EFFECT OF LOCK UP AND HARVEST DATES ON DAIRY PASTURE DRY-MATTER YIELDAND QUALITY FOR SILAGE IN SOUTH-WESTERN VICTORIA

At 2 sites in south-western Victoria, 132 plots of predominantly peren nial ryegrass pasture were randomly allocated, within 4 replicate bloc ks, to each of 3 lock up dates (L1, L2, L3) by 12, 12 or 9 harvest tim es. Harvesting commenced 2 weeks after initial treatment lock up with L1 and L2 being harvested 12 times (weekly intervals) and L3, 9 times. Lock up dates were 15 August (L1), 5 September (L2) and 26 September (L3) at site 1 and 17 August (L1), 7 September (L2) and 28 September ( L3) at site 2. For each treatment and harvest date, dry matter yield a nd botanical composition were determined and samples of total pasture and the ryegrass fraction were collected and assessed for dry matter d igestibility, crude protein and neutral detergent fibre. Dry matter yi eld was measured from the start of L1 (site 1, 15 August; site 2, 17 A ugust) until the final harvest date of L3 (site 1, 12 December; site 2 , 14 December). At site 1, L3 produced higher dry matter yields than L 1 and L2 at comparable lengths of lock up time, whilst there were no d ifferences at site 2. Over the total experimental period (site 1, 15 A ugust-12 December; site 2, 17 August-14 December) there were no differ ences in total dry matter yield (t/ha) between treatments at either si te (site 1-L1 5.79, L2 6.43, L3 5.94; site 2-L1 6.68, L2 5.07, L3 5.73 ). Treatments had little effect on botanical composition at either sit e when compared at the same time after lock up, both during the harves ting period or in the subsequent autumn. Pasture metabolisable energy and crude protein all declined with increasing length of lock up whils t neutral detergent fibre content increased, changes which were simila r for both the total pasture and the ryegrass fraction. The metabolisa ble energy of pasture in L1 and L2 was higher than that of L3 at least until week 8 at both sites. Initial crude protein values were higher for L1 and L2 than for L3 at site 1, whilst at site 2, L1 had higher v alues than either L2 or L3. Although longer lock up periods produced m ore herbage, if conserving forage is to be an integral component of ma naging surplus spring pasture, then dairy farmers should aim to produc e high quality pasture fbr forage conservation. This will be achieved through shorter lock up periods and harvesting pasture no later than e arly ear emergence in the ryegrass fraction of the sward. This managem ent will reduce dry matter yields, but allow more flexibility for main taining intensive grazing practices through the spring period. The dec ision about when to lock up pasture will depend on both plant growth r ates and animal feed requirements.