**1. Introduction**

274 Soybean Physiology and Biochemistry

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In Japan, the genetically modified herbicide-tolerant soybean cultivar cannot be grown in the commercial field without permission due to the public concern about the effects on the ecosystem and human health. Recently, interest for no-tilling, narrow row-spacing and dense cultivation in soybean has been increasing as a labour-saving technique. The no-tilling cultivation has an advantage in saving labor and drainage of soil, but the merit of narrow row and dense planting has not been clarified. The dense planting increases the competition among plants from the early stage and the risk of excessive growth which results in lodging. On condition that the planting density is equal, narrow row-spacing decrease the competition with plants during the earlier growth stage than wide row-spacing, and result in rapid leaf area expansion, higher crop growth rate and higher seed yield due to the development of branches, increase in the node number and pod number per node (Cooper 1977, Costa et al. 1980, Duncan 1986, Miura and Gemma 1986, Miura et al. 1987, Board et al. 1990a, 1990b, Bullock et al. 1998, Ikeda 2000). However, narrow row-spacing did not increase the yield (Beatty et al. 1982, Nakano 1989) and has been reported to even decrease the yield (Cooper and Nave 1974).

In this chapter, the factors affecting the increase in yield of narrow row and dense planting in soybean and yield determining process was clarified with reference to pod position (main stem/branches, raceme order). In order to analyze the advantages and disadvantages of narrow row and dense planting, we examined the effects of planting pattern and density on solar radiation utilization, dry-matter production and emergence of weeds.
