Anaerobic Digestate and On-Farm Compost Application: Effects on Lettuce (Lactuca sativa L.) Crop Production and Soil Properties

Abstract

A three-year field experiment was conducted in a Mediterranean environment on lettuce to study the production, characteristics and possible use of different amendments as substitution for nitrogen mineral fertilizers. The effects on soil dynamics were also investigated. The following treatments supplying 140 kg N ha−1 were compared: Stabilized anaerobic digestate from wine distillery wastewater (SAD); Non-stabilized organic material from wine distillery wastewater (NSAD); Olive pomace compost (OPC); Mineral N fertilizer (MIN); Commercial organic fertilizer (CORG). These treatments were compared with an unfertilized control (CONTR). No significant reduction occurred with SAD as compared to MIN, but its application significantly increased marketable yield in all experimental years compared to the unfertilized control. Furthermore, SAD treatment reached the highest marketable yield with an increase of 52.9% compared to CONTR in the year characterized by high unevenly rainfall distribution. Even with low absolute values, the application of mineral fertilizer not only had the highest level of nitrate in the leaves but also determined higher value of soil mineral N compared to by-products treatments, thereby increasing pollution risks. The NSAD and the OPC treatments had significantly lower biomass and marketable yield than MIN and presented the highest soil N mineral deficit. As a consequence, the choice and the production of the more appropriate agroindustrial by-product (in our research SAD treatment) is crucial to ensure lettuce yield and the sustainability of agro-ecosystem.