Growth of Vicia faba as affected by inoculation with vesicular-arbuscular mycorrhizae and Rhizobium leguminosarum bv. viceae in two soils

We studied the turnover of interlayer NH_inf4^sup+in three soils cropped with sugar beet. The three soils chosen for this study (Carpi, Cadriano, and Ozzano) are typical of the soils in the Po Valley where sugar beet is grown. The variation in interlayer NH_inf4^sup+content during the growing season was significant and very similar for the Carpi and Cadriano soils, while there was no significant variation in the NH_inf4^sup+content in the Ozzano soil during the same period. The turnover of interlayer NH_inf4^sup+in the Carpi and Cadriano soils was high, and appeared to cover a substantial amount of the N requirement of the crop. The turnover in these two soils showed a significant decrease during the initial phase followed by a period during which the pool of interlayer NH_inf4^sup+was replenished and reached the initial levels again. The spatial distribution of the root system, the pattern of N uptake by the sugar beet crop, and the processes of immobilization-mineralization of organic N all have an influence on the mechanisms of adsorption and release of interlayer NH_inf4^sup+. The release of interlayer NH_inf4^sup+, and thus its availability for plant uptake, was greater at the beginning of the growing season. The physicochemical characteristics of the soils, the K concentration, and the types of clay minerals present were found to be important in determining the dynamics of interlayer NH_inf4^sup+turnover of soils.