Soil salinity affects crop production, especially in arid regions such as Central Asia, by inhibiting cotton (Gossypium hirsutum L.) root growth and thus capacity to scavenge phosphorus (P) from soil. We hypothesized that acidifying rhizosphere pH would reduce salinity in rhizosphere soil and improve plant growth and P nutrition. A 2-year experiments was conducted in a drip-irrigated cotton field in Xinjiang, China, the largest oasis-type agricultural region in Central Asia, to test six combinations of localized nitrogen (N) and P applications. The cotton was drip-irrigated every 10–15 days after the early bud stage (60 days after sowing). The localized supply of superphosphate and ammonium sulfate as starter fertilizers decreased the pH from 7.6 to 7.4 and salt content from 2.1 to 1.7 g/kg in the cotton rhizosphere soil at the seedling stage, thereby increasing P uptake and aboveground biomass compared to the control (conventional farmers’ practice of broadcast fertilization). Furthermore, fertigation with ammonium sulfate at the flowering stage further decreased rhizosphere soil pH and increased P uptake, aboveground biomass. Thirdly, the lint yield was increased by around 15% by the fertilizer management of the localized supply of superphosphate and ammonium sulfate compared with the control. We conclude that localized ammonium sulfate and superphosphate may be an effective soil amelioration measure to improve cotton production in highly saline soils in dry regions.