Use of controlled-release fertilizers for young citrus trees

Abstract

The effects of several controlled-release fertilizer compounds were compared with those of a soluble fertilizer mixture on young citrus trees growing in sandy soils under a subtropical environment. Soluble fertilizers were found to be more readily available and had shorter residual effects on leaf and soil N and K than controlled-release fertilizers. The high rate Osmocote (Sierra) treatment gave the highest leaf Mg content in 1988, probably because MgO was included in Osmocote, while MgSO 4 was used in the other fertilizer formulations. In 1988, Osmocote treatments gave the highest leaf Fe concentrations, which could be attributed to the high Fe content in the Osmocote fertilizer. No difference in tree growth was found among soluble and controlled-release fertilizer treatments. Soluble fertilizers produced smaller size fruit and yielded less fruit than controlled-release fertilizers, but the differences in fruit yield were not significant. The lack of significance in fruit yield and in most fruit quality parameters between the soluble and controlled-release fertilizer treatments could be attributed to the highly variable data because it was the first fruit crop. Controlled-release fertilizers were very promising for sandy soils and subtropical environments as they can be applied in smaller amounts and less often than soluble fertilizers, without adverse effects on tree growth or fruit production and quality.