An investigation of problems of sward improvement on deep peat with special reference to potassium responses and interactions with lime and phosphorus

In experiments to determine the minimum fertilizer requirements for improved pasture on deep peat, yields were initially low and declined rapidly. Within 2 years persistence of sown species was poor when only 2·5 t lime ha^-1 was applied. Analytical data suggested that K deficiency and low soil pH were contributory factors. When K was omitted from a composite nutrient solution, clover yield was reduced by 50% when 2·5 t lime ha^-1 was applied but was not significantly reduced with 5·0 t lime. Clover alone produced little response to either P or K separately, but highly significant positive interactions were recorded. Clover, but not ryegrass, responded to K topdressing in field cut-herbage experiments. There was a 3-fold increase in ryegrass yield with combined P and K topdressing under grazing; 10 times more N and K were recycled in urine on this treatment than on the control.
It was concluded that at least 5·0 t lime, 60 kg P and 80 kg K ha^-1 are required for pasture establishment and that soil pH should be maintained above 5·0 to minimize K requirements. The significance of nutrient cycling and of lime × K and P × K interactions is discussed in relation to the persistence of sown species and the maintenance of improved swards on deep peat.     

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.     

Organic and inorganic fertilization compared in a natural Mediterranean grassland

The effect of goat slurry on species composition and herbage production as compared to inorganic fertilizer was studied in a natural grassland dominated by warm and cool season perennial grasses in Macedonia, Greece. Goat slurry was applied in early spring every 1 or 2 years at a rate of 40 t ha^-1 being equivalent to about 160 kg N ha^-1 and 100 kg, P₂O₅ ha^-1. Inorganic fertilizer was also broadcast in early spring at a rate of 80 kg N ha^-1 and 100 kg P₂O₅ ha^-1 every 2 years. Measurements of the basal cover of the dominant species or groups of species and herbage yields were taken for 6 years at the end of the growing period in June, while in the seventh year the experiment was grazed with goats. It was found that goat slurry improved species composition more than the inorganic fertilizer by depressing the less palatable warm season grasses and favouring the subdominant cool season grasses and legumes. Goat slurry significantly increased herbage yields in most of the years. It is suggested that the optimum rate of goat slurry is 40 t ha^-1 every 2 years as this encourages plants most preferred by goats.     

Effect of regrowth interval on the productivity of swards defoliated by cutting and grazing

Over three grazing seasons (1984-1986) a sward of perennial ryegrass, cv. Talbot, which received a total of 336 kg N ha^-1 each season, was cut or grazed with ewes at 3- or 4-week intervals on a rotational basis.
Sward productivity was higher under cutting than under grazing irrespective of the interval between defoliations. Under cutting, mean herbage organic matter (OM) yields over both intervals were 8·66, 9·62 and 8·17 t ha-¹ in 1984, 1985 and 1986 respectively while under grazing the corresponding yields were 7·65, 8·63 and 7·50 t ha^-1. The mean annual yield of herbage defoliated at 3-week intervals was 7·50, 8·64 and 7 ·20 t OM ha^-1 compared with 8·80, 9·60 and 8·46 t OM ha^-1 for swards defoliated at 4-week intervals in the three years respectively.
The nitrogen (N) content of both the available and the residual herbage was consistently higher under grazing than under cutting. Available herbage contained 31·3 and 27·7 g N kg OM^-1 and residual herbage 26·1 and 22·7 g N kg OM^-1 under grazing and cutting respectively.
The mean yield of N under cutting was 284 kg ha^-1 compared with 304 kg ha^-1 under grazing. Defoliation interval had no effect on N yield, the overall mean yield being 294 kg ha^-1 under both 3- and 4-week defoliation intervals. The effect of the treatments on tiller population was slight and inconclusive.
The process of grazing reduced yield probably as a result of damage to the sward through trampling; the positive effect of excretal N on yield was minimal on account of the short grazing periods.     

