Efficiency of inoculation by nodule bacteria of alfalfa grown in mixture with smooth bromegrass at various rates of phosphorus and potassium nutrition

Under the conditions of pot experiment it was studied the efficiency of alfalfa inoculation by nodule bacteria Sinorhizobium meliloti B-7411 while growing alfalfa in mixture with smooth bromegrass at varying norms of phosphoric-potassium nutrition. It was found that symbiotic alfalfa systems that were formed with the strain S. meliloti B-7411 differed in N 2 assimilation rate depending on dosage of phosphorus and potassium nutrition (PK), but had similar dynamics of increase of this index from stems formation to flowering stage. A number and weight of root nodules on alfalfa, at double dose of PK was reduced, which led to a decrease of biological atmospheric nitrogen fixation. The highest level of N 2 assimilation by alfalfa root nodules was found in the periods of stems formation, budding and flowering at the background of 1 norm phosphorus and potassium (by Helrigel), and the decrease of this index in 2.6, 3.6 and 2.9 times observed at the corresponding stages at the background of 2 norms of PK. Bacterization of alfalfa seeds contributed to the growth of the aboveground plant mass of both mixture components. The greater yield of green mass and dry matter was obtained in treatments with presowing inoculation of seeds by rhizobia S. meliloti В-7411 and with 1 dose of phosphorus and potassium without inoculation as compared to treatments with higher doses of PK (1.5 and 2 n). Positive dynamics of aboveground mass growth of smooth bromegrass was also observed during its cultivation in mixture with alfalfa, for different rates of input of phosphorus and potassium. At the same time, the smallest values of plants green mass growth of the grass component of mixture were also obtained for the double norm of PK.