J. agric. Engng Res. (1990)46, 153-170

A Cost-benefit Study of Alternative Policies in Making Grass Silage

M. B. MCGECHAN*

An improved operational research model for forage conservation systems has been devised which simulates the conservation process in relation to the weather and a cost-benefit study has been carried out of a number of alternative mechanization policies for making grass silage. These alternatives include wilting to various degrees or direct cutting, wilting in spread swaths with periodic tedding or leaving the mower windrow undisturbed, chopping to various degrees using a precision chop harvester with different set chop lengths, a double chop harvester, a flail harvester, or a big baler, and the use of additives. Each option has been costed. Benefits have been assessed in terms of the value of the reduction in requirement for concentrate supplementation in a ruminant diet with increased silage quality.

The study makes a good economic case for wilting silage and for harvesting using a precision chop harvester or, for a small farm, a big baler, but not for the use of formic acid based additives or for spreading or tedding treatments to swaths.

1. Introduction

An operat ional research model developed to study the economics of alternative forage conservation practices, 1 and an initial study using the model to compare hay and silage making 2 have been described by McGechan. The initial study, which took a small number of typical hay and silage systems as examples, concluded that silage is the most suitable conservation method for wet climates such as in Scotland, Wales and northern England. The purpose of the current study, however , is to examine the economics of a much wider range of possible alternative silage systems.

It is commonly assumed that the quality of grass silage is improved by wilting, short chopping, the use of additives, and by cutting grass at a less mature stage of growth. However , all these options incur costs. In this study, the benefits of such options are assessed in the context of the economics of a milk or animal product ion system, in order to ascertain whether the additional costs can be be justified.

2. Use of model for comparing economics of silage systems

The use of the model for the earlier study to compare hay and silage systems has been described in detail by McGechan. 2 For the current study, t rea tment of the silage systems was identical in most respects to that in the earlier study, so only the main points are repeated here.

Grass growth and field wilting were simulated using the model with weather data for a 10 year period, mainly for Prestwick Airpor t in the dairy farming area of south-west Scotland. For comparison, a few simulations were also carried out with weather f rom Dyce (Aberdeen Airport) in the drier east of Scotland area.

* Scottish Centre of Agricultural Engineering, Bush Estate, Penicuik, Midlothian, EH26 0PH, Scotland

Received 16 March 1989; accepted in revised form 7 October 1989

Presented at AG ENG 88, Paris, France, 2-6 March 1988

153

0021-8634/90/070153 + 00 $03.00/0 © 1990 The British Society for Research in Agricultural Engineering

154 A COST-BENEFIT STUDY IN MAKING GRASS SILAGE

N o t a t i o n

a swath drying rate coefficient ra E evaporat ion predicted by T

Penman 's equation, m m u f rainwater evaporat ion factor

M m.c.d .b . , fraction V M0 m.c.d.b, when cut, fraction A Me equilibrium m.c .d .b . , fraction Rn net radiation, W m -2 R~ solar radiation, W m -2 t~

cumulative adhered rainfall, mm temperature , °C wind speed 2 m above ground, m s - I vapour pressure deficit, mbar slope of saturation vapour pressure / tempera ture curve, mbar °C -1 relative humidity, %

Field operations simulated include cutting, in some cases spreading and tedding swaths, windrowing, picking up by a forage harvester , or for bagged silage, by a big baler, t ransport of silage or bales, and filling champs. Forage harvesting differs f rom all other operations in that the work rate is often limited by available tractor power; equations relating the work rate to factors such as harvester type, chop length setting, forage dry matter (dm) content, whether or not the trailer is being towed by the harvester tractor as a "three-in-l ine" combination, angle of uphill slope (assumed to be 3 °) and tractor power, have been presented by McGechan. l"a

Parameters used in the economic assessments, including costs of machines and storage structures (as described by McGechan, 2 Witney and Saadoun 4 and WitneyS), and costs of bought in feeds used to evaluate silage as a ruminant feedstuff (McGechane) , are listed in Table 1. McGechan, e in an analysis of a range of data f rom exper iments with animals, showed that intakes of silage by cows could be predicted in terms of factors such as dm content, D value and concentrate intake by an equat ion presented by Lewis; 7 this equation is incorporated into the silage evaluation routine.

