Root and shoot competition between established grass species and newly sown seedlings during spring growth

Competition between established Dactylis glomerata or Festuca pratensis / Taraxacum officinale swards and seedlings of Trifolium pratense was studied under field conditions in Norway. Root competition from the Festuca pratensis / Taraxacum officinale sward was significantly greater than that from a Dactylis glomerata sward. The balance in root and shoot competition varied between experimental years because of variation in environmental conditions. In the first experimental year, root competition had a greater effect on seedling dry weight than shoot competition, whereas the opposite was found in the second year. However, both root and shoot competition (full competition) in comparison with no competition gave proportionally the same effects in both years, indicating that an alleviation in root competition will be followed by intensified shoot competition. An increasing effect of shoot competition with time on plant dry weight was found. In a second experiment, seedlings of Lolium perenne and Trifolium pratense produced the highest plant dry weights in competition with an established Phleum pratense sward, followed by seedlings of Poa pratensis , Phleum pratense and Trifolium repens in decreasing order. However, no interactions between seedling species and competition treatments were found, indicating no differences in sensitivity between seedling species to competition from the established grass sward. The results are discussed in the context of renovating grassland by direct drilling.     

THE GROWTH AND DEVELOPMENT OF SOME GRASS SPECIES UNDER COMPETITIVE STRESS

Three experiments were carried out in a semi-controlled glasshouse environment to determine the response of individual plants to competition; (i) between seedlings of different species, (ii) between seedlings derived from seeds of differing sizes within a species, and (iii) between seedlings and established plants.
Differences were detected in seedling competitive ability between species and between plants derived from differing seed sizes. In associations of species of very high and very low competitive ability the differences in competitive ability were accentuated by an increase in plant density.
Established plants of Phalaris coerulescens were less aggressive to seedlings growing in close proximity than were plants of Lolium rigidum and H1 ryegrass. Despite the early death of established swards of L. rigidum , and the consequent removal of competitive stress, there was no rapid increase in the growth and development of seedlings in these swards. Possible mechanisms causing this effect are discussed.
There was evidence of a specific relationship between the species of the established sward and the seedling species, in particular seedlings of HI ryegrass were particularly susceptible to competition from established plants of their own species.
Dry weight per plant, tiller production, rate of leaf appearance and leaf size were ail affected by competition between seedlings; however, tiller production was generally more severely affected than rate of leaf appearance and leaf size.
Dry weight per plant, tiller production, seedling height, number of leaves per tiller and number of seeds per seedling were all affected by competition from established plants.     

The effect of sward height on responses of mini-swards of perennial ryegrass/white clover to slurry application

The influence of sward height at the time of slurry application on sward responses to slurry was investigated using perennial ryegrass ( Lolium perenne )/white clover ( Trifolium repens ) mini-swards under greenhouse conditions. Pig slurry, cattle slurry and a fertilizer control were applied either to: swards cut 1 d before slurry application to heights of 2, 4 or 8 cm (CH2, CH4 or CH8); or to swards cut to 4 cm with regrowth intervals of 1, 4 or 8 d before slurry application (RI1, RI4 and RI8). Scorch, smother and growth of marked clover stolons and grass tillers were monitored after slurry application. Dry-matter yields of both species were recorded over two harvests. Electrolyte leakage from leaves was used to assess leaf damage. Both slurries increased leakage, which was greatest from clover leaves, with biggest increases caused by pig slurry. Yield responses to slurry application varied with plant species and sward height. Reduced grass growth after slurry application to long swards (CH8, RI4, RI8) was probably caused by greater smother. In short swards (CH2), grass leaf growth was not depressed following slurry application but grass yields were reduced. Ammonia volatilization losses may have been greater in both long and short swards, contributing to yield reductions. Yield responses to slurry were greatest in swards cut to 4 cm, 1 d before application.     

Consequences for biodiversity of reducing inputs to upland temperate pastures: effects on beetles (Coleoptera) of cessation of nitrogen fertilizer application and reductions in stocking rates of sheep

