Developing a regional agronomic information system for estimating nutrient balances at a larger scale

Abstract The determination of nutrient surplus (fertiliser-offtake) is one of the indicators of potential losses from the agricultural system to the environment and can be applied at different geographical scales, from field to regional. When information is collected from individual farmers, the sample size is usually small as compared to the total number of the farms in a particular area. Official databases, when present, are more objective and contain information on all the farms in the area and as such provide information regarding the variability that exists between farms of a region. A geographical information system was built using all the information available in official databases to estimate soil surface nutrient balances at a regional scale within a 7773 ha area in Northwest Italy, where agriculture is very intensive. The nutrient surplus was calculated for the main farm types. Dairy farms showed the greatest surplus for all nutrients considered with values greater than 320 kg ha −1 for N and K and 110 kg ha −1 for P. Pig livestock farms followed next, with excesses greater than 270 kg N ha −1 , 100 kg P ha −1 and 220 kg K ha −1 . Cattle livestock farms showed the lowest surplus, compared to the other livestock farms, with values close to 190 kg N ha −1 , 80 kg P ha −1 and 230 kg K ha −1 . Farms without livestock showed the closest equilibrium between fertilisation and offtake, with a surplus in N, P and K equal to 40, 20 and 70 kg ha −1 , respectively. Despite the fact that local legislation only regulates slurry management precisely, it appeared that larger surpluses could be associated to the use of solid manure. Scenario analyses showed that manure exchange between farms in the area could lead to a drastic reduction in the use of mineral fertilisers, but at the regional scale an acceptable surplus can only be attained for N and K, while the excess of P remains a serious problem for the environment. The study indicated where the lack of information appears to be more critical and suggested options for a more accurate and organised acquisition of data. The results can be used for further studies, for instance with the aim of estimating the fate of nutrient surplus in the soil or in the air using simulation models.