Machine costs and workrates are listed in Table 2 and taken f rom information f rom a range of sources collected by McGechan. a Since the main theme of the current study is alternative field machine policies, only one type of silage clamp has been considered; this has a concrete floor and sides but no roof, plus effluent collection facilities (the "high

Table 1 Assumed parameters for economic assessment

Interest rate Investment rate Inflation rate Tax rate Tractor annual usage Shared implement annual usage Annual cost of storage structure in relation

to capital cost Formic acid additive cost Tractor fuel cost Labour cost Dairy concentrate cost Barley grain cost Barley straw cost Bought hay cost

12% 8% 4%

25% 1000h

300 h 5-1%

£0.53 1-1 £0.131 -l £3-50 h- 1 £220 t- 1 £120t -1 £35 t -~ £65 t-

M. B. McGECHAN 155

Table 2 Costs and workrates for silage making machines

Capital Annual Tractor for Machine cost, £ cost, £ implement Workrate

Tractor 45 kW, 2 WD 12 900 261 55 kW, 2 WD 14 500 2539 55 kW, 4 WD 18000 3148 65 kW, 4 WD 21 000 3670 75 kW, 4 WD 24 200 4226

Drum or disc mower, 1.6 m 1550 181 45 kW, 2 WD 1.5 ha h -~ 2-1 m 2800 322 55 kW, 2 WD 2.0 ha h- 1

Mower conditioner, 2-1 m 5200 597 65 kW, 4 WD 1.75 ha h -I 2.4 m 6000 690 65 kW, 4 WD 2-0 ha h -1

Two row rotary tedder/windrower, 4 m 2500 297 45 kW, 2 WD 2-5 ha h - t Forage harvester,

flail 4000 462 55 kW, 4 WD 7.0 km h-I (max*) double chop 4800 540 65 kW, 4 WD 7.0 km h- i (max*) precision chop 7200 805 75 kW, 4 WD 7-0 km h- i (max*)

Big round baler 9500 1064 65 kW, 4 WD 4-0 t h- Trailer, tipping with silage sides 3500 390 45 kW, 2 WD ÷ Trailer for bales 2000 260 45 kW, 2 WD 4-0 t h - Buckrake (for loading horizontal silo) 900 100 55 kW, 4 WD + Front end loader plus spikes 2850 319 45 kW, 2 WD 4-0 t h -~

* Or limited by tractor power; field efficiency 66% for three-in-line combination + Equal to forage harvester workrate

cost" system described by McGechanZ). The reason for costing the clamp was for a comparison with big bale systems. Storage costs are listed in Table 3.

Most simulations were carried out for a first cut starting at a grass D value of 65% over a conservation area of 40ha , and forage evaluated for a herd of 100 diary cows. A regrowth cut was considered to commence 6 weeks later over 20 ha only; the smaller area was chosen since herbage product ion rates are lower and a greater area is usually required for grazing later in the season in a typical milk or animal product ion system. A few simulations were also carried out over a range of first cut conservation areas, with proport ionate changes in the second cut area, dairy herd size and storage costs. These second cut areas and commencing D values differ f rom those in the earlier study (McGechanZ).

Table 3 Silage storage costs (for 40 ha first cut plus 20 ha second cut)

Type of storage Cost,

Clamp silo capital cost Effluent tank capital cost Polythene annual cost (for clamp silo) Total annual storage cost of clamp silage Annual cost of polythene bags Capital cost of concrete apron for storing

bagged silage Total annual storage cost of bagged silage

14400 1200

100 896 807

3000 960

156 A COST-BENEFIT STUDY 1N MAKING GRASS SILAGE

3. Alternative mechanization systems and policies

3.1. Wilting policy

Wilting policies considered are as follows.

1. No wilting, either direct cutting and picking up in a single operation with a flail harvester, or cutting with a mower and immediately picking up with any type of forage harvester. 2. Wilting to target dm contents of 20%, 25%, 30% or 35%, but with fall-back maximum periods in the field of 2, 3, 5 and 7 days respectively, after which the crop is picked up regardless of dm content. 3. Wilting for fixed periods of approximately 24 h or 48 h. 4. "Strategic wilting" i.e., wilting to 30% dm content in favourable weather, but not wilting when rain is forecast. A simple "weather forecast" is represented in the model by introducing a random error to the actual future weather in the weather data (McGechanl).

3.2. Mower and swath treatment policies

The alternatives of cutting with a simple drum or disc mower, or attempting to increase drying rates by using a mower conditioner, are considered with two alternative sizes for each (Table 4).

The standard swath treatment policy considered follows the most common practice in the UK of leaving swaths undisturbed in mower windrows, with a width of approximately half the cutting width, until just before picking up. Recent research work into swath drying rates (Lamond et al., 8 Glasbey and McGechan s) has shown that a greater increase

Table 4

Alternative mowers , swath treatment and pick-up policies

Cutting width, Windrow

Mower type m width, m Swath policy or treatment

Drying rate coefficient

a

Drum or disc mower 1.6 Drum or disc mower 2-1 Mower conditioner 2.1 Mower conditioner 2.1

Mower conditioner 2-1

Mower conditioner 2.1

Mower conditioner 2.1

Mower conditioner 2-4 Mower conditioner 2.4

Mower conditioner 2.4

Mower conditioner 2-4

0-8 Undisturbed mower windrow 0-080 1.1 Undisturbed mower windrow 0.080 1-1 Undisturbed mower windrow 0-096 1.8 Undisturbed wide mower windrow, 0.119

then rowed up before picking up 1.8 Undisturbed wide mower windrow 0.119

picked up by forage harvester with gathering wheels

- - Spread after cutting, wilted undisturbed 0.128 then rowed up before picking up

