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Soil Nitrogen Fertility and Soybean Growth Responses to No-tillage and Manure Compost Application on Paddy-upland Rotation Fields

ABSTRACT With the continuance of soybean (Glycine max (L.) Merr.) cropping on drained paddy soil in Japan, countermeasures against decreasing trend of the available nitrogen (N) are needed. We determined the effect of no-tillage (NT) soybean cropping with manure compost (MC) application on soil N availability and soybean growth under a rice (Oryza sativa L.) -wheat (Triticum aestivum L.) -soybean rotation on a drained paddy field in central Japan. NT significantly increased available N in surface soil after soybean harvest relative to conventional tillage (CT). Application of 2 kg MC m−2 before wheat sowing significantly increased available N just before soybean sowing. Tillage and MC treatments did not affect the ureide-N content in the stem of soybean, which reflects activities of N2 fixation at R6. The effect of NT on nitrate-N in the stem was not clear, but MC application significantly increased the content. NT and MC application significantly increased soybean aboveground biomass at R6, when biomass was maximum. The results indicate that MC application increased the soil N availability, and a higher nitrate uptake increased the aboveground biomass. In NT, however, the relationship between aboveground biomass and N assimilation was not clear. The seed yields were 313–330 g m−2 in 2014 and 213–244 g m−2 in 2015, and the difference among tillage and MC treatments were not statistically significant. Our results indicate that NT soybean cropping with MC application maintained N availability in paddy-upland rotation fields. MC application before wheat sowing is recommended.