Maataloustieteellinen Aikakauskirja Vol. 61: I—6, 1989 Evaluation of water and ammonium acetate tests as indices for available P in limed soils HELINÄ HARTIKAINEN Department of Agricultural Chemistry, University of Helsinki, SF-00710 Helsinki Abstract. The water and acid acetate extractions as predictors of the P uptake by plants were compared in a two-year pot experiment and a simultaneous incubation test. The accuracy of these methods was dissimilarly affected by individual cultivation measures, such as the addition of nutrient salts and liming. In contrast to acetate-extractable P, the water-soluble P proved to be sensitive to the salt addition reducing the water extraction test values markedly. On the other hand, in limed soils the water-soluble P seemed to be more closely related to the P uptake by plants than the acetate-extractable P which tended to overestimate available reserves. Index words: water-soluble P, acetate-soluble P, soil testing, liming Introduction For economic and environmental reasons, it is important that judicious amounts of fer- tilizers be applied to correct a shortage of nutrients. A sound basis for determining the necessary amounts of P fertilizers, however, has long been a subject of controversy. P test methods often explain the variation in yield response to P fertilization only poorly (Hol- ford 1983, Holford and Cullis 1985, Labh- setwar and Soltanpour 1985). There are also indications that no single ex- tractant will be superior to the others under very different soils and soil conditions (Hol- ford 1983, Mackay et al. 1984). This sug- gests that the accuracy of various P tests may be dissimilarly affected by previous cultivation measures, such as liming and addition of nu- trient salts. To test this hypothesis, the plant P uptake and water extraction dataof two fine sand soils (Hartikainen 1983 a and b, 1984) were collected and used for comparison with the P extraction results of the acid ammoni- um acetate method used for routine soil test- ing in Finland. Material and methods a) Pot and incubation experiment A two-year pot experiment with turnip rape (Brassica campestris v. oleifera f. annua) was 1 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=neBQIlt9pbXroWAl.iU2g0CZF_NrmDZaSSN2HKw.TbVcjFzf0AArI4HIfGARgJKtoeX4Je_QNHc6rnandQfPvQdLQbHUw0T_lPscC8M3mNL4O48oP4K6SOIZydA7kXxT-NyR17AAJSPKyCzcmSGBCJKMRxCVBisW04PLYLpwr_O4wYy3WTjA4kA1IsQLYXwrsMR5d1CRZkrRrfMTuxeLjCL0Tg Table 1. Characteristics of experimental soil samples. Soil 1 Soil 2 Clay % 22.422.5 Org. C % of D.M 3.06.4 pH (CaCl2 ) 4.84.8 Total inorg. P mg/kg 721 893 carried out with two acid surface soil samples whose properties are given in Table 1. The methods of soil and plant analyses as well as the fertilization treatments are described in detail in previous papers (Hartikainen 1983a and b). In brief, in thepot experiment (four replicates) 4.5 kg of moist soil (= 3.9 kg of air-dried muddy fine sand soil (1) and 3.6 kg of fine sand soil (2) were treated with calcitic limestone (6, 12 or 24 g), dolomitic limestone (24 g) or basic slag (blast furnace slag, 24 g). The control samples received no liming agents. The nutrients added were: 1 000 mg N as NH 4N03 , 200 mg Mg as MgCl2 ■ 6 H 2 O, 10 mg B as H 3B0 3 , 15 mg Cu as CuS04 • 5 H 2 O, 10 mg Mn as MnS04 • H2O, 10 mg Zn as ZnS04 • 7 H2O, 5 mg Mo as NaMo04 • H 2 O. Half of the soil samples were fertilized with 400 mg of P (as K 2HP04 ) and the pots without P fertilization received an equivalent quantity of K as KCI. An analogous incubation experiment was carried out