Impacts of site preparation techniques on runoff, soil and nitrogen losses during the establishment phase in hoop pine plantations of southeast Queensland

Abstract

Runoff, soil loss and associated nitrogen losses were measured over a 7-year period in recently re-established second rotation hoop pine (Araucaria cunninghamii) plantations and an undisturbed rainforest in southeast Queensland using small-scale catchment plots (ranging between 114 and 403 m2) with modified Gerlach troughs and tipping bucket technology. The effectiveness of prescription cover cropping systems in reducing hillslope erosion was assessed on general plantation areas ranging in slope from 10 to 25°, where the site had been prepared with burning regimes based on either push and burn or broadcast burn. A number of plots were maintained in a relatively vegetation-free state to assess the effectiveness of the cover crops.

The runoff coefficient (runoff/rainfall) throughout the study period was low across all plots with a range between 0.5 and 4.2 % and it was apparent that only small areas of the catchment appeared to be contributing to runoff. Total soil loss over the 7-year study period was typically low (< 5.4 5.4 ha−1) for plots where good germination and development of cover crops had occurred. Plots with poor development of cover crops and those maintained relatively free of cover had greater total soil losses ranging between 16.2 and 87.8 t ha−1. Soil erodibility declined over time in all plots (rainforest excluded) with most soil loss occurring in the first 2 years of the rotation. Subsequently, soil loss was comparable to that found in the undisturbed rainforest. Annual losses of total nitrogen were generally low (< 11 kg ha−1 yr−1) and comparable to estimated annual inputs from the atmosphere and biological fixation.