Abstract
Two trials were performed in Balcarce, Argentina (37° 45' LS; 58° 18' LW) during 1993-94, to assess the effect of eight herbicides applied individually or in tank mixtures, on nodule number, nodule dry weight, seed yield and N percent in seed in soybean Asgrow 3205, inoculated with Bradyrhizobium japonicum CB 1809. Individual herbicides and doses in kg ha-1 of a.i. were metribuzin (0.48), acetochlor (0.90), metolachlor (1), flumioxazin (0.075), trifluralin (0.96), imazaquin (0.20), imazethapyr (0.10) and chlorimuron ethyl (0.0125). The mixtures were metribuzin+acetochlor (0.48+0.9), flumioxazin+acetochlor (0.075+0.9), imazaquin+acetochlor (0.2+0.9), metribuzin+metolachlor (0.48+1.92), and flumioxazin+ metolachlor (0.075+1.92). A control treatment without herbicides was included. Both trials were laid out as randomized complete blocks with four replicates, on a loam illitic thermic petrocalcic Paleudoll, 5.7% organic matter (OM), 25% clay, 30.4 cmol kg-1 CEC. Nodules were sampled at V2 (second node), V6 (sixth node) and R5 (beginning seed) growth stages. Herbicides did not significantly affect the beginning of nodulation or nodule number and mass at R5, not either grain yield or N accumulation. This indicates lack of interference between soil interacting herbicides and N fixation in the high organic matter, loam soils of SE Buenos Aires province, even though a tendency in less number and dry weight of nodules was evident at the two latter growth stages.
Highlights
Soybean (Glycine max (L.) Merrill.) is a crop of major economic importance in Argentina, where 6 million ha are sown each year, with an average yield of 2,370 kg ha-1 (Giorda, 1998)
The present paper reports the results of two field experiments aimed to assess the effect of eight preplanting, preemergence or early postemergence herbicides applied alone or in tank mixtures on the nodulation, grain yield and grain N accumulation of soybean growing on a high organic matter (OM), loam soil from SE Buenos Aires province, in Argentina
The mean values for nodule number and nodule dry weight per plant at V2, V6 and R5 are shown in Figs. 2 and 3, from Experiment 1 and Experiment 2, respectively
Summary
Soybean (Glycine max (L.) Merrill.) is a crop of major economic importance in Argentina, where 6 million ha are sown each year, with an average yield of 2,370 kg ha-1 (Giorda, 1998). In the SE of Buenos Aires province, 100,000 ha are used to cultivate soybean, and this area has a potential yield of 5,500 kg ha-1 under intensive production (Andriani et al, 1991). If this optimum yield could be generalized, this region would be a major contributor to the national production. 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). Since herbicides are necessary to achieve maximum yields, their influence on nodulation may conflict with the crop management
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