simultaneously in a greenhouse. The quantities of soil, liming agents and nutrient salts added to plastic pots were 1/10 of those used in the pot experiment. b) Soil P tests Water-soluble P (P w): Air-dried samples were extracted with H2O at a soil-solution ratio of 1:60 (w/v). The suspensions were shaken for 1 h, allowed to stand for 24 h and reshaken for 10 min. After centrifugation (3 000 g) the supernatant solutions were filtered through a 0.2 pm membrane filter and analyzed for P04-P by a molybdenum blue- ascorbic acid method (Anon, 1969). NH 40Ac-soluble P (P AAc): Air-dried soil samples were shaken for 1 h with acid ace- tate solution (0.5 M CH3 COOH + 0.5 M CH 3 COONH 4 , pH 4.65) at a soil-solution ratio of 1:10 (w/v). The suspensions were filtered through a blue ribbon filter paper, and the filtrates were analyzed for P04-P by the molybdenum blue-stannous chloride method of Kaila (1955). Results and discussion The extractability of soil P and its changes due to incubation for 4 mo with nutrient salts and various liming agents are given in Table 2. In soil 1, the water-soluble P in the unin- cubated control sample about equalled that of the acetate-soluble P, but in soil 2 it was markedly higher. In both soils, the addition of nutrient salts (excepting phosphate) caused a substantial reduction in P w but no change in P AAc. An increase in ionic strength has, however, been proved to result in an enhanced P sorpt- Table 2. pH and soil P (mg kg-1) extracted by acetate and water in unincubated and incubated samples.* Treatment Soil 1 Soil 2 pH Paac Pw pH P^_ Unincubated 4.8 b 12.0» 10.7' 4.8 h 30.3»" 42.1" Incub., no lime 4.2» 12.2" 5.4" 4.4» 29.8» 28.9" » calcite 0.6 4.9 b 12.5" 5.6» 4.9" 31.5» b 28. 2 b » » 1.2 5.6d 14.0" 6.3'b 5.3'332.b"2b " 25.2» » » 2.4 6.3' 19.7" 7.3 b 5.9» 38. 5 d 23.6» » dolomite 2.46.0" 15.2" 6.8" 5.5' 33.3" 24.8» » basic slag 2.4 5.1' 11.8» 5.5» 5.0" 1 30.5»" 25.6» * Each column was tested separately. The means followed by a common letter do not differ at P = 0.05. 2 3 ion and in a decreased desorption or desorpt- ion rate (Lehr and Wesemael 1952, Ryden and Syers 1975, Barrow and Shaw 1979). Under field conditions, a practical conse- quence of the ionic strength effect is that the mobilization of P is promoted in autumn, when the ionic strength is diminished (Wik- lander and Andersson 1974, Kuo and Jel- lum 1987). Eriksson (1940) noticed that the KCI fertilization may even decrease yield by depressing the solubility of soil P. Thus, the extraction results suggest that the water-sol- uble P gives a more accurate estimate of short-term available reserves than the acetate- extractable P. Table 2 demonstrates that the P tests responded dissimilarly also to an increase in pH. Excluding the basic slag and the lowest dosage of calcite, the liming treatments dis- tinctly enchanced the extractability of soil P into the acid NH 4OAc. This effect was quite proportional to the increase in pH, even though relatively more pronounced in soil 1 than in soil 2. As for the water-soluble P, on the contrary, the soils reacted differently to decreasing acidity: in soil 1 it tended to in- crease and in soil 2 to decrease. However, con- sistently with P AAc, the liming-induced Table 3. The uptake of soil P (mg kg-'), and residual soil P (mg kg-1) and soil pH after cultivation.