Optimum coupling of micro-irrigation method and fertilization level on soil quality, young mango tree growth and water-fertilizer use efficiency

Objectives The coupling effect of micro-irrigation method and fertilizer application rate for young mango trees was studied.

Methods A field experiment was conducted in greenhouse of Kunming University of Science and Technology, using 2-year-old young mango tree ‘Guifeimang’ as experimental material. The 12 treatments were composed of three micro-irrigation methods: micro-sprinkler irrigation (SI), drip irrigation (DI), and micro-moistening irrigation (MI), and four fertilizer levels: 0, 93.2, 186.4 and 279.6 kg/hm² (denoted as F₀, F₁, F₂, and F₃). The root zone soils of young mango trees were sampled at 30 days after each fertilization (i.e. 3 days after each irrigation) for the determination of nutrient content (NO₃⁻-N, available P and K), enzyme activity (catalase, urease and phosphatase), and microbial quantity (bacteria, fungi and actinomyces). The mongo tree growth and water-fertilizer use efficiency were investigated. The comprehensive root zone soil fertility index (SQI) and the tree growth quality index (GQI) were evaluated using the membership function with factor analysis.

Results Micro-irrigation method and fertilization level had significant effects on soil nutrient contents, enzyme activities, microbial population, the increase range of morphological growth indices of both plant shoots and roots, and water and fertilizer use efficiency of young mango trees (P<0.05). Under the same fertilization level, soil nutrient contents were similar among the three irrigation methods, while the enzyme activities and microbial populations were in order of MI>DI>SI. Compared with SI, DI and MI increased soil enzyme activity by 15.09%−26.57% and 26.56%−48.86%, microbial quantity by 11.46%−30.19% and 12.87%−42.45%, irrigation water-use efficiency (IWUE) by 43.27% and 73.17%, partial factor productivity of fertilizer (PFP) by 33.96% and 54.44% (P<0.05). MI exhibited the highest increase in plant height and root volume, which were 100.29% and 54.06% higher than SI did. With the increase of fertilizer application levels, soil catalase activity, urease activity, microbial population, and IWUE reached peak at F₂, soil nutrient content and phosphatase activity kept increasing with fertilization rate, and the PFP decreased with fertilization rate on the contrary. The correlation analysis showed that all the soil nutrient content, enzyme activity, and microbial population were positively correlated with mango growth indicators, and the degree of correlation raised in order of soil nutrient content, enzyme activity, and microbial population. Both the comprehensive SQI and GQI reached maximum at MIF₂.

Conclusions Micro-moistening irrigation coupled with 186.4 kg/hm² of fertilizer (MIF₂) is the most effective combination for promoting mango growth and improving soil environmental quality.