fertiliser yield
            None 0.85
         Compost 2.34
             NPK 2.87
            None 0.67
         Compost 2.06
             NPK 2.98
            None 1.09
         Compost 2.21
             NPK 2.77
            None 0.83
         Compost 2.08
             NPK 3.03
            None 1.01
         Compost 1.92
             NPK 2.71