Agroecological practices for organic lettuce: effects on yield, nitrogen status and nitrogen utilisation efficiency

ABSTRACT Climate change tends to intensify extreme weather events worldwide, negatively affecting agriculture and threatening global food security. More resilient agroecosystems are required to assure yield stability. In this research, which was carried out in a Mediterranean environment in 2013–2015, the response of organic lettuce to cover crop management and organic fertilisation, in terms of yield, nitrogen status and efficiency, was investigated. A vetch cover crop was introduced before the lettuce and was terminated by the no-till roller crimper strategy (RC), which was compared with incorporation of the vetch into the soil as green manure (GM) and with a no-vetch control (No_V). Two organic fertilisers derived from waste recycling, anaerobic digestate (AD) and municipal solid waste compost (MSW), were compared with a commercial organic fertiliser (ORG) and with a control with no fertiliser (No_F). The RC treatment resulted in high lettuce yields in both years, whereas GM showed intermediate yield values (significant differences in 2014). Crop N status reflected yield, with improved values in RC plots. At harvest, particularly in 2014, the use of vetch and fertilisers increased soil mineral nitrogen concentrations compared with those in No_V and No_F treatments, though the differences were not statistically significant. Lettuce N use efficiency (NUE) had an inverse trend to that of the yield; the lower the yield the higher the NUE. The RC in combination with the use of organic fertilisers assured a satisfactory response to the variability in weather, in terms of both yield stability and preservation of soil fertility.