Soil treatments for improved timber production in Pinus radiata plantations in South Africa

Abstract

Production of Pinus radiata was greatly increased on poorly drained soils by planting trees on elevated planting beds or mounds and an application of phosphogypsum (PG). At 8.5 years of age, timber yields were improved five times by bedding alone or 10 times by bedding combined with PG application when compared to the yield of trees planted with the traditional method of soil pitting. At 20 years of age, the mean annual increment is expected to improve from 1.4 m 3 ha −1 per year in the pitting treatment to 14.9 m 3 ha −1 per year where bedding was combined with PG application. The estimated growth improvement is expected to increase profits to over US$ 2000 ha −1 for a 20-year timber production cycle. Such responses were possible due to improved soil physico-chemical properties. It is believed that other tree species that are sensitive to poor drainage (e.g. Pinus patula) could also benefit from bedding and PG application when planted on poorly drained soils.