OBSERVATIONS ON THE MOBILIZATION OF PEAT NITROGEN IN INCUBATION EXPERIMENTS Jaakko Kivekäs and Erkki Kivinen Department of Agricultural Chemistry. University of Helsinki, Received July 12, 1959 Peat lands contain considerable amounts of nitrogen, which for the main part however, occurs in such organic compounds as are not easily soluble and are slow in mobilizing, being thus scarcely or not at all available to plants. The mobilization of the natural supply of nitrogen into a form available to plants would thus be of considerable economic advantage in the cultivation of peat lands. Kaila, Soini and Kivinen (3) have investigated the effects of calcium, fertilizers, and ash on the mobilization of nitrogen, and state that calcium as a rule stimulated the nitri- fication, but on the amount of mineral nitrogen calcium has in general a negative effect. The effect of ash was, according to them, apparent mainly as a neutralizing quality. They did not observe any clear effect of trace elements, nor of calcium or phosphorus fertilizers. Having investigated the effect of lime on the accumulation of mineral nitrogen in incubation experiments with peat soils Kaila and Soini (5) states that liming does not always enhance the accumulation of mineral nitrogen, nor does it always cause an increase in the nitrate nitrogen. Kivinen (7) has in some experiments noted that liming and fertilizing clearly enhances the mobilization of peat nitrogen. Kaila, Köylijärvi and Kivinen (2) found that a higher temperature increased the amounts of ammonium nitrogen, though they might be caused by purely chemical phenomena. Since all the above mentioned investigations into the mobilization of peat nitrogen have been carried out with only comparatively few samples, it was decided to continue research by using more extensive material. Material and methods The material of this study consisted of 60 samples from peat soils in North Finland. All the samples were air-dried and ground with a Willey-mill. The pH was measured in water and N KCI suspensions (1:4) using a Beckman pH-meter with glass electrode. The ammonium nitrogen was extracted with an 0.1 N HCI. The ammonium nitrogen was deter- mined by shaking samples of fresh incubated peats weighing 20 grams in 100 ml of 0.1 N HCI for one hour, and by filtrating and washing the peat twice with 25 ml of the extractant. The ammonia in the extract was determined by distillation with MgO (5). https://www.c-info.fi/en/info/?token=aH698nxIa8pJzWSQ.Zylt_dlY-kG6DWiXU3sNyQ.NMwbrzgBLhzsSepI8cnfMiIvyBSmsCLMw51rrrzyUmGA2maDX7Pyccja3iGIMZifzuhFMMNh3wUR7s2iejsse5EvB1M3Ul8mEiP-KE9RM9at5cb3H-SKUtjSw9CJtqbQzDf95u-de8Ybt5YD_-ExIzH2KJ2m6hiOYEPVQLpVss9KMuIwoK2BMMqpIu4HyZ0z-Q2l 269 The soluble organic nitrogen was determined from the original samples by burning, in accordance with the Kjeldahl-method, a part of the solution obtained in determining the ammonium nitrogen and by distilling the nitrogen from this. The obtained amount of nitrogen minus the amount of ammonium nitrogen was taken as representing organic nitrogen. The nitrate nitrogen was extracted from fresh samples of 20 g with 100 ml of a CaSO, solution in which the samples were shaken for ten minutes. The determination was made from the filtrate by the phenoldisulphonic acid method (1) using an EEL-colorimeter. The presence of nitrite nitrogen was determined with Griess’ reagent. Also the amounts of calcium and potassium extractable with a N NH,CI solution were determined by adding 100 ml of this solution to 2 g of air-dried peat. The liquid was filtered through paper and the determination was made by using a Lange flamephotometer (4). Some characteristics of the peat samples are reported in Table 1. There are 20 samples in which the Sphagnum remains are dominant; the other 40 samples represent peat where the Carex remains are dominant. Table 1. Peat samples. No H Depth Weight Ash pH 1120 pHKcl 1 N NH,CI Total NH,-N NO,-N Min. N dm of % exchange- N g/kg g/kg g/kg volume able % Ca% Samples of BCp 9 o—l o—2 0,16 9.9 4,9 4.1 0.52 1.95 0.20 0.33 0.53 1 1 o—2 0.14 9.0 5.5 4.5 1.05 2.52 0.13 0.35 0.48 10 I—2 2—4 0.24 15.6 5.2 4.1 0.37 2.97 0.11 0.21 0.32 2 3 3—5 0.28 7.5 5.2 4.3 0.86 2.75 0.14 0.38 0.52 3 7 7—9 0.34 4.4 5.3 4.2 0.68 2.76 0.12 0.10 0.22 11 7 5—7 0.37 10.6 