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Doctoral Degrees (Crop Science)

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Browsing Doctoral Degrees (Crop Science) by Subject "Boron in plant nutrition."

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    Nutritional studies with a spanish-type groundnut on an avalon medium sandy loam soil.
    (1972) Snyman, Jacobus Wilhelmus.; Nathanson, Karl.
    Calcium requirements of a Spanish-type groundnut cultivar on an Avalon medium sandy loam soil. The effect of different levels of application of agricultural lime, dolomitic lime and gypsum on yield and quality of the Nelson Spanish groundnut cultivar was studied in a field experiment. The effect of the applied treatments was studied by means of detailed soil and plant analyses. The results reported were obtained in a season with below normal rainfall. The so-called "typical drought damage" symptoms were found to be largely due to nutritional deficiency conditions. A linear increase in kernel yield was obtained as a result of increased levels of exchangeable calcium in the soil. Calcium uptake by the fruit proceeded more efficiently where gypsum was used as calcium carrier. The calcium content of the fruit was increased as a result of increases in the level of exchangeable calcium in the soil. The gypsum treatments resulted in a marked increase in shelling percentage, percentage ovarian cavities filled and increased kernel yield. The mechanism of action of the gypsum treatments was not solely improved calcium nutritional conditions. A poor correlation between calcium content of the soil and the groundnut fruit, and shelling percentage and percentage ovarian cavities filled was obtained in the case of agricultural lime and dolomitic lime treatments. The level of exchangeable soil calcium and soil pH on the majority of groundnut fields investigated was found to be low enough to expect considerable increases in yield following on applications of agricultural lime. Such an increase in pH would result in an improved nitrogen status of the plants as a result of more efficient nitrogen fixation. Applications of agricultural lime should be supplemented with a supply of calcium in a more soluble form, such as gypsum. The more soluble calcium carrier would provide a supply of readily available calcium for uptake over periods of moisture stress. The relationship between chemical composition of the soil and plant, and yield and quality factors were studied. The occurrence, cause and control of hollow heart and black plumule damage in groundnut kernels Hollow heart and black plumule are symptoms of nutritional abnormalities in groundnut kernels. Although the occurrence of these symptoms are associated with the occurrence of drought conditions, the calcium and boron status of the Avalon medium sandy loam is low enough to result in the occurrence of these symptoms on a small scale under normal rainfall conditions. The supply of available boron in the soil is decreased as a result of fixation into an unavailable form during dry periods. Decreased boron concentrations in the plant under these conditions results in the occurrence of boron deficiency symptoms in the kernels (hollow heart damage). At the same time, it is suggested, that due to the nutritional association between calcium and boron in the plant, the decreased levels of boron in the plant results in a decreased metabolic activity of calcium indicated by the occurrence of black plumule damage (a calcium deficiency symptom). The critical level of boron in the kernel as far as both hollow heart and black plumule damage is concerned, appears to be between 10,2 and 13,9 ppm. Applications of gypsum resulted in a marked decrease in hollow heart and black plumule damage. This treatment resulted not only in increased levels of calcium in the kernel, but at the same time appears to prevent the fixation of boron thus allowing normal uptake of boron by the plant. Applications of agricultural and dolomitic lime had no effect on the occurrence of either form of damage. These treatments were associated with a marked increase in calcium content and a decrease in boron content of the kernels. The ratio Ca content of the kernel (ppm)/K content x Mg content of the kernel was found to be fairly closely correlated with the occurrence of black plumule damage. The calcium, potassium and magnesium status of the soil was of little value for the purpose of predicting hollow heart damage. The intensity of hollow heart and black plumule damage was increased by applications of urea. Cultivars differed in their susceptibility to hollow heart and black plumule damage. An application of 26 kg/ha borax virtually eliminated both forms of damage.
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    Soil amelioration and boron nutrition effects on the growth of sunflowers (Helianthus annuus L.) on an Avalon medium sandy loam.
    (1975) Blamey, Frederick Paxton Cardell.; Nathanson, Karl.
    Studies with sunflowers (Helianthus annuus) on an Avalon medium sandy loam, both in pots and in the field, indicated that the poor growth of this crop on this soil was largely due to soil acidity. Marked improvements in plant growth were brought about by liming as shown by measurements of emergence, seedling mass, population, plant heights, leaf areas and yield. Based largely on soil and plant analyses, it was concluded that improved growth with soil amelioration resulted from reduced aluminium toxicity and, since lime was more efficient than gypsum in neutralizing toxic Al, lime was markedly superior to the latter in improving plant growth. An annual application of 2 400 kg agricultural lime/ha increased seed yields >5 fold in the first and >10 fold in the second season in which the field experiment was carried out. In the pot experiment, no benefit of liming above the level required to neutralize toxic Al (-pH (N KCl) 4.5) was recorded and, on the contrary, yields tended to be depressed above this level. Highly significant linear relationships between yield and exch. Al (meq100g) were recorded in the pot and field experiements and, averaged over two seasons, seed yields in the field were increased 12% for each 0,1 meq/100g reduction in exch. Al. Another factor which decreased sunflower seed yields on this soil was boron deficiency and symptoms of B deficiency in the field were identified and described. At the levels of boron in the unfertilized soil, this deficiency affected the reproductive, rather than the vegetative stage of growth and correction of B deficiency by applying 10 kg borax/ha per annum increased seed yields by 38% and 18% in the two seasons, respectively. Soil amelioration had only a slight effect on the boron nutrition of sunflowers in this study. The chemical composition of the plant tissue was found to be a suitable means of quantifying B deficiency in sunflowers, the B concentration being a slightly superior method in most cases to the Ca:B ratio in plant tissue. Using field data, critical B concentrations in (i) month-old seedlings, (ii) the topmost, fully-mature leaf at flowering and (iii) in the seed were determined. The relationships were established between the amount of borax applied to the soil and the B concentration in plant tissues and these relationships could be used as a basis for recommending corrective B fertilization.