SOME CHARACTERISTICS OF SYMBIOTIC NITROGEN-FIXATION, YIELD, PROTEIN AND OIL ACCUMULATION IN IRRIGATED PEANUTS (ARACHIS-HYPOGAEA L)

The potential of peanuts for symbiotic nitrogen fixation is considerable and under optimal edaphic and climatic conditions it reached 222 kg N2/ha, which was 58% of the nitrogen accumulated in the plants. The effect of the Rhizobium inoculation on crude protein accumulation in the yield (kg/ha) was 3-4 times greater than its effect on the yield of pods and hay. There was an inverse relationship between the protein and oil content in the kernels. Seasonal changes in nitrogenase activity in the nodules were determined by the acetylene reduction method during two growing seasons. Under favorable conditions the specific activity of the nitrogenase reached a very high level (up to 975 μmoles C2H2 g dry wt nod/h) and the total activity (μmoles C2H4/plant/h) was also high in spite of the relatively poor nodulation (weight and number). The high activity was drastically reduced (to 75 μmoles C2H4 g dry wt nod/h) due to exceptionally hot and dry weather, which occurred in the middle of the second half of the growing season. It appears that N2-fixation (nitrogenase activity) is more sensitive to these unfavorable conditions, than is nodule growth. Maximum nitrogenase activity was observed during the podfilling stage; until 50-60 days after planting, nitrogenase activity was very low. © 1979 Martinus Nijhoff, The Hague/Kluwer Academic Publishers.