A STUDY OF WILTING CONDITIONS IN SOUTH-WEST ENGLAND

ANNE TAYLOR

Nutrition Chemist, N.A.A.S., Bristol

Moisture losses from swaths of long herbage were recorded on eleven occasions in May,June and September, in order to supply data on which to base advice on making prewiltedsilage. Mowing in the late afternoon and picking up the following afternoon and mowingin the morning and picking up in mid-afternoon both resulted in losses averaging 9-6%.These losses occurred in fairly dry weather throughout the season, even when it was cloudyand cool. Mowing in the late afternoon and picking up next morning, before dew orovernight rain had evaporated, resulted in negligible losses, averaging only 2-4%.

INTRODUCTION

Highly digestible roughage is essential foreconomic livestock production and silage-making is a particularly suitable method ofconservation, since grass can be preserved at ayoung, leafy stage of growth. In order to givethe greatest intake of nutrients, the silageshould have a good fermentation and a highdry-matter content.

Unfortunately, young grass has a highmoisture content and is difficult to ensile welland, to counteract this, farmers often resort toadditives. The additives are designed either toprevent the development of an unfavourablefermentation or to supply readily availablecarbohydrate to lactic-acid-producingorganisms, but they do not significantlyinfluence the dry matter of the silage.

The technique of prewilting grass for silage-making provides an alternative to additivesand has the merit of producing a silage with ahigher dry-matter content. The total dry-matter intake of wilted silage is about 3%greater than that of unwilted silage (1). Inaddition, wilted silages are reported to have ahigher dry-matter digestibility (6, 8, 9). Pre-wilting also considerably reduces nutrientlosses. Nash (7) concludes that nutrient lossesin the swath are negligible in wilting periods ofless than 24 hours and that the total dry-matterlosses in the ensilage process are 3-4% lessthan with unwilted silage (8). Seepage from thesilo is negligible when the moisture content ofthe silage is less than about 75%; this is an

318

important argument in favour of partial wilt-ing of grass for silage-making. Hamilton (3)estimates that a grass of 16% dry-matter willproduce 55 gallons of effluent per ton of grass.This amounts to nearly 30,000 gallons todispose of within the space of a few weeksfrom a 500-ton capacity silo. Moore andWalker (4) support these figures.

This preliminary study was designed toprovide information on the moisture losspossible from swaths under different weatherconditions and subject to different wiltingtreatments.

PROCEDURE

An area of permanent pasture was markedout in March 1962 and dressed with 35 unitsnitrogen, 35 units phosphorus and 52-5 unitspotassium per acre. It had been the intention tocut grass each week throughout the season,regardless of weather, but the drought periodin July and August prevented regrowth, so thatresults are available only for the months ofMay, June and September. Three strips ofgrass, 9 yards in length, were cut each weekwith an autoscythe.

The treatments were as follows: (a) cut at5 p.m., wilted until 10 a.m. the following day(17 hours); (b) cut at 5 p.m., wilted until 3 p.m.the following day (22 hours); (c) cut at 9.0 a.m.on the second day, wilted until 3 p.m. the sameday (6 hours).

Swaths were sampled and weighed at cutting,returned to the ground and, after wilting for

ANNE TAYLOR 319

I•1I

.1oS

tU I 1 |i 11 II I I.a

1 e b

=E"i l l I &I I^Kz 1° ". it ^ ii" • ^ . S l e 3 •"« 3 ' ° 'S -"S

E2 * 3 §<« E'^ "js 8 " 8

'f£E.

