Department of Agronomy

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Agroecosystem diversification for sustainability : the effects of crop rotation on soil microbial diversity, fertility and yield
(Stellenbosch : Stellenbosch University, 2016-03) Venter, Zander Samuel; Hawkins, Heidi-Jayne; Jacobs, Karin; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Agricultural intensification can involve the simplification of agroecosystems to crop monocultures requiring agrochemicals to maintain soil fertility and control pests. This can have negative impacts on the ecosystem services flowing to and from agroecosystems and thus, more sustainable management practices are necessary. Broader ecological theories propose that ecosystem biodiversity is important for ecosystem function. Within agriculture, increasing aboveground diversity through crop rotation, a component of conservation agriculture, can enhance the ecosystem services supporting an increase in cash-crop yield. The extent to which the belowground microbial diversity can be manipulated through crop rotations and may facilitate the yield increase is unclear. This thesis aimed at investigating (1) the relationship between above and belowground diversity in crop rotation systems, and (2) the relationship between diversity in (1) and agroecosystem function in terms of soil fertility, including nitrogen fertility, and crop yield. A quantitative review of the literature using a meta-analysis of 27 studies from around the world found that soils under a higher diversity of crops in rotation produced higher microbial richness (+15.11%) and diversity (+3.36%) scores. This effect was significantly influenced by the type of microbial analysis method used, the length of the study trial, and the percentage annual ground cover. There was a high between-study heterogeneity and no correlation to soil nitrogen fertility. A field study at Langgewens Experimental Farm (Western Cape Department of Agriculture’s 19-year wheat-legume crop rotation trial in the Swartland Local Municipality of South Africa) added to the meta-analysis. Community level physiological profiling (CLPP) and automated rRNA intergenic spacer analysis (ARISA) were used as measures of functional and genetic microbial diversity, respectively. Increasing crop diversity through rotations of wheat with medic (Wm) or a combination of medic and clover (Wmc) resulted in greater wheat plant stem length and N concentrations when compared to wheat monoculture (WW). This effect seemed to be less linked with microbial diversity per se than with the Rhizobium species present because both microbial analyses found no differences in soil microbial activity, richness or diversity with increasing crop diversity. The lack of relationship between above and belowground diversity is likely due to other abiotic drivers of microbial community structure such as P availability, Na and K excess, and pH, all of which correlated to microbial activity and functional richness in our study. The role that microbial diversity plays in the agroecosystem diversity-function relationship remains complex as revealed by the lack of correlation between functional and genetic diversity scores. However, the relation between crop diversity and functional components including wheat yield and soil N followed a hump-shaped curve. The results of this thesis suggest that soil biodiversity and function are decoupled in agroecosystems. This provides support for the hypothesis that ecosystem function may be a product of either specific productive species (selection effect), or the facilitative interaction of multiple species (complementarity effect). Further investigation into the role of specific functional microbial groups in the yield increase of crop rotation systems using next-generation sequencing is required.
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.
Allelopathic effects of green manure cover crops on the germination and growth of blackjack (Bidens pilosa L.) and rapoko grass [Eleusine indica (L.) Gaertn]
(Stellenbosch : Stellenbosch University, 2018-03) Rugare, Joyful Tatenda; Pieterse, P. J.; Mabasa, Stanford; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: The use of green manure cover crops to improve the nitrogen levels of soils and other physical as well as biological soil properties has been extensively researched and documented in several parts of the world. However, there is paucity of information on their use in weed management particularly through the exploitation of their allelopathic properties on some of the difficult to control weeds in arable crop production. Identification and integration of cover crops with weed suppressive ability is likely to reduce overreliance on herbicides and tillage-associated soil degradation. Moreover, the use of allelopathic mulches is likely to solve the problem of early season weed pressure commonly experienced in conservation agriculture where the use of pre-emergence herbicides is practically ineffective due to the presence of mulch at the time of planting. This study sought to establish the allelopathic potential of cover crops and evaluate their efficacy in suppressing weeds when their aqueous extracts and residues were used for weed control in maize. The study comprised different sets of experiments and was conducted between 2014 and 2017 at the University of Zimbabwe. The first study involved laboratory evaluation of 0, 1.25, 2.5, 3.75 and 5% wv-1 aqueous extracts of dry leaf, stem and root residues of ten cover crops on the germination, plumule and radicle growth of two test weed species namely, goosegrass (Eleusine indica (L.) Gaertn) and blackjack (Bidens pilosa L.) as well as of the crop species maize (Zea mays L.). The cover crops used included jack bean (Canavalia ensiformis (L.) DC), velvet bean (Mucuna pruriens (L.) DC var utilis), hyacinth bean (Lablab purpureus L), red sunnhemp (Crotalaria ochroleuca G. Don), showy rattlebox (Crotalaria grahamiana Wight & Arn.), common bean (Phaseolus vulgaris L.), common rattlepod (Crotalaria spectabilis Roth.), radish (Raphanus sativus L.), tephrosia (Tephrosia vogelii L.) and black sunnhemp (Crotalaria juncea L.). There was a significant interaction between extract concentration and extracted tissue with all cover crops and with all studied germination parameters of goosegrass and blackjack. Results showed that extracts of all cover crops exhibited an allelopathic potential on both test weeds that decreased in the order leaf > stem > root extract except with radish whose root extracts were more phytotoxic than extracts of the other tissues on goosegrass. In contrast, maize germination was not affected by aqueous extracts of the cover crops except for extracts of jack bean and common rattlepod. Most of the cover crops reduced seedling growth of maize except extracts of hyacinth bean and tephrosia. The second study involved an assessment of the allelopathic potential of soil incorporated biomass of the different cover crop tissues on the emergence and dry weight of goosegrass, blackjack and maize. The experiment which was laid out as a Complete Randomised Design (CRD) was carried out in the greenhouse. The soil incorporated leaf, stem and root residues of all cover crops significantly