To increase the efficiency of a biofertilizer, try to harvest the biofertilizer in the logarithmique phase of growth and do not wait till the culture go into the stationary phase. in the small scale of field and pot experiments, try to inoculate the cultivated seeds in the soil directly via the liquid culture at the rate of 40l/fed. (1 feddan~ 1/2 acre). Irrigate your experiment directly after inoculation ( 60% of the soil water holding capacity- WHC). You can come back to my published papers, you will find one of them talking about that.
In addition to what Abu-Bakr stated above, another approach is to use a combination of exponential phase growing algae/cyanobacteria/fungi and low percentage chemical fertilizers. Furthermore, pretreatment of soils with microalgae or nitrogen fixing cyanobacteria can go a long way to improve the quality of the crops you grow. We have observed that a combination of these procedures can lead to very interesting results!!! Good luck...
I think adding humic acid and superabsorbent polymers can Improve the efficiency of biofertilisers. of course I suggest you use safe bacteria(there are some evidence that pseudomonas, Herbaspirillum and Bacillus spicies are not safe in agriculture) in your experiment.Best wishes.
Nutrients or precursors or signal molecules can be added to enhance the efficiency. Can check my paper Singh et al 2014 (Science Research Reporter 4(1): 44-50).