The effect of different methods of inoculation on the yield and protein content of alfalfa and sweet clover

Studies have been carried on in two successive seasons (1914 and 1915) of the effect of inoculation by various methods at seeding time upon the yield and composition of the crops grown in the second, third, and fourth, seasons thereafter, on three different fields of University Farm, St. Paul, Minn. In this and in the preceeding paper of the same title, data are presented which show (a) the yield and protein content of the three successive cuttings in each of the two years from fourteen inoculated plots and the nine adjacent uninoculated check plots of alfalfa; (b) the yield and protein content of one year's crop from two inoculated and three uninoculated sweet clover plots; and (c) two successive seasons' analyses of the tops and roots from 3 square yards each of inoculated and uninoculated alfalfa and sweet clover. These data point clearly to the following conclusions with reference to the effect of inoculation upon the yield and composition of these leguminous crops when grown on soils of the type represented by those on University Farm. Inoculation at seeding time produces a very large increase in yield of dry matter per acre and in the percentage of protein in the dry matter in the second season thereafter (first harvestable crop), as compared with yield and composition of the crop from adjacent uninoculated plots. In the next season's growth (second harvestable crop), the differences are much less noticeable and they practically disappear in the following year, by reason of the rapid spread of the inoculating bacteria to the uninoculated plots. Inoculation of either alfalfa or sweet clover with soil from fields on which either alfalfa or sweet clover has been growing successfully is equally efficient in producing these effects. Inoculation with soil is generally more efficient in these respects than inoculation with the commercial culture which were used in our experiments. Liming the soil at seeding time (2 tons ground limestone per acre) slightly intensifies the above-mentioned effects of inoculation. One effect of inoculation is to give to the inoculated plants an increased capacity to utilize mineral soil nutrients, the increased growth resulting in the removal from the soil of very much larger amounts of potassium, phosphorus, and calcium. A second effect of inoculation is to make it possible for the inoculated plants to elaborate a somewhat larger amount of dry matter from a given amount of mineral plant food elements.