摘要:

Leaves of different ages were removed 7 times between June and October. Each defoliation was timed to match the appearance of successive leaves on each tiller. The removal of leaves at progressively younger stages reduced total production above ground, but the most severe treatment, the removal of all expanded leaves repeatedly, still produced about 75% as much as the least severely defoliated sward. Clipping with shears 3 times reduced yield as much as removing all expanded leaves 7 times. A crop allowed to grow untouched apparently produced more than any defoliated treatment, but this may have been an artefact.The lower production following increasingly drastic defoliation was not associated with reduced concentrations of nitrogen or potassium in the foliage removed, or in the crop left behind. The total quantity of these elements recovered in the crop was greatest in those treatments where least dry matter was produced. Explanations for the results depend on the capacity of swards of predominantly young leaves to assimilate carbon more rapidly than those containing old and senescent tissue.

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Microwave heating has recently been suggested as a method of drying herbage. A slightly modified commercial microwave cooking‐oven has been tested for this purpose and was found to dry 400 g of fresh herbage in 15‐20 min. The water‐soluble‐carbohydrate contents of herbage samples dried (a) by microwaves and (b) by freezing were

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The growth curves of closed grassland swards obtained during the growing seasons of six successive years were compared with each other and with theoretical growth rates calculated bydeWit's method and based on the mean light energy input data for the same years. The form of the growth curve consisted of a period with a constant rate, lasting for 6–7 weeks in May‐June, then rapidly shortening to 3 weeks in August‐September, after which there was a rather abrupt change to zero values. A comparison with theoretical values showed that a period of constant growth rate was possible, because the promoting influence of increasing LAI counteracted the effect of increasing respiration. Before the longest day this period was lengthened by an increasing daylength; thereafter the reverse was found. There is no ready explanation for the sudden decline to zero values. This is thought to be associated with changes in the rate of photosynt

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

A model of the electronic instrument described by Campbellet al. (3) was built at the Grassland Research Institute and was found to behave in a very similar way to their New Zealand model. A considerable amount of field work was undertaken with it in 1964 and this demonstrated that no general relationship of acceptable accuracy had yet been found; nor could it be sufficiently improved by the inclusion of the meteorological and botanical factors recorded. This forces one to a consideration of double‐sampling techniques, which appear worth while; they will be discussed in Part 2 of this pape

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The effect of the physiological status of grazing ewes on diet selection was studied, using ewes with oesophageal fistulae. The diets of dry ewes grazingPhalarisannual grasses and subterranean clover pastures, over a range of availabilities, were compared with those of ewes in various stages of pregnancy and lactation. There were no significant differences at any stage of reproduction in the botanical composition of the diets. However, small differences in diet digestibility, soluble carbohydrate and nitrogen content were found during pregnancy and lactation. These occurred at all levels of availability of pasture. The differences did not appear to have nutritional significance in the particular pasture ecosystems studied because levels of N, soluble carbohydrates and digestibility of the diet were such that selection for survival was unlikely to be necessary.It is concluded that dry fistulated ewes can be used to obtain samples for assessing diet N and soluble carbohydrate contents for ewes in other physiological states. The use ofin vitrodigestibility tests of diets of dry ewes to assess diet digestibility for ewes in other physiological states may be subject to error.

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Nitrogen levels of 0,184 and 368 Ib (0,83.47 and 166.94 kg) were applied, as calcium ammonium nitrate, in six dressings throughout the grazing season to a perennial ryegrass/white clover sward. Herbage samples taken, periodically from each treatment and analysed nitrate for, indicated that the latter increased with increasing levels of applied nitrogen. Herbage nitrate levels were higher towards the end of the grazing season than at any other time. There was no consistent relationship between applied nitrogen and total plant nitrogen, although the latter tended to run parallel with applied nitrogen levels during the early part of the year.Sheep performance was significantly increased with the first increment of 184lb (83.47 kg) of nitrogen; a second increment of 1841b resulted in a further, but non‐significant, increase. High‐nitrate pastures did not significantly reduce liver vitamin A storage in sheep. It is suggested that approximately 350 Ib (158.79 kg) of nitrogen, applied uniformly throughout the grazing season, results in pasture nitrate levels which have no adverse affect on sheep performa

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

In two experiments the growth of clover undersown to wheat was linearly related to the amount of light available. There were strong indications that clover growth and light within N.‐S. rows were superior to those within E.‐W. rows of wheat, and within N.‐S. rows, those along the middle position were superior to others. The large difference between the growth of clover sown alone and with wheat indicated that beneath wheat the clover suffered from competition for other factors, probably soil moisture, which was even greater than that for light. Beneath wheat at the reduced level of growth there was a positive linear relationship between yield of clover and available

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00580.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

The seed‐producing capacity of two varieties of meadow fescue, S215 and S53, sown at three different spacings, was compared. One level of nitrogen was applied on three different dates in the spring. Tiller counts were made periodically during the growth of the crop. Fertile‐tiller production was found to be related to vegetative growth.The varieties differed not only in yield, but also in growth dynamics. A larger percentage of overwintering shoots became fertile in the hay variety, than in the pasture variety.Drill spacings had significant effects on plant establishment and on vegetative‐and fertile‐tiller numbers. In both years N applied in March gave the highest production of fertile tillers. Date of N application did not produce marked trends in yield. The influence of spacing and date of N application on the number and density of spikelets indicated that the plant adjusted itself to environmental factors. Thus spikelet numbers were reduced in early heads with narrower drill spacing and with late applications of N. Head emergence was earlier in narrow drills, but time of N application in the spring did not produce significant differences in this

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00581.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

Two pot experiments were carried out in a semi‐controlled environment to examine the response of individual plants to competitive stress in simple systems incorporating varying cutting frequencies and soil–nitrogen levels. A third experiment was set up outdoors to examine the effect of competition on individuals in an association, on the association as a whole, and to extend the controlled environment studies to a more complex model involving micro‐plots.Phalaris coerulescens, although its seedlings possessed a high competitive ability, showed a dramatic decline in competitive ability in later stages of the association, this decline being associated with extensive floral development. In micro–plots the effect of competition was so severe as to prevent the expression of seasonal growth characteristics byP. coerulescens.Considerable inter‐specific differences existed in the response to competition of leaf‐area production per tiller during periods of regrowth.WhilstP. coerulescensremained highly productive and maintained a dense tiller population in monocultures, its tiller regeneration following flowering was severely suppressed in competition with vegetative plants of HI ryegrass orFestuca arundinacea.The number of heads produced per plant, head length and time of head emergence were all affected by competitive stress, the former response being a reflection of the relative competitive abilities at the time of floral initiation. The response of the latter two characters reflected the decline in competitive ability which occurred during later stages of the growth and development ofP. c

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00582.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

ISSN:0142-5242    

DOI:10.1111/j.1365-2494.1968.tb00583.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY