Agricultural and Food Science in Finland, Vol. 11 (2002): 143–152. 143 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 143–152. © Agricultural and Food Science in Finland Manuscript received November 2001 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 143–152. Harvesting strategy and N fertilization influence 134Cs uptake by forage plants Arja Paasikallio MTT Agrifood Research Finland, Environmental Research, FIN-31600 Jokioinen, Finland Riitta Sormunen-Cristian MTT Agrifood Research Finland, Animal Production Research, FIN-31600 Jokioinen, Finland The root uptake of 134Cs by forage plants was studied as a function of growth stage and N fertilization with biotite supplementation. The study was conducted by means of pot experiments with peat soil. In the growth stage studies, ryegrass, white clover and yellow-flowered lucerne were cut once 30, 60 or 90 days after sowing or three times at intervals of 30 days. In the one-cut system, at 90 d, the activity concentration of 134Cs in ryegrass and clover was higher and that in lucerne lower than in the three-cut system. In both treatments, the activity concentration in ryegrass decreased and that in legumes, generally, tended to increase with time. In the N fertilization studies, ryegrass was grown at different levels of ammonium nitrate (100, 200 and 400 mg N l-1) and biotite (0, 10, 20 and 40 g l-1) application. The addition of N to soil increased and that of biotite decreased the 134Cs activity con- centration in ryegrass. The differences in forage 134Cs between the two harvesting systems were small. Although ammoni- um nitrate increased the 134Cs uptake by ryegrass, in the event of fallout, moderate rates of ammoni- um fertilizer could be used provided that biotite or K are applied at adequate levels. Key words: Cs, nitrogen, biotite, peat, Lolium, legumes, seasonal variation Introduction Forages are the main source of feed for rumi- nants. The most important factors affecting the yield and quality of forages are growth stage and N fertilization. To obtain high quality forage it is recommended that herbage be harvested at an early stage of growth. However, owing to seasonal growth, harvest- ing at the time of highest quality does not usual- ly coincide with harvesting at the time of maxi- mum dry matter yield (Rinne and Nykänen 2000). In the event of radioactive fallout, farm- ers may be forced to relinquish their claims to nutritive value and amount of feeds. Little in- formation is available on the effect of growth stage on uptake of radiocaesium by legumes. 144 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Paasikallio, A. & Sormunen-Cristian, R. 134Cs uptake by forage plants An earlier study (Paasikallio 1999) showed that the 134Cs activity concentration in ryegrass on peat soil was reduced by biotite low in solu- ble potassium. Ammonium and potassium salts are known to be the fertilizers most effective in influencing plant uptake of radiocaesium. Potas- sium decreases and ammonium, in contrast to potassium, usually enhances caesium uptake (Evans and Dekker 1969, Haak and Eriksson 1973, Cawse 1990, Belli et al. 1995). It was hy- pothesized that the rate of ammonium fertilizer might play an important role in counteracting the ability of biotite to reduce radiocaesium uptake by plants. Peat was chosen as a growth medium because the radiocaesium uptake by plants from peat soil may present a serious problem due to the low caesium fixing capacity of peat. The addition of biotite made the peat substrate more like culti- vated peatland, and a high rate of biotite addi- tion was intended to simulate the effect of soil amendment application. The objectives of this study were to compare the uptake of radiocaesium by grass and legumes harvested at three different times during the growing season and, further, to investigate the effect of various rates of ammonium nitrate ap- plication on 134Cs uptake by grass grown on peat soil treated with different levels of biotite. Material and methods Pot experiments Outdoor pot experiments were conducted in Jokioinen, in 1997 (Exp. 