A COMPARISON OF SOIL AND MICROBIAL CARBON, NITROGEN, AND PHOSPHORUS CONTENTS, AND MACRO-AGGREGATE STABILITY OF A SOIL UNDER NATIVE FOREST AND AFTER CLEARANCE FOR PASTURES AND PLANTATION FOREST

Total, extractable, and microbial C, N, and P, soil respiration, and t he water stability of soil aggregates in the F-H layer and top 20 cm o f soil of a New Zealand yellow-brown earth (Typic Dystrochrept) were c ompared under long-term indigenous native forest (Nothofagus truncata) , exotic forest (Pinus radiata), unfertilized and fertilized grass/clo ver pastures, and gorse scrub (Ulex europaeus). Microbial biomass C ra nged from 1100 kg ha-1 (exotic forest) to 1310 kg ha-1 (gorse scrub), and comprised 1-2% of the organic C. Microbial N and P comprised 138-2 82 and 69-119 kg ha-1 respectively, with the highest values found unde r pasture. Microbial N and P comprised 1.8-7.0 and 4.9-18% of total N and P in the topsoils, and 1.8-4.4 and 23-32%, respectively, in the F- H material. Organic C and N were higher under gorse scrub than other v egetation. Total and extractable P were highest under fertilized pastu re. Annual fluxes through the soil microbial biomass were estimated to be 36-85 kg N ha-1 and 18-36 kg P ha-1, sufficiently large to make a substantial contribution to plant requirements. Differences in macro-a ggregate stability were generally small. The current status of this so il several years after the establishment of exotic forestry, pastoral farming, or subsequent reversion to scrubland is that, compared to lev els under native forest, there has been no decline in soil and microbi al C, N, and P contents or macro-aggregate stability.