Significant increase of soybean yield with Bradyrhizobium of high efficacy inoculated, pre-inoculated with or without fungicides in Venado Tuerto (Santa Fe Province).

Professionals in charge: Nari, Claudia; R. Rossi, (NIDERA S.A.) A. Perticari; J. C. Pacheco Basurco; B. Stegman y M. F. G. Fiqueni. (IMYZA-CNIA INTA Castelar) Daniel Servidio. (Laboratorios Biagro S. A.)

Introduction: In Santa Fe Province, during the agricultural cycle (C.A.) 1998/1999 2, 3 million hectares were planted with soybean. Of these, 320,000 hectares belonged to Venado Tuerto. Producers and technicians in the area say they do not generally inoculate soybean seeds due to the spontaneous nodulation of the crops. INTA IMYZA is conducting studies to evaluate the strains in soils with naturalized populations in the North and West of Buenos Aires (1) and the northwestern region of the country (2). Under these conditions, some response was observed in crop yield and biomass at harvest time with the application of some specific strains (1 y 2) and a preinoculation of the seeds (2). Taking into account the previous information and under request from NIDERA S.A., it was decided to conduct studies of selection of strains in this soybean cultivated area.

Objectives:
1- Determine the symbiotic capacity of native/naturalized isolations of the northwestern compared to the E109 strain and others of the IMYZA collection.
2- Validate the preinoculation method alone or with the application of seed cures as an alternative method.

Materials and methods: Strains: E109 y E212: Bradyrhizobium japonicum; E142: B. elkanii; E155 y E210: B. spp; Inoculation: the inoculant used was a commercial sterile peat-based one, prepared with the E109 strain. It supplied 1.10 rhizobia per seed approximately. Preinoculation: INTA-BIAGRO Protocol. Fertilization: 400 NU applied in Urea form in equal 1 parts in V3, V4, R2 and R3 states. Treatment with fungicides: contact fungicides (thiram 16% oily) and contact plus systemic (thiram+carboxim 20% Flo) were used. The trial was carried out in NIDERA S.A.'s experimental field situated in Venado Tuerto in a soil with an agricultural potential equal to 1, fertilized with 50 U of P2 O5. The soybean seed (Glycine max (L) M) used was A6445RG from NIDERA maturity group 6. The experimental design was in random blocks with 5 repetitions. The size of the experimental units: 4 rows of 6 meters long. The results were examined by means of an analysis of the variance and the comparison of the averages through the LSD Turkey test.

Evaluated parameters: Nodulation, Grain and Total Biomass yield.

Results:
Nodulation: the treatments with preinoculated E109 alone and/or with contact fungicide plus systemic, are the only ones that differ from the control.
Grain yield: E109 and E155 strains are the only ones that surpass the uninoculated control. Among the treatments with E209, the one preinoculated and cured with contact fungicide plus systemic produced a significantly better yield than the treatments preinoculated without fungicide and inoculated with contact fungicide. The treatments fertilized with 400 N U, as well as the ones inoculated with the E142, E210 and E212 strains, do not differ from the uninoculated control. There are no differences between the preinoculated E109 without curing and the commercial treatment.
Total Biomass at harvest time: The treatment preinoculated with E109 and cured with contact fungicide plus systemic surpasses the rest of the treatments. The E109 strains inoculated with E142, E155, and E210 fungicide differ from the control in this parameter.

Conclusions:

it is feasible to obtain concrete benefits with the inoculation of soybean in soils situated in Venado Tuerto, with moderate levels of naturalized populations of rhizobia, if the strains used are the selected ones for their high efficiency and the technology applied is the correct one.

Thanks to: NIDERA S.A.'s field personnel and to Mr. Rubén Arizmendi form INTA IMYZA. The present piece of work was done within the INTA-BIAGRO agreement.