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The effects of water, nitrogen and phosphorus on productivity of sandy grassland were investigated with a fully factorial experiment to find out the main factors limiting natural restoration of grassland productivity in the southeastern Keerqin sandy land. In total, eight treatments were designed as water addition (W), nitrogen fertilizer addition (N), phosphorus fertilizer addition (P), water + nitrogen fertilizer addition (WN), water + phosphorus fertilizer addition (WP), nitrogen fertilizer + phosphorus fertilizer addition (NP), water + nitrogen fertilizer + phosphorus fertilizer addition (WNP) and control (CK). Each treatment was replicated six times and randomly assigned to 48 plots (4 m × 4 m) that were separated by a 2-m buffer. Results show that restoration of productivity is only limited by nitrogen factor for sandy grassland of Keerqin sandy land and not limited by water and phosphorus. Relative to CK plots, the biomass and the aboveground net primary productivity (ANPP) of all the plots added with nitrogen fertilizer were significantly enhanced (P < 0.05) in 2005 growing season. Grass root mass is dominant in underground biomass. The present study possibly underestimates net primary productivity of grassland in northern China, due to limitation of underground biomass measurements.