Optimal adjustment on fruit-crop intercropping model Ⅲ maize intercropping experiment Forage quality of maize (Zea mays) stover among different varieties Response of Grain Yield to Plant Density and Nitrogen Application Rate for Maize Hybrids Released from Different Eras in Heilongjiang Province Response of Nitrogen Use Efficiency to Plant Density and Nitrogen Application Rate for Maize Hybrids from Different Eras in Heilongjiang Province