ai § O'O'a o o CiS o o o S ' ' ' ' d ° o _3 o u coo o c o 2OK U

i l l§l§ 88 gg

O O O

IIC JJ of

ra

2 l a 12 "S

88 gg ppppg SS gSSooooooo ooooooooooooooooooooooo

u ui ^'Z Z ai Z ZM\ ^ s.^ I pf ^ ^ ^.l l

oi r - p —I oo mo I (*l O

S S S p p g P = ? p g §O O O 6 O O o o O O O O O O O O O O O O

T" T T "T T" T" r **i p r- .-

r- p q\ ^T* ? f?""?— vo vo vo O «^ r^ M^ VI IO in« « vo«

<S rg m oo Tt rn m' 3 5°^5j.2!S.E*S!- o o - o o . - . o o o o o r s o o o « o o

I I M I++ M I M I I I I M I+ + +

+ I I I I I I I I I I M + + 1 I I I I I I i i I I i + + +

+1 I M I I 117 I M ++T77177 I T I i i i

G O o"-^ 00 00 00 oo oo 00 00

Eo

ja'S M M .S

IP |i |l II^t l 'T. rr 9? O <n T <?>3 g^_/ «-H -> <s (S CS r i

' C ^ ^ ^ v o ^ vo \O^ ^ VO O ^ v o vovo VD^ vovo \O

320 A STUDY OF WILTING CONDITIONS IN SOUTH-WEST ENGLAND

the prescribed time, were again sampled andre-weighed. It was thought that the eflfect onmoisture loss due to swath disturbance wouldbe small, and the carefully replaced swathresembled that left by a mower with attachedswath boards. Random handfuls of herbagewere taken from the swath to give a compositesample from which a final sub-sample of 2-3lb was taken for determination of moisturecontent. Swath weights were used to provide acheck moisture figure calculated from the lossin weight of the swath after wilting. They alsoprovided an approximate measure of yieldsper acre. Notes were made on the stage ofgrowth of the sward. Meteorological data wereobtained and, using these figures together withpersonal observations, estimates were made ofrainfall and sunshine on each swath.

RESULTS

Findings are tabulated (Table 1) in order ofdate of cutting (col. 2). Treatments 3a, 3b and5c are, for various reasons, missing. Themoisture determination from the samplingmethod is considered the more accurate figure,but only in seven cases, indicated by asterisksin the table, did the two methods differ to anymarked extent (standard deviation ±3-03).These diiferences probably arose from thedifficulty of sampling very wet or very dryswaths. In the case of 3c, the loss of moisturecalculated from the weight of the swath is thepreferable figure.

It should be noted that meteorological dataare given from 9 a.m. on the day of cutting to9 a.m. on the second day for the (a) and (b)treatments and frorn 9 a.m. on the second dayto 9 a.m. on the ifoUowing day for the (c)treatment. Treatment (b) is, however, greatlyaffected by the second day's weather and theweather figures for the corresponding (c)treatments should be taken into account.

Initial moisture content of swath

This varied from 59-9-87-6%, the higherfigures being caused by rain or dew. Treatment(c) had an average initial moisture content of80-7%, 2-3% greater than treatments (a) and (b)at cutting.

Change in moisture content

The range was wide, varying from -f-7-4 to—28-3% for all treatments. The average changefor treatment (a) was —2-4% (range +6-0 to-12-3%); for treatment (b) -9 -8% (range+7-4 to -28-3%) and for treatment (c) - 9 - 5 %(range +2-1 to —22-7%). It is interesting tonote that all the (a) treatments, with theexception of a7, where wilting conditions wereideal, had moisture losses not exceeding 6-5%.

Effect of weather

Weather has been classified into four types(Table 2) the rainfall and sunshine figuresbeing taken from columns 10 and 11 in Table1. The moisture losses obtained under a givenset of conditions have been entered under theappropriate heading.

The best wilting conditions were associatedwith dry, sunny weather with high maximumtemperatures and a north-easterly breeze.Losses were still quite high, averaging 12-3%,in warm but slightly cloudy weather, whichseemed to be characterized by S.W.-W. winds.(Although treatment 8 b received a heavy,thundery shower, other conditions were ful-filled, which brought it under the heading of"good weather"). Moderate losses, averaging7-3%, were obtained in cool, rather cloudyweather with intermittent showers, where thelow temperatures allowed precipitation of dew.Negligible losses occurred in warm, dampweather with less than two hours sunshine.

