The Utilization of Sulphate and Sulphur Dioxide for the Sulphur Nutrition of Alfalfa.

Though sulphur has long been recognized as an essential element in plants, particularly as a constituent of the proteins, it has not received much consideration in fertilizer studies. As shown by the work of HART and PETERSON (3), this was partly due to the older practice of determining sulphur in the ash of vegetation, which gave low results and did not indicate the true sulphur needs of the plants. In practical agriculture, sulphur deficiency has probably been uncommon, at least during the last century, because of important additions of the element from the atmosphere, and important, though unintentional, additions in commercial fertilizers. Regions of sulphur deficiency, however, have been shown to exist in the Pacific Northwest (6), in Western Canada, and in Northern Minnesota (2). The location of these regions where winds from industrial areas seldom blow, seems to emphasize the importance of atmospheric sulphur in supplying the needs of those regions in which there is industrial activity and favorable prevailing winds. ALWAY (1) has given an historical review of sulphur in agriculture in his presidential address to the American Society of Agronomy, in which this viewpoint was advanced and in which it was suggested that part of the sulphur requirements of plants might be supplied by direct absorption of sulphur dioxide into the leaves, as well as indirect absorption after the gas has been taken into the soil and changed to sulphate. SETTERSTROM, ZIMMERMAN, and CROCKER (8) have submitted evidence that sulphur dioxide can increase the growth rate of sulphur-deficient plants. In this paper a study has been made, using the large sand-culture installation (9), of the sulphur needs of alfalfa, and the possibility has been explored of substituting sulphur dioxide for sulphate as the source. The experiments were planned to determine the effect of sublethal concentrations of sulphur dioxide on the growth of alfalfa under a wide range of conditions-such as different hydrogen ion concentrations and different concentrations of the principal nutrient elements. In particular, the effects of sulphur. dioxide on sulphur-deficient vegetation were sought.