Effects of maize/soybean and maize/peanut intercropping systems on crops nitrogen uptake and nodulation nitrogen fixation

Cereal/legume-based intercropping systems have a significant effect on the soil by increasing nitrogen (N) content. To understand the trends of N uptake, N nutrient competition capacity, and the legume nodulation characteristics in a maize/legume intercropping system, we investigated the N absorption advantage in maize/soybean and maize/peanut strip intercropping systems. We conducted a field experiment to study N accumulation, N nutrient competition, and the legume nodulation N fixation regulation characteristics in different planting patterns, which were maize monoculture (MM), soybean monoculture (SS), maize/soybean intercropping (MS), peanut monoculture (PP), and maize/peanut intercropping (MP). The results showed that compared with the monocultures, intercropping decreased N accumulation in maize and soybeans and had no significant effect on the N accumulation in peanuts. The trend of total N accumulation in the five planting patterns was MS > SS > MP; PP and MM treatments exhibited the lowest accumulation and the difference was not significant. Moreover, the N accumulation of MS treatment was 21.8% higher than that of MP treatment. Additionally, N accumulation of maize in MS and MP treatments decreased by 20.5% and 11.7%, respectively, compared with MM treatment. N accumulation of grain, leaves, and stalks of maize in MP treatment was 8.9%, 21.2%, and 14.3% higher than those in MS treatment. Furthermore, N accumulation of soybean in MS treatment decreased by 28.5%, and the central and fringe rows decreased by 10.1% and 15.4%, respectively compared with SS treatment. The effect of MP treatment on peanut N accumulation was not significant. The value of N nutrition competition indicated that maize had a dominant position in MS, whereas it exhibited less competition in MP treatment. Compared with SS treatment, the number of soybean nodules in MS treatment was higher at the fifth trifoliate stage and lower after the full bloom stage. The effect of nodule fresh weight was not significant at the fifth trifoliate stage, and it decreased after the full bloom stage. Nitrogenase activity of soybean nodules in MS treatment decreased, and the decrease was greater in the central rows. Relative to PP treatment, the number and fresh weight of peanut nodules in MP treatment were higher at the early flowering stage and lower after the acicula forming stage. The nitrogenase activity of peanut nodules in MP treatment decreased, and the amplitude of the decrease was greater in the fringe row. Although the amount of N accumulation of crops in the intercropping planting patterns was reduced, the total N accumulation of the intercropping system was significantly higher than the monoculture planting patterns. The amount of N accumulation of MS treatment was the highest in the two intercropping planting patterns.