DISTRIBUTION OF EXTRACTABLE CALCIUM, MAGNESIUM. POTASSIUM, AND SODIUM IN VARIOUS DEPTHS OF SOME VIRGIN PEAT SOILS Armi Kaila and Jaakko Kivekäs Department of Agricultural Chemistry, University of Helsinki Received August 7,195f The distribution of plant nutrients in various layers of a peat profile depends on several factors. Among these are for example the intensity with which the nutrients are adsorbed or fixed by the peat, the quantities of nutrients carried by the water or by the air from the neighbourhood, and also the utilization of nutrients by the respective surface vegetation. In shallow peat lands the quality of the mineral subsoil is of importance, too. Our information even of the combined effect of all these factors on the nutrient content of various peat layers is rather poor. Only very few results concerning this problem are reported in Finland. In a previous publication one of us (2) tried to elucidate the distribution and forms of phosphorus in various depths of thirty virgin peat lands. Waren (4) gives data of calcium, magnesium, potassium, phos- phorus and sulphur soluble in 4% hydrochloric acid from nine peat profiles. In addition to these only some scattered reports exist. The authors were interested in the contents of plant available calcium, mag- nesium and potassium in various depths of peat lands. Therefore, an investigation was carried out in which samples from different layers of virgin peat soils were analysed, generally down to about a depth of one meter. The extraction with ammonium chloride solution was supposed to give an estimate of the available amounts of the cations. In addition to calcium, magnesium, and potassium also sodium was determined. https://www.c-info.fi/en/info/?token=GzWKPy1xsrxgq704.mFOSvzfNGkbzs-Q49bgbAg.G3W9XG4iL9No2e0MeaEGoWgKN3Hhubxb9ClPbjgrWOHEdTq4lB7iALUyEwsL4NsXlcgM3bKj5wspUTReiFRz4Zv_ttXy_Q6QmggnnfnOEFiMeNgrbx71FZZz1_cPUcbkbbBnaAhsRyAc8xNEGmIBvERw_AJ4i-UXKjO-BQrSjcQSOhpZKPcF5FWSCyCufuu_ Material and methods The material of the present investigation consisted of 85 samples taken from 25 peat lands. All of them were from Northern Finland and represented uncultivated soils. The surface vegetation type and degree of land quality of the sampling places were the following: 1. Sphagnum fuscum pine bog, Bo 1. 2. Treeless Sphagnum fuscum bog, Bo 1. 3. —i. Carex globularis pine bog, Bo 2. 5. Oligotrophic water-logged Sphagnum bog occupying hollows, Bo I—2.1 —2. 6. Treeless Sphagnum papillosum bog, Bo I—2.1 —2. 7. --8. Treeless Sphagnum papillosum -- Scirpus caespitosus bog, Bo 2. 9. 10. Treeless Sphagnum papillosum Carex lasiocarpa bog, Bo 3. 11.--15. Treeless Sphagnum papillosum Carex limosa bog, Bo 3. 16. Mesotrophic treeless Sphagnum papillosum bog, Bo 6. 17. 18. As number 16, occupying hollows, Bo 5. 19. 20. Treeless, water-logged Carex limosa bog, Bo i. 21. Flooded bog, without trees, Bo 5. 22. Mesotrophic water-logged treeless Bo 6. 23. Sphagnum Warnstorfianum fen, Bo 8. 24. 25. Scorpidium scorpioides fen, Bo 7. The depths of the sampling layers and the kind of the respective peat are reported in Table 1 which also gives the degree of humification for the peat samples estimated in the field according to the method of von Post (3). In addition to the peat samples also samples of mixed surface vegetation were collected from the peat lands n:ris 6—lo and 12—18. All the analyses described in the present paper were performed of air-drv peat ground in a Wiley mill. The pH-value was determined in a water suspension (1:4). The extraction of the cations was carried out with 1 N ammonium chloride solution. The ratio of soil to extractant was 1: 50, and the extraction period was two hours. The estimation of calcium, potassium, and sodium in the filtrate was performed