Effects of close cutting and nitrogen fertilizer on growth of a Siratro (Phaseolus atropurpureus) pasture at Samford, south-eastern Queensland

Abstract

Uninterrupted growth of Siratro (Phaseolus atropurpureus) in a Siratro-grass pasture was slow in spring, increased rapidly in mid-December, and attained a maximum growth rate of 79 lb dry matter an acre a day in February-March. The slow spring growth appeared to be associated with low temperatures. Yield and percentage of Siratro increased for at least 191 days after commencement of growth in spring. Yields of Siratro increased linearly from 1400 lb to 6500 lb dry matter an acre as the cutting interval increased from 4 to 16 weeks. Yields of other species declined as the cutting interval increased. With a 4-weekly cutting regime, the stand of Siratro was greatly reduced after one season. Lucerne subjected to the same treatment gave higher yields and the stand remained good. Urea reduced the mean yield of Siratro by 16 per cent and 33 per cent at the N,, and N,,, levels respectively, but increased total dry matter yields. The response of Siratro to cutting frequency was quite different from that reported for white clover. This difference may be of fundamental importance in the management of sub-tropical grass-legume pastures.