SOME ASPECTS OF THE NITROGEN: WATER INTERACTION ON GRASS SWARDS

Experiments were conducted on ryegrass swards using different amounts of N fertilizer applied as a single early dressing (S) or in repeated applications during the season (R). Over three years, the yield from R was generally higher, but under dry conditions (using plot covers) S gave the greater yield. The latter result is ascribed to the bigb yield obtained from S at the first cut, at which time N uptake was not limited by a lack of soil water. Irrigation at less than the full requirement resulted in lower total yields but it increased water-use efficiency by up to 70% (R) and 94% (S).     

A MATHEMATICAL RELATIONSHIP BETWEEN NITROGEN INPUT AND OUTPUT IN CUT GRASS SWARDS

The importance of predicting grass N yield lies in its controlling influence on grass DM output and thus on animal production. Results from 88 experiments studying the use of fertilizer N on cut grass swards show that the major part (97%) of the variation in grass N yield could be explained in terms of fertilizer N rate, an estimate of soil N and an interaction between the two. From this, it appears that high fertilizer N recovery is associated with a high uptake of soil N and vice versa.     

THE PLANT COMPONENT AS A FACTOR IN AMMONIA VOLATILIZATION FROM PASTURE SWARDS

The volatilization of ammonia which followed the application of urea to a pasture sod was determined over a period of 14 days. Significant ammonia losses were measured after foliar application of urea to sods in which the soil component had been previously isolated from the plant components by sealing the sods with an impermeable membrane. Losses of ammonia by volatilization over the experimental period were less from plant surfaces than from unsealed sods in which the soil contributed to losses. It is concluded that in addition to soil ureolytic activity, the plant and litter components of pastures may provide major pathways of loss in the N economy of grasslands.     

THE DELAYED APPLICATION OF NITROGEN FOR THE ESTABLISHMENT OF SURFACE-SEEDED SWARDS

It has been observed that, where surface seeding has been attempted, disappointing results occur on some sites due to delays in sowing the seeds mixture after lime and fertilizer applications have been made.
An experiment is described in which the time of application of nitrogen, in relation to the establishment and development of S24 and S23 perennial ryegrass seedlings in pots, was varied. The results of trials on this aspect of surface seeding, under conditions experienced in the north of Scotland, are also given.
More efficient utilization of nitrogen was obtained when applications were delayed until the seedlings had developed sufficiently to utilize the applied nitrogen. This delay enhanced the establishment of sown grasses under conditions where natural species, capable of responding to applied nitrogen, were present.
Where surface seeding is undertaken, consideration should be given to delaying the application of nitrogen until the sown seeds have brairded.     

THE USE OF CATTLE AND SHEEP FOR EVALUATING GRASS AND LEGUME SWARDS, A COMPARISON OF METHODS

A comparison was made of the effects of grazing with cattie and sheep separateiy hy two methods, continuous and rotationai on two forage mixtures. The two mixtures were timothy (Phleum pratense L.) with iadino white ciover (Trifolium repens L.); and brome grass (Bromus inermis Leyss) witii aifalfa (Medicago sativa L.). The rotationai system of grazing created different effects on sward composition from those caused hy the continuous grazing system. The legumes survived hetter under rotational than continuous grazing. Sheep, under both grazing systems, grazed more severeiy than cattie; they defoliated the ieaf portion of the plants and ieft more stem standing than did the cattle. Protein of the sward increased with the leaf portion, but in vitro digestibility was not altered as leaf to stem ratios changed. Although the gross effects of sheep and cattle were similar, there were differences in detail in the effect on these swards.     

