칠곡통의 식양질 논에서 답전윤환시 밭작물로 콩을 재배했을 때 Bradyrhizobium japonicum의 밀도변화와 토양 이화학성과의 상관관계를 조사하였다. B. japonicum의 서식밀도는 계속 논이용구에서 $10^1cells/g.soil$ 수준이었고 답전윤환구에서는 $10^1cells/g.soil$ 이상 수준이었다. 그리고 시비수준별 균주 밀도는 무비구가 관행시비구보다 2년주기 윤환시 1.9배, 3년주기 윤환 및 4년연속 밭이용시는 10배가량 높은 수준이었다. 토착 B. japonicum 밀도변화는 토양의 유기물함량$(r=0.83^*),;Ca/K(r=0.74^*)$ 및$(Ca+Mg)/K(r=0.72^*)$와 정상관 관계를 보였고 토양경도와는 부의 상관관계(r=-0.73*)를 보였다. 그리고, 계속 논이용구 대비 답전윤환구에서의 B. japonicum 밀도증가는 질소고정잠재능의 증가로 이어졌다.
The relatedness of naturalized Bradyhizobium japonitum populations with soil physico-chemical characteristics as affected by paddy rice-upland soybean rotation cropping with conventional and none fertilization in Chilgog clay loam soils were determined as follows. The populations of B. japonicum in soils were increased from about $10^1$ in continuous paddy upto $10^1cells/g.soil$ only in one-year rotation of upland use with soybean cropping. Compared to the densities in plots of conventional fertilization, those in none fertilization were high ranging from 1.9 to 10 fold in 2-year upland use rotation and both in 3-year upland use rotation and 4-year upland use, respectively. The populations were positively correlated with soil organic matter $contents(r=0.83^*),;Ca/K(r=0.74^*),;and(Ca+Mg)/K(r=0.72^*)$ and were negatively correlated with soil $hardness(r=-0.73^*)$. And the soil populations increased by paddy-upland rotation resulted in superior symbiotic potentials to those in continuous paddy use in terms of nodule mass, nitrogenase activity, and soy-bean shoot dry weight.
