Response of canola (Brassica napus L.) to increasing nitrogen application rates in contrasting environments

Van Zyl, J. E. (2007-12)

Thesis (MScAgric)--University of Stellenbosch, 2007.

Thesis

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

AFRIKAANSE OPSOMMING: Die projek het bestaan uit drie fases: 'n beheerde glashuis eksperiment om die reaksie. van canola tot stygende nitraat vlakke in die wortelsone vas te stel, 'n beheerde glashuis eksperiment om die reaksie van canola tot stygende nitraat vlakke in kombinasie met twee vlakke van waterstremming en nitraat loging vas te stel en 'n veld proef om die reaksie van canola teenoor stygende vlakke van N in kontrasterende omgewings vas te stel. Stygende vlakke van nitraat (0, 4.5, 6.75, · 9, and 11.25 me L-1 ) in 'n 1.5 ms cm-1 voedingsoplossing is aangewend onder glashuis toestande. Verhoging van droe materiaalproduksie (DM), blomsteelproduksie en plantlengte met stygende nitraatvlakke was opmerklik. 'n Tipiese s-vormige kurwe het 'n goeie passing (R2=0.99) op die DM data van 54 en 90 dae na plant (DAP) gelewer en sodoende is die reaksie van canola tot stygende vlakke van nitraat bevestig. Stygende vlakke van nitraat (0, 30, 60 and 90 kg N ha-1 ) is toegedien as KN03 onder glashuis kondisies in kombinasie met 'n hoe (N loging met geen water stremming) en 'n lae (geen loging met water stremming) besproeiings vlak. 'n Log(x) funksie het goeie passing van die DM data gelewer by beide die hoe en lae besproeiings vlakke (R2=0.99 en 0.98 onderskeidelik). Alhoewel betekenisvolle hoeveelhede N geloog het (tot 40.32% van toegediende N) is dit vasgestel dat waterstremming 'n groter invloed op DM produksie kan he as die beskikbaarheid van N per se. Onder veld toestande is stygende vlakke van N as KAN toegedien (0, 30, 60, 90 and 120 kg N ha-1 , waar 30 kg N ha-1 of breedwerpig gestrooi of gebandplaas is met planttyd) in vier kontrasterende omgewings in hoe opbrengs potensiaal gebiede van die Wes-Kaap (Langgewens, Elsenburg, Welgevallen and Roodebloem). Geen verskil in plante tellings is gevind waar N gebandplaas of breedwerpig uitgestrooi is nie. 'n Goeie korrelasie is gevind tussen DM en toegediende N (R2=0.97) oor beide seisoene. Hoogste opbrengs, gemiddeld oor lokaliteite, is in beide jare verkry met toedienings van 90 kg N ha-1 . Waardes van N gebruiks effektiewiteit was oor die algemeen laag, vanwee die klein reaksie van canola tot N bemesting, terwyl die skynbare N onginningswaardes hoog was. Proteinvlakke in die saad het verhoog en olievlakke het verlaag met 'n verhoogde toediening van N. Sleutelwoorde: Canola, Stikstof

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