A fixação do nitrogênio do ar pelas bactérias que vivem associadas com as leguminosas crotalária e mucuna

Catani, R. A.; Gargantini, H.; Gallo, J. Romano

doi:10.1590/S0006-87051955000100001

Resumos

Com a finalidade de conhecer a quantidade de nitrogênio fixado simbiòticamente por crotalária (Crotalaria juncea, L.) e mucuna anã (Stizolobium deeringianum, Bart.) e a influência de alguns fatôres sôbre o fenômeno, instalou-se uma experiência em vasos de Mitscherlich contendo solo tipo terra roxa misturada. Os tratamentos empregados foram os seguintes : 1) testemunha ; 2) NPK ; 3) NPK + calcário ; 4) NPK + inoculante ; 5) NPK + calcário + inoculante; 6) PK + calcário; 7) PK + calcário + inoculante. Dois meses após a germinação das sementes colheu-se o material para análise, dosando-se o N nas raízes e nas partes vegetativas das plantas. Nessa ocasião foram tiradas diversas fotografias, para documentação comparativa da nodulação das raízes nos diversos tratamentos.

A study was made of nitrogen fixation by bacteria in association with crotalaria (Crotalaria juncea L.) and velvet bean (Stizolobium deeringianum Bart). The experiment was performed according to the Mitscherlich pot technique. Three replications of each of the following treatment were made : 1) check ; 2) NPK ; 3) NPK + limestone ; 4) NPK + inoculation ; 5) NPK + limestone + inoculation ; 6) PK + inoculation ; 7) PK + limestone + inoculation. The amount of nitrogen, phosphorus, potassium, and limestone added to the pots that received these elements were as follows : 2.0 g of N in the form of NH4 NO3 ; 2.2 g of P2O5 as K2HPO4 ; 3.0 g of K2O as K2 HPO4 and KCl; 15 g of a dolomitic limestone in order to increase base saturation in the soil to 60 per cent. Inoculation of the seeds was made with a Rhizobium from the cowpea group. The plants were allowed to grow for two months and were then cut, dried at 60° C, and weighed. The roots were dug, washed carefully, and photographed to show the differences in nodule formation (figures 1 and 2). Nitrogen was determined separately in the stems with leaves and in the roots. This element was also determined in soil samples from treatments n.° 6 and n.° 7 prior to planting and after the plants had been removed from the pots. The data obtained indicated that nitrogen had not been absorbed from the soil. The amount of nitrogen fixed per pot by the nodule bacteria is given below : Treatment Nitrogen fixed by Crotalaria Velvet bean (g) (g) N.º 6 (PK + limestone) ------------------------------------------------------------- 0,52 1,18 N.° 7 (PK + limestone + inoculation) -------------------------------------------- 0,74 1,20

A fixação do nitrogênio do ar pelas bactérias que vivem associadas com as leguminosas crotalária e mucuna(^*)

Nitrogen fixation by bacteria in association with crotalária and velvet bean

R. A. Catani; H. Gargantini; J. Romano Gallo

Engenheiros agrônomos, Secção de Agrogeologia, Instituto Agronômico

RESUMO

Com a finalidade de conhecer a quantidade de nitrogênio fixado simbiòticamente por crotalária (Crotalaria juncea, L.) e mucuna anã (Stizolobium deeringianum, Bart.) e a influência de alguns fatôres sôbre o fenômeno, instalou-se uma experiência em vasos de Mitscherlich contendo solo tipo terra roxa misturada. Os tratamentos empregados foram os seguintes : 1) testemunha ; 2) NPK ; 3) NPK + calcário ; 4) NPK + inoculante ; 5) NPK + calcário + inoculante; 6) PK + calcário; 7) PK + calcário + inoculante.

Dois meses após a germinação das sementes colheu-se o material para análise, dosando-se o N nas raízes e nas partes vegetativas das plantas.

Nessa ocasião foram tiradas diversas fotografias, para documentação comparativa da nodulação das raízes nos diversos tratamentos.

SUMMARY

A study was made of nitrogen fixation by bacteria in association with crotalaria (Crotalaria juncea L.) and velvet bean (Stizolobium deeringianum Bart).

The experiment was performed according to the Mitscherlich pot technique. Three replications of each of the following treatment were made : 1) check ; 2) NPK ; 3) NPK + limestone ; 4) NPK + inoculation ; 5) NPK + limestone + inoculation ; 6) PK + inoculation ; 7) PK + limestone + inoculation. The amount of nitrogen, phosphorus, potassium, and limestone added to the pots that received these elements were as follows : 2.0 g of N in the form of NH₄ NO₃ ; 2.2 g of P₂O₅ as K₂HPO₄ ; 3.0 g of K₂O as K₂ HPO₄ and KCl; 15 g of a dolomitic limestone in order to increase base saturation in the soil to 60 per cent. Inoculation of the seeds was made with a Rhizobium from the cowpea group.

The plants were allowed to grow for two months and were then cut, dried at 60° C, and weighed. The roots were dug, washed carefully, and photographed to show the differences in nodule formation (figures 1 and 2). Nitrogen was determined separately in the stems with leaves and in the roots. This element was also determined in soil samples from treatments n.° 6 and n.° 7 prior to planting and after the plants had been removed from the pots. The data obtained indicated that nitrogen had not been absorbed from the soil.

The amount of nitrogen fixed per pot by the nodule bacteria is given below :

Treatment Nitrogen fixed by

Crotalaria Velvet bean

(g) (g)

N.º 6 (PK + limestone) _{-------------------------------------------------------------} 0,52 1,18

N.° 7 (PK + limestone + inoculation) _{--------------------------------------------} 0,74 1,20

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LITERATURA CITADA

Recebido para publicação em 31 de julho de 1954

Referências bibliográficas

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