Recently, there is an increasing trend of using metallic nanoparticles (NPs) in agriculture due to their potential role in remediating soil pollution and improving nutrient utilization from fertilizers. However, evidence suggested that these NPs were toxic to the soil life and their associated functions, and this toxicity depended on their dose, type, and size. Here, a dose-dependent (5, 50, and 100 mg kg-1 soil) toxicity of NiO NPs on poultry manure (PM: 136 kg N ha-1) decomposition, nutrient mineralization, and herbage N uptake were studied in a standard pot experiment. The NPs doses were mixed with PM and applied in soil-filled pots where then ryegrass was sown. Results revealed that the lowest dose significantly increased microbial biomass (C and N) and respiration from PM, whereas a high dose reduced these parameters. This decrease in such parameters by the highest NPs dose resulted in 13 and 41% lower soil mineral N and plant available K from PM, respectively. Moreover, such effects resulted in 32 and 35% lower herbage shoot and root N uptakes from PM in this treatment. Both intermediate and high doses decreased herbage shoot Ni uptake from PM by 33 and 34%, respectively. However, all NPs doses did not influence soil Ni content from PM. Hence, our results indicated that high NPs dose (100 mg kg-1) was toxic to decomposition, nutrient mineralization, and herbage N uptake from PM. Therefore, such NiONPs toxicity should be considered before recommending their use in agriculture for soil remediation or optimizing nutrient use efficiency of fertilizers.