2.2.Experimental design
The experimental design consisted of a split plot experiment with two
factors (monoculture and intercropping); the treatments included
nitrogen application and no nitrogen application, with a total area of
about 1,400 m2. Each intercropping treatment covered
an area of 60 m2 (5 mⅹ12 m). The configured lines of
intercropped mulberry and alfalfa were two and four, respectively. The
planting distance of mulberry was 45 cm, with a row spacing of 60 cm
(Figure 1). For alfalfa, row spacing was 30 cm. To avoid nitrogen
leaching and seedling burn, the nitrogen was applied at the bud stage of
alfalfa through an opening ditch. Phosphorus, potassium, and other
essential elements were applied in mid-April. In particular, we used 23
kg·667 m-2 of superphosphate and 6.67 kg·667
m-2 of potassium chloride. To avoid interference by
other elements, nitrogen was applied as urea (46% N). In both systems
(monoculture and intercropping), the same amounts of nitrogen were
applied. For alfalfa, we applied 5.86 kg·667 m-2 of
urea, while for mulberry, 22 kg·667 m-2 were applied.