Effects of Bradyrhizobia and Phosphate-solubilizing bacteria on soybean (Glycine max L. Merrill) cultivated on Ferrasols of Cujut district, DakNong province, Vietnam

Symbiotic nitrogen fixation, a key component in biological nitrogen fixation, has not been as successful in substituting for chemical fertilizer as initially expected. Rhizobial inoculants seem to be an attractive and cost effective source of N for soybean cultivation in the Mekong Delta, Vietnam [1]. Phosphorus plays an important role in the plant’senergy transfer system since phosphorus deficiency retards growth and tillering [2]. In soil, phosphorus is quite abundant but it reacts readily with iron, aluminum and calcium to form insolubly compounds. These reactions results in very low phosphorus avability and low efficiency phosphorus fertilizer used by plants [3].

Soybean (Glycine max) is one of the most important oil seed crop in the world. It contains 18 to 22% oil, highly desirable in diet and have 40 to 42% of good quality protein [2]; Soybean protein is rich in valuable amino acid lycine (5%) in which most of the cereals are deficient [4]. Soybean, like other legumes, fixes atmospheric nitrogen in association with gram-negative soil bacteria of the genera Bradyrhizobium and Sinorhizobium [5][6]. Many rhizobial inoculant products have been applied for soybean cultivation for along time [7]. However there were many researches showed that many PGPR as PSB supported good nodulation and rhizobia-legume symbiosis [8][9], the results led to high grain yield and protein content in seeds [10]. The biofertilizer (consisted of rhizobia and PSB) was not only as well as soybean grain yield applying with 100 kg N and 60 kg P O /ha but also quality soybean seed [protein and lipid content in seed] was higher than soybean seed using 2 5 of chemical fertilizers at Dong Thap province, Mekong Delta, Vietnam [11].

DakNong province is situated in the highland of Vietnam, it locates from 107o42’03”to 107o44’44” E and from 11o59’01” to 12o40’56” N and CuJut is a district of DakNong province, it locates the north of province (Figure 1) [DakNong province locates in Central High Land of Vietnam]. The soils are mainly red latosols (from origin of volcanic mountain) or ferralsols (FAO classification) with a pH range of 4.61-4.91. They are considered a good nutrient, with an average organic matter of 2.75 – 4.06%, a total nitrogen range of 0.11 – 0.13%, but it has concentrations of low available phosphorus, cation exchange capacity, exchangeable K [12](WASI, 2014). Many kinds of crop such as rubber, coffee, pepper, upland-rice, corn and soybean have been cultivated on ferralsols permanently.

In this study, selected bradyrhizobia strain CJ02 [13] and PSB strain S31 [14] were evaluated on yield component, grain yield and soil characteristics [after harvesting] and biofertilizer technology has taken a part to minimize production costs with granule fertilizer which suitable for soybean cultivation mechanise.