Masters Degrees (Forest and Wood Science)

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Browsing Masters Degrees (Forest and Wood Science) by Author "Badenhorst, Johannes Jurie"

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    The effect of fertilising pinus radiata stands at mid rotation age in the Western Cape Province on leaf area, growth efficiency and stand productivity
    (Stellenbosch : University of Stellenbosch, 2010-03) Badenhorst, Johannes Jurie; Du Toit, Ben; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Mid rotation fertiliser application is generally practised in forestry to enhance nutrient availability in areas were soils are impoverished and do not provide sufficient nutrients for high productivity. Generally speaking there is great potential for mid rotation fertiliser in pine plantations, but stand and site characteristics such as water availability, soil depth, stand density and available nutrients need to be considered before fertiliser treatments are implemented. Foliar nutrient analyses were used to estimate nutrient availability. These levels were measured throughout the study and were used to implement specific fertiliser treatments that would boost nutrient availability. Treatments consisted of an unfertilised control, a single fertiliser application (1F) and two fertiliser applications over two consecutive years (2F). Leaf area index (LAI) and stem volume increment were measured in order to evaluate its influence on growth efficiency. LAI was estimated using the gap fraction method with the use of a ceptometer. Volume increment was calculated with diameter and height measurements. Basal area was calculated by means of diameter measurements. These growth responses were used to determine the effect of increased nutrient availability and although increases were found in LAI, volume increment, basal area increment and growth efficiency, none were significant. The lack of significance may be due to relatively large variations in other factors such as stand density and initial volume of the experimental plots. The 18 month monitoring period apparently did not allow complete reaction time to increased nutrient availability and limited our understanding of the responses somewhat. Despite this, the magnitude of some growth responses was large as nutrient ratios in the foliage increased to levels within the norms range. Increases in current annual volume increment (CAI) of 3.48 m3 ha-1 a-1 and 3.62 m3 ha-1 a-1 in 1F plots at Grabouw and La Motte plantations indicated that it may be economically feasible to fertilise at mid rotation age as the NPV and IRR increased over a projected 25 year rotation. The Grabouw site had the most significant response with regards to CAI in 2F treatment with a mean volume increment of 5.43 m3 ha-1 a-1. The mechanism of the response was examined further by taking water availability and soil characteristics into account. The seasonal climatic effect (length of the moisture growing season) had a significant influence on the response to fertilisation.