ABSTRACT Heavy reliance on chemical fertilizer (CF) for achieving high yield in crops causes serious problems on the environment, development of pest resistance and deterioration of food safety. To resolve this, the co-application of organic fertilizer (OF) to reduce the amount of CF is considered as an effective fertilizer management to sustain agricultural crop production. Most studies, however, have focused on the effect of substitution of CF with OF or biofertilizer on crop production but little information on the effect of substitution of CF with microbial organic fertilizer (MOF) on the seed yield and quality especially in quinoa. Thus, field experiments were conducted to determine the effect of rates of substitution of CF by MOF on soil fertility, nutrient uptake, grain yield and quality in quinoa. Five treatments in two cropping season experiments in 2023 and laid out in randomized complete block design (RCBD) with three replications. These treatments were 100% chemical fertilizer application (CF100), 100% microbial organic fertilizer application (MOF100), 75% chemical fertilizer + 25% microbial organic fertilizer (CF75 + MOF25), 50% chemical fertilizer + 50% microbial organic fertilizer (CF50 + MOF50), and 25% chemical fertilizer + 75% microbial organic fertilizer (CF25 + MOF75). The results showed that the increase in the rates of substitution of CF with MOF increased soil pH and soil organic matter content (SOM) compared to CF100, while soil mineral N, available P, exchangeable K were highest at CF50 + MOF50 in both seasons. The substitution of CF with MOF at 25 and 50% enhanced nutrient uptake, promoted growth, and subsequently, increased yield and improved grain quality in quinoa. Overall, the results implied that substitution of CF by MOF at 50% was optimal for sustainable quinoa production.
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