Competition for nitrogen between Pinusradiata and pasture. II. Trends in plant and soil processes

Abstract

15N-labelled nitrogen fertilizer was used to examine the competition for N between 4-year-old Pinusradiata D. Don and pasture grasses during one 8-month growing season. Availability and tree and pasture uptake of 15N-labelled fertilizer applied in spring were measured. Larger quantities of 15NO3−-N than 15NH4+-N remained available in the soil throughout the growing season. However, P. radiata assimilated similar quantities of 15N when supplied as 15NO3−-N or 15NH4+-N and uptake by pasture herbage was greater for 15NO3−-N than for 15NH4+-N. Removing pasture by spraying with herbicide increased the availability of soil 15N soon after application and doubled the uptake of 15N by P. radiata although the pattern of N uptake was not greatly affected.