Short-term crop and soil response to C-friendly strategies in two contrasting environments

In southern Europe (Italy), a two-site field experiment with contrasting soil conditions (high clay—SOC-protecting soil near Napoli versus low clay—non-SOC-protecting soil near Torino) was conducted to evaluate the short-term potential of a carbon (C) friendly management to sustain and possibly increase both crop yields and soil organic C (SOC). Compost distribution (COM1, COM2) and minimum tillage (MT) were compared to conventional management (CONV) in a maize-based cropping system. COM1, MT, and CONV each received 130 kg N ha−1 in compost or urea form. A double dose was applied to COM2 while the plowed control plots (0 N) were not fertilized. Fertilizers were applied for three years (from 2006 to 2008); residual soil fertility was assessed during the fourth year (2009). Results suggested that only the SOC protection strategy via MT could be agronomically sustainable in the high clay content soil near Napoli. There, a short-term SOC increase was recorded with either compost or MT application. In fact, in the same soil, compost use depressed both yield and N availability for maize, which we attribute to the reduction of SOM mineralization due to hydrophobic protection by added humified organic matter coupled with soil physical protection. Compost addition increased SOC (55.1% of added C) in the soil near Torino, where high native N availability buffered its low mineralization and allowed high yields. Alternatively, MT showed no effect on short-term C dynamics, probably because the low organic matter protection favored oxidation and mineralization of root-derived C.