Effect of date of cutting and stage of growth ofgrass

Yields varied from 1 -0 to 2-9 tons dry-matterper acre (5-15 tons wet matter per acre). Thesefigures, together with an assessment of thematurity of the grass, give an indication of thethickness and stemminess of the swath. Themature grass had a lower initial moisturecontent than the young grass and the rate ofloss of moisture was about twice as great asthat of the young grass. Partly for this reason,the rate of loss of moisture from swaths ofmature grass in June was greater than in eitherMay or September, when the grass was com-paratively young.

Very goodNo rain

Greater than 6 hrs.sunshine

Av. max. temp. 67°F(66 and 68)

Av. min. temp. 47°F(41 and 53)

Light N.E. wind

MoistureTreatment change %

4 b - 2 1 54 c - 2 0 17 b -28-37 c -22-7

Average — 23 1

ANNE TAYLOR

TABLE 2. The influence of weather conditions on wilting

Good

Little or no rain4-7 hrs. sunshine

Av. max. temp. 64°F(63-66)

Av. min. temp. 52°F(47-57)

S.W.-W. winds

MoistureTreatment change %

5 b - 1 3 77 a -12-38 b - 1 1 58e - 1 4 59 b -12-99 c - 8 8

Average —12 3

ModerateA little rain, heavy dew orheavy rain before cutting

24-7 hrs. sunshineAv. max. temp. 58°F

(56-60)Av. min. temp. 45°F

(39-50)Winds variable

MoistureTreatment change %

1 c - 8 02 a - 6 42 b -7-52 c - 6 83 c - 7 04 a - 4 5

10 b - 9 010 c - 9 2

Average —7-3

321

PoorRain, drizzle or heavy

dew0-2 hrs. sunshine

Av. max. temp. 61-5°F(56-68)

Av. min. temp. 51°F(47-57)

Winds variable

MoistureTreatment change %

1 a -1-5-51 b -2-65 a -2-76 a -4-06 b -t-I-96 c -t-0-58 a -1-09 a -2-2

10 a -2-711 a -f6-011 b -f7-411 c -2-6

Average -)-0-7

Rate of loss of moisture

The figures quoted (Table 1, column 8) havebeen obtained by dividing the change in mois-ture content by the number of hours of wilting.Treatment (a) had the lowest average rate of0-14% per hour, followed by treatment (b)0-45% per hour and, finally, treatment (c)1-57% per hour. Under exceptionally goodwilting conditions these rates may be almosttrebled, as in trial 7.

Fresh weight losses

These varied from 16-0% in poor weather to39-0% in good weather.

Discussion

Nash (7) carried out a similar and moredetailed study in south-east Scotland in 1953,and the results obtained for moisture loss, rateof wilting, fresh-weight loss and the differencesbetween the moisture content of grass in theevening and morning agree with those reportedhere.

The aim of wilting for silage-making shouldbe to achieve a silage dry-matter content ofbetween 25 and 30% (5, 7). A value greater

than this would increase the risk of over-heating and mouldiness in the silage (5, 10)and, although values between 20-25% wouldbe fairly acceptable, any herbage ensiled with adry-matter content lower than this willproduce large amounts of effluent (3, 4).

From Table 2 it would seem that lossesbetween 7 and 13% are desirable, depending onthe initial moisture content of the swath. Suchlosses can be obtained in all but wet, sunlessweather by either cutting in the early eveningand wilting until the following afternoon or bycutting in the morning and wilting until theafternoon of the same day. Only in excep-tionally dry, warm weather will much wiltingoccur overnight. Thus the practice of pickingup herbage at 9 or 10 a.m., as in treatment (a),is a poor one. Time should be allowed for dewor any overnight rain to evaporate com-pletely by wilting until the afternoon. Again,in very good weather the time of wilting can beshortened in treatments (b) and (c).

If deliberate wilting is to be adopted, achange of approach will be needed. The farmershould concentrate operations into a period ofa few days for which a reasonably accurate

322 A STUDY OF WILTING CONDITIONS IN SOUTH-WEST ENGLAND

local weather forecast can be obtained. Aperiod with little or no rain is the main require-ment, preferably with some sunshine. Theacreage cut on each occasion should bematched to carting capacity, which should inturn allow rapid filling of the silo in order toreduce the risk of overheating.

