Partial substitution of chemical fertilizer with organic fertilizer and slow-release fertilizer benefits soil microbial diversity and pineapple fruit yield in the tropics

The partial substitution of chemical fertilizers with organic fertilizer and slow-release fertilizer is an effective approach for improving crop yield and soil quality. However, few studies have paid close attention to pineapples in the tropics. Here, a 2-year field experiment was conducted to elucidate the differences in pineapple rhizosphere soil microorganisms, bulk soil chemical characteristics, and pineapple fruit yield under different fertilization treatments (CK: no fertilizer application; FP: conventional chemical fertilizer application; OPT: reduced chemical fertilizer application; OPTO: based on OPT, with organic fertilizer replacing 20 % of nitrogen (N); OPTS: based on OPTO, with slow-release fertilizer replacing 15 % of N), and the links between soil microorganisms and soil chemical properties and pineapple fruit yield were analyzed. Compared with FP, OPT, OPTO and OPTS treatments significantly increased bulk soil pH and organic matter (OM) content while reducing the amount of available phosphorus (AP), available potassium (AK), nitrate nitrogen (NO3−) and ammonium nitrogen (NH4+); in addition, they also highly increased the bacterial diversity index and pineapple yield (P < 0.05). It was found that Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria were the four major bacterial phyla (relative abundances >10 %) in all treatments, while Ascomycota was the main phylum of fungi. Specifically, the OPTS treatment increased the abundance of Chloroflexi, Acidobacteria and Basidiomycota but decreased the abundance of Proteobacteria, Actinobacteria and Ascomycota. Correlation analysis found that bulk soil pH, OM, AP, AK, NO3− and NH4+ levels were all important factors influencing the formation of the rhizosphere soil microbial community. Overall, the OPTS treatment resulted in relatively high soil nutrient content, microbial diversity and the number of beneficial microorganisms, which increased pineapple yield. Therefore, OPTS can be used as a high-yield and sustainable fertilization method for pineapple.