Producing quality grass silage

The two vital components of silage quality are: (1) Feed value of crop at harvest. This depends on: crop maturity at harvest; eg stemmier, more mature crops have a lower feed value; sward type, eg many old pasture swards dominated by poor grasses have lower feed value than swards of perennial ryegrass; sward conditions, eg lodged, wet crops can rapidly lose quality and therefore have a disappointing feed value at harvest. Similarly, swards that were not grazed sufficiently short in late autumn or spring can have a stemmy, decaying butt that can reduce feed value at harvest. (2) Efficiency with which the crop is ensiled, preserved and fed. This depends on: only attempting to wilt the crop if it can genuinely dry rapidly; ensiling it free of contamination from soil, animal manure, etc; even and adequate application of appropriate additive if required; fast filling followed by immediate perfect sealing, to ensure the ensiled forage is stored in an air-free environment. Protection of this seal throughout storage; management at feedout that minimises the duration of exposure of silage to air. Balancing grass digestibility with yield: In the majority of Ireland, the most rapid grass growth in normal years is during May and early June, and this is particularly evident in silage swards. At the same time, the grass plant is getting progressively stemmier and heads out. As the latter happens, its feed value/digestibility declines rapidly, especially that of the stem component. The optimal digestibility for silage within any grass-based cattle system will vary depending on factors such as: the level and type of animal production required; the duration for which silage will be offered and its proportion in the diet; intake and conversion efficiency characteristics required of the forage; the value of the animal produce; cost and supply of silage; cost, quality and availability of alternatives; costs of land, buildings and labour. Within these average values, considerable differences occurred between years in grass DM yield on a particular date, and to a lesser extent yearly differences also occurred in digestibility. In general, lighter yields on the swards at the start of May were reflected in lighter yields in late May/early June. Averaged over the six years, grass growth rates were excellent, although they slowed progressively as the season advanced. During the first 35 days, the average growth rate was 140 kg DM/ha/day, while during the final 28 days the average was 72 kg DM/ha/day. Grass digestibilities were good during much of May, and fell more rapidly during June than May. Thus, grass DMD fell by 0.31 percentage units per day during the first 35 days and by 0.39 percentage units per day during the final 28-day duration. These values indicate that for the sward types, location and management systems prevailing, excellent digestibility with a reasonable yield would have been achieved by harvesting at the start of the final week in May. Such silage might suit lactating dairy cows or finishing beef cattle. In contrast, excellent yields of moderate digestibility would have been achieved at the end of the first week in June, and the resultant silage would have suited dry beef suckler cows. Ten tips for making quality first-cut silage: 1. Some farmers consistently make good quality silage. Their repeated success is not just a matter of good fortune. Clearly they use a plan that works. Flexibility will be vital for the plan to succeed, because of the need to adapt to the weather. 2. Preparing silage fields: use livestock to graze silage swards short in late autumn, or graze them in early spring, to avoid the accumulation of an aged low quality butt on the crop; roll the fields when the grass is still quite short but when growth rates are taking off. Soil conditions need to be firm but pliable - they should be firm enough to avoid wheel damage to the field and soft enough to allow levelling by the roller and have any moderate sized stones pushed down. Don't roll the grass after it starts to elongate as this can crush the stems and impair growth; consider controlling weeds such as docks in early May, or prepare to spray them in the regrowth following the first-cut; remove larger stones, pieces of timber and other such obstacles from the silage fields; tidy-up gateways and trim hedges adjacent to them. 3. Apply total nitrogen (N) at from 100 to 125 kg/ha from the combined input of inorganic fertiliser (eg CAN, urea, etc.) and slurry; apply fertiliser and/or slurry evenly and as early as feasible; allow approximately 7 kg N per 4500 litres (1000 gallons) undiluted cattle slurry applied in Feb./March; if N is applied to grazing ground in early spring, assume that 20% remains available for first-cut silage; slurry should only be spread on bare stubble or short grass; there is little real advantage to the silage sward from splitting the application of N fertiliser. 4. Prepare silage and effluent storage facilities: clean out the silos, effluent channels and storage tanks etc and prepare them in plenty of time for the harvest. Carry out any repairs in sufficient time to allow adequate curing of concrete, etc; stack tyres beside the silo to facilitate quickly placing them on the polythene cover once the silo is filled; purchase polythene sheets that conform to the standard IS 246 1989; carefully agitate slurry in tanks so it can be spread on the bare stubble quickly after harvest. Prepare warning notices to go outside gateways onto public roads. Ensure children and strangers do not come too close to the silage-making. 5. Monitor the development of swards. Check out the services and costs of available contractors, and book the contractor of choice in time. 6. If wilting is a target for a farmer, this clearly requires good drying conditions and exposure of a significant amount of the crop to sunshine. Under such conditions: monitor the weather forecast carefully; mow after the dew has dried off the crop, as dew will dry faster from a standing compared to a mown crop; aim that the mown crop would not spend more than one night on the ground; spreading grass to give it full ground cover (ie tedding) immediately after mowing results in the fastest rate of wilting, whereas mowing and combining two or three wide swaths results in the slowest wilting rate. Thus, there can be a significant benefit from the simple technique of opening the gates wide behind the mower conditioner and leaving a wide rather than a narrow swath. Remember that wilting grass is dried mainly by sunshine, so the greater the extent to which mown grass is spread out in thin layers the faster the rate of wilting (weather permitting); - with light crops in good drying conditions, don't overwilt. 