Nitrogen fixing efficiency of native rhizobium symbiosis with mungbean cultivars grown in central region of Thailand

Abstract

This study selected an area at Prince Chakrabandh Pensiri Center for Plant Development, Saraburi Province, central of Thailand. This research area conducted the soil properties with pH ranging from 7.22 to 7.77 and 1.80 to 2.20 %OM in topsoil (0-15 cm) and subsoil (15-30 cm), respectively. This area is one of the fields that produce mungbean in central Thailand. In order to reach the target of finding more efficient rhizobium inoculation application and fertilizers managements for increasing the yield and quality of mungbean plantation, this study was undertaken. The main objective of the study focused on the suitable variety of mungbean that provides the highest nitrogen fixation, the nitrogen fixing efficiency of native thizobium strains, and the management of organic fertilizers and triple superphosphate (TSP) application in combination with native rhizobium on mungbean production. Rhizobia were isolated from three mungbean varieties (Maejo 3: MJU 3. Khampangsan 2: KPS 2, and Chainat 72: CN 72), collected from 10 undamaged fresh nodules at Prince Chakrabandh Pensiri Center for Plant Development, Saraburi Province, Thailand. The 16S rDNA analysis identified the three rhizobia isolates as Bradyrhizobium sp. (SB1), Bradyrhizobium elkanii (SB2) and Rhizobium sp. (SB3). In a Leonard jar trial, the study consisted of 5 treatments and 4 replications with a completely randomized design as follows: 1.) control, 2.) applied potassium nitrate 3.) SB1 4.) SB2 and 5.) SB3. MJU 3 inoculation with isolate SB2 resulted in the highest shoot fresh and dry biomass of mungbean host. Further, the mungbean inoculated with SB2 had the highest number of root nodules, nodule fresh dry weight, chlorophyll content index, nitrogen content in shoot and root. The effect of different rhizobium strains on nitrogen fixation of mungbean was assessed by ureide and 15N abundance methods. The study consisted of 12 treatments and 4 replications with split-plot in a completely randomized design. Three genotypes of mungbean (MJU 3, KPS 2, and CN 72) were used as the main plot factor and 1.) without rhizobium (-Rh), 2.) SB1, 3.) SB2 and 4.) SB3 as the sub-plot factor. Nodule fresh and dry weight were significantly reported with the peak by inoculated rhizobium SB2 strain at R7 stage. Rhizobium SB2 gave the maximum of total nitrogen whereas SB3 gained the highest shoot fresh and dry weights both at R3.5 and R7, respectively. Macjo 3 variety trended to prove with the high-level of %Ndfa both by ureide technique and IsN abundance. The largest percentage of nitrogen derived from the air was significantly determined by SB2 inoculation at R3.5 and R7 stages. The estimation of N2 fixation of mungbean by ureide technique and 15N abundance showed the regression coefficient metric at R2-0.7184 (R3.5) and R2=0.7671 (R7). This result indicated that the ureide technique and ISN abundance could use for estimation of nitrogen fixation and assimilation by mungbean native rhizobia strain in Thailand. The efficiencies of SB2 and the MJU 3, the best strain and variety, were determined under field experiment. This experiment consisted of 8 treatments and 4 replications with split-plot in the randomized complete block design. Triple superphosphate (TSP) fertilizer application (20 kg/rai) and without TSP fertilizer application were used as main plot factor; Rhizobium strains 1.) without Rhizobium (-Rh), 2.) SB2, 3.) Rhizobium mixed strains (SB1+SB2+SB3: SBMix) and 4.) Rhizobium from the department of agriculture (DOA)) were used as the subplot factor. Triple superphosphate combined with rhizobium SB2 provided the highest nodule fresh and dry weights, ureide, amino acid, %RUI (73.51%), %Ndfa (86.33%), total N, amount of nitrogen fixed by mungbean (37.15 kg N/rai), thousand grains weight, number of seeds per pod, grain and yield (182 kg/rai) at R7 stage. Besides, to find the appropriate method for fertilizers management combined with rhizobium inoculation in low available phosphate and organic matter were investigated. Randomized in a complete block design (RCBD) with 4 replications and 5 treatments as follows: 1.) control (without TSP and organic fertilizer), 2.) TSP at the low rate (20 kg/rai), 3.) TSP at the high rate (40 kg/rai), 4.) TSP at low rate (20 kg/rai) plus organic fertilizer (1,000 kg/rai) and 5.) TSP at the high rate (40 kg/rai) plus organic fertilizer (1,000 kg/rai) was taken in this experiment. Rhizobium SB2 was inoculated for 3 mungbean varieties as MIU 3, KPS 2, and CN 72. Particularly, the TSP low rate mixed with organic fertilizer proved the highest yield (195 kg/rai), in MJU 3 variety. The soil management in this research can inform farmers for choosing additional phosphate fertilizer at 20 kg/rai with organic fertilizer (1,000 kg/rai) inoculated with native rhizobium. This tool could provide a higher benefit-cost that was not significantly different from applying phosphate fertilizer at 40 kg/rai.