The capability of individual tillage practices was evaluated by comparing the values of the slope of the regression lines, and the statistical difference of the slope with
value one, which used as an index of the stability (Borrelli et al., 2014).
A slope value higher than one indicates that the performance of the treatment is better in high-yielding years; conversely, it indicates better performance in low-yielding years.
The slopes of the regression lines were compared by using the STATA statistical software package (Stata 12.0, StataCrop, College Station, TX, USA).