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The effect of interval between harvests and nitrogen application on the proportion and yield of crop fractions and on the digestibility and digestible yield and nitrogen content and yield of 2 perennial rye grass varieties in the 2nd harvest year

Wilman, D.; Koocheki, A.; Lwoga, A.B.

Journal of Agricultural Science 87(1): 59-74

1976

Studies were made with 'S. 23' and 'S. 321' perennial ryegrass during a 30 wk period. In 'S. 23' the "stem" was divided into true stem, leaf sheath, unemerged leaf and unemerged inflorescence. There was marked ingress of unsown species in the 2nd harvest year with 3-, 4- and 5-wk intervals in 'S. 321'. The combination of 262.5 or 525 kg N/ha yr and 8- and particularly 10-wk intervals over 2 yr was too severe a treatment for the satisfactory survival of 'S. 23'. With 525 kg N and 10-wk intervals, 'S. 321' was equally badly affected. The application of 525 kg N/ha yr compared with nil reduced the proportion of green leaf in total herbage of the sown species by 11 percentage units, on average, and increased the proportion of "stem" by 12 percentage units, in the 2nd harvest year. The effect of N application on the proportion of crop fractions was found in both cultivars and in all months of harvest. The effect was much greater than in the 1st harvest year. In 'S. 23' the application of 525 kg N compared with nil in the 2nd harvest year increased the proportions of both true stem and leaf sheath (in total herbage of the sown species), true stem being the more important of the 2, in this context, with the longer intervals and leaf sheath being the more important with the short intervals. Digestibility was not in general affected by N application despite the higher proportion of stem and leaf sheath and the lower proportion of green leaf blade resulting from N application. N did, however, tend to reduce digestibility at the harvests at which the proportion of stem was highest. Digestibility varied from one time to the year to another with a constant interval between harvests, but not as much as in the previous year. Lower digestibility of leafy crops in summer and autumn than in April and early May in both years may have been partly due to a higher proportion of dead material. Three periods were distinguished approximately in both years: May-June, July-Aug. and Sept.-Oct. Only in the first of these periods was there a substantial increase in yield of digestible organic matter as a result of doubling the interval between harvests. Doubling the interval reduced digestibility in all 3 periods, but especially at harvests within the 2nd period. Yield response to N was large in the 1st period, intermediate in the 2nd, and low in the 3rd. Apparent recovery of N was low and N content of herbage unduly high in the 3rd period. N content of herbage was low with the long intervals between harvests at harvests in the first 2 periods. Applied N increased N content at these harvests and at all other times.

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