IX. Canterbury Plains, Kirwee

Abstract

N fixation by Trifolium repens L., cv. ‘Grasslands Huia’ in rotationally grazed, dryland and irrigated sheep pastures, was estimated over 2 years, using the acetylene reduction assay. Estimates of total N fixed annually ranged from 106–145 kg N/ha (dryland) to 152–226 kg N/ha (irrigated). There was negligible fixation over winter and pronounced peaks of activity in spring and autumn, with a trough in summer. Spring and autumn fixation rates correlated well with clover growth rates and temperature. Summer fixation rates were affected by drought on the dryland farmlet and a further factor, probably N mineralisation.