LEYS AND SUBSEQUENT ARABLE PRODUCTIVITY*

T. E. WILLIAMS

The Grassland Research Institute, Hurley, Berks

Leys have appeared in most of the croprotations practised in this country since theearly nineteenth century. Enclosure, and theadoption of regular crop rotation, against abackground of practices aimed at goodconservation of animal and plant residues,increased crop yields. The legumes in the leyscontributed in no small degree to the generalimprovement.

Red clover and sainfoin in various regionsand on difTering soil types became firmlyestablished in leys. Sainfoin varieties wereavailable that would last for many years toproduce long leys that vtere productive ofherbage and aiso increased the fertility of soilswhich were otherwise difficult to maintain in areasonable degree of productivity. These werethe thin chalk or oolitic soils and calcareoussandy soils. In all these districts well adaptedlocal varieties of sainfoin were found. Althoughlucerne was well known to many ofthe agricul-tural innovators towards the end of theeighteenth and the early nineteenth centurythe plant did not at the time become esta-blished as a farm crop of any importance. It isonly in recent decades that lucerne has becomewell established and then only in parts ofsouth and east England.

The higher rainfall regions with their moreor less acid soils were, comparatively, not sowell served in respect to herbage legumessuitable for leys longer than one or two yearsuntil, early in this century, the value of wildwhite clover and the significance of obtainingseed from old pastures were recognised. Inthose regions where a long ley featured in thecropping sequence the impact of using wildwhite clover was as marked in its effect on theyield of tillage crops as on the productivity ofthe ley itself. The value of wild white clover in

the ley and its impact on tillage crop yieldsare well illustrated in accounts of farmingsystems in north-east Scotland by Cruick-shank (1925. 1936) covering the period ofintroduction of wild white clover in the leys.

The value of the ley in alternate husbandryis based very largely on the experience ofestablished praetice. The beneficial efieets ofthe ley in crop rotation have been extolledfrom earliest times (see Stewart & Eusscll.1929) and more recently by others (Elliot1898, Stapledon & Davies 1942). However,what is of greatest interest at present is thenature of the many changes whieh occur in thesoil when the land is in ley and the relativeinfluence of these individual changes on theproductivity of crops which follow leys. Ofequal importance is the fact that leys areestablished from widely differing seeds mix-tures and are subjected to different manage-ment practices. This paper mainly deals withthese latter considerations of the effect ofvarious types of leys and their managementon the yield of thi; following crops.

It was not by chance that the earliest leysu.sed in English farming were in the mainalmost exclusively based on sowings of cloveralone. The proportion of clover to grass has amost marked effeet on subsequent crop yields(other than a leguminous crop). Yields of twosuccessive wheat crops following leys with andwithout white clover are given in Table 1.Considering the yields of the first crop ofwheat, without fertilizer nitrogen, the highestfollowed a ley produced from a sowing ofwhite clover alone which was 3-5 cwt. per acreheavier than that following a perennial rye-grass-white clover ley and 9-5 cwt. heavier thanthat after the all grass sward.

•Read at the Winter Meeting ofthe British Grassland Society, London, II December 1959,

189

190 LEYS AND SUBSEQUENT ARABLE PRODUCTIVITY

TABLE I. The yield of wheat in the first and second crop after three-year leys: cwt. grain per acre

while clover S 100

Fertilizer N to wheat; per acre

Grazed swardsPerennial ryegrassPerennial ryegrassWhite clover S 100

Seed production cropsCocksfoot in 2 ft, drillsTimothy '- red clover broadcast

Standard error (columns)Standard error (rows)

Nil

26-732-7362

24'824-5

Isl crop35 Ib.

30-332-535-1

32-125-1

I 461̂ 32

2nd cropNil 35 Ib.

28-829-6

25822-8

32-533-932-5

33-927-7

+178\A2

The seed production stands can be taken asexamples of leys without legumes (the redclover being present only in the first year) andwithout the influence of the excreta of thegrazing animal. Yields after both seed produc-tion crops are lower than after any of thegrazed swards.

In the second wheat crop the yields aresimilar after each of the three grazed swardsbut as a group they have been followed bybetter yields than after the seed productioncrops.

There is a significant interaction betweenthe type of ley and the response of the wheatto nitrogen fertilizer top dressing; there beingno response to nitrogen fertilization of thewheat following those leys which producedthe lowest or highest yields, namely thetimothy seed crop sown broadcast and theperennial ryegrass/white clover or white cloverleys; this observation will be commented onagain.

40-0

30-0

200

Fig.

