CHANGES IN SOIL PROPERTIES AND FOLIAGE NUTRIENT COMPOSITION IN DIFFERENT AGE CLASSES OF <em>EUCALYPTUS</em> <em>CAMALDULENSIS</em> PLANTATION

Abstract

A study was carried out on the changes in soil properties and foliage nutrients of
Eucalyptus camaldulensis plantation in arid areas to determine the effect of establishing plantations on the fertility of a desert soil and their management. Distributions of soil organic matter (SOM), nutrients, pH and their influences on growth and foliage nutrient composition were investigated in a randomly selected block plantation representing different age classes, namely, 4 years (Y₄), 6 years (Y₆), 8 years (Y₈), 10 years (Y₁₀), 12 years (Y₁₂) and 18 years (Y₁₈). Height and diameter at breast height (dbh) of the stand ranged from 9.2 to 25.7 m and 9.4 to 21.5 cm respectively, depending on the age of the stand. Foliage nutrients were in order of Ca>N>K>Mg > P and differed considerably between different ages. Foliage N and P increased until Y₁₂ and decreased afterwards. The other nutrients did not show any clear trend of increasing/decreasing except for Mn and Fe. Changes in canopy size and nutrient mobilisation during tree development were important in foliage nutrient compositions. This is due to change in biogeochemistry of the soil, particularly the amount of SOM which increased with increasing age of the stand. Soil organic matter and nitrogen (NH₄-N + NO₃-N) were significantly higher in the 0-15 cm layer compared with the 15-30 cm layer. Soil nutrients were significantly higher in the plantation area compared with the non-planted control plot. Soil pH, PO₄-P, Ca, Mg and K concentrations decreased with stand age whereas SOM, NH₄-N, NO,-N, Cu, Zn and Mn increased. There was a general decrease in basic cations; however, SOM, NH₄-N and NO₃-N increased in the soil. The study thus suggested that plantations require fertiliser application and/or thinning after 12 years to manage the problem of nutrient depletion.