Mixed slow‐release fertilizer and urea improve yield, water and nitrogen use efficiency, and economic returns in corn–sunflower intercropping

Water scarcity and the need for more efficient nitrogen management are major constraints to sustainable dryland agriculture. Fertilization strategies that improve crop productivity while increasing water and nitrogen use efficiency (WUE and NUE) are therefore important for intercropping systems. We conducted a 2‐year field experiment to evaluate the effects of slow‐release fertilizer mixed with urea on yield, WUE, NUE, and economic returns in a corn ( Zea mays L.)–sunflower ( Helianthus annuus L.) intercropping system. Three fertilization treatments were established: slow‐release fertilizer (S), urea (U), and slow‐release fertilizer mixed with urea at a 7:3 ratio (M), combined with two row configurations: 2 rows of corn ‖ 2 rows of sunflower (C 2 S 2 ) and 2 rows of corn ‖ 4 rows of sunflower (C 2 S 4 ). Compared with single‐fertilizer treatments, the M treatments generally produced greater leaf area index and aboveground dry matter accumulation in both crops and higher soil organic matter and total nitrogen in the 0–20 cm soil layer. Compared with urea alone, MC 2 S 2 increased total system yield by up to 36.7%, WUE by up to 26.70% (and by up to 37.02% compared with UC 2 S 4 in 2022), and NUE by up to 28.6%. The MC 2 S 2 treatment also produced the highest system yield and net income, with a 2‐year average of 37,650 yuan ha −1 , exceeding the other treatments by 4.13%–41.57% in 2021. Overall, the combination of slow‐release fertilizer and urea at a 7:3 ratio with C 2 S 2 configuration was the best performing treatment combination among those evaluated under the experimental conditions. These findings support further evaluation of mixed slow‐release fertilizer and urea strategies across locations, years, fertilizer ratios, and nitrogen rates in corn–sunflower intercropping systems.