摘要:

AbstractDactylis glomerataandLolium perennewere grown in single‐species stands and in mixed‐species stands in boxes for 1 year. Plants were grown in paired rows in each box with full competition below ground, but aerial partitions prevented shoot competition. The rows were cut either frequently (six cuts) or infrequently (three cuts).In single‐species stands, frequent defoliation reduced the root competitive ability ofD. glomerataplants, when growing with infrequently defoliated plants, though this occurred only if no N fertilizer was applied. Frequent defoliation did not affect the root competitive ability ofL. perenneplants, in single‐species stands, whether or not N fertilizer was applied.In mixed‐species stands, the root competitive ability ofD. glomeratawas always greater than that ofL. perenne, though N fertilizer applications and frequent cutting both reduced the root competitive ability ofD. glomeratarelative toL. perenne.Mixtures of frequently cut and infrequently cut plants, in unfertilized single‐species stands, always yielded more than the mean of the uniformly treated stands (frequently or infrequently cut); they usually yielded more than the highest‐yielding uniformly treated stand. Mixtures of frequently and infrequently cut plants, in fertilized single‐species stands, always yielded less than the mean of uniformly treated stands.Mixed‐species stands usually yielded more than the mean yield of the component species, and sometimes yielded significantly more than the highest yielding component. This effect generally increased with time.Relative yield totals (RYT) were consistently greater than 1·0, in both single‐species and mixed‐species stands, when no N fertilizer was applied. RYT were greatest (1·2–1·6) when neither N nor P fertilizer was applied, and generally increased with time.The results are discussed in relation to the effects of cutting on root competition and the probable val

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01497.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA forage capacitance‐measuring scheme is presented which uses the earth and plants growing in it as one plate of a two‐plate capacitor. Low frequency analogue circuitry is coupled with digital circuitry to sense and read out digitally the capacitance as a function of the forage under the sensing head. The circuitry is linear, reasonably stable and offers the opportunity for electrically confining the sensed area. The apparatus behaviour is characterized by a mathematical describing funct

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01498.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSix groups of five 18‐month‐old wether sheep received a diet of dried grassad libitumwith a pelleted ground barley/oat supplement containing various levels of salt for 30 d. The first group received grass of high Na concentration (7·3 g per kg DM) with no added salt in the supplement, a second group received low sodium grass (4·2 g per kg DM) with no salt additions, and the other four groups received the low sodium grass with varying levels of salt added to the supplement to provide a final dietary Na concentration ranging from 7·0 to 18·0 g per kg DM.Dry matter (DM) and organic matter (OM) intakes were significantly reduced for groups receiving salt supplementation. The digestibilities of DM and OM were reduced for all groups on the low sodium grass diets compared with the high sodium grass diet, but were not affected by salt supplementation.No consistent changes were observed in the molar proportions of volatile fatty acids in rumen fluid, but N availability and retention were higher for the animals on the high sodium grass diet.The high sodium grass diet gave a better apparent availability and retention of minerals than the low sodium grass diets and, while addition of salt tended to improve the availability of minerals, the urinary loss of minerals increased with salt addition to the diet.There were no changes in plasma Na levels, and plasma K changes were inconsistent. However, plasma Ca concentration was reduced significantly for salt‐supplemented diets with a Na concentration above 7·0 g per kg DM, and plasma Mg was significantly depressed at dietary Na concentrations above 15·0

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01499.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSites 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‐1with no fertilizer to 9190 kg ha‐1with an application of 100, 26 and 50 kg ha‐1N, 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