There is no reason why the time taken to filla silo should be any greater when the herbagehas been wilted. West and Morgan (11) studiedsilage-making on a farm in two seasons. In thefirst year unwilted silage was made, and in thesecond the herbage was prewilted. They foundthat, although an extra operation was involvedin prewilting, the time taken by three men tofill the 400-ton capacity silo in both years was17 days, mainly because the wilted materialcould be handled more easily. This is encour-aging, since it would be an important drawbackto the system if operations were so prolongedthat herbage became too mature and of lowfeeding value.

AddendumThe potential use of desiccant sprays, such as

diquat, for increasing the dry matter of grasscrops and the side effects, if any, on regrowth.

A preliminary study, in co-operation withthe Grassland Husbandry Department, wascarried out on three occasions. Rates of appli-cation varying from 0-75 to 3 oz. diquat ion peracre were used and wilting was allowed to takeplace for between 30 and 48 hours. The maxi-mum loss achieved at these low rates of appli-cation was 2-7% water. This loss is negligiblewhen compared with losses from control

swaths which were wilted naturally. Althoughhigher rates of spray usage might producehigher losses of moisture, both the expense ofthe chemical and the time lag in its action makeit of doubtful value for use in silage-making.Regrowth appeared fairly normal and dicotyle-donous weeds were controlled to some extent.

ACKNOWLEDGEMENTSI wish to thank Mr. J. R. Griffiths for his guidance in

carrying out this study and in the preparation ofthe paper.Thanks are due also to Messrs. W. H. Hogg and A. J.Pearson for supplying the meteorological data and to thelaboratory and field staff for technical assistance.

REFERENCES1. GORDON, C . H. , DERBYSHIRE, J. C. and KANE, E. A.

1960. Consumption and feeding value of silages asaffected by dry-matter content. Dairy Sci. Vol. 42,6, p. 866.

2. MINISTRY OF AGRICULTURE, N . IRELAND. 1961. Acomparison of ad lib. feeding of high-dry-matterlacerated and low-dry-matter unlacerated grasssilages. Res. Exp. Rec. Ministry Ag. N. Ire. Vol. 10,1, pp. 9-19.

3. HAMILTON, W . D . E . 1960. Silage and silageeffluent. Scott. Agric. Vol. 3, pp. 80-2.

4. MOORE, W. and WALKER, H. R. 1961. The disposalof silage effluent. Fm. Mechaniz. Vol. 5, pp. 79-84.

5. MURDOCH, J. C. 1960. The effect of pre-wiltingherbage on the composition of silage and its intake bycows. / . Brit. Grassl. Soc. Vol. 15, 1, pp. 70-3.

6. MURDOCH, F . R . , et at. 1958. Nutrient losses andfeeding value of wilted and direct cut forages stored intower silos. / . Dairy. Sci. Vol. 41, 10, p. 1483.

7. NASH, M . J. 1959. Partial wilting of grass crops forsilage. / . Brit. Grassl. Soc. Vol. 14, 1, pp. 65-73.

8. NASH, M. J. 1959. Partial wilting of grass crops forsilage. / . Brit. Grassl. Soc. Vol. 14, 2, pp. 107-15.

9. NEWLANDER, J. A. and RIDELL, W . H . 1958. Highmoisture versus wilted grass silage for raising dairycalves. Herb. Abs. Vol. 28, p. 264. {Vermont Agric.Exp. Sta. Bull., 602. 1957, p. 19).

10. NORDFELDT, S. 1958. The effect of wilting onnutrient loss and quality of silage. Herb. Abs. Vol.28, p. 102. (Nord. Jordbrotorstn, 1957, Vol. 39,pp. 23-7).

11. WEST, A. J. H. and MORGAN, D . E. 1961. Wiltingfor self-feed silage. Agriculture, Vol. 68, 3, pp. 147-9.

(Received for publication 5 March 1963)