using the flame photometer by Lange. The total calcium -\- magnesium content of the filtrate was determined by the versenate titration (1) and the amount of magnesium was calculated on the basis of the calcium content estimated bv the flame photometer. Obviously, the data obtained by this method do not correspond to the content of exchangeable cations in these soils. A more reliable estimation of their amount could have been gained if barium chloride instead of ammonium chloride had been used and if the extraction had been completed by some thorough washings. The disturbing effect of barium on the flame photometric determination of the other cations prevented its employment, and it was necessary to resort to ammonium chlo- 238 ARMI KAILA and JAAKKO KIVEKÄS Table 1. Calcium, magnesium, potassium and sodium extracted by 1 N ammonium chloride Irom various layers of the peat lands Depth Kind Ash Ca Mg K Na No of H pH w v dm peat % kg/ha 1 o—3 S 1 4.2 0.08 5.9 660 180 30 20 4—6 S 1 4.4 0.08 3.9 750 150 10 10 6—B CS 5 4.5 0.25 5.8 220 450 30 10 - o—2 S 1 4.5 0.11 4.9 1080 310 140 10 2—4 CS 2 4.6 0.23 5.0 2000 340 170 20 4—6 CS 4 4.6 0.25 4.3 1750 270 70 10 3 1 2 S 1 4.5 0.11 4.2 1500 80 230 100 2—3 S 2 4.6 0.17 4.5 2300 120 280 120 3—4 CS 5 4.6 0.39 5 5 3000 150 210 80 4 o—3 LCS 2 4.2 0.09 3.4 410 400 470 40 3—5 4 4.4 0.25 9.7 860 750 320 670 7—lo 6 4.3 0.36 6.2 850 850 130 300 .">. o—2 S 1 3.7 0.05 1.4 180 150 90 40 2—5 3 3.6 0.09 1.5 410 220 40 30 5—9 r. 3.8 0.21 2.9 710 350 50 50 9— H 7 4.2 0.32 2.4 1130 580 60 30 6. Plant matter 4.3 0.07 7.2 350 320 490 30 o—2 S 1 3.9 0.29 5.7 1200 1000 150 10 3—5 S 3 4.0 0.34 4.0 1000 580 30 10 B—lo SC 5 4.1 0.30 3.1 780 410 20 0 7. Plant matter 4.4 0.06 6.9 280 190 310 4" o—3 S 1 4.5 0 12 5.2 480 350 10 10 5—7 CS 4 4.3 0.30 3.5 960 660 10 20 B—lo CS 5 4.1 0.35 4.0 1260 850 10 10 8. Plant matter 4.3 0.10 5.8 480 240 740 150 I—3 CS 3 3.8 0.33 7.8 1000 280 140 Tu 3—5 SC 7 4.2 0.42 11.0 920 280 60 40 9. Plant matter 4.5 0.07 7.9 620 320 620 30 o—2 S 1 4.4 0.28 10.8 1800 780 360 20 3—5 C 3 4.5 0 29 10.0 1200 500 110 20 lo Plant matter 4.5 0.09 8.5 620 360 760 130 I—3 SC 4 4.3 0.34 6.2 1800 350 240 200 3—5 LC 7 4.6 0.31 5.3 1300 320 60 60 U Ol S 1 4.2 0.09 5.0 850 290 50 40 2—3 SC 3 4.9 0.34 6.1 2300 610 120 20 4—6 C 5 4.9 0 34 6.1 2500 750 40 10 12 3 4 5 6 7 8 9 10 11 12. Plant matter 4.9 0.07 22.6 920 320 590 70 o—2 SC 3 4.9 0.26 16.7 1250 570 90 20 3—5 SC 2 4.8 0.25 4.0 2250 860 40 20 B—lo SC 2 4.8 0.20 6.5 1550 760 70 20 13. Plant matter 4.4 0.09 12.9 650 340 740 50 2—4 SC 4 4.3 0.34 6.5 1550 750 90 20 6—B SC 3 4.5 0.30 3.7 1150 880 10 20 B—lo C 5 4.1 0.31 5.5 1250 650 130 30 14. Plant matter 4.5 0.07 7.3 640 320 1230 70 I—3 SC 2 5.0 0.25 12.3 3000 880 210 90 4—6 SC 4 4.2 0.30 5.8 1750 840 70 30 B—lo C 7 5.8 0.37 7.2 6700 3400 70 20 15. Plant matter 4.8 0.09 5.9 900 610 680 20 I—3 SC 2 4.7 0.38 8.0 3200 1060 210 40 5—6 LC 3 5.0 0.34 5.5 2500 1160 10 10 B—9 C 6 5.1 0.37 8.7 3000 1250 10 10 16. Plant matter 4.8 0.09 8.3 1000 130 750 70 o—2 C 3 4.7 0.30 5.5 2000 820 250 20 3—5 C 3 4.8 0.25 5.1 1400 600 30 30 B—lo C 4 4.9 0.23 4.2 1400 480 60 60 17. Plant matter 5.0 0.11 10.7 1170 460 220 50 .I—3 SC 4 5.0 0.26 5.6 2500 900 60 20 4—6 5 5.2 0.37 5.5 4100 1440 40 70 8 -10 6 5.3 0.40 5.0 5100 1840 30 50 18. Plant matter 5.0 0.12 22.9 1200 500 550 40 I—3 SC 3 5.1 0.26 16.9 2000 620 70 20 4—6 5 5.1 0.35 7.9 4200 700 50 70 B—lo 7 5.2 0.37 7.4 7100 1440 50 40 19. o—l SC 3 4.4 0.27 9.8 2800 700 90 10 I—3 C 4 4.9 0.28 5.1 2200 620 10 10 5—7 C 4 5.1 0.26 4.9 1750 570 10 10 -O- o—2 SC 4 5.5 0.27 15.4 1800 400 30 10 3—5 C 7 5.4 0.46 8.1 3100 650 20 10 6—B C 6 5.4 0.30 4.8 2300 780 10 10 21. o—2 SC 3 3.6 0.23 24.4 760 970 280 120 3 9 5 3.5 0.32 3.5 1060 1300 160 120 10—13 7 4.2 0.40 13.2 1560 