Study on the Effect of Straw Mulching on Farmland Soil Water

Table 1

Factor level design scheme of the response surface method.

Experiment factor	Coded value	Factor level and coding design
		-1	0	1
Film thickness (mm)		0.01	0.02	0.03
Straw returning amount (kg/hm^2)		3000	4500	6000
Straw particle size (cm)		3	5	7
Straw returning depth (cm)		15	25	35