Nutritive value of pasture: I. Seasonal variations in the productivity, botanical and chemical composition, and nutritive value of medium pasturage on a light sandy soil

Abstract

An account has been given of an investigation into the seasonal changes in the productivity, botanical and chemical composition, and nutritive value of pasture grass, the work constituting the initial stage of a comprehensive study of the nutritive properties of different types of pasture. The pasture on which the work was carried out was situated on a light sandy soil of low water-retaining capacity; the pasturage was of medium quality.Grazing was imitated by the daily use of a motor-mowing machine, the system of cutting being such as to ensure the whole plot being cut over once per week. The season was divided into ten periods, each period corresponding with the duration of a digestion trial carried out on two wether sheep. The main feature of the weather conditions during the season was the extremely low rainfall during the period from early June to mid-July.The pasture plot results were compared with corresponding results obtained from contiguous plots which were allowed to grow for hay, and from which, after removal of hay, several successive aftermath cuts were taken. The main findings of the investigation are summarised below:Seasonal changes in the botanical composition of the herbage. Although precise and systematic botanical analyses of the herbage of the pasture were not carried out, yet careful surveys made at an early and a late date in the season, together with general observations made during the whole course of the experiment, enabled interesting conclusions to be drawn in respect of the seasonal activity and persistency of the different species of grasses in the sward. During the spring season,Bromus mollis, Lolium perenne, Poa annuaandPoa trivialisaccounted for almost 80 per cent, of the herbage.

Investigations into the Intensive System of Grassland Management. By the Agricultural Research Staff of Imperial Chemical Industries, Limited. II. The Mineral Content of Intensively Treated Pasture and a Relationship Between the Nitrogen and Phosphorus Contents.

“…Under dry conditions, therefore, intensive herbage becomes ill-balanced in respect of lime and phosphoric acid, being relatively low in the latter constituent, and it is recommended that at such times a supplementary ration should be fed which is relatively rich in phosphoric acid compared with lime. A similar finding and recommendation have been made by Woodman and his associates (7,8,9,10).…”

“…The results are at variance with the general finding of others, that the lime content of pasture shows a regular seasonal variation, rising to a maximum summer value and then falling again. The phosphoric acid content of the intensive pastures is, except in the abnormally dry season of 1929, rather higher than the average values given by Godden(4) and by Orr and Thomson (17) for good cultivated 15-2 pasture, though a little lower than the values reported by Woodman and his associates (7,8,9,10) and by Griffith and Phillips(ii). The seasonal variations in the phosphoric acid content are discussed later.…”

“…by Orr and Thomson (17) for good cultivated pasture in Great Britain, a difference which may possibly be explained by a slightly lower clover content of the intensive pastures. The high clover content of the herbage also probably accounts for the values of about 1-5 per cent, obtained by Woodman and his associates (7,8,9,10) at Cambridge, on untreated pastures under systems of frequent, close cutting. The lime content is also somewhat lower than that reported by Griffith The irregular fluctuations in the lime content of the herbage from intensive pastures, with a lack of any definite seasonal trend, together with the constancy of the average values irrespective of centre or season, are not readily explained, and are matters requiring further investigation.…”

“…Cruickshank's data from four untreated Scottish pastures show a positive correlation. Moreover, a further study of the data obtained by Woodman and his associates at Cambridge (7,8,9,10) appears to show that, in pasture cuts at three-weekly intervals, there is a closer association between nitrogen and phosphorus than in cuts made at weekly or fortnightly intervals. The data obtained by Fagan and his associates (16) at Aberystwyth are less easy to appraise in this connection, since they refer separately to leaf and stem from weekly and monthly cuts of Italian rye grass.…”

Studies of grazing of crop forages by sheep

“…Furthermore, the application to free-grazing animals of maintenance requirements determined with sheep confined in respiration experiments is open to criticism. As late as 1926, values for maintenance requirements of sheep calculated independently by Armsby (1917) and by Woodman et al (1926) differed by as much as 70%. However, the classic work of Wood and Capstick (1926) resulted, from the statistical analyses of a large number of feeding experiments with sheep, in the calculation of maintenance requirements which have been widely used, with only minor modifications, since that date.…”