Abstract:
Proc. Aust. Soc. Anim. Prod. 1996 Vol. 2 I REGROWTH OF A LATE MATURING SOYBEAN FOLLOWING GRAZING AT VARIOUS STAGES OF GROWTH W.K. EHRLICH, R.T. COWAN and N.D. CASEY Dept of Primary Industries, Mutdapilly Research Station, MS 825, Ipswich, Qld 4306 With high stocking rates and intensive management of tropical grasses in a sub-tropical dairying system (Ehrlich et al. 1994), part of the summer grass area could be replaced with crop legumes. Zero tillage technology, used on areas where cultivation is not sustainable, allows a higher quality feed to be offered in autumn. The aim of this experiment was to ascertain the regrowth potential of soybeans. The soybean variety Leichhardt was oversown into a grass pasture and individual plots were grazed starting at 4 weeks after planting and thereafter at 10 day intervals. Pre- and post- grazing yields were measured as well as regrowth yield to late autumn (17 May). Leaf and stem yield measurements were taken at every sampling. Total yield was estimated using the sum of pre-grazing yield plus regrowth. Two 400m2 paddocks were planted to soybeans on 9 February 1995 using a minimal till planter with 300 mm rows to give a final population of 225 000 plants/ha. Grass was controlled with glyphosphate at 2L/ha, 24 hours before planting. The 2 paddocks were each divided into four 20 by 50 metre plots. Five yearling Holstein-Friesian steers were introduced into the allocated plot at 0830 hours and removed the following day when the majority of leaf had been consumed. Plots were irrigated on 1 occasion to prevent plant death. Yields were restricted because of the late planting date and low rainfall during growth. Grazed plots produced similar total dry matter yields (P>O.O5) regardless of the time of grazing, though regrowth potential declined with time. The ungrazed plot produced 1357 kg DM/ha (PcO.01). Leaf percentage was high up to 60 days after planting (average 6 1%) and then declined to an average of 46% for the remaining sample times. Leaf protein declined up to flowering (Table 1) but increased at pod set to 20.6% (PcO.05). Leaf organic matter digestibility and neutral detergent fibre were initially 76 and 23% respectively at the first sampling and averaged 69 and 34% for samplings in the vegetative stage and 74 and 38% in the pod fill stage respectively. Flowering commenced at 2 May sampling and was virtually completed by 11 May with pods starting to fill at the last sampling on 17 May. Table 1. Dry matter yields and leaf protein content at pre-grazing and regrowth and total yield of soybean plots grazed at 10 days intervals EHRLICH, WK., COWAN, R-T., ROMANO, D.A., CROUCH, D.A. and LOWE, K.F. (1994). Proc. Aust. Sot. Anim. Prod. 20: 379. 361