1430 100 290 --• I—3 C 3 4.6 0.21 4.5 1400 360 10 5 5—7 C 3 4.2 0.20 3.1 1400 560 10 5 11 14 LC 4 4.4 0.23 5.3 1300 640 10 5. DISTRIBUTION OF EXTRACTABLE CALCIUM, MAGNESIUM 241 12 3 4 5 6 7 8 9 10 11 23. o—2 EuSC 3 4.4 0.18 18.4 2800 1150 550 160 3—5 5 4.7 0.32 4.9 6100 1500 110 130 B—lo 7 4.3 0.38 5.1 4000 1800 90 120 24. o—l BC 1 4.9 0.16 9.9 1700 290 90 60 2 BC 2 5.2 0.24 15.6 1800 170 40 60 5—7 BC 7 5.0 0,37 10.6 3000 540 10 140 25. o—2 BC 1 5.5 0.14 9.0 2900 310 100 110 3 BC 3 5.2 0.28 7.5 4800 620 170 160 7—9 BC 7 5.3 0.34 4.4 4600 500 110 100 ride. It is known to be a less effective exchanger in peat soils than barium chloride and it appears to be able to dissolve some calcium sulphate. On the other hand, it may be possible that the amounts of cations extracted by any solvent from the air-dried and ground samples markedly differ from those exchangeable from fresh samples. In any case, the results obtainable by the method employed probably yield a rough estimate of the fairly easily available amounts of calcium, magnesium and potassium in the peat samples. Since more attention was paid to the relative contents than on the absolute amounts it did not appear to be desirable to use any constant coefficient to improve the possibly too low results obtained by using only one extraction. Results The data in Table 1 show that the kind of peat in the various layers of the same peat land is almost equal or only slightly tends to improve with the depth. Generally the degree of humification and the volume weight increase on going deeper but changes in the pH values are fairly small and irregular. The ash content of all the samples is rather low indicating no marked presence of mineral matter in these virgin peat soils. The amounts of the extractable cations are reported as kilograms per hectare in a layer of 2 dm. Thus, the markedly varying volume weight of the samples was taken into consideration and the comparison of the cation content could occur on a basis better corresponding to the natural conditions than if the results were presented per weight. These values are, of course, somewhat artificial, since volume weights estimated on air-dry and ground peat are used for the calculation, but they can be supposed to give a fairly reliable picture of the relative amounts of the extrac- table cations in the different layers. In almost all the samples calcium appears to be the dominating cation, alt- hough also the content of magnesium may often be of the same order. The potassium and sodium contents of the peat samples are far lower and, on the average, nearly equal to each other. Only in samples of undecomposed plant material the potassium content, even when expressed on the volume basis, can be higher than the calcium and magnesium contents of the respective samples. Table 2. The relative contents of extractable cations in various depths of the peat lands Depth Kind Per volume Per weight No of Ca Mg K Na Ca Mg K Na dm peat 1. o—3 S 100 100 100 100 100 100 100 100 4—6 S 115 85 40 30 115 85 40 35 6 CS 330 250 100 55 105 80 30 15 2. o—2 S 100 100 100 100 100 100 100 100 2—4 CS 185 110 120 500 90 55 55 200 4 CS 160 90 50 125 70 40 20 50 3. I—2 S 100 100 100 100 100 100 100 100 2 S 150 150 120 120 95 100 80 80 3 CS 200 185 90 80 55 50 25 25 4. o—3 LCS 100 100 100 100 100 100 100 100 3—5 210 190 70 1700 75 70 25 560 7 210 210 30 750 50 55 5 170 5. o—20—2 S 100 100 100 100 100 100 100 100 25 230 150 45 75 130 80 20 40 5 400 230 55 125 95 55 15 30 9—ll 630 390 65 65 100 60 10 10 6. Plant matter 30 30 330 600 120 135 1400 2300 o—20—2 S 100 100 100 100 100 100 100 100 3 S 85 60 20 140 70 50 20 100 8— 10 SC 65 40 15 0 60 40 10 0 7. Plant matter 60 55 3100 400 115 110 6500 900 0— S 100 100 100 100 100 100 100 100 5—7 CS 200 