Fertility Evaluation of Limed Brazilian Soil Polluted with Scrap Metal Residue

Table 3

Soil fertility and available content of heavy metals in the soil mixtures used in the experiment (after incubation).

Attribute	Proportion of contaminated soil (%)					Equation	Regression coefficient^a
	0	25	50	75	100		𝑅^2
pH CaCl2	5.2	6.4	6.9	7.2	7.5	𝑦=−2.3𝐸−04𝑥^2+4.5𝐸−02𝑥+5.3	0.98*
OM (g kg^−1)	23.2	23.8	25.3	25.6	26.6	𝑦=−3.2𝐸−05𝑥^2+3.8𝐸−02𝑥+23.13	0.52*
P (mg kg)	39.0	40.6	48.2	30.0	25.0	𝑦=0.3𝑥+38.7	0.52*
K (mmolc kg^−1)	2.3	2.0	2.7	2.4	2.8	𝑦=5.5𝐸−05𝑥^2+7.5𝐸−04𝑥+2.2	0.27*
Ca (mmolc kg^−1)	90.8	193	288	242	285	𝑦=4.7𝑥+95.1	0.80*
Mg (mmolc kg^−1)	27.6	48.6	57.6	61.6	66.8	𝑦=0.8𝑥+28.9	0.84*
H + Al (mmolc kg^−1)	28.0	15.8	12.2	11.4	9.0	𝑦=0.003𝑥^2−0.4𝑥+26.9	0.95*
CEC (mmolc kg^−1)^b	148	259	360	317	363	𝑦=5.1𝑥+153	0.80*
SB (%)^c	80.6	93.6	96.6	96.6	97.6	𝑦=0.5𝑥+81.7	0.89*
S (mg kg^−1)	2.4	14.4	26.0	45.0	82.2	𝑦=6.6𝐸−03𝑥^2+0.1𝑥+4.2	0.83*
B (mg kg^−1)	0.2	5.1	9.3	11.2	14.9	𝑦=−5.5𝐸−04𝑥^2+0.20𝑥−0.36	0.98*
Cu (mg kg^−1)	5.3	15.8	25.0	22.9	29.8	𝑦=0.4𝑥+5.9	0.87*
Fe (mg kg^−1)	55.0	56.8	58.8	56.2	47.4	𝑦=0.2𝑥+54.3	0.27*
Mn (mg kg^−1)	52.3	34.0	26.8	19.9	15.6	𝑦=0.003𝑥^2−0.7𝑥+51.4	0.99*
Zn (mg kg^−1)	1.9	134	220	226	325	𝑦=4.6𝑥+12.9	0.92*
Cd (mg kg^−1)	0.02	0.2	0.4	0.4	0.8	𝑦=1.4𝐸−05𝑥^2+5.5𝐸−03𝑥+4.9𝐸−02	0.91*
Cr (mg kg^−1)	0.01	0.01	0.02	0.02	0.03	𝑦=1.6𝐸−07𝑥^2+7.9𝐸−06𝑥+0.01	0.69*
Ni (mg kg^−1)	0.6	1.2	1.6	1.7	2.5	𝑦=2.2𝐸−05𝑥^2+1.5𝐸−02𝑥+0.7	0.89*
Pb (mg kg^−1)	1.5	12.3	35.3	24.1	18.3	𝑦=0.9𝑥−0.4	0.41*

aSignificant at 𝑃<0.05 (*).
^bCation exchange capacity = Ca²⁺ + Mg²⁺ + K⁺ + H⁺ + Al³⁺.
^cBase saturation = (Ca²⁺ + Mg²⁺ + K⁺ + Na⁺/CEC ) * 100.