1, growth stage) and in 1998 (Exp. 2, N-fertilization). Plastic pots, ca- pacity 3.5 litres, were filled with peat soil in four replicates. Different rates of biotite (Kemira Agro Oy, Siilinjärvi) were added to the soil, which consisted of slightly decomposed, sieved Sphagnum fuscum moss peat and was originally unfertilized and unlimed (pH 3.5–4.5 and 99% organic matter according to the producer, Kek- kilä Oy, Parkano). The clay fraction (< 0.002 mm) of biotite was < 1% (Paasikallio 1999). The pots were placed at random and protected from rain. The soils were kept at constant moisture (about 60% of the water holding capacity). In 1997, mean temperature in June, July and Au- gust (16.1, 17.8 and 17.8°C, respectively) was higher than that for a 30 year period (14.3, 15.8 and 14.2°C). In 1998, mean monthly tempera- ture during the growing season was a little low- er (13.7, 15.2 and 13.0°C) than normal. Meteor- ological data from Jokioinen were obtained from Monthly Reports of Finnish Meteorological In- stitute. Growth stage Biotite was mixed in peat soil at a rate of 20 g l-1. Italian ryegrass (Lolium multiflorum Lam., var. Tetraploid Turgo) was fertilized with 200 mg N (NH4NO3) and 1.4 g Ca (CaCO3) per litre of soil and white clover (Trifolium repens L., var. Jö- geva) and yellow-flowered lucerne (Medicago falcata L., var. Karlu) with 50 mg N and 2.8 g Ca l-1. Other fertilizers added were 150 mg K (KCl), 150 mg Mg (MgSO4·7H2O), 50 mg P (NaH2PO4·2H2O), 40 mg Fe (FeSO4·7H2O), 20 mg Mn (MnSO4·H2O), 5 mg Cu (CuSO4·5H2O), 5 mg Zn (ZnSO4·H2O), 1 mg B (H3BO3) and 1 mg Mo (Na2MoO4) per litre of soil. Caesium 134 (CsCl in aqueous solution) was mixed in the fer- tilized soils at a rate of 370 kBq per pot. About 0.6 litre of the soil per pot was left uncontami- nated. A half of it was put at the bottom of the pot and after filling the pot with contaminated soil another half was put at the soil surface. The depth of each uncontaminated soil layer was about 15 mm. Before they were sown, the seeds of legumes were treated with inoculant (Rhizo- bium bacteria). Seeds were sown on 12 June. After each cut, the soils of harvested and unhar- vested plants were fertilized with half a dose of N and P. In treatment 1, the plants were cut once about 30, 60 or 90 days after sowing (11 July, 8 August and 8 September). In treatment 2, the 145 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 143–152. plants were cut three times at intervals of about 30 days (dates as above). The first cut was com- mon for both treatments. The comparison of forage dry matter produc- tion of a single harvest to 3-cut system was achieved by cumulating the individual harvest of 3-cut system. The corresponding 134Cs con- centrations in 3-cut system were calculated by means of the weighed mean concerning also pre- vious cuts. N-fertilization with biotite addition Italian ryegrass was grown on peat soil with bi- otite addition at a rate of 0 (control), 10, 20 and 40 g l-1. Each of the soil-biotite mixtures was fertilized with 100, 200 and 400 mg N (as NH4NO3) and with 1.4 g Ca (as CaCO3) l -1. Cae- sium 134 (CsCl in aqueous solution) was added at a rate of about 240 kBq per pot. Seeds were sown on 29 May. The plants were cut three times at intervals of about 30 days (3 July, 3 August and 2 September). Otherwise fertilization and the experiment were conducted in much the same way as with ryegrass in the growth stage exper- iment. Sample analysis Ashed plant material was dissolved in HCl, and the plant K concentration was determined by plasma emission spectroscopy. Cesium 134 was measured in dry plant material using a gamma counter with a NaI(Tl) well-type crystal detec- tor. The activity concentration of 134Cs, the con- centration of K, and yield are expressed as dry matter. Statistical methods In the growth stage experiment, the effect of the two cutting systems on the 134Cs activity con- centration and yield and the differences in these factors between plant species were evaluated by analysis of variance. In the fertilization experi- ment, the effect of N and biotite on the 