Department of Soil Science

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Browsing Department of Soil Science by browse.metadata.advisor "Agenbag, G. A."

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    Response of canola (Brassica napus L.) to increasing nitrogen application rates in contrasting environments
    (Stellenbosch : Stellenbosch University, 2007-12) Van Zyl, J. E.; Agenbag, G. A.; Hoffman, J. E.; Stellenbosch University. Faculty of Agrisciences . Dept. of Agronomy.
    ENGLISH ABSTRACT: The project consisted of three phases: a controlled greenhouse experiment to determine the response of canola to increasing rates of nitrate in the root zone, a controlled greenhouse experiment to determine the response of canola to increasing rates of nitrate in combination with two levels of soil moisture stress and nitrate leaching and a field experiment to determine the reaction of canola to increasing levels of N in four contrasting field environments that was replicated over two seasons. Under controlled greenhouse conditions increasing nitrate levels (0, 4.5, 6.75, 9, and 11.25 me L-1 ) were applied in a 1.5 mS cm-1 nutrient solution. Increases of dry matter production (DM), flower stem production and plant length with increasing concentrations of nitrate was profound. A typical S-shaped response curve of DM to N03 provided a good (R2=0.99) fit of the DM to N03 rates at both 54 and 90 days after planting (OAP). Thus the reaction of canola to increasing levels of N in the root zone was confirmed. Under controlled greenhouse conditions increasing levels of nitrate was added as KN03 (0, 30, 60 and 90 kg N ha-1 ) in combination with a high irrigation regime (N leaching with no soil water stress) and low irrigation regime (no N leaching with periods of soil water stress). A log(x) function provided a good fit to the DM data of both high and low irrigation regimes (R2=0.99 and 0.98 respectively). Although significant amounts of N leached (up to 40.32% of applied N) it was concluded that soil water stress had a greater influence on DM production. Under field trial conditions increasing levels of N was applied as LAN (0, 30, 60, 90 and 120 kg N ha-1 , where 30 kg N ha-1 was either placed or broadcast at the time of planting) in four contrasting environments of the high yield potential growing areas of the Western Cape Province (Langgewens, Elsenburg, Welgevallen and Roodebloem). No difference in plant counts were observed between treatments where N was placed or broadcast at the time of planting. A good correlation was found between DM and applied N (R2=0.97) over both seasons. In both years the highest yields, on average for all localities, were obtained with application rates of 90 kg N ha-1 . Values of nitrogen use efficiencies for all treatments were generally low, due to low N responses while apparent N recovery rates where high. Protein levels in the seed increased while oil levels decreased with increasing N application rates. Keywords: Canola, Nitrogen