Table 2 Plackett–Burman design factor levels and coding values.

From: Calibration of soil contact parameters for planting sand shrubs in the desert regions of Inner Mongolia

Parameters

Low level (− 1)

High level (1)

Soil–soil restitution coefficient (N1)

0.15

0.75

Soil–soil static friction coefficient (N2)

0.44

0.68

Soil–soil rolling friction coefficient (N3)

0.01

0.40

Soil–steel restitution coefficient (N4)

0.20

0.60

Soil–steel static friction coefficient (N5)

0.30

0.70

Soil–steel rolling friction coefficient (N6)

0.10

0.40

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