Doctoral Degrees (Agronomy)

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Browsing Doctoral Degrees (Agronomy) by Author "Mbangcolo, Mongezi Morrison"

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    The influence of granular and liquid top-dressed nitrogen on nitrogen use efficiency (NUE), grain yield and quality parameters of spring wheat (Triticum aestivum L.)
    (Stellenbosch : Stellenbosch University, 2018-12) Mbangcolo, Mongezi Morrison; Pieterse, P. J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy.
    ENGLISH ABSTRACT: Nitrogen use efficiency (NUE) of major cereal grains including wheat (Triticum aestivum L.) is estimated to be approximately 50% due to losses from leaching, soil denitrification, gaseous plant emissions, volatilization and surface runoff. Use of liquid nitrogen fertiliser to improve grain yields and quality parameters and N use efficiencies has demonstrated positive results; however, responses are inconsistent. Low N use efficiencies indicate the need to improve crop N recoveries and possible lower environmental pollution and the already high production costs. Studies on application of granular and liquid N topdressings to wheat are limited in South Africa. Studies were conducted from 2013-2015 to evaluate the response of NUE, yield and quality parameters of spring wheat to granular (broadcast) and liquid (sprayed) N topdressings under field conditions at two locations (Roodebloem - 34o 13’31.55”S; 19o 26’13.76”E and Langgewens - 33° 16' 33.96" S; 18° 42' 14.4" E) of the Western Cape Province, and controlled glasshouse conditions (2013, 2014 and 2016, and 2014, 2015 and 2016) at the Department of Agronomy, University of Stellenbosch, South Africa. Following applications of N as limestone ammonium nitrate (LAN 28%) at 30 kg N ha-1 at sowing, granular [(LAN (28%), granular urea (46%)] and liquid [urea ammonium nitrate (UAN 32%), liquid urea (46%) solution] N topdressings (30 and 60 kg N ha-1) were applied by means of single (tillering), and split (tillering and flowering) application on spring wheat. The field study results showed that the interaction between locality and growing season significantly affected NUE and grain yields and Roodebloem showed significantly better responses in grain yield in two (2014 and 2015) of the three study years compared to Langgewens. The effect of N rate showed that higher mean grain yield was produced through the application of N at 60 kg ha-1 (3 920 kg ha-1) compared to 30 kg ha-1 (3 577 kg ha-1) at Langgewens in 2013. The N rate x method of N application interaction showed that grain yield was significantly improved by liquid N topdressing at 30 kg ha-1 compared to granular N at 30 kg N ha-1 and liquid N at 60 kg N ha-1. Roodebloem (3 090 kg.ha-1) produced significantly higher mean grain yield compared to Langgewens (2 084 kg ha-1). The protein content and falling number were not significantly affected by N treatment. In the first glasshouse experiment, UAN applied at 60 kg N ha-1 significantly improved grain yield compared to other treatments. The responses showed that 60 kg N ha-1 promoted significantly higher yields and yield parameters compared to 30 kg N ha-1 and that liquid N topdressings were superior compared to granular applied N throughout the study. Similarly, in the second glasshouse experiment, plant responses increased with increasing N rates. The method x timing interaction showed significant differences due to timing of N application for liquid N topdressings. Plants treated with liquid N once at tillering showed superior responses compared to split applications of liquid N. NUE studies showed that different N use efficiency parameters were significantly improved by liquid N topdressings where the effects were significant both under field and glasshouse conditions. Seasonal rainfall was overall the main contributing source of variation in the studies conducted under field conditions .