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 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 RELATIONSHIP BETWEEN LIGHT BENEATH WHEAT CROPS AND GROWTH OF UNDERSOWN CLOVER

In two experiments the growth of clover undersown to wheat was linearly related to the amount of light available. There were strong indications that clover growth and light within N.-S. rows were superior to those within E.-W. rows of wheat, and within N.-S. rows, those along the middle position were superior to others. The large difference between the growth of clover sown alone and with wheat indicated that beneath wheat the clover suffered from competition for other factors, probably soil moisture, which was even greater than that for light. Beneath wheat at the reduced level of growth there was a positive linear relationship between yield of clover and available light.     

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 WHITE CLOVER AND NITROGENOUS FERTILIZER ON THE PRODUCTION OF A SWARD

Data from an experiment already reported (2) are used to examine a statistical method proposed by Walker et al . (8) for apportioning the nitrogen harvested in grass in a grass/ legume sward to legume, fertilizer and soil. Multiple regressions of the yield of N in the grass (G_n) upon N harvested in the associated legume (C_n) and N applied in fertilizer (F_n) were highly significant; but they were very variable, mainly because of the strong (negative) correlation between C_n and F_n. In some cases the coefficient for clover N was negative, in some cases the coefficient for fertilizer N exceeded unity; and the residual constant varied widely among 4 sets of plots on the same soil. The interpretation of such equations in physical terms is criticized on these grounds. The use of pure grass swards in conjunction with mixed swards gave estimates of the recovery of fertilizer N, and of the transfer of N from clover to grass, which agreed better with other published data than did the coefficients in a multiple regression. A simple regression of the estimate of transferred N in the grass upon the N harvested in the clover yielded a second constant. This constant, which varied considerably from one series of plots to another, is thought to indicate interactions between the various sources of N, which would be attributed to a direct effect of soil N if the multiple regressions were interpreted as Walker et al . suggest.     

THE EFFECT OF STAGE OF GROWTH AT DEFOLIATION ON WHITE CLOVER IN MIXED SWARDS

Four experiments are described in which various defoliation methods and frequencies were imposed on grass/white-clover swards. Clover was not reduced in any of these hy increasing the length of growth period or hy cutting at a late stage of growth, but intensive sheep grazing reduced clover compared nitb cutting and taking a silage cut in a grazing sequence improved clover yield. These results do not support the contention that cutting a mixed sward for hay or silage suppresses clover because of competition for light: with a ‘big white’ type of clover infrequent defoliation may cause no more shading than frequent. Alternatively, any additional shading may be compensated for by an increase in clover growth, stimulated hy the longer growth period. It is suggested that, in practice, competition for nutrients and moisture also contrihute towards clover suppression when swards are cut for hay or silage.     

A STUDY OF THE INFLUENCE OF NITROGEN ON THE ROOT WEIGHT AND NODULATION OF WHITE CLOVER IN A MIXED SWARD

Experiments are described in which a study was made of the top growth, root weight, nodule number, and type of nodules of white clover growing in a grass sward in the field. Soil cores were taken and the clover root-system examined after removal of soil by washing.
The most important factor governing the total number of nodules and the number of large (2 mm. or more in length) nodules under the sward was the amount of clover root-material present.
Nitrogenous fertilisers and the return of dung and urine by grazing sheep reduced the amount of clover root-weight and consequently the number of nodules found under the pasture. 36 1b. of nitrogen applied in the early spring of 1956 had a beneficial effect on both clover top-growth and nodulation. 80–100 1b. of nitrogen per acre had no effect on the number of nodules per gram of root. However, the application of 200 1b. of nitrogen per acre caused a significant decrease in the number of large nodules per gram of root.
The numbers of large nodules present reached a midsummer peak where nitrogen was not applied.
During the autumn many nodules showed part green and part pink colouration or were completely green or brown, an indication of a decline in nitrogen-fixing ability. Decaying nodules increased considerably in number when the legume was being suppressed by nitrogen application and top growth was poor. The practical application of these results is discussed and methods of maximising the benefit from clover and fertiliser nitrogen are suggested.     