134Cs ac- tivity concentration, yield and K content of plants was evaluated by repeated measurements analysis of variance. Completely randomized design was used in both experiments. In the N fertilization experiment, three cuts were taken from each pot and the cuts of one pot were correlated. This correlation was taken into account in the statistical models. The covariance structure of the three repeated measurements was obtained by comparing all biologically sensible structures using Akaike’s and Schwartz’s Baye- sian information criterion (Wolfinger 1996). The unstructured covariance structure proved useful in each analysis of variance. For the fertiliza- tion experiment, the statistical model was as fol- lows: Yijk = µ + treatmenti + potk (treatmenti) + cutj + (treatment × cut)ij + εijk where µ is the intercept, and treatmenti rep- resents the fixed effect associated with the ith treatment. Treatments are factorial combinations of the biotite and N levels in the fertilization experiment. Potk (treatmenti) is the normally dis- tributed random effect of the pots. Cutj and (treat- ment × cut)ij represent the fixed effect associat- ed with the jth cut and treatment × cut interac- tion, respectively. εijk are correlated residual er- rors with covariance structures as defined above. In the growth stage experiment, the cuts were analysed separately. Thus, the model included only intercept, treatment and residual effects from the model of the fertilization experiment. The assumptions of statistical models were checked by graphical methods: boxplot for nor- mality of errors and plots of residuals for con- stancy of error variance (Neter et al. 1996). The constancy of error variance was achieved by log or square-root transformation. The parameters of the models were estimated by the restricted max- imum likelihood (REML) estimation method using the SAS system and the MIXED proce- dure. 146 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Paasikallio, A. & Sormunen-Cristian, R. 134Cs uptake by forage plants Results Growth stage Sixty days after the sowing, the activity concen- tration of 134Cs was higher in one-cut (treatment 1) than in three-cut (treatment 2) ryegrass (P < 0.001), whereas legumes had equal 134Cs concentrations in both cut systems (Fig. 1a). At 90 d, the activity concentration was higher in one-cut ryegrass and clover, but lower in one- cut lucerne than in the corresponding three-cut plants (P < 0.001). The plant species × cut inter- action was significant for both cut systems after 60 and 90 days from sowing (P60, 90 < 0.001). In early growth, the 134Cs activity concentration in ryegrass was clearly higher and in later growth lower than that in legumes. In contrast to leg- umes, ryegrass 134Cs decreased with time and number of cuts. In later growth, in the one-cut system, clover 134Cs was significantly higher than the 134Cs of other species and in the three-cut system, legume 134Cs was higher than the 134Cs of ryegrass (Table 1). The yield of one-cut plants was significantly higher than the cumulative yield of three-cut plants (P60 < 0.001 and P90 d 0.01) (Fig. 1b). The plant species × cut interaction was significant for both cut systems (P60 = 0.02, P90 < 0.001). In early growth, the yield of ryegrass was higher than that of legumes. The yield and cumulative yield of all plant species increased considerably with time and number of cuts. At 60 d, the yield of all one-cut plants was equal, whereas in three- cut plants, the yield of lucerne was lower than that of the other species. At 90 d, in both cutting systems, the yield of clover was significantly higher than that of the other plants (Table 1). Soil pH, determined at the end of the experiment, was 6.3 for grass, 6.8 for clover and 7.0 for lucerne. N fertilization with biotite addition In general, the 134Cs activity concentration of ryegrass increased significantly (P < 0.001) with increasing N fertilization. It was highest on con- trol soils (no biotite) and decreased significant- ly (P < 0.001) with increasing biotite level of the soil (Fig. 2, Table 2). At