- - Spread after cutting, tedded periodically 0-156 during wilting, rowed up before picking up

1.2 Undisturbed mower windrow 0-096 2-4 Undisturbed wide mower windrow 0.128

rowed up before picking up 2.4 Undisturbed wide mower windrow, 0.128

picked up by forage harvester with front mounted pick-up

2.4 Undisturbed wide mower windrow, 0.128 picked up by forage harvester with nylon brush wide pick-up

M. B. M c G E C H A N 1 5 7

in drying rate can be achieved by spreading swaths than by conditioning and leaving in a windrow. Alternative policies of setting a mower conditioner to lay down wide swaths, or of laying down swaths of normal width and immediately spreading to cover the whole field, in a separate operation with a hay tedder/windrower, are also considered. It is common practice in some continental European countries to wilt silage to high dm contents in spread swaths, carrying out a number of tedding operations during the wilting period (e.g. Bosma and Verkaik~°); this practice is also considered.

The swath drying equation used in the model is based on the work of Penman, ~ and has been described by McGechan ~ and by Glasbey and McGechan: s

M = (M0 - Me)e -a(E-fr~) + Mc (1) where

Me = 0-033 + 0.095{-1n (1 - 0-01q~)} 15 (2)

0.0015RnA + 0.0072(1 + 0-54u)V E

0 A + 0.66 (3)

Rn = -20 + 0-63Rs (4)

A = 0.443 + 0-0295T + 0.000665T 2 + 0.0000188T 3 (5)

f = 1.5 (6)

The drying rate coefficient ["a" in Eqn (1)] for each mower and swath treatment policy is listed in Table 4.

For all treatment policies, low yielding regrowth swaths are windrowed before picking up in order to increase the work rate of the forage harvester or baler. Normal width first cut swaths are not windrowed; however, wide mower windrows and spread swaths need to be windrowed in order to be taken in by a forage harvester with a typical pick-up width in a single pass.

3.3. Harvester and chop length policy

Chopping policy generally depends on the type of forage harvester selected. Typical median chop lengths are 80, 60 and 30 mm, respectively for flail, double chop and precision chop harvesters (McGechan12"13). However, for a precision chop harvester, an alternative shorter setting can give a median chop length down to about 10 ram, but with a penalty of a higher power consumption and lower workrate. The silage intakes by cows predicted by the Lewis equation ~ are increased by 10 and 15%, respectively for the standard and short settings of a precision chop harvester, compared with flail, double chop harvested, or big bale, silage; this adjustment was found to be necessary to represent animal experiment data, particularly those of Castle and Watson, 14 and of Dulphy and Demarquilly, TM since chop length was the only factor not adequately represented in the Lewis 7 intake equation (McGechanS).

All forage harvester types are assumed to tow a trailer as a three-in-line combination. Some possible adaptations to a standard forage harvester, to enable it to take in a wide

or spread swath without a separate windrowing operation, are also considered. These include ground driven "gathering wheels", a low cost addition which can increase the take-in width to about 1-8 m. There are currently available some offset front mounted pick-ups, driven off the tractor hydraulics, which transfer a swath or part of a swath onto the top of the swath being picked up by the forage harvester; the use of one of these, with a capital cost of £3800 is considered. An experimental prototype pick-up with nylon brushes instead of steel tines has been developed by Klinner and Wood. TM This can pick up wide swaths with pick-up losses much lower than those for a tine pick-up (Knight~7).

158 A COST-BENEFIT STUDY IN MAKING GRASS SILAGE

Use of this device, with the pick-up loss reduced f rom the value o f 0.15 t ha -~, assumed for a tine pick-up (McGechan12"le), to 0-002 t ha -1 as found by Kl inner and W o o d , TM is also considered.

The alternative o f making bagged silage with a big baler is considered.

3.4. Silage additives

The following opt ions are cons idered for using formic acid based additives.

1. No additive. 2. Addi t ive at the s tandard rate of 2.5 1 t - 1 of fresh material . 3. Addi t ive de te rmined by the "L i scombe star sys tem" (ADASlS) . Addi t ive is applied at a high rate (5 .01 t -1) , at the s tandard rate or not at all according to a "s tar ra t ing" de termined f rom the stage of growth , wea ther condi t ions , degree of wilt achieved and chop length, Table 5. Varying addit ive dosage in this way is part icularly valuable in conjunct ion with strategic wilting. Star ratings f rom Table 5 for average fertilizer ni t rogen and perennial ryegrass at a leafy growth stage are assumed in every case. Star ratings are chosen as appropr ia te for the wilting and chop length policy adop ted , and for wea ther condit ions are based on sunshine hours during the 2 days pr ior to cutt ing.

3.5. Cutting policy

Two policies are cons idered , three cuts each start ing when the grass D value drops to 70% (at approximate ly 4 week intervals), or the s tandard policy assumed elsewhere in this paper , of two cuts start ing at a D value of 65% (at approx imate ly 6 week intervals).