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.     

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

Seven species or varieties of grass, and a mixture of 3 of them, were sown in pure swards, treated with 4 levels of nitro-chalk (0, 17·5, 35, and 70 Ib N/ac/cut) and cut 4 or 5 times each year. Each species and the mixture were also sown with white clover, and the effect of fertilizer N on the yield of N in each grass was compared with the effect of clover on the yield of N harvested from the grass/clover swards.
The regression line for response in yield of N with increasing levels of fertilizer N showed slight, but significant, upward curvature. The grasses differed in their uptake of N from the soil, S37 cocksfoot and S48 timothy showing relatively high uptakes, and the ability of each grass to take up fertilizer N was usually related to its uptake of N from the soil. Differences in the yield of dry matter between the species, at a similar level of N, are discussed, and it was concluded that perennial ryegrasses were most efficient and Agrostis tenuis was least efficient in using the N taken up in the production of DM.
In general, there were no significant differences between the yields of N of the grass/clover mixtures; the N yields of the grass components were significantly different and tended to be inversely related to the N yields of clover.
Grasses which gave high yields of N with fertilizer were also high yielding when grown in association with clover. Pure grass swards required more than 200 Ib fertilizer N/ac/yr in order to yield the same amount of N as the grass/clover swards. The amount of N estimated to have been derived by grass from clover (indirect effect of clover) increased each year; it was highest with S37 cocksfoot and lowest with Irish perennial ryegrass, averaging 46 and 23 Ib N/ac/yr, respectively.     

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.     

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 EFFECTS OF WHITE CLOVER AND APPLIED NITROGEN ON THE NITROGEN CONTENT OF VARIOUS GRASS/CLOVER MIXTURES

Percentages and yields of N in various grasses and grass mixtures with clover and in associated clover grown at various levels of N application over 5 years are given. Grasses varied consistently in N content, percentages being highest in meadow fescue (cv. S53) and lowest in perennial ryegrass (cv. S24). N application did not significantly affect the N percentage in clover, but the associated grasses had a highly significant effect Percentages were highest in clover associated with meadow fescue and lowest in clover associated with ryegrass. The apparent transfer of N to grass per Ib N in associated clover was calculated for various treatments each year. Reasons for the changing levels of apparent transfer from year to year are considered.     

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 TESTING OF GRASS VARIETIES IN SWARDS WITH CLOVER: THE EFFECT OF GRASS SEED-RATE ON COMPARISONS OF GROSS YIELD

Three experiments were carried out to examine the influence of grass seed-rate upon the amount of clover growing with different varieties of perennial ryegrass. The bred varieties S23 and S24 were compared with Irish ryegrass. A larger quantity of clover grew with Irish ryegrass than with bred varieties at any given seed-rate. If the varieties were to be compared in terms of herbage of similar clover content, then Irish ryegrass sown at 20 lb/ac had to be compared with S23 or S24 sown at about a quarter of that rate. Reducing the seed-rate of the bred varieties from 20 to 5 lb/ac had only a small effect upon yield of ryegrass, and this was offset by an increase in yield of clover. Since weed grasses also took advantage of low grass seed-rate, it is concluded that other factors in the management of variety trials must be so controlled as to produce a satisfactory clover content without too drastic a reduction in the seed-rate of any variety. The relationship between grass seed-rate and yield of clover varied markedly with the availability of moisture.     

