Differences of Nitrogen Uptake and Utilization and Nitrogen Regulation Effects in Maize between Maize/Soybean and Maize/Sweet Potato Relay Intercropping Systems

The aim of this study was to investigate the differences of maize nitrogen uptake and utilization and nitrogen regulation effects between two main intercropping systems including maize intercropped with soybean and sweet potato respectively in a four-year field experiment at two major maize producing areas of Sichuan in southwest China. Results showed that maize nitrogen accumulation(A), nitrogen harvest index(HI), nitrogen absorption efficiency(AE), and nitrogen distribution proportion to grain in maize/soybean relay strip intercropping were increased by 7.11%, 2.00%, 7.83%, and 1.76% respectively at maturity, on an average of two experimental sites, but the distribution proportion to leaves and stem/sheath decreased by 5.85% and 2.75% respectively. After strip rotation, maize intercropped with soybean showed obvious advantages even at early growing stage due to the effects of preceding crops on soil nutrients and relay intercropping advantage, with an increase of 11.85% in A and 11.84% in AE on average at maturity. During the key period of nitrogen accumulation, maize nitrogen accumulation was significantly higher when intercropped with soybean under low-nitrogen treatment than that when intercropped with sweet potato. However the resultswere insignificant or even opposite under high-nitrogen treatment. So did the results of nitrogen partial factor productivity(NPFP), nitrogen agronomic efficiency(NAE), and NRE. NAE, NRE and nitrogen distribution proportion to grain of maize were significantly higher in the treatment with nitrogen application of 180 kg ha–1 when intercropped with soybean, and in the treatment of 180–270 kg ha–1 when intercropped with sweet potato. After flowering stage, nitrogen assimilation amount after anthesis(AANAA) in maize/soybean was higher than that in maize/sweet potato significantly; consequently, nitrogen transfer(NT) and AANAA were higher in both intercropping systems with nitrogen application of 180–270 kg ha–1.