Woody residue management to reduce nitrogen and phosphorus leaching from sandy soil after clear-felling Pinus radiata plantations

We studied the potential of woody residue management to reduce N and P leaching from sandy soils after clear-felling Pinus radiata D. Don. stands in southeastern Australia. Treatment variables were (i) branch diameter, (ii) branch mass, (iii) branch placement (surface or buried), and (iv) branch comminution. Treatments were applied to zero-tension lysimeters containing homogenized soil, forest floor, and green needles. Leachates from these treatments were collected weekly for 2 years and analysed for mineral N (N-m), soluble organic N, and total soluble P. Addition of 60 Mg.ha(-1) of branch residue to the soil surface reduced N-m leaching by 13%, but the same quantity of buried branch reduced N-m leaching by 27%. Comminuting branches before burying further reduced N-m leaching. Much of the effect of placement, mass, and comminution on N, leaching was related to differences in the surface area of branch material in contact with soil. Comminuting and burying branches reduced P leaching by 31%. An increase in branch N content after 2 years was linearly related to the reduction in N-m leached but accounted for only 23-48% of this reduction. Irrespective of treatment, there were linear relationships between the N and P concentrations in remaining material and the relative mass loss of wood and bark.