*2.4. Statistical Analysis*

Data were analyzed by using the following linear mixed model, following the rules suggested by Onofri et al. [27]. In particular, the field (two levels), the year (four levels) and the system (three levels) were added as fixed e ffects with all their two- and three-way interactions. It should be noted that the 'year × field' interaction corresponds to the crop e ffect, as the crops are univocally identified by one specific field in one specific year. The blocks within fields and the plots within blocks within fields were added as random e ffects to account for blocking units and repeated measures. The 'field × year × system' interaction was always significant and the corresponding means were compared by using a generalized multiple comparison procedure with multiplicity adjustment [28]. All analyses were conducted by using the R statistical environment [29].