The influence of surface and sub-surface application methods for pig slurry on herbage yields and nitrogen recovery

Experiments were conducted on a grassland site at Wrest Park, Silsoe, Bedfordshire between 1987 and 1989, to compare herbage yields from slurry applied by deep and shallow injection, low trajectory and conventional vacuum tanker methods. Slurry application rates for all spreaders were calibrated at 86 ± 5 t ha^-1, an equivalent of c. 200 kg NH₄⁺-N ha^-1 applied in autumn or in spring.
As expected, herbage yields following spring applications were higher than from autumn applications, with average mineral fertilizer equivalents of 122 and 89 kg N ha^-1 respectively. Yields from the conventional and low trajectory spreaders showed no consistent differences. However, in both years, first cut yields from plots were significantly lower ( P < 0·05) where slurry had been injected than where surface applications had been used by an average of 0·7 t DM ha^-1. Subsequent cuts in 1988 demonstrated higher residual effects from injection so that annual total yields were similar from all slurry applications irrespective of spreader type.
Analysis of N content revealed high N levels in herbage from deep injection plots. Mean concentrations of N in the herbage, expressed as a percentage of the dry matter, were 1·43 for surface treatments and 1·79 for deep injection in 1988, and 1·84 for surface treatments, 2·13 for shallow injection and 2·68 for deep injection in 1989.     

Further experiences of beef production on permanent pasture in 1976–78

Between 1976 and 1978 a further 154 beef animals were grazed in separate groups on Alberts and Far field at Begbroke Hill, the former being a paddock system and the latter being set-stocked. Each year part of Alberts received complete fertilizer (147–180 kg ha^-1 N) and part did not. All of Far field received complete fertilizer (140–190 kg ha^-1 N). Drought caused a reduction in output in 1976, but in 1977 and 1978 total production of live weight was 9·07 and 8·74 t respectively from 11·65 ha grassland. Calculations of corrected outputs show that maxima of 829 kg ha^-1 in Alberts and 908 kg ha^-1 in Far field were achieved from fertilized grass. The highest output in Alberts represented 929 livestock unit grazing days per ha or 87·9 GJ ha^-1 in 1978.     

Effect of plant density and removal of ears on the quality and quantity of forage maize in a temperate climate

The present study was aimed at testing the hypothesis that a dense maize stand (320–720·20³ plants ha^-1) will produce more dry matter of acceptable quality than a stand sown at the density generally advocated (10⁵ plants ha^-1). It was also aimed at proving that grain is not essential in order to obtain a high yield of good-quality forage maize.
It was found that dry matter yield increased with density, especially at the early stages of growth. When ear-formation was depressed by increasing plant density, the resulting reduction of ear yield and its quality due to the absence of ear was partly compensated for by the increased yield and quality of the stem.     

Cattle slurry as a source of nutrients for red clover: herbage production and clover contribution

An established sward of red clover cv. Hungaropoly sown pure received approx. 30 kg P ha^-1 and 200 kg K ha^-1 each year for 3 successive years. The P and K were applied either as cattle slurry, inorganic fertilizer or combinations of these. Treatments were applied either in spring or after the first harvest. There were a total of six treatments and these were harvested three times each year. The average yields of total herbage DM over all the treatments in the first, second and third years were 15·2, 14·2 and 14·2 t ha^-1 respectively and the various treatments had no significant effect on the overall yields.
Treatments had a significnt effect on red clover DM yields and percentage red clover in one harvest in each of the first 2 years and all three in the third year. Yields of red clover were lower and grass higher in treatments receiving cattle slurry only. On this treatment there was a total yield of 23·2 t ha^-1 red clover DM in the 3 years compared with 30·2 t ha^-1 on the inorganic fertilizer treatments. However, by applying P and K fertilizer in the spring, followed by cattle slurry after the first harvest, it was possible to maintain a high proportion of red clover in the sward and to produce yields of red clover DM similar to those on the inorganic fertilizer treatments.     

