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.     

The effect of fertilizer nitrogen rate, white clover variety and closeness of cutting on herbage productivity from perennial ryegrass/white clover swards

Four varieties of white clover (small-leaved cv. Aberystwyth S184. medium-leaved cv. Grasslands Huia and large-leaved cvs Linda and Olwen) were sown at 3 kg ha^-1 together with 10 kg ha^-1 perennial ryegrass cv. Talbot. Herbage productivity was measured for three harvest years, 1979-81, over four annual rates of fertilizer N (0,120,240 and 360 kg ha^-1) and two closeness of cutting treatments (80 and 40 mm from ground level). A simulated grazing regime of six cuts per year at 3- to 6-week intervals was used.
Production of total herbage DM was increased by increasing N rate; mean annual DM production ranged from 783 1 ha^-1 with no N to 11701 ha^-1 at 360 kg ha^-1 N. Mean herbage response to N (kg DM per kg N applied) was 73,90 and 108 for the three successive N increments relative to no N. Mean white clover DM production was reduced from 4 14t ha^-1 with no N to 051 t ha^-1 at 360 kg ha^-1 N.
The large-leaved clover varieties were more productive than the small- or medium-leaved varieties at all N rates. Close cutting increased total herbage and white clover by a mean annual 16% and 31%. respectively. White clover varieties did not interact with either N rate or closeness of cutting.
It is concluded that repetitive N application over the growing season is incompatible with white clover persistence and production, even with large-leaved clover varieties or with close cutting, two factors which improved clover performance in the experimental swards.     

THE POTENTIAL OF LOTUS spp. FOR HILL LAND IN WALES

Thirty-four introductions of Lotus corniculatus and L. uliginosus , obtained from Europe, North America and New Zealand, were grown in plots with Aberystwyth S23 ryegrass at three centres in Wales (230–400 m a. s. 1.) to assess their potential as legumes for poor acid hill soils. The control white clover varieties were generally successful in these difficult conditions, whereas all the Lotus introductions were poor in two experiments and in the third experiment gave way to volunteer white clover by the third harvest year. These results indicate that none of the numerous Lotus varieties tested would be a useful addition to pasture seeds mixtures for hill lands in Wales.     

Improving the effectiveness of wood‐ash fertilization in mixed mountain pastures

Mountain pastures can be improved by the application of wood ash, but its effectiveness as a source of N, P and other elements requires improved management practices. Two application rates of wood ash (6 and 12 t ha^?1) were tested in a 4‐year trial on a low‐input fertilized pasture. Ash was complemented with mineral P, and N fixation was encouraged by sowing white clover. Wood‐ash application led to increased pasture yield (by 100%) and to increased proportions of white clover and ryegrass (60%), thus improving pasture feed value. N fixation by white clover, and possibly increased mineralization because of higher pH, may have compensated for lack of N in the wood ash. Addition of mineral fertilizer improved the supply of P, although incorporation of the wood ash into the soil may also have enhanced release of P from non‐extractable components. High amounts of compounds containing Ca and Mg contributed to the long‐term maintenance of soil reserves of these elements. Despite high inputs of K (175–350 mg kg^?1) from wood ash, annual additions of K are required to counteract depletion via plant uptake and leaching. Increased Mn availability after the treatment (up to 400 mg kg^?1) may limit repeated applications of wood ash, at least on poorly aerated soils.     

The response of white clover to different strains of Rhizobium trifolii in hill land reseeding

S184 and Grasslands Huia white clover were surface seeded into native Molinia pasture on a wet stagnogley hill soil containing no indigenous Rhizobium trifolii . Seedlings were 'spray inoculated' after emergence with each of five strains of R. trifolii . The two best rhizobial treatments produced a sevenfold increase in seedling establishment followed by nearly fivefold improvement in dry matter production in the following year. There was a strong interaction between Rhizobium strains and plant varieties. Results re-affirm the potential for improving clover performance through inoculation and also demonstrate the need for a better understanding of the factors leading to establishment of successful plant- Rhizobium associations before predictable performance can be achieved in these harsh hill environments.     