Current policies for upland pasture management in the UK encourage the integration of environmental objectives with livestock production through extensification of grazing systems. This study tested the hypothesis that a greater sward height in the summer would increase the diversity and abundance of grassland beetles (Coleoptera) as has been demonstrated for insects of indigenous grasslands. The hypothesis was tested with an experiment on an upland sheep pasture in mid‐Wales. Experimental treatments received different nitrogen fertilizer inputs (0 or 50 kg ha^?1), sheep stocking densities (12 or 9 ewes ha^?1) and average sward heights in summer were constrained to 3·5 or 5·5 cm by conserving surplus grass for silage in subplots. Five treatments, replicated in three randomized blocks, combined the two stocking densities and two sward heights without nitrogen fertilizer inputs, with the fifth combining the higher stocking density, shortest sward height and the nitrogen fertilizer input. Beetles were sampled with twelve pitfall traps in each of the fifteen plots from June to September in 1993 and 1995. In years 1 (1993) and 3 (1995) of the experiment, more Coleoptera species occurred in the tall sward (an average of nine species in addition to the forty‐one species present in the sward with the conventional sward height). Continuously grazed as opposed to ensiled subplots supported more beetle species but fewer individuals. Species composition of ground (Carabidae) and rove (Staphylinidae) beetles varied between treatments more than the arithmetic differences in species number. The experimental results supported the hypothesis but the benefits of taller swards to species diversity were small in the sown pastures of the study compared with indigenous upland grasslands (c. 33% fewer species). Inheritance effects of drainage, fertilizer and lime inputs, and the different species and management of cultivated pastures, may constrain the conservation benefits of altered pasture management compared with indigenous grasslands.     

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 5. The effect of stocking rate and reduced levels of nitrogen fertilizer

The implications for UK upland sheep systems of reducing nitrogen fertilizer application to perennial ryegrass/white clover swards were studied over 3 years. Sward height (3·5–5·5 cm) was controlled for ewes with lambs until weaning using surplus pasture areas for silage; thereafter, ewes and weaned lambs were grazed on separate areas, and sward height was controlled by adjusting the size of the areas grazed and using surplus pasture areas for silage if necessary. Combinations from three stocking rates [10, 6 and 4 ewes ha⁻¹ on the total area (grazed and ensiled)] and four nitrogen fertilizer levels (150, 100, 50 and 0 kg ha⁻¹) provided six treatments that were replicated three times. Average white clover content was negatively correlated with level of nitrogen fertilizer. The proportion of white clover in the swards increased over the duration of the experiment. Control of sward height and the contribution from white clover resulted in similar levels of lamb liveweight gain on all treatments. All treatments provided adequate winter fodder as silage. It is concluded that the application of nitrogen fertilizer can be reduced or removed from upland sheep pastures without compromising individual animal performance provided that white clover content and sward height are maintained. Resting pastures from grazing by changing ensiled and grazed areas from year to year sustained white clover content over a 3-year period.     

Animal production evaluation of herbage varieties. 1. Comparison of Aurora with Frances, Talbot and Melle perennial ryegrasses when grown alone and with clover

Comparative herbage characteristics and sheep production (ewes and lambs until weaning and lambs thereafter) from swards of Aurora (very early flowering), Frances (early flowering), Talbot (intermediate flowering) and Melle (late flowering) varieties of perennial ryegrass ( Lolium perenne ) were studied under a continuous variable stocking management based on sward surface height guidelines. The varieties were assessed as grass-only (215 kg N ha⁻¹ fertilizer) and grass/clover (83 kg N ha⁻¹ fertilizer) pastures.
Over 2 years (1985-86) total annual lamb production per hectare from grass-only swards of Aurora was 19% more than that from Frances despite similar herbage productivity. Differences between the varieties in lamb output were more pronounced as grass/clover swards, with Aurora producing 29 and 18% more lamb than Melle and Talbot respectively and with Frances also giving 16% more than Melle. Overall lamb production from grass/clover swards was 10% more than that from the grass-only pastures, mainly due to 69% advantage in individual lamb growth rates after weaning. Herbage organic matter digestibility, during the post-weaning period, was higher on grass/clover than on grass-only swards, and similarly with Aurora versus the other varieties. Under a frequent cut simulated grazing regime the relative herbage productivity of the four varieties differed, with Aurora 13% less productive than Frances.
The results are discussed in relation to the limitations of assessing performance under cutting, and the significance of the interaction in animal productivity between the two sward types.     