7. If an additive is being used, it is important to estimate grass ensilability: Sugars can be measured on farms using a refractometer, while both sugars and buffering capacity can be measured on samples submitted to laboratories; monitor predicted weather conditions; estimate the fresh yield being harvested - this necessitates weighing a strip or trailer-load of grass at harvest time; decide which additive and what application rate is required; ensure the target application rate is achieved, and that the additive is applied evenly. Remember, that many crops do not require treatment with additives. 8. Silo filling and sealing: fill the silo quickly and seal properly beneath two sheets of black 0.125mm polythene; cover completely with a layer of car tyres, placed edge-to-edge; seal the edges with a layer of sandbags, silt, etc; fence the silo from livestock, etc; as the silage sinks somewhat in the silo during the following week or two, check the plastic seal to ensure no ingress of air will occur; ensure the effluent collection system is working properly, and spread effluent on bare silage stubble; if you observe any gas visibly emanating from the silage, stay upwind of it and keep all humans and livestock away from it until it disperses; inspect the polythene cover periodically, and patch any damage that has occurred. 9. Measure the amount of silage in the silo, as this influences subsequent grassland management during season. 10. Long-term: decide where grass silage fits into the farming system, what fields are best suited to silage-making, and how to manage them for next year. How much silage will be realistically needed for next winter, and how much land is required to provide this; ensure land used for silage-making is well drained and is not compacted. Throughout silage-making, slurry and fertiliser spreading, etc., try to avoid causing soil compaction; use perennial ryegrass swards, preferably of intermediate- to late-season cultivars. If reseeding, invest the effort in seedbed preparation, seed-mix selection, sowing, etc. that a 10-year (minimum) investment warrants; ensure adequate soil P and K status, and pH, to permit optimal grass growth. This should be based on regular soil analysis and full cognisance of animal manures spread and inorganic fertiliser applied. Although additional sulphur may be required in some situations, benefit from such application is most likely for second cut silage from sandy soils. Problems with preservation: Each year there are farmers who produce silages that preserve poorly. Among the likely reasons for this are • sward dominated by plants that are difficult to preserve (eg sward of low ryegrass or high clover content) • late, uneven or excess application of nitrogen fertiliser and/or slurry • harvesting very wet grass • mown grass on the ground for a few days without drying • contamination of grass with soil or manure • delayed filling and sealing of the silo If a crop that will be difficult to preserve is about to be harvested, the options open to a farmer include: • don't commence mowing unless soil and weather condition permit the quick completion of harvesting. This could involve deferring mowing and harvesting until the weather picks up, which on some occasions has been a very long delay. • proceed to harvest, but avoid especially wet patches in fields so as to reduce the risk of soil contamination • lift mowing height if possible and adjust machine settings to avoid soil contamination • once the crop is mown, complete harvesting immediately unless a pick-up in weather is imminent • quickly wilt the crop towards a dry matter content of 30%, weather permitting. • apply adequate effective preservative • if grass sugar contents are low and/or buffering capacity is high, the crop will be difficult to preserve properly. The main additive options under these conditions are to apply (a) acid additives through the mower or forage harvester. Developments such as the use of ammonium tetraformate have considerably reduced the corrosion problems associated with acid additives. (b) sugar sources such as molasses on the mown swath or at the silo. The main challenge here is to ensure sufficient additive is evenly applied. (c) sugar sources such as molassed beet pulp or citrus pulp applied at the silo. The overall use of silage additives has decreased considerably in recent years. This is due to • the expansion in the amount of wilted silage (including baled silage) • the delay of harvesting until early June as part of a system of taking a single large cut of stemmier silage (eg for beef suckler cows) • a reluctance by contractors to apply additives in general, and acid or bulky additives in particular • many merchants not being keen to service the application systems for the bulkier additives • better overall silage-making practices reducing the need for preservative additives • an emphasis by farmers on reducing input costs where appropriate Making high DMD silage: • High yielding ryegrass crops are easier to manage, the optimum growth stage at which to harvest them is easier to determine and they more readily preserve as silage (they naturally have high contents of sugar). • Avoid old or dead herbage accumulating at the base of a crop as it can readily reduce crop digestibility by 5-6% units - this means that a crop that should have been 75%DMD on 23 May would be 69-70%DMD instead. Therefore, cattle should graze the silage fields bare before the previous winter or, more likely, graze these fields before late March. • Take full account of the mineral and slurry nitrogen applied for early grazing and silage because excess nitrogen can predispose heavy-yielding crops to lodging in wet windy weather. Whereas the DMD of a normal crop of grass would be expected to decline by about 3% units per week in late May/June, a lodged crop lying under wet conditions can decline by up to 9% units during the same week. • Control weeds such as docks - even leafy docks in silage have a digestibility of only 65%DMD • Don't decide to harvest on a calendar date chosen too early. As a general statement, intermediate-heading ryegrasses are at around 75% DMD when their first seed-heads start to peep from the grass plants. Late-heading ryegrasses can be harvested 8 days later than intermediate-heading varieties with both types of crops having similar yield and ensilability characteristics, but with the later heading crops having a slightly higher digestibility. • Do everything necessary to ensure the silage preserves properly - excellently preserved silage will have a digestibility close to that of the grass from which it was made while poorly preserved silage could lose up to 5% units DMD and have low intake characteristics. Therefore, - only attempt to wilt a crop if it will be genuinely drying while on the ground. A successfully wilted crop will preserve properly. - if using an additive, ensure the full rate of an appropriate product is applied evenly - harvest the grass free of contamination by any dirt - fill the silo quickly and seal perfectly (or wrap bale perfectly) - ensure any effluent can quickly escape from the silo and is safely collected.