affected seedling emergence, dry weight and vigor indices of both weeds. Overall jack bean and hyacinth bean residues exhibited the highest phytotoxic activity on weed seedling emergence and growth. On the other hand, none of the cover crop residues exhibited deleterious effects on maize emergence, dry weight and vigor indices. Samples of the cover crop tissues were subjected to Liquid Chromatography Mass Spectrometry (LC-MS) at the Central Analytical Facilities (CAF) at Stellenbosch University in order to determine the phenolic composition of the extracts. The analyses showed the presence of kaempferol, naringenin, rutin, and genistein in jack bean. On the other hand genistein, atropine and kaempferol were detected in velvet bean tissues. A new compound was detected in the tissues of both cover crops and was tentatively identified as quercetin 3-O-glucoside 7-O-rhamnoside. Thereafter, standards of compounds detected in the samples were used to carry out germination bioassays using goosegrass and blackjack as test species. Highest inhibition of seedling growth of the two test weed species was obtained with standards of kaempferol and rutin. The effect of post emergence sprays of aqueous extracts of jack bean and velvet bean alone or in combination with reduced atrazine dosages on the test weed species and maize was evaluated in a greenhouse experiment that was laid out as a CRD. Application of the different treatments at the 3-4 leaf stage of test species significantly reduced chlorophyll content, plant height, and dry weight and resulted in irreversible weed damage at 6 and 10 days after spraying of blackjack and goosegrass, respectively. Maize was not affected by the repeated post emergence applications of the different herbicidal treatments. Field experiments were carried out during the summer cropping seasons 2014-15 to 2016-17 on two fields at the University of Zimbabwe and on one field at CIMMYT, Harare station in Zimbabwe. A Randomised Complete Block Design (RCBD) was used to evaluate the effect of different maize-cover crop rotations on the weed community composition. Soil samples were taken at 0-5, 5-10 and 10-15 cm depths in a bid to evaluate the influence of maize-cover crop rotations on weed seed bank size and species composition in an experiment that was laid out as a split plot design under greenhouse conditions. The results showed that there were no significant differences in weed density and species composition among maize-cover crop rotations in all seed banks. However, there was a significant decline in weed densities in the second maize phase of the rotations. Weed species richness, evenness and diversity was also significantly affected in the second year of the rotation although there were no significant variations among maize-cover crop rotations. Generally, cover crop rotations significantly reduced blackjack density in the second maize phase of the rotation but the density of goosegrass remained unchanged. The effect of maize-cover crop rotation type on weed emergence was significant. Maize-velvet bean and maize-red sunnhemp rotations consistently reduced total weed density and biomass across seasons. However, the different cover crop rotations did not exhibit deleterious effects on maize emergence and height. Based on the findings of this study it can be concluded that all the cover crops are allelopathic to goosegrass and blackjack and could be used to manage weeds either as surface mulches in maize-cover crop rotations or as post emergence sprays when weeds are still very small.
Application of Hazard Analysis Critical Control Points (HACCP) in improving the global competitiveness of the fish industry with special reference to the Nile Perch (Tanzania)
(Stellenbosch : Stellenbosch University, 2000-03) Mlolwa, Mwanaidi Ramadhani; Hoffman, Louwrens C.; Stellenbosch University. Faculty of AgriScience. Dept. of Agronomy.
ENGLISH ABSTRACT: Not only have non-trade barriers been applied in Europe and the US to agricultural products from developing countries, but protective policy is also likely to continue. Owing to the omission of fish from the discussions in the final round of agreement at Uruguay, where tariffs were significantly reduced for other agricultural products, the fish industry has not had any non tarriff barier relief in recent years. The failure of the November 1999 World Trade Organisation Meeting at Seattle to reach any agreement, has again shattered hopes of international relief for fishery products. The main assumption underlying the study was that the production of fish in Tanzania could improve significantly if the HACCP (Hazard Analysis Critical Control Points) principles were applied rigorously. It was believed that neither the prerequisite programmes, nor HACCP principles were probably applied as stringently as international standards require. The aim of the study was to review the literature on HACCP, programmes that are prerequisite for HACCP and factors that_ determine competitiveness in business and to examine the Tanzanian Nile perch industry against this background. The overall goal was to determine how the industry could become more internationally competitive. This was achieved by comparing the socio-economic reality of Tanzania with factors that are considered in the literature to affect competitiveness in general and in the fish industry specifically. To achieve the first of these aims, Tanzania's socioeconomic position as a developing country was examined. To achieve the latter, the commitment of fish processing factories to the application of HACCP principles and their compliance with prerequisite programmes were evaluated in a field study. The literature study confirms that HACCP has received international recognition in the fish industry as a factor to prevent hazards and gain competitiveness in the global fish market. However, conditions in Tanzania were shown to be insufficient to support the fisheries sector in attempting to gain such a competitive advantage. Although, Tanzania has the comparative advantage of a fishery resource base, a favourable trade policy and foreign technology and management, the macro-factors that include the infrastructure, human resource capital, foreign policy environment and the supporting industries are not supportive. For the time being, therefore, improvement can only come from the government and from the industry itself. There are several factors to which the government needs to pay attention in order to support this industry - and others - in achieving international success. These include the provision of infrastructure and facilities, the improvement of the transportation network, technological capabilities, human resource capital and the provision of safe water and electric power. However, the fish industry cannot rely on the government alone. The improvement of their product is also dependent on their own efforts. According to the findings of this study, the industry needs to comply with the basic sanitation factors and provide the necessary training to the employees and fish suppliers. Having examined the situation more closely, the assumption is proved to be correct. The fish industry in Tanzania does indeed appear to have the potential to become internationally competitive. Such success, however, will be heavily dependent on cooperation between the government and the industry