Effects of rates and times of application of starter dressings of nitrogen fertilizer to surface sown perennial ryegrass-white clover on hill peat

The effects on clover and grass growth of five levels of ammonium nitrogen (NH₄-N) applied before sowing, at sowing and after nodule initiation have been investigated. A pot experiment in which S184 white clover was grown in a peat soil showed that NH₄-N up to 688 mg N per pot (approx. equivalent to a field rate of 120 kg ha^-1 N) applied before sowing and at sowing did not affect clover growth. N-fixing activity (C₂H₂-reduction), on the other hand, was reduced progressively up to the highest level (688 mg N per pot). Application after nodule initiation increased growth relative to the zero-N treatment at all levels of application. Maximum growth and N fixation occurred at 516 mg N per pot where the DM yield was 70% higher than in the absence of added N. A field trial in which S184 clover and S24 perennial ryegrass were surface sown on to a peat soil showed an increase in grass and clover growth in the first year in response to 120 kg ha^-1 N applied at sowing. Grass growth alone was increased at 120 kg ha ^-1 N applied 40 d before sowing. Lower rates of application before sowing and at sowing did not affect clover or grass growth. The effect of the delayed application of NH₄-N on legume growth was less marked than that in the pot experiment, 90 kg ha^-1 N stimulating clover growth by 40% in the first year. The effect was however different from that in the pot experiment, in that, whilst 30kg ha^-1 N increased N fixation relative to the zero-N treatment, plants exposed to higher levels showed a depression in N-fixing capacity. N-fixation was correlated with nodule numbers in the delayed NH₄-N application, the closest correlation being with the number of multilobed nodules which was highest at 30 kg ha^-1 N and lowest at 120 kg ha^-1 N. It is suggested that circumstances exist when the use of a relatively low starter N dressing (20–60 kg ha^-1 N) at sowing would not increase clover or grass growth in the early stages of the establishment of a hill reseed. Under such circumstances higher rates of application (100 kg ha ^-1 N), preferably delayed until the seedlings are in a position to take up the nitrogen rapidly, would have the greatest effect.     

Nitrogen fixation by white clover in hill pasture

An experiment is described in which the amount of nitrogen fixed by the white clover component of a surface-sown hill sward was determined using small quantities of ¹⁵N-labelled ammonium sulphate. Between 11 July and 22 August 1974 25 kg ha^?1 N was fixed. No evidence of a transfer of N from clover to the associated perennial ryegrass was detectable over this period although the N content of the grass growing with the clover was higher. The relative advantages of the isotope technique and the acetylene reduction assay are discussed.     

Herbage and nitrogen yields,fixation and transfer by white clover to companion grasses in grazed swards under different rates of nitrogen fertilization

In grass–legume swards, biologically fixed nitrogen (N) from the legume can support the N requirements of the grass, but legume N fixation is suppressed by additional fertilizer N application. This study sought to identify a fertilizer N application rate that maximizes herbage and N yields, N fixation and apparent N transfer from white clover to companion grasses under intensive grazing at a site with high soil‐N status. During a 3‐year period (2011–2013), swards of perennial ryegrass and of perennial ryegrass–white clover, receiving up to 240 kg N ha^?1 year^?1, were compared using isotope dilution and N‐difference methods. The presence of white clover increased herbage and N yields by 12–44% and 26–72%, respectively. Applications of N fertilizer reduced sward white clover content, but the effect was less at below 120 kg N ha^?1. The proportion of N derived from the atmospheric N fixation was 25–70%. Nitrogen fixation ranged from 25 to 142 kg N ha^?1 measured using the isotope dilution method in 2012 and from 52 to 291 kg N ha^?1 using the N‐difference method across all years. Fertilizer N application reduced the percentage and yield of fixed N. Transfer of N from white clover to grass was not confirmed, but there was an increased N content in grass and soil‐N levels. Under intensive grazing, the maximum applied N rate that optimized herbage and N yields with minimal effect on white clover content and fixation rates was 60–120 kg N ha^?1.     