5.0 3.9 0.40 3.62 0.14 0.20 0.34 Samples of Cp 29 I—2 5—7 0.20 5.1 4.6 3.9 0.37 1.99 0.17 0.15 0.32 44 3 I—2 0.34 16.4 4.5 3.9 0.45 3.12 0.26 0.18 0.44 13 3—4 I—3 0.28 5.1 4.9 4.0 0.39 3.47 0.13 0.25 0.38 14 3—4 5—7 0.26 4.9 5.1 4.1 0.34 2.67 0.19 0.17 0.36 25 3—4 I—3 0.21 4.5 4.6 3.7 0.34 2.33 0.17 0.25 0.42 26 3—4 5—7 0.20 3.1 4.2 3.7 0.35 2.40 0.18 0.24 0.42 40 3—4 I—3 0.29 10.9 5.8 4.6 0.39 3.06 0.09 0.17 0.26 43 3—4 o—l 0.35 11.1 4.9 4.1 0.50 3.12 0.22 0.29 0.51 45 3—4 o—l 0.31 5.6 4.9 4.2 0.71 3.60 0.25 0.56 0.81 46 3—4 I—2 0.33 2.3 4.1 3.6 0.60 3.20 0.24 0.36 0.60 51 3—4 o—2 0.27 5.3 4.8 3.7 0.46 2.94 0.23 0.17 0.40 52 3—4 o—2 0.29 4.7 4.4 3.8 0.54 2.98 0.18 0.37 0.55 36 5 4—6 0.34 6.1 4.9 3.8 0.37 2.54 0.10 0.08 0.18 55 5 o—2 0.23 8.8 4.8 4.0 0.56 3.62 0.15 0.16 0.31 56 5 o—2 0.27 8.4 4.7 3.7 0.55 3.78 0.19 0.15 0.34 41 5—6 2—6 0.28 3.5 4.2 3.7 0.39 3.61 0.21 0.09 0.30 20 6 6—B 0.30 4.8 5.4 4.3 0.38 2.88 0.18 0.16 034 4 6—7 3—6 0.35 6.6 5.2 4.1 1.35 2.73 0.14 0.09 0.23 19 7—B 3—5 0.46 8.1 5.4 4.3 0.34 3.52 0.24 0.15 0.39 60 B—9 10—14 0.53 7.0 4.9 3.7 0.36 2.56 0.33 0.29 0.62 Xo H Depth Weight Ash pH H2O pHKCj 1 N NH,CI Total NH,-N N03 -N Min. N dm of % exchange- N g/kg g/kg g/kg volume able %o Ca % Samples of SCp 28 1 o—3 0.20 6.5 4.5 3.9 0.45 1.74 0.19 0.12 0.31 12 2—3 o—l 0.27 9.8 4.4 3.9 0.51 3.40 0.14 0.72 0.86 35 2—3 4—6 0.26 5.0 4.4 3.6 0.34 1.03 0.19 0.08 0.27 18 3—4 o—2 0.27 15.4 5.5 4.4 0.33 4.51 0.25 0.46 0.71 24 3—4 6—B 0.35 2.2 5.1 4.0 0.66 2.51 0.17 0.03 0.20 59 5—6 o—s 0.45 9.6 5.3 4.1 0.30 5.07 0.34 0.14 0.48 Samples of EuSCp 57 3 o—2 0.25 8.5 5.5 4.5 1.40 2.56 0.15 0.16 0.31 58 3 o—2 0.28 5.9 5.3 4.5 1.25 3.20 0.16 0.18 0.34 47 3—4 o—2 0.24 7.1 5.9 5.3 2.35 3.00 0.17 0.26 0.43 48 3—4 o—2 0.27 7.2 5.9 5.4 2.40 3.24 0.22 0.91 1.13 5 3—4 4—6 0.27 5.3 5.4 4.9 1.40 2.53 0.17 0.20 0.37 Samples of LC- and LSCp 27 4 11—14 0.23 5.3 4.4 3.7 0.29 2.04 0.22 0.27 0.49 23 4—5 4—6 0.32 2.0 5.0 4.0 0.79 2.37 0.17 0.05 0.22 30 5—6 2—5 0.34 4.7 4.8 3.9 0.36 2.73 0.18 0.10 0.28 Samples of CSp 16 I—2 o—2 0.26 10.3 4.4 3.5 0.30 2.44 0.29 0.40 0.69 16 I—2 o—2 0.21 8.5 4.3 3.6 0.30 2.67 0.10 0.38 0.48 17 I—2 o—2 0.18 6.5 4.4 3.6 0.34 2.11 0.16 0.51 0.67 38 2 2—4 0.23 5.0 4.6 3.0 0.43 2.23 0.62 0.21 0.83 49 2—3 o—2 0.18 4.8 4.5 3.6 0.49 3.03 0.20 0.27 0.47 50 2—3 o—2 0.22 4.3 4.3 3.6 0.50 3.25 0.12 0.25 0.37 53 3 o—2 0.23 5.6 4.6 3.8 0.46 3.26 0.18 0.12 0.30 54 3—4 o—2 0.26 4.1 4.6 3.8 0.50 3.03 0.16 0.13 0.29 39 3—4 4—6 0.25 4.3 4.6 3.1 0.35 2.12 0.28 0.21 0.49 8 4—5 3—4 0.39 5.5 4.6 3.9 0.39 2.41 o.oil 0.23 0.32 33 5 6—B 0.25 5.8 4.5 3.3 0.44 2.61 0.21 0.08 0.29 42 6—7 2—4 0.39 12.4 3.9 3.3 0.30 2.37 0.13 0.09 0.22 Samples of Sp 6 o—l I—2 0.11 4.2 4.5 3.6 0.70 1.19 0.12 0.47 0.59 21 o—l o—2 0.09 8.0 4.3 3.1 0.62 0.85 0.21 0.08 0.29 31 o—l o—2 0.08 5.9 4.2 2.9 0.41 2.44 0.21 0.14 0.35 32 o—l 4—6 0.08 3.9 4.4 3.0 0.47 1.46 0.23 0.16 0.39 34 o—l o—2 0.09 5.0 4.2 3.4 0.34 1.03 0.20 0.37 0.57 37 1 o—2 0.11 4.9 4.5 3.1 0.49 1.45 0.21 0.17 0.38 7 I—2 2—4 0.17 4.5 4.6 3.8 1.06 1.49 0.19 0.20 0.39 22 I—2 2—3 0.14 2.8 5.0 4.1 0.63 1.15 0.17 0.09 0.26 270 271 The samples came from the surface layers of bogs as well as from layers deeper down. Consequently the degrees of humification differed relatively much. The volume weights and the amounts of ash indicate that there were no notable amounts of mineral matter in the samples, which is natural enough since the main part of the samples came from bogs in natural state situated rather far from roads etc. Most of the samples were clearly acid and the amounts of exchangeable calcium were low. The amounts of total nitrogen were the same as are common in Finnish peats (6). The amounts of mineral nitrogen were rather high in most of the samples. The drying and grinding of the samples may be a reason for this, as has been shown possible by Kivekäs (8) expressly where ammonium nitrogen is concerned. No nitrite was found in the samples. All the results have been calculated in relation to dry matter as mg/kg or kg/ha (to the depth of 20 cm). The incubation experiments The object of the investigation was to elucidate the phenomena that appear in peat nitrogen under favourable conditions with regard to moisture and other circumstances. It is hardly necessary to emphasize that in a laboratory