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This article in AJ

  1. Vol. 76 No. 3, p. 451-454
     
    Received: May 20, 1983


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doi:10.2134/agronj1984.00021962007600030019x

Effect of Fungicides and Herbicides on Nodulation and N2 Fixation in Soybean Fields Lacking Indigenous Rhizobium japonicum1

  1. R. J. Rennie and
  2. S. Dubetz2

Abstract

Abstract

Growing soybeans [Glycine max (L.) Merr.] under irrigation requires the use of herbicides and seed-applied fungicides to control weeds and root diseases. Soils in southern Alberta contain no indigenous Rhizobium japonicum and thus inoculation is essential to the establishment of a successful N2-fixing symbiosis in soybeans. Unfortunately, these chemicals may be incompatible with survival of the inoculated rhizobia. Accordingly, an evaluation was made of the effects of three seed-applied fungicides, captan {N-I{(trichloromethyl) thio]-4-cyclohexene-l,2-dicarboximidef, thiram [bis(dimethylthiocarbamoyl)disulfide], and carbathiin (5,6,-dihydro- 2-methyl-l,4-oxathiin-3-carboxanilide); four herbicides applied as preplant incorporated, chloramben (3-amino-2,5-dichlorobenzoic acid), linuron [3-(3,4-dichIorophenyl)-l-methoxy-l-methylurea], metribuzin [4-amino-6-tert-butyl-3-{methylthio)-as-triazin-5(4H)-on], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine); and one post-emergence herbicide, diclofop |2-[4-(2,4-dichlorophenoxy) phenoxy]propanoic acid}, on shoot N, seed yield, nodulation, acetylene-reducing activity (ARA), and 15N-determined N2 fixation of soybean line ‘King Grain X005’ inoculated with granular rhizobial inoculant. The soil was an irrigated Chin loam (Typic Haploboroll).

None of the fungicides or herbicides affected seed yield. Thiram and captan applied at 1.0 g kg−1 seed reduced shoot N yield at anthesis but a lower rate of thiram (0.54 g kg−1 seed) increased N yield. None of the fungicides affected ARA. Metribuzin applied at recommended rates caused erratic germination. Linuron significantly reduced ARA whereas trifluralin stimulated it in 1 year but had no effect in the other year. This alteration in ARA was not reflected in N or seed yield. 15N isotope dilution at levels of 15N natural abundance showed the plant received approximately 50% of its N from N2 fixation at anthesis, and in agreement with ARA, showed no effect of chemical when proper rates were applied. We conclude that these herbicides and seed-applied fungicides have no effect on nodulation and N] fixation under these experimental conditions when granular inoculant is applied.

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