Effect of water-fertilizer coupling on photosynthetic characteristics, fruit yield, water and fertilizer use of mango

Mango (Mangifera indica L.) is one of the most important economic crops in dry and hot regions of southwest China. The yield is unstable due to seasonal drought, no irrigation or flood irrigation, and irrational fertilizer. Given the current situation of water and fertilizer supply as well as future scenarios, it is important to delineate strategies for improving water and fertilizer use efficiency and crop productivity. In this study, the native 4-year-old mango (Mangifera indica L., cv. ‘Guifei’) was chosen as experiment material. The field experiment was conducted during main growing seasons (from January to July in 2018) in an experimental mango orchard in Yuanjiang Country, Yunnan, China. We investigated the effect of water and fertilizer regulating on canopy structure, photosynthetic characteristics, fruit yield, irrigation water use efficiency (IWUE), and fertilizer partial productivity of mango. The irrigation and fertilizer treatments were designed in orthogonal experiment (L9 (34)). Four experimental factor were included the supply fertilizer at the three growth stages (flower bud differentiation stage (FⅠ), flowering stage (FⅡ) and fruit expansion stage (FⅣ)) and irrigation level. Three fertilization levels were 75 kg/hm2 (F75), 50 kg/hm2 (F50), and 25 kg/hm2 (F25), and three irrigation levels were full irrigation (FI-100%ETc, ETc means crop water requirement), mild deficit irrigation (DIM-75%ETc), and severe deficit irrigation (DIS-50%ETc), respectively. The results showed that compared with FI, DIS reduced significantly LAI, net photosynthetic rate (except for 15:00), transpiration rate, stomatal conductance and carboxylation efficiency (P<0.05). After fertilizer application at fruit expansion stage, T8 treatment (FIFⅠ50FⅡ25FⅣ75) had the largest LAI and transpiration rate, and the net photosynthetic rate, stomatal conductivity and carboxylation efficiency at 11:00 of T6 treatment (DIMFⅠ75FⅡ25FⅣ50) were higher than that of other treatments. In addition, the leaf instantaneous water use efficiency (LWUE) at 11:00 of most DIM was much higher than FI (P<0.05). Under the condition of quantitative fertilization in the whole growth period, the increase of the proportion of fertilizer distribution in flower bud differentiation and fruit expansion could increase the fruit yield and the fertilizer partial productivity at FI, and could improve IWUE at DIM. T8 treatment had the largest fruit yield (14 480.46 kg/hm2) and fertilizer partial productivity (96.54 kg/kg), and T6 treatment had the highest IWUE (6.67 kg/m3). The order of factors affecting the fruit yield, water and fertilizer use efficiency was obtained by the range analysis as follows: irrigation level> flowering stage fertilization> fruit expansion period fertilization> flower bud differentiation stage fertilization. The comprehensive scoring method evaluation indicated that, the optimal mode of coupling between variable fertilization at different growth stages and irrigation was irrigation level of 75%ETc, fertilizer rate of flower bud differentiation stage of 75 kg/hm2, flowering stage of 25 kg/hm2, and fruit expansion stage of 50 kg/hm2 (DIMFⅠ75FⅡ25FⅣ50). The study results could provide a scientific reference to water and fertilizer managements of mango in dry and hot regions.