Observations on the incidence of plant parasitic nematodes in grassland in England and Wales

Soil samples taken from one- to four-year-old swards of white clover and perennial ryegrass at 34 sites, and from older clover/grass swards at 56 sites in England and Wales, were examined for plant parasitic nematodes. Stolons of white clover from 46 of these sites were examined for nematodes. Clover cyst nematode ( Heterodera trifolii ) and white clover stem nematode ( Ditylenchus dipsaci ) were found in 62% and 41% of sites respectively. The grass cyst nematode ( Punctodera punctata ) was present in 56% of 71 sites examined, and other grass cyst nematodes ( H. bifenestra and species of the H. avenae group) occurred in 13% and 17% of sites. Two root-knot nematodes were found, Meloidogyne naasi and M. hapla, in 15% and 4% of the samples examined. Migratory nematodes were extracted from 63 samples, and spiral, pin and lesion nematodes were found in more than 90%. Stunt nematodes were less frequent (65%) and criconematids (19%) were found relatively infrequently. The significance of these observations to grassland productivity is discussed.     

WHITE CLOVER TRIAL

Yields were recorded from a potato crop grown in the first year following a grazing trial comparing four strains of white clover, previously described in this journal (2 & 3). The Kent clover strain, which was the most persistent and which had produced the greatest live-weight increase per acre, gave the highest yield of potatoes. The Dutch white clover, which had been the poorest in the grassland trial, gave the lowest yield of potatoes.
A 2 × 2 × 2 N, P, K fertilizer design was superimposed in the form of split plots. Nitro-chalk at 5 cwt. per acre and muriate of potash at 2 cwt. per acre both caused significant reductions in yield, and this was thought to be due to the exceptionally high soil fertility status of the field. The fertilizer × clover interactions were non-significant, and contributed little towards an explanation of the fundamental basis of the soil fertility differences caused by these four clover strains.     

WILD WHITE CLOVER SEED PRODUCTION

Field experiments on the management of ryegrass/white-clover pastures for seed production were carried out from 1958 to 1961. Replicated trials with ¹/₆-acre plots compared continuous grazing, rotational grazing and cutting once at the silage stage of growth as methods of pasture management from April to June. An additional mechanical method, gang mowing, was introduced in 1960 and Hayter mowing was used in 1961. In 1958 to 1960 the treatments were studied with and without the application of 70 lb nitrogen per acre. Clover flower heads per square foot, clover seed and ryegrass seed yields were greatest under continuous grazing, although in some years comparable results were obtained from the mechanical defoliation treatments. There were substantial differences between potential and harvested clover seed yields, the latter ranging from 20% to 75% of the potential yield. The weight of ryegrass seed harvested was highest under continuous grazing and least under the cutting treatments. The nitrogenous fertilizer increased the production of herbage dry matter and of ryegrass seed, but greatly reduced clover seed yields. The results are discussed in relation to the influence of weather on the incidence of flowering and the influence of methods of defoliation on flower-bud emergence. It is concluded that mechanical methods of defoliation can produce yields similar to those obtained under continuous grazing, provided that cutting is carried out at the correct stage of growth.     

大豆孢囊线虫病鉴定病土毒性稳定性研究

通过对大豆孢囊线虫病4号生理小种病土进行换土、施药、冷冻、研磨、加热等处理，研究影响大豆孢囊线虫病发生的的因素。经方差分析换土与其它处理有显著差异，施药、对照、冷冻、研磨处理间没有显著差异，但它们与加热处理有显著差异。所以我们认为鉴定用病土最好用刚开始稳定发病的病圃病土，而且使用次数不宜过多，如果是旧病圃，最好采取换土的方法提高孢囊侵染量。     

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.     

THE EFFECT OF WHITE CLOVER ON THE PRODUCTION OF YOUNG AND OLDER GRASSLAND COMPARED TO THAT OF NITROGEN FERTILIZER

The result of a study over many years on the effect of white clover (Trifolium repens L.) and nitrogen fertilizer on the production of young and old grassland are discussed. In young and old grassland, clover and N fertilizer increased production and N content. The effect of clover on production was somewhat greater in young grassland than in old. This difference was associated with a difference in the clover percentage in the sward. Statistical treatment of the results of similar studies by other workers showed that, given equal percentages, the clover in an older sward clearly had a greater effect than the clover in the first few years after sowing. Variation in the production of both young and somewhat older grass/clover swards are mainly due to differences in the clover percentage.