APATITE AS A PHOSPHORUS FERTILIZER Martti Salonen Agricultural Research Centre, Department ofAgricultural Chemistry and Physics, Tikkurila Received September 16, 1968 When the investigations into the possibilities of utilizing the apatite deposit, found in the parish of Siilinjärvi, Finland (Salonen et ah, 1966), were started, an experiment with finely ground, chemically untreated apatite concentrate was included in the pot tests. The tests were first carried out in acid mineral soil (pH 4.9), that was extremely poor in phosphorus. Oats were used as test plants and the experiment was continued for three years. No indication of a phosphorus effect could, however, be observed. Already in 1935 similar results had been obtained at our department when the influence of Kola apatite on an acid mineral soil (pH 4.3, Teräsvuori, unpublished manuscript) was studied. Comparable results have been noted in investigations abroad. Huikari (1964, p. 16), however, presents positive results for forest fertilizations with apatite on bog peat soils. For this reason it was decided to carry out another studies into the phosphate fertilizing effect of apatite on bog peat. At the same time the ability of pine and oats to utilize the not easily soluble phosphorus of apatite was compared. Pot tests with apatite The apatite concentrate used in the tests was deliveredby Lohjan Kalkki- tehdas Oy, which had prepared it from the Siilinjärvi apatite. The material was very finely ground, having passed through a sieve with 0.06-mm holes. According to analyses the concentrate contained: P 205 total » soluble in amm.citrate » » » 2 % citric acid » » » water CaO MgO GOj F 1) 21.00 % 0.17 » 0.14 traces only 49.70 % 1.83 » 21.40 » 1.10 » l ) Made at the Research Laboratory of Rikkihappo Oy under the supervision of Dr. T. Vahervuori. https://www.c-info.fi/en/info/?token=wbAiKIgKRb4Px6wz.vLbuHopdg8-81_MZIMgBJg.1FWMzNSbZ5PF3SZAkEE3MKTn2yEhsRru1k1pky2laqH8Ckyfcek47hKiySvaCsKNeR84kzkW0qg5pIpg99G8qfUuBXA-Uie5Z-zdgovZEltpSrZ4JJVo5wiRkLc_g4OOtp_LEyjITE5ZUNpUt1csF7926pPKl5MwDrr4kQ 210 The material was half apatite and half limestone and contained a small amount of dolomite. The fluorine content was smaller than in the well-known Kola apatite, which the Siilinjärvi apatite resembles in many respects, judging by the X-ray diffraction dia- grams1). The soil used in the test was Sphagnum fuscum peat, obtained from a natural peatland area at the Leteensuo Experimental Station. The pH of the peat was 3.9 and it was ex- tremely poor in exchangeable calcium and plant nutrients. In the autumn it was shredded fine and carefully mixed while still moist. Over the winter the soil was kept in a cool place and in the spring it was put in the test pots (enamelled Mitscherlich pots) after application of fertilizers and other compounds. In this way it was possible to mix the components homogeneously into the peat. The volume of the soil in each pot was 4.5 1. Treatments. The experimental treatments were the same irrespective of the test plant and sowing time. All pots were filled at the same time and kept under similar moisture and temperature conditions. The following basic fertilization was applied to all pots: ammonium nitrate potassium sulphate magnesium sulphate 2.858 g/pot 0.925 » 2.000 » trace element mixture (Cu, B, Mn, Mo) ferri-EDTA 10 ml 15 mg/pot The amount of potassium in particular was small for the oats, whereas for the pine it was adequate, at least in the beginning. Too much potassium could have been harmful to the pine, especially during its early stages of development. Experimental treatments: Liming; 1. 0 2. calcium carbonate, 6 g/pot 3. » » 12 » 4. » » 24 » Phosphorus application: 1. 