PATTERNS OF SPRING GROWTH IN SWARDS OF DIFFERENT GRASS VARIETIES

Production of dry matter by swards of ryegrass and cocksfoot varieties in winter and spring is dependent on a number of growth processes, each with different environmental requirements. Growth in the strict sense with the production of new leaves has been found to continue throughout the winter in Aberystwyth, although the rate of production fell very low during periods when the mean air temperature approached freezing, especially in cocksfoot varieties.
Because of the ceiling set by the natural balance between leaf death and leaf formation, net increases in weight of above–ground parts in undefoliated plants may not occur for extended periods during winter. When, however, tiller numbers start to increase, or the ceiling is raised by an increase in size of tillers, dry–weight increases can come about. The extension of leaves and intern odes in spring, measured in terms of sward height, seems to be largely governed by flower initiation. A certain degree of extension was found to be present before this in an Algerian type.
Practical distinctions between early and late types, which are based on flowering dates or sward height, or on parameters influenced by these characters, are not associated with similar differences in production of above–ground parts. These distinctions do not, therefore, permit a completely full and accurate picture to be obtained of winter– and spring–growth potentials in different varieties.     

SOME COMPARISONS OF INCLINED POINT QUADRAT AND AIRFLOW PLANIMETER METHODS FOR MEASURING LEAF-AREA INDEX OF GRASS SWARDS

The leaf-area indices (LAI) of simulated swards of three populations of Festuca arundinacea Schreb. were estimated by use of an inclined point quadrat and an air-flow planimeter.
Both for comparisons of leaf areas before defoliation, and for comparisons of leaf areas removed by defoliation, very highly significant relationships were found between estimates by the two methods. In five out of six cases the airflow-planimeter estimates of leaf area became greater than those from the inclined point quadrat as sward leaf area increased.
It is suggested that the major factor responsible for departure from complete agreement between the methods is a difference in leaf areas actually measured by the two methods; in addition, there was some indication of operator error with the inclined point quadrat. The results indicated that these factors were not greatly influenced by leaf canopy arrangement.     

SEASONAL TILLER POPULATIONS OF GRASS AND GRASSJCLOVER SWARDS WITH AND WITHOUT IRRIGATION

The number of tillers per unit area of pure swards of S23 and S24 perennial ryegrass, S37 cocksfoot, S48 timothy and of a S23 perennial ryegrass/white clover sward, were examined at intervals of 4 weeks during a period of two years. The monthly appearance of new tillers and the death of tillers of S23 and S24 ryegrass and S48 timothy were followed for 15 months. The studies were made with and without irrigation.
The number of tillers varied with season through the year. Tiller numbers increased rapidly in late winter or early spring, and then declined until midsummer. Numbers rose again between June and August. This seasonal pattern of tiller numbers was most marked in ryegrass and timothy and least in cocksfoot. The effect of irrigation on tiller numbers was variable, and usually small in relation to the overall seasonal fluctuations in tiller numbers, but dry soil conditions could delay an increase in tiller numbers between June and August. The relationship between seasonal fluctuations in tiller number and root growth of swards is discussed.     

THE RECOVERY OF FERTILIZER NITROGEN FROM VARIOUS DEPTHS BELOW SWARDS

A microplot technique for the placement of nitrogen at depth under an established grass sward is described. The effect of nitrogen placement at various depths on the dry matter yields, root yields and nitrogen uptake of two grass species is recorded. The results for cocksfoot and red fescue indicate that there is little fall-off in uptake of nitrogen from placement at depths down to 12 inches, and that cocksfoot also recovers substantial amounts of nitrogen from 18 inches and 2 feet. Recovery by red fescue at these depths was not investigated.
Althotigh there is little difference between the two grasses in their relative ability to absorb nitrogen at the various depths, there is an indication that, weight for weight, cocksfoot roots are probably more efficient absorbers of nitrogen than those of red fescue.
The significance of the findings is discussed in the light of present-day methods of fertilizer application.     

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.     

FERTILIZER N AND THE YIELD OF CUT GRASS SWARDS IN EASTERN ENGLAND

Single spring dressings of N were compared with split applications over the first two growth periods of the year at ten sites in eastern England in the period 1964–67. None of the four spring periods was unusually dry and the single application of N in spring did not outyield a similar total N rate applied some before and some after the first cut. At nine out of ten sites split applications of N yielded considerably more in the second growth period than the single spring dressing. It is concluded that the split applications of N in the spring, already shown superior to single dressings under moist west country conditions, are correct for many seasons in the drier east of England.     

