THE EFFECT OF WHITE CLOVER AND NITROGENOUS FERTILIZER ON THE PRODUCTION OF A SWARD

Three-year leys of cocksfoot/white clover and cocksfoot alone were dressed with 0, 35, 105 and 210 lb. N per acre every year to provide information on the effect of clover and N on annual production.
White clover contributed 40% of the dry-matter yield but its presence was responsible for 77% of this yield where no N was used: it was responsible for less than 8%, and contributed 5%, where 210 lb. N per acre was applied annually, lt was estimated that grass alone receiving 160 lb. N per acre would yield as much dry matter as a mixed sward receiving none.
Clover had the indirect effect of raising yield of nitrogen in the companion grass by 60 lb. per acre per year. A maximum of l06 lb. was recorded in 1958.
The response of the tnixed sward averaged 10 lb. of dry matter per lb. N. Prevailing economic circumstances will determine if this level is satisfactory in practice.
The recovery of N by grass alone varied from 54% at the lowest level of N to 80% at the highest. On mixed swards apparent recovery was negative or low: N was to a large extent only replacing the effect of clover which was suppressed by its use.
Factors influencing response and the difference between that obtained under experimental and practical conditions are discussed.
The use of N to produce out-of-season grass may give good response, but may cause a reduction in clover contribution.     

THE GRAZING ANIMAL AND SWARD PRODUCTIVITY

A trial designed to show the effects of animal excreta on sward productivity is described.
It was estimated that the grazing sheep returns in a season nutrients capable of immediate uptake by the plant equivalent to 5–6 cwt. nitro-chalk and 2–21/2 cwt. 60% muriate of potash per acre.
A large part of sward yield depended on animal return. Clover depression from the effects of animal excreta and, under mowing treatment, from the effects of fertilizer nitrogen, did not result in marked loss of transferred clover nitrogen. There appeared to be a gain in clover soil-nitrogen from a reduction of the clover stand.
A comparison is made between the restilts obtained from sheep excreta on the sward with those obtained from mowing treatment.
The interaction between animal or fertilizer nitrogen and the clover plant is discussed.     

CLOVER NITROGEN AND SWARD PRODUCTIVITY

Under mowing conditions in the absence of the animal, ultra-simple swards based either on ryegrass or cocksfoot gave large increases in yield of dry matter and nitrogen from the inclusion of white clover in the seeds mixture. Raising the clover seed rate from 1 to 3 lb./acre gave a further response in yield.
As the swards aged, the continuing effect of increased clover seed rate was dependent on applied nitrogen.
The rate of transference of nitrogen from clover to the soil depended upon the species of the associated grass, the clover seed rate, the age of the sward and the degree of reduction of the clover in the sward.
Suppression of clover led to an increase in soil nitrogen, particularly with high seed rates of clover.
Dry matter response to applied nitrogen (69 lb./acre/annum) was greater in cocksfoot than in ryegrass. Fertilizer nitrogen had little effect on the yield of nitrogen from the sward except where the high seed rate of clover had been used.     

THE EFFECT OF URINE AND ITS COMPONENTS ON THE BOTANICAL COMPOSITION AND PRODUCTION OF A GRASS/CLOVER SWARD

A study was made of the effect of sheep urine and some of its components on herbage production. The return of urine to the sward increased production from the grass species; the clover content of the sward was reduced.
The application of nitrogen or potassium fertilizer equivalent to the normal return of nitrogen and potassium in urine increased production, but not as much as urine. The return of nitrogen and potassium fertilizer together increased production and altered botanical composition in much the same way as did urine.
On a grass-dominant urine-treated sward the application of nitrogen fertilizer increased the "efficiency" of urine.
The effect of urine on a grass/clover sward was almost entirely due to its nitrogen and potassium content. The water and indole acetic acid content of urine had no effect on pasture production or composition.     

