Yield and quality changes in lucerne of different fall dormancy ratings under three defoliation regimes

Abstract This study determined how fall dormancy rating (FD2, FD5 or FD10) of lucerne genotypes affected crop yield and quality. One field experiment was measured for three growing seasons as a seedling crop and then three defoliation frequency regimes (DF) of 28 (DF28), 42 (DF42) or 84 (DF84) days were imposed (October 2014 to April 2017). Annual shoot dry matter (DM) yields ranged from 5.2 t DM/ha in DF28 crops to 17.5 t DM/ha in DF84 crops. Higher shoot DM was associated with greater shoot elongation which was modified by photoperiod (Pp). In an increasing Pp environment, the rate of DM accumulation in shoots was ∼ 91 kg/ha for each 1.0 cm increase in shoot height. In a decreasing Pp environment, the rate of DM accumulation in shoots was constant at ∼50 kg/ha/cm. In the DF84 crops, shoot yield declined due to leaf senescence by ∼31 kg/ha/cm when lucerne was ≥65 cm height. The leaf stem ratio (LSR) declined by 0.56 for each 1.0 cm increase in plant height. The crude protein (CP) and metabolisable energy (ME) accumulation in whole shoots or in leaf, soft stem and hard stem followed an allometric relationship. As DM increased, CP and ME increased in a similar pattern for all treatments. Thus the relationship between the yield and quality of lucerne was independent of genotype and phenological stage and was explained allometrically by the leaf and stem ratio, associated with changes in plant height, as affected by photoperiod. These results suggest universal defoliation management strategies can be developed based on ontogeny and independently of genotype, growth stage and growing conditions.