The respiration drift of harvested pasture plants during drying

IntroductionThe slow loss of water from crops cut for high dry-matter silage, pre-wilting before grass drying and particularly from crops cut for hay, causes loss of dry matter and reduction in nutritive value. The total loss of dry matter can be very large and Klinner (1976) states that as much as 30% of the dry matter in the original crop can be lost during hay-making. In addition to the purely mechanical losses caused by fragmentation, dry matter can be lost as a result of continued respiration after a crop has been cut and Greenhill (1959) found that 7% ofthe original dry matter in ryegrass and white clover could be lost in this way. Woods (1972) calculated from the data of Pizarro and James (1972) that 7% of the dry matter in peretinial ryegrass could be lost in a 9-day drying period as a result of continued respiration. Rain falling on to a cut crop will increase losses by leaching out soluble nutrients and the losses are greater if the crop has been mechanically damaged to increase drying rate. Thus Kormos and Chestnutt (1968) found that laceration increased leaching losses. Demedde and Wilmschen (1969) subjected grass of low water content to simulated rainfall and found that the serious losses of dry matter which occurred were greater if the grass had been previously crushed.Mechanical conditioning treatments such as crushing, crimping and flailing have been used for many years to accelerate the field drying of forage crops. Reviews by Bruhn (1959) and Klinner (1975) indicate that greater severity of treatment produced bigger increases in drying rate but also resulted in greater losses of dry matter. While mechanical treatments open new pathways of water loss by physical rupture of tissues, chemical conditioning treatments could facilitate water loss from the existing pathways by reducing stomatal and cuticular resistance. Such treatment may avoid the losses associated with mechanical conditioning.The pathways of water loss have been the subject of considerable research effort in the case of the growing plant, but the literature on the function of these pathways in the cut plant is much less extensive. The reduction in the water content of the growing plant during 1 day resulting from the excess of transpiration over water uptake is very small compared to the reductions which are necessary to produce hay which can be safely stored. Thus Willard (1931), showed that, with lucerne, soya beans, red clover, sweet clover and alsike clover, the decrease of water concentration during the day is never more than 3%. With grasses, Greenhill (1936) observed a similar fall in water concentration between 09.30 and 15.00 hours. It is therefore unlikely that data on the loss of water from the growing plant will be relevant to the process of drying in the cut plant, except in the very early stages. A further area of interest in the drying plant is the extent to which stem water continues to be transferred to and lost from the leaves after cutting.The object of this paper is to review existing literature on these topics...

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confidence: 99%

Pathways of water loss from legumes and grasses cut for conservation

Harris¹,

Tullberg²

1980

“…Previous investigations (1,5,6,11) into the drying of herbage have attempted to evaluate the various factors that influence the rate of drying. The more important variables include: species or variety; maturity stage; respiration rate and therefore DM loss; method of harvesting, i.e.…”

