Masters Degrees (Agricultural Economics)

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Browsing Masters Degrees (Agricultural Economics) by browse.metadata.advisor "Combrink, N. J. J."

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    The influence of boron at different calcium levels on the growth, yield and mineral content of canola, Brassica napus L.
    (Stellenbosch : Stellenbosch University, 1999-12) Hanekom, Dirk Johan; Combrink, N. J. J.; Arkcoll, D. B.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agricultural Economics.
    ENGLISH ABSTRACT: Oilseed rape plants were grown in pots in two glasshouse trials during 1992 and 1993. Plants received 2 calcium (Ca) rates and 4 boron (B) rates in a factorial design. During the first experiment B rates were 0.2, 0.5, 0.8 and 1.1 and 0.1, 0.5, 0.8 and 1.1 ppm during the second experiment. Ca rates were 117.4 and 182.1 during the first experiment and 56.7 and 182.1 ppm during the second experiment. A study of the vegetative growth showed that, Ca had no consistent effect on growth or the parameters measured, nor did it show any interaction with B. In general B application rates during the first experiment had little effect on vegetative growth. During the second experiment low B (0.1 ppm) had a significant influence on most of the variants measured. Leaf-, stem-, and root growth as well as total plant dry matter were detrimentally affected at the later stages of plant development. Analysis of the reproductive growth showed that, Ca had no significant effect on the parameters measured, nor did it show any interaction with B. B application rates during the first experiment had no significant effect on the amount of pods, pod mass, seeds per pod, thousand kernel mass or dry mass of crop residue, but did affect the amount and mass of seeds produced per plant. During the second experiment low B (0.1 ppm) had a significant effect on the formation of pods and the production of seeds. The amount of pods, pod mass, seeds per pod, seeds per plant, seed mass per plant, dry mass of crop residue and harvest index (HI) were all negatively affected. High B (1.1 ppm) had a positive effect on the thousand kernel mass (TKW). Leaf, stem and pods from the second experiment (1993) were analyzed at different sampling dates to determine the influence of Ca and B application on the accumulation of elements in different plant organs. The data confirmed that levels of all elements vary between plant tissues and with their physiological age. Ca, Mg, Mn and B tend to build up in the leaf tissue of the plant while N, P, K, Na, Cu, Zn and Fe were diluted at rates that depended on the growth of the specific plant part analyzed. The effect of applied Ca on plant Ca content was small and Ca effects on the concentrations of most elements were very small or negligible and unclear. Some effects on K and Mg were observed and can be explained by differences in the concentrations applied due to cation corrections. Low B (0.1 ppm) resulted in elevated levels of N, P, K, Ca and Mg in the main- and side stem tissue which was probably caused by a reduction in growth of these plant parts induced by B deficiency. The only consistent effect of B was a negative effect on the Mn content of all of the tissue analyzed. B appeared to accumulate in the leaf. but not in the stem as the plants aged, making the latter more suitable for analysis when physiological age of tissue cannot be accounted for. Low B (0.1 ppm) caused low B values in stem tissue but increasing B levels did not increase the B concentrations in tissue to follow linearly. This could give a false indication of availability of B as higher B applications were not reflected in tissue levels. As B tend to accumulate in leaf tissue the physiological age of leaf tissue is therefore critical when used for analysis. B content in leaf tissue followed the application rates more closely than that of other tissue analyzed and gave a better indication of availability of B, but was dependent on the physiological age of the tissue.