Table 5 "Liscombe Star System" (ADAS 19)

Grass variety timothy/M Fescue * (sugar content) perennial ryegrass, Lolium perenne **

italian ryegrass, Lolium multiflorum ***

Growth stage leafy silage 0 stemmy mature *

Fertilizer heavy (125 kg/ha +) -* nitrogen average (40-125 kg/ha) 0

light (below 40 kg/ha) *

Weather conditions dull, wet (less than 2% sugar) -* (over several days) dry, clear (2.5% sugar) 0

brilliant, sunny (3% sugar or more) *

Wilting none (15% dm content) -* light (20% dm content) 0 good (25% dm content) * heavy (30% dm content) **

Chopping and/or flail harvester or forage wagon * bruising double chop **

precision/twin chop ***

Star ratings are added (or subtracted for negative star ratings) for each of above six categories to determine rate of additive application: 5 stars, no additive needed; 3 or 4 stars, additive at recommended rate; 1 or 2 stars, additive at higher recommended rate; 0 stars, unsuitable conditions for making silage

M. B. McGECHAN 159

4. Results

The forage evaluation procedure used in the study calculates the gross annual value of the silage produced by each policy, in terms of the total cost of bought in feedstuffs for which it can substitute (McGechanl°e). Production costs are then subtracted to give the net annual value. Results, in terms of gross and net value of silage produced, and costs in various categories from simulation and feed evaluation runs with the model, are shown in Figs 1-7. Variations in the forage value often arise because variations in losses influence the quantities of forage produced. Some examples of annual herbage production, and how it is reduced by losses in various categories to give the quantity of silage produced, are illustrated in Figs 8-11.

4.1. Wilting policies

Results for the precision chop harvester at Prestwick (Fig. 1) show substantial benefits from wilting compared to no wilting. Marked increases in silage net value occur with an increase in degree of wilt up to 25% target dm content, with a small further increase up to 30% dm content. However, there is a small drop in the net silage value with a further increase in target dm content to 35%.

Silage of very slightly lower net value is obtained by wilting for fixed periods than for wilting to target dm content values, although wilting for 24h is roughly equivalent to wilting to 25% target dm content. Silage of an even lower net value is obtained by strategic wilting.

For the precision chop harvester at Dyce (Fig. 1), results follow a similar pattern to those at Prestwick, except that the drop in net value with increase in target dm content from 30 to 35% is very small. This fall in forage value with increase in wilt time arises mainly because of an increase in respiratory and leaching loss (Fig. 8), but the increase is less marked in the drier area.

For the flail harvester, a similar increase in forage value with increase in wilt occurs (Fig. 1). The value of the very wet silage produced by direct cutting and picking up in a single operation is particularly low. This arises because the assumed equation for feed intake in terms of a range of factors (McGechan, 1 Lewis 7) gives very low intakes for very wet silage, as commonly found in practice. When unwilted silage is cut and picked up in separate operations, wilting takes place at a very fast drying rate immediately after cutting, for the short period swaths lie on the stubble; this results in forage of somewhat higher value compared to that produced by direct cutting in a single operation.

4.2. Mower policy

When the different width mowers and mower conditioners are compared, the higher cost machines result in silage of higher gross value, but the extra costs of the machines roughly cancel this out (Fig. 2). The 2-1 m drum or disc mower gives clamp silage with the highest net value, while for big bale silage that made with the 2.1 m mower conditioner is just of the highest value.

4.3. Swath and pick-up policy

The standard UK practice of wilting in an undisturbed mower windrow gives silage of high net value (Fig. 3). This is not matched by any of the alternative swath policies considered for the 2.1 m mower conditioner. All the policies which require additional operations to be carried out using a windrower/tedder, i.e. spreading, tedding or

160 A C O S T - B E N E F I T S T U D Y IN M A K I N G G R A S S S I L A G E

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(c )

Fig. 1. Gross value, production costs and net value o f silage produced with alternative wilting policies. 40 ha first cut, wilted in undisturbed mower windrows except where unwilted or direct cut. (a) Prestwick; flail harvester, cut with 1.6m drum or disc mower; (b) Prestwick; precision chop harvester, cut with 2.1 m mower conditioner; (c) Dyce; precision chop harvester, cut with 2.1 m

mower conditioner

M. B. McGECHAN 161

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conditionerJ condi t ioner I conditioner I

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[ 2 5 30 Wilting,°/odrn I 25 I

Fig. 2. Gross value, production costs and net value of silage produced with alternative mower policies. Prestwick; 40ha first cut, wilted in undisturbed mower windrows except where direct cut.

