Abstract:

In order to understand the effect of long fertilization to nitrogen metabolism, we studied the effects of long-term(13 years) fertilization on activities of key enzymes (NR,GS,GOGAT and GDH) related to nitrogen metabolism (ENM) of maize leaf. The experiment was conducted in the base of soil fertility and fertilizer effect monitoring in fluvo-aquic soil in Changping County, Beijing, China with 8 treatments as CK(no fertilizer), NPK(N, P, K fertilizers), NPKM(N, P, K fertilizers and manure), NPKS(N, P, K fertilizers and stalk mulching), N(only N fertilizer), PK (P, K fertilizers), NK(N, K fertilizers), NP(N, P fertilizers). The rates of fertilizer application were 150 kg N ha^-1, 75 kg P₂O₅ ha^-1 and 45 kg K₂O ha^-1 per cropping season, and the manure and maize stalk were applied with 22.5 t ha^-1 and 2.25 t ha^-1 per year. The key enzymes related to nitrogen metabolism were measured. Yield investigation showed that NPKM treatment had the highest grain yield, and N treatment had the lowest one. Balanced fertilization treatments such as NPK, NPKM and NPKS had higher activities of enzymes related to nitrogen metabolism (ENM) of maize leaves during the grain filling phase and higher yields than the treatments of imbalanced fertilization systems (N, NK, NP and PK treatments). Long-term imbalanced fertilization systems such as NP, N, NK, PK and CK did not well match the high activities of enzymes related to nitrogen metabolism (ENM) with high grain filling phase, resulting in lower active growth and lower yields. The high activity of only some single enzyme had little effect on maize yield and quality. That all the key enzymes related to nitrogen metabolism (ENM) of maize leaf had higher activities could be effective on maize yield and quality formation. Even if the Glutamine sybthetase (GS), Glutamate synthase (GOGAT) and Glutamate dehydrogenase (GDH) activities on average of N and CK treatments were higher than others, the grain yields of these treatments were lower markedly than others. Different enzymes have different roles in the formation of grain yield and quality, so the study on all enzymes related to the activities of nitrogen metabolism (ENM) will help to understand the nitrogen metabolism of maize and improve the efficiency of fertilizer utilization.

Key words: Long-term fertilization, Maize (Zea mays L.), Nitrogen metabolism, Enzyme activity