摘要:

AbstractThe statistical properties and applicability of the Dry‐Weight‐Rank (DWR) method of pasture sampling are examined. Formulae for the expected value and variance of the DWR estimates are presented.The extent of bias in DWR is examined using several mathematical models. DWR is shown to break down when estimating multinomial proportions; however it provides good estimates for a subset of models simulated from a class of compound probability distributions.The success of DWR in practice does not rest on a theoretical basis. It appears to be a remarkable empirical discovery that DWR estimates are virtually unbiased on most pasture types. Several cases are considered where difficulties may be encountered in using DWR. Provided the theoretical reservations of this paper are borne in mind, DWR will continue to be a useful practical tool, especially in the absence of non‐destructive observational alterna

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01606.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractVarieties of Italian, perennial and Italian × perennial ryegrasses, tall fescue and cocksfoot were used to determine the effects of soil moisture on grass growth. Weather conditions were monitored and herbage accumulation, leaf extension rate, leaf appearance rate and tillering were recorded under natural (control), covered and irrigated treatments.Water deficit reduced crop growth rate in the spring and drought was the major factor influencing crop growth rates in all varieties during the summer. The ryegrasses appeared most sensitive to drought, and particularly poor recovery growth was exhibited by the Italian ryegrass RvP and the hybrid ryegrass Snowdon.Leaf extension rate and leaf appearance rate were both reduced by increasing soil water deficit. Herbage accumulation was increased by irrigation when potential soil water deficits were greater than 100 mm. When water deficits were large, irrigation increased leaf extension more than leaf appearance or tiller number. Increasing moisture deficit had a greater effect upon tiller number than on leaf extension

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01607.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThree groups of cows were continuously stocked on pasture and offered supplementary concentrates according to the herbage height measured weekly with a grass disc. Concentrates were offered when the mean herbage height fell below 9 cm for treatment A, 7 cm for treatment B and 5 cm for treatment C at a rate of 1 kg d‐1for each 0·2‐cm decline below these threshold levels. If the herbage height declined by more than 1·2 cm (8 kg concentrates d‐1) hay was offered in additionad libitum.The stocking rates for all three treatments were 5·2, 3·2 and 3·2 cows ha‐1for three successive 8‐week periods. For treatments A, B and C the mean concentrate DM intakes were 3·2, 1·2 and 1·2 kg d‐1(treatment A also received 0·2 kg hay DM d‐1), and the mean daily milk yields were 17·2, 16·2 and 15·2 kg respectively. The increasing level of supplementary feeding from treatment C to A also resulted in an increase in liveweight and body condition score change, an

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01608.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe frequency and severity of defoliation of individual grass tillers and clover plant units was studied inLolium perenne‐Trifolium repensswards grazed by sheep at stocking rates ranging from 25 to 55 sheep ha‐1and either receiving no N fertilizer or 200 kg N ha‐1. On average, sheep at the highest stocking rate defoliated individual tillers once every 4·2 d compared with once every 9·2 d at the lowest stocking rate with the removal of 58% and 47% of the leaf length of each tiller leaf at these stocking rates. Clover plant units were defoliated once every 4·2 d at the highest stocking rate and once every 7·2 d at the lowest stocking rate with the removal of 51% of its leaves and 12% of its stolon at the high stocking rate and 42% and 4% respectively at the low stocking rate. Differences in frequency and severity of defoliation between N fertilizer treatments were smaller than between stocking rates. Grass tillers and clover plant units were both defoliated less frequently and less severely in swards fertilized with N, though the difference in defoliation frequency between fertilizer treatments decreased as stocking rate increased. Defoliation frequency was related to the length of grass leaf per tiller or number of clover leaves per plant unit, and to the number of these tillers and the herbage

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01609.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractRecords of grassland productivity were kept for 2 years on 152 dairy and 179 beef farms. Results were collated for six lowland zones, delineated primarily on the basis of average rainfall, and an upland zone. Contemporary and long‐term average meteorological records were also collected.In most of the lowland zones stocking rates and use of fertilizer N were similar, but utilized metabolizable energy (UME) output from grass varied; it was 25% higher in the wet, cool zone of north‐west England and east Wales than in the dry zone of eastern England. The ranking of zones for utilized output corresponded closely with the ranking for summer rainfall.On upland farms stocking rate was 25% lower and UME output 15% lower than on lowland farms, but this was achieved from little more than half the N input.The differences between zones were similar to those shown in other published farm data. They also showed a similar trend to that demonstrated in grass cutting experiments. This suggests that farmers were, on average, able to exploit the extra grass grown in wetter climates. The incidence of difficult topography and impeded drainage was similar in dry and wet zones, but did have a more serious effect in the wet zones. The much higher level of concentrate feeding in the driest zone may have reduced the utilization of gr

