[Effects of water and nitrogen source types on soil enzyme activity and nitrogen utilization efficiency of wheat]

To provide basis for high-yield and high-efficiency of wheat production, with two wheat cultivars, 'Zhengmai 366' (strong gluten) and 'Bainong 207' (medium gluten), we investigated the effects of four nitrogen source types, ammonium chloride (NT₁), calcium nitrate (NT₂), urea (NT₃) and calcium ammonium nitrate (NT₄), applied under two water treatments, no irrigation (W₁) and irrigation at jointing and heading stages (W₂), on soil N-supplying capacity, grain yield and nitrogen utilization efficiency. The results showed that content of soil ammonium and nitrate at flowering stage decreased with increasing soil depths. Compared with the corresponding value of 'Zhengmai 366' under W₁ treatment, W₂ treatment decreased the contents of soil ammonium and nitrate in the 0-60 cm layer, and enzymes activities of urease, invertase and catalase by 10.0%, 13.3%, 7.5%, 2.8%, and 3.9%, respectively. For the two wheat cultivars, the content of ammo-nium was significantly higher under NT₁ and NT₃ treatments than that of others, while the content of nitrate under NT₂ and NT₃ treatments was significantly higher than that of others. Additionally, NT₃ and NT₄ treatments increased soil urease and invertase activities at the middle and later stages of grain filling. Compared with NT₁ treatment, NT₃ and NT₄ fertilization increased grain yield and nitrogen use efficiency of cultivar 'Zhengmai 366' by 14.9% and 20.7%, 25.6% and 13.9%, under W₂ treatment, respectively. Soil nitrate content in the 0-20 cm layer and the ammonium content in the 20-40 cm layer were positively correlated with wheat grain yield and nitrogen utilization efficiency. Under both water conditions, applying urea and calcium ammonium nitrate improved soil enzyme activity at the middle and later stages of grain filling, which was beneficial for wheat yield and nitrogen use efficiency.