RESPONSE OF GRASSLAND TO NITROGENOUS FERTILIZER IN THE WEST OF ENGLAND

Extensive replicated plot experiments were carried out at Henley Manor Farm from 1956–1961 to obtain accurate measurements of herbage production and response to nitrogenous fertilizers under West of England conditions. 356 plots were used; use of the herbage by both cutting and grazing was studied. The principal results are: Grass/ clover swards (containing approx. 35% clover) grown without nitrogenous fertilizer averaged 75 cwt dry matter per acre per annum. Application of nitro-chalk to initially grass/clover swards reduced the clover content of the herbage. About 133 lb N/annum was required by an all-grass sward to equal the production of a grass/clover sward without N. Attempts to increase production of grass/clover swards by using N for early growth and relying on clover for mid-season growth were unsuccessful in 2 out of 3 years. Swards (initially grass/clover) gave significant increases in total dry-matter production from regular use of the lowest level of N (26.0 or 34.7 lb N/acre/cut or graze) in 44 out of 49 cases. Extremely high yields were obtained from the heaviest use of N (104.2 lb N/acre/silage cut). 52.1 lb N/acre/cut or graze was the optimum rate of application on ail-grass and grass/clover swards. Up to about 350 lb N/acre/annum the dosage-response curve was very nearly straight for all-grass and grass/clover swards. On the grazed plots herbage left ungrazed amounted on average to only 6% of the total. The health of all stock on the high nitrogen plots (as well as all others) was excellent.     

THE INFLUENCE OF TWO LEVELS OF NITROGENOUS FERTILIZING ON THE LONG-TERM PRODUCTIVITY OF LEYS

Two levels of nitrogen application (70 and 180 lb per acre per annum) were compared on 6 long-duration leys. The treatments were repeated for periods of up to 4 years on tiie same swards. The higher N dressing produced 2230 lb more dry matter per acre than the low rate, an increase of 28%, and the yield was also more evenly spread throughout the season. There was virtually no clover on the high-N swards. The proportion of clover varied under low N but tended to increase as the season progressed. The sown grasses remained the dominant sward constituents throughout the experiment, and there was no sign of loss of vigour on the high-N swards. Utilized-starch-equivalent outputs were calculated from 3 different swards for 1956–8 and there was a significant positive correlation between the dry-matter yields and utilized-starch-equivalent output of swards.     

THE EFFECT OF NITROGENOUS FERTILIZER ON AN ESTABLISHED WHITE CLOVER SWARD

The effect of nitrogenous fertilizer on a white clover sward was studied to obtain information to be used in the evaluation of white clover in grassland. There was no evidence of a yield response. The weight of nodules was depressed by the addition of fertilizer.
Where management is adjusted to maintain white clover in swards receiving large quantities of nitrogenous fertilizer the clover may use part of this fertilizer at the expense of symbiotic fixation.
The relation of the results obtained to the assessment of the benefit derived from white clover in mixed swards is briefly discussed.     

THE PERSISTENCE OF WHITE CLOVER UNDER POULTRY GRAZING

An experiment was carried out in two parts to investigate lack of persistency of white clover in a meadow fescue/white clover sward when grazed by poultry. It was found that poultry manure was responsible for a considerable part of this depressing effect. Grazing by poultry in the autumn and winter was nearly as effective in reducing the clover conlent of the sward as grazing for the whole year, autumn grazing being particularly harmful. Autumn and winter grazing alone increased the number of sown grass tillers and reduced Poa tririalis tillers in comparison wilh all-the-year-round grazing. Range and fold grazing at a high stocking rate (312 per acre in the first winter) both had the same effect on the sward. The effects of drought and continual close mowing on white clover persistence are discussed. Fertilizers containing calcium, potassium and phosphorus might counteract the depressing effect of poultry grazing and manure on white clover.     

