Wayne Frederick Truter

PLANT RESPONSES ON SOILS AMELIORATED WITH WASTE PRODUCTS

The South African mining industry has been the backbone of the countrys economy for much of the past century. Mining has, however, had major impacts on both agricultural resources and the urban environment. Rehabilitation of such impacted soils, which are often characterized by high acidity and low fertility, requires major inputs to ensure the successful establishment and sustainability of a protective and restorative vegetation. The safe use of biosolids has been made feasible by combining it with coal combustion products. The resultant product (SLASH) has been shown to have a positive effect on the pH, Ca, Mg and P of a moderately acid agricultural soil and on the production of a range of vegetable and flower crops. With a view to using such a product in the rehabilitation of impacted soils, SLASH was applied to an infertile soil and a range of forage species, used in different revegetation programs, were used as test crops. These included an annual cereal crop (Triticale -Triticum x Seca/e), commonly used to ensure early stabilization of minelands and/or as a stubble mulch for the establishment of perennial species, as well as perennial legumes (Sweet Clover -Melilotus alba and Crown Vetch Coronilla varia) and grasses such as KentuckY Bluegrass Paa pratensis, Tall Fescue Festuca arundinaceae and Buffelgrass Cenchrus ciliaris). SLASH had marked beneficial effects on productivity of forage as well as root development for as long as two years after initial treatment. Additional

Seasonal dry matter production, botanical composition and forage quality of kikuyu over-sown with annual or perennial ryegrass

The seasonal growth and low forage quality of kikuyu restrict milk production. The aim of this study was to determine the yield and nutritional value of irrigated kikuyu over-sown with perennial, Italian or Westerwolds ryegrass grazed by dairy cows. The three pasture systems reached optimum growth during different months and seasons. Lowest growth rates occurred during winter. Peak growth rates occurred during spring for the Italian ryegrass–kikuyu, summer for the Westerwolds ryegrass–kikuyu, and late spring and early summer for perennial ryegrass–kikuyu pasture. All three pasture systems had similar total annual dry matter yields (kilograms dry matter [DM] per hectare) during year 1, but the perennial ryegrass–kikuyu pasture achieved a higher annual DM yield during year 2. As kikuyu density increased in kikuyu–ryegrass pastures from winter to summer, the DM and neutral detergent fibre content increased, whereas the metabolisable energy content decreased. All three treatments were deficient in calcium during all seasons and in phosphorus during summer and autumn as a pasture for high-producing dairy cows.

The effect of soil carbon on symbiotic 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.

Grazing capacity, milk production and milk composition of kikuyu over-sown with annual or perennial ryegrass

Kikuyu (Pennisetum clandestinum) is a highly productive pasture species that supports high stocking rates and milk production per hectare, but production per cow is low due to low nutritive value. The aim of this study was to determine the grazing capacity, milk production and milk composition of dairy cows grazing irrigated kikuyu over-sown with Italian (Lolium multiflorum var. italicum), Westerwolds (L. multiflorum var. westerwoldicum) or perennial ryegrass (L. perenne) during autumn. The grazing capacity of the kikuyu–ryegrass systems was lower during winter and autumn than during spring and summer, with the seasonal grazing capacity of the perennial ryegrass treatment more evenly distributed than that of the Italian and Westerwolds ryegrass treatments. The perennial ryegrass treatment had a lower butterfat and milk production per lactation than the Italian and Westerwolds ryegrass treatments, but had the highest milk solids and fat corrected milk production per hectare. The latter was a result of the higher annual grazing capacity achieved by the perennial ryegrass treatment. It was concluded that because kikuyu over-sown with perennial ryegrass supported a higher number of animals and had a more evenly distributed fodder-flow, it achieved higher animal production per hectare than kikuyu over-sown with annual ryegrass varieties.

