Table 3: Effect of ozone in ascending doses on the soil pH and the release of bioavailable forms of P, Zn, Fe and Mn.

Time of ozonation	Dose (g.kg^-1O3)	pH^a	M-3 P^b (ppm)	DTPA^c-Zn (ppm)	DTPA^c-Fe (ppm)	DTPA^c-Mn (ppm)
Control	0	7.9	34	0.5	16	116
10 min	0.5	7.75	38	0.9	24	24^d
13 min	0.7^e	7.7	37	0.8	21	141
15 min	0.8^e	7.8	33	0.7	17	115
17 min	1.1^e	7.8	38	0.7	20	123
20 min	1.2^e	7.8	37	0.7	22	24^d
25 min	1.4^e	7.8	36	0.7	21	42^d

^aThe soil ozonation did not show a correlation between ozone doses and variation in soil pH.

^bBioavailable form of phosphorous in response to ozonation was measured with the Mehlich-3 method, and showed no correlation between ozone dose and M-3 P.

^cBioavailable forms of zinc, iron, and manganese in response to ozonation were measured using the DTPA extraction method. No correlation was detected between ozone dose and the variations in DTPA forms of Zn, Fe or Mn.

^dDifferences between DTPA-Mn numbers are of an order of ppm. This is a normal and non-significant difference between soil samples from the same soil.

^eDifference in dosage increase in response to the same increase in ozonation duration (2 min) is due to the difference in ozone absorption by the soil samples. This fluctuation depended on how tightly submerged the ozone diffuser was in the soil sample. Doses presented are averages of dosage measurements of 12 samples of the same ozonation duration.