0 2. superphosphate (sf) 5.128 g/pot = 1000 mg P 80 6 3. apatite concentrate (ap) 4.760 » = 1000 » » All treatments were not included each year. The various treatments in the respective years are presented in Tables 1 and 2. Sowing, attendance and harvest of test plants Pine [Firms silvestris, Scotch pine) was sown from seeds collected in November 1965 from pines at Tikkurila. Because the initial growth of pine seedlings is always slow and because we had only one growing season at our disposal, we extended this period by first keeping the pots in a greenhouse. On March 9, 1966, 40 seeds of pine per pot were sown. •) Made at the Research Laboratory of Rikkihappo Oy under the supervision of Dr. T. Vahervuori. Emergence was satisfactory in the limed as well as in the unlimed pots fertilized with apatite. At the beginning of June the pots were moved outdoors into a wire net cage. In the warmth of the greenhouse and with an abundance of plant nutrients, the growth was rapid with the exception of the pots without liming and without apatite. Moving the pots outdoors did not seem to disturb the growth, which continued at the same rate until the harvest in early September. At the time of the harvest the height of the tallest plants was 28 cm and they were 6 mm in diameter. Many plants were branched. The harvest took place September B—l2, 1966. The stems were cut at soil surface. After drying it was easy to separate stems and needles. The pine roots were also harvested. The separation of the roots from the peat soil was relatively easy. It may be mentioned that the pine roots were covered with mycorrhiza, although no inoculation had been performed. Oats (variety Pendek) were used as trial plants side by side with pine in 1966. Because no unlimed treatments were included for coats in 1966, and these later proved to be in- dispensable, thepot tests with oats were repeated in 1967. The repeated tests were carried Fig. 1. Test pots 8/8-66, pine. Treatments and numbers of test pots: phosphorus" fertilization 0 sf ap liming: 0 497 498 499 12 g/pot 500 501 502 24 „ 503 504 505 Fig. 2. Test pots 17/8-67, oats. Treatments and numbers of test pots: phosphorus fertilization 0 sf ap liming: 0 372 373 374 6g/pot 375 376 377 12 „ 378 379 380 211 212 Table I. Dry matter yields for different liming levels and yield increases by phosphorus fertilisation, g/pot. Without liming Liming 6 g/pot Liming 12 g/pot Liming 24 g/pot Significance yield yield incr. yield yield incr. yield yield incr. yield yield incr. phosph. liming phosph. sf ap sf ap sf ap sf ap ' ert - ' ert> liming Pine 1966: needles 0.2 0.2 25.9 2.7 20.9 2.7 1.8 20.2 —O.l stems 0.1 0.0 15.3 1.1 15.2 1.2 0.6 12.8 —O.l roots 0.0 (J.l 16.4 2.7 15.5 2.7 1.2 17.0 0.0 total 0.3 0.3 57.6 6.5 51.6 6.6 3.6 50.0 —0.2 56.64*** 7.12* 433.66*** Oats 1966: grain 2.8 38.6 2.9 4.1 40.2 0.9 straw 5.5 38.5 3.1 7.2 41.2 1.2 total 8.3 77.1 6.0 11.3 81.4 2.1 2261.01*** 4.22 6.67* Oats 1967 1 ): grain 0.3 0.1 33.3 2.4 36.1 14.6 1.6 37.9 2.7 straw 2.0 0.4 35.1 5.6 33.6 15.5 6.5 36.7 1.6 total 2.3 0.5 68.4 8.0 69.7 30.1 8.4 74.6 4.3 34.54** 77.10** 496.89*** *) 1967 liming 12 g/pot without replications; not included in statistical tests; applies to all tables. 213 out using the same bog peat soil and the same techniques as in 1966. The pots were packed in March and kept in a greenhouse, but the oats were sown at the end ofMay in both years. The oats grew fairly well in pots with liming and phosphate fertilization and in un- limed pots with apatite fertilization. In the pots showing the best growth, brown stains typical of potassium deficiency were noted in the glumes of the oats when ripening time approached. The oats were harvested when the normally grown plants were ripe. Grain and straw yields, expressed as dry matter g/pot, are given in Table 1. It should be mentioned that in both years I—21 —2 weeks after the treatments plenty of green algae was observed on the surface of the peat soil in all pots which had received phosphorus fertilization, superphosphate or apatite. Presentation of experimental yields In order to facilitate the interpretation of the test results, the yields of pine and oats are presented together in Table 1. The results for the oats are for two growing seasons, but as can be seen the same treatments have given the same results in both years (liming 12 g/pot in 1967 without replications). Table 1 shows that the apatite concentrate has been an effective phosphorus fertilizer for pine as well as for oats in unlimed Sphagnumfuscum peat, which was so acid that when Table 2. Plant nutrient contents of experimental yields, mg/pot. Without liming Liming 6 g/pot Liming 12 g/pot Liming 24 g/pot no sf ap no sf ap no sf ap no sf ap phos. phos. phos. phos. Pine 1966: N n.d. n.d. 1) 856 P 206 1 5 300 K 2 O 2 7 526 CaO 1 2 199 MgO 1 2 131 Oats 1966: N p 2o5 K2 O CaO MgO Oats 1967: N 46 95 747 195 762 P 206 5 53 450 12 633 K 2O 20 49 436 110 438 CaO 3 2 95 19 289 MgO 4 15 136 15 169 *) n.d. = not determined. 