EFFECTS OF PASTURE IMPROVEMENT AND INTENSIVE CULTIVATION ON MICROBIALBIOMASS, ENZYME-ACTIVITIES, AND COMPOSITION AND SIZE OF EARTHWORM POPULATIONS

We investigated the quantity and distribution of organic C, microbial biomass C, protease, arylsulphatase and arylphosphatase activity, and earthworm numbers and biomass in the soil from a 37-year-old grazed pa sture supplied with superphosphate at rates of 0, 188, and 376 kg ha-1 annually. The results were compared with a non-irrigated wilderness s ite which had not been used for agriculture and an arable site that ha d been intensively cultivated for 11 consecutive years. In the 0- to 5 -cm layer, organic C followed the trend arable < wilderness = control < low phosphate = high posphate and soil biological activity generally followed a similar trend. For example, protease and arylsulphatase ac tivity and microbial biomass C followed the order arable < wilderness < control < low phosphate = high phosphate. The greater activity in th e control than the wilderness site was attributed to the more regular turnover of organic matter throughout the year in the control due to t he activity of the grazing animals. Earthworm numbers increased in the order arable < wilderness < control < low phosphate < high phosphate. In the improved pasture sites the earthworm population was dominated by Aporrectodea caliginosa (77-89% of total numbers) although Lumbricu s rubellus made an increasing contribution to the population with incr easing superphosphate rates. In the unirrigated wilderness site the po pulation consisted of 56% A. caliginosa and 44% L. rubellus. While Oct olasion cyaneum and A. rosea made up a small proportion of the populat ion in the improved pasture sites, they were not present in the wilder ness or arable sites. A. caliginosa was the only species present in th e arable site. The mean fresh weight of individuals followed the order arable < control = low phosphate = high phosphate < wilderness and th e proportion of jeveniles in the population was greatest in the arable and lowest in the wilderness site.