the condi- tions are considerably more favourable and regular than in the field, and since the samples had been dried and ground the results obtained are certainly not applicable to the natural processes in the field. Moreover, the arrangement of the experiments was such as to give an indication of the interaction between the different phenomena like ammonification, nitrification, and denitrification at the moment of analysis, but not to give any idea of the leaching or the influence of plants, etc. that take place in the field. Each sample was ground and mixed and placed into four glass jars, each jar containing 50 g. Of the four jars two were limed with an amount of lime correspond- Figure 1. The effect of the incubation on the acidity of peat samples. 272 Table 2. The effect of incubation on the pH Hao of peat samples No before 1 month of 3 months of incubation incubation incubation unlim- lim- unlim- limed ed ed ed Samples of BCp 9 4.9 5.8 6.7 4.9 5.6 1 5.5 4.9 6.6 4.6 6.4 10 5.2 5.7 6.4 6.1 6.8 2 5.2 5.3 6.1 4.8 5.7 3 5.3 5.8 6.4 4.8 5.3 11 5.0 5.6 6.0 5.4 6.2 average 5.2 5.5 6.4 5.1 6.0 L.S.D. 95% 0.2 0.3 0.5 0.5 Samples of Cp 29 4.6 5.1 5.9 4.8 5.5 44 4.5 5.0 5.2 5.9 6.1 13 4.9 5.4 5.3 5.1 5.9 14 5.1 5.6 6.4 6.0 6.3 25 4.6 5.3 5.8 4.3 4.2 26 4.2 4.8 5.5 4.9 5.2 40 5.8 6.0 6.4 5.1 5.6 43 4.9 5.0 5.4 5.9 6.2 45 4.9 5.2 5.6 5.9 6.1 46 4.1 4.4 5.0 4.9 5.1 51 4.8 5.0 5.2 5.1 4.7 52 4.4 5.1 5.4 5.1 4.6 36 4.9 5.3 5.4 5.2 5.4 55 4.8 5.6 5.9 4.2 5.0 56 4.7 5.3 5.7 5.3 5.0 41 4.2 4.2 4.7 4.6 5.2 20 5.4 4.8 5.4 5.7 5.9 4 5.2 5.6 6.1 4.4 4.9 19 5.4 5.2 5.5 5.7 5.0 60 4.9 5.5 5.8 5.3 4.9 average 4.8 5.2 5.6 5.2 5.4 L.S.D. 95% 0.2 0.2 0.2 0.3 Samples of SCp 28 4.6 5.1 5.9 4.8 5.5 12 4.4 5.0 6.2 5.1 5.7 35 4.4 4.8 5.4 5.2 5.4 18 5.5 4.2 5.0 4.4 5.6 24 5.1 5.9 6.3 4.8 5.0 59 5.3 6.1 5.9 6.0 6.3 average 4.9 5.2 5.8 5.1 5.6 L.S.D. 95% 0.6 0.5 0.5 0.1 No before 1 month of 3 months of incubation incubation incubation unlim- limed unlim- limed ed ed Samples of EuSCp 57 5.5 5.8 6.0 5.2 5.7 53 5.3 5.7 6.2 5.2 5.6 47 5.9 6.0 6.6 5.5 6.2 48 5.9 5.8 6.4 5.7 6.2 5 5.4 5.4 6.0 5.0 5.7 average 5.6 5.7 6.2 5.3 5.9 L.S.D. 95% 0.1 0.1 0.1 0.1 Samples of LSC-and LCp 27 4.4 4.9 5.4 4.7 4.7 23 5.0 5.7 6.4 4.1 4.0 30 4.8 5.1 5.6 5.2 5.2 average 4.7 5.2 5.8 4.7 4.6 L.S.D. 95 % 0.2 0.2 0.2 0.5 Samples of CSp 15 4.4 4.7 5.2 5.5 5.0 16 4.3 4.5 5.1 5.0 4.4 17 4.4 4.5 5.2 4.9 4.7 38 4.6 4.8 5.4 4.3 5.2 49 4.5 4.8 5.5 5.1 4.7 50 4.3 4.4 5.3 5.0 4.8 53 4.6 5.2 4.7 4.4 4.7 54 4.6 5.2 5.6 5.0 5.0 39 4.6 4.8 5.3 4.3 4.7 8 4.6 5.0 5.8 5.8 6.2 33 4.5 4.7 5.5 4.8 5.4 42 3.9 3.6 4.1 4.3 4.8 average 4.4 4.7 5.2 4.9 5.0 L.S.D. 95 % 0.3 0.3 0.3 0.3 Samples of Sp 6 4.5 4.9 4.9 4.8 5.4 21 4.3 4.7 5.6 4.0 4.1 31 4.2 4.2 5.3 4.7 5.3 32 4.4 4.0 5.8 4.7 5.2 34 4.2 4.5 5.7 4.9 5.5 37 4.5 5.0 5.8 4.7 5.5 7 4.6 4.7 5.5 5.6 4.6 22 4.3 4.7 5.6 4.0 4.1 average 4.5 4.6 5.5 4.7 5.0 L.S.D. 95% 0.l 0.1 0.2 0.2 273 ing to 4 tons per hectare. The samples were moistened to a moisture degree of about 70 per cent. Water evaporating during the time of incubation was replaced by moistening performed at intervals. The moistened and well mixed samples were incubated at a mean temperature ofabout 17—18° C. Although the optimal tempera- ture for the nitrification organisms is higher, the above mentioned temperature was considered suitable mainly because it is easily available, and because it corres- ponds, at least to some extent, to conditions in nature. The contents of the jars were analysed after one month and three months of incubation. The pH, the am- monium and the nitrate nitrogen were determined from a fresh sample. In Table 2 and in Figure 1 the effects of the incubation on the acidity are reported, the mean values are calculated per peat type, as well as the significant difference at 95 per cent level. In order to facilitate comparison the values determined before incubation have also been given in the tables. The figures in Table 2 show that incubation during one month has in most cases caused a decrease in the acidity, although also a few contradictory cases are noted. In the limed samples the rise in the pH was greater than in the unlimed ones. After three months of incubation in part of the samples an increase in the acidity was to be seen, although the pH continued to be