Issues relating to making first-cut grass silage

Padraig O'Kiely

 Teagasc, Grange Research Centre

[Article for Irish Farmers Journal, April 2003]

 

This article will cover the following topics:

·         Silage quality matters - a reminder after last season

·         Balancing grass digestibility with yield

·         Ten tips for making quality first-cut silage

 

Silage quality matters - a reminder after last season

The wet and cold weather last May and June meant that when many farmers eventually managed to salvage their meadows for silage, they produced quantities of feedstuffs that supported very disappointing animal performance. On some farms silage quality barely supported the maintenance of livestock during the winter. Clearly, the delayed harvest together with the associated wet crops, soft ground conditions, etc., combined to lower a number of aspects of silage quality.

Silage quality, or feed value, determines the amount of forage cattle will eat when they are given ad libitum access to it, the efficiency with which they will convert it into meat and/or milk, the quantity and often the quality of the meat/milk produced, and sometimes the general health of the animals. The two vital components of silage quality are:

(1)  Feed value of the crop at harvest. This depends on:

-         crop maturity at harvest - e.g. stemmier, more mature crops have a lower feed value

-         sward type - e.g. many old pasture swards dominated by poor grasses have lower feed value than swards of perennial ryegrass

-         sward conditions - e.g. 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 in 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

 

The feed value of the crop at harvest reflects its concentration of available energy, protein, minerals and vitamins, as well as how much an animal will voluntarily eat. The dry matter digestibility (DMD) is the most frequently used objective index of this feed value. Thus, well preserved silage with digestibilities of 60 (very stemmy), 65, 70 and 75 (very leafy)% DMD can support liveweight gains of 0.31, 0.49, 0.66 and 0.83 kg/day, respectively, when offered ad libitum and unsupplemented to finishing steers. Clearly, it is not appropriate to produce top digestibility silage for all animals. For example, for a spring-calving suckler beef cow herd where the progeny are being brought through to slaughter at 18 (heifers) to 23 (steers) months of age, and where the farm is in REPS, it can work well to take an early first-cut (22 May) from some fields to produce 75%DMD silage for the progeny, and on the remaining silage fields harvest the first-cut in the second week of June to produce lower cost but nutritionally appropriate silage for dry beef cows (i.e.65-67%DMD).

The efficiency of ensiling reflects how much of the feed value of the harvested crop is still present in the silage. It is reflected in the general standard of preservation (measured by silage pH, ammonia-N concentration, lactic acid content, etc.) and the extent of rotted or mouldy material present. Clearly, whereas farmers require different silage digestibilities for cattle with different performance targets, top quality is always required for every silage in terms of good preservation and the absence of mould. Thus, quality matters for all silages.

 

Balancing grass digestibility with yield

Throughout the majority of Ireland , the most rapid grass growth in normal years occurs 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. There are therefore conflicting changes occurring with crop yield increasing rapidly while crop digestibility declines. These changes have a major influence on the optimal time to harvest, and ultimately on the profitability of the majority of livestock production systems that involve making and feeding grass silage. The optimal digestibility for silage within any grass-based cattle system will vary depending on factors such as

(a)  the level and type of animal production required

(b)  the duration for which silage will be offered and its proportion in the diet

(c)  intake and conversion efficiency characteristics required of the forage

(d)  the value of the animal produce

(e)  the cost and supply of silage

(f)    the cost, quality and availability of alternatives

(g)  the costs of land, buildings and labour.

The optimal digestibility for silage therefore varies with changing economic circumstances and the optimal balance between grass digestibility and yield differs with the requirements of each farm.

Knowledge of the patterns of change in grass yield and digestibility are clearly important for identifying the best balance for individual farms. Table 1 summarises a Grange experiment that studied the average pattern of change of three different permanent grassland swards during a period of 6 years. Each crop was closed after a tight grazing the previous November, received 115 kg N/ha in March and had replicated plots harvested from the primary growth at weekly intervals between early May and early July.

 

Table 1. Grass yield and digestibility

Harvest date	1 May	8 May	15 May	22 May	29 May	5 June	12 June	19 June	26 June	3 July
Yield (t DM/ha)	2.92	3.99	4.98	5.96	6.79	7.82	8.48	8.93	9.50	9.83
DMD%	79.9	77.9	77.5	76.6	74.6	69.2	67.9	64.3	63.5	58.2

Source: Teagasc, Grange Research Centre

 

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 very 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.      Put pen to paper and write out a complete plan of how you will successfully make appropriate quality silage for your farm. Some points in the plan will have long-term effects for several years, while others will relate specifically to the upcoming harvest. Flexibility will be vital for the plan to succeed, because of the need to adapt to our variable weather. In years like 2002, this may be easier said than done.

It will be important to base decisions on quantified information whenever possible.  The decisions also need to be allied to the timely and correct execution of each component of silage making, storing and feeding.

 

2.      Preparing silage fields:

-         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 any 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 115 to 140 (reseed) kg/ha from the combined input of inorganic fertiliser (e.g. CAN, urea, etc.) and slurry.

-         apply fertiliser and/or slurry evenly and as early as feasible

-         allow approximately 10 kg N per 4500 litres (1000 gallons) undiluted cattle slurry applied in Feb./March

-         slurry should only be spread on bare stubble or very 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 upcoming 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 onto the bare stubble quickly after harvest. Take the necessary precautions to avoid exposure to slurry gases. Ensure slurry tanker is in working order for spreading slurry immediately after the first-cut is harvested.

-         prepare warning notices to go outside gateways onto public roadways. Ensure children and strangers will not come too close to the silage-making operation.

 

5.      Monitor the development of swards. Check out the services and costs of available contractors, and book the contractor of choice in time. Aim to harvest when the balance between grass yield and stage of maturity are optimal for your system(s).

 

6.      It is difficult in our climate for wilting to be anything other than opportunistic or fortuitous on intensively managed grassland farms with large operation contractors being used. However, 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 (i.e. tedding) immediately after mowing results in the fastest rate of wilting, whereas mowing and combining two 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 : take samples of grass that are genuinely representative of the crop to be harvested. Measure grass sugar concentration (expressed as a proportion of grass juice) and preferably also buffering capacity. 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. Consult your Teagasc advisor if in doubt.

 

 

 

8.      Silo filling and sealing:

-         fill the silo quickly and seal properly beneath 2 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 should influence subsequent grassland management during the season. A month or more after ensiling, representatively core sample the silage and obtain an analysis from a reputable laboratory. The analysis should tell you the DM and protein content of the silage, its standard of preservation and its digestibility. This information is important in planning the feeding regime for next winter. It will also help to evaluate the success of the recent silage campaign and indicate the strengths and weaknesses of the system you adopted. Your Teagasc advisor can play an important role in this exercise.

 

10.  Long-term:

-         decide where grass silage fits into your farming system, what fields are best suited to silage-making, and how you need to manage them each year. How much silage will you realistically need, 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.