Table 4. Detailed information about the assessment units.

Assessment unit	Land use	Slope gradient (°)	Altitude (m)	Soil organic matter (g/kg)	Total nitrogen (g/kg)	Available phosphorus (mg/kg)	Available potassium (mg/kg)	Bulk density (g/cm3)	Soil texture (physical clay content ≤0.01 mm) (%)	Soil water content (%)	Main species
1	Arable land	7	1170	14.29	0.41	4.64	203.78	1.60	17.52	9.45	Solanum tuberosum
2	Arable land	5	1127	22.26	0.39	15.83	420.90	1.57	12.99	12.16	Setaria italica
3	Arable land	0	1155	16.02	0.24	7.36	244.80	1.59	11.37	12.09	Zea mays
4	Forestland	15	1195	9.54	0.22	5.12	269.09	1.53	6.01	3.71	Populus simonii
5	Forestland	14	1201	13.84	0.35	5.87	279.82	1.60	7.07	4.46	Populus simonii
6	Forestland	10	1170	12.50	0.26	5.17	176.56	1.54	5.14	2.00	Pinus tabulaeformis
7	Forestland	12	1154	5.80	0.07	3.77	72.55	1.55	6.59	3.78	Populus simonii
8	Forestland	17	1175	3.08	0.05	3.14	133.91	1.56	6.86	3.91	Populus simonii
9	Grassland	17	1160	2.90	0.12	3.06	119.29	1.60	9.21	3.90	Stipa bungeana
10	Grassland	15	1196	1.99	0.08	2.46	92.97	1.58	19.13	3.51	Medicago sativa
11	Grassland	20	1189	8.14	0.16	4.58	116.34	1.58	2.27	3.64	Medicago sativa
12	Grassland	30	1204	6.23	0.13	3.95	297.40	1.61	12.45	8.60	Lespedeza daurica
13	Grassland	10	1237	11.02	0.22	7.28	157.24	1.59	39.50	9.54	Stipa bungeana
14	Grassland	9	1152	6.38	0.14	4.11	85.04	1.59	18.86	8.17	Stipa bungeana
15	Grassland	18	1197	2.46	0.08	2.98	186.94	1.57	20.52	8.50	Stipa bungeana