Browsing by Author "Pretorius, Johannes Jacob"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Evaluating the effect of low flow drip irrigation on selected growth parameters of citrus trees
    (Stellenbosch : Stellenbosch University, 2023-03) Pretorius, Johannes Jacob; Hoffman, Josias Eduard; Raath, Pieter Johannes; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: The use of low flow drip irrigation is preferred nowadays in South Africa due to easier irrigation management, increased ability of precision irrigation and claims of increased water-use efficiency. The aim of the study was to investigate the validity of such claims since there is mounting pressure for all industries to find new methods to save water. Furthermore, it is imperative to investigate the effect that any new irrigation method has on both the soil environment and plant productivity. This study investigated the performance of three different drip delivery rate treatments (T1-1.6 L.h⁻¹, T2-0.7 L.h⁻¹ and T3-0.4 L.h⁻¹) with regards to soil water content (SWC) distribution, soil electrical conductivity and pH distribution, water-use efficiency, tree stress, fruit yield and quality. The soil water content distribution showed that the use of pulsed irrigation with a higher emission rate such as T1-1.6 L.h⁻¹ was most successful in preventing the movement of water out of the active rootzone, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹. For T3-0.4 L.h⁻¹ it was concluded that the application rate was very similar to the overall uptake rate of the trees since there was also a reduced movement of water beyond the active root zone and very small changes in the water content of the main wetted core even as irrigation was applied. The higher application rate of T2-0.7 L.h⁻¹, compared to T3-0.4 L.h⁻¹ led to a greater degree of water movement beyond the active root zone. The calculated water-use efficiencies showed very good agreement with the measured SWC distributions since T1- 1.6 L.h⁻¹ had the highest water-use efficiency, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹ respectively. The electrical conductivity showed good agreement with the soil water distributions since there was an increase in salts at the periphery of the wetted volumes; this became more prominent as the drip delivery rate decreased. All treatments showed severe acidification directly beneath the drippers which was ascribed to the form and quantity of nitrogen that was applied to the trees. The predawn leaf and midday stem water potential measurements taken during the main phenological phases of fruit growth during the 2022 production season concluded that no single treatment was constantly subject to more stress compared to the other. The results did however indicate that all treatments displayed symptoms similar to trees that only have a fraction of the root zone exposed to sufficient water content ranges. Considering the results already discussed, it could be concluded that the availability of soil water to the plants was not only influenced by the physical distribution thereof, but it was also less available due to chemical constraints. The fruit yield of the 2021 production season was mainly influenced by differences in the applied irrigation volumes with T1-1.6 L.h⁻¹ having the highest yield, followed by T2-0.7 L.h⁻¹ and T3-0.4 L.h⁻¹ respectively. Alternate bearing also seemed to have played a role in the yield differences observed for the 2021 and 2022 production seasons. The yield of the 2022 production season was mainly affected by tree physiology and T1-1.6 L.h⁻¹ again had the highest yield, followed by T3-0.4 L.h⁻¹ and T2-0.7 L.h⁻¹ respectively. Overall, the fruit quality was always at acceptable export levels for all treatments.