Thesis (MScAgric)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1934. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Sc.(Agric.))(Agronomy)--University of Pretoria, 2007. / Includes summary. Includes bibliographic references. Available on the Internet via the World Wide Web.

Two series of tests were performed in summer 1993 and repeated in summer 1994 to investigate effects of potassium, calcium and water table depth on mechanical properties of tomato fruit. In the first group of tests five mechanical properties stress, strain, ER (ratio of stress to strain at break), energy and toughness were calculated from the force-deformation curve obtained by compression of pericarp disks taken from tomato fruits (cv New Yorker) at the breaker stage. In the second group of tests force, deformation and energy were obtained from puncture tests on whole tomato fruit. The textural parameters were used to compare the effects of the potassium, calcium and water level depths on the mechanical properties of tomatoes. Results showed the effects of calcium and water table depths on the mechanical properties were significant. Tomato fruits exposed to increasing moisture stress levels by increasing water table depth exhibited increased firmness. Increased application of calcium also resulted in increased firmness. Application of different potassium levels had in general no significant effect on breaking stress, strain, ER, energy and toughness of tomato fruit pericarp. / A new method of measuring skin strength of tomatoes is described. The method, refered to as loop method, overcame the problems with the existing method using mechanical grips. Further, the loop method was applied to measure the effect of potassium and calcium on skin strength of tomato. Using the loop method, data were collected on relaxation of tomato skin (epidermis). A computer program was written to model th tensile stress relaxation behaviour of tomato skin. The program was employed to calculate linear and non-linear coefficients of a relaxation model. The fitted values were in a very good agreement with experimental data (R$ sp2>$0.99).

No description available.

Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Localized calcium (Ca) deficiencies frequently develop independent from total Ca supply and total fruit Ca concentration. Bulk mineral analyses is therefore not completely suitable for determination of the susceptibility of fruit in developing Ca-linked fruit physiological disorders like bitter pit, as it supplies insufficient information regarding the spatial accumulation of Ca within the fruit. Additional Ca is applied either as soil or foliar applications, where soil applications are applied either after fruit set (pre-harvest) or in the period after harvest. The contribution of these different methods of Ca application to the total Ca concentration in "Braeburn" fruit was quantified over three consecutive growing seasons. Foliar applications have been proven to be successful in suppressing bitter pit development and improving the Ca status of the fruit. The effectiveness of different formulations of foliar Ca products in influencing these parameters was also determined. Furthermore, the distribution pattern of fruit Ca resulting from different application strategies was mapped using particle induced X-ray emission technology. In the "Braeburn" trial, mineral analyses indicated no significant differences between treatments in terms of Ca concentration at 80 days after full bloom (dafb). However, when soil applications occurred with active root growth (visually monitored), treatments differed significantly 80 dafb. Weekly foliar Ca applications from 28 dafb resulted in higher fruit Ca concentrations 80 dafb than a pre-harvest soil Ca application (January, 2010). A possible explanation for the inefficiency of pre-harvest soil Ca is the disintegration of xylem vessels from 40 dafb (before root uptake) for sensitive cultivars such as Braeburn. Bitter pit initiation has been shown to occur in the earlier part of the season. This, together with a reduced Ca supply to the fruit early in the season due to xylem disintegration (for sensitive cultivars), indicates the importance of early season foliar Ca applications. PIXE analyses were used to establish the radial Ca distribution in apples. Ca was concentrated in the skin and core, with very low values in the outer cortex. PIXE results indicated fruit Ca concentrations to be the lowest in the pre-harvest soil application treatment. This was in agreement with mineral analyses results. Ca enriched areas resulting from effective Ca delivery via the vascular bundles, had a profound effect on fruit Ca concentrations in the immediate core and cortex. At harvest, this effect was much more subtle and emphasizes the importance of untimely xylem rupturing on eventual fruit Ca concentration. At 80 dafb, treatments where foliar Ca was applied showed higher Ca concentrations in the outer cortex (where symptoms of bitter pit typically occur). Calflo™ fruit had significantly higher Ca concentrations in "Braeburn" compared to fruits from Foliar GS™ and GG™ treatments. Calflo™ and Calcimax™ had a higher active Ca percentage (12%) compared to Foliar GSTM and GGTM (10%). Adding the Lecithin™ (surfactant) to Calcimax™ is not recommended as it did not improve its uptake. In "Golden Delicious", the commercial spray program of seven, weekly foliar applications (Calcinit™) resulted in fruit with significantly higher Ca concentrations compared to other treatments. / AFRIKAANSE OPSOMMING: Kalsium (Ca) tekorte ontstaan gewoonlik in gelokaliseerde areas in die appelvrug en ontwikkel dikwels ten spyte van voldoende totale vrug Ca. Minerale analises van heel vrugte verskaf dus nie genoeg inligting aangaande die verspreiding van Ca in die vrug wanneer die ontwikkelling van fisiologiese defekte soos bitterpit ter sprake is nie. Addisionele Ca word gewoonlik aangewend as blaar- of grondtoedienings, waar grondtoedienings tipies voor-oes (net na set) of in die na-oes periode, toegedien word. Die bydraes van die verskillende toedieningsmetodes tot die totale Ca konsentrasie van "Braeburn" appels is geëvalueer oor drie agtereenvolgende seisoene. Blaartoedienings van Ca word algemeen gebruik om die voorkoms van bitterpit te beheer en die Ca konsentrasie van die vrug te verhoog. Die effektiwiteit van `n reeks blaartoedienings-produkte om hierdie faktore te verbeter, is ook ondersoek. Die spesifieke verspreiding van die Ca in die vrug is gekarteer na gelang van elke toediening deur middel van PIXE-analises (Particle induced X-ray emission). In die "Braeburn" proef was daar geen beduidende verskille in terme van vrug Ca konsentrasie op 80 dnvb (dae na volblom) nie. Daarteenoor, was daar wel beduidende verskille by 80 dnvb toe grond toedienings saam met aktiewe wortelgroei geskied het (visuele inspeksie). Weeklikse blaartoedienings vanaf 21 dnvb het gelei tot vrugte met betekenisvol hoër Ca konsentrasies as die behandeling waar grondtoedienings slegs voor-oes geskied het (Januarie 2010). `n Moontlike oorsaak vir die oneffektiwiteit van voor-oes grondtoedings is die vroeë disintigrasie van xileem vesels in die vrug (soms voor 40 dnvb en voor die aanvang van wortelopname) in sensitiewe kultivars soos "Braeburn". Hierdie vroeë inhibering van Ca voorsiening, tesame met die vroeë inisiasie van bitterpit, beklemtoon die belangrikheid van blaarbespuitings vroeg in die seisoen. Die PIXE-analises wat aangewend is om die radiale verspreiding van Ca in die vrug te bepaal het getoon dat Ca meestal in die skil en kern van die vrug gekonsentreer was, met baie lae konsentrasies in die buitenste korteks. Die laagste Ca konsentrasies is waargeneem in vrugte van die behandeling waar voor-oes Ca slegs as `n grondtoediening geskied het. Hierdie waarneming is in ooreenstemming met die mineraalanalise resultate. Ca verykte areas, afkomstig van die naby geleë vaatbundels (xileem vesels), het egter die grootste effek op vrug Ca konsentrasie gehad. Hierdie effek was nie so groot by oes nie en beklemtoon dus die belangrikheid van die funksionaliteit van die vaatbundels. Blaartoedienings kon die Ca konsentrasie in die buitenste korteks suksesvol verhoog - waar simptome van bitterpit tipies voorkom. Die Calflo™ behandeling het beduidende hoër Ca konsentrasies gehad as die Foliar GS™ en GG™ behandelings. Die Calflo™ en Calcimax™ behandelings het `n hoër aktiewe Ca persentasie (12%) relatief tot die Foliar GS™ en GG™ (10%) behandelings bevat. Die byvoeging van Lecithin™ by Calcimax™ word nie aanbeveel nie, omdat dit geensins Ca opname vermeerder het nie. In die "Golden Delicious" proef het die kommersiële behandeling (Sewe weeklikse spuite van Calcinit™) gelei tot vrugte met die hoogste Ca konsentrasie van al die behandelings.

