Abstract
Maize is an important food source worldwide and is of considerable industrial importance. Low maize yields are mostly due to low soil fertility, so expensive mineral fertilizers are often used to offset the lack of nutrients. Poultry litter (PL) is one of the most valuable and phosphorous-rich animal wastes. However, PL usually contains veterinary antibiotic residues, particularly fluoroquinolones (FQs), which may alter soil microorganism diversity and resistance patterns. In this study, we aimed to understand the impact of applying mineral (triple superphosphate - STP) or organomineral (STP with PL and reactive Bayovar phosphate with PL) fertilizers (130 or 260 kg/ha of total P2O5) on the structure and composition of the soil bacteriome and on phosphate-mineralizing bacteria associated with the maize rhizosphere. Maize plants were sampled at 60 and 90 days after sowing and a clear rhizosphere effect was observed in all samples. No specific groups of bacterial genera predominated (>3% relative abundance) according to the different fertilizer treatments and most of the genera were shared among samples. Multivariate analyses of 16S rRNA sequences revealed clear clustering based on sampling time and distinct separation from bulk soil samples. Abundances of phosphate-mineralizing bacteria varied depending on the sampling time. We observed a positive effect on phytase activity under the 260 kg STP with PL treatment. Although the FQ enrofloxacin and its main metabolite ciprofloxacin were detected in PL, their concentrations in fertilized soils were below quantification thresholds. Quinolone resistance genes were not detected in the maize rhizosphere or bulk soil. Together, these results suggest that the rhizosphere effect, plant age and applied amounts of fertilizer are more influential on bacterial communities than the type of fertilizer used. Thus, application of PL as an organomineral fertilizer does not appear to have extensive impacts on the bacterial diversity of maize rhizosphere, so it could be an excellent option for enhancing maize production.
Highlights
IntroductionMaize (Zea mays L.) is an important human food source (mainly in southern and eastern Africa, Central America and Mexico), a major component of livestock feed, and it has several industrial uses, such as starch, sweeteners, oil, beverages, glue and industrial alcohol (Ranum et al, 2014)
Maize (Zea mays L.) is an important human food source, a major component of livestock feed, and it has several industrial uses, such as starch, sweeteners, oil, beverages, glue and industrial alcohol (Ranum et al, 2014)
The diversity and composition of the bacterial communities in the maize rhizosphere subjected to different fertilization treatments were determined using direct-extraction of bacterial community DNA (60 and 90 days after sowing maize)
Summary
Maize (Zea mays L.) is an important human food source (mainly in southern and eastern Africa, Central America and Mexico), a major component of livestock feed, and it has several industrial uses, such as starch, sweeteners, oil, beverages, glue and industrial alcohol (Ranum et al, 2014). Maize production has grown steadily over the years, low yields in many countries are mostly due to poor fertility of the cultivated lands. Low phosphorus (P) and nitrogen (N) availability are the major constraints to maize production, so mineral fertilizers are applied to offset these nutrient deficiencies. Water-soluble phosphates (superphosphates, diammonium phosphate) and rock phosphates are among the most applied inorganic phosphate fertilizers (Ramachandra, 2006). The Bayovar phosphate mine located in Peru is one of the biggest rock deposits in South America, producing 3.9 million metric tons per year. Direct application of phosphate rock is an interesting low-cost option for supplying phosphorus to soil, different studies have already demonstrated that consequent crop yield is not enhanced to levels obtained for soluble phosphates (Chien and Menon, 1995; Franzini et al, 2009)
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