Soil properties in relation to the occurrence of grass sickness in horses

Abstract

Any conclusions drawn from the foregoing results will of course apply only to the necessarily limited range of soils in one county. This range is limited geologically and the Aberdeenshire soils belong largely to the class of light to medium acid soils of low base status. The results for these soils indicate that:(a) The occurrence of grass sickness is not confined to soils of any particular geological origin.(b) The range of textural conditions in the soils examined is a wide one covering loams, sands and peaty types with a few moderately heavy soils. There does not appear to be any relationship between soil texture and the incidence of grass sickness.(c) The soils examined all fall into the class of acid soils and in only a very few—about 5 to 10%—could the addition of lime be considered unnecessary from the general agricultural point of view. As against this there are no striking abnormalities in the ratios of exchangeable or readily soluble cations in the soils, which might serve as a clue to the occurrence of grass sickness. Although little is known of the actual magnesium, manganese and strontium requirements of hay and pasture plants, the range of values covered in the soils examined is sufficiently wide to make it very unlikely that there is any relationship between the incidence of grass sickness and the magnesium, manganese or strontium contents of the soil. In view of the relatively widespread acidity in the soils examined, the possibility of a relationship between the occurrence of grass sickness and soil acidity has to be borne in mind. It would be of value to find out if grass sickness occurs to an appreciable extent on limestone soils, or on soils which have been systematically limed and which have pK values in the neighbourhood of 7.(d) The majority of the soils are, from the general agricultural point of view, somewhat low in readily soluble or available potash and phosphate, but against this about 30% of the soils have satisfactory phosphate contents and about 20% of the ordinary surface soils and 46% of the top 2 in. samples, in which occur the bulk of the plant roots, have satisfactory potash contents. It does not appear likely therefore that the occurrence of grass sickness is to be related directly to the phosphate and potash contents of the soil. As far as reserves of the common plant foods are concerned there is likewise no abnormality which could account for the disease.