Evaluation of white clover varieties under grazing and their role in farm systems

Four experiments were established in 1981–84 to investigate the effect of defoliation treatments on white clover varieties when grown with S23 perennial ryegrass. Treatments included a cutting only regime, as used in National List trials, and grazing systems simulating as near as possible those used on farms.
Differential effects of cutting and continuous sheep stocking on white clover varieties, together with significant variety × defoliation interactions, illustrated the importance of the grazing animal in the evaluation of white clover. Differential effects of cattle and sheep grazing were also evident. Cattle grazing was less detrimental to white clover than was sheep grazing, i.e. cattle were not selective, and less stolon was removed. In general, with both cattle and sheep grazing the larger the clover leaf size the greater the loss in stolons, which in turn decreased persistency. The results illustrate how alternating cutting, sheep grazing and cattle grazing managements can be used to maintain optimum clover/grass balance.
Successful clover/grass swards depend on the retention of clover, yet avoiding clover dominance. The difference in N transfer between clover varieties, especially those within the same leaf category, and the extra grass produced without fertilizer N, emphasized the importance of varietal choice. Breeding programmes have been concerned with the selection of larger-leaved, long-petioled varieties for growing in competition with grass in the presence of fertilizer N. However, the present results showed that, under continuous sheep stocking, increase in leaf size does not increase clover yield or persistency.
The results presented emphasize the importance of the grazing animal in the evaluation of white clover varieties and indicate that yield of clover dry matter should not be the major criterion for selection of varieties for farm systems.     

Effect of three clover varieties on growth, 15N uptake and fixation by ryegrass/white clover mixtures at three sites in Wales

Grass and clover production and nitrogen cycling were compared in 1983 and 1984 at three sites: an upland peaty gley and upland and lowland brown earths. The clover varieties Olwen and S184 were compared in 1983 and S100 and S184 in 1984. Ammonium and nitrate sources of ¹⁵N were used to measure nitrogen recovery from fertilizer and soil, nitrogen fixation and nitrogen transfer from clover to grass. Acetylene reduction was measured once, in 1983, but isotope dilution was used in both years.
Olwen clover produced more dry matter and took up more ¹⁵N than S184. Olwen fixed more nitrogen than S184 over the whole season, as measured by ¹⁵N isotope dilution. Companion grass took up more soil nitrogen when growing with S184 than with Olwen. The clover variety S100, tested at the lowland site in 1984, caused no significant variations in dry matter accumulation or N fixation.
In the dry 1984 season, grass dry matter accumulation and ¹⁵N uptake were less than in 1983, and plants actually lost total nitrogen from their roots to the soil. Fixation rate varied more in 1984 than in 1983. Nitrogen transfer from clover to grass was detected by isotope ratio differences in 1983, and by total N differences in 1984.
Site differences were dominated by the greater dry matter accumulation of Olwen in the lowland in 1983, but in that year there was also increased dry matter accumulation and increased ¹⁵N fertilizer uptake, but less nitrogen fixed on the mineral upland site than on the peat soil.
Whether ¹⁵N was given as ammonium or nitrate made little difference in these experiments.     

The effects of clover variety, cutting interval and nitrogen application on herbage yields, proportions and heights in perennial ryegrass-white clover swards

Six varieties of white clover, each grown with perennial ryegrass, four intervals between cuts and two levels of applied nitrogen in all combinations, were compared in a field experiment during the first 27 months after sowing.
Increasing the interval between harvests from 3 or 4 to 8–12 weeks increased the yield of white clover and generally did not reduce the proportion of clover in total herbage. Increasing the interval between harvests reduced the number of grass tillers but increased grass yield and the size of grass leaves and increased grass height more than clover height; it also increased the proportion of petiole relative to leaflet in the clover. Differences between varieties in response to interval between harvests were small but supported the view that medium large-leaved varieties can with advantage be defoliated rather less frequently than small-leaved ones. The adverse effect of applied N on clover appeared almost equally great with all four intervals between harvests and further research on this topic is suggested. Applied N increased grass height more than clover height and increased the number of grass tillers, the size of grass leaves and grass yield. The medium large-leaved varieties seemed more tolerant of applied N than the smaller varieties.     

