BIOLOGICAL AND AGRONOMIC ASPECTS OF LEGUME INOCULATION IN ISRAEL

Abstract

Inoculants prepared for farm use consist of cultures of rhizobial strains selected for their invasiveness and effectivity in greenhouse and field trials. The acetylene reduction assay, hemoglobin content of nodules and plant nitrogen content were used for evaluation of nitrogen fixation intensity. An autoclaved local enriched peat constituted a very suitable substrate for all fast-growing rhizobia, but was often toxic to slow-growing ones. This was overcome by culturing the slow-growing rhizobia together with fast-growing (non-infective), slime-producing bacteria. Chemically treated and fragile seeds, e.g. common bean or peanut, were inoculated by applying the bacterial suspension directly into the planting furrows. For soils not bearing local specific rhizobia, relatively small amounts of inoculant (100–500 g/ha) were sufficient for adequate nodulation. However, to overcome competition of native rhizobial population, it was often necessary to use greatly increased amounts of inoculant. The effect of irrigation regimes commonly used in Israel on success of inoculation, rate of nodulation, and plant vegetative and reproductive development was investigated. In nitrogen-poor soils, symbiotic nitrogen fixation could not only substitute for mineral nitrogen, but even provide higher yields than nitrogen fertilization. A high content of available soil nitrogen may lead to serious difficulties in legume inoculation practice. Ways of overcoming these difficulties were examined. In certain soils fertilization with adequate amounts of phosphorus was found to be a prerequisite for proper nodulation and symbiotic nitrogen fixation. In calcareous and alkaline soils, application of iron chelate was necessary for N 2 fixation to occur.