where Y is the mean yield, n-1 is the standard deviation of yield
for specific treatment across years, and Ymax is the maximum yield
obtained under that treatment in any year. Since n-1 measures the
variation in yield caused by soil and climatic factors, low n-1 suggests
sustainability of the system (Efthimiadou et al., 2010), while
high n-1 indicates unsustainable management practice