Effect of different rates of sulphur fertilization on fruit yield and leaf mineral composition of 'Valencia' oranges in the subtropical environment of South Africa
2013
Murovhi, N.R.
Although sulphur is one of the essential nutrients for plant growth with a crop requirement similar to phosphorus (P), this nutrient element has received little attention because it is supplied in insecticides, fungicides, manure and from the atmosphere. With the relaxation of this requirement, and restrictions on sulphur dioxide emissions by industries it has become apparent that sulphur deficiency is widespread throughout the world. The majority of farmers submitting samples for soil and leaf nutrient analysis do not request a sulphur (S) test. This is due to the fact that farmers are still under the impression that there is enough sulphur in the soil. This study was carried out at Nelspruit, South Africa, to determine the influence of sulphur fertilizers on fruit yield and leaf mineral composition of a 13-year-old ‘Valencia’ (Citrus sinensis) orchard. Forty five plants, in as good physiological condition as possible were selected. Brimstone 90 fertilizer was used as the source of sulphur and the following five rates were applied (0, 60, 120, 180 and 240 g S tree-1 season-1). A randomized complete block design with three replications was used in the experiment. Data revealed that soil pH, potassium (K), sodium (Na) and zinc (Zn) decreased with increasing levels of sulphur while P and Al increased. Increasing the rate of sulphur at 240 g tree-1 increased the leaf sulphur content from 0.29 to 0.36% which is considered as a critical level for optimum fruit production in orange trees. Leaf Mg content increased with increasing levels of sulphur while nitrogen (N), iron (Fe) and boron (B) contents of the leaves significantly decreased. The application of sulphur at 240 g S tree-1 significantly (P<0.05) increased fruit yield as well as the number of fruit tree-1. The results emphasized the importance of applying sulphur to facilitate an increase in fruit yield of ‘Valencia’ orange trees.
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