208 867 317 99 698 92 12 336 24 7 252 6 69 512 160 61 484 58 44 387 102 51 462 52 16 123 32 11 118 10 221 934 340 228 1197 259 13 696 24 15 402 20 162 514 278 221 520 234 33 480 55 56 410 71 17 224 29 26 228 32 694 223 870 232 98 13 657 23 382 153 516 211 107 32 402 44 94 21 215 26 Table 3. Analyses of the water percolating through the soil columns, contents in autumn at the end of test, mg/1. Without liming Liming 6 g/pot Liming 12 g/pot Liming 24 g/pot Significance no sf aP no sf aP no rf ap no sf ap phosph. liming phos.fert. Pine as test plant, 1966 P H 3.0 2.9 3.6 4.3 4.9 6.1 7.2 6.9 7.5 111.68*** 1990.01*** 27.56*** P,0 6 mg/1 1.6 324.0 80.9 0.2 151.3 0.4 0.2 10.3 6.4 156.91*** 92.22*** 48.23*** K aO » 140 149 3 106 4 79 117 5 108 Ca ° » 56 208 106 430 301 381 557 316 510 9.91** 205 27*** 24 71*** MgO » 97 132 55 66 46 58 62 36 59 Oats as test plant, 1967 P H 3 - 2 3- 1 3 - 7 4.1 4.0 4.4 4.9 4.6 5.0 255.72*** 1512.33*** 17.66*** PjOj mg/1 1.8 202.3 14.3 0.5 30.0 3.2 0.5 17.0 6.0 55.26*** 3800*** 3082*** K a O » 132 115 9 86 39 17 78 9 67 Ca ° » 51 158 67 151 265 136 244 306 308 49.02*** 71.10*** 3 27 MgO » 33 31 8 22 14 10 24 12 23 214 215 superphosphate was used as a fertilizer no noticeable growth could be recorded. Even a scant application of lime, 6 g/pot, received only by the oats in these tests, has made the superphosphate usable and caused a very marked decrease in the effect ofapatite. Adequate liming has completely counteracted the effect of apatite. The quantities of the plant nutrients are given in Table 2 as sums of the nutrients in the yields. It is apparent that the phosphorus of the apatite really appears in the plants in cases where apatite fertilization has increased the dry matter yield. The two treatments, apatite without liming and superphosphate with liming, show no pronounced difference in the amounts of phosphorus. In cases where the growth has been best, the amount of potassium in the yields has equalled the amount originally supplied by fertilization. As the Sphagnumfuscum peat contains practically no potassium there has been a severe deficiency of potassium at the end of the growing period. Examining the total amounts ofplant nutrients in theyields onecan furthermore observe that they have been about the same for both the experimental plant species, despite their utter dissimilarity. The most important difference is the amount of phosphorus which the oats have taken up in much greater quantities in relation to other plant nutrients than the pine. The plant nutrient contents of water percolating through the soil of the experimental pots In the Mitscherlich method used in the tests, the pots were kept outdoors. It was there- fore impossible to exclude precipitation. At the time of the harvest there was water in the base-dishes. In 1966 the largest quantity was 700 ml and in 1967 it was 2500 ml. Each base- dish was made to contain the same amount ofwater by using the above mentioned quanti- ties and pouring water into the soil of the pots lacking in this respect. The percolated water in each pot was then analysed, and the results are given in Table 3. In particular one must point out thephosphorus contents of the percolated water. When unlimed bog peat was treated with superphosphate the contents were very high. Liming has markedly decreased the phosphorus content of the water. The apatite concentrate has under no circumstances noticeably raised the phosphorus content of the percolated water. In pots showing good growth, the potassium content of the percolated water has in fact been very low. Analyses of the soils in the pots after the harvest After the harvest pH determinations in water suspension as well as in 1 N KCI-solution were made from the soils in the test pots. The results of these determinationsas well as those of the soil analyses made according to the ammonium acetate method (Vuorinen and Mäkitie 1955; Kurki et ah, 1965) are presented in Table 4. As can be seen there