*C.I. Confidence interval Table 3 many water samples were collected and analyzed. Their saline characteristics were determined (pH, electrical conductivity, Na*, K*, Ca’* and Mg”* cations and CI, SO,” and HCO; (Canovas 1980)). It was particularly important to know the concentrations of other ions such as nitrate, nitrite, ammonium, iron, manganese, zinc, phosphate, borate, cadmium, chromium, and nickel, so that a global balance of all elements could be calculated including those added during irrigation. The results are shown in Table 3. Characteristic parameters of irrigation water Results and discussion Total amount of cadmium, chromium, and nickel There was a very low concentration of cadmium in the soil samples, which makes its determination quite difficult. The quantity present (approximately 0.5 mg/kg dry mat- ter) varies in an irregular way and the results are not a C Ss. d ear indication of an increase in t he concentration of this metal due to sludge application (Fig. 1). The contribution of the sludge to Cr and Ni is muc hown by the increases in the concentrations in the surface horizons where sludge has been a h more important as pplied. There is no evi- t ence of a relevant increase at depth, although the 15- 30 cm horizon is affected as shown in the third sample of he LA treatment in the case of Ni. This element seems to be more mobile than the other metals. there was no variation with depth. These quantities were obtained in the LA treatment. This metal is very insoluble. Compounds of Cr (IH and VI) precipitate quickly in a calcareous soil. Only the presence of organic compounds that react with the extracting agent allows the obtaining of Cr in its soluble or exchangeable forms (Reisenauer 1982). TL ara qe qQ qianineant iInereaca in pweehanasahla ee aleal wnth ee ee a, Ee ME eT Se, eRe eR Exchangeable Cr, Cd and Ni concentrations are very low (Fig. 2). The amount of exchangeable cadmium increases significantly with increasing sludge treatment in the first sampling in each horizon. Its concentration is very low, and there is a positive relationship with the presence of sludge in the 0-15 cm horizon. Exchangeable chromium concentrations were detected only in the second sampling of the highest treatment, and in the upper ones. In the treated columns there is a ten- dency to decrease with depth and time. Nickel compounds present in sludge seem to be solubilized easier by ammonium acetate compared to Cd and Cr. the upper level, and finally increasing again at the end of the experiment. The determination of available Cr through the use of chelating agents such as EDTA and DTPA is very limited due to the slowness of the exchange process from complexed Cr to extracted Cr with such extracting agents (Reisenauer 1982). However, this extraction is a useful indication of the effect of the sludge addition, as it clearly shows a positive effect in the increment of this metal in LM and LA. Nickel shows significant variations with the treatments ii the upper half part of the soil column, and the lowest hal! remains similar to the respective controls during the experiment. With time, nickel contents decrease. This means that either the soil compounds retain more Ni, or | is lost with the washing, in a way that it must be present in the leaching. The use of DTPA to evaluate Ni and Cd is a valid method, as the stability constants of the chelates go between the ones for Zn, Cu and Mn (Baker and Amacher 1982). To prevent an excess of dissolution of metals at pH=7.3, it is necessary to use triethanolamine, as the biodisposition of the metals depends much on pH (Pastor and others 1996). In the first sampling, Cd ii increases with the sludge treat- ments in relation to the control at every depth, although it cannot be said it is directly proportional to quantity of sludge applied (Fig. 4). There are no significant variations with depth; in general, the last samplings show lower levels than the first ones. ‘ns No significance; *, **, *** significant at the 0.05, 0.01 and 0.001 probability levels, respectively Cd, Cr, and Ni contents(tg/L) in leachates Table 4