The coal industry of Mpumalanga Province is faced with the problem of developing cost effective ways of using large volumes of calcium and magnesium sulphate enriched waste waters. Use of the waste waters for agricultural production may contribute as a stabilising factor with regard to yields in this high potential agricultural area. The objectives of this study were to determine the effect of such waste waters on yield and to compare crop response to calcium and magnesium sulphate salinity at different nutrient levels. Two separate glasshouse experiments were conducted. Wheat (Triticum aestivum L. cv. SST 825) was grown in calcium and magnesium sulphate salinised nutrient solutions (Ca:Mg 2: 1) with differential levels of NO3, NH4, P and K. A soil pot experiment was subsequently conducted with maize (Zea mays, cv. PAN 6256), three gypsum and magnesium sulphate salinity levels and a 6 x 2 x 3 factorial combination of N, P and K. Calcium and magnesium sulphate salinity decreased the biomass production of both crops. This was mainly due to interactions of Mg with the uptake of essential nutrients in wheat and a Mg toxicity andlor Ca deficiency induced by high levels of Mg andlor SO4 in maize. The application of NO3, NH4, and K at rates different from the level considered beneficial for non-saline conditions improved wheat growth under sulphate saline conditions. Strongly inhibitory salinity levels controlled the maize yield of the highest salinity treatment regardless of the level of fertiliser application. A beneficial effect of higher NH4 supply was observed in both experiments. This can be ascribed to the antagonistic effect that NH4 exerted on Mg concentrations in plants (both experiments) and SO4 (soil pot experiment) and/or to a higher N-utilization efficiency where N was supplied as NH4 compared to NO3. Differential application levels of P had no effect on the yield of wheat. Phosphorus concentrations in maize were marginal to low, even at extremely high soil Bray I-P levels. This was probably caused by the precipitation of P as insoluble calcium phosphate complexes in the soil andlor between the free space of the cortex cells of plant roots. These results could also indicate that the Bray I extraction method does not give a true reflection of plant available P in sulphate saline soil. Further experimentation is needed to verify these results under field conditions and determine the optimal rate, method and timing of especially NH4 and PO4 fertilisers when irrigating crops with these calcium and magnesium sulphate enriched waste waters. / Dissertation (MSc (Plant Production and Soil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

M.S.

Thesis (MscAgric (Horticulture))--University of Stellenbosch, 2007. / Production of quality fruit is the main aim in horticultural crops. Numerous research reports stress the important role of calcium (Ca) in maintaining firmness and preventing the development of physiological disorders in fruit. This study focused on the effect of water and nutrient management strategies, rootstocks and foliar Ca applications on fruit Ca content. Final Ca content/concentration in apple fruit at harvest did not differ significantly between treatments water with micro jets (hand nutrition), water and nutrients with fertigation, or water and nutrients with pulsating drip when applied to ‘Brookfield Gala’ trees in third leaf, on two rootstocks (M793 and M7). In the second trial, three Ca levels were applied to ‘Brookfield Gala’ trees through a pulsating drip system during three phenological periods to evaluate the effect on Ca uptake of the fruit. During the second season, application of high Ca levels for the period full bloom to harvest gave a higher fruit Ca concentration than with applications of standard or low Ca.

In the tobacco production area of Nelspruit, a problem is experienced in increasing the phosphorus content of tobacco leaves to above0.25% despite of the high phosphorus content of the soil (higher than 30 mg/kg Bray 1). The aim of this study was to investigate the reasons for the low P content in tobacco leaves and how P and Ca content in the soil and soil compaction influence it. During the 1998/99 season, field tests were conducted at 3 different localities in the Nelspruit area to investigate the influence of soil compaction, phosphorus and calcium supply on P uptake. Treatment consisted of 2 calcium treatments, 2 soil treatment actions and 5 phosphorus levels. Leaf samples were taken for chemical analysis, 115 to 120 days after planting and the different treatments were harvested as they ripened physiologically and cured in a tobacco drying oven. This was used to calculate the yield, quality and income per hectare. A pot experiment were done under controlled conditions at the experimental farm of the University of Pretoria with soil from one of the field plots. With the pot experiment different bulk densities were simulated with 3 phosphorus and 2 calcium levels, to evaluate the effect thereof on P uptake. As the leaves ripened physiologically they were picked and dried for chemical analysis. On all the data an analysis of variance was performed. A final conclusion can be made that, high levels of P fertilization are unnecessary and attention must be paid to soil compaction, and that gypsum must be applied with care. Although not investigated in this study the low P content of leaves can be due to the genetic characteristics of the tobacco cultivars used in the Nelspruit area and the high levels of zinc in the soil which can cause P precipitation in roots that could restrict the P transport to the leaves. With the pot experiment it is proved that high P applications lead to a decline of the percentage zinc in the leaves. The conclusion is made in this study that when soil compaction were overcome, high and low dosages of phosphorus and the increase of calcium levels in the soil did not show a constant increase in P values above 0.25%. / Dissertation (MSc)--University of Pretoria, 2005. / Plant Production and Soil Science / unrestricted