are differences in the test results for the different years regardless of the fact that the amount of soil and the treatments were the same in both years. The use of another test plant and the different amounts of water in the base-dishes have influenced the results. From the pH figures it appears that the apatite concentrate, on account ofits carbonate content, has somewhat decreased the acidity and increased the content of exchangeable calcium in the soil. In this connection the phosphorus figures are the most interesting ones. For the Sphagnumfuscum peat, which is extremely deficient in phosphorus, even without Table 4. Results of soil analyses 1 ) at harvest time in autumn. Without liming Liming 6 g/pot Liming 12 g/pot Liming 24 g/pot Significance no sf ap no sf ap no sf ap no sf ap phosph. liming phos.fert. phos. phos. phos. phos. fert. liming Pine as test plant 1966 pH in water 3.5 3.4 3.8 4.8 5.2 5.8 7.3 6.9 7.5 98.09*** 3547.60*** 22.24*** pH in 1 JV KCI 2.9 2.9 3.3 4.5 4.8 5.6 7.2 6.9 7.4 44.53*** 2188.03*** 9.67*** P mg/1 soil 4.3 68.0 17.7 3.6 53.2 4.9 3.0 73.6 4.0 574.29*** 11.57*** B.34*** K » » 117 100 20 100 25 90 113 33 108 124.38*** 6.23*** 93.37*** Ca » » 200 383 467 1500 1617 1800 2633 2917 3183 20.10*** 950.88*** 1.27 Oats as test plant 1967 pH in water 4.0 3.8 4.1 4.7 4.3 4.9 5.0 4.8 5.2 184.22*** 282.24*** 15.16** pH in 1 JV KCI 2.9 3.0 3.2 3.7 3.5 3.9 4.5 4.1 4.5 226.36*** 882.29*** 7.29* P mg/1 soil 2.4 17.7 6.7 1.3 10.8 2.7 1.4 18.4 1.7 662.52*** 190.03*** 33.11*** K » » 65 48 20 60 65 37 50 20 45 46.64*** 2.68 16.68*** Ca » » 258 350 542 742 752 1050 1150 1450 1400 58.44*** 411.49*** 3.59 l ) P, K and Ca analysed by Department of Soil Science. 216 217 any phosphorus fertilization, moderate phosphorus numbers have been obtained. This phenomenon, which has been known for a long time, is obviously due to the fact that pure bog peat contains no phosphorus fixing substances, and thus even traces of phos- phorus can be disclosed in the analysis. For the same reason apatite has apparently some- what raised the phosphorus figures, especially in peat without liming. Superphosphate has raised the phosphorus figures considerably and by approximately the same amount in limed and unlimed peat. Discussion Many research workers in various countries have studied the phosphorus effect of chemically untreated finely ground apatite, although the results have generally been negative, e.g. Frank (1943), Lundblad (1957) and Döring (1958). Ansorge (1966), using lupine as a test plant, obtained a slight phosphorus effect for Kola apatite. Munk (1960) studied the influence of the grade of fineness and reached the conclusion that Kola apatite may exert a phosphorus effect ifthe particles are less than 0.002 mm in diameter. Höweler and Woodruff (1968) obtained similar results. The majority of the studies on the phosphorus effect of apatite have been made using acid mineral soil. Under such circumstances we did not observe any effect either. Beside being very acid, the culture medium apparently must not contain any phosphorus fixing constituents. Pure Sphagnum fuscum peat satisfies these requirements. As test plants we used pine and oats. Even though these two plant species are very dissimilar, there seems to be no major difference between them with regard to the uptake of phosphorus from superphosphate on the one hand and from apatite on the other. It is, however, possible that the solubility of the phosphate of apatite and the availability of it for plants conclusively depends on the qualities of the culture medium. Thus the only requirement is that the plants endure these extreme conditions. Although apatite, under certain conditions, may be a useful phosphorus fertilizer for oats, it cannot be considered important in practical agriculture. On the other hand it is possible that in forest fertilization, on bog peat soils, it could be utilized. Apparently the calcium (magnesium) carbonate, included as an impurity, is also beneficial. Its proportion could probably be even greater than in the concentrate used in the present tests. It can be anticipated that fertilization of large bog peat areas with easily soluble phosphates, on account of the water percolating