lower biotite levels, the 134Cs uptake by plants increased with increas- ing rates of N relatively less than it did at higher biotite levels. The N × biotite interaction was significant for each cut (P < 0.001). On biotite soils, plant 134Cs decreased markedly with number of cuts, especially at higher soil N lev- els. Table 1. Significance between plant species for data of 134Cs activity concentration and yield (Exp. 1). Cutting Cutting Significance system time Ryegrass Ryegrass Clover (d) vs. clover vs. lucerne vs. lucerne Activity concentration of 134Cs One-cut 60 0.01 < 0.001 0.01 Three-cut 60 < 0.001 n.s. < 0.01 One-cut 90 < 0.001 n.s. < 0.001 Three-cut 90 < 0.001 < 0.001 n.s. Yield One-cut 60 n.s. n.s. n.s. Three-cut* 60 n.s. < 0.005 < 0.005 One-cut 90 < 0.001 < 0.001 < 0.005 Three-cut* 90 < 0.001 n.s. < 0.001 * = cumulative yield, n.s. = non-significant. 147 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 143–152. Fig. 1. Activity concentration of 134Cs (a) and yield (b) for ryegrass, clover and lucerne at different times after sowing. In treatment 1(1 cut), plants were cut once at the age of 30, 60 or 90 days. In treatment 2 (3 cuts), plants were cut three times at intervals of 30 d. In treatment 2, both cumulative (3 cuts-i) and individual (3 cuts-ii) harvest and corresponding 134Cs concentrations are presented. Data points denote means and SD of four (* = three) replicates. (Exp. 1). 148 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Paasikallio, A. & Sormunen-Cristian, R. 134Cs uptake by forage plants Some of the N (mg l-1) – biotite (g l-1) combi- nations had an equal effect on the 134Cs activity concentration in plants: N-biotite combination rates of 100-0 and 400-20 gave about 250 × 10-2 cpm, those of 200-10 and 400-40 about 170 × 10-2 cpm and those of 100-10 and 200-40 about 33 × 10-2 cpm 134Cs g-1. The yield was lowest in the first cut and on all soils without biotite. In later cuts, the yield increased with increasing biotite and N fertili- zation (Table 3). In the first cut, K was taken up effectively, but in later cuts, on soils without bi- otite, the K content of plants was very low. With an increase in the biotite level from 0 to 40 g l-1, the soil pH, determined at the end of the experi- ment, rose from about 5 to 7 (Paasikallio 1999). Discussion The radiocaesium activity concentration in pas- ture plants has been reported to be higher in spring than in autumn (Bunzl and Kracke 1989, Schechtner and Henrich 1990, Salt et al. 1992, Ehlken and Kirchner 1996), which is in accord- ance with the data on ryegrass in our growth stage experiment. Late harvest time has been recommended by Schechtner and Henrich (1990) as a means to reduce the 137Cs concentration in grassland forage, provided that N and K fertili- zation is sufficient. On the other hand, late har- vest reduces the nutritional quality of forage. Besides the season, the slow-releasing K in bi- otite probably accounted for the decrease in rye- grass 134Cs with time. On the other hand, the ten- dency of the 134Cs concentration in legumes to increase during the growing season was suggest- ed to be due to their symbiotic bacterial fixation of N and hence, at least at the later stage of the growth, more ammonium was available to them than to ryegrass. Because the ammonium ions are known to increase the radiocaesium concen- tration of plants, their effect on legume 134Cs might have surpassed the decreasing effect of K ions. Fig. 2. Activity concentration of 134Cs for ryegrass in three cuts at different rates of N and biotite application to peat soil. Means and SD of four (* = three) replicates. (Exp. 2). 