* Uptake Residual pH Paa, P» Soil 1 Unlimed 22.8" 9.8" 5.9* 4.2» Calcite 6 33.1" 8.4" 5.1» 4.9" » 12 29.0»" 9.3"b 5.6» b 5.5" » 24 33.8" 15.515.90 65r Dolomite 24 29.5»» 11.4C 6.2' 6.0s Basic slag 24 36.3" 9.3"» 5.5"b 5.1c Soil 2 Unlimed 58.6" 23.8" 27.5' 4.5" Calcite 6 60.7" 23.8" 24.1' d 5.1b » 12 57.0" 24.2" 23.1 1» 5.5" » 24 49.7" 31.1' 20.5" 6.1' Dolomite 24 49.8" 26.4b 22.4b 5.8C Basic slag 24 59.4" 23.5" 25.0" 5.2= * Each column was tested separately. changes in Pw remained statistically insignifi- cant in the lowest calcite treatment, and in soil 1 also in the basic slag treatment. In fact, the close positive correlation found for P ex- tracted from all the incubated samples by water and acetate solution (r = o.94***, n = 12)was seeming and did not hold true for soil 2 (r = —0.76). The total removals of soil P by two harvests in the pot experiment are given in Table 3. Owing to a great variation between the repli- cates, the differencesbetween treatments often remained statistically insignificant. There is, however, a tendency that the liming agents augmented the utilizationof P reserves in soil 1, whereas in soil 2 the highest dosages of cal- cite and dolomite depressed it. Comparison of the results of the pot and incubation experiments (Tables 2 and 3) reveals the P removal by shoot yields to be in- consistent with the P test values of the in- cubated samples. For instance, in soil 2 the highest dosage of calcite increased soil PAAC (by 29 %) but reduced the P utilization (by 15 °7o). The P uptake seemed to be more ac- curately predicted by P w being congruently reduced (by 18 %). In soil 1, on the contrary, this treatment promoted the utilizationof soil P (by 48 %) and increased PAAc markedly more (by 62 %) than P w (by 35 %). The long-term available P in limed soils seems to be underestimated in the water extraction test, where the effect of liming on the solubility of P obviously was masked to some extent by a high nutrient salt concentration. The soil remaining after cultivation (Table 3) was the greater the higher the liming intensity was, but it seemed not to be related to the P quantities removed by the shoots. On the other hand, in soil 1 the residual soil P w was not markedly affected by liming and an enhanced P uptake, whereas in soil 2 it was lowest in the samples where also the P uptake had been lowest. The recovery of fertilizer P by the NH4OAc and water extractions (Table 4) shows that most of the added P (104 and 114 mg kg-1 to soil 1 and 2, respectively) was retained. The Table 4. The recovery of fertilizer P (mg kg-') by NH4OAc and water extraction in the incubation test and the apparent uptake of added P (mg kg -1) in the corresponding pot experiment. Liming Soil 1 Soil 2 g/pot Paac Pw Uptake l\ Uptake No lime 5.08.3 35.06.7 17.124.5 Calcite 0.6 (6) 7.38.8 29.46.8 15.325.1 Calcite 1.2 (12) 8.58.2 42.19.3 15.122.5 Calcite 2.4 (24) 12.08.6 30.314.7 13.623.2 Dolomite 2.4 (24) 8.08.0 25.410.9 12.430.0 Bas. slag 2.4 (24) 7.18.6 17.77.7 14.516.8 lime-derived changes in the extractability of fertilizer P showed similar trends found for soil P. The higher the soil pH, the more NH4 OAc was able to recover the applied P, which is in accordance with results of an earlier study on a large Finnish soil sample material (Paasikallio and Häkkinen 1977). The results indicate the extraction power of NH4OAc to be highly dependent on soil pH. Similar observations have been made by Griffin (1971) for a modified Morgan test (NH 4 OAc, pH 4.8). The recovery of fertilizer P by water extraction, on the contrary, seemed not to be as markedly dependent on liming in- tensity. This implies that the solubility of soil and fertilizer P into water was equitably promoted by liming. The apparent utilization of fertilizer P by yields (included