Cropping System Model for Integrated Evaluation of Agricultural Activities
University of Milano
Agriculture plays an important role in environmental pollution, mainly related to leaching of nitrate, sediment, nitrogen and phosphorus in surface water and greenhouse gas emissions. Cropping systems at field, farm and land scale are driven by different driving forces, such as market, policies, climate, and soil characteristics. Policy-makers and farmers have to develop, respectively, a set of regulations and management strategies to obtain simultaneous environmental and economic sustainability. The use of the cropping system model, describing all relevant processes involved with water and nitrogen in plant-soil system and adequately supported by networks of field experiments, allows for a priori evaluation of current cropping systems under alternate management scenarios. Since Po Valley (Northern Italy) is characterized by intensive agriculture, then an adequate analysis of cropping systems is required. This area accounts for 68 percent of dairy cattle, 61 percent of other cattle, 85 percent of pigs and 80 percent of poultry of the total livestock reared in Italy, with about 7 ml of livestock units, and a density of about 1.7 LSU ha-1 of utilized agricultural area (UAA), and has the largest aquifer in Europe. In Po Valley, 67 percent of the UAA is considered a Nitrate Vulnerable Zone (NVZ) and arable cropping systems including maize, winter or summer herbage and grassland represent the 64 percent of UAA. An analysis to support policy-makers and farmers based on ARMOSA model was carried out on different cropping systems scenarios in the Lombardy region (44 percent of LSU and 24percent of UAA of the Po Valley) in order to estimate N losses and in particular nitrate leaching. Lombardy UUA for extensive crops was divided using the 2-step cluster analysis into 35 homogenous districts with similar pedo-climatic characteristics and agricultural management practices. According to the regional agricultural database and regional soil map i) representative crop rotations, ii) N load calculated from livestock density, iii) two representative soil types were identified for each district. N leaching was estimated over 20 years. Then a weighted mean of leaching was obtained for the whole district (Fig 1). ARMOSA model was subsequently used to simulate different cropping systems scenarios (A and B), characterized by the same total N input (about 350 kg ha-1 y-1) but a different amount of N from livestock manure (170 and 280 kg ha-1 y-1, respectively for A and B). B scenario is based on the use of long growing seasons and high nitrogen uptake crops, introduction of catch crops. B scenario shows yields similar to the A scenario and a clear decrease in N losses. A scenario is not compliant with the EU threshold for water drinkability of 50 mg NO3- l-1.Since the European Nitrates Directive 91/676/EEC allows for the possibility for a derogation in respect to the maximum amount of 170 kg N ha-1 y-1for livestock manure in NVZ, the simulation results are a scientific base for the derogation asked by Italian Government, currently under revision by the EU Nitrate Committee. A detailed analysis of current condition and cropping case meeting derogation guidelines is provided, showing that the Directive?s objectives are still achieved.