The way to reduce agrochemicals to ensure safety food production is plant inoculation with biological agents. BioprotectantTrichodermaand biofertilizerAzotobacter arewidely used in sustainable agriculture. The objective of this pot experiment was to evaluate the effect of dual inoculation, Azotobacter sp. and Trichoderma harzianumon the growth of choy sum (Brassica rapa L. var. Parachinensis) and available N in soil.Pot experiment was set up in randomized block design with nine combination of inoculation times and doses of carrier-based mix inoculum. All plants were maintained in green house for a month. The effect of biological agents inoculation at any application time and doses on shoot height, fresh weight and dry weight was not significant, but irrespective to statistical analysis, certain treatment increased plant growth. However, the soil treated with lower dose of biological agent at one week before transplanting significantlyincreased more N-NH4+ and N-NO3- content in soil. This pot experiment concluded that dualinoculation of T.harzianum and Azotobacter sp. bring benefits to availability of nitrogen in soil and could enhance plant growth.