Aspects of honeybush tea (Cyclopia species) propagation
(Stellenbosch : Stellenbosch University, 2008-12) Mbangcolo, Mongezi Morrison; Reinten, E.; Agenbag, G. A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
Honeybush (Cyclopia spp. Fabaceae) is indigenous to the fynbos botanical biome of the Eastern and Western Cape of South Africa. The increase in the international demand for honeybush tea for health benefits, concern over exploitation of wild populations and the lack of published agronomic information necessitated this study to evaluate different aspects of honeybush propagation. The main objectives of this study were to evaluate the effect of species and cutting position on rooting of cuttings of Cyclopia species using different rooting hormones, to evaluate the effect of an organic plant fertilizer and cutting position on growth and establishment of rooted cuttings and to study the influence of different seed pre-treatments on germination of Cyclopia species. Terminal and sub-terminal cuttings of C. intermedia and C. genistoides treated with different rooting hormones were rooted under day/night temperature controlled glasshouse conditions. Intermittent mist was used as means of moisture supply to the cuttings for 45-60 seconds daily every 30 minutes. C. genistoides rooted significantly better compared to C. intermedia as measured by rooting percentage, number of roots per cutting, length of longest root and mean root length during the summer season. The cutting position had a significant effect on rooting of the cuttings in summer compared to winter and spring season. The interactive effect of species, treatment and cutting position resulted into 86% of rooting in summer from the terminal cuttings of C. genistoides, while only 4% was recorded as the highest rooting percentage in both winter and spring seasons. The highest number of roots and the greatest root length per cutting were obtained with 2 and 4 g L-1 IBA from terminal cuttings of C. genistoides and these hormone concentrations were not significantly different to each other. To evaluate the effect of an organic plant fertilizer and cutting position on plant growth and establishment, rooted cuttings of two Cyclopia species (C. intermedia and C. genistoides) from two cutting positions (terminal and sub-terminal) were transferred to pots (576 cm3) and treated with Nitrosol fertilizer at application rates of 3.33 ml.L-1, 1.67 ml.L-1 and 0 ml.L-1 (control). Cyclopia plantlets were uniformly inoculated once with a symbiotic Rhizobium bacteria to improve the formation of nodules. Nitrosol® at 3.33 ml.L-1 significantly affected fresh and dry plant weight, fresh and dry root weight, number of shoots and nodules per plant compared to either 1.67 ml.L-1 or the control. Relative to species, C. genistoides performed better in terms of fresh and dry plant weight, fresh and dry root weight, and number of shoots and nodules per plant compared to C. intermedia. The origin of the cutting position did not significantly affect the above mentioned parameters. Plant mineral analysis revealed that most of the essential elements increased with increasing Nitrosol® application rates, with C. genistoides having higher levels of mineral elements than C. intermedia. This could be an indication of the differences between the two species in terms of nutrient uptake, utilization and distribution within the plant tissues. In the germination studies, seeds obtained from different seed sources of Cyclopia species were subjected to different pre-sowing treatments. Seed treatments were sulphuric acid (95%), hot water (100°C), water with smoke paper disk, and demineralised water (control). The study revealed that all the treatments had a significant effect on germination with the exception of eight year old seeds obtained from C. subternata (seed source two). Although hot water treatment improved germination compared to smoked paper disk and the control, seeds treated with hot water degenerated rapidly. The highest overall germination (77.33%) was found with one year old seeds compared to other seed sources older than one year. Although smoked paper disks generally did not improve germination compared to the control, in one year old seeds from seed source one, this treatment greatly influenced germination, suggesting that seed age might have influenced germination of these seeds. In terms of germination rate, germination generally started after four days in most treatments.
Benefits are limited with high nitrogen fertiliser rates in kikuyu-ryegrass pasture systems
(MDPI, 2020) Viljoen, Charne; Van der Colf, Janke; Swanepoel, Pieter Andreas
Nitrogen (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-Text
Biomass production, yield and quality response of spring wheat to soil tillage, crop rotation and nitrogen fertilisation in the Swartland wheat producing area of South Africa
(Stellenbosch : University of Stellenbosch, 2003-03) Maali, Safiah Hasan; Agenbag, G. A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Agronomy.
ENGLISH ABSTRACT: A long term experiment was conducted at the Langgewens Experimental Farm, near Malmesbury in the Western Cape province of the Republic of South Africa. The effect of soil tillage, crop rotation and nitrogen fertiliser rates on mineral-N levels in the soil, nitrogen levels in plants, wheat growth and yield components, grain yield as well as quality parameters of spring wheat were determined. Although the tillage treatments tested were initiated in 1976, present crop rotations and nitrogen application rates were only applied since 1990. Most of the data that are discussed however was recorded during the 1997 to 2001 period. The trial was designed as a randomised complete block with a split-plot arrangement and four replicates. Main plots were tillage methods namely conventional tillage (CT), tine tillage (TT), minimum tillage (MT) and no tillage (NT). Crop rotations used were continuous wheat (WW) and wheatl lupin/wheat/canola (WLWC). Both soil and crop data were recorded. The results of this study showed the differences in total mineral-N content of the soil. N-contents of wheat, wheat growth and yield components as well as wheat quality parameters were found between tillage treatments, crop rotations used as well as N- fertiliser rates applied. Response however, varied largely between years due to annual variation in especially total precipitation and distribution of rainfall. The inclusion of a legume crop (lupin) and canola in the rotation with wheat was found to have only a small effect probably due to the fact that lupins were grown once in a four year cycle only. Application of different nitrogen rates did increase the mineral-N in the soil, but the effect did not last very long in most years due to either N-leaching or plant uptake. To ensure sufficient mineral-N levels, late application of N-fertiliser will therefore be needed. Minimum tillage or reduced tillage performs better than conventional tillage in low rainfall years. In general these tillage systems should be combined with crop rotation to ensure that yields are comparable to that obtained with conventional tillage.
