Organic versus inorganic fertilizers: Response of soil properties and crop yield

The decrease in soil productivity and quality caused by the continuous and abusive use of mineral fertilizers makes necessary to adopt more sustainable agricultural soil management strategies that help to maintain soil edaphic fertility. In light of these considerations, we have evaluated the effect of organic vs. inorganic fertilization on soil microbial communities, soil quality, and crop yield in a melon crop. The following treatments were tested: i) aerobic sewage sludge from a conventional wastewater treatment plant (WWTP) using aerobic bacteria (SS); ii) aerobic sewage sludge from a WWTP using a bacteria-microalgae consortium (B); iii) N-P-K mineral fertilizer (M); iv) a treatment in which 50% of the N was contributed by SS and 50% by mineral fertilizer (M + SS); v) a treatment in which 50% of the N was contributed by B and 50% by mineral fertilizer (M + B); and vi) a no-fertilized control soil. Melon yield and fruit quality were determined in addition to several soil physical, chemical, biochemical and microbiological parameters. Organic fertilizers (SS and B) increased the percentage of soil water-stable aggregates (52 and 60% respectively) as well as the content of organic C (18 and 31%), water soluble C (21 and 41%), N (15 and 41%) and available P content (41 and 82%) compared to inorganic fertilization. They also stimulated bacterial and fungal abundance to a greater extent than mineral fertilizers (189 and 242% vs 85%, and 57 and 122% vs 29%, respectively), as well as soil respiration, and dehydrogenase, β-glucosidase, phosphatase, urease, and glycine aminopectidase activities. The analysis of principal components with parameters linked to soil quality clearly showed that organic fertilizers cause a greater improvement in soil characteristics and microbial community than mineral fertilizers. Results demonstrate that organic and combined fertilization could be used as substitutes for nitrogen mineral fertilizers in melon crop, since these treatments led to similar melon production and quality while improving soil characteristics and microbial population size and activity.