An experiment was conducted between February and. July 1982 to study the effect of size of woody framework on edible dry matter accumulation during summer of Leucaena leucocephala cv. Peru. The objective was to determine the effect of spring and early summer grazing management on summer accumulation of feed for autumn/winter grazing.
The site was the CSIRO Samford Pasture Research Station (27⁰S, 152⁰E) in Southeast Queensland, which has a subtropical environment with a mean average rainfall of 1,100 mm.
Cutting treatments at 30, 60 or 120 cm above ground level to simulate severity of prior grazing were applied to a 20 year old leucaena stand on a Prairie soil at altitude 56m, in February after heavy grazing. The treatments were
arranged in a randomized complete block with 5 replications arranged in ascending bush size. The leucaena pasture area was protected from grazing for five months and six sequential destructive harvests were made at four week intervals by cutting at ground level to determine dry matter accumulation, and yield composition and edible dry matter availability for autumn/winter grazing.
Stem size < 6mm in diameter was assumed to be consumed by animals; therefore, leaf and stem < 6 mm were termed edible dry matter.
Edible dry matter increased, with cutting height and period of exclosure and reached an average maximum of 3.0 t/ha in June but dropped 1.5 t/ha in July due to severe frosts which caused loss of leaves. Stem < 6 mm was not affected and contributed to edible dry matter in July compensating in part for leaf loss.
High dry matter accumulation was associated with greater branch length and more growing points which resulted in more leaf development.
The wood dry matter (stem > 6 mm) contributed most to total dry matter yield and ranged from 92% to 72% in February and June respectively. A marked change in yield composition was measured for leaf dry matter which increased rapidly with favourable rainfall and temperatures from 0.3% in February after grazing to 17% in June and dropped sharply
to 5% in July due to frosts.
Results suggested that early regrowth of the three cutting treatments was primarily associated with movement of carbohydrate reserves particularly from stem 6- 25 mm. However regrowth from stumps cut at ground level was rapid indicating translocation of carbohydrate reserves from the roots; a bush height of 125 cm and bush width of 90 cm was attained in the 6 month period with a total dry matter yield, of 800 kg/ha in spite of leaf loss from frosting.
The implications of these results for the summer grazing management of leucaena stands i-s discussed.