higher than the original pH value. On examining the effect of incubation on the acidity of the peat samples on the basis of the mean values it is evident that in all peat groups there was a rise in the pH during one month of incubation. The rise varies in unlimed samples by 0.1—0.5 while in the limed samples it was 0.6—1.2 pH degrees. After three months of incubation the pH had sunk, although it was still higher than the original pH values in all the peat groups except the limed LC- and LSC peats. In the limed samples, with the exception of the LC and LSC peats, the pH was higher than in the unlimed samples. In general the changes in the pH are very similar in all peat groups. Any clear differences between the different peat groups cannot be noted. The rise in the pH that occurs during the first month of incubation can probably be attributed to the ample formation of ammonia during the first stages of incubation, as Kaila and others (3) and Kaila and Soini (5) have stated. Later, when the ammonia has changed into nitrate the pH sinks again. Table 3 shows the effect of incubation on the amounts of ammonium and nitrate nitrogen. Examining the figures in this Table, one finds that this effect was very variable. Since the variations are big even within one and the same type of peat, it is difficult to get a clear view of the matter by examining the values of the single samples. For this reason the mean values of the different types of peat have been calculated in Table 3. On the basis of these figures it can be stated, that an incubation of one month increased the amount of ammonium nitrogen in all peat groups except the SC peat groups, and that liming in some cases enhanced the forming of NH 4-N. A considerable decrease in the nitrate nitrogen can be noted, this being greater in the unlimed samples than in the limed ones. If the amounts of ammonium nitrogen and nitrate nitrogen in the original samples and those in the incubated ones are compared, it will be found that in 1 month of incubation 3 months of incubation Sample Before incubation unlimed limed unlimed limed Sol.org. NH.-N NO,-N Min. N NH,-N N0 3-N Min. N NH,-N N0 3-N Min. N NH,-N N0 3-N Min. N NH.-N N0 3 -N Min. N N Samples of BCp 9 470 200 330 530 555 0 555 625 125 750 715 490 1 205 155 880 1 035 1 415 135 350 485 90 300 390 75 485 560 160 475 635 105 590 695 10 505 110 210 320 220 45 265 325 55 380 560 50 610 825 105 930 2 395 140 380 520 80 105 185 65 125 190 435 280 715 360 270 630 3 495 120 100 220 230 20 250 290 10 300 340 230 570 180 325 505 11 385 140 200 340 215 5 220 370 10 380 610 5 615 835 20 855 average 445 140 295 435 230 80 310 290 135 425 470 255 725 410 365 775 Diff. 90 —215 —125 150 —l6O 10 330 40 290 270 70 340 L.S.D. 95% 180 120 145 215 190 210 210 215 340 350 335 210 Samples of Cp 29 590 165 150 315 50 5 55 55 5 60 125 15 140 105 10 115 44 975 255 175 430 460 70 530 460 40 500 650 225 875 65 655 720 13 590 130 250 380 440 75 515 210 285 495 185 335 520 150 445 595 14 385 190 170 360 420 15 435 370 15 385 530 100 630 480 345 825 25 625 165 250 415 330 30 360 240 85 325 445 30 475 140 265 405 26 515 175 240 415 300 35 335 290 35 325 420 35 455 380 45 425 40 660 90 165 255 345 35 380 235 60 295 140 270 410 220 115 335 43 790 215 285 500 330 35 365 335 20 355 485 110 595 30 440 470 45 935 250 555 805 505 80 585 520 80 600 655 65 720 30 455 485 46 900 240 360 600 310 15 325 295 20 315 420 10 430 5 390 395 51 645 225 170 395 375 20 395 290 105 395 320 15 335 95 305 400 52 650 175 365 540 395 20 415 435 25 460 455 15 470 105 430 535 36 635 100 80 180 250 10 260 285 10 295 270 10 280 290 15 305 55 745 145 160 305 455 20 495 375 100 475 150 310 460 85 410 495 56 540 185 150 335 405 15 420 385 20 405 445 25 470 50 405 455 41 455 210 90 300 585 10 595 500 10 510 595 10 605 15 505 520 20 435 180 160 340 265 10 275 275 15 290 460 10 470 520 15 535 4 615 140 85 225 310 30 340 310 35 345 410 305 715 210 520 730 19 500 240 150 390 340 15 355 365 10 375 585 85 670 260 315 575 60 600 325 290 615 400 25 425 385 15 400 455 35 490 215 145 360 average 640 190 220 410 350 30 380 405 50 455 405 110 515 170 315 485 Diff. 160 —l9O —3O 215 —l7O 45 215 —llO 105 20 95 75 274 275 Samples of SCp 28 720 185 115 300 110 5 115 150 5 155 365 15 380 140 105 245 12 480 720 