THE EFFECT OF SHEEP EXCRETA AND NITROGENOUS FERTILIZER ON THE BOTANICAL COMPOSITION AND PRODUCTION OF A LEY

Results are presented for the final two years of a previously described experiment.
The return of dung and urine by sheep to a ryegrass/white-clover ley was controlled by suitable harnesses to give four treatments (no dung or urine, dung, urine, dung and urine) which were combined in a replicated factorial design with four levels of nitrogenous fertilizer application (0, 52, 182, 312 1b. N per acre).
Applied nitrogen and urine were the dominant factors affecting botanical composition. The percentage of ryegrass increased and that of clover decreased with the progressive increases in nitrogen application. Volunteer species (mainly Poa spp.) contributed up to 20 per cent by the final year, the maximum occurring under the medium-high nitrogen treatment.
Urine restricted the incursion of weed grasses.
Combined with urine or the full return of excreta, high levels of applied nitrogen increased herbage production by up to 120 per cent. There was little response to dung except at the highest nitrogen level.
The yield response to applied nitrogen was almost linear. In the absence of animal returns response was poor, partly due to shortage of potash. When both excreta were withheld the light nitrogen dressing depressed the annual production compared with the control; where both excreta were returned together with this dressing no reduction occurred in annual yield and the spring yield was improved (p <0.05).     

THE EFFECT OF WHITE CLOVER AND NITROGENOUS FERTILIZER ON THE PRODUCTION OF A SWARD

Three-year leys of cocksfoot/white clover and cocksfoot alone were dressed with 0, 35, 105 and 210 lb N per acre every year to provide information on the effect of clover and N on production.
Data from the grass-alone swards allowed an estimate to be made of the effect of N on production at different cutting dates. This was compared with the effect of clover.
The effect of N was greater than that of clover in the mid- and late-season cuts. Clover made its greatest contribution, both directly and indirectly, at the first cut, taken in May.
Under very dry conditions (1959), N was more effective than clover in maintaining production and the proportional response was large in relation to that produced under moist conditions.
The results are discussed with reference to the present seasonal use of N on grassland and an argument is advanced for increasing its use in mid-season.     

THE EFFECT OF DUNG AND URINE AND ITS INTERACTIONS WITH APPLIED NITROGEN, PHOSPHORUS AND POTASSIUM ON THE CHEMICAL COMPOSITION OF PASTURE

The importance of the grass/clover balance of a pasture in determining the effects of manurial returns and fertiliser applications on the chemical composition of the sward is shown.
The response to applied nitrogen was very dependent on the presence or absence of the animal excrements. For example, the N recovery from an application of 18 cwt. per acre of nitro-chalk was only 2% in the absence but 68% in the presence of the grazing animal.
Urine caused a marked increase in the N and K content and the yield of pasture, particularly when returned in quantity to a high-producing grass-dominant sward, and at the same time tended to depress the Ca, P and Mg content. Urine K was superior to fertiliser K, per pound of K returned or applied, in raising the K content of the pasture.
By comparison, dung had little direct effect on chemical content; even when returned in large amounts it affected the Ca and K content of the pasture to a relatively small extent. The P returned in the dung had little effect on the P content of the pasture and was inferior to superphosphate in this respect.
Together, as in normal grazing, dung and urine tended to counter or enhance their individual effects.
There was a positive correlation between the Mg and P content of the pasture and a negative correlation between Mg and K. Brief mention is made of the possible importance of the nutrient balance in pasture as a factor in animal health.     

THE EFFECT OF FERTILIZER NITROGEN AND FREQUENCY OF DEFOLIATION ON YIELD OF GRASSLAND HERBAGE

The effects of 4 levels of applied nitrogen, ranging from nil to a maximum of 417 lb N/ acre/annum, in all combinations with 3 frequencies of defoliation, ranging from 2 to a maximum of 10 cuts per annum, on herbage production from a perennial ryegrass/ timothy/meadow fescue/white clover sward were measured. These treatments were operative for 2J years, and in a subsequent year the residual effect of cutting frequency was tested. Dry-matter yields of total herbage and of the clover fraction are quoted, together with N yields of total herbage. Yield response to N was higher than in some other experiments in the U. K. Cutting frequency had a very large effect and, in general, the longer the interval between cuts, the higher was the dry-matter (though not the N) yield. There was a marked interaction between cutting frequency and level of N: at the high cutting frequency, dry-matter yield increased linearly with increasing level of N; at the medium frequency, response tended to fall off at the highest level of N; at the low frequency, yield declined with increasing level of N beyond 139 lb N per acre per anum.     