through the peat, may cause harmful effects in water systems. With the use of not readily soluble phosphates this risk is considerably diminished. Summary In pot trials, where very acid Sphagnum fuscum peat has been used as a growth subs- tance, a finely ground but chemically untreated apatite concentrate has given a notice- able phosphorus effect for pine as well as for oats. Even a scarce liming has signi- ficantly diminished the phosphorus effect and a satisfactory liming has altogether stopped it. Apatite may be a suitable phosphorus fertilizer in forest manuring on bog peat soils. The carbonate included as an impurity in apatite may also be beneficial. By the use ofnot 218 readily soluble phosphorus fertilizers one may diminish the possibilities of phosphorus entering water systems; this should be taken into consideration when the areas to be fertilized are very large. LITERATURE Ansorge, H. 1966. Untersuchungenüber die Phosphorsäureaufnahme aus Kola-Apatit und »Hyperphos» durch Lupinen und Hafer. Albrecht-Thaer-Archiv 10: 153—166. Döring, H. 1958. Untersuchungen über die bessere Düngewirkung des weicherdigen Rohphosphates Hyperphos im Vergleich zum kristallinen Kola-Apatit. Z. PflErnähr. Düng. 83: 140—148. Frank, O. 1943. Jämförande gödslings- och kalkningsförsök med apatithaltig dolomitisk kalksten frän Ainon. Lantbrukshögskolan, Jordbr.förs.anst., Medd. Nr 8. Huikari, O. 1964. Erilaisten fosfori- ja typpilannoitteiden soveltuvuudesta ojitettujen suometsien lan- noitukseen. Leipä leveämmäksi 12/1: 13—17. Höweler, R. H. and Woodruff, C. M. 1968. Dissolution and availability to plants of rock phosphates of igneous and sedimentary origin. Soil Sei. Soc. Amer. Proc. 32: 79—82. Kurki, M., Lakanen, E., Mäkitie, 0., Sillanpää, M. and Vuorinen, J. 1965. Viljavuusanalyysien tulos- ten ilmoitustapa ja tulkinta. Summary: Interpretation of soil testing results. Ann. Agric. Fenn. 4; 145—153. Lundblad, K. 1957. Om räfosfater och jämförande forsök med sädana fosforgödselmedel pä myrjord. Stat. Jordbr. förs. Medd. Nr 80. Munk, H. 1960. Über P 206 -Wirksamkeit und Teilchengrösse bei Apatiten. Landw. Forsch. 13: 296—302. Salonen, M., Tainio, A. and Tähtinen, H. 1966. Kalsiumkarbonaattipitoisesta apatiitista valmistettujen emäksisten fosforilannoitteiden käyttöarvoa koskevia tutkimuksia. Summary: Studies on the value of alkaline phosphate fertilizers prepared from calcite-containing apatite. Ann. Agric. Fenn. 5:12— 25. Vuorinen, J. and Mäkitie, O. 1955. The method of soil testing in use in Finland. Agrogeol. julk. 63. SELOSTUS APATIITTI FOSFORILANNOITTEENA Martti Salonen Maatalouden tutkimuskeskus, maanviljelyskemian ja -fysiikan laitos, Tikkurila Tutkittaessa Siilinjärveltä löydetyn apatiitin käyttömahdollisuuksia on astiakokeissa ollut mukana myös hienoksi jauhettu, mutta kemiallisesti käsittelemätön apatiittirikaste. Happamalla ja suuresti fosforilannoituksen tarpeessa olevalla kivennäismaalla se ei antanut mitään fosforivaikutusta kauralla enempää kuin männylläkään. Tulos on yhdenmukainen useimpien aikaisempien tutkimustulosten kanssa. Pelkällä raa’alla rahkaturpeella ( Sphagnum fuscum) sensijaan sekä kaura että mänty saivat apatiitista runsaasti fosforia. Jos kuitenkin rahkaturve kalkittiin sopivaksi katsottavalla määrällä, apatiitin teho lop- pui (taul. 1 ja 2). Kokeissa olleiden kasvilajien välillä ei ollut eroa apatiitin fosforin käytössä niin kaikin puolin erilaisia kasveja kuin kaura ja mänty ovatkin. Apatiitin fosforin käyttökelpoisuus on ratkaisevasti riippunut kasvualustan ominaisuuksista. Maan pitää ilmeisesti olla paitsi hapan myös vapaa fosfaattia pidättävistä aineista. Pelkkä rahkaturve vastaa näitä vaatimuksia. Kun pelkälle rahkaturpeelle fosfori on annettu veteen liukenevana superfosfaattina, on maan läpi valuneen veden fosforipitoisuus ollut paljon korkeampi kuin annettaessa vaikeasti liukenevaa apatiittia (taul. 3). Tämä seikka on hyvä tietää lannoitettaessa suuria rahkasuoalueita ja pyrittäessä välttämään fosforin joutumista vesistöihin. Maa-analyysin tulokset (taul. 4) osoittavat, että käytetyllä apatiittirikasteella on ollut selvän maan happamuuttavähentävä ja vaihtuvaa kalkkia lisäävä vaikutus, mikä johtuu sen sisältämästä kalsiumkarbo- naatista.