The Effect of Fertigation on Cabbage (<i>Brassica oleracea</i> L. var. <i>capitata</i>) Grown in a Greenhouse

Understanding the response of crop growth to water and fertilizer is helpful to improve their management and use efficiency. Three water and fertilizer coupling treatments were designed to carry out a two-season trial on two cabbage (<i>Brassica oleracea</i> L. var. <i>capitata</i>) cultivars in spring and autumn in the Beijing–Tianjin–Hebei region. The irrigation timings of the three treatments were controlled by the soil moisture content of 0–20 cm soil layer. Treatment 1 (L_WH_F): when the soil moisture content was decreased to 75% of the field capacity (<i>θ_f</i>), irrigation was carried out (i.e., the lower limit of irrigation was 75%<i>θ_f</i>), the critical soil moisture content for stopping irrigation was 90%<i>θ_f</i> (upper limit of irrigation), and the nitrogen (N) application amount was 400 kg/ha; treatment 2 (H_WL_F): the lower and upper limits of irrigation were 85%<i>θ_f</i> and 100%<i>θ_f</i>, respectively, and the N application amount was 200 kg/ha; and treatment 3 (M_WM_F): the lower and upper limits of irrigation were 75%<i>θ_f</i> and 100%<i>θ_f</i>, respectively, and the N application amount was 300 kg/ha. The results showed that the yield and its related parameters of cabbage in spring were higher than those in autumn because of the use of different cultivars and seasons. The growth indices of H_WL_F and M_WM_F in the two seasons were larger than that of L_WH_F, and the yields of H_WL_F were the highest, 78.37 t/ha (spring) and 64.42 t/ha (autumn), respectively. The nitrogen use efficiencies (NUEs) of L_WH_F in spring and H_WL_F in autumn were the highest, 213.29 kg/kg and 391.83 kg/kg, respectively. In general, there were statistically significant differences in the cumulative increment in plant height, stem diameter and leaf area in the two-season trial, yield in autumn and NUE in spring among the three treatments. In addition, there was a significant positive linear correlation between almost all indices in different growth stages and the corresponding evapotranspiration (ET<i>_i</i>). It is suggested that the application of drip irrigation under mulch should be approximately 114.7–125.0 mm, and the N fertilization should be about 200 kg/ha.