JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND Maataloustieteellinen A ikakauskirja 270 Vol. 50:270-275, 1978 Leaching of plant nutrients from cultivated soils II Leaching of anions Helinä Hartikainen University of Helsinki, Department of Agricultural Chemistry,oo7lo Helsingi 77 Abstract. Leaching of anions from three soil samples (sand, fine sand and sandy clay) representing the plough layer was studied in a lysimeter experiment under conditions corresponding to the fallow. The effect of fertilization and that of acid irrigation solution on the amounts of anions washed out was also studied. The extraction of anions from different soils seems to correspond to that of cations; the coarser the soil, the higher the nutrient losses. This was valid for nitrate and sulfate, but the amounts of phosphate extracted were insignificant. The sum of the anion equivalents leached was lower than the respective sum of cations in all the leachates indicating that a part of the cations was leached as bicarbonate. The physical properties of the soil regulating the infiltration of water affect the movement of anions bonded non-specifically. The anions in pores of soil aggregates seem to be protected against leaching to a certain degree. However, the biological value of an anion is an important factor. It seems that microbiological processes may decrease the leaching losses of nitrate. Introduction The sorption mechanism largely determines the liability of an ion to leaching. Anions adsorbed specifically form a coordination complex on the surface of the adsorbing material (Hingston, Posner and Quirk 1972) and are difficult to wash out. Anions retained unspecifically are in the diffusive part of the surface electric double layer separated at least by one water molecule from the surface of the particle (Hingston, Atkinson, Posner and Quirk 1968) and are liable to leaching. Obviously, the movement of ions like these in the soil is to a great degree determined by the same factors that regulate the movement of the water in the soil. Chemical properties of the soils and microbiological activity may also be of importance. It has been noted, for example, that in contrast to the cation exchange capacity, the sorption capacity of the anions increases with increasing acidity (Wiklander 1964). The purpose of this study was to investigate the leaching of native and applied nitrate, sulfate and phosphate anions in different soils, and to compare the effect of water and diluted acid on it. https://www.c-info.fi/en/info/?token=iQaUr7eyo5ZBFwYc.h3MPgMJ_ys83icsMcjXMDw.lLW_eLNGTnBcSYG_U-NKmOLLg2OCC11c1M7XyvJT7bBhXlJdTXC8ps9-HzSpB9Gtb12zgAMCeCA_LlvmJuR9fqxw5zh2yUHOFK8UOaYbIM0MHjed7Xor65OJig1jbMORhkeQNpXJ2dBgJeqdlRGcxbdcNoOrUtNj5xLN4Uu4r2uhTIJR1A 271 Materials and methods The lysimeter experiment was carried out under greenhouse conditions with three crushed, unsieved soil samples: sand, fine sand and sandy clay soil. Their properties and the experimental design are presented in the previous work (Hartikainen 1978). One half of the lysimeters received the following amounts of nutrients per 1.7 lof soil: 100 mg Nas KN0 3 , 100 mgS as MgS04 - 7 H 2 O and 50 mg Pas Ca(H 2PO 4 ) 2 • H 2O. The solutions percolated during twentyfour hours were measured and analysed for nitrate by using a specific electrode (Orion lonanalyzer meter). The average amounts of the total leachates collected were: 1330 ml from the sand, 1370 ml from the fine and and 1363 ml from the sandy clay soil. Sulfate was determined turbidimetrically as BaS0 4 (Korkman 1973). Gum arabic was used for the stabilization of the suspension. The measurement of the transmission of the sample was done by a »Lange J» colorimeter with a blue filter. Phosphate was analysed by the molybdenblue method by using ascorbic acid as the reductant (Anon. 1969). Results The sums of the different anions leached by five percolations are presented in Table 1 with 95 per cent confidence limits. The leaching of nitrate and sulfate from the three soil samples differed strikingly. The cumulative curves in Figure 1 describe the losses of fertilizer nitrogen from the lysimeters during the experimental period. All the nitrate added in the chemicals was washed out from the sand soil sample. Its leaching from the fine sand soil was sta- tistically significant only on the third irrigation treatment and the nitrogen losses were lower than in the sandy clay soil sample. Irrigation with the acid solution enhanced the extraction of nitrate, espe- cially in the fine sand sample (Figure 1), in which it increased the nitrogen losses almost threefold. The leaching of fertilizer sulfate was practically complete in coarser soils, but in the clay soil sample water extracted only low amounts of this anion. The analytical results from the leaching of phosphate remained somewhat questionable. Turbidity of the leachate interfered with the colorimetric measurements and caused a great variation between the analytical data. The results of the clay soil sample indicating an exceptionally high leaching may to a large degree be due to the suspended clay, from which the acidic reagents may dissolve phosphate during the phosphorus analysis (e.g. Lee 1969). The effect of fertilization was statistically significant only in the fine sand soil, but it was the reverse to the effect on the other anions studied: the amounts of phosphorus washed out by water were higher in the unfertilized lysimeters than in the fertilized ones. Besides microbial processes this may be due to the increase in the salt concentration in the soil solution reducing the solubility of phosphates held by aluminium and iron compounds. Futher, it is possible that the leachate from fertilized lysimeters was not so turbid as that from unfertilized ones. 272 Table 1. Total leaching of anions by infiltrating solution mg/1 soil. Irrigation solution Salts added N03 -N S04-S P04 -P* Sand HaO 0 44.1 ± 25.7 59.4 ± 10.5 0.03 ± 0.01 + 104.2 ± 11.7 114.6 ± 11.9 0.02 ± 0.01 H2S04 0 48.1 ± 11.3 0.02 ± 0.01 + 110.2 ± 14.7 0.02 ± 0.00 Fine sand H2O 0 3.4 ± 2.6 83.5 ± 7.9 0.03 + 0.00 + 7.7 ± 5.1 149.8 ± 58.2 0.02 ± 0.01 H2S0 4 0 8.0 ± 19.8 0.03 ± 0.02 4- 19.3 ± 15.5 0.02 ± 0.00 Sandy clay HjO 0 8.3 ± 2.5 22.0 ± 6.1 0.34 ± 0.06 + 27.5 ± 16.0 41.5 ± 11.4 0.23 ± 0.07 H2S04 0 6.0 ± 3.4 0.78 ± 1.13 4- 31.9 ± 12.5 0.54 ± 0.49 •Four percolations only. Cations and anions are likely to be washed out in equivalent amounts. Comparing the sums of leached anion equivalents to the respective sums of the basic cations calculated from the analytical data from the previous work (Hartikainen 1978) it was found that the amounts of anions were always Figure 1. Leaching of fertilizer nitrogen form different soil samples 273 considerably lower than those of the cations. The chloride content was less than 1 meq in all the lysimeters and can be neglected. The portions of anion equiv- alents from the corresponding amounts of cations are presented in percentages in Table 2. The losses of phosphorus were so low that they were not taken into account. Thus, the percentages indicate the portions of cations washed out as nitrate or sulfate. The rest of the cations was obviously leached mainly as bicarbonate. Table 2. The leaching of anions as percentage of the corresponding leaching of cations.* Irrigation solution Salts added Sand Fine sand Sandy clay H 2 O 0 39.9» 31.3» 57.8«<> + 48.9 C 48.1« 62.3er H 2 S04 0 53.2 cd 47.6" 68.2' + 51.4 C