140 860 435 20 455 515 15 530 270 395 665 190 495 685 35 675 190 80 270 225 10 235 200 20 220 270 15 285 210 15 225 18 545 250 460 710 50 370 420 25 470 495 160 410 570 190 540 730 24 425 165 30 195 395 20 415 375 25 400 465 30 495 455 45 500 59 655 325 290 615 400 25 425 385 15 400 455 35 490 215 145 360 average 585 305 185 490 270 75 345 275 90 365 330 150 480 235 225 460 Diff. —35 —llO —145 —3O 95 —125 25 35 —lO —7O 40 —3O L.S.D. 95% 175 150 140 190 195 155 125 205 140 115 240 230 Samples of EuSCp 57 535 145 160 305 330 40 370 145 160 305 65 310 375 40 280 320 58 590 160 175 325 420 15 435 335 10 345 90 340 430 55 330 385 47 765 165 260 425 430 60 490 350 95 445 90 360 450 335 80 415 48 625 220 905 1 125 100 340 440 100 370 470 90 470 560 365 85 450 5 470 170 200 370 50 305 355 40 325 365 310 585 895 460 670 1 130 average 595 170 340 510 265 155 420 195 190 385 130 415 545 250 290 540 Diff. 95 —lB5 90 25 —l5O —125 —4O 75 35 80 —5O 30 L.S.D. 95% 225 190 75 175 185 85 125 140 260 235 300 410 Samples of LSC- and LCp 27 525 215 270 485 340 25 365 275 35 310 405 35 440 330 45 375 23 605 165 45 210 470 20 490 460 30 490 355 160 515 90 415 505 30 575 175 95 270 255 5 260 320 5 325 415 10 425 455 30 485 average 570 185 135 320 355 15 370 350 25 375 390 70 460 290 165 455 Diff. 170 —l2O 50 165 —llO 55 205 65 140 105 30 135 L.S.D. 95 % 270 25 285 235 35 250 75 200 125 460 550 175 276 ""*■"**'■ Samples of SCp «m Clr" 15 470 290 395 685 550 50 600 ' 610 145 755 1 07tf 80 1 150 350 655 1 005 16 505 100 380 480 300 15 315 400 40 440 580 25 605 160 480 640 17 455 160 510 670 395 35 430 475 65 540 560 35 595 340 360 700 38 695 620 205 825 985 30 1 015 930 50 980 1 330 15 1 345 \ 260 10 1 270 49 725 200 270 470 420 15 435 490 35 525 575 15 590 390 145 535 50 810 120 250 370 335 15 350 455 45 500 495 5 500 245 255 500 53 700 180 120 300 340 20 360 100 405 505 195 145 340 70 500 570 54 605 155 130 285 360 20 380 355 30 385 300 10 310 190 130 320 39 690 275 205 480 520 45 565 510 50 560 700 5 705 710 25 735 8 510 85 230 315 245 60 305 245 25 270 560 50 610 480 85 565 33 545 210 80 290 260 15 275 380 20 400 365 20 385 590 40 630 42 580 125 90 215 400 5 405 430 10 440 480 25 505 20 545 565 average 605 210 240 450 425 25 450 450 75 525 600 35 635 400 270 670 Diff. 215 —215 0 240 —165 75 390 205 185 190 30 220 L.S.D. 95 % 125 10 125 125 70 120 200 25 195 215 145 160 Samples of Sp 6 515 120 470 590 360 50 410 340 55 395 285 55 340 245 55 300 21 375 210 75 285 470 30 500 570 70 640 670 65 735 205 470 675 31 640 210 140 350 455 20 475 445 55 500 635 50 685 410 250 660 32 580 230 155 385 435 35 470 535 65 600 650 60 710 255 440 695 34 685 200 365 565 310 20 330 385 15 400 465 40 505 335 175 510 37 745 210 165 375 1 230 70 1 300 1 365 140 1 505 1 380 10 1 390 1 655 15 1 670 7 540 190 200 390 615 70 685 755 85 840 1 355 85 1 440 480 85 565 22 490 165 85 250 470 40 510 275 115 390 155 205 360 135 130 265 average 570 190 205 395 540 40 580 585 75 660 700 70 770 465 200 665 Diff. 350 —165 185 395 —l3O 265 510 —135 375 275 —5 270 L.S.D. 95 % 245 20 260 295 35 320 380 50 365 420 145 365 Carex domin. pe;ts 200 235 435 295 70 365 305 100 405 345 200 545 270 270 540 Diff. 95 —165 —7O 105 —135 —3O 145 35 110 70 35 105 L.S.D. 95 % 45 30 35 45 40 40 55 55 55 60 70 65 Sphagnum domin. peats 200 220 420 480 30 510 515 75 590 650 50 700 430 235 665 Diff. 280 —l9O 90 315 —145 170 450 —l7O 280 230 15 245 L.S.D. 95% 110 10 115 215 40 125 170 25 170 185 95 150 277 Carex-dominated peats, except in forest peats and limed Carex-dominated peats, a reduction in the amount of nitrogen has taken place. On the other hand, the amounts of ammonium nitrogen and nitrate nitrogen in Sphagnum peats are bigger in the incubated samples than in the original ones owing to the rich formation of ammonium nitrogen. After three months of incubation it can be established that in the unlimed samples there is more ammonium nitrogen than in the original ones, excepting the EuSC-peats. In general there has been an increase also in comparison with the samples that have been incubating for one month only. There is still less nitrate nitrogen than in the original samples, although the amount is greater than in samples incubated for one month excepting again the EuSC-peats. In the limed samples