Sustainable Agriculture Through Compost Tea: Production, Application, and Impact on Horticultural Crops

As part of the European Green Deal, the Farm to Fork strategy was introduced with the idea that environment, agriculture and food are interconnected topics. Reducing the use of synthetic fertilizers by 20% before 2030 through the adoption of circular economy principles is one of the goals to be achieved. There are several bioproducts that can be obtained from the valorization of agro-industrial wastes used to increase crop yields under low-fertilizer applications. However, the aim of this review is to describe production methods and the use of compost tea on horticultural crops to understand its real potential in providing plant growth support. The effects of compost tea on crops can vary widely depending on the waste material used, compost quality, compost tea production process and parameters, and the interaction between horticultural species and compost tea application dose. Therefore, because of this heterogeneity, it is possible that we would achieve real, positive impacts on the environment and horticultural production if there were more collaboration between the research sector and private farms. This collaboration would allow the development of protocols for compost tea production and customized use according to real farm needs. This would reduce both the costs associated with the disposal of waste produced on the farm and reduce the costs associated with the supply of synthetic fertilizers. The adoption of on-farm guidelines for compost tea use would achieve a balanced trade-off between agricultural productivity and environmental sustainability. The literature review shows that the most-used dilution ratios, regardless of the type of starting compost, range from 1:5 to 1:10 compost–water (<i>v</i>/<i>v</i>). Although a complete understanding of the biostimulatory mechanisms activated by compost tea is lacking, the application of this bioproduct would improve the physiological and productive performance of many horticultural species of interest, especially under suboptimal conditions such as organic production.