The influence of cultural practices on soil organic matter, soil biomass size and nitrogen leaching : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science (Agricultural Environmental Science) at Massey University, New Zealand

Abstract

The effects of bare fallow, cultivation and nitrogen application on soil organic matter, soil biomass and nitrogen leaching were compared against the backgrounds of permanent grass pasture and grass/clover pasture. Cultivated plots were dug annually to a depth of 15cm. All plots received an annual dressing of 300kg ha·1 of Potassic Super. The Nitrogen treatment was applied as two equal applications of 100kg ha·1 Calcium Ammonium Nitrate in November and December each year.

The results indicated that both bare fallowing and cultivation reduced soil organic matter and soil microbial biomass. The use of N-fertilizer did not promote either the soil organic matter or soil microbial biomass; this is contrary to the general finding.

Legume nitrogen was found to leach as readily as the applied nitrogen and hence posed an environmental threat to groundwater quality. In all cultural practices the largest concentration of nitrate nitrogen (NO3-N) was observed at the 50 - 100m depth, below the root zone. Vertical movement of groundwater was estimated at lm year·1 This confirmed the concern of possible groundwater pollution by nitrate nitrogen from agricultural activities.