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01500.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractAn investigation of the carbon economy of single S184 white clover plants nodulated with an effective strain ofRhizobium trifoliigrowing on N‐free nutrient solution and supplied with 150 parts/106N as NH4NO3has shown that 10% more of the C fixed per day is available for growth in the plants supplied with combined N. The difference between the two groups of plants is a result of higher respiratory activity in the roots of plants growing exclusively on N2. In terms of shoot growth, however, the difference in growth rate is likely to be less than 10%, because the rate of root growth is greater in the plants supplied with a moderate level of combined N. There is no evidence that NO‐3and CO2compete for photosynthetically produced reductant in the leaves of plants grown on N2+NH4NO3, since no reduction in net photosynthesis was observed in plants assimilating combined N.An experiment carried out on detached leaflets of white clover grown on N2and on N2+ NH4NO3has shown that NO‐3‐reducing activity is present in the leaflets of plants grown on N2+ NH4NO3but not in plants grown on N2and that the activity is light‐dependent. Measurements of14CO2respired in the light and dark by leaflets previously allowed to photosynthesize14CO2showed that the ratio of14CO2output in the light to14CO2output in the dark was no higher in plants grown on N2+ NH4NO3than in plants grown on N2. This observation is consistent with the finding that N source does not affect net photosynthesis in who

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01501.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA 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‐1carbetamide, 0·8 kg ha‐1propyzamide and 0·6 kg ha‐1paraquat. 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‐1propyzamide); 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‐1propyzamide. Potential uses to achieve legume dominance by grass‐suppression are suggested and the needs for further

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01502.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractTwo experiments were conducted to estimate the influence of initial cutting dates in March and April and of cutting frequencies on Guinea grass, elephant grass and star grass productivity. Increasing delay in date of first cut in the season resulted in a progressive increase in dry‐matter yield. 72–81% of the tiller population at any cut were vegetative and this helped to maintain good aftermath yield for each date of first cut. Early April cuts gave the highest dry‐matter yield and early March the least.Harvesting frequencies affected the sward productivity such that the annual dry matter yield increased with increasing harvesting interval from 6800 kg ha‐1for a 3‐week interval to 13,000 kg ha‐1for a 10‐week interval. The proportion of green leaf in the dry matter dropped from 57·7% at 3‐week intervals to 32·0% at 10‐week intervals. Seasonal effects showed that potential yield was reduced by a short interval between harvests early in the season but not late in the season. Species differences in quality and in the harvesting interval that gave the maximum yields were noted. These results are discussed in relation to management of the sward throughout

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01503.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effect of sowing date, within the period from late May to mid‐August, on the DM yield of five leafy forage brassica crops sown to a stand was examined over the period 1976–78. Kale was the crop most sensitive to variation in sowing date and yields declined progressively with later sowings. There was no yield benefit from sowing rapes or stubble turnips earlier than mid‐ to late‐June.Raphanobrassicaproduced yields as good as rape when sown in June. In 1978, DM yields of rape, kale andRaphanobrassicaincreased from September to early November, largely as a result of stem growth; kale was slower to accumulate DM than rape in late summer but continued growing longer into the autumn. The DM concentrations of all crops increased from September to December. Rape had a higher DM concentration than stubble turnip.Raphanobrassicawas 10–25 g kg‐1lower in DM concentration than rape or kale.Raphanobrassicaproduced 23–59% flowering plants from late‐May to early‐June sowing. Harvest date affected DM yield and concentration, leaf: stem ratio and flowering percentage. The effects of sowing dale on DM concent

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01504.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractHerbage dry‐matter yields of sown plots of white clover were greatly reduced by a natural infection of clover rot (Sclerotinia trifoliorum), the extent of the reduction being related to the level of infection. Examination of seasonal yield patterns suggested that although the plants apparently recovered from the disease it re‐exerted its influence later in the season. No effects on seed yield could be detected but effects on the development of inflorescences and the proportion of ripe heads surviving to harvest were noted. Marked differences between varietal types existed for some of the characters exami

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01505.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractA simple technique for extracting stem nematodes from air‐dried samples of lucerne is described. The technique was found to be suitable for use in a breeding programme to improve resistance to stem nematodes in lucern

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1980.tb01506.x

出版商:Blackwell Publishing Ltd    

年代:1980

数据来源: WILEY