that have been incubating for three months there is more ammonium nitrogen than in the original samples, with the exception of the C and SC peats, but in general the ammonium nitrogen content is smaller than in the unlimed samples. Of nitrate nitrogen there was found more in the limed samples after three months of incubation than in the original ones, excepting the EuSC and S peats. On exami- ning the total amounts of ammonium nitrogen and nitrate nitrogen after three months of incubation it is found that they have increased in all peats except the SC peats. Liming has in some instances stimulated the mineralization. In order to establish the effect of incubation on the Carex- and Sphagnum- dominated samples the mean values of these two groups are given in Table 3. The BC, C, EuSC, SC, LSC, and LC peats (altogether 40 samples) have been considered Carex-dominated, and the CS and S peats (altogether 20 samples) have been consi- dered Sphagnum-dominated. In addition the possible increases or decreases in the amounts of mineral nitrogen as compared to the amounts in the original samples are also given. The results show that one month of incubation has in the Carex- dominated samples caused an increase in the amount of ammonium nitrogen, the increase being slightly greater in the limed samples than in the unlimed ones. The amount of nitrate nitrogen has decreased considerably after one month ofincubation, the decrease being slightly larger in the unlimed samples than in the limed ones. After three months of incubation the formation ofammoniumnitrogen in the unlimed samples has continued. In the limed samples, again, there is now less ammonium nitrogen than in the samples that had been incubating only one month, never- theless they still contain more ammonium nitrogen than the original samples. After three months of incubation the amount of nitrate nitrogen shows an increase as compared to what it was after one month, however, it is still slightly lower in the unlimed samples than in the original ones. In the limed samples, on the other hand, there is already slightly more nitrate nitrogen than in the original samples; accord- ingly liming has to some extent enhanced the forming of nitrate. On the basis of these results it would seem that after one month of incubation the amount of ammonium nitrogen and nitrate nitrogen together in the Carex-domi- nated samples, limed as well as unlimed, is slightly smallerthan inthe original samples. After three months the amount is greater than in the original samples. Liming has neither caused a distinct increase, nor a decrease in the amount, to some extent it has, however, enhanced the formation of nitrate. In the Sphagnum-dominated 278 samples one month of incubation has doubled the amount of ammonium nitrogen compared to the amount in the original samples; the increase is slightly larger in the limed samples. The amount of nitrate nitrogen has decreased considerably in the Sphagnum-dominated samples after one month of incubation. The decrease was smaller in the limed than in the unlimed samples. After three months the amount of ammonium nitrogen had further increased in the unlimed samples. In the limed samples, on the other hand, a decrease in the amount ofammonium nitrogen had taken place, although the amount is not nearly as small as in the original samples. The amount of nitrate nitrogen had increased also in the Sphagnum-dominated peats, true, only slightly in the unlimed samples, while in the limed ones the amount by now exceeded the amount of nitrate in the original samples. The total amount of ammonium nitrogen and nitrate nitrogen is clearly higher in the incubated samples, especially after three months of incubation, than in the original ones. If the changes in the nitrogen compounds of these two peat types are compared, it will be seen that they very much resemble each other. It is interesting to note that in the original samples there were on an average, equal amounts of ammonium nitrogen and nitrate nitrogen in both groups. It is also interesting to find that after three months of incubation the total amounts of ammonium and nitrate nitrogen are distinctly higher in the Sphagnum-dominated than in the Carex-dominated samples. It should be noted, however, that in this connection the results have been counted on the basis of the weight units. If the volume units are taken as the means of comparison, for instance the mobilization in kilograms per hectare (Fig. 2), the Carex peats are found to be better mobilizers of nitrogen. As regards the mobilization of nitrogen expressed in kg per ha as shown in Fig. 2 it is apparent that the mobilization is very similar in all peatgroups except the S-peats, whose mobilization ability is rather less than that of the other groups. On comparing Carex-dominated and Sphagnum-dominated peats it is found that Figure 2. Mineral nitrogen in kg/ha in different peat types. At each peat type the first pilars represent the orginal samples, the second and third pillars the situation after one month of incubation, and the fourth and fifth the situation after three months of incubation. 279 slightly more nitrogen is mobilized from the Carex-dominated peats, the difference is noticeable especially after an incubation period of three months. Since the material was fairly large and diverse it was considered justifiable to examine, using the correlation coefficient, to what extent the mobilization ofnitro- gen is dependent on other qualities in the samples. The coefficients were calculated only for the Carex- and the Sphagnum-dominated peats. In a few cases, only, a signi- fican correlation was obtained. Between the soluble organic nitrogen and the ammo- nium nitrogen in the limed Carex-dominated samples that had been incubating for three nonths a clear correlation was obtained (0.553***). A correlation was also obtained between the soluble organic nitrogen in the original samples and the mobilized nitrogen in the limed Carex-dominated samples that had been incubating for three months (0.425**). Discussion: On the basis of the results it can be stated that in these experimental conditions the differences between the various peat types in the mobilization of nitrogen are fairly small. To draw a clear line between the different peat types is difficult, in part even impossible. The same observation has earlier been made by Kaila, Soini and Kivinen (3). They have presumed that e.g. the low degree of humifi- cation in the peats could possibly account for the similarities. In this investigation, however, peats in many different stages of humification have been used, nevertheless no clear differences have been obtained. In addition the dispersions have been so great that even if there were in some cases differences between the mean values, the great dispersion makes them unreliable. It is interesting to note that in samples thathave been incubating for one month there is in many cases a smaller amount of mineral nitrogen than in the original samples. It is possible that there are many reasons for this, one of them might be the original great amount of extractable mineral nitrogen in the dried and ground samples. When the samples are moistened anew and are incubating, the effects of the drying and grinding might gradually disappear. The results obtained by Kive- käs (8) with regard to the effect of drying and grinding on the results of analyses, are an indication of this. Liming seems in general to stimulate the nitrification. Kaila, Soini and Kivi- nen (3) have reached the same conclusion. This was particularly apparent in the samples after three months of incubation. On the other hand liming has seldom an increasing effect on the total amount of mineral nitrogen, even if one can not speak about a decreasing effect of liming, as has been stated by Kaila and Soini (5). A relatively interesting point is the fact that by dividing the peats into only two groups, the Carex-dominated and the Sphagnum-dominated peats, the total amount of mineralized nitrogen is found to be higher in the Sphagnum-dominated than in the Carex-dominated peats. This, however, holds good only if the results are calculated on the basis of the weight unit; if the volume unit is used the Carex peats seem to mobilize more nitrogen. 