190 60 200 80 75 25 75 B—lo CS 260 240 140 70 90 85 50 25 8. Plant matter 50 85 530 210 155 280 1760 730 1— 3 CS 100 100 100 100 100 100 100 100 3—5 SC 90 100 45 60 70 75 35 50 9. Plant matter 35 40 170 150 140 160 680 500 0—2 S 100 100 100 100 100 100 100 100 3—5 C 70 65 30 100 70 65 30 75 10. Plant matter 35 100 320 65 130 380 1210 240 1— SC 100 100 100 100 100 100 100 100 35 LC 70 90 25 30 80 100 30 35 11. o—l S 100 100 100 100 100 100 100 100 2 SC 270 210 240 35 70 55 60 100 46 C 290 260 80 15 80 70 20 50 242 \k.MI KAILA and JAAKKO KIVEKÄS 12 3 45 (5 7 89 10 11 12. Plant matter 75 55 650 440 280 21(1 2340 1600 o—2 SC 100 100 100 100 100 Hki 100 100 3—5 SC 180 150 45 125 190 150 45 125 B—lo SC 125 135 80 125 160 170 85 165 13. Plant matter 40 45 820 250 155 175 3160 970 2—4 SC Kid 100 100 100 100 100 100 100 4—6 SC 75 120 15 100 85 120 15 100 B—lo C 80 85 145 125 85 95 160 135 14. Plant matter 2d 35 590 80 75 130 2140 300 I—3 SC 100 100 100 100 100 100 100 KM) 4—6 SC 60 95 35 35 50 80 25 30 B—lo C 220 390 35 20 150 260 20 20 15. Plant matter 30 60 320 50 115 240 1350 260 I—3 SC 100 100 100 100 Kid 100 100 100 5—6 LC 80 110 5 2(1 80 120 5 20 B—9 C 95 120 5 20 95 120 5 20 16. Plant matter 50 80 350 200 170 270 1200 720 o—2 C 100 100 100 100 100 100 100 100 3—5 C 55 75 15 85 70 90 20 120 B—lo C 55 65 30 170 75 90 35 220 17. Plant matter 50 50 350 250 110 120 900 550 I—3 SC 100 100 100 100 100 100 100 100 4—6 165 160 65 350 115 110 45 225 s— lo 205 205 50 250 130 130 35 150 18. Plant matter 60 80 790 200 130 175 1750 380 I—3 SC 100 100 100 100 100 100 100 100 4—6 210 115 70 350 160 85 55 250 B—lo 355 230 70 200 250 160 r,r> 150 19. o—l SC 100 100 100 100 100 100 100 100 I—3 C 80 90 10 80 75 85 10 15 5—7 C 65 80 5 70 65 85 5 15 20. o—2 SC 100 100 100 100 100 100 100 100 3—5 C 170 160 70 100 100 95 30 50 6—B C 130 195 40 60 115 175 30 50 21. o—2 SC 100 100 100 100 100 100 100 100 3—9 140 135 55 100 105 100 40 75 10—13 210 145 35 240 120 85 20 145 22. I—3 C 100 100 100 100 100 100 100 100 5 -7 C 100 155 90 100 105 165 100 100 11 l4 LC 95 180 110 100 85 165 100 100 243DISTRIBUTION OF EXTRACTABLE CALCIUM, MAGNESIUM . ARMI KAILA and JAAKKO KIVEKÄS244 12 3 4567 89 10 11 23. 0 2 EuSC 100 100 100 100 100 100 100 100 3 s 220 130 20 80 125 70 10 50 B—lo 140 155 15 75 70 75 10 40 24. o—l BC 100 100 100 100 100 100 100 100 2—3 BC 105 60 45 100 70 40 30 70 5—7 BC 175 185 10 230 75 80 5 100 25. o—2 BC 100 100 100 100 100 100 100 100 3 5 BC 165 200 170 145 80 100 90 70 7 9 BC 160 160 110 100 65 65 45 40 In peat lands of better quality the amount of extractable calcium tends to be somewhat higher than that of the peat lands of lower quality. The corresponding differences in the contents of other cations seem to be less marked. Considerable variations exist in the distribution of calcium in different layers of the peat soils. Generally, an increase in the calcium content with the depthcan be noted. The same seems also to hold true with the magnesium extracted by this procedure, but the distribution of potassium is reverse. Particularly the potassium content of undecomposed plant material appears to be far higher than that of the lower peat layers. The distribution of sodium seems to be less regular. The general trends in the distribution of the extractable cations in various depths may be easier to observe if instead of the absolute amounts the relative contents are examined. Therefore, the cation contents of the surface samples were given the value of 100, and the respective relative values for the other layers were calculated. These results are listed in Table 2. The relative calcium and magnesium contents calculated on the basis of the kg/ha-values seem most often to increase with the depth, although there also are profiles