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7.Decomposition Characteristic of Green Manure Legumes and Microbial Activity of the Incorporated Soil

-Cabbage production, Soil Chemical Properties and Microbial Activities in the Cropping -System of Crotalaria-Cabbage-

Shigekata YOSHIDA, MAPPAONA, Toru TASHIRO and Tatsuhiro EZAWA(University Farm, School of Agriculture, Nagoya University)

Crotalaria(Crotalaria juncea) was found to be the most useful green manure plant from the standpoint of the capacities of biomass production and nitrogen fixation among eight species of legumes tested.
Besides, the plant material was also recognized to rapidly release the higher amounts of inorganic nitrogen after the incorporation into soil.
In the first experiment, Crotalaria was grown in soil-bed (3m×0.85m、0.25m depth) as the preceeding green manure plant of cabbage cultivated under 4 fertilizer levels(zero[O], Low[L], medium[M], and high[H]) for three years (1992-1994).
Subsequently, the incorporation effect on cabbage production and some soil properties was investigated.
In the second experiment, nodulating (T202) and non-nodulating (T201) soybeans were simultaneously cultivated in same bed under non-fertilized condition, and the residual effect of green manure incorporation on the soybean growth, plant-rhizobium symbiosis and mycorrhizal infection was investigated.
The results obtained were as follows.

1.The incorporation of crotalaria resulted in the increase of cabbage production in any years, and the effectiveness seemed to be higher in lower levels of fertilizer.

2.Soil chemical properties was not largely influenced by the incorporation of crolataria. However, soil physical properties ( increase of soil aerial phase, decrease of soil solid phase, soil hardness) was markedly improved by the incorporation of crotalaria.

3.Plant growth and pod yield of non-nodulating soybean grown after the cultivation of crotalaria - cabbage for 3 years increased by the incorporation of crotalaria while those of nodulating one did not show a definite tendency.
On the other hand, plant growth and pod yield of nodulating soybean were markedly higher than those of non-nodulating one in any application treatments of fertilizer and green manure.It implies that nitrogen supply from nodules is the most important source on the plant growth and pod yield of soybean.

4.Nitrogen fixing activity measured by acetylene reduction method increased by the incorporation of crotalaria in many cases.

5.The higher possitive significant correlation was observed between top fresh weight and edible pod weight. Besides, they also correlated with nodulation and nitrogen fixing activity,possitively and significantly.

6.Mycorrhizal infection percent was about 70 on the root of non-nodulating soybean, and the infection percents was not dependent on fertilizer level and incorporation of manure.
On the contrary, the infection percent on the root of nodulating soybean was in the range from 40 to 60% and it tended to decrease with increase of fertilizer level.

Keywords: Leguminous plant, Crotalaria, Cabbage, Cropping system, Nitrogen fixation, Mycorrhiza