Standard error of estimate ± 3-2 cwi

300 600Shoots per 36 sq. fc.

Relationship between lucerne shoot numbersand following wheai yield.

Within the investigation which is sum-marized in Table I various lucerne leys werealso included for comparison. Establishment oflhe lucerne was highly variable betweenreplicates and treatment plots but the relation-ship between the lucerne tiller numbers in thesummer before ploughing, and the followingwheat yields is given in Fig. 1. The relationshipbetween the two variates is marked: a fullpopulation of lucerne was followed by a yieldof circa 40 cwt. which is greater than thatfollowing the best of the grazed leys.

Parallel results for white clover have beenreported by Aldrich et al. {1958). In thisinstance persistent varieties of white cloverwere better than a non-persistent variety intheir effect on the following potato erop.The Rothamsted experiments reported byNicol (1933) also indicated that the residualvalue of lucerne for the growth of cereal cropswas greater than that of red or white clover,alsike or sainfoin. On the light Woburn soilsgrazed grass-clover leys were followed by betterpotato yields than were cut lucerne leys(Mann & Boyd 1958).

There is no evidence that different grassspecies have any material influence on theyield of the following crops which can beattributed to differential soil fertility other thanby influencing the proportion of clover orlucerne in a mixed sward. However, fieldinvestigations have shown that grasses mayinfluence subsequent wheat yields by har-bouring varying numbers and species of stemboring larvae, mainly of the genera Oscinella,Opomyza and Geomyza which after ploughingmigrate to, and damage the wheat plant

T. E. WILLIAMS 191

(Jepson & Heard 1959). Red fescue andAgrostis were found to harbour larger num-bers of larvae pathogenic to wheat than didperennial ryegrass; cocksfoot, timothy, mea-dow and tall fescue were largely free of them.

It is to be expected that such practices ascutting and complete removal of the crop orgrazing would produce marked differences inthe nutrient status of soils carrying the leys.Thus crops following cut leys have been shownto suffer more from potash deficiency thangrazed leys (Mann & Boyd 1958) when level offertilizer input was the same for each manage-ment. Continuous cutting of grass removes largequantities of plant nutrients. Under grazingthe bulk of the plant nutrients is directlyreturned to the soil. Cutting or grazing prac-tices would also effect the grass/clover ratio inleys.

TABLE 2. Yield of wheat after grazed or hayed four-yearleys: cwt. grain per acre

Fertilizer N to whcal, per acre Nil 35 Ib.Grazed grass/clover leys 31-9 35'7Hayed grass/clover leys 24-9 28-3

SE L 0 39

In Table 2 some examples are given of yieldsof wheat following a variety of grass/cloverfour-year leys either grazed or cut for hay.The differences in yield are probably due todifferential return of stock excreta and thedifference in the grass/clover ratio of the twoforms of management. In this instance potas-sium and phosphorus were used in sufficientquantities to cover the removal of thesenutrients in the herbage harvested and thewheat also received a PK fertilizer. The greateryield following grazed leys is therefore likelyto be the result of a greater accumulation ofsoil nitrogen.

Since the proportion of white clover, andother legumes, in a ley has an important bear-ing on following cereal yields it is pertinent to

enquire about the effect of using nitrogenousfertilizers on the mixed ley, owing to their wellknown effect of decreasing the proportion ofclover. Data relative to this question are givenin Table 3 in respect to three-year grass/whiteclover leys receiving up to 280 Ib. of nitrogenin each year. On grazed leys the use of increas-ing quantities of nitrogen has increased theyield of the following wheat but on cut leysyields are depressed. There is some indicationthat the yield of wheat after a cut ley tends toincrease at the highest rate of nitrogen fertili-zation. These results were obtained where allplots received 0-51 cwt. P2O5 and 0-60 cwt.KoO each year while in ley and for the wheat;the cut leys received supplementary dressingswhich returned 0-8 Ib. P A and 3-0 Ib. KgOper 100 Ib. of dry matter cut and removed. Itwould appear that under cutting conditionsthe loss of white clover, as a result of usingnitrogen fertilizer, is not corrected by the inputof nitrogen fertilizers and wheat yieldsdecreased. White clover is also depressed bythe use of nitrogen on the grazed plots but theextra quantities of herbage produced result inincreased return of stock excreta, the effect ofwhich more than counterbalances the loss ofwhite clover. Results of experiments reportedby Wheeler (1958) showed similar effects of theuse of nitrogen on grass/clover leys under bothcutting and grazing managements.

