Reduction of nodule numbers and growth, produced by the addition of sodium nitrate to lucerne in sand culture

Abstract

A sand-culture experiment with inoculated lucerne was made to test the effect of increasing doses of sodium nitrate upon the yield and nitrogen content of tops and roots, and upon the number and development of nodules. The pots were divided into six series receiving from 0 to 10 gm. of sodium nitrate per pot containing 12 kg. of sand. There was no correlation between yield or nitrogen content of the lucerne, and the dose of nitrate. The number of nodules, though unaffected by 1 gm. of sodium nitrate, was progressively decreased by the stronger doses. The length of nodules was reduced about 30 per cent, by 1 gm. of sodium nitrate, and decreased progressively with stronger doses. Nodules were found to show a definite relationship between their overall length and the volume of contained bacterial tissue. Using this relation, the mean volumes of bacterial tissue per nodule and per pot for each series were calculated. The reduction effected by nitrate was far greater when measured in this way, owing to the small contribution of bacterial tissue derived from nodules less than 1·5 mm. in length.