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The Effect of Fertilization on the Nutritive Value of Pasture Grass

Macdonald College, Quebec

Abstract

The nutritive value of pasture herbage has been given an important place in agricultural investigational work during recent years. From these studies and from general observance of grasslands, it is evident that a great deal of variability exists in the nutritive value of different pastures. Furthermore, it has been amply demonstrated in much of the experimental work that the application of fertilizers to pastures increases the nutritive value of herbage.

The question of the change in the constitution of the herbage which is responsible for this difference or change in nutritive value offers a problem which has not as yet received much attention.

It is generally agreed that fertilization brings about an increase in the percentage of protein and minerals (Ca and P) and a reduction in the percentage of fibre in the herbage, and it is thus assumed by many investigators that these changes are responsible for the increase in nutritive value resulting from fertilization. It is possible, however, and from the literature on the subject fairly evident, that pasture herbage under average natural conditions contains sufficient total protein and minerals (Ca and P) to meet the requirements of grazing animals.

Fibre is generally considered a dilutent to other nutrients in the diet on account of its low coefficient of digestibility. It would, therefore, appear that a reduction in the percentage of fibre would increase the digestibility of the organic matter and thereby increase the energy value of the herbage. It is found, however, that the application of fertilizer decreases the percentage of dry matter in the herbage thus offsetting an increase in digestibility, and causes no increase in the energy value of the herbage diet.

It, therefore, seems evident that the increase in nutritive value of pasturage as a result of fertilization and observed differences in the nutritive value of different pastures cannot be explained on the basis of the ordinary chemical feeding stuffs analysis.

This paper reports a study of the nutritive value of fertilized versus unfertilized pasture herbage, with particular reference to the quality of the protein, as measured by comparative feeding trials.

Significant differences in nutritional worth were found not only between certain pure species of grasses (Timothy and Reed Canary Grass) but also between the mixed herbage of fertilized and unfertilized pastures, which could not satisfactorily be explained on the basis of the usually advanced theories, viz. energy value, protein level or mineral (Ca and P) content of these feeds.

From the results obtained in these studies, the conclusions seem warranted that (1) quality of protein (amino acid balance) may be an important factor determining the nutritive value of pasture herbage and (2) the improvement in feeding value of such herbage brought about through fertilization may be the result of a change in the constitution of its proteins.