Effect of applications of fine limestone. I. The yield and nitrogen content of sweet clover and alfalfa grown on Shelby loam and Clinton silt loam

Two acid Iowa soils, namely, Shelby loam and Clinton silt loam, were selected for a greenhouse investigation of the effects of small amounts of fine limestone applied in the row with the seed upon the yield and nitrogen content of sweet clover and alfalfa. The experiments were set up on a statistical basis and all boxes completely randomized. The plants were analyzed for total nitrogen by the Kjeldahl method. The data obtained for the dry weight and nitrogen content of the plants were analyzed statistically according to the method of analysis of variance. Limestone, irrespective of the method of application, did not depress the early growth of sweet clover or alfalfa grown on Shelby loam. Early plant growth was retarded, however, on Clinton silt loam when limestone was applied in the row or broadcast. In general, fine limestone applied in the row on Shelby loam promoted plant growth, as measured by height, and this was the case also with full applications of lime applied broadcast. Shelby loam which received the full limestone application produced highly significantly greater yields of sweet clover and alfalfa than the same soil receiving limestone in the row or beside the row. The nitrogen content of the plants showed an even greater difference in favor of the fully limed soils. The statistical analysis showed that the total dry weight and total nitrogen content of sweet clover and alfalfa grown on the untreated soils employed in this experiment were highly significantly less than those secured on the soils receiving limestone. One exception to this was found when limestone was applied beside the row on Shelby loam. In that instance no greater yields were obtained than were secured on the untreated soil. There was a greater number of nodules present on the roots of plants grown on fully limed soils than on any of the other variously treated soils. The general trend of the results was for both the percentage of nitrogen and the total nitrogen content of the plants grown on Shelby loam to increase with the following order of treatments: No treatment, limestone beside the row, limestone in the row, and full lime. The application of small amounts of fine limestone in the row greatly benefits the growth of sweet clover and alfalfa on Shelby loam and Clinton silt loam. No movement of limestone was found as measured by determinations of pH made 120 days after the beginning of the experiment. This would indicate that the area most favorable for nitrogen fixation would be very small since fixation is greater in soils near neutrality. The beneficial effects of small applications of fine limestone applied in the row are greater when measured by the total dry weight of the plants than when measured by the nitrogen content of the plants. Apparently, such treatments improve the conditions necessary for plant growth to a greater extent than they affect the nitrogen fixation.