Key as Fig. 1

windrowing before picking up, incur higher machinery costs which are not justified by increases in silage gross value. Also, wide or spread swaths incur higher losses at pick-up (Fig. 9) since a larger area of stubble must be cleared. One alternative policy, laying down wide swaths and picking up with a forage harvester fitted with gathering wheels so that a separate windrowing operation is not required, produces silage with a net value similar to the standard policy. In this case, the reduction in respiratory and leaching losses achieved because of faster wilting, almost exactly matches the increase in pick-up loss arising because the wilting crop has been spread over a greater area of stubble.

For the policies based on the 2.4 m mower, neither the costs of additional windrowing operations, nor the additional expense of a high cost front mounted tine pick-up, are justified by adequate increases in silage gross value, compared to the standard policy. However, the policy of wilting in a wide swath and picking up with a nylon brush wide pick-up (Klinner and Wood 18) is justified. In this case, lower respiratory and leaching losses occur, compared to the standard policy, and pick-up losses are at a very low level despite the wilting crop being spread over the full width of the mower (Fig. 9). The average annual increase in silage net value is £355, assuming that the brush pick-up costs no more than a standard tine pick-up. Alternatively, if the brush pick-up costs more, it can be justified provided its additional cost is no more than £355 pa, about £3200 in additional capital cost (or a 44% increase in the cost of a precision chop harvester) for a 40 ha conservation area.

4.4. Harvester and chop length options

Worthwhile benefits are obtained by harvesting with a precision chop rather than a flail forage harvester, particularly when associated with wilting. The higher cost of the

162 A C O S T - B E N E F I T S T U D Y IN M A K I N G G R A S S S I L A G E

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mower conditioner. Key as Fig. 1

M. B. M c G E C H A N 163

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0 H a r v e s t e r

x~</xxv~ ~///////~

f l a i l

Z

double chop

~xYxYvx2

4 \ \ \ \

precis ion chop

W i l t i n g , °/o dm 25 20 25

prec=sion big round chop, sho r t ba ler

25 30

Fig. 4. Gross value, production costs and net value o f silage produced with alternative harvester and chop length policies. Prestwick; 40 ha first cut, cut with 2.1 m drum mower, wilted in undisturbed

mower windrows. Key as Fig. I

Herd size for silage evaluation, cows

25 50 100 150 200 360 | i I I I I I I

3 2 O

"7 300 ½ r,

= 280 -

~ 2 4 0 - >

220

200

~ 180

/ io i ! z

140 ond c t con

120 0

IO0 0 10 20 40 60 80

F i r s t cut conservation area, ha

Fig. 5. Forage net value with alternative harvesters and a range o / f a r m sizes. Prestwick, cut with 2.1 m drum mower and wilted in undisturbed mower windrows except where direct cut. ra, direct cut with flail harvester; +, flail harvester wilted to 25% dm; ~>, double chop harvester wilted to 20% dm;

~ , precision chop harvester wilted to 25% dm; x , big bales wilted to 30% dm

164 A C O S T - B E N E F I T STUDY IN M A K I N G GRASS S I L A G E

precision chop harvester is more than justified by increases in net forage value (Fig. 4). For a precision chop harvester a very short chop length setting, rather than a more normal setting, further increases the gross silage value; however, the costs of additional fuel and lower workrates result in almost exactly the same net silage value. A choice of chop length setting for a precision chop harvester can therefore be made on the grounds of convenience; in most instances this will favour the longer setting (set chop length 20 mm, median chop length 30 mm), to give a higher workrate and a lower tractor power requirement. A double chop harvester costs more than a flail harvester but produces silage of similar quality; hence there is a very poor economic case for using a double chop harvester compared with the other two types. The net value of big round bale silage is markedly higher than that made with a flail forage harvester.

Fig. 5 compares alternative harvesting systems for a range of conservation areas and shows that for small areas, big bale silage has a higher net value than precision chopped silage, due mainly to its low mechanization cost, but for larger areas the precision chop system is the optimum.

4.5. Additive policy

The application of an additive at a fixed standard rate incurs a very high additional cost for only a small increase in silage gross value (Fig. 6), so it cannot be recommended. If the additive is applied selectively to low dm content silage according to the Liscombe star system, costs are still slightly greater than increases in silage gross value (Fig. 6), despite a substantial reduction in storage losses (Fig. 11). It is difficult to justify expenditure on an additive, when much greater benefits can be obtained from other options such as wilting.

4.6. Cutting policy

Compared with two cuts at a D value of 65%, three cuts of a D value of 70% produces a smaller quantity of higher quality silage, and incurs a higher mechanization cost. The silage evaluation procedure, which takes account of both quality and quantity, attributes a higher net value to the higher quantity of lower quality silage produced by two cuts (Fig. 7).

5. Effect of variations in financial parameters

Values of the financial parameters (Table 1) used for the economic assessment were current at the time this study was carried out, but are liable to change. In particular, interest, investment and inflation rates move up and down at frequent intervals. Changes to these parameters will affect the absolute values of the results of this study, and by reference to Figs 1-7 it is possible to envisage how the relative positions of different policies may change.

