Effects of spray inoculation equipment on the viability of Rhizobium spp. in liquid inoculants for legumes

Abstract

Pumping equipment designed for seedbed inoculation of legumes with liquid inoculants was set up on a test bed in the laboratory. Experiments, in which liquid inoculant was circulated through the equipment, were conducted to determine the effect on inoculant viability of variables likely to be encountered when farmers used the equipment in the field. Provided that peat cultures of Rhizobium spp. were used to make liquid inoculant, neither pump type, operating pressure up to 173 kPa, water temperature up to 35¦C, nor water impurity up to a level equivalent to 170 ¦S/cm conductivity seriously reduced inoculant populations during the first hour of treatment, although a significant decline in numbers occurred in three out of 16 experiments. When inoculant was exposed to the various treatments for long periods, a significant loss of viability occurred, in 7 out of 13 experiments, between 4-8 h. R. meliloti was least affected by treatment and R. leguminosarum most affected, but this may have been due to strain differences as much as to species differences. Liquid inoculants which were made from broth cultures lost viability very quickly. R.. meliloti liquid inoculant, prepared from a peat culture and introduced by spraying into a dry soil of neutral pH in the absence of any host plant, did not lose viability during a period of four weeks. The spray inoculation equipment was also used successfully in a field experiment to add water to the seedbed to aid in the germination of soybean seed sown into drying soil.