Effects of nitrogen application on plant growth and forage yield in seasonal growing alfalfa (Medicago sativa L.)

摘要

Providing adequate nitrogen (N) fertilizer is essential for high yields of alfalfa (Medicago sativa L.) in the seasonal cultivation system (growing alfalfa from autumn to the next spring or early summer) in southeastern China.The objective of this study was to determine the optimum N application rate during seedling growth period in autumn and rapid growth period in next spring of alfalfa.The response of seedling growth to different N application rate (0, 4, 8, 12, 16 and 20 mmol N L-1, which was adjusted from Hoagland solution and applied at 3 leaves stage) was studied by using 3 cultivars, Icon (FD7), Supersonic (FD9) and WL903 (FD9) in pot experiment.Plant height (PH), leaf area per plant (LA plant-1), plant dry weight (DW) and N content (％ DW) of the seedling were investigated at 38 days after N treatment.The influence of four N treatments (60, 120,180 and 240 kg N ha-1) on forage yield, yield components and N content of leaf (％ DW) was investigated with Sanditi (FD6) in two years field experiment.The several parameters, pH, LA plant-1, shoot DW and DW yield of alfalfa were investigated at each harvest time.The main results showed that seedling growth was enhanced significantly (P ＜ 0.05) with increasing N application rate when N application was less than 8 mmol N L-1, then stabilized on the peak when N application changed from 8 to 16 mmol N L-1, and tended to decrease at 20 mmol N L-1.The N content of seedling was 2.92-3.30％ when growth response stabilized to N application.pH, LA planf-1, shoot DW and DW yield were the greatest at the application of 180 kg N ha-1, meanwhile N content of leaf was 3.06-3.15％.The results indicated that N content of seedling or leaf may be used as the indicator for N application in alfalfa cultivation, and 2.9-3.3％ is a critical value.