Regulating the content of white clover in mixed swards using grass-suppressing herbicides

A preliminary investigation evaluated six grass-suppressing herbicides applied on two occasions in late winter to a predominantly ryegrass ley containing only 15% ground cover of white clover. Substantial increases in clover growth, estimated visually, and flower head numbers per unit area were recorded in the first summer after treatment with 2·8 kg ha^-1 carbetamide, 0·8 kg ha^-1 propyzamide and 0·6 kg ha^-1 paraquat. To achieve these increases, visual estimates suggested that spring growth of grass was reduced by 40–80%. However, grass growth recovered fully by mid-summer on the majority of the treatments.
The following year five of the herbicides were compared in a field experiment. Dry matter (DM) and nitrogen (N) assessments of the grass and legume components were made at three harvests in the first growing season and a single harvest in the second year. Carbetamide, paraquat and, especially, propyzamide increased the proportion of clover in the DM (to 89% in the case of 1·2 kg ha^-1 propyzamide); in general, using herbicides to raise clover contents above 20% lead to reductions in spring grass growth of about 70%. However, such reduction was offset by subsequent increased growth so that total annual yields were largely unaffected. The increased legume content resulted in an increased N concentration in both grass and legume components, measured in the second summer. At this time, the greatest increase in total N yield (up to 35%) was recorded from 0·6 kg ha^-1 propyzamide. Potential uses to achieve legume dominance by grass-suppression are suggested and the needs for further research are outlined.     

Grass production studies in the uplands of north-east Scotland 1. The effects of soil parent material, altitude and soil major group

Sites were established on good quality grass swards in areas representative of three of the most extensive soil parent materials in north-east Scotland and covering an altitudinal range of 260–460 m. Overall yields of herbage dry matter in 1975 were high, ranging from 6280 kg ha^-1 with no fertilizer to 9190 kg ha^-1 with an application of 100, 26 and 50 kg ha^-1 N, P and K respectively. Differences in production between parent material and altitude groupings were found to be associated with differences in major soils group and past land use, with long-enclosed brown earths outyielding podzols recently reclaimed from heather moorland by about 30% overall. Increasing inputs of fertilizer appeared to reduce the effects of soil and climatic conditions. Brown earths showed higher apparent recoveries of N fertilizer than did podzols.     

Assessment of contrasting perennial ryegrasses, with and without white clover, under continuous sheep stocking in the uplands. 5. Herbage production, quality and intake in years 4–6

Herbage characteristics were studied over years 4–6 (1988–90) in three perennial ryegrass ( Lolium perenne L.) varieties as grass-only (200 kg N ha^-1) and grass/clover ( Trifolium repens L.) swards which received 75kg N ha^-1 in 1988 and 0kg N ha^-1 in 1989 and 1990 when continuously stocked with sheep. Mean total annual herbage production of Aurora, a very early flowering variety, was 11% more than that of late-flowering Aberystwyth S23 due to 21% higher growth as grass/clover pasture. The grass/clover sward of Meltra, a tetraploid late-flowering variety, out-yielded S23/clover by 17%. Herbage production of grass/clover was 86% of that of grass only in 1988 but only 54% of the grass-only swards averaged for 1989 and 1990.
In vitro organic matter digestibility (OMD) of Meltra was 38g kg^-1 OM and 27g kg^-1 OM higher than that of S23 and Aurora respectively. OMD of grass/clover was 15g kg^-1 OM higher than that of grass only during the post-weaning period. Herbage intake was positively correlated with OMD of herbage.
The herbage attributes were related to lamb performance reported previously. Lamb output was positively correlated with intake of digestible organic matter.
Differences between the three varieties in herbage characteristics were greater as grass/clover than as grass-only swards, reflecting their compatibility with white clover. In this respect Meltra was the best and S23 the poorest variety.     

Lime and major nutrient fertilizers required to establish a perennial ryegrass/white clover pasture on a non-calcareous gley in the Scottish uplands

A field experiment with mixed swards of perennial ryegrass and while clover carded out in 1982–83 using small cut plots is described. With perennial ryegrass, lime slightly decreased annual dry matter (DM) production in 1982 (the sowing year) but increased it in 1983 (the first harvest year) by about 1 t ha^-1. Applications of N and P produced small increases in DM in 1982 and greater increases in 1983. In the latter season annual DM production varied from an average of 3·5 to about 10 t ha^-1 with 0 or 480 kg N ha^-1 applied in three equal-sized dressings throughout the growing season. Application of 40 kg P ha^-1 in 1982 increased DM production by about 2·5 t ha^-1 in 1983 but higher rates had little effect. Fifteen mg extractable P kg^-1 soil seemed sufficient to support levels of production normally expected from ryegrass pastures in upland Scotland, Applications of K did not affect DM production. N increased tiller weight and sward height of ryegrass; lime and P tended to increase tiller weight but this effect was not statistically significant. Leaf appearance and tiller number were not affected by treatments.
The white clover content of the pasture was decreased 10-fold by application of N and increased by lime and P (1·45 and 1·46-fold. respectively). The DM response to P was most apparent in limed soil and was also affected by the siting of the plots in the experimental area. Effects of lime and P on growth of white clover were to increase the number of stolon growing points and root nodule numbers per unit area.
The results emphasize the importance of lime and P fertilizer for establishment and growth of pasture in this soil and the differences between white clover and ryegrass in their responses to these.     

