Seasonal changes in the proportion and quality of plant parts of nine Stylosanthes lines

Abstract

The distribution of dry matter between leaves, stems and inflorescences, and the nitrogen, phosphorus and sulfur concentration and in vitro digestibility of these parts were measured in uncut swards of nine accessions of seven Stylosanthes spp. grown in northern Queensland over 22 months. Despite above average rainfall in both dry seasons, which greatly reduced the normal moisture stress, only S. guianensis cv. Oxley retained a significant proportion of green leaf in the winter period. However, Oxley set little seed in either year. Plants of the three short-lived species S. hamata, S. humilis and S. subsericea died back to the crown at the end of each wet season, while adult plants of the strongly perennial shrubs S. viscosa, S. scabra and S. fruticosa shed most of their leaves by July. All accessions flowered in both years, and all, except Oxley, set a heavy seed crop by the second year. Some inflorescence was retained on the living stems of the perennial lines until October. This inflorescence had a nutritive value only just below that of young leaf, while the mature stem was low in nitrogen and digestibility in all accessions. The leaf and stem litter had a similar chemical composition to standing material but rapidly became mouldy. The two cultivars of S. humilis, Paterson and Gordon, and S. subsericea had significantly higher levels of nitrogen, phosphorus, sulfur and digestibility than the other accessions. S. viscosa had significantly lower levels of all four attributes. The utilization of the various accessions for improving cattle nutrition is discussed.