Performance of white clover/perennial ryegrass mixtures under cutting

Clover persistence in mixtures of two varieties of perennial ryegrass (Lolium perenne) with contrasting growth habits and three white clover (Trifolium repens) varieties differing in leaf sizes was evaluated at two cutting frequencies. An experiment was sown in 1991 on a clay soil. The plots received no nitrogen fertilizer. In 1992, 1993 and 1994, mixtures containing the large-leaved clover cv. Alice yielded significantly more herbage dry matter (DM) and had a higher clover content than mixtures containing cvs Gwenda and Retor. Companion grass variety did not consistently affect yield or botanical composition. Cutting at 2 t DM ha^?1 resulted in slightly higher total annual yields than cutting at 1.2 t DM ha^?1, but did not affect clover content. In 1992 the mixtures yielded, depending on cutting frequency and variety, 10·6–14·6 t DM ha^?1 and 446–599 kg ha^?1 N, whereas grass monocultures yielded only 1·2–2·0 t DM ha^?1 and 25–46 kg ha^?1 N. From 1992 to 1994 the annual mean total herbage yield of DM in the mixtures declined from 12·2 to 10·5 to 8·7 t ha^?1, the white clover yield declined from 8·7 to 6·5 to 4·1 t ha^?1 and the average clover content during the growing season declined from 71% to 61% to 46%, whereas the grass yield increased from 3·4 to 4·0 to 4·5 t ha^?1. The N yield decreased from 507 to 406 to 265 kg N ha^?1 and the apparent N fixation from 470 to 380 to 238 kg N ha^?1. Nitrate leaching losses during the winters of 1992–93 and 1994–95 were highest under mixtures with cv. Alice, but did not exceed 10 kg N ha^?1. The in vitro digestible organic matter (IVDOM) was generally higher in clover than in grass, particularly in the summer months. No differences in IVDOM were found among clover or grass varieties. The experiment will be continued to study clover persistence and the mechanisms that affect the grass/clover balance.     

黑龙江省玉米品种状况分析与研发对策

“七五”至“十五”期间黑龙江省共审定推广了181个玉米新品种,其中中熟和中晚熟品种占74.6%;科研院所和大专院校育成的品种占67.4%。民营研究所育成的品种在逐步增加。20年来品种子粒的商品品质有较大改善,但营养品质变化不大。育成品种的数量虽多,但突破性品种较少。根据育种存在的问题,提出了研发对策。     

The effects of variety, cutting interval and nitrogen application on the morphology and development of stolons and leaves of white clover

Six varieties of white clover, each grown with perennial ryegrass, four intervals between cuts and two levels of applied nitrogen in all combinations, were compared in a field experiment during the first 27 months after sowing. Information about yields, crop fractions, heights and ryegrass tillers has been presented in an earlier paper (Wilman and Asiegbu, 1982). The present paper is concerned with the more detailed studies of white clover, which help to explain the yield results and contribute to the understanding of the response of this species to management when grown in competition with grass. Increasing the interval between harvests increased the length of clover stolon per unit area of ground and increased stolon diameter, petiole length, weight per leaf and number of leaves harvested as a proportion of the number present in the sward while only slightly reducing the rate of leaf emergence, helping to explain the positive effect of increasing the interval on clover yield noted in the earlier paper. During regrowth, successive leaves had longer petioles and the length of individual petioles increased beyond the stage at which the leaflets were fully opened. Weight per leaf in clover increased considerably from April to June and declined to below the April value by October. It was shown that weight per leaf can be greatly increased by increasing the interval between harvests without reducing the number of leaves harvested per unit area per year. The stolon length measurements provided some support for the view that medium large-leaved varieties of white clover can with advantage be defoliated rather less frequently than small-leaved varieties. Stolon length was less adversely affected by applied N in the medium large- than in the small-leaved varieties. The small-leaved varieties had thinner stolons than the medium large-leaved varieties but about twice the stolon length when no N was applied, and a relatively high proportion of leaves which escaped defoliation. The application of N reduced stolon diameter, increased petiole length and had little or no effect on weight per clover leaf.     

