How does soil change after repeated cycles of growing eucalyptus plantations?

Details

This study investigated how soil properties and water infiltration differed across successive rotations of production Eucalyptus plantations in headwater catchments of Phu Tho province, Vietnam. It used a field comparison of 15 plots, each 500 m², representing five rotation cycles—from the first to the fifth—and a natural forest control.

Following Vietnamese national standards (TCVN), researchers assessed soil physical properties—hardness, dry bulk density and porosity—and chemical properties: pH, total organic carbon, total nitrogen, phosphorus and potassium. They also measured infiltration dynamics over 120 minutes using a double ring infiltrometer.

Soil became progressively more compact across rotations. Penetration depth declined from 9 mm in the first rotation to 4 mm in the fifth, and porosity decreased from 38.13% to 28.95%. Porosity in the natural forest control was 46.72%.

Chemical fertility also decreased across rotations. Total organic carbon fell by 39%, from 1.55% to 0.94%, and total nitrogen fell by 33%, from 0.18% to 0.12%. Phosphorus decreased by 45% and potassium by 62%. Soil pH declined from 3.61 to 3.26, compared with 3.71 in the natural forest.

Infiltration followed the same downward pattern. The reported average 5-minute infiltration rate dropped from 72 mm in the first rotation to 33 mm in the fifth. Cumulative infiltration over 120 minutes decreased from 1,808 mm to 812 mm, compared with 2,065 mm in the natural forest.

The researchers concluded that successive Eucalyptus rotations without restorative interventions significantly degrade soil structure, nutrient status and hydrological function.