THE EFFECT OF THE GRAZING ANIMAL ON THE N STATUS OF GRASS SWARDS

Thirty-one sets of N yield data were considered, taken from seven experiments grazed by sheep. N yield could be explained in terms of fertilizer N rate, an estimate of soil N and an interaction between the two. Fertilizer N increased grass N yield more on grazed swards than on cut swards, and this effect was greatest on soils with high available soil-N. It is concluded that N recircula-tion can be substantial on heavily-stocked swards receiving high rates of fertilizer N, so increasing the efficiency of fertilizer as a source of N in these conditions.     

THE EFFECTS OF DEFOLIATION ON EMERGENT ANNUAL GRASS SWARDS UNDER SIMULATED GRAZING

For three weeks after emergence, micro-swards of Lolium rigidum were defoliated to a height and at a frequency which represented a range of set stocking rates of less than, similar to, and more than 7–8 sheep/ha as based on the results of Greenwood and Arnold (6) and referred to as D₁, D₂ and D₃ respectively. The effects of these defoliation regimes on the growth and development of emergent swards were evaluated according to their effect on increments of DM from plant parts, rate of appearance of leaves and tillers, concentration of soluble carbohydrates, and on the uptake and concentration of inorganic nutrients. Defoliation began five days after emergence, when the dry weight of the shoot was 3g/m². After 20 days of treatment, 6±7 g/m² of DM had been removed from D₁, 5±5 g/m² from D₂ and 51 g/m² from D₃; and the dry weight of shoot remaining was 13, 7 and 4±5 g/m² on D₁, D₂ and D₃ respectively. The effect of defoliation on dry weight of plant parts increased in severity in the order leaf 1, stem+sheaths, leaf 2, roots, leaf 3, tiller 1, tiller 2, leaf 4. Average relative growth rate of the sward was reduced from 17% per day on D₁ to 13% per day on D₃. There was no necrosis of root tissue. Emergence of the later leaves and of the tillers was retarded by up to three days by more frequent defoliation. Alcohol-soluble carbohydrates in the root fell from over 6% to about 1±5% on all treatments. Uptake of N. P and K was limited by increasing intensity of defoliation and because concentrations of those elements were not greatly affected, the limitation could be ascribed mainly to the effects of defoliation on plant size. The plausibility of the technique for the experimental simulation of grazing of emergent annual grass swards in Western Australia is discussed. It is concluded that for set-stocking rates of less than about 12 sheep/ha, grazing, while reducing DM production just after emergence, is unlikely to produce severe physiological stresses in the sward.     

THE RELATIONSHIP BETWEEN TOTAL N INPUT AND YIELD OF CUT GRASS SWARDS

The response of clover-free grass swards to fertilizer N when cut repeatedly at grazing and silage stages of growth was measured in four experiments at North Wyke. There was variation between years in the yield obtained at a given fertilizer N rate (Fn) and this was attributable to differences in soil-N supply. By estimating soil-N supply from the N-yield of the non-fertilized plots (Zn), total N inputs (Tn) were assessed. Over a number of reported experiments it was found that grass-N yield (Gn) was related to Tn by the equation Gn=0.57 Tn, where Tn=Fn+l.7 Zn. The level of grass-DM yield depended on stage of growth at cutting, as well as on total N supply. These results, and others examined from the literature, suggest that while total N input is the main determinant of grass-DM yield, account must be taken of the time available, before defoliation, for the N taken up to be utilized in DM production. The use of Tn values has allowed the collating of N responses obtained over a range of sites, seasons and workers.     

