Abstract:

The use of alfalfa （Medicago sativa） green manure in the cultivation of maize （Zea mays） is an effective way to improve soil quality and increase maize yield， but the mechanism by which alfalfa green manure increases maize production is still unclear. To determine the effects of green manure on maize plants， we conducted a field experiment with the following treatments： maize planted in ryegrass （Lolium perenne） soil and addition of ryegrass green manure （ryegrass green manure treatment）， maize planted in alfalfa soil and addition of alfalfa green manure （alfalfa green manure treatment）， and maize planted in ryegrass soil and addition of nitrogen （N） fertilizer to provide the same amount of N as that in alfalfa green manure （alfalfa-equivalent N treatment）. It was found that both the alfalfa green manure treatment and the alfalfa-equivalent N treatment resulted in significant increases in plant height and the aboveground biomass of maize； the aboveground biomass was 48.77% and 37.73% higher， respectively， in those treatments than in the ryegrass green manure treatment. However， there was a significant difference in N fertilizer partial productivity between the alfalfa green manure treatment and the alfalfa-equivalent N treatment， with an increase of 48.77% and a decrease of 9.61%， respectively， compared with that in the ryegrass green manure treatment. The alfalfa green manure treatment increased the N contents in new leaves， old leaves， and leaf sheaths in maize， which were 9.59%， 9.97%， and 33.90% higher， respectively， than their values in the ryegrass green manure treatment， and these increases were greater than those in the alfalfa-equivalent N treatment. The N content in the root tip was highest in the alfalfa-equivalent N treatment， followed by the alfalfa green manure treatment （78.07% and 23.08% higher， respectively， than that in the ryegrass green manure treatment）. The transcript levels of key genes related to N transport， ZmNPF6.4 and ZmNPF6.6， were upregulated by 96.48% and 234.08%， respectively， in the roots of maize plants in the alfalfa green manure treatment. In the alfalfa green manure treatment， ZmNRT2.1， ZmNRT2.2， and ZmNPF6.6 were significantly upregulated in leaves during daytime （AM 10：00）， whereas ZmNPF6.4 and ZmNPF6.6 were significantly downregulated in leaves during nighttime （PM 10：00）. These results indicate that alfalfa green manure effectively promotes maize plant growth， and increases the aboveground biomass of maize by affecting the absorption and transport of soil N by roots.

Key words: alfalfa, maize, green manure, nitrogen translocation