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01610.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractThe effects of sheep grazing on the development of and production from heather swards and on intake and diet selection by grazing Scottish Blackface wether sheep were studied in an experiment in which sheep numbers were adjusted to remove 0, 40% or 80% by weight of current season's shoots in summer and in autumn for a period of 5 years. All combinations of season and level of grazing were provided. The plots were divided after 2 years and grazing was continued for a further 3 years on one subplot but discontinued on the other.Sward productivity during the 5 years of grazing was unaffected at the 40% level of shoot removal but at the 80% level was reduced by up to 66%.After a season's uninterrupted growth at the end of the experiment heather cover and herbage mass were lower and current season's shoots as a proportion of total mass were higher on those treatments which received the greatest severity of grazing. Weight of current season's shoots was unaffected on treatments which had received the 40% level of shoot removal but was reduced by 40% and 50% on treatments which had received the 80% level in summer and autumn respectively. On the rested subplots sward recovery was such that no treatment effects remained after 3 years except with respect to 80% shoot removal in autumn where herbage mass was reduced compared with other treatments.Intakes of digestible organic matter per sheep were higher at the 80% than the 40% level of grazing in the fifth year of the experiment. This was ascribed to the ingestion of new shoot growth from the twig bases on the 80% level of removal treatments. Intake and digestibility were higher in the summer on those treatments which had received the 80% level of removal in previous autumns. Over the 5 years of the experiment there was a small decline in intake and digestibility values, with the decline being greatest in the summer and at low levels of grazing.Floristic changes differed on the rested and grazed areas. On the rested subplots in the fourth year after grazing stopped, heather height was lower and cover by grasses, sedges and herbs was greater on treatments which previously had received the highest levels of utilization. On bare areas the rate of recovery of heather was rapid where shoots as well as seedlings contributed to recovery growth. On the grazed subplots, with the exception of the low‐growing ruderalRumex acetosella, cover due to grasses, sedges and herbs remained low as species other than heather were selectively grazed.Relationships among stocking rates, grazing behaviour and heather utilization are discussed and guidelines for the recognition of overgrazing are outline

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01611.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractTwelve varieties of cocksfoot,Dactylis glomerataL., were analysed for three mineral elements (Na, K, Ca) and their dry matter (DM) yields were measured in pot and field trials. Among these characteristics there were strong varietal differences in Na concentration, whereas in other cases the varietal differences were less significant. The concentrations of individual mineral elements were, in most cases, independent of yield and of one another.Parent plants and their clonal derivatives were highly correlated in Na and Ca concentration as well as in DM yield. Tiller size or position on the parental plant had no significant effects on the mineral concentrations or DM yields of clones derived from separated tillers.Within varieties continuous variation was observed for Na concentration and the range of variation increased with increasing mean Na concentration. When plants were grown under different experimental conditions there was a high repeatability in Na concentration within varieties over cuts and years. This result was taken as an indication of a strong genetic basis for Na concentration. The results obtained in this study show that it is possible to develop grass varieties of defined potential Na concentration.

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01612.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

AbstractFive trials were carried out in 1979 to assess the influence of cultivar, seed rate, fertilizer application and the inclusion of oats as a companion crop on the dry matter (DM) yield of forage peas grown in the west of Scotland. Despite the season being abnormally cold the crop consistently produced between 6 and 8 t DM ha‐1. There was little difference between cultivars in the yield of forage produced but there were considerable differences in the time taken to reach maturity. All cultivars lodged. There was no yield response to seed rate of between 80 and 280 kg ha‐1nor to fertilizer N and K applications. The inclusion of oats in the seeds mixture greatly reduced lodging and had no marked effect on DM yield but the organic matter digestibility and crude protein concentration were lower than recorded for peas grown alone in previous ye

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1982.tb01613.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY