Managing soil fertility in eucalypt plantations in China

More than 1.5 M ha of eucalypt plantations have been established in south China, increasing by about 100,000 ha y. Productivity is uneven and low, only about 25-50% of the world average for eucalypt plantations. Most land available for eucalypts are degraded oxisols and utilsols which also are acidic, highly leached and deeply weathered. Phosphorus deficiency is very severe and its availability is reduced because of limited compatible ectomycorrhizal fungi. Nitrogen supply is limited because of low organic matter content in the topsoil. This paper reviews a decade of field trials in the region concerning the use of fertilisers, harvest residue management and inoculation with ectomycorrhizal fungi. One of the key questions addressed is whether the productivity of plantation eucalypts in south China can be increased to the world average by nutrient management across a rotation. Some of the key findings are: Application of superphosphate at establishment substantially increased growth, tree survival and nutrient uptake. Coppice response to P was lower than the response to P in the first rotation. Inoculation with ectomycorrhizal fungi affected stand volume. Field effects were isolate-dependent, and poorly related to performance of isolates in the greenhouse. Reduction in the amount of residue removed during harvest increased tree growth by increasing available nutrient supply and reducing the loss of soil organic C. Intercropping with N-fixing trees enhanced tree growth. More than 80% of nutrient accumulation by trees was lost via harvesting practices. It is concluded that productivity of plantation eucalypts can be improved to 10-20 m ha y, the average productivity in the world, by nutrient management. Harvest residue retention and coppice regeneration are recommended as operational practices in the second rotation. Research indicates that the productivity of well-managed plantations can be sustained whereas poor management practices result in dramatic yield declines across rotations.