ISSN:
1573-5036
Keywords:
15N isotope dilution
;
Bradyrhizobium japonicum
;
Glycine max
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract The practice of seeding soybeans following paddy rice in Thailand has encountered difficulties in seedling germination, nodulation and crop establishment. This research project evaluated the choice of a non-fixing control to quantify N2 fixation by15N isotope dilution, and the effect of tillage regime, soybean cultivar, strain ofBradyrhizobium japonicum and P fertilization on yield and N2 fixation after paddy rice in northern and central Thailand. Japanese non-nodulating lines Tol-0 and A62-2 were the most appropriatecontrol plants for15N isotope dilution for Thai soybeans in these soils which contained indigenous rhizobia. Cereals such as maize, sorghum and barley were also appropriate controls at some sites. The choice of the appropriate non-fixing control plant for the15N isotope dilution technique remains a dilemma and no alternative exists other than to use several possible controls with each experiment. Acetylene reduction assay (ARA) proved of little value for screening varieties on their N2 fixing capacity. The recommended Thai soybean cultivars (SJ1, 2, 4, 5) and an advanced line 16–4 differed little in their ability to support N2 fixation or yield, possibly due to similar breeding ancestry. The ten AVRDC (ASET) lines showed considerable genotypic control in their ability to utilize their three available N sources (soil, fertilizer, atmosphere) and to translate them into yields. None of these lines were consistently superior to Thai cultivars SJ4 or SJ5 although ASET lines 129, 209 and 217 showed considerable promise. Neither recommended Thai or ASET cultivars were affected by tillage regime. Zero tillage resulted in superior N2 fixation and yield at two sites but conventional tillage was superior at another site. Soybean cultivars grown in Thailand were well adapted to zero tillage. Levels of N2 fixation were similar to world figures, averaging more than 100 kg N ha−1 and supplying over 50% of the plant's N yield. However, seed yields seldom exceeded 2 t ha−1, well below yields for temperately-grown soybeans. It is not clear why Thai soybeans support N2 fixation, but do not translate this into higher seed yields.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02139994
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