The effects of plowing under hairy vetch on the yield of cotton and on Lufkin fine sandy loam

Experiments were conducted on Lufkin fine sandy loam at College Station, Tex., from 1937 to 1942 to determine the effect of plowing under fertilized and unfertilized hairy vetch on the yield of cotton and on the soil. The application of superphosphate and potash produced highly significant increases in the yield of vetch, but had no appreciable effect on the nitrogen and phosphorus content of the vetch. Soil that received superphosphate and potash, with or without vetch, produced significantly larger yields of cotton than the untreated soil or soil on which unfertilized vetch was plowed under. The latter treatment, however, did not produce significantly larger yields than the untreated soil, although the difference in yield approached significance on the .05 level. The amount of nitrate nitrogen in the soil during the growing season was roughly proportional to the amount of nitrogen added in the treatments. The soil on which unfertilized vetch was plowed under contained significantly more nitrate nitrogen than the soil treated with 4-8-4 fertilizer, although the latter treatment produced decidedly larger yields of cotton. On the average, fallow soil contained about 60% more nitrate nitrogen than soil cropped to cotton. Soil treated with vetch and superphosphate had considerably greater nitrifying power than soil receiving other treatments. The addition of superphosphate, with or without vetch, greatly increased the amount of available phosphoric acid in the soil. The quantity of available phosphoric acid, however, varied from season to season and with the use of the land, whether devoted to cotton or left fallow. The plowing under of vetch did not increase the availability of the soil phosphorus. The plowing under of vetch increased the acidity of the soil, at least during the growing season of cotton which followed the vetch. The acidity was greater in fallowed soil than in soil cropped to cotton. The nitrifying power of the soil and the amount of available phosphoric acid were more highly correlated with the yield of cotton than was the amount of nitrates in the soil.