in Table 4) was calculated as the difference between the P quantities taken up from soil samples with and without P treat- ment. In soil 1, initially poorer in PAAc and Pw than soil 2, the utilization of added P was more effective. On the other hand, utilization seemed to be somewhat reduced by liming, which may be at least partly attributable to an enhanced withdrawal of soil reserves, especially in the basic slag treatment (c.f. Table 3). However, when comparing the results of the incubation and pot experiments in Table 4, one can conclude that the acetate extraction may overestimate the efficiency of lime in enhancing the utilization of added P. Although the extractability of fertilizer P into NH 4OAc was more than doubled by the highest dosage of calcite, the removal of applied P seemed not to be affected, or it was even decreased. The observations made in the present study suggest that the accuracy of the water and acetate extractions are dissimilarly affected by individual cultivation measures, such as addition of nutrient salts or liming. Although the water-soluble P proved to be sensitive to the salt addition, it seemed, especially in limed soils, to be more closely related to the P uptake by plants than was the acetate-extract- able P which tended to overestimate available reserves. The results are in accordance with the con- clusions drawn by Sibbesen (1983), who reviewed numerous pot experiments with con- trasting soils: the soil P status was most accurately estimated by the resin method, followed by the water and bicarbonate extrac- tions. The acetate buffer extraction fell into the group of least accurate methods. Also in an earlier two-year pot experiment with Finn- ish soils, the water extraction was found to be superior to the acetate extraction in the asses- ment of soil P status (Sippola and Jaakkola 1980). Recently, Sippola and Saarela (1986) reported similar observations in a large field experiment where the variation in the yield in- crease due to P fertilization was explained better by the water extraction (68 %) thanby the NH 4OAc method (53 %). 4 References Anon. 1969. Juoma- ja talousveden tutkimusmenetelmät. Elintarviketutkijain Seura. 169 p. Helsinki. Barrow, N.J. & Shaw, T.C. 1979. Effects of ionic strength and nature of the cation on desorption of phos- phate from soil. J. Soil Sci. 30: 53—65. Eriksson, S. 1940. Über die Einwirkung der Kalidiingung auf die Festlegung der Phosphorsäure im Boden. Ann. Agric. Coll. Sweden 8; 87—130. Griffin, G.F. 1971. Effect of liming on the soil test level of phosphorus as determined by three methods. Soil Sei. Soc. Amer. Proc. 35: 540—542. Hartikainen, H. 1983a. Effect of liming on phosphorus in two soils of different organic matter content. I Changes of native and applied phosphorus in incuba- tion experiment. J. Scient. Agric. Soc. Finl. 55: 345—354. Hartikainen, H. 1983b. Effect of liming on phosphorus in two soils of different organic matter content. II Changes in the availability of phosphorus to turnip rape (Brassica campestris). J. Scient. Agric. Soc. Finl. 55: 355—362. Hartikainen, H. 1984. Peat ash and basic slag as substi- tutes for lime with reference to phosphorus uptake by turnip rape. J. Agric. Sci. 56: 291—298. Holpord, I.C.R. 1983. Differences in the efficacy of various soil phosphate tests for white clover between very acid and more alkaline soils. Aust. J. Soil Res. 21: 173—182. Holford, I.C.R. & Cullis, B.R. 1985. Effects of phos- phate buffer capacity on yield response curvature and fertilizer requirements of wheat in relation to