Bradyrhizobia and rhizobia are symbiotic bacterial partners forming nitrogen fixing nodules on legumes. These bacteria share characteristics with plant growth promoting rhizobacteria (PGPR). Nodule inducing bacteria, like other PGPR, are capable of colonizing the roots of non-legumes and produce phytohormones, siderophores and HeN. They also exhibit antagonistic effects towards many plant pathogenic fungi. The potential of nodule inducing bacteria to function as PGPR, was examined by using radish as a model plant. Three percent of the 266 strains tested were found to be cyanogens, while a majority (83%) produced siderophores. Fifty eight percent of the strains produced indole 3-acetic acid (IAA) and 54% solubilized phosphorus. Some of the bacterial species examined were found to have a deleterious effect while others were neutral or displayed a stimulatory effect on radishes. Bradyrizobium japonicum strain Soy 213 was found to have the highest stimulatory effect (60%), and an arctic strain (N44) was the most deleterious, causing a 44% reduction in radish dry matter yield. A second plant inoculation test, performed in growth cabinets, revealed that only strain Tal 629 of B. japonicum significantly increased (15%) the dry matter yield of radish. This indicates that specific bradyrhizobia have the potential to be used as PGPR on non-legumes.
Lalande, R., Gagnon, B., Simard, R. R. and Côté, D. 2000. Soil microbial biomass and enzyme activity following liquid hog manure application in a long-term field trial. Can. J. Soil Sci. 80: 263-269. Liquid hog manure (LHM) addition to soils in corn silage (Zea mays L.) production may benefit microbial activity by providing C and other nutrients. The objective of this study was to compare the effects of a LHM application to that of inorganic fertilizers (IF) on the biological activity of a Le Bras silt loam soil (Humic Gleysol) under continuous corn production and LHM fertilization. Amounts of 0 to 120 m 3 LHM ha -1 and 150 N-150 P 2 O 5 -150 K 2 O kg ha -1 were applied to silage corn. The 0-to 15-cm and 15-to 30-cm soil layers were sampled 28 d after the 18th yearly LHM application. The LHM inputs, particularly at 90 m 3 ha -1 , resulted in higher enzyme activities and microbial biomass C (MBC) than IF or the unamended control in the 0-to 15-cm soil layer. The 90 m 3 LHM ha -1 also gave higher microbial biomass N (MBN) than IF in this soil layer. Application of LHM had no effect on the activities of the enzymes studied or on the MBC and MBN contents in the 15-to 30-cm layer. Ammonifier population was highest with 60 m 3 LHM ha -1 in both soil layers. Nitrifier population was not affected by LHM in the top soil layer, but was linearly increased by LHM rates in the 15-to 30-cm layer. This study showed that LHM addition may enhance enzyme activities, microbial biomass and the N mineralizer population in the plow layer of a soil in a corn silage monoculture. , a produit des activités enzymatiques et un C de la biomasse microbienne supérieurs au témoin non amendé ou à la fertilisation inorganique dans la couche de sol 0-15 cm. Le LP à 90 m 3 ha -1 a aussi procuré un N de la biomasse microbienne plus élevé que les engrais minéraux dans cette couche de sol. L'apport de LP n'a pas eu d'effet sur l'activité des enzymes étudiés dans la couche 15-30 cm et sur son contenu en C et N de la biomasse microbienne. La population d'ammonificateurs a été la plus élevée avec 60 m 3 LP ha -1 dans les deux couches de sol. La population de nitrificateurs n'a pas été affectée par LP dans la couche 0-15 cm mais a augmenté linéairement avec la dose de LP dans la couche 15-30 cm. Cette étude a démontré que l'apport de LP peut favoriser l'activité enzymatique, la biomasse microbienne et la population minéralisatrice du N de la couche de labour d'un sol en monoculture de maïs-ensilage.
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