Exploring the coupling mode of irrigation method and fertilization rate for improving growth and water-fertilizer use efficiency of young mango tree

Unsuitable irrigation and soil nutrient deficiency affect the normal physiology and growth of mango (Mangifera indica L.) of tropical fruit tree in Southwest China. To obtain optimal fertigation mode for mango, the effects of three micro-irrigation methods (i.e., micro-sprinkler irrigation (SI), drip irrigation (DI) and micro-moistening irrigation (MM)) on photosynthetic characteristics, hydraulic conductivity, growth and water-fertilizer use efficiency of young mango tree were investigated under four fertilization rates (i.e., 0 g plant⁻¹ (FN), 9.3 g plant⁻¹ (FL), 18.6 g plant⁻¹ (FM) and 27.9 g plant⁻¹ (FH), a compound water-soluble fertilizer) using a randomized block design experiment. The results indicated that DI and MM increased net photosynthetic rate (Pₙ) by 17.50 and 28.95%, root hydraulic conductivity (Kᵣ) by 39.65 and 52.69%, shoot hydraulic conductivity (Kₛₕ) by 48.63 and 82.38%, total dry mass (DM) by 27.44 and 47.13%, water use efficiency (WUEET) by 43.27 and 73.17%, fertilizer agronomic efficiency (FAE) by 45.92 and 95.41%, and partial factor productivity of fertilizer (PFP) by 33.96 and 54.44%, but reduced transpiration rate (Tᵣ) by 6.61 and 16.38%, leaf with petiole hydraulic conductivity (Kₗ₊ₚ) by 13.11 and 30.32%, and water consumption (ET) by 10.38 and 14.85% when compared with SI. Compared with FN, enhancing fertilization rate significantly increased Pₙ, Tᵣ, total hydraulic conductivity (root to leaf), total DM, healthy index (Hᵢ) and WUEET, and their maximum values appeared in the FM. FAE firstly increased and then decreased, while PFP gradually reduced with the increase of fertilization rate. MMFM had the highest total DM and WUEET, 2.32 and 2.58 times of SIFN (CK), and the largest FAE of 4.95 kg⁻¹. Thus, MMFM (micro-moistening irrigation with moderate fertilization rate of 18.6 g plant⁻¹) significantly promoted growth and improved water-fertilizer use efficiency of young mango tree, which was the best coupling mode of irrigation method and fertilization rate.