Maataloustieteellinen A ikakauskirja Vol. 56: 97—100, 1984 RESEARCH NOTE Effects of different ammonium nitrate levels on the amounts of exchangeable soil magnesium and applied magnesium in eight mineral soils RAILI JOKINEN University of Helsinki, Department of Agricultural Chemistry, SF-00710 HELSINKI, Finland Abstract; Eight mineral soils (pH(CaCl 2) 4.6—6.1, clay 4—65 %, org. C 1.9—5.7 <7o) were treated with ammonium nitrate and magnesium sulphate solutions adding 0, 20 or 40 mg mineral N and 0 or 4 rag Mg per 100 g soil. The soils were incubated for seven weeks at a constant temperature of 20 °C and a 25 % moisture level. After incubation, the exchangeable Mg was extracted with 1 M neutral ammonium acetate. The exchangeable magnesium content seemed to increase in some soils and to decrease in other soils with increasing ammonium nitrate amounts. The applied magnesium was fixed in a non-exchangeable form, especially at the highest ammonium nitrate level, in two clay soils taken from the rapakivi area of south-eastern Finland. In the other soils all applied magne- sium was exchangeable irrespective of the amount of ammonium nitrate. Introduction A great part of the mineral N in compound N-P-K fertilizers is in the form of NH4-N. According to several studies (e.g. Nommik 1957, Schachtschabel 1961, Kaila 1962), the mineral soils have the ability to fix applied NH 4 + in a non-exchangeable form. The cations Ca2+ or Mg2+ have no effect on this fixation (Nommik 1957). Only few studies on the effects of different mineral N levels on the exchangeable cation content of the soil are available (Sippola et ai. 1973). In laboratory studies on exchange- able cations a common practice is to treat the soil with NH 4 + acetate or chloride. The NH 4 + -N containing fertilizers may have the same effect, even though the NH 4 + con- centration in the soil remains lower than in laboratory studies. In a pot experiment, the apparent recovery of fertilizer Mg was low in some clay soils (Jokinen 1981 a). The antagonism between NH 4 + and Mg2+ in the cation uptake by Index words: Ammonium nitrate, magnesium sulphate, exchangeable Mg, non-exchangeable Mg, fine sand, finer fine sand, silty clay, sandy clay, heavy clay. 97 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=fa7taDDgCNyFhpv6.4EP3GkUgZzL04PzSWRB_5w.bxEoTvAsI464WwTILUeNW4StzSquLRE3QnK4pQt8JuG2s_s_z4OqyopeUVFjiAIRJwheFazotIzayM7g3tfU64Lpx9Oyh5969q0RlCOWaNlsI20iut5JzlTXrzHqkeCJUvW-7bI7v8oAn5pKJGBeteUYNSv-Vf8iQdAv plants was assumed to be the main reason for this. The effects of ammoniumnitrate on soil Mg and applied Mg were not studied. The aim of the present incubation experi- ment was to study the effects of different ammonium nitrate levels on the exchange- able Mg content of eight mineral soils and on the amounts of exchangeable Mg applied with magnesium sulphate. Materials and methods Eight mineral soils were incubated at 20 °C for seven weeks. The soil samples, three non-clay and five clay soils, repre- sented the plough layer of cultivated soil from southern Finland. The same soils were used in an earlier pot experiment (Jokinen 1981 a) and incubation experiment (Jokinen 1981 b). The numbers and characteristics of the soils are given in the latter report. One of the soils, muddy silt (4), was not included in this study because of the too small amount of soil available. The soils were air-dried and crushed to pass a 2-mm sieve. For the experiment, 100 g soil was weighed into 0.5 litre plastic pots and treated with ammonium nitrate and magnesium sulphate adding the following amounts of N and Mg: Symbol N,Mg0 N.Mg, N2Mg0 N.Mg, Treatment 20 mg N 20 mg N + 4 mg Mg 40 mg N 40 mg N -I- 4 mg Mg The treatments without N fertilization (N OMgO and N OMg,) were common with the incubation experiment on liming and Mg fer- tilization (Jokinen 1981 b). The fertilizer solutions were thoroughly mixed with the soil. Four replicates were made. Both experi- ments were incubated at the same time and in the same place. The moisture of the soils was maintained at 25 °7o of the soil weight, ad- ding de-ionized water as necessary. The pots were covered with