The effects of land use and landscape on soil nitrate availability in Southern Italy (Molise region)

- We conduct the first assessments of NO3-N availability at landscape scale.
- Multivariate geostatistics were used to model nitrate spatial variability.
- Nitrate lost from agricultural soil occurs as a result of land use and bad management practices.
- Best management practices (BMP) were needed to mitigate soil nitrate leaching.
- Animal manure has an important role in determining soil nitrate leaching.

The aim of this study was to verify the significance of land use on nitrate availability (NO3-N) at landscape scale in two different sites by using multivariate geostatistical methods. NO3-N and several other soil properties of Nitrate Vulnerable Zone (NVZ) monitoring network of 71 and 63 top-soils, respectively were measured in Venafro and Campomarino areas of Southern Italy (Molise region). Data analysis was performed firstly with classical descriptive statistics assuming spatial independence of samples; secondly, geostatistical analysis was performed in order to investigate spatial dependence and estimate map soil indices. The result of the distribution of NO3-N contents indicates the existence of many hot spots (high kurtosis) with high NO3-N concentration in both the study areas. Higher NO3-N levels in Venafro were distributed in the central zone that appeared to be correlated with animal manure applied to the fields in the summer strongly associated to high values of soil organic matter (SOM) and total nitrogen (Ntot). In Campomarino, the highest NO3-N concentrations occurred in random spots that appeared lesser correlated with high SOM content and low C/N ratio. Factor co-kriging analysis was applied separately to the two data sets to synthesize the complex multivariate variation of the two areas in a restricted number of zones so they could be ranked as at different risks of NO3-N leaching. The loading values of the factors indicate that Venafro SOM and clay and, to a lesser extent, Ntot and C/N are the variables that mainly affect the first factor at shorter range. On the other hand, cation exchangeable capacity (CEC) and, to a less extent, silt, SOM, C/N and fine sand content weighed more, but negatively, on the first factor at longer range. For Campomarino, clay content and available water capacity (AWC) and, to a lesser extent, NO3-N, weighed more and positively on the first factor at shorter range. The first factor at longer range was quite exclusively dominated by elevation and partially and negatively by pH and CaCO3. Soil factor map appears more variable in both the NVZ areas, characterized by many spots indicative of intensive land use and management. The highest NO3-N levels were found in intensive land use and in dairy farming located for the most part in Venafro catchment. The maps of the two factors at small scale for Campomarino appear to be quite erratic owing to the small size of the farms with different cropping systems differently managed. The results, of the present research, provide data useful to support land use planning and soil management, to mitigate soil nitrate leaching. Reduction in soil NO3-N could be achieved by enhancing useful recommendations in N fertilization and animal manure application to farmers.