Southern African pasture and forage science entering the 21st century : past to present

Given the global challenges of mitigating and alleviating land degradation and ensuring food security, particularly through protein production, pasture and forage science together with rangeland science will remain imperative to sustainable livestock production systems. Recognising the scientific principles developed in this discipline the past 50 years and more in Southern Africa, customary to our diverse and unique environmental conditions will continue to guide and identify future research priorities. A journey from the past to the present can assist in avoiding reinvention and repetition of pasture research. This review highlights how research priorities have either remained the same over time or where research has received less or more priority. The review further illustrates that there has been more interest in species adaptation to drought, pasture and forage water relations, alternative pasture and forage species, and the combination of pasture species in the 21st century than in the 20th century. In conclusion, the soil–plant– livestock complex can serve as a conceptual basis for more effective research together with pasture breeding and nutrition. Finally, researching pasture and forage sciences in an inter- and multi-disciplinary manner clearly supports the principles of holism applied by General JC Smuts, one of the first pioneers of pasture and forage sciences.

Performance of simple irrigation scheduling calendars based on average weather data for annual ryegrass

Poor irrigation management in pastures can lead to yield and quality reduction as well as loss of income through extra pumping and leaching of nitrate fertiliser. A number of irrigation scheduling techniques of varying levels of sophistication have been developed over the years to address limited irrigation water availability and maximise productivity. Despite this, the adoption of irrigation scheduling tools by farmers remains low. The objective of this study was to assess the use of simple irrigation scheduling calendars based on average weather data to improve irrigation management in ryegrass. The calibrated Soil Water Balance (SWB) model was used to generate simple irrigation calendars and assess effectiveness for different scenarios by mechanistically simulating water dynamics and pasture growth. Scheduling irrigation using the calendars gave similar irrigation applications, water losses and yields compared to a more scientific real-time scheduling (in response to soil water depletion by the crop). While site-specific irrigation scheduling calendars can easily be generated by consultants and irrigators, even simpler monthly estimates of average daily water use can also be useful. Application of calendars by farmers is encouraged to improve water and nutrient use efficiency of irrigated pastures, if real-time irrigation scheduling is not employed.

Forage yield and quality response of annual ryegrass (Lolium multiflorum) to different water and nitrogen levels

Water and nitrogen shortages in annual ryegrass (Lolium multiflorum) production can be improved by using proper irrigation and nitrogen scheduling methods. The aim of this research was to analyse the effect of water and nitrogen application on dry matter production and forage quality of annual ryegrass. Treatments consisted of three irrigation levels, scheduling application to field capacity once every two weeks (W1), once a week (W2) or twice a week (W3), and three nitrogen (N) levels, top-dressing after each harvest at a rate of 0 (N1), 30 (N2) or 60 (N3) kg N h−1 cycle−1. Yield increased as a function of the amount of water and nitrogen fertiliser applied. The dry matter (DM) content, in vitro organic matter digestibility (IVOMD), crude protein (CP) and metabolisable energy (ME) were higher in the treatments being irrigated once every two weeks. These results conclude that higher irrigation coupled with high N application significantly improved the dry matter yield, while water stress, to some extent, did improve the quality of the pasture by increasing the DM content, IVOMD, CP and ME values.

Yield, resource use efficiency and trace metal uptake of weeping lovegrass grown on municipal sludge‐amended soil

BACKGROUND There are concerns that fertilization using sludge in semi-arid areas, where water is limiting, will compound the effect of drought, resulting in the decline of yield from potential salt accumulation. This study investigated impacts of annual sludge application at 0, 4, 8 and 16 Mg ha-1 on weeping lovegrass hay yield, crude protein (CP) content, rainfall use efficiency (RUE), nitrogen use efficiency (NUE) and trace metal uptake over eight consecutive years. RESULTS Both hay yield and RUE increased by 5-53% as the sludge rate increased. Hay yield was highest (13.3 Mg ha-1 ) during the wet season and RUE (27.1 kg mm-1 ) during the dry season. RUE was highest at sludge rates of 16 Mg ha-1 and NUE at 4 Mg ha-1 . Similarly, municipal sludge application increased CP content as well as crop Cr and Zn uptake from the 16 Mg ha-1 treatment. CONCLUSION Results from this study indicated that eight consecutive years of treated municipal sludge application increased weeping lovegrass hay yield, CP content and RUE. Similarly, trace metal uptake by crop did not differ between the zero control and the 16 Mg ha-1 treatment, except for Zn and Cr, which showed a slight increment. Nonetheless, all trace metals remained well below the maximum tolerable dietary concentrations for domestic animals.

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.