Effect of fertilizer nitrogen on six-year-old red clover/perennial grass swards

Three diploid red clover cultivars—Sabtoron, Violetta and Essex—and three tetraploid, Hungaropoly, Teroba and Red Head, were sown separately in pure culture and with each of three companion grasses: timothy (Aberystwyth S48), tall fescue (Aberystwyth S170) and perennial ryegrass (Aberystwyth S24).
The effects of fertilizer N on yield and on clover/grass ratio over a 2-year period (seventh and eighth harvest years) subsequent to 6 harvest years during which no N fertilizer was applied were investigated. The data for productivity and persistence have already been published (McBratney, 1981; 1984).
Application of fertilizer N increased DM yields in the eighth year. In this year, the highest yield, 11·9t ha^-1, averaged over the six clover cultivars, was given in association with tall fescue. Tall fescue contributed 90% of this yield. Clover content continued to decrease in all swards but the decrease was greatest in the swards receiving fertilizer N. The yield of clover DM averaged over the six cultivars under N treatment declined from 5·6t ha^-1 in the seventh year to only 0·4t ha^-1 in the eighth year.
The results from this trial demonstrate the potential of red clover sown either pure or in mixture with a suitable perennial grass, to maintain high output of quality herbage over a 6-year period without the aid of fertilizer N. They further demonstrate that following decline in red clover content, both herbage yield and quality may be restored by the application of N fertilizer, particularly where the clover was seeded with a highly productive companion grass.     

The effect of companion perennial ryegrass cultivars on red clover productivity when timing of the first cut is varied

Replicated plots of Hungaropoly red clover were sown on a sterilized area in May 1975 alone (seed rate 11 kg ha^-1) or with one of six cultivars of perennial ryegrass (seed rate 3·5 kg ha^-1) viz. Cropper and S24 (early heading), Barlenna and Hora (medium heading) and Melle and Perma (late heading). In 1976 and 1977 primary growth was cut at one of four dates ranging from mid-May to mid-June and thereafter plots were harvested twice each year.
Varying the time of first cut did not have a significant effect on total dry matter (DM) yield in either year despite differences in means of cutting treatments on annual red clover yields of the order of 6–9%.
In some companion grass treatments total DM yield in 1976 was increased and total red clover yield and percentage red clover contribution were reduced relative to swards sown only with red clover. In 1977 a similar but non-significant trend was found. Swards containing early ryegrasses had higher total herbage DM yields but lower red clover yields and contents than all other swards at the first harvest in both years.
Delay in date of taking the first harvest in 1976 reduced DM digestibility in the first cut and increased it in the second in both years.
It is suggested that by cutting early and increasing the number of harvests from three to four per year, differences in the content of red clover between the first and second cut might be reduced, and it is concluded that more benefit is derived from red clover when medium or late heading ryegrasses are used as companion grasses.     

The effect of strategic fertilizer nitrogen and date of primary harvest on the productivity of a perennial ryegrass/white clover sward

Four management systems involving different dates for first harvest (simulated grazing, early silage, late silage and hay) and two fertilizer N rates in spring (0 and 80 kg ha^-1) were imposed on a perennial ryegrass cv. Talbot/white clover cv. Blanca sward during 1981-82. In each year, annual total herbage DM was increased by spring application of N but white clover production and content in the total herbage were reduced; however, white clover, which was depressed in the harvests immediately after N application, recovered during the season to amounts and contents in the total herbage similar to those given no spring N.
Annual total herbage DM production increased as the date of primary harvest was delayed (935 to 1197 t ha^-1 over two years) but mean organic matter digestibility values for the same period decreased (0-769 to 0700). First-harvest production made up substantial proportions of the annual production in the conservation systems. White clover, as shown by its production and the amount of stolon present, was tolerant of conservation systems, especially with no applied N.
It is concluded that grass/white clover swards are suitable for management systems which involve cutting for conservation. The use of strategic spring N seems a viable option, but more knowledge of rates would be valuable since this experiment only compared 80 kg ha^-1 with no applied N.     

