Conservation agriculture and cover crop practices to regulate water, carbon and nitrogen cycles in the low-lying Venetian plain

Sustainable land management (SLM) practices, aimed at balancing competitive agricultural production and environmental protection, have been encouraged throughout the EU through policy and subsidisation. Adoption of SLM practices that regulate biogeochemical cycles requires further study, especially given the effects of local pedo-climatic variability. Conservation agriculture (CA) and cover cropping (CC) as opposed to conventional agriculture (CV), were carried out in field experiments and evaluated with modelling studies in order to mitigate the loss of soil organic carbon (SOC) and water and air pollution. All experimental treatments utilised a three-year crop rotation (maize, soybean, and wheat), and crop residues remained either atop the soil surface (CA) or were incorporated with tillage operations (CC and CV). As of March 2016, 17-month recordings from three soil-water monitoring stations per treatment (9 in total) were combined with climatic data to estimate water and N fluxes in the 0–60 cm layer. Carbon fluxes were quantified considering SOC and biomass contents. The biogeochemical model DeNitrification DeComposition (DNDC) was employed to evaluate long-term (105-yr) C dynamics and quantify greenhouse gas (GHG) emissions as affected by SLM practices and climate conditions. Experimental results showed significant differences in crop production between treatments, with lower average yields in CA (5.4 Mg ha−1) than in CC (7.9 Mg ha−1) and CV (8.5 Mg ha−1). Continuous soil cover in CA and CC determined the soil-water balance through increased evapotranspiration and reduced percolation (−30%) relative to CV. On the other hand, CC and CV tillage operations significantly affected NO3-N concentrations, with higher soil solution concentrations in tilled (CV = 74.6 mg l−1; CC = 58.1 mg l−1) than in untilled (CA = 14.0 mg l−1) systems. Model results emphasised that SLM practices responded differently in the short and long terms due to initial inertia to C changes and lower N2O fluxes, followed by higher SOC sequestration, and increased N2O emissions. These results demand time–dependent studies that weigh agro-environmental benefits provided by SLM practices against management alternatives to find a suitable compromise for stakeholders.