in which the surface layer appears to be the richest one. In most of the cases potassium is concentrated in the surface vegetation and also the surface layer of peat generally contains a higher amount of extractable potassium than the lower ones. The distribution of sodium in some profiles resembles that of potassium, whereas in other cases an increase in the sodium content with increasing depth may be found. If the relative values calculated on the basis of the cation content expressed per weight are examined the concentration of potassium and sodium in plant matter is the most striking feature. Also the magnesium content in all the cases and the calcium content in most of them are highest in the surface vegetation. Generally, the potassium content is very low in the deeper layers, but the distribution of the other cations appears to be fairly variable in the different profiles. An approximate general view of these results may be presented by the average values of the respective relative cation contents in various layers. Owing to the fact that the sampling depths were not equal in all the peat lands only a rough DISTRIBUTION OF EXTRACTABLE CALCIUM, MAGNESIUM . 245 estimation can be gained. The relative distribution of the extractable cations in four peat layers and fresh plant material appears, on the average, to be the follo- wing: Per volume Per weight Ca Mg K Na Ca Mg K Na Plant material 40 60 690 240 140 200 2030 790 o—3 dm 100 100 100 100 100 100 100 100 3—6 dm 150 130 60 200 110 80 30 100 6—lo dm 170 170 50 140 100 110 40 80 10—14 dm 310 240 70 140 100 100 40 80 The effect of depth on the relative amounts of extractable cations was also studied by computing the correlation coefficients between these quantities. The 12 samples of plant material were excluded, and only the peat layers were examined. The following total correlation coefficients were obtained for the depth and the relative content of cations: Cation content per volume Cation content per weight Ca r = 0.22 r = 0.1.8 Mg r = o.s4*** r = 0.30* K r = 0.27* r = o.4B*** Na r = 0.09 r = 0.04 According to these figures no correlation exists between the depth and the content of extractable calcium or sodium in these peat lands. The correlation coefficients between the depth and the magnesium content appear to be somewhat higher than could have been expected on the basis of the average values reported above, particularly if the data concerning the magnesium content per weight are examined. The negative correlation between the content of extractable potassium and the depth is distinct, although not very close. Discussion The results reported in this paper do not reveal any clear picture of the distri- bution of plant-available cations in various depths of virgin peat lands. The only distinct feature seems to be the accumulation of extractable potassium in the living surface vegetation and also, although in a less degree, in the surface layers of peat. Almost in every case, also the percentic content of sodium, magnesium, and calcium in the surface vegetation was somewhat higher than that of the peat below. The accumulation of the easily extractable potassium in surface vegetation may be taken to arise from the scanty occurrence of this important plant nutrient in peat lands. Since it was found that also in the peat layers almost all of the total potassium was extractable by 1 N ammonium chloride, there is probably no reason to suppose that potassium would be markedly more tenaceously adsorbed in the lower and more humified peat layers than in the plant material and in the surface layers. JAAKKO KIVEKÄS246 ARMI KAILA and Of course, the possibility of the washing out of potassium from the lower layers of peat lands can not be excluded. On the basis