Changes in bought feed costs affect silage gross values, but will change all policies by roughly the same percentage. Changes in labour and fuel costs affect part of the hourly mechanization costs; their effect is relatively small, but highest for the systems with low workrates, particularly those based on a flail forage harvester. Polythene costs are small, except with the big bale system. Additive costs are important but it would require a large reduction in their costs to change the conclusion found about the economics of using them. Storage structure costs and most of the mechanization costs are the costs of ownership of these items, and depend mainly on the "net" interest and investment rates, i.e. the difference between these rates and the inflation rate. Only where differences

M. B. McGECHAN 165

1. l 16

14- O o 1 2 - - - O

q4 l O - - - a; _= nO 8 - >

Cn 6 - t~

tn 4 -

18.

16- 14 Z

12-

8~ 6~ 4S 2~ O-

I I I

I I

none L iscornbe l none star I

I direct cut I

Y////4

Liscombe star

u n w i l t e d I I (a)

I I I qZ-Z,2 r ~ ,x",.\\\"~ "////~, y///.~

I "

i

I I I

//~/~/ / / / / /I/.< / / / "//,~,

none L iscombel n o n e L i scombe s ta r I s ta r

20*/ .d in I I 25"/ . dm

2-

0 A d d i t i v e

Wilt ing unwi l ted

none L iscornbe s tanda rd star rate

A d d i t i v e

Wilting

Liscombe Liscombe star star

20"I. dm

o o o

d 3

ra >

(b)

,>

none L i s c o m b e star

I s t ra teg ic

Fig. 6. Gross value, production costs and net value o f silage produced with alternative additive policies. Prestwick; 40ha first cut, wilted in undisturbed mower windrows except where unwilted or direct cut. (a) flail harvester, cut with 1 .6m drum or disc mower; (b) precision chop harvester, cut

with 2.1 m mower conditioner. Key as Fig. 1

166 A C O S T - B E N E F I T STUDY IN M A K I N G GRASS S I L A G E

16

o o 12-/ /,

10-

; . )X y,

0 No. o f cu t s 2 3

Fig. 7. Gross oalue, production costs and net value of silage produced with alternative cutting policies. Prestwick ; 40ha first cut, 2.1 m mower conditioner, precision chop harvester, wilted to 25%

dm in undisturbed mower windrows. Key as Fig. 1

between the net values of silage produced by different policies are small, such as for alternative mower policies and some alternative swath policies, are changes in ownership costs likely to change the conclusions reached. The differences between alternative harvester policies are so large that their relative position would be changed only by a most unlikely change in ownership costs. Wilting policies are almost unaffected by ownership c o s t s .

6. Further comments about losses incurred during silage making

This study is mainly concerned with alternative policies with regard to the field mechanization system. In many cases, variations in silage net value between policies have been shown to arise because of variations in levels of field losses. However, field losses represent only a small proportion of the total losses which occur in silage (Figs 8-11) . Hence the potential for improving the economics of a silage system by reducing field losses is relatively small, whereas the potential for reducing storage losses is very large indeed. However, whereas the processes of loss occurrence in the field are reasonably well understood and quantified, the mechanisms of loss occurrence during storage are very complex and only partially understood.

Effluent is an environmental problem and incurs costs for storage and handling. However, it consists mainly of water, and represents a very small proportion of the dm loss in storage. Also, there is a body of reasonably consistent data describing quantities of effluent produced from which the effluent production/dm content relationship used in this study has been derived (McGechanl"12"13).

"Invisible storage losses" include losses arising due to the silage fermentation process, plus air infiltration losses during filling of silos, during storage, and during feeding out; they are thought to depend on such factors as grass maturity, silage dm content, chop length and density, and whether or not an additive has been used (McGechanl"12"~3). Surface waste, which is caused by more serious air infiltration, is also thought to depend on similar factors, as well as aspects of clamp management. For the current study, tentative values of invisible storage losses and surface waste were assembled from

M. B. M c G E C H A N 1 6 7

E ~J

8 D

o EL

260

2 4 0 -

2 2 0 -

200-

180-

160

140-

120-

100-

80-

60 -

40 -

20-

0 Wil t ing unwi l ted 20°1o

dm

, / / / / / , ~ ' / / / / ( , \ \ \ , \ \ \ , " / , ~ \ \ \ , , ,

25°1o 30°/o 350/= 24h 4 8 h strate¢ dm dm dm

key: to Figs S-11 grass dry matter produced ~ effluent loss; surface waste; invisible storage losses; mechanical losses; respiratory plus leaching losses; net silage dry matter produced