phosphate tests. Aust. J. Soil Res. 23: 417—427. Kaila, A. 1955. Studies on the colorimetric determina- tion of phosphorus in soil extracts. Acta Agralia Fenn. 83: 25—47. Kuo, S. & Jellum, E.J. 1987. Influence of soil charac- teristics and environmental conditions on seasonal variations of water-soluble phosphate in soils. Soil Sci. 143: 257—263. Labhsetwar, V.K. & Soltanpour, P.N. 1985. A com- parison of NH4HC03-DTPA, NaHCOj, CaCl2 , and Na2-EDTA soil tests for phosphorus. Soil Sci. Soc. Amer. J. 49: 1437—1440. Lehr, J.J. & Wesemael, J.Ch. van 1952. The influence of neutral salts on the solubility of soil phosphate with special reference to the effect of the nitrates of sodium and calcium. J. Soil Sci. 3: 125—135. Mackay, A.D., Syers, J.K., Gregg, P.E.H. & Tillman, R.W. 1984. A comparison of 3 soil-testing procedures for estimating the plant availability of phosphorus in soils receiving either superphosphateor phosphate rock. N. Zeal. J. Agric. Res. 27: 231—245. Paasikallio, A. & Häkkinen, U. 1977. Acid ammonium acetate and acid ammonium acetate/EDTA as extrac- tants for phosphorus-32, aluminium and iron in soils. Ann. Agric. Fenn. 16: 227—237. Rvden, J.C. & Syers, J.K. 1975. Rationalization of ionic strength and cation effects on phosphate sorption by soils. J. Soil Sci. 26: 395—406. Sibbesen, E. 1983. Phosphate soil tests and their suitabi- lity to assess the phosphate status of soil. J. Sci. Food Agric. 34: 1368—1374. Sippola, J. & Jaakkola, A. 1980. Maasta eri menetelmil- lä määritetyt typpi, fosfori ja kalium lannoitustarpeen osoittajina astia- jakenttäkokeissa. Maatalouden Tut- kimuskeskus, Maanviljelyskemian ja -fysiikan laitos, Tiedote n:o 13. Sippola, J. & Saarela, I. 1986. Some extraction methods as indicators of need for phosphorus fertilization. Ann. Agric. Fenn. 25: 265—271. W islander, L. & Andersson, A. 1974. The composition of the soil solution as influenced by fertilization and nutrient uptake. Geoderma 11: 157—166. Ms received January 12, 1989 5 SELOSTUS Vesi- ja ammoniumasetaattiuuton soveltuvuus käyttökelpoisten fosforivarojen arviointiin kalkituissa maissa Helinä Hartikainen Helsingin yliopiston maanviljelyskemian laitos, 00710 Helsinki Tutkimuksessa vertailtiin kevätrypsin fosforin ottoa lannoitetuista ja kalkituista maista vesiuutolla ja happa- malla asetaattiuutolla saatuihin fosforiarvoihin. Aineis- tona käytettiin kaksivuotista astiakoetta ja sitä vastaa- vaa muhituskoetta, joissa kahta hapanta hietamaata oli käsitelty dolomiittikalkilla, masuunikuonalla tai nouse- villa kalsiittikalkkimäärillä. Ravinnesuolojen lisääminen maahan pienensi vesiuut- toisen fosforin määrää 30—50 %, mutta ei vaikuttanut asetaattiuuttoisen fosforin määrään. Koska suolapitoisuu- den laskiessa (esim. kasvien ravinteiden oton seuraukse- na) fosforin vapautumisen maanesteeseen tiedetään lisään- tyvän, lannoitetuista maista tehty vesiuutto saattaa ali- arvioida fosforireservejä, jotkaajan mittaan voivat tul- la kasvien käyttöön. Toisaalta asetaattiuutto näytti yli- arvioivan kalkituksen tehokkuutta fosforin käyttökelpoi- suuden parantajana. Vesiuuttoisen fosforin määrissä ta- pahtuneet muutokset vastasivat paremmin kalkituksen vaikutusta kevätrypsin fosforin ottoon.Toisessa koemaas- sa kalkitus pyrki vähentämään kevätrypsin fosforin ot- toa (suurin kalsiittimäärä 15 ff/o), vaikka asetaattiuuton perusteella käyttökelpoisuuden olisi pitänyt selvästi pa- rantua (29 %). Tässä maassa vesiuuttoinen fosfori ku- vasi paremmin käyttökelpoisia varoja, sillä sen määrä vä- heni kalkituksen intensiteetin noustessa (18 %). 6