Spraying Agro-Industrial Compost Tea on Baby Spinach Crops: Evaluation of Yield, Plant Quality and Soil Health in Field Experiments

Abstract

Compost tea is a liquid fraction extracted from composts, and it is of great interest in sustainable agriculture because it reduces the unsustainable use of chemical-based pesticides and fertilizers. In this study, during two spinach field cycles, we evaluated the potential beneficial effect of the foliar application of a compost tea made from onion and vineyard composts either by itself (CT) or implemented with the beneficial microorganism Trichoderma harzianum T78 (CT + Th) on the “healthy quality” and yield of baby spinach. Results showed that both the CT and CT + Th treatments produced a higher spinach yield than the control, but these treatments did not result in an increase in soil dehydrogenase activity (DHA) or soil nutrient content. Furthermore, CT + Th treatment showed the highest yield, phenolic content, antioxidant capacity and flavonoid levels. Nitrate levels were below legal amounts, and they were significantly (p ≤ 0.05) lower in the CT and CT + Th treatments than in the control. Data suggest that compost tea extracts from onion waste and vineyard compost and/or enriched with T. harzianum can be used in a sustainable agriculture to increase yield and quality of baby spinach.

Effect of Compost Extract Addition to Different Types of Fertilizers on Quality at Harvest and Shelf Life of Spinach

“…The oxalate content decreased in each fertilizer treatment throughout the storage time, in agreement with previous studies carried out in spinach [42] and other five leafy vegetables [43], which could be advantageous for improving the health benefits of spinach. The content of phenolic compounds found in our experiments was similar to that observed by other researchers [2,19]. The initial TAC in all the compost extract treatments was higher than the content observed for those treatments without, as indicated by Ros et al [19] in the winter cycle.…”

“…The content of phenolic compounds found in our experiments was similar to that observed by other researchers [2,19]. The initial TAC in all the compost extract treatments was higher than the content observed for those treatments without, as indicated by Ros et al [19] in the winter cycle. Then, all the treatments followed the same behaviour with a decrease after 6 days and values close to the initial on day 12.…”

“…Other authors [27] have reported that the application of two microbial compost teas did not result in improved crop yields in spinach. Nevertheless, Ros et al [19] demonstrated that the foliar application of a compost tea made from onion and vineyard composts produced a higher spinach yield than the control treatment. This different effect of the application of CE on yield can be attributed to a combination of factors.…”

“…At harvesting, only in the control treatment, nitrate content was reduced by the addition of CE, while the application of CE did not affect the nitrate content in the other fertilization treatments. Recently, Ros et al [19] demonstrated in spinach that the foliar application of compost tea produced plants with lower nitrate content than the control treatment. This could be due to the potential organic mineralization rate from the incorporated CE, which would produce nitrates and thus, reducing nitrification processes provoked by the inhibition of nitrifying bacteria.…”

“…Moreover, compost extracts (CE), a compost-derived product, are used as a source of nutrients to improve crop production, representing an inducer of systemic acquired resistance against soil-borne diseases. CE can contain biostimulant agents that increase the photosynthetic function of the plant, which can induce the activation of the plant's secondary metabolism, causing an increase in the content of total phenolics and flavonoids and boosting the antioxidant capacity in baby spinach [19]. Additionally, Giménez et al [20] demonstrated that the CE application in lettuce did not have an effect on the microbial load of the final product at harvest and during shelf-life.…”