149 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 11 (2002): 143–152. It was assumed that for pure peat soil of this study the caesium fixation by small amounts of biotite was not of major importance, although the clays and also the micas are known to fix Cs (Sawhney 1964, Zachara et al. 2002). The evi- dence supporting this assumption is e.g., the observed long-term plant availability of Cher- nobyl radiocaesium in British upland areas with- out showing significant ageing effects (Howard et al. 1990, Rigol et al. 1998) and the findings of Ehlken and Kirchner (1996) who did not ob- serve any ageing process of radiocaesium in peat soil. Furthermore, the presence of organic mat- ter is known to reduce the fixation of caesium by clay minerals (Dumat and Staunton 1999, Staunton et al. 2002). Another factor, which is reported to decrease plant uptake of radiocaesi- um with time, is its migration in the rooting zone. However, in this study, 134Cs was mixed in the soil and hence its migration was unlikely. Table 2. Results of analysis of variance for 134Cs activity concentration data (Exp. 2). Degree of freedom Source of variation Numerator Denominator F-value P-value N 2 36 3629 < 0.001 Biotite 3 36 4000 < 0.001 Biotite × N 6 36 270 < 0.001 Cut 2 71 1085 < 0.001 N × cut 4 71 211 < 0.001 Biotite × cut 6 71 52 < 0.001 Biotite × N × cut 12 71 45 < 0.001 Table 3. Yield and K content of ryegrass in three cuts at different rates of N and biotite application to peat soil. Yield (g/pot) K (g kg-1) Biotite Significance (g l-1) N (mg l-1) 100 200 400 100 200 400 Yield K 1st cut 0 9 10 10 37 38 38 n.s. n.s. 10 10 12 11 50 54 42 < 0.005 < 0.001 20 10 11 11 48 53 45 n.s. < 0.001 40 10 11 11 49 55 46 < 0.005 < 0.001 2nd cut 0 9 14 17 6 3 5 < 0.001 n.s. 10 13 22 24 24 26 28 < 0.001 n.s. 20 13 25 27 25 25 34 < 0.001 < 0.001 40 12 24 31 24 26 40 < 0.001 < 0.001 3rd cut 0 8 8 *2 5 5 *8 < 0.001 0.05 10 13 20 *26 30 25 *23 < 0.001 < 0.001 20 14 24 31 31 36 35 < 0.001 < 0.001 40 15 24 35 30 36 38 < 0.001 < 0.001 Means of four (*= three) replicates, n.s. = non-significant. 150 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Paasikallio, A. & Sormunen-Cristian, R. 134Cs uptake by forage plants At the end of the growing season, in both cutting systems, the 134Cs concentration in grass was lower than that in clover, which is consist- ent with earlier findings (Garrett et al. 1971, Schechtner and Henrich 1990, Salt et al. 1992, Veresglou et al. 1995). The radiocaesium con- centration in white clover has been reported to be higher than that in lucerne (Evans and Dekker 1968, Schechtner and Henrich 1990); here, how- ever, this was not always the case. Belli et al. (1995) reported that the 137Cs concentration in grass (Phleum pratense) was higher than that of a legume (Lotus corniculatus). Their results cor- roborate the findings of our study at the early growth stage, when 134Cs uptake by ryegrass was clearly higher than that by legumes. In the N fertilization experiment, ammoni- um nitrate substantially promoted 134Cs transfer to plants, thus supporting the findings of sever- al earlier reports (Jackson et al. 1965, Evans and Dekker 1969, Cawse 1990, Schechtner and Hen- rich 1990, Lasat et al. 1997), according to which ammonium ions markedly increase the radiocae- sium concentration in plants, particularly when the soil K is low. Ammonium ions decrease the fixation of caesium ions in soil and, consequent- ly, the caesium concentration increases in soil solution and in plants. Haak and Eriksson (1973) reported that ammonium and urea fertilization increased the 137Cs concentration in wheat straw and timothy more than did nitrate fertilization. The effect of N fertilization depended on the N and K rates and soil type. According to them, the increase in the 137Cs concentration in plants due to an ammonium fertilizer was most effec- tive in coarse mineral and organic soils. Grauby et al. (1990) recommended that ammonium fer- tilizers not be used in the event of a nuclear ac- cident. On the other hand, according to Schech- tner and Henrich (1990) and Belli et al. (1995), ammonium or urea fertilization did not increase the radiocaesium concentration in plants, which was attributed to the diluting effect of the growth of plant biomass on the radiocaesium concen- tration. In our study, biotite application considera- bly decreased the 134Cs concentration in plants, as was reported by Paasikallio (1999). The ef- fect of biotite was attributed mainly to its low- soluble K. Potassium salts are known to