Effects of an established sward of Lolium perenne L. on the growth and development of Rumex obtusifolius L. seedlings

Seedlings of Rumex obtusifolius L. were grown in gaps (11 cm diameter) in an established sward at Lolium perenne L., Root competition from the surrounding sward was controlled by PVC tubes and shoot competition was controlled by cutting the sward frequently. All combinations, with and without root competition and with and without shoot competition, were used.
Plants received either 40 or 80 kg N ha⁻¹ month⁻¹ and 0 or 300 kg K₂O ha⁻¹ and were harvested 39 d after emergence; a second harvest was made 12 d later, after shading to 20% of full sunlight.
The shoot dry weight per plant of R. obtusifolius was much more affected by root competition than by shoot competition, especially at low nitrogen applications. Potassium supply had no effect.
More dry matter was allocated to the leaf petioles under shaded conditions and the specific leaf area was greater. This morphological plasticity enabled R. obtusifolius to grow well under shading and to be affected only slightly by shoot competition from L. perenne.
The results suggest that competition for nitrogen was the main factor limiting the initial grown of R. obtusifolius in a ryegrass sward and that the morphological characteristics of R. obtusifolius make it less susceptible to competition for light in the early stages of its development.     

The effect of sward height on the liveweight gain of farmed yearling red deer (Cervus elaphus) stags

The effect of sward height on the liveweight gain of yearling farmed red deer stags grazing permanent upland pastures in the UK in two successive years is described. The swards received nitrogen fertilizer at a rate of 218 kg ha⁻¹. Red deer stag calves, which had been weaned in September and housed over winter on a hay and concentrate diet to gain on average 57 g d⁻¹ in year 1 and 75 gd⁻¹ in year 2, grazed at one of fourmean sward heights of 4, 6, 8 and 10cm from the beginning of June until September. Liveweight gains were recorded over a period of 15 weeks. All animals were slaughtered and carcass weights were recorded after the end of the grazing period. Liveweight gains and final live weights and carcass weights were significantly ( P <0·05) lower on the 4-cm sward than on the other swards, but there were no differences between the performance of animals on the 6-, 8- and 10-cm swards.     

South-west England grassland survey 1983

A survey of grassland on 127 farms in south-west England was conducted in order to investigate the cutting and grazing management of grassland, botanical composition and the use of fertilizer N, and to quantify recent trends in reseeding and the age structure of swards. Twenty-six percent of the grassland surveyed was classified as arable grassland (in rotation with crops) and 74% as permanent grassland. Only 37% of the established grassland on dairy farms was aged over 20 years compared with 53% on livestock farms. Mowing was practised on 52% of the grassland, two-thirds of it every year, and virtually all grassland was grazed for part of the year. The average fertilizer N input was 168 kg ha⁻¹ with considerable variation with sward age (average 113 kg ha⁻¹ for over-20-year-old swards) and between dairy farms (average 217 kg ha⁻¹) and livestock farms (100 kg ha⁻¹)- The average proportion of sown species (mainly Lolium perenne) ranged from 90% in young swards to 36% in swards aged over 20 years, with considerable variation within age groups. L. perenne was associated with high inputs of fertilizer N, good drainage, sheep grazing and organic manures, e.g. among swards aged over 20 years it contributed 38% on average where >250 kg N ha⁻¹ were applied, but only 12% where no fertilizer N was applied. A continuous network of Trifolium repens occurred in 27% of the grassland–this was associated with low inputs of fertilizer N, good drainage and sheep grazing. Agrostis spp. were the most abundant unsown species and Cirsium arvense, Ranunculus spp. and Rumex spp. the most common broad-leaved weeds. Features of the sample are compared with those in the south-west England region and in England and Wales as a whole.     

AN INVESTIGATION INTO THE SIMULATION OF NUTRIENT RETURNS BY THE GRAZING ANIMAL IN GRASSLAND EXPERIMENTATION

An experiment is described that examined mowing with the return of excreta and mowing with the return of clippings as methods of simulating the return of nutrients by grazing animals in experiments where grazing is impracticable. These treatments were applied to a pure grass and to a grass/clover sward. Both methods gave herbage nearer in yield and composition to that resulting from natural grazing than did mowing with no return, but neither was suitable for use on sites outside experimental stations. Although the nitrogen returned in excreta was rather inefficiently used, it appeared to be the major factor in increasing yield on the grass sward and in changing the grass/clover balance on the mixed sward. The return-treatments had a marked effect on the potassium nutrition of both swards and the results suggest that omitting the grazing animal from trials assessing potassium fertilizer requirements may invalidate the results.     