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confidence: 99%

Investigations on the Drying of Herbage at Temperatures Up to 50°c*

Rees

1974

Experiments to detemiine the exposed layer drying rate of cut leaves and stems of a tetraploid (Sabel) and diploid (S23) ryegrass are described. Drying was achieved by passing air through the crop; the changes in weight were monitored continuously. Airflow was fixed throughout the experiments at 37-5 ft/min (0-190 m/s) and the temperatures were controlled in the range ZS^C to 50°C. Comparisons were also made of the drying rates at different stages of maturity. Drying curves were determined and moisture content was shown to decay exponentially with time, the relationship approximating closely to a two term exponential. INTRODUCnONPrevious investigations (1, 5, 6, 11) into the drying of herbage have attempted to evaluate the various factors that influence the rate of drying. The more important variables include: species or variety; maturity stage; respiration rate and therefore DM loss; method of harvesting, i.e. whether the crop is to be dried whole, chopped or lacerated; the degree of wilting; the moisture content at the start of drying. In general, workers (3, 4, 12) have tended to use relatively large amounts of material which have either been allowed to dry under controlled conditions in a chamber or by being subjected to various airflows of known temperature and speed. Apart from requiring large quantities of homogeneous material these techniques cause differential drying within the mass and consequently the formation of a moisture gradient from the outer to the inner layers.*For a list of the symbols used in this paper, see page 55.To avoid these restricting factors and to ensure that the water holding capacity of the air was never a limiting factor the technique of drying in thin-layers was adopted (1,7, 13); a thin layer being one in which the moisture content gradient in depth and over the cross-sectional area during drying is negligible. Data produced by this technique could be used to predict drying rates under different conditions experienced in barn dr>'ing of hay, to compare the effect of various crop treatments on the drying rate, and to simulate, with a computer, deep-layer drying. Various aspects of herbage drying using the thin-layer techniques have been investigated. Tuncer (13) investigated the drying behaviour of certain grasses (including ryegrass and timothy) and the effect on the drying rate of chop length and the humidity and temperature of the drying air. No attempt was made to evaluate a relationship between the rate of drying and drying conditions, and discussion on the rate of drying did not include the possible effects of maturity and initial moisture content. EXPERIMENTAL Crops. Two strains of ryegrass, S23 which is a diploid perennial and Sabel which is a tetraploid hybrid between perennial and Italian, were dried. An estimate of stage of growth was obtained from plant size as recorded in Table 1; enabling the efFect of maturity to be investigated and also to compare the drying rates of each cultivar. Apparatus. The apparatus has been described previously (9) and consists of eight d...

“…Other researchers (Fleischman 1912;Nash, 1959) have also reported increases in dry weight during favourable conditions of wilting and have suggested that this may be the result of photosynthetic activity. Greenhill (1959) and MacGregor (1966) have also reported that photosynthesis occurs during suitable conditions of drying.…”

Section: Resultsmentioning

confidence: 95%

“…In addition to the loss of moisture which occurs during the initial stages of drying, the following biochemical and microbiological changes have been suggested: increase in soluble N resulting from proteolytic activity (Kemble and Macpherson, 1954;McDonald, 1981), changes in carbohydrate content resulting from respiratory, photosynthetic and enzymatic activities (Greenhill, 1959;McDonald and Henderson, 1964;Miller et at., 1967;McDonald, 1981) and increase in populations of bacteria on the plant materials (Gregory et at., 1963). In general, there is an overall loss in dry matter (DM) during the wilting period; this usually results from plant respiration, from the possible leaching by rain and by leaf shattering (Miller et at., 1967;Jones and Prickett, 1981).…”

Section: Introductionmentioning

confidence: 99%

“…In general, there is an overall loss in dry matter (DM) during the wilting period; this usually results from plant respiration, from the possible leaching by rain and by leaf shattering (Miller et at., 1967;Jones and Prickett, 1981). Several researchers (Fleischman, 1912;Greenhill, 1959;Nash, 1959;MacGregor, 1966) have indicated, however, that photosynthetic activity occurs during the early stages of drying and this may lead to an increase in DM during this period.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Some changes associated with the field drying of lucerne and timothy

Alli

Robidas

Noroozi

et al. 1985

Lucerne (approximately 10% flowering, 270 g dry matter kg~') and timothy (boot stage, 310 g dry matter kg"') were harvested and allowed to wilt for a period of 52-5 h. During the early stages of wilting of lucerne there were increases in the proportion of leaf material (dry weight basis), as well as increases in total available carbohydrate and water soluble carbohydrate concentrations. Approximately 50% of the leaf material in lucerne and in timothy was lost after a drying period of 52-5 h and after tedding and raking operations prior to baling of the hay. This resulted in considerable reduction in the protein content of both lucerne and timothy. (Results are means (and standard errors) of three samples. t DM basis. J CP=crude protein; TAC = total available carbohydrates; WSC = water soluble carbohydrates.