BIOLOGICAL FIXATION OF N2, SYMBIOTIC BACTERIA OF LEGUMES IN POLISH SOILS AND ESTIMATION OF THEIR NUMBERS

Abstract

Yields of legumionous plants, as well as other arable crops, depend on numerous environmental, agro-technical and biological factors. In the case of legumes colonization of soils with a specific group of symbiotic bacteria which fix atmospheric nitrogen is also an important factor influencing the development and yields of these crops. Results of our survey have shown that symbiotic bacteria (rhizobia) of clover, faba bean and pea commonly occur in soils of Poland, even in soil not planted to these crops for a long time. These bacteria have not been detected only in about 5% of soils (out of 80 examined) and these were light and strongly acidic (pHKCl < 4.5) soils. Symbiotic bacteria of lupine and field bean were not found in about 25% of the studied Polish soils. Symbionts of lupine were most numerous in light- and medium-textured soils with slightly acidic pH. In the majority of Polish soils symbiotic bacteria of alfalfa and soybean were not detected or their numbers were low, except those soil on which these plants were cropped recently.
Due to the lack of selective media to count root nodule bacteria in soils and other materials (inoculants) populations of these bacteria are usually assessed by indirect methods based on biotests with legume seedling inoculated with increasing dilutions of a studied soil. In this article different biotests and methods of estimation of rhizobial numbers are described.