White clover contribution to continuously stocked sheep pastures in association with contrasting perennial ryegrasses

White clover content and herbage production in grass/clover swards were studied at contrasting altitudes in Wales. The lowland experiment (1) compared the performance of three clover varieties grown with four diploid perennial ryegrass ( Lolium perenne ) varieties with a range of heading dates. In the upland experiment (2) the productivity and persistence of Aberystwyth S184 (small-leaved) clover was studied in association with three perennial ryegrasses.
In experiment I. clover content and dry matter production with Aurora (very early) ryegrass was superior to that with Frances (early), Talbot (intermediate) and Melle (late). Furthermore, the performance of Kent wild white clover (small-leaved) was better than that of medium-leaved Menna and Grasslands Huia. Averaged over two years (1985 and 1986) mean clover content of Kent was 22% compared with 9% and 10% of Menna and Huia.
Performance of S184 clover during the five years (1986–90) of experiment 2 was better with Meltra (late tetraploid) than with Aberystwyth S23 (late diploid) and intermediate with Aurora. Clover stolon length and growing point number declined to a low level in 1988 but increased dramatically in 1989 and 1990 after cessation of applying fertilizer N.
Results from both sites were related to animal performance data previously published. It is concluded that small-leaved clover varieties are needed to ensure a high proportion of clover in sheep pastures and also that choice of companion ryegrass can have a significant effect on the performance of the legume component.     

The relationships between stolon characteristics, winter survival and annual yields in white clover (Trifolium repens L.)

Five white clover populations of Swiss origin and three bred varieties were grown in binary mixtures with two perennial ryegrass varieties, Aurora and S23. The seasonal yields of clover and grass plus clover were measured under a cutting regime during the second and third years after establishment. A series of destructive detailed sward measurements was made during the late autumn to spring period preceding each harvest year. In this way changes in the amounts of stolon, leaf plus petiole and numbers of growing points were monitored during the winter.
There were large differences in clover yield between populations in both years. These were evident from the first (spring) harvest in each year. Higher-yielding clovers in spring tended to produce higher annual clover yields. No grass × clover interaction was evident at any harvest. Large differences between clovers were also apparent in the morphological characteristics measured, with the Swiss material generally having greater amounts of stolon, leaf plus petiole and numbers of growing points present in early spring. It is proposed that these factors contribute to the high spring yield in the Swiss populations. Loss of stolon length over each winter was less in the Swiss material, indicating that its good spring growth was not obtained at the expense of winter hardiness. Annual clover yield was found to be significantly positively correlated with the amount of stolon present in spring, exemplifying the importance of stolon survival over the winter.     

The effect of variety and fertilizer nitrogen level on red clover production

Established swards of two diploid and two tetraploid red clover varieties sown pure received 0, 75, 150, 225 or 300 kg ha^?1 N fertilizer and were cut three times in June, August and October 1971. The total yields of herbage DM for red clover varieties ranged from 8.01 to 11.32 t ha^?1; swards sown with tetraploids Hungaropoly and Hera Pajbjerg were superior by 25% in DM yield and 23% in CP yield. The red clover contribution to these total yields of DM ranged from 6.05 to 10.69 t ha^?1; tetraploid clovers outyielded diploids by 42% in DM yield and 39% in CP yield. The mean effect of N level on yield and on compositional attributes was slight. Total yields of herbage DM, averaged over all varieties, ranged from 9.50 to 10.22 t ha^?1 and of total herbage CP from 1.76 to 1.91 t ha^?1. The influence of N level on the red clover contribution was negligible. DM yields ranged from 8.54 to 8.72 t ha^?1 and CP yields from 1.60 to 1.64 t ha^?1. Superiority of tetraploid clovers over diploids was again confirmed. Red clover swards sown pure can give high yields without the application of fertilizer N.     

