Effetti della Nitrapirina sulla fertilizzazione organica in un sistema ad indirizzo cerealicolo-zootecnico

Intensive farming requires increasing nitrogen (N) inputs due to the low crops nutrient use efficiency, that result in their losses to other environmental compartments. Particularly when using effluents from the livestock sector such as manure and digestate, that can have a nitrogen use efficiencies (NUE) between 40 and 60%. This makes the agro-livestock sector among the most impactful anthropogenic activities globally on water quality, due to an excessive nitrate (NO3-) concentration, and air quality due to emissions of acidifying (NH3) and climate-altering gases (N2O, CH4 and CO2). Nitrification inhibitors (NI) have an inhibitory action on the microbiological nitrification process that, at soil level, slowed down NO3- production accumulating N in the form of ammonia, which is more easily adsorbed on the colloidal phase of the soil and is the main absorbed nitrogen form by the plant root system. They can help to improves crops NUE, reduces NO3- leaching losses, ammonia (NH3) and nitrous oxide (N2O) emission into the atmosphere, potentially optimizing crop yield. In this study, the effect of a Nitrapyrin based NI, on NH3 and greenhouse gases from the organic fertilization of maize and ryegrass succession cereal system for livestock use was investigated. Five treatments were compared: untreated liquid digestate (DIG 0), untreated cattle slurry (CAT 0), liquid digestate and cattle slurry additivated with an NI dose of 2.5 l ha-1 (DIG1-CAT1) and an unfertilized blank plot (TEST). Greenhouse gas emissions were measured with a closed chamber system, NH3 emissions were assessed with passive samplers (Alpha-Samplers), while NH4+ and NO3- concentration in the soil was determined by soil analyses. Thanks to the direct injection, NH3 emissions range between 0.6% (CAT) and 0.4% (DIG) of the total nitrogen applied. During maize cultivation, the average N2O emissions were 10.58 kg N2O ha-1 for CAT0 and 5.69 kg N2O ha-1 for DIG0; the nitrification inhibitor addition generated 4.43 kg N2O ha-1 in CAT1 and 4.68 kg N2O ha-1 in DIG1, with a reduction of 58% and 18% for CAT and DIG, respectively. In the ryegrass cultivation, the lower temperatures during the winter period resulted in significantly lower N2O emission fluxes than in the maize cultivation system: average cumulative N2O emissions were 0.41 kg N2O ha-1 and 0.25 kg N2O ha-1 for CAT0 and CAT1, and 0.73 kg N2O ha-1and 0.43 kg N2O ha-1 for DIG0 and DIG1 respectively, resulting in emission reductions of 39 and 41%. Cumulative CO2 emissions in both crops, ranging from 4712 kg CO2 ha-1 and 6891 kg CO2 ha-1, showed no significant differences among treatments. Similarly, the results on CH4 emissions are in line with numerous existing studies, which reported negligible or negative methane emissions from fertilized agricultural soil. NO3- and NH4+ in the soil solution did not show significant differences between the different treatments. However, the tested nitrification inhibitor showed an increase in crop yields: maize yield increased on average by 12%, while in the case of ryegrass there was an average increase of 15%. Results of this study indicate that the use of NIs in combination with livestock manure and digestate has a potential role in reducing GHG emissions (mainly N2O) and nitrate leaching losses by increasing the NUE of crops, resulting in higher crop yields. Its effectiveness has been influenced both by the environmental conditions and by the characteristics of the manure.