Effects of mineral nitrogen and soil temperature on nitrogen fixation of field beans (Phaseolus vulgarisL.)

Abstract

In two greenhouse experiments, one in sterilized Leonard jars with sand and one in pots with a Red-Yellow Podzolic soil, the effects on nodulation and nitrogen fixation of low mineral nitrogen applications, were studied at two soil temperatures in field beans. Application of 23 ppm of N at planting and 20 days after, in Leonard jars avoided the hunger stage after the seed reserve had been exausted. Due to much faster initial plant growth, nodule numbers and nodule weight increased with mineral nitrogen. The same amount of N applied to soil did not affect nodulation or plant growth. Twice the amount of mineral N (46 ppm) increased plant growth, especially at the higher soil temperatures. In the cooled post some of the strains fixed nitrogen equivalent to the mineral N application of 45 ppm (92 kg/ha). Soil temperatures above 32°C (daily maxima) decreased nodule efficiency, but some strains were able to compensate by an increase in nodule number and size at the higher soil temperature.