Bionomics and control of the fruit flies, Ceratitis capitata (Wied.) and Pterandrus rosa (Ksh.), in the Western Cape Province
(Stellenbosch : Stellenbosch University, 1956-03) Myburgh, Andre Cyril; Nel, R. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: no abstract available
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.
A comparison of experimental designs for cultivar evaluations
(Taylor and Francis, 2020) Saul, Hae; Booyse, M.; Swanepoel, P. A.
Spatial heterogeneity and the lack of clear or significant treatment responses in agricultural field experiments complicates recommending the most suitable cultivar(s) to producers for a specific area. Increased attention should be given to the experimental design of cultivar trials, as failure to capture spatial heterogeneity may increase the unexplained variance and thus might influence the accuracy of results. A randomised complete block design (RCBD) is the most popular design in variety trials in South Africa. However, latinised row-column designs (LRCD) is widely recommended in literature for field experimentation, because of the efficiency to control heterogeneity in two dimensions. The aim of this study was to compare the efficiency of RBCD with LRCD and recommend the more appropriate design for use by practitioners in cultivar trials. Wheat (Triticum aestivum) was used as a test crop. An analysis of variance was performed on the data produced from both designs conducted on wheat in the Swartland region of South Africa over a two-year period. An LRCD provided better accuracy and model or design estimations than RCBD. The results demonstrated the value of eliminating variance in two directions rather than one direction. We therefore recommend the use of LRCD in preference to RCBD in variety trials.
Controlled release fertiliser as a management tool for productivity of tunnel-grown tomatoes
(Stellenbosch : Stellenbosch University, 2022-04) Potgieter, Johan; Le Roux, Marcellous; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: To be able to grow crops such as tomatoes on a commercial scale under stringent controlled conditions in what is termed controlled environment agriculture (CEA), requires a great amount of expertise and technology. Therefore, the aim of this study was to see if the use of controlled release fertilizer as an alternative low expertise and low technology-based fertilization method could produce the same yields and marketability than the conventional fertigation fertilization methods used in greenhouse tomato production. The study assessed this by (1) determining if the ratio of perlite to coco coir in the growth medium had any effect on the yield response to an industry recommended controlled release fertilization recommendation, (2) trying to establish an appropriate mixing ratio of controlled release fertilizer (CRF) and liquid fertilizer (LF) to determine if a follow up fertilization application of the pre-plant applied CRF can obtain improved yields. From the results it was evident that by applying a mixture of 80% CRF (based on the fraction of the total % nitrogen applied) and 20% LF with additional monthly manual application of calcium sulphate or calcium nitrate to each planting bag, CRF could potentially replace a 100% LF fertilization programme in greenhouse tomato production. Some results here indicate that a spike in temperature at the beginning of the growing season may have contributed to the premature release of nutrients from the CRF prill, causing a spike in EC. This stunted the growth of the plants for the rest of the season, which could have been attributed to an initial toxic level of salts in the rootzone and a prolonged deficit of other essential nutrients. The growth media trial for the determination of the optimal perlite: coco coir ratio revealed that a mix consisting of 20% perlite to 80% coco coir, or 40% perlite and 60% coco coir were the best ratios that yielded the highest. Thus, for tomato production the effect of CRF would be greatly improved if applied in an environment where the temperature and growth media properties are favourable for the slow release of the nutrients. The evidence here did not support the utilisation of 100% CRF as a replacement of the currently employed LF for commercial greenhouse tomato production. In addition, it is imperative that additional calcium (Ca2+), Sulphate (SO42-) and Nitrate (NO3-) be supplemented to reap the full benefits of CRF due to the ongoing technological research into the ability to coat calcium-based fertilizer products as a CRF.
Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 2. effect of different cover crops and cover crop management practices on grapevine performance
(South African Society for Enology and Viticulture, 2006) Fourie, J. C.; Louw, P. J. E.; Agenbag, G. A.
The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), situated in the Coastal Wine Grape Region of the Western Cape. Sixteen treatments, consisting of three grain species and five legumes, managed according to two cover crop management practices, were included. The one cover crop management practice consisted of cover crops being sown annually and full surface post-emergence chemical control being applied before bud break and when the berries reached pea size (BB). The other management practice consisted of cover crops being sown biennially and postemergence chemical control applied to the vine row before bud break and full surface when the berries reached pea size (AB). From 1999/2000 to 2002/03 the cover crops were sown annually, while the full surface post-emergence chemical control applied at the end of November was advanced to mid-October. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full surface post-emergence chemical weed control was applied from before bud break to harvest (weedchem) was also included. During the 1994/95 season, the shoot mass of the two-year-old grapevines in the BB treatments was significantly higher than that of the control and the AB treatments. In the following season, the shoot mass and grape yield of the BB treatments was, with the exception of Vicia faba L. v. Fiord (faba bean) and Avena sativa L. v. Overberg, significantly higher than that of the control and weedchem. The grape yield of the control and AB treatments was significantly less than that of weedchem. Although significant differences in shoot mass (2000/01 and 2002/03) and grape yield (2002/03) were detected between treatments, no significant differences could be detected between the BB and AB treatments, with the exception of the shoot mass of Medicago scuttelata v. Kelson (‘Kelson’ medic). The mean petiole NO3-N concentration for the period 1994/95 to 1998/99 tended to be lower in the AB treatment of a cover crop species compared to that of the BB treatment of the same species. In the case of ‘Kelson’ medic (BB) the petiole NO3-N and juice N concentrations were significantly higher than that of the control and weedchem. The juice N concentration of the control and weedchem was significantly less than that of the faba bean treatments during 2000/01 and 2001/02, the Vicia dasycarpa Ten (grazing vetch) and ‘Kelson’ medic treatments during 2000/01, as well as that of Medicago truncatula Gaertn. (BB) and Trifolium subterraneum L. v. Woogenellup (BB) during the 2001/02 season. Wine quality did not differ between treatments.
Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Region, South Africa. 3. effect of different cover crops and cover crop management practices on organic matter and macro-nutrient content of a medium-textured soil
(South African Society for Enology and Viticulture, 2007) Fourie, J. C.; Agenbag, G. A.; Louw, P. J. E.
The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium-textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), which is situated in the Coastal wine grape region of the Western Cape, South Africa. Sixteen treatments, consisting of three cereals and five legumes, managed according to two cover crop management practices, were included. These treatments were compared to a control, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from bud break to harvest (approximately the first week of February). A treatment in which no cover crop was sown and full-surface post-emergence chemical weed control was applied from before bud break to harvest (BB) (weedchem) was also included. After five seasons, the soil organic matter (SOM) content in the 0 to 300 mm soil layer increased in all the cover crop management treatments. In weedchem and in the control, SOM remained unchanged and decreased by 16% respectively. The SOM content in the 0 to 150 mm soil layer of the cover crop treatments was, with the exception of Vicia dasycarpa Ten. (grazing vetch), significantly higher than that of the mechanically-cultivated control after a period of 10 years. The SOM content in the 0 to 300 mm soil layer of Secale cereale L. v. Henog and the treatments in which the N-fixing cover crops were sown (with the exception of grazing vetch) was significantly higher than that of weedchem. The total inorganic N (TIN) concentration of the 0 to 150 mm soil layer in the BB treatments of the two Medicago species and Trifolium subterraneum L. v. Woogenellup, as measured for the 1996/97 season during full bloom of the grapevines, was significantly higher than that of the control, weedchem, and the treatments in which full-surface chemical control was applied after bud break (AB). The TIN concentration of the 0 to 600 mm soil layer in the AB treatment of a species, measured after harvest in 2002/03, tended to be higher than that of the BB treatment of that species. The applied treatments had no significant effect on the exchangeable K, Ca and Mg.
Cover crop management in a chardonnay/99 Richter Vineyard in the Coastal Wine Grape Region, South Africa. 1. effect of two management practices on selected grass and broadleaf species
(South African Society for Enology and Viticulture, 2006) Fourie, J. C.; Louw, P. J. E.; Agenbag, G. A.
The trial was conducted over a period of 10 years (1993/94 to 2002/03) on a medium textured soil in a Chardonnay/99 Richter vineyard near Stellenbosch (33°55’S, 18°52’E), situated in the Coastal Wine Grape Region of the Western Cape. Sixteen treatments, consisting of three grain species and five N-fixing broadleaf species managed according to two cover crop management practices, were included. These treatments were compared to a control treatment, in which no cover crop was sown and the weeds were controlled mechanically in the work row and chemically in the vine row from the first week of September to the end of March (grapevine growing season). A treatment in which no cover crop was sown and full surface post-emergence chemical control was applied during the grapevine growing season was also included. The different weed control actions were carried out during the first week of September and/or at the end of November, as well as mid October (1999/00 to 2002/03). Secale cereale L. v. Henog (rye), Avena sativa L. v. Overberg (‘Overberg’ oats), Avena strigosa L. v. Saia (‘Saia’ oats) and Vicia faba L. v. Fiord [only if sown annually and controlled chemically before bud break (BB)], showed the ability to produce, on average, significantly more dry matter during winter than the weeds in the region. The dry matter production of all the cover crops increased from the end of August to the end of November if left to complete their life cycles, with the exception of rye and ‘Overberg’ oats sown in early April. None of the cover crop species were able to reestablish successfully. Continuous effective suppression of winter growing weeds (less than 20% of the weed stand in the control) was achieved with ‘Overberg’ oats (BB) and ‘Saia’ oats (BB), while total suppression was achieved for six and five of the 10 years, respectively. Effective, long-term control of the summer growing weeds was obtained with rye (BB), ‘Overberg’ oats (BB) and ‘Saia’ oats (BB).
Cover crop management in a Sauvignon blanc/Ramsey vineyard in the semiarid Olifants River Valley, South Africa. 1. effect of management practices on selected grass and broadleaf species
(South African Society for Enology and Viticulture, 2005) Fourie, J. C.; Louw, P. J. E.; Agenbag, G. A.