perforated plastic film. After incubation, the soils were air-dried at room temperature and repassed through a 2-mm sieve. The exchangeable Mg was ex- tracted by 1 M neutral ammonium acetate and exchange acidity (AI + H) by 1 M KCI (Kaila 1971). The amount of applied Mg found exchangeable in the soil was calculated as the difference Mg,-Mg0 . The exchange- able NF14 + was extracted with 0.25 M K 2S0 4 (soil : solution = 1 : 10, w/v, 2 h) and deter- mined by destination. The N03 ~ was deter- mined from the same aliquot of extract after reduction with Devarda’s alloy. The amounts of applied mineral N found in the soils were calculated as the differences N,- N 0 and N 2-N 0 . Results and discussion After seven weeks of incubation, almost all the mineral N (NH 4 +-N + N0 3 ~-N) ap- plied was found in the soils extractable in 0.25 M K 2S04 at the N, level. In finer fine sand (3), sandy clay (6) and silty clay (8), the nitri- fication of NH 4 + -N seemed to be complete, since the amount of NOf-N increased in the same proportion. At the N 2 level, the nitrifi- cation of applied NH 4 + was observed in sil- ty clay (8) only, possibly because of the high amount of mineral N applied. In finer fine sand (3) and in clays (6—9) without ammonium nitrate, the exchange- able Mg content seemed to be somewhat higher than with N (Table 1). Increased activ- ity of micro-organisms in soils 3, 6 and 8 by N fertilization was concluded on the basis of increased N0 3 - -N content during incuba- tion. Some of the exchangeable Mg may be involved in the biological fixation. In fine sand (1) and silty clay (5), the exchangeable Mg content seemed to increase with increas- ing ammonium nitrate amounts. Some of the non-exchangeable Mg in these soils may be- come exchangeable without difficulty, e.g. by chemical weathering. This may explain the ability of ryegrass in the pot experiment to take up non-exchangeable Mg from fine sand (1). 98 Table 1. Exchangeable Mg content, mg/100 g soil, in eight mineral soils after seven weeks of incubation. (Mg0 = without Mg fertilization. Mg! = Mg fertilization 4 mg/100 g soil). Mgo MgrMg0 N„ N, N 2 N 0 N, N 2 1. Fine sand 1.2» 1.5b 1.6b 4.3" 4.3» 4.4" 2. Fine sand 5.9" 6.0» 6.1» 4.5b 3.7» 3.6» 3. Finer fine sand 16.0- 13.6» 14.3" 3.8 b 4.0" 3.1» 5. Silty clay 10.9» 11.4" 11.5" 3.9» 4.1» 4.1» 6. Sandy clay 24.1» 23.6» 23.9» 4.7" 3.0» 2.4» 7. Sandy clay 52.3» 48.7» 49.2» 4.4» 4.6» 5.1» 8. Silty clay 34.5" 32.6» 33.4» b 4.4» 4.3» 3.6» 9. Heavy clay 77.0» 75.5» 75.5» 6.1» 4.5» 4.5» Results of an individual soil with the same letter do not deviate significantly (P = 5 %). The datas of Mg0 and Mg|-Mg„ were studied separately by Duncan’s new multiple range test. Without ammonium nitrate the applied Mg (4 mg/100 g soil) was found exchange- able in all soils after incubation (Table 1). Considerable amounts of Mg were released from heavy clay (9) in the exchangeable form during incubation. With ammonium nitrate the applied Mg was partly tied up by fine sand (2) and sandy clay (6) at both N levels and by finer fine sand (3) and silty clay (8) at the N 2 level. The soils 6 and 8 originated from the rapaki- vi area of south-eastern Finland where, ac- cording to Sippola (1974), K-feldspar is more common than elsewhere in Finland. In these soils the fixation of NFI4 + -N into a non-exchangeable form seemed to be low be- cause of the high K content (Scherer 1982). Hence it is possible that applied NH 4 + -N contributed to the formation of non- exchangeable Mg compounds. In finer fine sand (3), the fixation of applied Mg in the non-exchangeable form may be a conse- quence of the formation of insoluble Al-Mg compounds (HuNSAKERand Pratt 1970), since the 1 M KCI extractable Al 3+ content of this soil decreased with increasing amounts of ammonium nitrate. The content of H + remained constant. With increasing amounts of ammonium nitrate the reactions against applied Mg deviated in two clays (6 and 7) as well as in two silty clays (5 and 8). From soils 5 and 7 Mg was released in the exchangeable form and in soils 6 and 8 the fixation of Mg in non-exchangeable form occured during in- cubation. The