Turfgrass with sand-based root zones, such as golf course putting greens, are highly important economically and require intense management. However, problems are often associated with sand-based root zones such as low nutrient retention and limited microbial activity. Soil additives may increase soil biological activity, improve nitrogen (N) cycling efficiency, and thus reduce fertilizer N inputs. A two-year experiment was conducted on a sand-based creeping bentgrass (Agrostis stolonifera L.) putting green to investigate whether humic products could increase soil biological activity and improve turfgrass quality. Treatments included humic-coated urea (HCU; 2/3 rate and full rate), HCU + humic dispersing granules (HDG), HCU + black gypsum (BG), urea, HDG, and a nontreated control. Minimal differences were seen in microbial biomass and activity besides HCU + BG. The HCU + BG had 60% greater potentially net N mineralization (PMN) relative to the HDG and the nontreated control. Overall, incorporating humic substances with N fertilizer did not increase turfgrass quality, cover, and clipping biomass compared to N fertilizer alone. However, the addition of BG to N fertilizer enhanced microbial activity (i.e., PMN).