The effects of soil compaction and fertilizer application on the establishment and growth of Pinus radiata

Ground-based harvest operations in planted forests can adversely affect the soil and subsequently the productivity of the plantation. This study examined the effects of compaction, site preparation, and fertilization on soil physical and chemical properties and tree growth in a trial established at a second-rotation harvest on an imperfectly drained clay loam located in the North Island, New Zealand. Treatments were installed following harvest of Pinus radiata D. Don. There were four physical treatments: no treatment, compaction in rows by skidder, site preparation (rip and disk), and compaction followed by site preparation; the three nutrient treatments included no fertilizer, nitrogen (N), and N plus phosphorus (P). Response of P. radiata was studied for the first 4 years of growth. Compaction reduced survival of P. radiata at planting and during the first year of growth as the result of an increased oxygen deficit, caused by a reduction in macropore volume, and a shallower depth to the perched water table. Site preparation improved both survival of the seedlings and growth over 4 years. There was an initial growth response to N, but fertilizer did not increase survival of the seedlings. After 4 years, both site preparation and N plus P treatments gave approximately 10% extra growth, suggesting that N plus P may have been as effective as site preparation for improved growth of the trees that survived the first 2 years. However, since survival of seedlings is important to the economics of plantations, especially where planting densities are low, site preparation of soils with low macropore volume should be considered as a management tool.