of the present material it is impossible to conclude which of these phenomena, the most economical utilization of the poor sources of potassium in the peat lands or the washing out of this nutrient, is the more important one. According to the opinion of the authors, the former reason seems to be more probable than the latter one. If the potassium content of the surface layers of these peat lands is compared to the uptake of this nutrient by a medium crop of oats or timothy, it will be found that most of these peat lands contain enough easily available potassium for the growth of one or two crops. However, there are peat lands, such as the numbers 1,7, 20 and 22 in which the lack of available potassium probably prevents the growth of a satisfactory crop. If the amounts of calcium and magnesium extracted by the present method are available for plants, these nutrients do not generally play the role of minimum factors in peat soils. Summ a r y It has been attempted in the present paper to study the distribution of plant- available calcium, magnesium, and potassium in various depths of 25 virgin peat lands. The amounts of these cations extractable by 1 N ammonium chloride are supposed to give a rough estimation on the available content of the nutrients. Also the quantities of extracted sodium are reported. It has been found that the percentic content of these cations in the surface vegetation are higher than in the peat. Particularly marked is the accumulation of potassium in living plants and, although in a less degree, in the surface layers of peat. The variation in the distribution of the extractable amounts of the cations in various depths of the peat lands is considerable. A significant correlation exists between the depth and the magnesium content, and a negative correlation between the depth and the amount of extractable potassium. So far as the amount of cations extracted by 1 N ammonium chloride repre- sents nutrients available for plants, calcium and magnesium are not generally minimum factors in peat soils, whereas in most soils the sources of potassium probably will be depleted by the first crops. REFERENCES (1) Cheng, K. L. & Bray, R. H. 1951: Determination of calcium and magnesium in soil and plant material. Soil Sei. 72: 449—458. (2) Kaila, A. 1956. Phosphorus in various depths of some virgin peat lands. J. Sei. Agric. Soc. Fin- land 28: 90—104 (3) Post, L. von 1924. Das genetische System der organogenen Bildungen Schwedens. Com. Intern. 1'•■dol. IV Comm. 22:287—304. (4) Waren, H. 1924. Untersuchungen über die botanische Entwicklung der Moore. Wiss. Veröff. Finn. Moorkulturver. No 5. Helsinki. DISTRIBUTION OF EXTRACTABLE CALCIUM, MAGNESIUM . 247 SELOSTI'S: UUTTUVAN KALSIUMIN, MAGNESIUMIN, KALIUMIN JA NATRIUMIN" MÄÄRISTÄ ERÄITTEN LUONNONTILAISTEN SOITTEN ERI SYVYYKSISSÄ Armi Kaila ja Jaakko Kivekäs Yliopiston maanviljelyskemian laitos, Helsinki Tutkimuksessa on esitetty 1 n ammonium kloridin uuttamat kalsiumin, magnesiumin, kaliumin ja natriumin määrät 25 luonnontilaisen suon eri kerroksista pinnasta noin 1 m:n syvyyteen. Lisäksi analysoitiin 12 suon pintakasvustoa. Todettiin kasvien sisältävän enemmän uuttuvia kationeja kuin alla olevan turpeen. Etenkin kasviaineksen kaliumin pitoisuus oli erittäin suuri verrattuna turpeen vastaavaan arvoon. Turpeen uuttuvan kaliumin määrä aleni tavallisesti syvemmälle mentäessä, mutta muitten kationien kohdalla muutokset olivat epäsäännöllisempiä. Uuttuvan magnesiumin pitoisuus näytti lisääntyvän syvemmissä kerroksissa. Sikäli kuin saadut tulokset kuvastavat soitten käyttökelpoisia ravinnevarastoja, näyttää siltä, että kalsium ja magnesium vain harvoin ovat minimitekijöinä. Kalium sen sijaan riittänee tavallisesti tyydyttämään vain ensimmäisten satojen tarpeen.