This trial was conducted over a period of ten years on a sandy soil in a Sauvignon blanc/Ramsey vineyard in Lutzville (31°35’S, 18°52’E), situated in the semi-arid Olifants River Valley of the Western Cape. Twenty-three treatments were applied. Eight cover crop species that received the same amount of fertilizer were controlled chemically at the end of August or at the end of November. Two treatments were also applied in which Avena sativa L. v. Saia (‘Saia’ oats) and Vicia dasycarpa Ten. (grazing vetch) were controlled mechanically during bud break. In addition to these eighteen treatments, two fertiliser application rates were applied to ‘Saia’ oats and grazing vetch. A mechanically cultivated control in which no cover crop was sown was included in the trial. Secale cereale L v. Henog and Ornithopus sativus L. v. Emena produced, on average, the highest amount of dry matter at the end of August (3.29 t/ha and 3.06 t/ha, respectively) after receiving on average 278 mm of water, of which 172 mm was supplied by means of a micro-sprinkler irrigation system. The average dry matter produced by Medicago truncatula Gaertn. v. Paraggio and ‘Saia’ oats at the end of August was not significantly lower than that of the firstmentioned two species. Under conditions of this experiment, it seemed that P and K at a concentration of 10 mg/kg and 78 mg/kg, respectively, in the top 300 mm soil layer supplied the needs of grazing vetch. Saia oats performed poorly unless 30 kg P, 30 kg K and 42 kg N were applied during establishment and the early growing phase. All the species, except M. truncatula Gaertn v. Parabinga, produced additional fibre from September to the end of November following a dry winter (rain and irrigation totaling 201 mm), while none produced additional fibre if the water supply was luxurious up to the end of August (rain and irrigation totaling 364 mm). The cover crops did not produce enough seeds to re-establish successfully over a period of five years. It will, however, be possible to reduce the seeding density of grazing vetch (40% after two seasons) and the two M. truncatula varieties (20% after five seasons) if the species were left to ripen their seeds.
Crop response in the Western Cape of South Africa to liming soil under no-tillage and following once-off tillage in a no-tillage regime
(Stellenbosch : Stellenbosch University, 2021-03) Liebenberg, Adriaan; Swanepoel, Pieter Andreas; Hardie-Pieters, Ailsa G.; Labuschagne, Johan; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Soil acidity, and the stratification thereof, was found throughout the Western Cape Province. Soil acidity is especially prevalent in the Swartland, where 19.3% of soils in this region have been found to contain at least one soil layer, in all cases deeper than 5 cm, with pH(KCl) ≤ 5.0. The mean acid saturation percentage of the Swartland region was above the 8% threshold for wheat production. The wide adoption of no-tillage has presented challenges to address subsoil acidity. Since soil acidity is a limiting factor for wheat (Triticum aestivum), barley (Hordeum vulgare) and canola (Brassica napus) grown in these regions, acidity should not remain unaddressed. Therefore, it is crucial that liming is done with the correct combination of liming material, method of application and physical incorporation, or lack thereof. These variables were evaluated on sandy loam soil with pH(KCl) 5.5. Results from this field trial indicate that micro-fine lime pellets and Class A calcitic lime yield similar results on soil chemical properties and crop response under the soil and climatic conditions that prevailed during this study. The in-row application of a small amount (40 kg ha-1) of micro-fine lime pellets had a negligible effect on soil chemical properties and the treatment where only 40 kg ha-1 of micro-fine lime pellets were applied was the only treatment, along with the control, where soil pH(KCl) decreased over the course of this trial. Comparison between samples taken in-row and between crop rows in the treatments where liming material was applied in-row and broadcast, showed a greater (p ≤ 0.05) increase in Ca content in the samples taken between crop rows than in-row. Of the crop response variables measured, canola showed treatment responses (p ≤ 0.05) in leaf area index (LAI), aboveground biomass and oil content. Canola LAI’s only differed at 90 days after emergence (DAE), with the treatments where soil was disturbed and where micro-fine lime pellets were applied at 19% below the recommended rate having the highest LAI’s. Where a disc plough was used and where micro-fine lime pellets were applied in-row only, oil contents were the lowest (p ≤ 0.05). The crop responses in only some variables can be ascribed to the resilience of canola and the fact that lime application was done in the same year, thus the liming materials did not have sufficient time to react with soil acidity. In the following year, wheat was planted on the same site. This was done to monitor treatment effects over two years. Wheat showed treatment responses (p ≤ 0.05) in plant population and aboveground biomass at 150 DAE. Where a disc plough was used, both the plant population and aboveground biomass was the highest. Increases in soil pH in the 5 – 15 cm soil depth layer positively correlated with increased aboveground biomass and wheat grain protein content. Increasing effective cation exchange capacity also correlated with increased aboveground biomass in wheat. The amount of rainfall, as well as rainfall distribution, may have contributed to the few treatment differences in 2020.
