Effects of Paper-Mill Sludge as a Mulch versus Topsoil Incorporation on Potassium Uptake and the Grain Yield of Rain-Fed Wheat in a High Specific Surface Loess Soil with Illite Dominance in Clay Fraction

Table 1

Chemical and physical analysis of the soil and combined sludge.

Factors	Soil	Combined sludge
Sand (%)	10	—
Silt (%)	62	—
Clay (%)	28	—
Specific surface (m^2/g)	130	—
Saturation moisture (%)	49	273
Dry bulk density (g cm^−3)	1.7	0.25
EC (dS m^−1)	0.8	3.1
pH	7.7	7.38
Neutral material (%)	5.5	—
Organic C (%)	1.43	22.4
NO3-N (mg kg^−1)	18	600
Total N (%)	0.14	1.2
NH4-N (mg kg^−1)	0.12	0.97
Available P (mg kg^−1)	7	22
Total P (%)	—	0.25
Extractable K (mg kg^−1)	380	540
Total K (%)	—	0.128
Extractable Ca (meq l^−1)	6.6	—
Extractable Na (meq l^−1)	1.3	12.6
Available Ca (mg kg^−1)	—	1600
Total Ca (%)	—	0.412
Extractable Mg (meq l^−1)	5.8	—
Available Mg (mg kg^−1)	—	440
Total Mg (%)	—	0.145
CEC (cmol kg^−1)	20.3	82.6
Total Fe (mg kg^−1)	—	35
Total Mn (mg kg^−1)	—	22.8
Total Cu (mg kg^−1)	—	10.4
Total Zn (mg kg^−1)	—	15.7
Total Ni (mg kg^−1)	—	0.73
Total Cd (mg kg^−1)	—	0.42
Total Pb (mg kg^−1)	—	4.7
Total Cr (mg kg^−1)	—	0.12
Total As (mg kg^−1)	—	4.5
Total Se (mg kg^−1)	—	2.5
Total Hg (mg kg^−1)	—	2.7
Total Mo (mg kg^−1)	—	6