THE EFFECT OF A RYEGRASS COMPANION GRASS AND THE VARIETY OF RED CLOVER ON THE PRODUCTIVITY OF RED-CLOVER SWARDS

An experiment was conducted to measure the effects of differrat ryegrass companion grasses and red-clover varieties on the productivity of red-clover swards. Three silage harvests per year were taken over a 2-year period. The addition of a companion grass increased total herbage yields; S24 perennial ryegrass gave the highest herbage yield over the two years, followed by Reveille perennial ryegrass. Because of lack of persistence, Tetila Italian ryegrass yielded poorly the second year. A companion grass had little effect on red-clover yields in the mixed swards but improved percentage digestibility of the OM of the total herbage and lowered the CP percentage. Its presence also reduced the ingress of unsown species. The variety of red clover used had little effect on total herbage yields or red-clover yields in the first harvest year. In the second year, Hungaropoly and Tilo persisted better and so gave higher total herbage yields and red-clover yields than Dorset Marl or Essex. The fall in total herbage yields from the first to the second year was entirely due to a fall in red-clover yield since yields of the ‘non-red clover’ fraction of the total herbage increased. A red-clover/grass sward may have advantages over a pure red-clover sward nutritionally, for silage-making and for its effect in diluting the oestrogenic activity of a pure clover sward. A major reappraisal of the role and potential of red-clover swards in the UK is warranted because of their many valuable attributes, particularly their ability to give high herbage yields of high nutritive value without the addition of fertilizer N. The improved persistency of some of the tetraploid varieties of red clover enhances the value of the plant.     

THE EFFECTS OF CUTTING AND GRAZING SYSTEMS ON HERBAGE PRODUCTION FROM GRASS SWARDS

Studies were made on two perennial ryegrass–dominant swards of the effects of cutting and grazing systems of herbage production. A motor scythe was used for cutting and sheep in small enclosures for grazing. In both systems, herbage production was measured by a ground-level sampling technique, using sheep shears, and the difference between pre-treatment and post-treatment herbage was expressed as ‘utilized yield’. Correction for soil contamination is ensured by quoting all results on an organic-matter basis. Grazing treatments averaged 14–16% more organic matter and 36–45% more crude protein than cutting treatments in both experiments. These differences were ascribed to recycling of N under grazing. Infrequent defoliation gave higher yields than frequent, and severe defoliation higher yields than lenient under both cutting and grazing systems. The trends shown by cutting and grazing intensities are comparable and can be quantified. There is need to examine closely the relationships between the effects of cutting and grazing techniques on herbage production, since such knowledge would allow a more accurate prediction of the relevance to the grazing situation of results obtained under cutting.     

A DISCUSSION ON THE INFLUENCE OF RELATIVE MOISTURE AVAILABILITY ON THE SWARDS RESULTING FROM STANDARD GRASS SEEDS MIXTURES

Results are given of analyses made over a three-year period, 1955–57, on swards produced from a standard seeds mixture sown under a wide range of ecological conditions. The results are related lo available moisture on the different soils in the areas examined.     

A COMPARISON OF COCKSFOOT- AND TALL FESCUE-DOMINANT SWARDS FOR OUT-OF-SEASON PRODUCTION

Swards based on a mixture of SI 70 tall fescue and S215 meadow fescue were very early in spring, gave high yields for conservation in mid-season and, rested from mid-August, gave good grazing in November-December. Under this treatment, the tall fescue assumed dominance, and the swards were persistent and remained productive. The digestibility of the tall fescue swards was always higher than that of swards based on cocksfoot with which they were compared. During spring and autumn the former sward was better grazed by stock, but the position was reversed in mid-summer. Cattle grazing tall-fescue-dominant swards made better liveweight gains than those grazing cocksfoot swards during November-December.     

THE MANAGEMENT OF LONG GRASS AS A BIRD REPELLENT ON AIRFIELDS

Authorities responsible for the safety of aircraft have for a number of years been very concerned with the dangers and the damage caused by aircraft striking birds while in flight, particular since the introduction of the jet engine. Methods of reducing this risk have been sought, which have brought about the method of grass management described in this paper.