Growth responses to lime and fertilizers and critical concentrations in herbage of white clover in Scottish hill soils

The responses in dry matter (DM) production and changes in nutrient concentration in the shoots of white clover (cv. New Zealand Grasslands Huia) to additions of lime, N, P, K and Mg were investigated in pot and field experiments in a deep peat soil and to additions of N, P, K in two other hill soils in pot experiments. DM production and nutrient concentrations were assessed also for perennial ryegrass in the field experiment. There was no response by white clover to N, but in all soils, and in particular a deep peat, production of shoot DM was increased greatly by lime, P and K, and slightly by Mg. Interactions between lime and P and between P and K were observed. Critical concentrations of nutrients (g kg⁻¹) for white clover appeared to be about 2.0 for P, 10·15 for K and 20 for Ca. Herbage production and nutrient contents of ryegrass and white clover grown on a deep peat in the field suggests that critical concentrations may possibly help to diagnose the need fur maintenance fertilizer dressings.     

Establishment, persistence and nitrogen fixation of white clover and marsh trefoil on blanket peat

White clover (cv. S184 or Blanca) or marsh trefoil (cv. Grasslands 4703 or Grasslands Maku) were sown alone and in combination with a companion grass (tall fescue, red fescue, perennial ryegrass or ryegrass cleanings) on a peat area of hill land originally dominated by Juncus articulatus and Molinia caerulea.
Lime and ground rock phosphate were applied in 1973, the area rotavated to a shallow depth and seeds sown in May 1974. No fertilizers were applied except at sowing time and two harvests were taken per annum for 4 years.
Differences in yield and legume content between companion grass treatments were small. After the first full harvest year Blanca swards usually had the lowest DM yields and those containing Maku the highest. The contribution of marsh trefoil to total herbage yield increased from 4·2% in 1975 to 22% in 1978, whereas white clover decreased from 4·2 to 1·2%. Legume yields in 1978 were less than half those in 1977. Overall, N yields were low, Maku swards fixing most N estimated to be highest in 1977 at 35 kg ha^-1.
It is concluded that marsh trefoil grows well on upland peat but more information on its response to grazing is necessary before conclusions can be drawn about its value in hill land improvement.     

Fertilizer requirements for maintenance of a perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) pasture growing on a humus iron podzol in N.E. Scotland

Ryegrass/white clover pastures were reseeded on heather moor in north-cast Scotland in 1978/79. By 1981, despite moderate fertilizer applications, the pastures had deteriorated and dry matter (DM) production was low. After preliminary soil and herbage analysis an omission trial was carried out in 1982/83 at two sites (A and B) to identify the factors which limited production.
At site A depressions in growth occurred in the absence of N, P and K. Perennial ryegrass was severely N deficient with concentrations in leaves of less than 22 g N kg⁻¹ in spring and summer even after application of 120 kg N ha⁻¹ annually. Rates of nitrogen fixation were high in spring but rapidly declined in June and July as the soil moisture tension increased. Application of N fertilizer also reduced the N₂ fixation rate. Deficiencies of F and K occurred despite apparently high levels of extractable F in the soil. Uptake of these nutrients was inhibited in the dry soil during the summer. White clover was more susceptible to drought than perennial ryegrass, probably because it rooted at a shallower depth.
Growth at site B was limited by acidity and lack of N and K. The soil pH was 4 8 (s.d. = 0middot;75) at 1-5 cm depth. Application of 2 5 t lime ha⁻¹ in spring 1982 had not altered the pH by autumn 1983.
It was concluded that methods of incorporating lime into the soil, together with ways of increasing the rates of N₂ fixation by white clover and transfer to grass, should be investigated further. Regular small applications of N and K may be necessary to sustain DM production at the level required by the farming system.