Improving effect of potassium in organic amendments on sodic soils

Figures & data

Figure 1. Amount of outer sphere complexed cations in Tongliao soil with composts mixed at various ratios. Dotted line indicates the initial contents in the soil. Error bars indicate standard deviation (n = 3)

Table 1. Properties of the compost samples used

Compost	Cattle manure	Rice straw A	Rice straw B	Rapeseed pomace
pH	8.5	7.5	6.3	4.5
EC (dS m^−1)	3.3	2.4	2.2	2.3
Total C (g kg^−1)	387	332	372	456
Total N (g kg^−1)	23.0	8.90	7.88	4.50
CEC (mmolc kg^−1)	103	25.0	20.8	23.7
Water-soluble cation (mmolc kg^−1)
K	696	407	426	232
Na	205	29	24	2
Ca	31	36	41	98
Mg	48	37	48	202
K/Na ratio	3.4	14.0	17.8	116

Table 2. Contents of water-soluble basic cations and basic cations forming outer sphere and inner sphere complex in Tongliao soil

Element	K	Na	Ca	Mg
Water-soluble (mmolc kg^−1)	1.40	37.6	21.6	10.4
Outer sphere complex (mmolc kg^−1)	0.56	7.36	11.8	4.33
Inner sphere complex (mmolc kg^−1)	3.65	5.37	5.68	2.01

Figure 2. Amount of inner sphere complexed cations in the Tongliao soil with composts mixed at various ratios. Dotted line indicates the initial contents in the soil. Error bars indicate standard deviation (n = 3)

Figure 3. Relationship between the mixing ratio of the compost and soil pH. Error bars indicate standard deviation (n = 3)

Open circle, cattle manure; open square, rice straw A; closed triangle, rice straw B; and closed square, rapeseed pomace.

Table 3. Dispersibility, electrical conductivity (EC), exchangeable potassium percentage (EPP), and exchangeable sodium percentage (ESP) of Tongliao soil with compost mixed at various ratios

Compost	Mixing ratio (%)	Dispersibility (%)	EC (dS m^−1)	EPP (%)	ESP (%)
Control	0	79	0.54	5	16
Cattle manure	2	46	1.01	19	12
	5	39	1.75	33	13
	10	35	3.08	42	13
Rice straw A	2	59	0.67	14	11
	5	50	0.89	21	9
	10	43	1.36	25	10
Rapeseed pomace	2	48	1.10	9	4
	5	44	1.71	14	3
	10	39	2.22	19	4

Figure 4. Relationship between soil electric conductivity (EC) and dispersibility

Figure 5. Relationship between amount of water-soluble K and K_out (a) or K_in (b) content

Figure 6. Relationship between relative abundance of Kin in total cations forming the inner sphere complex and dispersibility† (a) and that between amount of water-soluble K and dispersibility (b).

^†Regression equation when the data from control soil (dispersibility, 79%) was excluded is: y = -1.13x +100 (R² = 0.67; P < 0.01)