The similarity in yield of wheat followinggrazed or cut ley receiving no nitrogen needsa comment. The loss of return of animal excretaon the cut ley has been rectified in respect tophosphorus and potassium through the in-creased quantities of fertilizer used under thismanagement while in ley. Also the cut ley con-tained on the whole a greater proportion ofwhite clover than did the grazed ley but thedifference could not reasonably be expected toprovide the same quantity of nitrogen to the

TABLE 3. The influenee of the use of nitrogen fertilizer on three-year grass/white clover leys on the following wheatyields

Fertilizer N to ley: Ib./acre/year Nil 70 140 280Yield of wheat: cwt. grain per acre

Grazed ley 339 360 39 2 41-8Cut ley 32.5 3t.2 27-6 30-1

S.E. ± I 24

192 LEYS AND SUBSEQUENT ARABLE PRODUCTtVITY

TABLE 4. The persistence of the efTecl on crop productivity of (hrec-year grazed leys compared with a one-year ley

Following one-year leyFollowing three-year ley grazed

1st cropwheat: cwt./acre

29\37-7

2nd cropkale: ton/acre

16.5191

3rd cropbarley: cwt./acre

28-5333

soil as would (he stock excreta, ft certainlysuggests that the nitrogen returned in dung andurine, largely in the latter, is subject to highlosses. That such loss occurs has been shownby Doak (1952).

The effect of the three-year ley. relative to aone-year ley on crop productivity is at leastevident in the third crop after the ley (seeTable 4). Thus the yields following a three-yearley exceeded those following a one-year ley by30 per cent in the first crop which was wheatand by 16 and 17 per cent in the subsequentcrops which were kale and barley.

The results of these comparative fieldexperiments show that leys vary substantiallyin their effect on the produetivity of thefollowing crops. The effect of leys on soilphosphorus or potassium status can bebroadly predicted from the pattern of use ofthe ley and the input of fertilizers containingthese elements during the life of the ley. How-ever, it may well be that changes in soil condi-tion which occur when land is laid down toleys may affect the whole economy andavailability of soil phosphorus and potassiumbut as yet this aspect has not been investigatedwithin the range of conditions found in thealternation of leys and tillage crops. When soilphosphorus and potassium status are main-tained under the ley then the legume in the leyis an important requisite for increase in cropproductivity. At the same time the use offertilizer nitrogen on the grazed ley ean aug-ment the increase in crop productivity and inthis context the use of nitrogen fertilizers has alonger term effect than what is normallycredited to such quick acting fertilizers. Thesituation may be summed up in stating thatthose practices which increase the live-stockcarrying capacity of the ley will also result inimproved crop productivity.

Any differences that arise in crop produc-tivity as a result of the presence or absence ofleys or between different leys of different type

or differing management are the expression ofthe many soil changes which have occurredunder the ley. Soil organic matter increasesunder a ley and up to the third or fourth yearofthe ley the increase is largely accounted forin the weight of the root and undergroundplant organs of the ley present at the time ofploughing. However, the significance on cropproductivity of the root mass incorporatedinto the soil and subjeet to decompositionneeds to be viewed with some caution. Dif-ferent grasses establish different weights ofroots but these differences are not large anddetailed investigation is required to establishthese differences. Also frequency of grazingor cutting will also affect root weight, beinggreater with less frequent grazing. However,no particular direct relationship exists betweenroot weight and crop productivity the latterbeing more dependent on the nitrogen contentof the root mass. Thus the presence of a largeroot mass at the time of ploughing may in factreduce the following crop yields. This isiiiustrated by the data given in Table 1 in thecase of the yields of wheat following seedproduction stands of cocksfoot in drills andtimothy broadcast; the root weight was greaterunder the broadcast crop. Without nitrogenfertilizer to the wheat yields were similar butresponse to a dressing of 35 Ib. of nitrogendilfcred considerably after the two seed produc-tion leys. After cocksfoot in drills the responseamounted to 7 3 cwt. of grain but only 0-6cwt. after the broadcast timothy. This stronglysuggests that the decomposing root mass aftertimothy was in fact locking up nitrogen to thedetriment of the wheat crop. In this instancethe root weights were different owing to thedifferent culture ofthe two grasses rather thana species difference between cocksfoot andtimothy. Encouragement of a large root massunder leys should therefore be viewed withsome caution if this is achieved by lenient

T. E. WlLLtAMS 193

grazing or taking a hay cut since such practicesreduce the white clover which would accen-tuate the depression in the nitrogen content ofthe root mass.