THE EFFECT OF WHITE CLOVER, FERTILIZER NITROGEN AND SIMULATED ANIMAL RESIDUES ON YIELD OF GRASSLAND HERBAGE

An experiment is described which measures the effects of white clover, fertilizer nitrogen and simulated animal residues, alone and in all combinations, on total herbage production from a perennial ryegrass sward. Yields of oven-dry herbage and of nitrogen are quoted. Two cuts were taken in the seedling year and four to six in each of three full harvest years.
Yield response to fertilizer nitrogen was similar to that in some other experiments in the U.K., while the beneficial effect of clover on yield was rather greater.
Negative nitrogen ± clover and positive nitrogen ± animal residues interactions were found throughout the yield data. There was a positive clover ± animal residues interaction in the first harvest year (dry-matter yield only), and a negative nitrogen ± clover ± animal residues interaction in the second harvest year.
The results are discussed in relation to other published work and to their application in practice.     

A RESPONSE TO PHOSPHATE ON AN ALL-GRASS SWARD

Results are presented from part of an experiment involving the application of nitrogen, phosphorus and potassium to a pure grass sward which had also received sheep dung and urine. The yield of oven-dry grass was increased significantly by about 30% by superphosphate application, but only where nitrogen had also been applied at 260 lb: N per acre per annum.     

THE INFLUENCE OF VARIOUS FORMS OF NITROGENOUS FERTILIZER ON THE GROWTH OF A PERENNIAL RYEGRASS / WHITE CLOVER SWARD IN EARLY SPRING

The effect of 4 or 5 forms of nitrogenous fertilizer on the yield and botanical composition of a perennial ryegrass/white clover sward was examined in 3 different years. The uptake of N by the grass was also estimated. Ammonium nitrate (as Nitro-Chalk), ammonium sulphate and urea gave similar yield increases, although in one year, when high rainfall followed the application of fertilizer, urea was slightly inferior. Gas liquor gave variable responses in the 3 years. Nitroform, a urea-formaldehyde, was generally less effective than the other forms of fertilizer. The uptake of N from Nitro-Chalk, sulphate of ammonia and urea did not vary greatly from year to year although the uptake of soil N by the untreated control did.
Response to N in the yield of dry-matter varied from year to year. This variation was due partly to differences in the amount of clover present and partly to differences in the extent to which N taken up by the grass was used for the synthesis of dry-matter.
The white clover content of the sward was not greatly reduced in spring by the application of the fertilizer, and there were no consistent differences between the effects on clover of the forms of the fertilizer. A reduction was apparent in the summer but not in the autumn.
It may be necessary to increase replication above the level of 3 to 6 which is frequently employed in field experiments if more precise quantitative estimates of response and of the relative efficiency of various forms of nitrogenous fertilizer are required.     

A COMPARISON OF THE REACTION OF DIFFERENT GRASS SPECIES TO FERTILIZER NITROGEN AND TO GROWTH IN ASSOCIATION WITH WHITE CLOVER

Seven species or varieties of grass, and a mixture of 3 of them, were sown in pure swards and treated with 4 levels of nitrogenous fertilizer (0,17·5, 35 and 70lb N per acre per cut). Each species, and the mixture, was also sown with white clover. The experiment was cut 4 or 5 times per year. The effect of fertilizer on the yield of each grass was compared with the effect of clover on the yield of the grass/clover swards. Mean annual yields showed an approximately linear response to N; there was a small but significant fall in response to the highest level of N. Response among the species ranged from 20 to 30 Ib of dry matter per Ib N applied for the intermediate level of fertilizer and from 14 to 23 Ib for the final increment of fertilizer.
S37 cocksfoot, S48 timothy, S24 ryegrass, and a mixture of these grasses, were high yielding and responded well to fertilizer N; Irish ryegrass and Agrostis tenuis were less productive and gave poorer responses to N. S215 meadow fescue and S23 ryegrass were intermediate in yield and response.
There were no significant differences between the annual yields of the 8 grass/clover mixtures; the yields of the grass and clover components of each mixture were inversely related. The effect of clover on the yield of the grass/clover mixtures was estimated to be equivalent to the effect of an annual application of 205 lb N per acre to Agrostis tenuis and 120 lb N to S48 timothy. The fluctuations in annual yields were greater with grass/ clover mixtures than with grass swards receiving N.
The yields of grasses when sown with clover were in similar order to their yields when sown pure; but whereas the latter tended to fall from year to year, the yields of the grass components of mixtures (except Irish ryegrass) did not.     

