The regrowth of Aberystwyth S. 22 Italian ryegrass, S. 24 perennial ryegrass and S. 37 cocksfoot was studied in field swards with and without applied nitrogen during the 21 days following a cut or grazing, there being a total of five periods of study at different tunes of year and in different years.The proportion of cell content in the harvested herbage, as measured by neutral detergent, increased by nearly 9 percentage units from day 3 to day 18 of regrowth. The proportion of cell content as measured by acid pepsin also increased during regrowth, but to a lesser extent. The proportion of cell content in leaf blades of two age categories, as measured by neutral detergent, also increased during regrowth. The above increases in proportion of cell content were found in all three grasses. The increases were associated with increases in the proportion of crude protein in dry matter, which were only partially offset by reductions in the proportion of water-soluble carbohydrate. The broad pattern of change in N and nitrate-N content of Italian ryegrass herbage during regrowth in spring with different amounts of N applied, noted in earlier experiments, was confirmed and found to apply to perennial ryegrass and cocksfoot also. During a September-October period of study there was little sign of decline in nitrate-N content within the 21 days where N had been applied. Younger leaf blades had a rather lower nitrate-N content and a slightly higher total N content, on average, than, older blades. The application of N increased the proportion of crude protein more than it reduced the proportion of water-soluble carbohydrate and it increased the proportion of cell content. The increase in proportion of cell content was sufficient to explain the positive effect of N application on digestibility. The average proportion of total herbage N which was found in the cell wall fraction was about 12%.There appeared to be a relationship between chemical composition and dry-matter content. The chlorophyll content of leaf blades increased during regrowth and was increased by N application. The experimental results on balance, particularly those for proportion of cell content, suggest an improvement in nutritive value of grass during regrowth up to about 3 weeks in contrast to the well-recognized decline in nutritive value where regrowth proceeds beyond about 3 weeks.It has been noted (Wilman et al. 19776) that the proportion of cell content in Italian ryegrass, as The dry-matter content, leaf water potential measured by incubation in acid pepsin, was rather and digestibility of three grasses in the early stages low after 1 week of regrowth in spring and of regrowth after defoliation with and without increased appreciably during the second and third applied N have been considered in an earlier paper weeks of regrowth. We have noted the same effect (Wilman & Wright, 1978). In the same experiments in late summer-early autumn regrowth in Aberystthe proportions of cell content, N, nitrate-N and wyth in samples from an experiment with Italian wat...
The effect of six intervals between harvests and three levels of N application on the concentration of nitrate-N and total N in total herbage, green leaf and 'stem' was studied in two varieties of perennial ryegrass during 30-week periods in each of the first two harvest years of a field experiment. The effect of two intervals between harvests on the concentration of nitrate-N in Italian ryegrass total herbage was studied in the same experiment. The effect of two intervals between harvests and three levels of N application on the concentrations of nitrate-N and total N in total herbage was studied in five grasses during a 32-week period in a second field experiment.Increasing the interval between harvests tended to increase the concentration of nitrate-N in herbage; however, this seemed due mainly to the average date of harvest being later in the year with the longer intervals. The concentration of nitrate-N in herbage increased from June to September. Italian and hybrid ryegrass and tall fescue were much higher than perennial ryegrass in nitrate-N concentration at the highest level of applied N (525 kgN/ha per year). Apart from the species and time of year effects, the nitrate-N concentration seemed to be determined mainly by the amount of N applied divided by the number of days between the date of application and the date of sampling. The 'stem' of perennial ryegrasa tended to be slightly higher in nitrate-N concentration than green leaf. The proportion of nitrate-N in total N was increased by increasing the interval between harvests and by applying N and was nearly twice as high in 'stem' as in green leaf. Both the nitrate-N and the total N concentration of herbage, particularly the latter, seemed to be inversely related to solar radiation receipt.
The regrowth of Aberystwyth S. 22 Italian ryegrass, S. 24 perennial ryegrass and S. 37 cocksfoot was studied in field swards with and without applied nitrogen during the 21 days following a cut or grazing, there being a total of five periods of study at different times of year and in different years.The dry-matter content of the harvested herbage deoreased by 4-8 percentage units on average from day 6 to day 18 of regrowth, supporting the evidence of earlier experiments with ryegrass and suggesting that a decrease at about this stage is typical. In the present experiments the same trend was evident after removal of surface moisture. Dry-matter content before removal of surface moisture was sometimes as low as 10 %, which could adversely affect animal production. The water potential of fully expanded leaf blades was typically more negative on days 2 and 5 of regrowth than subsequently, so that the moderately high dry-matter content during the first week of regrowth seems to indicate some degree of moisture stress. Emerging leaves were less stressed than fully expanded ones during the very early stages of regrowth. Leaf water potential tended to be rather less negative in the cooksfoot than in the ryegrasses. The application of N reduced dry-matter content, but did not affect leaf water potential.The digestibility of the harvested herbage was little affected by the stage of regrowth. The cocksfoot was less digestible than the ryegrasses. The application of N generally increased digestibility, particularly in cocksfoot.
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