**4.2 13C isotope discrimination and water use efficiency**

Both 13C isotope discrimination and WUEg were not significant among the treatments within each environment except at Ruace in 2018. This suggests that these two parameters measured at the R3 stage were not dependent on the application of the inoculant. Like our findings at R3 growth stage in soybean, Zhao et al. [50] also reported that no significant difference existed in C isotope discrimination and corresponding WUEg at wheat harvest time. Also, Yang et al. [51] reported no clear significance differences in the amount of carbon isotope composition among C3 plants in the Yellow River region in China. For the case of Ruace in 2018 a negative relationship was observed between 13C isotope discrimination and WUEg. Values of 13C isotope discrimination generally decrease with reductions in water availability. Reduced water

availability leads to a decline in transpiration rate hence increased water-use efficiency [22, 35, 52]. Also earlier reported was a negative relationship between 13C isotope discrimination in wheat at tillering stage and WUE of above ground biomass measured over the seedling to tillering period [50]. The change in 13C isotope discrimination in relation to the environment may differ with plant growth stages due to variation in physiological processes within the plant that define its functionality requirements [53]. Since we measured 13C isotope discrimination and WUEg at one stage for all the treatments, the likelihood of soybean functionality being comparable was high and more dependent on the environment. Therefore, 13C isotope discrimination can be used to determine differences in WUEg of different soybean growth stages rather than a variation associated to inoculation at a single stage [54].

### **4.3 Soybean yield**

Inoculation increased yield in all the three sites between an average of <sup>602</sup>1124 kg ha<sup>1</sup> . Our results agree with a study conducted in 2013 and 2014 in the same locations using storm a non-promiscuous variety that recorded an increase of <sup>523</sup>989 kg ha<sup>1</sup> [6]. These results of yield increase due to inoculation also confirms previous report [5, 8] where inoculation alone led to higher soybean yield that uninoculated. Although numerical average increase in yield due to inoculation was higher in Angonia and Ruace than Nampula across the seasons, percent rise in production was higher at Nampula 620766 kg ha<sup>1</sup> (65%) than Angonia 918<sup>1124</sup> (60%) and Ruace 602974 (52%). Chibeba et al. [6] reported and increased of 47% in yield of inoculated over the uninoculated soybean variety storm. Association between the introduced rhizobia strain and soybean was enhanced in the humid environments of Angonia and Ruace than the drier Nampula. Adequate moisture is required to take full advantage of the BNF process in inoculated soybean. The numerical rise in yield is also a pointer to the earlier reported enhanced nodulation in the inoculated soybean regardless of the placement on seed or soil. Across the sites, average soybean yield of 1440 kg ha<sup>1</sup> for the uninoculated fields is above the Mozambique national average of 1216 kg ha<sup>1</sup> [55, 56]. Therefore, use of inoculation in this study indicated that soybean yield can be increased by 1052 kg ha<sup>1</sup> over the national average figure. Our study observed that inoculant application on seed (2308 kg ha<sup>1</sup> ) gave higher yield than soil application (2228 kg ha<sup>1</sup> ) agrees with the report by [57] where seed inoculation 2842 kg ha<sup>1</sup> was greater than 2678 kg ha<sup>1</sup> for soil inoculation on planting line. Seed inoculation plus good adhesive agent and proper mixing of the seeds in the bag enables better distribution of the rhizobia cells per seed-grain. As a result, the rhizobia cells remain close to the seed and can attach to the root as soon as it germinates leading to better nodulation and BNF process that promote increased yield production. Seed inoculation led to a difference in yield was also noted between the liquid and solid inoculants. Solid inoculants (peat or powder) gave higher yield of 2389 kg ha<sup>1</sup> than the liquid inoculant 2147 kg ha<sup>1</sup> across the environments. Similar results where solid inoculants gave higher yields than liquid inoculants were reported from a study comparing the two forms of inoculants in Vietnam on promiscuous soybean varieties where identical rhizobia strains of in peat inoculant outyielded the liquid counterparts between 40 and 60 kg ha<sup>1</sup> [42]. These results demonstrates that farmers in Mozambique have a basket of inoculation options to choose from in enhancing soybean yield on their fields. However, selection of suitable inoculant should be made with consideration of environmental site conditions especially soil moisture availability over the growing season and the easiness of application.

*Inoculant Formulation and Application Determine Nitrogen Availability and Water Use… DOI: http://dx.doi.org/10.5772/intechopen.102639*

### **5. Conclusions**

Inoculation improved soybean nodulation by increasing the number of nodule count and its dry weight. Increase in nodulation could be associated to improved soybean productivity through high plant N uptake and yield. Nitrogen uptake and yield increased with application of inoculants. Farmers in Mozambique are likely to produce more soybean through using of solid cased inoculants applied on the seed than the liquid inoculants plus soil application. Although WUEg related to 13C isotope discrimination at R3 stage did not vary with inoculation, it is recommended that further study be conducted to determine cumulative WUE of the whole plant for the complete growing season while segregating for different growth stages. This could offer information on how to time soybean planting to take advantage of shifting growing seasons characteristics due to climate change. As such, soybean varieties could be selected for adaptability and resilience in specific agroecologies based on carbon assimilation, WUE and plant N uptake that affect yield. Data on inoculation and 13C isotope discrimination could be utilized by breeders in selection of high yielding soybean varieties adapted to drought conditions like those found in Mozambique. The varieties developed would have high transpiration efficiency and WUE.

### **Acknowledgements**

The authors greatly acknowledge financial support from the Consortium of International Agricultural Research Centers (CGIAR) through the Research Program on Grain Legumes and Dryland Cereals (CRP-GLDC) and United States Agency for International Development (USAID) through Feed the Future Mozambique Improved Seeds for Better Agriculture (SEMEAR) project in Mozambique. Thanks to the IITA technical staff at Angonia, Nampula and Ruace stations in Mozambique for managing the trials and collecting of field-related data.

### **Conflict of interest**

The authors declare that the research was conducted in the absence of any commercial or financial benefits that could be construed as a potential conflict of interest.