THE PERFORMANCE AND SURVIVAL OF CONTRASTING NATURAL POPULATIONS OF WHITE CLOVER WHEN PLANTED INTO AN UPLAND FESTUCA/AGROSTIS SWARD

A technique is described for the assessment of white clover populations implanted as rooted cuttings into an upland Festuca/Agrostis sward.
Five natural populations of white clover, taken from widely different soils and habitat conditions, were tested by this technique on an acid soil, low in calcium and phosphate and just outside the natural limits of clover distribution.
Throughout the experiment, populations from acid upland soils showed a superior performance and a lower percentage mortality than did populations from lowland calcareous soils and from medium-fertility soil at a very high altitude.
After two years, plants of the acidic populations alone remained alive, and of these only 19–25% of the number originally planted.
The order of performance in the natural sward was an almost complete reversal of the order of performance as spaced plants on a high-fertility lowland soil.
The results indicate that the differential response to soil fertility factors, previously shown to exist between natural populations of white clover by soil- and sand-culture techniques and by field fertilizer trials of spaced plants, became even more marked when the plants were subject to competition from native species.
The possibility of breeding white clover varieties adapted to acid upland conditions is discussed, particularly in relation to compatibility with native species.     

THE EFFECT OF THE BIPYRIDYL HERBICIDES ON HILL COMMUNITIES AND THEIR ROLE IN THE IMPROVEMENT OF HILL GRAZING

The improvement of hill land is important to the national economy of the United Kingdom. An increase in the amount of enclosed productive land results in a greater stock-carrying capacity of a hill farm. Improvement is not always possible by conventional implements, and herbicides are being used to kill the old sward. The bipyridyl herbicides offer a means of destroying or modifying the indigenous vegetation. The application of low doses of paraquat or diquat to an association containing Molinia caerulea, Nardus sfricta and Festuca avina resulted in a change in equilibrium in favour of the fescues. The application of 2 lb paraquat per acre practically eliminates all grass species in a sward and it is then possible to establish desirable pasture species after lightly cultivating the dead surface litter.     

THE WEED FLORA OF CHEMICALLY-RENEWED LOWLAND SWARDS

The viable-seed content of soils under grass swards was investigated in relation to the potential weed flora which may occur in chemically-renewed swards. The viable-seed populations in the top 6 in. of the soils ranged from 46 million per acre for a 1-year ryegrass ley to 1·7 million in an old permanent pasture. On the limited evidence available, there appears to be no close correlation between the broad-leaved weed species present in the original pasture, the viable seeds in the soil, or the volunteer species in the new sward. Large populations of viable seeds of indigenous grass species occurred in most swards, while there was an almost complete lack of seeds of cultivated grasses. The effect of surface cultivation following the application of paraquat to a grass sward is to stimulate the dormant weed seeds in the upper layers of the soil to germinate. If these layers were left undisturbed a relatively weed-free environment would eventually be achieved.     

THE EFFECT OF FERTILIZER NITROGEN AND WHITE CLOVER ON HERBAGE PRODUCTION

The effect of a range of N rates on herbage production from grass/white-clover and grass swards was investigated in two long-term grazed experiments. The mixed sward yielded more than the grass swards over the range of fertilizer rates tested which were 0–120 lb N/ac (134.5 kg/ha), but the response of the mixed sward to fertilizer N was less than that of tbe grass sward. Tbis was due to the direct and indirect effect of clover, which was considerable with no fertilizer N but decreased witb increasing rates of application. However, clover was not completely suppressed by N at eitber site and contributed to berhage yields at all N rates. Rate and time of N application and the amount of clover in tbe sward affected tbe seasonal distribution of DM yields. The mid-season decline was less marked at bigb- tban at intermediate-levels of N supply.