NITRIFICATION IN NUTRIENT SOLUTIONS WITH LOW LEVELS OF POTASSIUM

Abstract

An active culture of nitrifying bacteria was established by adding moist garden soil to a high-K nutrient solution and incubating the system at room temperature with adequate aeration. By a succession of transfers into a low-K nutrient solution the soil particles were eliminated and the K level reduced to 0.40 p.p.m. Inoculum from this soil-free, low-K nitrifying culture was then used to study nitrification in buffered nutrient solutions that contained even less K.When the nutrient solutions contained 0.40 p.p.m. K or more, there was no effect of the K level on the nitrification of NH4 added as (NH4)2SO4. Nitrification was impaired, however, when the K level was less than 0.35 p.p.m. In a solution that contained virtually no K there was negligible nitrification after a second transfer was made to eliminate the K added by the original inoculum. Under these conditions, the number of nitrifying bacteria apparently decreased, but some of them persisted for at least 48 days. Upon the addition of K, nitrification occurred to about the same extent as if ample K had always been present.