Soil properties and lodgepole pine growth on forest landings rehabilitated by tillage and fertilizer application

Abstract

Soils on forest landings are often degraded and unable to support optimal growth of planted conifers unless rehabilitation practices are applied. This study evaluated the effects of tillage and fertilization on soil properties and growth of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seedlings on rehabilitated forest landings in the central interior of British Columbia. Six study sites were rehabilitated in 1998 (but without topsoil replacement) and planted with lodgepole pine in 1999. Tillage treatments were: (i) no tillage; (ii) low intensity (one pass of an excavator and six-toothed rake, target clod size 8–10 cm); (iii) medium intensity (two passes, target clod size 4–7 cm); and, (iv) high intensity (three passes, target clod size 1–3 cm). Fertilizers were applied at the time of planting as slow-release formulations; treatments included: (i) no fertilizer; (ii) NPK-fertilizer; and, (iii) NPK + S-fertilizer. After 5 yr, soil mechanical resistance was higher on the untilled control than the tilled treatments. Neither tillage nor fertilization had any effects on soil chemical properties (total C and N, pH, cation exchange capacity, exchangeable cations). Tillage effects after one growing season were variable; however, after four or five growing seasons, the low-intensity tillage resulted in greater seedling height and diameter growth than the untilled control. After one growing season, fertilization increased seedling height and diameter growth relative to the untreated control, but after four or five growing seasons, fertilization had no effect on lodgepole pine growth. Our findings indicate that a single pass with the excavator and rake was the most suitable rehabilitation practice on these sites. Key words: Forest soil rehabilitation, landing and road rehabilitation, soil conservation, soil degradation, soil compaction, soil productivity