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.     

Grass production studies in the uplands of north-east Scotland 2. The effects of fertilizer treatment

The effects of fertilizer treatment were studied over two seasons on a 2 × 2 factorial arrangement of altitude and major soil group. The soil groups were brown earths and podzols and the altitudinal zones were 260–320 m and 380–440 m. Major responses were found to N only and these were generally linear in terms of overall dry matter yield up to the highest treatment level of 176 kg ha^-1. Productivity on brown earths was significantly higher than on podzols and differences between soil groups were not removed by increasing fertilizer input. In most instances 88–132 kg ha^-1 N would have to be added to podzols to achieve the same yields as on brown earths with no N input. Apparent fertilizer recoveries and responses per unit of fertilizer input did not, however, differ markedly between soil groups. Overall yields were comparable with those from lowland situations at similar levels of N input, but the growing season was short and 60–80% of production was obtained by early July.     

The effects of temperature and fertilizer nitrogen on the spring growth of tall fescue and cocksfoot

A detailed study of the spring growth curves of two forage grasses, tall fescue and cocksfoot, over three successive years showed a large variability of growth over the vegetative phase. This variability was evident at levels of fertilizer N which were considered to be non-limiting (60 kg N ha^-1 in autumn plus 120 kg N ha^-1 in February).
At this level of N there was a relationship between yield in the vegetative phase and accumulated temperatures from the last cut in the autumn which was described by a regression common to the three years. The slope of this regression represents the potential growth of a variety. At a lower level of N a separate regression was needed in each year to relate growth to accumulated temperature.
Variation in spring growth was not related to accumulated net radiation. Growth in the reproductive phase was related to accumulated temperature and accumulated net radiation from the 10-cm ear stage.     

The sulphur status of intensive grassland sites in southern Scotland

Field trials were carried out at five sites in southern Scotland to examine the sulphur status of intensively grown grass under varying Inputs of atmospheric and rainfall sulphur. Sulphur budgets were prepared by comparing amounts of sulphur removed at harvest with sulphur inputs from rainfall, the atmosphere and fertilizers.
No yield responses to added sulphur were obtained, although soil-derived sulphur was essential for the maintenance of optimal sulphur levels in herbage. Where no fertilizer sulphur was added, mineralization of soil organic sulphur supplied approximately 8 to 18 kg S ha^-1 annually during the growing season. Maintenance requirements of 5 to 10 kg S ha^-1 annually were indicated at the Dumfriesshire and Midlothian sites and 20 kg S ha^-1 annually at the Berwickshire sites to prevent a decline in soil sulphur reserves. Total sulphur concentrations of less than 2 g S kg^-1 dry matter were observed in herbage at some samplings indicating marginal sulphur sufficiency. Sulphate levels in herbage, expressed as a percentage of total sulphur, also indicated that sulphur supplies barely matched crop requirements.     

The development of response to fertilizer nitrogen in the first regrowth of perennial ryegrass

The experiment was undertaken to examine the interactions between yield responses to secondary applications of fertilizer N and length of regrowth interval following three levels of primary N. A sward of S24 perennial ryegrass received all combinations of three fertilizer treatments, nil, 50, and 100 kg ha^-1 N for primary growth harvested on 21 May and four treatments, nil, 33, 66 and 100 kg ha^-1 N for the second growth harvested 2, 3, 4, 5, 6 or 7 weeks later.
Cubic equations of growth were derived from the yields of dry matter and both the direct response to secondary N and the residual responses to primary N increased as regrowths developed. A positive residual effect to increasing primary N was obtained at the three lower levels of secondary N for weeks 4–7 but a negative response was obtained with the highest level of secondary N. The implications are discussed in terms of target responses and yields and the growth interval required to attain these targets.