Doctoral Degrees (Soil Science)
Permanent URI for this collection
Browse
Browsing Doctoral Degrees (Soil Science) by browse.metadata.advisor "Hoffman, J. E."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- ItemDetermination and modelling of evapotranspiration of bearing and non-bearing apple trees at Grabouw in the Western Cape(Stellenbosch : Stellenbosch University, 2024-03) Meyer, Aline; Van Zyl, J. L.; Hoffman, J. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.ENGLISH ABSTRACT: The irrigation of apple trees is important to ensure sustainable production and good quality fruit, especially in regions where rainfall does not contribute adequately to the water demand. Effective scheduling is the key to efficient water use to ensure profitability and sustainability on farms. Quantitative knowledge of the water use and the effect of irrigation application on young apple trees will improve on-farm decision making regarding scheduling. A study was conducted on Malus domestica “Bigbucks‟ (a mutation of “Corder Gala‟) trees grown in a gravelly soil at Grabouw in the Western Cape to determine the effect of three irrigation cycles on the water use, root growth characteristic and tree performance over four growing seasons (October to May) from planting to the first year of bearing. Treatment one (T1) was a short irrigation cycle receiving ca. 15 mm of water per irrigation with an average of 42 irrigations through the growing season, treatment two (T2) was a medium irrigation cycle receiving ca. 27 mm of water with an average of 21 irrigations through the growing season and treatment three (T3) was a long irrigation cycle receiving ca. 37 mm of water with an average of 13 irrigations through the growing season. Crop evapotranspiration (ETC) was determined for all three treatments based on the soil water balance. The ETC of all three treatments increased from the first to the fourth growing season as the leaf area index (LAI) of apple trees increased. T1 had a higher consumptive water use than T2 and T3. Studies done using micro-lysimeters to determine the orchard floor evaporation revealed that T1 lost more water through evaporation compared to T2 and T3, but water loss from the soil mainly occurred through transpiration, irrespective of the treatment. In situ and destructive root studies revealed that both root length density (RLD) and the number of fine roots within the soil profile is strongly related to soil water extraction (SWE). SWE increased with an increase in RLD and the number of fine roots. These results revealed that growing roots can continuously grow into moist regions of the soil. Significantly more fine roots penetrated deeper soil layers and at a greater distance from the tree for the two drier irrigation cycles (T2 and T3). The root index (RI) of T2 and T3 was also higher in deeper soil layers compared to T1 suggesting that soil moisture conditions of T2 and T3 were more favourable in deeper soil layers. It was concluded that short irrigation cycles will favour shallow root growth while longer irrigation cycles promote roots into deeper soil layers. There were no significant differences among treatments in terms of diurnal plant water status, vegetative growth, yield and fruit quality. These results suggest that longer irrigation cycles can be used to save water while simultaneously increasing root growth to deeper soil layers without compromising tree performance. Statistical analysis performed on ETC and RLD data revealed that there is a strong, positive correlation (R² = 0.741) between ETC and RLD. The data was used to develop a statistically significant model in which ETC can accurately be predicted using RLD data or vice versa. The model can be used as a reference for apple producers in South Africa to encourage more precise and effective irrigation scheduling while simultaneously increasing RLD for better water and nutrient uptake resulting in optimal crop production and quality.
- ItemDetermination of optimal soil conditions and foliar nutrient levels in commercial rooibos tea production(2023-03) Smith, Jacobus Francois Naude; Hardie-Pieters, Ailsa G.; Hoffman, J. E.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
- ItemUsing diluted winery effluent for irrigation of Vitis Vinifera. Cv. Cabernet Saugvignon and the impact thereof on soil properties with special reference to selected grapevine responses.(Stellenbosch : Stellenbosch University, 2016-03) Howell, Carolyn Louise; Hoffman, J. E.; Myburgh, P. A.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.ENGLISH ABSTRACT: Wine production is an important industry in the Western and the Northern Cape regions of South Africa. Wineries produce large volumes of poor quality wastewater, particularly during harvest. International requirements, as well as national legislation, are putting pressure on wine producers regarding the responsible management of winery wastewater, which may have a large-scale detrimental impact on the environment. Currently, the Department of Water and Sanitation is drafting new legislation aimed at wineries to allow beneficial crop irrigation as a General Authorisation. In this regard, a multidisciplinary research project to investigate the impact of diluted winery wastewater on soils, crop growth and product quality was initiated and funded by the Water Research Commission of South Africa. The project was also co-funded by Winetech and the Agricultural Research Council. The possible re-use of winery wastewater for vineyard irrigation was investigated in a Cabernet Sauvignon vineyard in a sandy soil near Rawsonville in the Breede River Valley. Wastewater obtained from a co-operative winery was diluted to levels of 100, 250, 500, 1000, 1500, 2000, 2500 and 3000 mg/L chemical oxygen demand (COD), using water obtained from the Holsloot River. The dilution was carried out individually for each concentration in 15 m3 tanks at the vineyard. Control grapevines were irrigated with river water. In addition to the field trial, a pot trial was also included to determine the effect of diluted winery wastewater on near-saturation hydraulic conductivity (K) of four different soils. In general, soil potassium and sodium increased with an increase in COD level of the diluted winery wastewater, i.e. a decrease in dilution of the wastewater. Although irrigation using diluted winery wastewater had almost no other effects, element accumulation particularly with respect to potassium and sodium, might be more prominent in soils with higher clay contents or in regions with low winter rainfall. After three years, near-saturation hydraulic conductivity of shale-derived soil, alluvial and aeolian sands decreased with a decrease in the level of wastewater dilution. This indicated that severe degradation in hydraulic properties can occur if diluted winery wastewater is used for irrigation, and might even be aggravated if undiluted winery wastewater is used. Irrigation of grapevines using diluted winery wastewater did not affect grapevine water status, vegetative growth, production or evapotranspiration, irrespective of the level of dilution. Results showed that irrigation of grapevines using diluted winery wastewater did not have detrimental effects on juice characteristics with regard to ripeness parameters and ion content. Wine sensorial characteristics were not affected by irrigation using diluted winery wastewater. The grapevines did not respond to level of COD per se. This indicated that sufficient aeration occurred between irrigations which allowed organic carbon breakdown. Although salinity and sodicity levels in the diluted winery wastewater were below the thresholds where growth and yield reductions are expected for grapevines, it should be monitored frequently. The low salinity and sodicity levels in the diluted winery wastewater could be a further explanation why the grapevines did not respond negatively to the wastewater irrigation. Based on the above-mentioned results, the following criteria should be considered for possible amendments to the General Authorisations for wineries when using diluted wastewater for vineyard irrigation: (i) COD must be diluted to 3000 mg/L or less, preferably to less than 2000 mg/L to avoid unpleasant odours in the vineyard during irrigations, (ii) electrical conductivity (ECiw) must be less than 0.75 dS/m, (iii) sodium adsorption ratio (SARiw) must be less than 5, (iv) the soil must have a low cation exchange capacity, (v) unrestricted internal drainage in the root zone, (vi) irrigation water must not percolate beyond the root depth, (vii) only micro-sprinklers should be used, (viii) irrigation must be applied in such a way that bunches are not wetted, (ix) at least 50% plant available water depletion should be allowed between irrigations to allow sufficient aeration for oxidation of organic material applied via the irrigation water and (x) irrigation frequency and volumes must be such that wine quality is not reduced.