Browsing by Author "Parker, Imaan"

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    Comparison of nutrient use efficiencies in citrus under different fertilization and irrigation management practices
    (Stellenbosch : Stellenbosch University, 2024-03) Parker, Imaan; Hardie-Pieters, Ailsa G.; Raath, Pieter J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
    ENGLISH ABSTRACT: Excessive applications of nitrogen and phosphorus can lead to soil acidification, runoff, leaching and groundwater contamination. Additionally, the production of synthetic nitrogen fertilisers is an energy- intensive process, while phosphorus fertilisers are derived from non-renewable sources. This underscores the need for the citrus industry to adopt more sustainable management practices, with focus on improving nutrient use efficiency (NUE). Despite extensive research on the NUE of annual crops such as cereal grains and maize in South Africa, little research has been conducted on perennial crops such as citrus. Additionally, there is a need for NUE benchmarks that producers can use to compare their own NUE values with to. The main aim of this study was therefore to gain an understanding of the factors affecting nutrient use efficiency (NUE) of citrus, and to quantitively compare the NUE of different production systems currently used within the citrus industry. Various NUE indices were evaluated over two production seasons, in four of the main citrus production regions of South Africa. Within each region, three to four different irrigation-fertiliser production systems were selected, namely, conventional drip [1.6 L h-1] with fertigation (Drip), low-flow continuous drip [< 1 L h-1] with fertigation (LowFlow), micro-sprinkler irrigation with fertigation (MicroFert) and micro-sprinkler irrigation with granular fertiliser (MicroGran). There were significant differences between production systems in terms of partial factor productivity (PFP), partial nutrient balance (PNB) and internal utilization efficiency (IE). The MicroGran treatment consistently had higher PFP in both seasons of the study. Furthermore, the results showed that production systems (treatments) that applied excessive fertiliser rates or had low yields, exhibited significantly lower PFP and PNB values, this was seen in the LowFlow production systems (treatments) during both seasons. In the 2021/22 season the MicroGran treatment exhibited the highest average yield (62 ton ha-1), while in the 2022/23 season the MicroFert treatment obtained the highest average yield (81 ton ha-1). No significant differences were found between PFP and PNB values among the Drip, MicroFert and MicroGran production systems (treatments), when looking at the main effects of production systems (treatments). When yields between 50-80 ton ha-1 are obtained, producers can expect to achieve PFPN of 406- 424 kg kg-1, and PNBN values 0.68-0.76 kg kg-1, when using Drip, MicroFert and MicroGran production systems. Whereas for LowFlow production systems (treatments) can expect PFPN and PNBN values of 178 and 0.30 kg kg-1. Additionally, the study calculated indices that make use of data from a control plot which received no fertiliser. These indices include agronomic efficiency (AE), crop recovery efficiency (RE) and physiological efficiency (PE). These indices showed the crop response specifically to the fertiliser applied. Results highlighted the significance of interpreting leaf analysis and NUE along with soil analysis, as there were some significant correlations between soil properties and these factors. Soil analysis is especially important for interpreting PNB values. Furthermore, the study showed that NUE is not only dependent on the fertiliser applied but also influenced by mineralizable nutrients in the soil and the remobilization of nutrients stored within the plant biomass. To achieve optimal NUE, it is important to consider all these factors.