Effects of faba bean (Vicia faba L.) root exudate on soil available nutrients and microbial population in different purple soils

In order to improve the fertility of purple soil and make reasonable use of faba bean, this study collected faba bean root exudates by solution cultivation and obtained the concentrated solution by vacuum rotary evaporator. Then a soil cultivation experiment was carried out with 2 levels (low level of 6 mL and high level of 12 mL) of concentrated solutions of faba bean root exudates added separately to three types of 60 g purple soils (acid purple soil, alkaline purple soil and neutral purple soil) in constant temperature box. The aim of the study was to determine the effects of faba bean root exudates on soil available nutrients and microbial population in different purple soils. The results showed that compared with the control, both alkali-hydrolysable N and pH decreased significantly while available P, K, Zn and Fe along with microbial population increased significantly in the three types of purple soil after adding concentrated solutions of faba bean root exudates to the soil. Moreover, the above trends increased with increasing level of the root extrudates. The decreasing effects of high amount of faba bean root exudates on soil alkali-hydrolysable N and pH were most obvious in acid purple soil compared with in alkali and neutral purple soils. However, the most significant increasing effect on soil bacteria and fungi amounts was also observed in acid purple soils. The above four indicators in acid purple soils with high level faba bean root exudates addition were respectively 68.00%, 95.49%, 4.51 times and 10.00 times those of the control. In alkali purple soils, the addition of high amount of concentrated faba bean root exudates showed most significantly increasing effects on soil available P, K, Zn and Fe contents, which were 4.48 times, 2.04 times, 147.00% and 128.00% of those of the control, respectively. In conclusion, there were different effects on soil available nutrients and soil microbial activity after faba bean root exudates addition to different types of purple soils. This had a profound effect on the fertility of cultivated purple soils in the study area.