The amount of organic material in the rootsand short stubble of leys in their third orfourth year will frequently amount to 4 or 6tons of dry matter which is equivalent to theorganic matter in about five times this weightof farm yard manure. If on any soil type orsystem of cropping a value can be placed onthe largely undecomposed or partially decom-posed organic matter represented by the rootmass under the ley. other than from its contentof plant nutrients, then the ploughing under ofleys is one of the most ready means of incor-porating organic matter in quantity.

When arable land is laid down to grass it iswell known that the physical structure of thesoil changes. There is an increase in water-stable soil aggregates but the rate ofchange isslow (Low 1955). On medium or heavy tex-tured soils many years must lapse before thephysical condition of the soil reaches thatfound under permanent pastures. Only smalldifferences in soil aggregation arise from theuse of different grass species or from differenttypes of management (Pringle & Coutts 1954:Clement & Williams I958K The workabilityof soils difficult to cultivate is improved after aperiod in grass and seed bed tilths are moreeasily produced. However, what effect theimprovement of the physical structure includ-ing any improvement in soil moisture retainingproperties, as produced by a medium durationley, has on subsequent crop productivity isnot clear. As yet there is no evidence that theimprovement in the physical eondition of thesoil after leys contributes to the improvedyields of crops quoted in this paper. Theresults of the experiments conducted atHurley indicate that the improved yields afterleys can be almost entirely attributed to theincrease in the nitrogen status ofthe soil. Thisnitrogen is contained in the organic residues ofthe ley—the roots, stubble, plant debris andstock excreta. The availability of the nitrogento crops after the ploughing of leys depends onthe carbon/nitrogen ratio of the organicresidues and the rate of decomposition. A high

degree of relationship has been shown to existbetween the amount of nitrate- and ammonia-cal-nitrogen released from ley soils and theyield of the following cereal crop (Clement1958). The relationship accounts for thegreater part of variation in crop yields follow-ing various types of ley and no improvementin the relationship is brought about by takinginto account the improvement in soil structure.If the improvement in soil structure after aperiod in ley cannot be shown to have a directinfluence on crop yields there still remains theintangible value of the improvement in theworkability of the soil. The value of thisimprovement will vary with the soil type-weather conditions and the skill displayed indoing the right cultivations at the right lime.

Leys arc frequently introduced into croprotations specifically with the object ofreducing the incidence of certain crop pestsand diseases and with success (Budden &Garnett 1944; Wehrlc & Ogilvie 1955). Theexamples of varying crop yields after variousleys quoted in the foregoing tables have beenobtained in the absence of cereal diseases. Ifdisease control is brought about by leys thentheir influence on crop yields would beincreased in proportion to the severity of itsincidence before the ley was introduced.

As far as is known all types of mediumduration leys are equally valuable in thecontrol of the common cereal root invadingpathogens and the protection given againstsuch diseases is independent of the build upof nitrogen under the ley. For instance grassseed production stands have a low value inrespect to the build up of soil nitrogen statusbut they are of value, in the control of cerealroot diseases, in those circumstances wherethe tillage land is largely devoted to cerealgrowing. In praetice the growing of grass seedcrops has been established in recent years inthose districts where the.se circumstances existand seed crops have had a positive effect on thefollowing yields.

Also the alternation of crops and leys helpsin the control of weeds but tbe value of thisattribute ofthe ley is being much reduced withthe introduction of chemical herbicides.

194 LEYS AND SUBSEQUENT ARABLE PRODUCTIVITY

In conclusion when leys are included inarable rotations the inherent crop producti\ityofthe soil is increased. This is much dependenton the type and management ofthe ley. Subse-quent crops are increased in relation to theproportion of legume in the ley and is greaterunder grazing than cutting. The use of nitrogenfertilizers on grazed swards increases the buildup in crop productivity. The use of nitrogenousfertilizer on grazed grass has therefore a resi-dual value. Changes in phosphate and potashstatus can be fairly well predicted from aconsideration of the use of these fertilizers onthe ley and the use made ofthe grass.

The improved productivity following leyscan in the main be attributed to the increase insoil nitrogen status. This influence of the leycould be measured in terms of its value inreducing the requirement of fertilizer nitrogenfor the growth of the following crops. Thecontrol of plant pests and disease broughtabout by breaking an otherwise arable rotationby the introduetion of leys would considerablyenhance the effect of leys on crop productivity.What is the value of the improvement in soilstructure is not clear. There may exist somesoils of particular texture, structure andorganic matter eontent that growth of agricul-tural crops would be improved if their physicalcondition was bettered by a period in ley, butsueh cases are probably rare in Britain.

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