IC

F i g . 8. Silage dry matter production and losses with alternative wilting policies. Prestwick; 40ha first cut, precision chop harvester, cut with 2 .1m mower conditioner, wilted in undisturbed mower

windrows except where unwilted

2 6 0 |

24°1 2 2 0 - ~ 200~

/ / / / / / u 1 4 0 - / / / / / /

I I I I I I 1 2 0 - / / / / / /

iii i i i em 8 0 - / / / / / /

~-) 6 0 - / / / / / / _- - .- / / /

4 0 _ / / / III / / / / / /

20_/// /// i i i / / I 0 / / , / / / / ,

Swath normal wide

/ / / / / / I I / / / / / I / I I I I I I I I I I I I I I I I I I I I I I I I I l l I I I I I i I I I I I I I [ I I I I I I I I l l I [ I I l l / / / / / /

i i i wide spread spread an¢

> ~ X X

N

/ / / / / / / / /

i i n o ~ a l wide

/ / / I / / I / / / / / / / / / / / / / / I / / / I / / / / I I /

/ I / / / / / / / / / /

wi'~e .,'~e Windrow windrow windrOWS and tedded Nindrow windrow windrow windrow

rowed picked up rowed up then rowed up I~cked up picked up up using rowed up I using using

gathering I f ront nylon Ix-ulh wheels J mounted pick-up

I p ick-up

M o w e r 2-1m m o w e r c o n d i t i o n e r 2"4m m o w e r cond i t i one r

Fig. 9. Silage dry matter production and losses with alternative swathing policies. Prestwick; 40 h first cut, precision chop harvester. Key as Fig. 8

168 A C O S T - B E N E F I T S T U D Y IN M A K I N G G R A S S S I L A G E

260

2 4 0 -

2 2 0 -

E 2 0 0 -

1 8 0 -

G 1 6 0 -

~u 140-

o 120-

100-

8 0 -

~n 6 0 -

4 0 -

2 0 -

O" H a r v e s t e r f lai l double precis ion

chop chop

Wi l t i ng , * / . dm 25 20 25 30

/ / / / / / / / / pS . \ \ \ \ \ '

precis ion chop, sho r t

25

/ / / / / / / / / / ~

\ \ \ \ \ \

big round baler

Fig. 10. Silage dry matter production and losses with alternative harvester and chop length policies. Prestwick; 40 ha first cut, cut with 2.1 m drum mower, wilted in undisturbed mower windrows. Key

as Fig. 8

2 6 0

2 4 0 -

220-

E 2 0 0 - o

180-

160-

8 140-

o 120- o.

lOO-

e 8 0 -

6 0 -

4 0 -

20-

0 A d d i t i v e n o n e

I

I

Liscombe n o n e

s t a r

i

I I I

. . . . • I \ \ \ v< . .< , ,~ .~ II \ \ \,/////<

Liscombe none Liscornbe none Liscombe

star s ta r star

Wil t ing d i r ec t cut unw i l t ed I I 20"/o d m I I 25=/. dm

Fig. 11. Silage dry matter production and losses with alternative additive policies. Prestwick; 40ha first cut, flail harvester, cut with 2.1 m mower conditioner, wilted in undisturbed mower windrows

except where unwilted or direct cut. Key as Fig. 8

M. B. M c G E C H A N 169

literature sources (Table 2 in McGechanl); these are based on experimental data reported by Bastiman and Altman 2° and by Mayne and Gordon, 21 plus information from studies of the mechanisms of loss occurrence (e.g. McDonald, ~ Rees et a l .~ ) .

A number of models of the processes of silage fermentation and air infiltration into silage, including the occurrence of dry matter losses, have recently been developed, e.g. Pitt et al., 24 Leibensperger and Pitt, 25 and Pitt; 2e studies of these processes are continuing further at various research centres. It is anticipated that it will eventually be possible to derive more reliable values for storage losses, in terms of the suggested factors, from work with these models. This would enable some alternative silage clamp management policies to be studied, as well as allowing the results of the current study to be confirmed.

The data on which the assumed levels of invisible storage losses and surface waste were based, were determined in experiments with clamp silos. No such data for big bale silage could be found. For big bale silage, it has therefore been assumed that storage loss levels vary similarly in relation to the same factors as for clamp silage; totally spoiled material in the vicinity of holes or joins in the polythene is represented by the surface waste figures. Work with models of silage fermentation and air infiltration could later provide information about storage loss levels specific to big bale silage.

7. Conclusions

The study described makes a very strong economic case for wilting silage to about 25-30% dry matter content, ~'nd harvesting using a precision chop harvester set to give a median chop length of about 30 mm. The economics of a big bale system are also favourable, particularly for a small farm. A big bale system is superior to one based on a flail forage harvester. However, the study suggests that the use of a formic acid based additive is difficult to justify. Also, any wide or spread swath treatments which require additional operations with a windrower/tedder in first cut crops, or expensive additional machines, cannot be justified. However, a swath treatment in which material is laid down by the mower in a wide swath, then picked up by a novel low loss wide pick-up, would be worthwhile.