apparent recovery of fertilizer Mg by ryegrass (total of 8 cuts) was for the »rapaki- vi» soils (6 and 8) very low at the N, level (1.6 % and 0.4 %), but somewhat higher values were obtained at the N 2 level (13.6 % and 39.7 %) in the pot experiment (Jokinen 1981 a). Ryegrass seemed to be able to take up fixed Mg from these soils during the two growing seasons studied. From the agricultural point of view the high amount of ammonium nitrate may have positive effects on the exchangeable Mg con- tent of some soils. The applied Mg seemed to be fixed in the non-exchangeable form in some soils and this may contribute to the low recovery of fertilizer Mg. The antagonism between Mg2+ and NH4 + or K + in the ca- tion uptake by plants is the main but not the only reason for the restricted Mg uptake. 99 References Hunsaker, V. E. & Pratt, P. E. 1970. The formation of mixed magnesium-aluminum hydroxides in soil minerals. Soil Sei. Soc. Amer. Proc. 34: 813—816. Jokinen, R. 1981 a. Soil magnesium and fertilizer magnesium uptake by ryegrass on nine mineral soils at two ammonium nitrate levels 1. Magnesium up- take. Ann. Agric. Fenn. 20: 231—243. 1981 b. Effect of liming on the magnesium status of some mineral soils and on the fate of fertilizer magne- sium. J. Scient. Agric. Soc. Finl. 53; 126—137. Kaila, A. 1962. Fixation of ammonium in Finnish soils. J. Scient. Agric. Soc. Finl. 34: 107—114. 1971. Aluminium and acidity in Finnish soils. J. Scient. Agric. Soc. Finl. 43: 11—19. Nommik, H. 1957. Fixation and defixation of ammo- nium in soils. Acta Agric. Scand. 7: 395—436. Schachtschabel, P. 1961. Fixierung und Nachlieferung von Kalium- und Ammonium-lonen. Landw. Forsch. Sonderh. 15: 29—47. Scherer, H. W. 1982. Fixed NH 4*-N in relation to EUF-extractable K. Plant and Soil 64: 67—71. Sippola, J. 1974. Mineral composition and its relation to texture and to some chemical properties in Finnish subsoils. Ann. Agric. Fenn. 13; 169—234. —, Erviö, R. & Eleveld, R. 1973. The effects of simul- taneous addition of ammonium and potassium on their fixation in some Finnish soils. Ann. Agric. Fenn. 12: 185—189. Ms received March 15, 1984 SELOSTUS Ammoniumnitraatin vaikutus maan magnesiumin ja lannoituksena annetun magnesiumin uuttuvuuteen kahdeksasta kivennäismaasta Raili Jokinen Helsingin yliopisto, maanviljelyskemian laitos, 00710 Helsinki 71 Muhituskokeena tehdyn tutkimuksen maat oli otettu viljeltyjen maiden muokkauskerroksesta eri puolilta Suomea. Maa Maalaji Kunta n:o 1 Karkea hieta Ruukki 2 Karkea hieta Mikkeli mlk 3 Hieno hieta Toholampi 5 Hiesusavi Laukaa 6 Hietasavi Anjalankoski 7 Hietasavi Vantaa 8 Hiesusavi Anjalankoski 9 Aitosavi Jokioinen Laboratoriossa kuivia ja jauhettuja maita lannoitet- tiin ammoniumnitraatti- ja magnesiumsulfaattiliuoksilla niin, että 100 g kohti maata lisättiin seuraavat määrät typpeä (N) ja magnesiumia (Mg): N O Mg0 Ilman N N O Mg, Ilman N + 4 mg Mg (n. 80 kg/ha) N,Mg0 20 mg N (n. 400 kg/ha) N,Mg, 20 mg N + 4 mg Mg N 2 Mg0 40 mg N N 2 Mg, 40 mg N + 4 mg Mg Maat kostutettiin (25 % kosteus) ja niitä muhitettiin 20 °C vakiolämpötilassa seitsemän viikkoa. Ammoniumnitraatin lisääminen aiheutti muutamissa maissa (1,2 ja 5) lievän vaihtuvan magnesiumin määrän lisääntymisen mahdollisesti kemiallisen rapautumisen seurauksena (Taulukko). Toisissa maissa vaihtuvan magnesiumin määrä näytti vähenevän vilkastuneen pieneliötoiminnan aiheuttaman biologisen pidättymisen vuoksi. Kaakkois-Suomen rapakivialueelta otetuissa savi- maissa (6 ja 8) osa lannoituksena annetusta magnesiu- mista näytti pidättyvän vaihtumattomaan muotoon. Biologisen pidättymisen lisäksi maassa näyttäisi tapah- tuvan kemiallista pidättymistä vaikealiukoisiksi yhdis- teiksi. Useimmissa koemaissa lannoituksena lisätty mag- nesium oli kaikki vaihtuvana, siis kasveille käyttökelpoi- sena, ammoniumnitraatin määrästä riippumatta. Aikaisemmin tämän tutkimuksen mailla tehdyssä as- tiakokeessa raiheinä otti vain pienen osan lannoituksena annetusta magnesiumista juuri niillä mailla, joilla tässä muhituskokeessa todettiin magnesiumin pidättymistä vaihtumattomaksi. Raiheinä kykeni ottamaan vaihtu- matontakin magnesiumia. 100