Cultivation aspects of hydroponic cut tulip (Tulipa gesneriana) production in South Africa
(Stellenbosch : Stellenbosch University, 2013-12) Derbyshire, Geline; Kempen, Estelle; Hoffman, L. (Lynn) (Horticulturalist); Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Tulip cut flowers are considered speciality flowers, but are cultivated on a limited scale in South Africa. Published research done on the cultivation aspects of Tulipa spp. in warm climates is sparse and insufficient. The production potential of this valued floriculture crop under South African conditions however prompts a need for research as profitable returns can only be realised when cut tulip producers deliver high quality tulips, both for the local and potentially the export market. Understanding how cut tulips react to different cultivation aspects under local conditions is key in developing successful and profitable forcing programs for cut tulip production in South Africa. In order to produce quality tulips it is vital that producers minimize the occurrence of physiological disorders by optimizing cultivation aspects such as nutrition, bulb quality and age, cultivar selection as well as postharvest treatments. To study the nutritional requirements of cut tulips produced in a hydroponic system under South African conditions two similar experiments were conducted, using early-forcing and late-forcing tulip bulbs respectively. In each experiment the effect of four different nutrient solution formulations (“Current SA”, “Standard Steiner”, “Europe”, “Europe+NH4”) and four different cut tulips cultivars (‘Leen van der Mark’, ‘Jan van Nes’, ‘Ill de France’, ‘Royal Virgin’) on growth, quality and vase life was evaluated. Results showed that although nutrient solutions did not significantly affect the scape growth of cut tulips, vase life was significantly affected by nutrient solution formulation for both early- and late-forcing bulbs. For early-forcing bulbs nutrient solution “Europe” produced tulips with a significantly longer vase life than other nutrient solutions and for late-forcing bulbs nutrient solution “Standard Steiner” produced tulips with a significantly longer vase life than other nutrient solutions. Cultivars differed significantly in terms of growth, quality and vase life for both early- and late-forcing bulbs. It was found that the cultivar ‘Leen van der Mark’ presented the longest stem length, greatest fresh weight and longest vase life of all cultivars evaluated for both early- and late-forcing bulbs and it seems to be a cultivar with a low risk in terms of quality and vase life for forcing hydroponically in warm climates. As stem topple, a physiological disorder which can be prevalent in hydroponically produced tulips, has been shown to be reduced by the application of calcium fertilizers, the next experiment was conducted to investigate the role of foliar sprays to reduce or eliminate this common disorder. Various foliar spray treatments, including calcium nitrate (CaNO3), CalTrain, NonTox Silica® and an untreated control, were evaluated for their effect on the occurrence of postharvest stem topple and the vase life of the two tulip cultivars ‘Jumbo Pink’ and ‘Strong Gold’ respectively. Trends indicated that foliar sprays containing calcium, “CaNO3” and “CalTrain”, reduced the incidence of postharvest stem topple. The vase life of hydroponically forced cut tulips was significantly increased by the use of foliar fertilizer sprays as compared to the control. The vase life of cut tulips is an important parameter directly affecting quality. In a final experiment, the efficacy of three postharvest treatments to extend the vase life and minimize postharvest stem elongation of the four cut tulip cultivars ‘Deshima’, ‘Synaeda Orange’, ‘White Marvel’ and ‘Margarita’ was evaluated. Treatments consisted of an untreated control, an overnight stem pulse of Chrysal BVBPlus, a four hour fumigation of Chrysal Ethylene Buster® (1-MCP) and a combination of the latter treatments. Vase life, postharvest stem elongation and vase-solution used were parameters measured. No statistically significant effects on any parameters measured could be identified between the various treatments. Trends observed suggest that treatments containing BVBPlus may prolong the vase life, minimize postharvest stem elongation and improve the usage of vase life solution of hydroponically produced cut tulips. BVBPlus thus shows potential for use as an essential postharvest treatment for cut tulips produced hydroponically under warm climate conditions, but further research is needed for conformation. This research is a first report on key agronomical aspects of the hydroponic cultivation of cut tulips in South Africa and aims to serve as a basis for future research, ultimately to support successful commercial cultivation of tulips on a larger scale in South Africa as well as internationally.
Developing management strategies to support sustainable production of lucerne in long-rotation cropping systems
(Stellenbosch -- Stellenbosch University, 2020-03) Van der Westhuizen, Christoff George; Swanepoel, Pieter Andreas; Labuschagne, Johan; Brand, T. S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Lucerne (Medicago sativa L.) forms part of long-rotation cropping systems integrated with livestock in the southern Cape of South Africa. The lucerne phase is five to seven years long, followed by five to seven years of cash crops. Lucerne swards allow for the integration of livestock into cropping systems, improved resource utilisation, is a high-quality animal forage, biologically fix N, break disease cycles and may improve subsequent cash crops yields. However, some farmers consider excluding lucerne from crop production cycles. The main reasons for the exclusion of lucerne swards are low summer and winter herbage production due to moisture stress and lucerne’s natural winter dormancy. Low herbage production during these periods create considerable fodder flow deficits and make the management of fodder flow programmes challenging for farmers. The oversowing of dryland lucerne swards with annual winter growing forage crops, to create lucerne-based multiple species pastures, was investigated to determine if fluctuations in fodder flow programmes could be reduced through increased winter herbage production. Field experiments were conducted at Tygerhoek Research Farm (Riversonderend) during the 2018 and 2019 growing seasons. Both single species treatments and mixes were oversown into an existing lucerne base. Single species treatments included black oats, forage barley, stooling rye, Westerwolds ryegrass, forage radish and canola. Mixes consisted of various combinations of hybrid ryegrass, Italian ryegrass, forage barley, black oats, various annual Medicago and clover species, vetch and forage radish. The effect of oversown species and mixes on herbage production, pasture and soil quality was monitored for the duration of this study. Drought conditions after oversowing restricted the performance of the oversown species and mixes and had a knock-on effect that persisted for the duration of this trial. No treatment had a higher herbage yield to that of the control at any stage in the growing season (p>0.05). Small grains and mixes that contain small grains did however show the most potential to improve herbage production, especially in late winter. Due to poor performance of oversown treatments, herbage samples mainly consisted of the lucerne base and ryegrass, both as an oversown species and weed. The relatively similar species composition from different treatments yielded no clear and or obvious treatment that improved pasture quality, however, grazing management ensured that all treatments were of a high quality at the time of sampling. Similar returns of organic matter, both quantatively and qualitatively resulted in soil quality that was similar between all treatments. Different results may be obtained if oversown species establish well and this study should be replicated in years of normal rainfall distribution to fully comprehend how changes in pasture composition will affect herbage production and pasture quality. Soil physical, chemical and biological parameters should also be monitored over an extended period of time as changes in soil quality may take several years in Mediterranean climates.
