Tillage impacts on soil microbial biomass C, N and P, earthworms and agronomy after two years of cropping following permanent pasture in New Zealand

Conversion of pasture land to crop rotation by plow tillage and reversion t o pasture for replenishment of nutrients is a common practice in New Zealan d. It is known that plow tillage decreases soil organic matter and causes b iological degradation. The objective of this study was to investigate the e ffects of tillage practices on soil microbial biomass carbon (MBC), microbi al biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and earthwor m (Aporrectodea caliginosa) populations used as indicators of soil biologic al status and of sustainability of permanent pasture (PP) to crop rotation using different tillage practices. The experimental site at Massey Universi ty (Turitea Campus) was established in 1995, where PP land was converted to double crop rotation using plow tillage (PT) and no-tillage (NT), Crops we re summer fodder maize (Zea mays L.) and winter oat (Avena sativa L.); and PP was used as a control. Plant establishment and crop yields were similar in NT and PT, although adoption of NT reduced weed growth. Microbial biomas s contents in PP and NT treatments were almost twice as much in 0-5 cm dept h soil as in 5-10 cm depth soil. No quantitative differences occurred betwe en 0-5 and 5-10 cm depths in the PT treatment. Conversion of PP to PT cropp ing resulted in a 45% decline in MBC, 53% in MBN and 51% in MBP in the 0-5 cm soil layer. Microbial biomass content ratios in the 5-10 cm layer did no t differ significantly among the tillage practices and cropping regimes. At 0-10 cm depth, concentrations of MBC, MBN and MBP were significantly highe r in the PP and NT than in the PT treatment. MBC and MBN levels in autumn w ere significantly higher than in summer and winter. Earthworm populations a nd live mass were also significantly higher in the PP and NT than in the PT treatment. It was concluded that adoption of NT can protect soils from bio logical degradation and maintain soil quality as compared with PT managemen t. (C) 1999 Elsevier Science B.V. All rights reserved.