Potato tubers are low in calcium due to limited calcium transport in the xylem and immobility of calcium in the phloem. Low tuber calcium content results in the occurrence of necrotic cells in the medullary tissues, which is a physiological disorder known as internal brown spot (IBS). A high incidence of IBS results in reduced tuber quality and market value. The objective of the study was to apply additional calcium to the potato crop using different calcium sources (gypsiferous mine water, gypsum and calcium rich water) to determine the impact on tuber yield and quality. Commercial field trials were conducted at Kleinkopje mine on the Mpumalanga Highveld from August 2001 to January 2002 and from September 2002 to January 2003. The response of the potato cultivar Up-to-date to irrigation with gypsiferous mine water as a calcium source was investigated. At Kleinkopje there was no control field (irrigated with normal water) for direct comparison. Another field trial was established at University of Pretoria Experimental Farm where gypsum at four levels was broadcast and incorporated prior to planting. Pot trials were conducted under controlled conditions because calcium uptake is not affected only by the amount of calcium applied or the location of the calcium application. Factors that affect calcium uptake such as temperature and humidity also play a role. Two pot experiments were conducted under controlled conditions from July to October 2002 and from October 2002 to January 2003. In these experiments, the effect of applying increasing calcium concentrations in calcium rich water at high (27/17oC) and low (22/14oC) controlled temperatures and humidities (35% and 85%) on tuber calcium content and quality were investigated. The parameters measured included growth analysis, leaf and tuber chemical analysis, tuber yield and quality. For the field trials soil sampling was done at the beginning and at the end of the cropping season for chemical analysis. Irrigation with gypsiferous mine water did not have a negative impact on overall potato growth. Higher levels of calcium (in irrigation water or gypsum) also did not have a negative effect on other nutrient levels. Irrigating potato plants with gypsiferous mine water resulted in high tuber yields of 52 t/ha in 2001 and 62 t/ha in 2002 seasons, which are good yields for Mpumalanga. Applying higher gypsum levels as a preplant broadcast resulted in high tuber yields (52 t/ha), which is a good yield for Hatfield. Application of gypsum as a preplant broadcast and irrigation with gypsiferous mine water resulted in good quality tubers (SG > 1.075 and chip colour > 45). This implies that gypsiferous mine water can possibly be used for irrigation of potatoes as a calcium source. The calcium nutrition of the potato tubers was not affected by the amount of calcium applied to the plants, calcium uptake or distribution within the plant only. Environmental conditions (temperature and humidity), which affect these functions also played a role. It has been discovered that lowering the temperature (22/14oC) and low humidity (35%) had beneficial effects on the tuber yield. Maintaining plants at low temperature (22/14oC) and high humidity (85%) could improve the tuber quality. However, high humidity (85%) and high temperature (27/17oC) improved calcium uptake by the tubers.
Dissertation (MSc (Agric) Agronomy)--University of Pretoria, 2007.