Developing nitrogen fertiliser management strategies for canola (Brassica napus L.) under conservation agriculture practices in the Western Cape
(Stellenbosch : Stellenbosch University, 2018-12) Du Toit, Etienne; Labuschagne, Johan; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Nitrogen (N) is one of the most important nutrients in canola production systems. Improper N supply due to lack of knowledge regarding canola N management and inappropriate fertiliser guidelines, frequently results in low canola yield and profitability in the Western Cape. Current N guidelines are based on international literature or adapted from wheat guidelines. Conservation agriculture practices have also changed soil N dynamics. More N is mineralised from soil organic matter than conventional systems, which were historically practised. Canola N guidelines should therefore be refined to account for the abovementioned changes. The aim of this study was to determine the effect of different topdress N rates, foliar N application at stem elongation and N source on plant parameters, canola seed yield, oil content and N use efficiency, whilst monitoring the effect of different topdress N rates on the soil mineral N concentration at plant, pre-topdress, post topdress and at harvest. This study was conducted at five canola producing areas in the Western Cape during 2016 and 2017. The trial was laid out as a randomised block design consisting of seven different topdress N rates (0, 25, 50, 75, 105, 135 and 165 kg N ha-1) applied at the rosette stage. For all the above mentioned treatments, 25 kg N ha-1 was applied at planting. A control treatment was included that received no N. A foliar N application that consisted of 20 kg N ha-1 (urea ammonium nitrate) was applied at stem elongation. Five N sources were evaluated, applied as topdressing at rosette stage. Increasing topdress N rate increased (p<0.05) soil mineral N concentration. Plant population at harvest and biomass production did not respond (p<0.05) to topdress N rates, a result not expected but could be ascribed to the relative dry seasons experienced in 2016 and 2017. Canola yield responded (p<0.05) to topdress N rate. Maximum yield response was recorded at lower topdress N rates than expected. The N use efficiency (NUE) decreased (p<0.05) as topdressed N rate was increased, with a drastic reduction in NUE when total N application was increased above 25 kg N ha-1. Foliar N application at stem elongation did not (p>0.05) influence yield or oil content at most sites. Nitrogen source did not influence (p>0.05) plant population, biomass production or yield, except at one site (Langgewens) in the Swartland in 2017 where the urea + inhibitor outperformed LAN. No differences (p>0.05) were recorded in oil content between different N sources in 2016. Generally, in 2017, oil content was lower compared to 2016 and inconsistent results were recorded between N sources. This was possibly due to the dry conditions during 2017, which may have influenced oil production. It is apparent that N fertiliser recommendations have to be adjusted for certain areas. Current N recommendations may result in over-fertilisation and reduced profitability at sites in the southern Cape. Current N recommendation at the Swartland sites has a low NUE and further increase in topdress N rates would likely result in pollution of the environment. Nitrogen source did not affect canola productivity. Selection of N source should be based on cost. In general, CA practices tended to decrease fertiliser N requirement for canola production. Refined N fertiliser guidelines may result in more consistent canola yield and ensure profitability. Guidelines will only be finalised on completion of the research project after at least four years of data capturing.
Developing nitrogen fertiliser management strategies for wheat (Triticum aestivum) under conservation agriculture practices within the Western Cape
(Stellenbosch : Stellenbosch University, 2018-03) Neethling, Paul Johannes; Labuschagne, Johan; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
ENGLISH ABSTRACT: Nitrogen (N) is one of the most limiting plant nutrients. Supplying enough N to growing crops is one of the most critical factors influencing wheat production. There has been a strong drive towards conservation agriculture in South Africa, especially within the Western Cape Province. Conservation agriculture brings forth changes in soil physical, chemical and biological properties that influence the plant-available soil mineral N content, specifically an increased potentially mineralisable N content. The aim of this study was to do a complete analysis of the effect that different preceding crops, N rates, forms of N, and timing of N application would have on the yield, yield components and protein content of wheat, whilst monitoring the effect of different N rates on the soil mineral N concentration throughout the growing season. The first objective of the study was to determine the effect of different fertiliser rates on the grain yield, selected yield components, quality parameters and N use efficiency. The second objective was to determine the effect of a late-season foliar N application on the yield and grain protein content of the wheat crop. The third objective was to test the effect of different N sources on crop growth, yield and quality of wheat. This study was conducted during 2016 and 2017 on nine sites within the dryland grain producing areas of the Western Cape. The trial was subdivided into two separate studies: i) topdressed N rates with or without foliar applications of N and ii) N sources at topdress. Increasing topdress N rates had a less profound effect on crop yields than expected, where most of the sites in both years showed no increase (P > 0.05) in yield with increasing topdress N rate. Five of the research sites in Year 1 and all the research sites in Year 2 showed no response (P > 0.05) in the number of ear-bearing tillers, as influenced by increasing topdress N rates. An increase (P < 0.05) in grain protein content with the increasing topdress N rates was recorded at all the research sites in Year 1. The N use efficiency of wheat decreased (P < 0.05) with increasing topdress N rates in both years. Foliar N application at post-anthesis had limited success in increasing yield and grain protein content of wheat. No profound effect of fertiliser N source on the yield, yield components or quality of wheat was recorded. After doing a complete analysis of the N requirement of wheat produced under conservation agriculture practices and dryland conditions in the Western Cape Province, it was apparent that fertiliser N recommendations will possibly have to be adjusted. The N guidelines to produce wheat lead to over-fertilisation in some areas, which may, in turn, lead to environmental pollution and economic losses. Determining the optimal N source might entail choosing the most cost-effective and accessible source.

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