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

Abstract

Conversion of pasture land to crop rotation by plow tillage and reversion to pasture for replenishment of nutrients is a common practice in New Zealand. It is known that plow tillage decreases soil organic matter and causes biological degradation. The objective of this study was to investigate the effects of tillage practices on soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and earthworm ( Aporrectodea caliginosa) populations used as indicators of soil biological status and of sustainability of permanent pasture (PP) to crop rotation using different tillage practices. The experimental site at Massey University (Turitea Campus) was established in 1995, where PP land was converted to double crop rotation using plow tillage (PT) and no-tillage (NT). Crops were 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 biomass contents in PP and NT treatments were almost twice as much in 0–5 cm depth soil as in 5–10 cm depth soil. No quantitative differences occurred between 0–5 and 5–10 cm depths in the PT treatment. Conversion of PP to PT cropping 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 not differ significantly among the tillage practices and cropping regimes. At 0–10 cm depth, concentrations of MBC, MBN and MBP were significantly higher in the PP and NT than in the PT treatment. MBC and MBN levels in autumn were significantly higher than in summer and winter. Earthworm populations and 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 biological degradation and maintain soil quality as compared with PT management.