Soil quality indicators as influenced by no-tillage, conventional tillage and nitrogen fertilization after 3 years of continuous maize in the Po Valley

An experimental trial was carried out over three years at Cavacurta (Lodi, Northern Italy) on continuous maize. The soil was a coarse-loamy over sandy, mixed, mesic Fluventic Ustochrept (Soil Taxonomy) or a Calcaric Cambisol (FAO). The experimental design was a split-plot with four replicates; the main factor was the soil management system (conventional tillage, CT, and no-tillage, NT), while the secondary factor was the rate of applied nitrogen (N0 = 0 and N1 = 270 kg N ha(-1)). At the end of the third year soil samples were taken at four depths (0-5, 5-10, 10-15 and 15-20 cm). For these samples, pH, electrical conductivity, organic matter, total N, available P, exchangeable K, cation exchange capacity and carbonates were determined. Water aggregate stability was determined only for the 0-20 cm layer. Statistical analysis shows that no-till positively influenced all the indicators except for carbonates and CEC, whereas N fertilization had no significant effects. There were no significant interactions for any of the indices. As regards the 0-20 cm layer, which is the most interesting from an agronomic point of view, the most important results are as follows. The OM content in NT plots was significantly higher than in CT plots (31.6 vs 29.5 g kg(-1)), as was the total N (2.03 vs 1.92 g kg(-1)). NT had a very clear effect on the available P content, which for NT was 59% higher than CT. As for the exchangeable K. this was 33% higher in the untilled plots compared to ploughed plots, but not significantly so. The most remarkable result was found for WAS: for NT the value was almost 2.5 times that for CT (34.1 vs 14.1%).