Abstract
Stabilized organic amendments (SOA) from poultry are used in agriculture to improve the conditions of the soil. SOAs favor the growth of the crops and reduces the effect of soil-borne plant-pathogens. However, in northern Chile, there are no studies to support this observation, nor have the mechanisms involved in the beneficial effects observed in the field been established. This work aims to establish whether the promotion of growth and control of soil fungi in tomato observed in the field as a result of commercial SOA application can be attributed to different endospore-forming bacteria (EFB). The effect of commercial SOA on nutrient availability was determined. EFB isolated from a commercial product, and the application of bacterial isolates were compared with the commercial formulation of SOA, for plant growth promotion (PGP) and biocontrol of Fusarium oxysporum fsp. radicis-lycopersici (FORL). The local tomato cultivar Poncho Negro was used given its sensitivity to different nutritional alterations and FORL. A series of measurements of growth parameters were carried out in plants submitted to different mixtures of SOA treatments. Isolates were identified by biochemical tests and sequencing of the 16S rRNA gene. Eleven EFB were isolated from SOA, and some tests were performed to determine the PGP and biocontrol of FORL activities of each isolate. Notably, isolates BAC22 (Bacillusmegaterium), BAC21, and BAC23 (B. amyloliquefaciens/velezencis) were associated with PGP, highlighting the ability to produce indole-3-acetic acid, a trait that in many cases is key to explaining the effects of Bacillus spp.
Highlights
The soil of the Azapa Valley (Arica, Chile) is naturally poor in organic matter [1], and the cultivation of vegetables requires incorporating organic amendments in large quantities to achieve acceptable production levels
Some physical and chemical characteristics of stabilized organic amendments (SOA) were analyzed, showing high levels of organic matter in SOA, and high levels of electrical conductivity (EC) and nitrates (Table 1), suggesting its application could generate toxicity in plants. To determine this toxic effect, an assay was carried out in tomato plants, in which different doses of SOA were used in a mixture with perlite, and a sample of the percolating irrigation was taken daily for chemical analysis
The application of manure and other biosolids allows the recycling of nutrients and the restoration of soil fertility [33]
Summary
The soil of the Azapa Valley (Arica, Chile) is naturally poor in organic matter [1], and the cultivation of vegetables requires incorporating organic amendments in large quantities to achieve acceptable production levels. The stabilized organic amendments (SOA), generated from spent beds of the poultry industry, are mainly used in tomato production, and its incorporation allows the improvement of the biological conditions of the soil. The application of SOA, derivated from the poultry industry, favors the growth and mitigation of the effect of soil-borne plant pathogens, such as Fusarium oxysporum in tomato crops. Different authors have shown that the use of manure as an amendment can replace the use of synthetic fertilizers, providing nutrients, improving soil structure, water retention capacity, porosity, as well as increasing the beneficial microbial population [2,3,4,5,6]. The microbial population present or induced as a result of the application of manure is largely responsible for the effects attributed to the Agronomy 2020, 10, 1636; doi:10.3390/agronomy10111636 www.mdpi.com/journal/agronomy
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