280 Among the reasons for the similarity in the results obtained from differentpeats, the effect of the artificial conditions in a laboratory may be considered the most important one. The incubation experiments were carried out with dried and pulveri- zed samples in room temperature and constant moisture conditions, in which the possible harmful effects of the physical differences in the peats were unable to exercise any influence. Moreover, in experiments of this kind the effects of plants and the washing down of nutrients are excluded; and, what is most important, in this kind of experiment only the final results of the phenomena are stated (3 and 5). Thus the results obtained from these experiments are not directly applicable to conditions in the field. Summary 60 peat samples from northern Finland representing different types of peat were incubated in a laboratory at a temperature of 17—18° C. The ammonium nitrogen, the nitrate nitrogen and the pH in the samples were determined after one month of incubation as well as after three months of incubation. The results were compared to results from determinations made before incubation. An attempt was made to elucidate the factors that influence the mobilization of nitrogen. On the basis of the above results it is evident that the differences between the various peat types as mobilizers of nitrogen are under these circumstances not very distinct, nor do these differences seem to be dependent on the types of peat. The following facts can, however, be established: In the amounts of ammonium nitrogen an increase takes place in most groups of samples during the first month. This increase is fairly big in the Sphagnum-dominated peats. The increase in ammonium nitrogen continues in the unlimed samples in most peat groups during all three months of incubation. After three months of incubation the amount of ammonium nitrogen in the limed samples is smaller than in the unlimed samples, although it is usually bigger than in the original samples. After the first month of incubation the amounts of nitrate nitrogen in all types of peat have decreased compared to the amounts in the original samples. In the limed samples the decrease is not as great as in the unlimed ones. After three months of incubation the amount of nitrate nitrogen has consider- ably increased as compared to the amount after one month of incubation. In the limed samples itmight to some extent exceed the original amount of nitrate nitrogen, however, this is seldom the case in the unlimed samples. If the results are calculated on the basis of weight unit, it can be stated that the ability to mobilize nitrogen is greater in the Sphagnum peats than in the other peat groups. Working out the results in kg per ha it will be noted that somewhat more nit- rogen is mobilized in the Carex-dominated than in the Sphagnum-dominated peats. The results obtained by experiments in the laboratory are not directly applic- able to conditions in the field. 281 REFERENCES (1) Berge, T, O. 1941. Determination of nitrate-nitrogen with a photoelectric colorimeter. Soil Sci 52: 185—191. (2) Kaila, A., Köylijärvi, J. & Kivinen, E. 1953. Influence of temperature upon the mobilisation of nitrogen in peat. J. Sci. Agr. Soc. Finland 25: 37—46. (3) —» — Soini, S. & Kivinen, E. 1954. Influence of lime and fertilizers upon the mineralization of peat nitrogen in incubation experiments. Ibid. 26; 79—95. (4) —» — & Kivekäs, J. 1956. Distribution of extractable calcium, magnesium, potassium and sodium in various depths of some virgin peat soils. Ibid. 28: 79—95. (5) » — & Soini, S. 1957. Influence of lime on the accumulation of mineral nitrogen in incubation experiments of peat soils. Ibid. 29: 229—237. (6) Kivinen, E. 1933. Suokasvien ja niiden kasvualustan kasvinravintoainesuhteisti. Acta agr. fenn. 27. (7) —»— 1954. Turpeiden typen mobilisaatiosta. Suo 4: 35—41. (8) Kivekäs, J. 1958. Turpeiden kuivaamisen ja jauhamisen vaikutuksesta analyysituloksiin. Summary: The effect of drying and grinding of peat samples on the results of analyses. J. Sci. Agr. Soc. Finland 30: I—9. SELOSTUS: HAVAINTOJA TURPEEN TYPEN MOBILISAATIOSTA MUHITUSKOKEISSA Jaakko Kivekäs ja Erkki Kivinen Yliopiston maanviljelyskemian laitos, Helsinki Laboratoriossa muhitettiin 60 pohjois-Suomen soilta otettua turvenäytettä 17—18° C lämpö- tilassa ja n. 70% kosteudessa, sekä seurattiin turpeessa NH4-N ja N0 3 -N määrien vaihteluja 1 ja 3kk pituisten koejaksojen kuluessa. Turpeiden välillä todettiin eroavaisuuksia, mutta ne eivät noudattaneet turvelajeja. 4