Browsing by Author "Nieuwoudt, Stephanus Francois"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    The effect of residue management on the nutrient cycle in the production of rooibos (Aspalathus linearis) at Nieuwoudtville, Northern Cape
    (Stellenbosh : Stellenbosch University, 2017-03) Nieuwoudt, Stephanus Francois; De Clercq, W. P.; Hardie-Pieters, Ailsa G.; Stellenbosch University. Faculty of AgriScience. Dept. of Soil Science.
    ENGLISH ABSTRACT: Rooibos (Aspalathus linearis) is a sensitive fynbos species with a large genetic variation, adapted to acid, nutrient poor soils, and can only be grown in certain parts of the Western- and Northern-Cape. Rooibos yields are getting poorer with increasing age of the field and the lifespan of rooibos are also just a maximum of 5 years commercially produced. A lot of medicinal/health research has been done and published on rooibos, but not much on the agricultural production aspects of rooibos. In order to increase the production and lifespan of rooibos tea further research needs to be done to better understand the rooibos plant in its cultivated environment. The role of leaf litter in fynbos, particularly in the cultivated rooibos nutrient cycle is still a grey area that could open up key management principles regarding plant water availability and plant nutrition style. The hypothesis is that the method of harvesting the rooibos seed by removing the litter layer without returning it under the plant can have a negative impact on the nutrient pools and cycle and thus lead to a shorter lifespan. The main aim was thus to look at the effect of different residue treatments on the rooibos plant nutrient cycle (uptake and nutrient pools). Four sites across the Nieuwoudtville Bokkeveld region were selected with all the rooibos plants being ± 2 years old. Four different mulch treatments; a bare soil (leaf residue removed) treatment imitating seed harvesting (A), an added rooibos mulch (B), a natural leaf mulch (C) and an enriched rooibos mulch (D) were prepared at 4 sites. The chemical properties of soil and plant tissue from rooibos plants were tested. 5TE soil probes were used to measure the volumetric water content, EC and temperature at two soil depths of each treatment. All measurements were also duplicated using near-infrared spectroscopy (NIRS), to generate a database for future reference and to build calibrations that will be able to predict the nutrient content in the soils and plants. It was found that soil chemical properties including P (mg kg-1), Na (cmolc kg-1), K (cmolc kg-1), Ca (cmolc kg-1), Mg (cmolc kg-1), Zn (mg kg-1), Mn (mg kg-1), C (%) and % Na (at pH 7); and plant chemical properties including Na (%) and plant N (%), P (%), K (%), Al (mg kg-1) and Fe (mg kg-1) all had a significant effect of the regrowth models using multiple regression analysis. Soil P, Mg and K had the biggest positive influences on the regrowth models. During this process it was found that the N:P ratio in soil plays an important role in the uptake of N and growth. Only at treatment D, with the lowest soil N:P ratio, plant N (%) had a positive influence on the regrowth multiple regression model. Plant N and P had a moderate positive correlation (R2=0.56). Nutrient uptake by the rooibos plant was very high from July 2015 to September 2015. These nutrients included N, P, K, Ca, Mg, Zn, Mn, Fe and Al. From September 2015 to January 2016 however the uptake was lower for all the nutrients, but for K and Mg the uptake was higher compared to the other nutrients. The decrease in plant nutrient concentration from September 2015 to January 2016 is a result of less nutrient uptake and nutrient dilution following rapid growth of plant. There was an increase in soil exchangeable Mg and Ca from July 2015 to September 2015 due to increase in soil pH during this time. Soil exchangeable Ca (R2=0.49) and Mg (R2=0.61) correlated positively with pH, thus the increase in soil exchangeable Ca and Mg can be due to the increase in pH. For all the treatments there was a total decrease in soil N (significant for A and B) and plant N over the one-year period. The plant Al and Zn for all the treatments also increased over the one-year period. The increase in plant Al was not significant and the increase in plant Zn was significant for all treatments. From July 2015 to January 2016 there were differences in growth between the treatments. Treatment A resulted in the lowest estimated dry matter increase during this period and for treatment B it was the highest. The difference in estimated dry matter increase between these two treatments was also statistically significant. The estimated dry matter increase for treatment C and D was higher than treatment A but it was not significant. The mulch treatments, especially treatment B, resulted in higher P, K and Mg uptake. For all the treatments, except treatment D, the soil P decreased over the one-year period. For treatment B and D the plant P increased significantly compared to treatment A and C where the increase was not significant. The mulch treatments showed an increase in plant K, but it was only significant for treatment B over the one-year period. For all the treatments there was an increase in plant Mg, but only for treatment A the increase was not significant. All the mulch treatments also conserved more water for longer compared to treatment A. The combination of nutrient leaching from the mulch (Mg and K) and the conservation of more soil water may be the reason for the higher nutrient uptake by treatment B and thus the better growth. From the NIRS study it was found that for these sandy soils it was only exchangeable Mg that could be predicted with good accuracy (RPD>2). The soil chemical properties pH, H (cmolc kg-1), K (mg kg-1), Ca (cmolc kg-1), Fe (mg kg-1) and C (%) models showed satisfactory predictability. For plant samples NIRS predicted P (%) and Mg (%) with good accuracy. The prediction models for N (%), K (%), Ca (%) and Na (mg kg-1) were only satisfactory and for the rest it was unreliable. From these results it was thus not possible to quantitatively predict all the chemical properties in the soil and plant samples but there is potential for better calibrations in the future. Differences in growth and vigour can also be attributed to location. The micro conditions in which a single plant grows, related to the impact of normal agricultural practices, was found to also determine the success of rooibos production. The hypothesis was supported by treatment C (the plant where natural mulch was not removed) having a higher estimated dry matter increase compared to treatment A (bare soil), but this difference was not significant. Treatment B (added mulch) however showed to have a significant impact. Rooibos production systems are far from being optimized and the amounts of unknown impacts were narrowed down by this work. This research indicates that the rooibos plant is genetically unrefined and that agricultural practices should focus more towards the natural state of fynbos nutrient availability and growth.