Frequency of stocking rate adjustments required on contrasting upland perennial ryegrass pastures continuously grazed to a sward height criterion from May to July

The use of sward height as a criterion for determining the time and extent of stocking-rate changes on continuously grazed swards was investigated over a 2-year period (1985–86) in a sheep production experiment. Swards of three contrasting perennial ryegrass ( Lolium perenne L.) varieties were established with and without Aberystwyth S184 small-leaved white clover ( Trifolium repens L.) at an upland site (310–363 m) in mid-Wales. From spring (late April) until weaning (mid-July) the pastures were continuously stocked with Beulah Speckled Face ewes and Suffolk cross lambs. During this period sward heights of 4 ± 0.5 cm were obtained and maintained by regular adjustment of animal number on individual paddocks. Grass-only swards received 160 and 200 kg N ha⁻¹ and the grass clover swards were given 80 and 75 kg N ha⁻¹ in 1985 and 1986 respectively.
Differences were observed between the treatments in sward height profiles over the season necessitating contrasting adjustments to stocking rates. Mean stocking rate necessary on early flowering Aurora (22 6 ewes ha⁻¹) was respectively 27% and 17% higher than on late-flowering Aberystwyth S23 and Meltra (tetraploid) ryegrasses; mean stocking rate on grass-only swards was 19% higher than on the grass-clover pastures.
It is concluded that sward height is a useful criterion on which to make adjustments to stocking rates to compare the potential performance of contrasting swards, under continuous grazing. The infrequent adjustments required to maintain a constant sward height, especially on the late flowering diploid perennial ryegrass variety on which many upland pastures are based, suggest that the criterion of sward height could be successfully employed on farms as an aid to efficient grazing management.     

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.     

Fertilizer and lime-pellet requirements for seed of white clover used for improving permanent pastures†

Permanent pastures on acid soils in the northeastern USA produce far below their potential due to lack of legumes in the swards. This experiment was done to study the effects of lime-pelleted white clover seed and fertilizer combinations (B, Cu, K, Mg, Mo, P, S and Zn) on clover nodulation and growth in four acid (pH 4.3–4.9), Vermont permanent-pasture soils in the greenhouse. Potassium was applied in all treatments. Lime pelleting and Mg and P fertilization increased both proportion of plants nodulated and seedling weight. Lime pelleting resulted in the largest increase in nodulation but P application produced the greatest gain in seedling weight. Molybdenum interacted with P to enhance seedling nodulation more than either element applied alone. Phosphorus also interacted with Mg to increase seedling weight more than either one applied alone. Sulphur had no influence on seedling nodulation or yield. Applications of B, Cu and Zn depressed nodulation and yield, possibly because excessively high levels were applied. Using lime-pelleted seed and a fertilizer combination of K. Mg. Mo and P could improve white clover establishment and growth on permanent-pasture soils in the northeast.     

Interactions between leaf lifespan and defoliation frequency in temperate and tropical pastures: a review

In continuously stocked swards or pastures the frequency at which individual tillers and individual leaves are defoliated by ruminant livestock, relative to leaf lifespan of the grass species within the sward, determines the proportion of each leaf defoliated before senescence, and hence the efficiency of harvesting of herbage. In this paper, sets of data obtained in a range of climatic conditions and with a range of grass species are used in order to document this relationship. It is shown that the frequency of defoliation of individual tillers or individual leaves is closely linked to the average stocking density used within a period of time for maintaining a steady state sward or pasture height, herbage mass or leaf area index. Consequently, any decrease in herbage growth rate should lead to a decrease in the efficiency of harvesting of herbage and then to a more than proportional decrease in total herbage consumption by ruminant livestock. These effects will be more important for grass species having short leaf lifespan than for species with long lifespan. In rotational stocking, the link between herbage growth rate and frequency of defoliation of leaves can be broken by controlling the grazing interval, so any decrease in herbage growth would not be systematically associated with a decrease in efficiency of harvesting of herbage. Rotational stocking should be more efficient than continuous stocking in low herbage production conditions, while in high herbage production systems rotational and continuous stocking would have similar efficiency. The implications of these conclusions for the management of swards and pastures to meet different objectives are discussed briefly.     

Effects of grass defoliation on the establishment and growth of slot-seeded white clover

White clover was slot-seeded into a low-fertility permanent pasture in May 1979. The effects of cutting interval (1, 2 and 4 weeks) and cutting height (3 and 7 cm), in the presence and absence of above-ground partitions, were recorded in terms of clover establishment and growth up to 15 weeks. The partitions resulted in a considerable increase in growth, stolon production and survival of clover plants, especially from 6 weeks after sowing, indicating a large effect of shoot competition from the surrounding sward. However, the effectiveness of defoliation in reducing grass competition appeared limited; close cutting did give some benefit to establishing clover but cutting frequency had little effect. In view of the limited success in reducing grass competition by cutting, further attempts at alleviating root competition are needed, possibly involving fertilizer placement and the use of grass-suppressing herbicides.     

