RESUMO
The search for new sustainable alternatives for plant disease control has gained interest in the last decades. Compost extracts are nowadays considered a remarkable alternative to agrochemicals due to their biopesticidal properties. However, these properties could be affected by the different variables of extraction protocols and by starting compost. This work focused on the physicochemical and biological characterization of compost extracts obtained from a wide range of composted materials and different extraction protocols (CEP). CEP-1 and CEP-4 involved incubation at 20 °C for 48 h and 14 days, respectively; CEP-2 incubation for 24 h at 40 °C; while CEP-3 were incubated for 12 h at 70 °C. Electrical conductivity, pH, total organic carbon (TOC) and phenolic content were determined as well as the actinobacterial count and enzyme profiles related to plant pathogen suppression. Additionally, the influence of the different materials and protocols on the in vitro growth inhibition of Alternaria alternata and Botrytis cinerea was determined. The starting materials and extraction protocols significantly influenced the physicochemical and biological characteristics of extracts. Treatments based on long incubation times at 20 °C, as well as those based on short incubation times at 40 °C, resulted in extracts with increased suppressive properties. However, extracts derived from CEP-3 protocol were characterized by high phenolic and TOC content, low functional biodiversity, and a more discreet antagonistic capacity. Therefore, the development and optimization of suitable extraction protocols could lead to compost extracts with increased phytoprotective capacities, thus becoming an effective and sustainable alternative to chemical inputs.
RESUMO
The abuse of chemical fertilizers in recent decades has led the promotion of less harmful alternatives, such as compost or aqueous extracts obtained from it. Therefore, it is essential to develop liquid biofertilizers, which in addition of being stable and useful for fertigation and foliar application in intensive agriculture had a remarkable phytostimulant extracts. For this purpose, a collection of aqueous extracts was obtained by applying four different Compost Extraction Protocols (CEP1, CEP2, CEP3, CEP4) in terms of incubation time, temperature and agitation of compost samples from agri-food waste, olive mill waste, sewage sludge and vegetable waste. Subsequently, a physicochemical characterization of the obtained set was performed in which pH, electrical conductivity and Total Organic Carbon (TOC) were measured. In addition, a biological characterization was also carried out by calculating the Germination Index (GI) and determining the Biological Oxygen Demand (BOD5). Furthermore, functional diversity was studied using the Biolog EcoPlates technique. The results obtained confirmed the great heterogeneity of the selected raw materials. However, it was observed that the less aggressive treatments in terms of temperature and incubation time, such as CEP1 (48 h, room temperature (RT)) or CEP4 (14 days, RT), provided aqueous compost extracts with better phytostimulant characteristics than the starting composts. It was even possible to find a compost extraction protocol that maximize the beneficial effects of compost. This was the case of CEP1, which improved the GI and reduced the phytotoxicity in most of the raw materials analyzed. Therefore, the use of this type of liquid organic amendment could mitigate the phytotoxic effect of several composts being a good alternative to the use of chemical fertilizers.
