Fixação do nitrogênio do ar pelas bactérias que vivem em simbiose com as raízes da centrosema Translated title: Fixation of the atmospheric nitrogen by bacteria which live symbiotically on centrosema

Abstract

Continuando a série de trabalhos sôbre a quantidade de nitrogênio atmosférico fixada por bactérias que vivem em simbiose com raízes de leguminosas, são relatados os resultados encontrados em centrosema (Centrosema pubescens Benth). Foram utilizados vasos de Mitscherlich, com terra-roxa-misturada. A colheita das plantas foi efetuada por ocasião do florescimento. A parte aérea foi pesada para cálculo da quantidade de massa verde produzida, e, em seguida, juntamente com as raízes, sêca a 60°C até pêso constante. Determinaram-se os teores de nitrogênio na parte aérea e subterrânea das plantas, assim como da terra dos vasos. Os resultados mostraram elevada capacidade de fixação simbiótica de nitrogênio pela centrosema correspondente a cêrca de 204 quilogramas de nitrogênio por hectare.

Translated abstract

Following a series of research work with the purpose of verifying the amount of atmospheric nitrogen fixed by symbiotic bacteria, the authors report in this paper the results on their research with the leguminous plant Centrosema pubescens Benth. This experiment was conducted in Mitscherlich pots containing terra-roxa-misturada obtained from a 20 cm deep layer of soil taken from the Central Experiment Station "Theodureto de Camargo", in Campinas. The plants were cut in the blooming period, as this is the proper season for turning over green manure crops. The aerial portion of the plants was weighed so as to determine the total production of green matter and then it was dried together with the roots at 60°C. Thus, nitrogen of the total plant was determined and the same analysis was done at the end of the experiment for the soil removed from the pots. According to the results of this experiment, it was found that 204 kilograms of nitrogen per hectare were fixed, showing therefore that centrosema has a high capacity of symbiotic nitrogen fixation.