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

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 japonicumand 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‐[{(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 N2fixation 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−1seed reduced shoot N yield at anthesis but a lower rate of thiram (0.54 g kg−1seed) 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 N2fixation 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.

Effect of soil interacting herbicides on soybean nodulation in Balcarce, Argentina

“…Differences in nodulation atributes between treated and control plots (Figs. 2 and 3) were not evident on yield or N accumulation, probably because the soybean plants assimilated more soil N to compensate for eventually lower N 2 fixation rates as demonstrated by Rennie et al (1982) and Rennie & Dubetz (1984).…”

“…Hence, the inoculated seed has to provide the incoming rhizosphere with enough microorganisms to nodulate and fix nitrogen. Under these conditions, the successful inoculation is critical for the establishment of the symbiosis (Rennie & Dubetz, 1984). The infective phase of the symbiosis begins just before the contact occurs between bacteria and root hairs (Fisher & Long, 1992) and during this period, the association is highly sensitive to the soil environment (Keyser et al, 1993).…”

Rhizobium inoculant and seed-applied fungicide effects on field pea production

“…Granular inoculants, which are placed in the seed row in close proximity but not necessarily in contact with fungicide treated seed, would therefore be expected to be less affected by fungicide. This was true for Captan, Thiram and carbathiin application on soybean seed in Alberta, where nodulation, N 2 fixation and seed yield were not affected when granular inoculant was used (Rennie and Dubetz 1984). In two field experiments with fungicidetreated bean seeds, granular inoculant showed greater nodule number and nodule fresh weight than the seed-applied or lime-pelleted inoculants (Graham et al 1980).…”

Herbicidas na nodulação e na atividade da nitrogenase em cultura de amendoim

“…No inoculado, essa fixação foi 4,6 vezes maior que a fixação da testemunha. RENNIE & DUBETZ (1984) verificaram que linuron aplicado em pré-emergência, na cultura da soja, reduziu significativamente a fixação do nitrogênio, enquanto trifluralin estimulou a fixação no primeiro ano e não teve nenhum efeito no ano seguinte. BOLLICH et al (1985) relataram que a aplicação de alachlor (2,2kg/ha) em solo arenoso acarreta diminuição na produção de C 2 H 4 /planta/hora, o que não ocorreu nesse caso até 50 dias.…”