The effect of summer management of perennial ryegrass-dominant swards on plant and animal responses in the autumn when grazed by sheep. 1. Tissue turnover and sward structure

An experiment was conducted lo compare the effects of the grazing by ewes and weaned lambs on aftermath and previously continuously grazed perennial ryegrass-dominant swards, at two sward heights (4 and 8 cm) in (he autumn, on changes in structure and growth of the swards. The experiment had a factorial design, was replicated twice and was conducted from mid-August to early November with measurements being made on three occasions in the autumn. Aftermath swards had lower tiller population densities and lower herbage masses than those that had been previously continuously grazed, the differences being greatest in August. On an area basis net growth rates of herbage on aftermaths were lower than those on previously continuously grazed swards in August and September but not in October. Growth rates of herbage were higher on the taller sward, but the senescence rates were similar at the two sward heights. It was concluded that autumn swards may be managed at taller sward heights than summer swards without increasing senescence of the sward and a consequent reduction in efficiency of utilization. The effects of previous sward management on tissue turnover in the autumn were not long lasting.     

Effects of spring fertilizer nitrogen and sward height on production from perennial ryegrass/white clover swards grazed by beef cattle

An experiment was carried out to compare the effects of two compressed sward height treatments, each at two fertilizer nitrogen (N) treatments (0 and 50 kg ha⁻¹ in spring), on the date of turnout and liveweight gain of steers grazing a perennial ryegrass/white clover ( Lolium perenne/Trifolium repens ) sward sited on clay loam in south-west England. The sward height treatments were 6 cm all season, and 4 cm in the spring rising to 6 cm in June; these were maintained using continuously variable stocking with Hereford × Friesian steers. Cattle were turned out on average 11·5 days earlier on the 4-cm sward height compared with the 6-cm sward height treatment. Liveweight gain early in the season was lower on the 4-cm swards than on the 6-cm swards. Liveweight gain ha⁻¹ over the whole season was similar for the two sward height treatments. Fertilizer N did not affect turnout date or liveweight gain.     

不同浓度海藻液肥对辣椒幼苗生长的影响

[目的]研究不同浓度海藻液肥对辣椒幼苗生长状况的影响。[方法]以辉腾8号为研究对象,设置清水（CK）、1 200倍稀释液、1 600倍稀释液、2 000倍稀释液和2 400倍稀释液共5个处理,研究不同浓度的海藻液肥对辣椒苗期生长的影响,观测辣椒幼苗生长指标,以筛选辣椒壮苗培养的最适施用浓度。[结果]在辣椒穴盘育苗过程中叶面喷施2 000倍海藻液肥,可提高辣椒幼苗的根粗、根冠比、壮苗指数和G值,有助于辣椒幼苗的生长。[结论]建议叶面喷施2 000倍海藻液肥,是培育辣椒穴盘壮苗的最佳浓度,可在生产中推广应用。     

Reproductive tillers in cut tall fescue swards: differences according to sward age and fertilizer nitrogen application, and relationships with the local dynamics of the sward

The effects of sward age and fertilizer‐nitrogen (N) application rate on reproductive tillers and their involvement in the dynamics of swards of perennial grasses were investigated using sown swards of tall fescue (Festuca arundinacea). Treatments included plots representing two sward ages (two and six‐year‐old swards) and two fertilizer‐N rates (150 and 350 kg N ha^?1 yr^?1) on the same experimental field. In each of 2 years all plots were cut at the silage stage and three times afterwards. After each cut, during two growing seasons, the vegetative tillers and stubs of cut reproductive tillers were counted in ten permanent quadrats for each of the four treatments, using a grid of 150 cells, each of 2 cm × 2 cm. The results showed a higher density, and a greater proportion of reproductive tillers, on the higher fertilizer‐N rate treatment and on the older swards. The density of vegetative tillers was found to be greater in close proximity to the reproductive tillers in all sward treatments and in both assessment years. Thus, cutting the reproductive tillers did not result in thinning of the swards. It is suggested that a mother‐tiller effect, enhancing renewal of tillers, was likely, although zones bearing reproductive tillers during the second spring were sometimes already denser than zones in the rest of the quadrats before the winter.     

水稻单株栽培产量效益分析

通过对单株、双株、三株栽培的对比试验研究,结果表明:单株栽培秧苗健壮,叶色较绿,带蘖率86.3%,发根力为2.8条,充实度为0.318g/cm;单株栽培产量达513.64kg/667m2,较双株和三株栽培分别增产26.68kg/667m2、53.36kg/667m2。