Study of simulation model of alfalfa plants development based on growing degree days

Based on the experimental data of planting alfalfa at the grass field of Jilin Academy of Agricultural Sciences in 2014, the models of the physiological development period and growing degree days were established and validated by the observational data from local meteorological stations. The results showed that the limit temperature from reviving period to branching period of 5 alfalfa cultivars was 5 ℃,from branching to budding period of 5 alfalfa cultivars was 16 ℃, from buding to flowering period of 5 alfalfa cultivars was 18 ℃, from flowering to poding period of 5 alfalfa cultivars was 23 ℃. The parameter of growing degree days in different development stages was quantified and different development stages were predicted systematically by lower limit temperature of alfalfa. The GDD of alfalfa from reviving period to branching period was 38.18 ℃·d, from branching to budding was 90.16 ℃· d, from budding to efflorescence was 76.6 ℃·d, from efflorescence to poding was 23.96 ℃·d. The root mean square errors(RMSE) of 5 different alfalfa varieties were 1.1～2.72 d. The relative estimation error (RE) of 5 different alfalfa varieties were 9.48%～17.87%. These results suggested that GDD might be suitable to predict alfalfa development stages.