Calculating the soil surface nitrogen balance at regional scale : example application and critical evaluation of tools and data

Agro-ecological indicators (AEIs) allow evaluating sustainability for a large number of farms. The SITPAS Information System developed for the agricultural park "Parco Agricolo Sud Milano" (northern Italy) contains detailed farming and cropping systems information for 731 farms that can be used for these analyses. We used the SITPAS database to evaluate N management with an AEI and to evaluate the suitability of the SITPAS data model for this type of applications. The AEI (soil surface N balance) was calculated for each crop at field scale, as the difference between the sum of N inputs (atmospheric depositions, biological fixation, fertilisers, residues from previous crop) and crop N uptake; the results were aggregated at rotation and farm levels. The farming systems with the highest surplus (> 300 kg N ha-1) are dairy, cattle and pig farms, in which chemical N fertilisers are used in addition to animal manures. The crops with the highest surplus are Italian ryegrass and maize (183 and 172 kg N ha-1, respectively), while rice and wheat have the lowest surplus (87 and 85 kg N ha-1). The data model allowed to store and analyse complex information not manageable otherwise; its main limitation was the excessive flexibility, requiring a complicated procedure for the calculations of this example, and the exclusion of most data at the farming systems level (corresponding to 82% of the studied area) for missing, incomplete, out-of-range or inconsistent data. These results suggest to promote actions towards better N management in cropping systems in the Park and to develop simple data models based on minimum data requirements when sustainability evaluations are to be conducted.