indicating that variable crop-weed interactions can enhance weed management. In addition, yields in the main cash crop (wheat) were highest where crop diversity was highest, regardless of whether the system contained grazed phases. 5. Synthesis and applications. Diverse rotation systems produced high yields, and the inclusion of grazed forage phases maintained these yields at lower applications of herbicides and fertilizers: integrated livestock can therefore improve the sustain- ability of no-till systems. The role of grazing as a filter imposing a contrasting se- lection pressure to other weed control options could be further explored to improve weed management in different farming systems.

Southern African pasture science in the 21st century

African Journal of Range and Forage Science 2015, 32(2): iii–iv http://dx.doi.org/10.2989/10220119.2015.1060693 Copyright

Nodulation potential of four Trifolium repens cultivars under field conditions

Four Trifolium repens (white clover) cultivars were evaluated under field conditions to determine the potential of these cultivars to sucessfully develop Rhizobium-associated root nodules. Nodulation of T. repens is often poor, because of suboptimal environmental conditions or absence of host-specific rhizobia. The cultivars Huia, Haifa, Ladino and Regal were selected, as these are popular cultivars available in South Africa. Thousand seed mass (TSM) of each cultivar was measured to determine viability of seed and the possible interaction between TSM and nodulation. Mean TSM values of the cultivars differed significantly, with Huia having the highest TSM followed by Haifa, Ladino and Regal. Biomass production was also measured as an indicator of nitrogen fixation efficiency. The cultivar Huia, with the highest TSM values, resulted in the highest biomass production. Nodulation indices were determined from the size, number and colour of the nodules. All plants, regardless of cultivar, formed nodules within 8 weeks. It was concluded that TSM had no 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 under environmental conditions that prevailed during the study.