The results of this study are very dependent on the assumptions made about the intake of silage by animals. It is widely accepted that there is a lack of understanding of some of the factors which influence the voluntary intake of feedstuffs by ruminants, and that there is a need for further research in this area. However, the intake equations assumed represent a good summary of currently available information. The study has also demonstrated substantial potential benefits from measures to reduce the very large losses which occur during the storage of silage, indicating a fruitful area for further research into the mechanisms of loss occurrence. Despite some reservations concerning assumptions made about intake and storage losses and likely variations in financial parameters, many of the findings of the current study, such as the large benefit from wilting, are so decisive that they would be unlikely to be overturned by a study with any set of assumptions which is within the range of credibility.

References

1 McGechan, M. B. Operational research study of forage conservation systems for cool, humid upland climates. Part 1: Description of model. Journal of Agricultural Engineering Research 1990, 45:117-136

2 McGechan, M. B. Operational research study of forage conservation systems for cool, humid upland climates. Part 2: Comparison of hay and silage systems. Journal of Agricultural Engineering Research 1990, 46:129-145

170 A COST-BENEFIT STUDY IN MAKING GRASS SILAGE

3 McGechan, M. B. Mechanisation aspects of forage conservation models--A review of alternative systems and their parameters. Departmental Note SIN/462, Scottish Institute of Agricultural Engineering, Penicuik, January 1986 (unpublished)

" Witney, B. D.; Saadoun, T. Annual costs of farm machinery ownership. The Agricultural Engineer 1989, 44(1): 3-11

5 Witney, B. D. Choosing and using farm machines. Harlow; Longman, 1988 • McGechan, M. B. A procedure for evaluating farm produced forage for use with a forage

conservation model. Departmental Note 4, Scottish Centre of Agricultural Engineering, Penicuik, 1988

7 Lewis, M. Equations for predicting silage intake by beef and dairy cattle. Proceedings of 6th Silage Conference, Edinburgh, 1981

a Lamond, W. J.; Spencer, H. B.; Glasbey, C. A.: Haughey, D. P. Field wilting and drying of grass in cool moist climate. Research and Development in Agriculture 1988, 5(1): 23-28

9 Glasbey, C. A.; McGechan, M. B. A relationship between weather and drying rates in grass swaths. Departmental Note SIN/480, Scottish Institute of Agricultural Engineering, Penicuik, 1986 (unpublished)

lo Bosma, A. H; Verkalk, A. P. Developments in forage conditioning. AG ENG 86 International Conference, Nordwijkerhout, Netherlands, 1986, pp. 181-182

11 Penman, H. L. Natural evaporation from open water, bare soil and grass. Proceedings of the Royal Society, London 1948, A193:120-146

12 McGechan, M. B. Losses during forage conservation--review of available information for use in a forage conservation system model. Departmental Note SIN/487, Scottish Institute of Agricultural Engineering, Penicuik, March 1987 (unpublished)

la McGechan, M. B. A review of losses arising during conservation of grass forage. Part 2, storage losses. Journal of Agricultural Engineering Research 1990, 45: 1-30.

14 Castle, M. E.; Watson, J. N. Silage and milk production: comparisons between silages of three different chop lengths. Grass and Forage Science 1979, 34:293-301

is Dulphy, J. P.; Demarquiny, C. Influence de la machine de recolte sur les quantites d'ensilage ingerees et les performances des vaches laitieres. (Influence of the type of forage harvester on the silage intake level of the performance of dairy cows.) Annales de Zootechnie 1975, 24(3): 363-371

le Kiinner, W. E.; Wood, G. M. An experimental field rig for collecting forage crops and separating out stones and metal objects. Departmental Note 1954, National Institute of Agricultural Engineering, Silsoe, 1981 (unpublished)

17 Knight, A. C. Personal communication, 1988 la McGechan, M. B. A review of losses during conservation of grass forage. Part 1, field losses.

Journal of Agricultural Engineering Research 1989, 44:1-21 19 ADAS. Silage, Liscombe grass bulletin 2. Liscombe EHF, Dulverton, 1984 2o Bastiman, B.; Airman, J. B. V. Losses at various stages of silage making. Research and

Development in Agriculture 1985, 2(1): 19-25 21 Mayne, C. S.; Gordon, F. J. The effect of harvesting system on nutrient losses during silage

making. 2. In-silo losses. Grass and Forage Science 1984, 41:341-351 ~" McDonald, P. The biochemistry of silage. Chichester: John Wiley and Sons, 1981 2a Rees, D. V. H.; Andsley, E.; Neale, M. A. Some physical properties that affect the rate of

diffusion of oxygen into silage. Journal of Agricultural Science, Cambridge 1983, 100(3): 601-605

24 Pitt, R. E.; Muck, R. E.; Leibensperger, R. V. A quantitative model of the ensilage process in lactate silages. Grass and Forage Science 1985, 40:279-303

zs Leibensperger, R. V.; Pitt, R. E. A model of clostridial dominance in ensilage. Grass and Forage Science 1987, 42(3): 297

2e Pitt, R. E. Dry matter losses due to oxygen infiltration in silos. Journal of Agricultural Engineering Research 1986, 35:193-205