Browsing by Author "Scheepers, Gerhardus Petrus"

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    The effect of wood ash on the soil properties and nutrition and growth of Eucalyptus grandis x urophylla grown on a sandy coastal soil in Zululand
    (2014-12) Scheepers, Gerhardus Petrus; Du Toit, Ben; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: A field trial of six replications was established to test the effect of various wood ash and fertilisers application rates on soil chemistry, tree nutrition and early growth rate of a clonal Eucalyptus grandis x urophylla stand. Wood ash from pulpmills is currently disposed of in landfills. Increasing costs and potential environmental risks have driven companies to investigate alternative disposal methods. Ash consists of a combination of carbonates, hydroxides and other calcium containing minerals that induce the liming effect if ash is applied to a soil. The trial was established near Richards Bay in October 2013 on a sandy soil with a low buffer capacity and a pH of approximately 5.5. The trial consists of four wood ash application rates in combination with three levels of fertiliser, viz. no fertiliser, 150 g conventional NPK fertiliser mixture, or 320g NPK controlled release mixture. Fertiliser mixtures and application levels were based on previous fertiliser trials in the region. Ash application rates for the field trial were based on a lab incubation study done with soil samples from Richards Bay, to which increasing amounts of lime were added. The study tested wood ash application rates of 0, 300, 600 and 1200 kg/ha. Field measurements were taken at 4 and 8 months after trial establishment. The primary objective was to investigate which application levels in combination with the type of fertiliser could be applied to soils without negatively affecting the stand nutrition or increase the levels of potentially harmful elements in the soil; thus investigating the feasibility of safely disposing wood ash on plantation soils as an alternative disposal method. Soil nutrient concentrations were not affected by individual wood ash treatments, but more a product of the time interval after the ash additions were made. Soil C, P, K+ and Mg2+ showed decreased concentrations from 4-8 months after establishment. Ca2+ concentrations increased in the same time interval. In addition, Na+ and B concentrations decreased from 4-8 months. Soil heavy metal concentrations for Cd, Hg, Cr and Pb, analysed for 0-1200 kg/ha ash rates, were well below toxic levels at both time intervals. Wood ash induced a temporary liming effect. Mean soil pH increased with 0.6 units for the period 0 - 4 months and decreased with 0.4 units at 4 - 8 months after trial establishment. Foliar nutrient analyses and assessment techniques revealed sub-optimal nutrient concentrations for P, K and Zn at 4 and 8 months of age. Concentrations were defined as sub-optimal, as none of the nutrients were below critical levels. Foliar heavy metal concentrations for Cd, Hg, Cr and Pb, measured at both time intervals, were less than 1mg/kg. The small concentrations found in this project were attributed to the low bioavailability of all four elements and were likely a product of the edaphic factors at Richards Bay, which was representative of a large greater portion of the Zululand coastal plain sites. The response in biomass index ranged between 13 % and 683 % relative to the control treatment (A0F0). Results showed that application of purely wood ash, or in combination with a supplementary N and P source increased growth up to 8 months after trial establishment for wood ash applications up to 1200 kg/ha. This project demonstrated that 1200 kg/ha wood ash can safely be disposed of on a typical Zululand coastal sand with little environmental risk and no supressed growth, provided that it is balanced with an appropriate NP fertiliser.
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    Potential for utilization of wood ash on coastal arenosols with limited buffer capacity in KwaZulu-Natal and its effect on eucalypt stand nutrition and growth
    (Italian Society of Silviculture and Forest Ecology, 2017) Scheepers, Gerhardus Petrus; Du Toit, Ben
    ENGLISH ABSTRACT: A field trial was established to test the effects of various wood ash and fertilizer application rates on the nutrition and early growth of a clonal Eucalyptus grandis × urophylla stand near Richards Bay, KwaZulu-Natal province, South Africa. The trial consisted of wood ash treatments of 0, 0.3, 0.6 and 1.2 t ha-1, combined with fertilizer treatments of no fertilizer (control), 150 g tree-1 of conventional ammonium sulphate fertilizer or 320 g tree-1 of controlled release fertilizer mixture containing N, P and a balanced suite of several plant nutrients. The experiment was conducted on a young sandy soil of aeolian origin with a very low buffer capacity. Ash application rates were chosen after a pilot study was conducted to test the effect of CaCO3 on the soil reaction. At 4 and 8 months after treatment, soil heavy metal concentrations for cadmium (Cd), mercury (Hg), chromium (Cr) and lead (Pb) levels were substantially lower than toxic levels. Foliar heavy metal concentrations (for the same elements) were less than 1mg kg-1 at both time intervals. The wood ash induced a temporary liming effect up to 8 months after application. Foliar nutrient assessments revealed sub-optimal nutrient concentrations for phosphorous (P), potassium (K) and zinc (Zn) at 4 months and K at 8 months of age. The positive growth responses (expressed as a biomass index) at 8 months, ranged between 13% and 683% relative to the untreated control. At 21 months, the growth response to ash and fertilizer combinations ranged from -0.5% to 50% relative to the control. This research demonstrated that 1.2 t ha-1 of wood ash can safely be disposed of on a typical, poorly buffered Zululand coastal sand with little environmental risk and minimal growth suppression, provided that it is balanced with an appropriate NPS plus trace element fertilizer mixture.