reduce the transfer of radiocaesium to plants, especial- ly in peat soils of low K status (Haak and Eriks- son 1973, Jackson and Nisbet 1990, Rosén 1991). Potassium ions dilute the radiocaesium concentration in soil solution, thus decreasing its transfer to plants. The K content of the plants in soil without biotite was rather high in the first cut, but in later cuts, the plants suffered from K deficiency and had poor growth, because K-fer- tilization was given only once at the beginning of the experiment. Potassium and ammonium ions compete with radiocaesium for uptake and they are reported to be equally effective in releasing soil-fixed caesium in organic soils having non-specific exchange sites (Schulz 1965). That ammonium increased caesium uptake relatively less at low- er than at higher biotite levels was attributed to interactions between K and ammonium, which are known to be complicated in plant nutrition (Wang et al. 1996). Conclusions The study indicates that the differences in for- age 134Cs between the harvest systems were small although statistically significant. The differenc- es might have been caused as well by other fac- tors, e.g. climatic conditions, the effects of which were not studied. The study also indicates that, although ammonium nitrate markedly increased the plant radiocaesium concentration, in the event of nuclear fallout, moderate rates of am- monium fertilizers could be used on peat soils, provided that adequate rates of biotite or potas- sium fertilizer are applied to reduce radiocaesi- um transfer from soil to herbage. Acknowledgements. 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References 152 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Paasikallio, A. & Sormunen-Cristian, R. 134Cs uptake by forage plants Zachara, J.M., Smith, S.C., Liu, C., McKinley, J.P., Serne, R.J. & Gassman, P.L. 2002. Sorption of Cs+ to mica- ceous subsurface sediments from the Hanford site, USA. Geochimica et Cosmochimica Acta 66: 193– 211. SELOSTUS Korjuuaika ja typpilannoitus vaikuttavat rehukasvien radiocesiumpitoisuuteen Arja Paasikallio ja Riitta Sormunen-Cristian MTT (Maa- ja elintarviketalouden tutkimuskeskus) Kasvuvaihe ja typpilannoitus ovat tärkeimpiä rehu- kasvien laatuun ja satoon vaikuttavia tekijöitä. Laa- dukkaan rehun tuottamiseksi sato on korjattava var- haisessa kasvuvaiheessa. Ydinlaskeumatilanteessa kasvin mahdollisimman matalasta aktiivisuuspitoi- suudesta tulee rehun ravitsemuksellista laatua tär- keämpi tekijä. Koska kasvien radiocesiumpitoisuus vaihtelee kasvukauden aikana, on oikean korjuuajan valitseminen tärkeää. N-lannoituksen määrällä on myös merkitystä, sillä sen tiedetään toisinaan lisää- vän kasvin radiocesiumpitoisuutta varsinkin kun lan- noitteena käytetään ammonium-typpeä. Tutkimuksen tarkoituksena oli verrata niitettyjen ja niittämättä jä- tettyjen rehukasvien radiocesiumpitoisuutta kasvu- kauden aikana sekä selvittää ammoniumnitraatti-lan- noituksen vaikutusta radiocesiumin kulkeutumiseen heinään. Korjuuajan ja -kertojen vaikutusta raiheinän, val- koapilan ja sirppimailasen radiocesiumpitoisuuteen tutkittiin astiakokeiden avulla. Kasvualustana oli 134Cs:lla käsitelty turvemaa, johon oli lisätty biotiit- tia 20 g l-1. Radiocesiumpitoisuus määritettiin kol- mesti niitetyistä ja niittämättömistä kasveista kolme kertaa 30 päivän välein kylvöstä laskettuna. N-lan- noitustutkimuksessa raiheinää kasvatettiin 134Cs:a si- sältävässä turvemaassa, johon oli lisätty typpeä am- moniumnitraattina 100, 200 ja 400 mg l-1 ja biotiit- tia 0, 10, 20 ja 40 g l-1. Heinä niitettiin kolme kertaa 30 päivän välein. Niittämättömän, 90 päivän ikäisenä korjatun hei- nän ja apilan radiocesiumpitoisuus oli suurempi ja mailasen pienempi kuin vastaavien kolmesti niitetty- jen kasvien viimeisen niiton aktiivisuuspitoisuus. Heinän aktiivisuuspitoisuus pieneni ja palkokasvien yleensä suureni jonkin verran aikaa myöten, mikä saattoi johtua siitä, että palkokasvit saivat heinää enemmän ammonium-typpeä symbioottisen N 2 -sidon- nan kautta. N-lannoitustutkimuksessa ammoniumnit- raatti lisäsi huomattavasti heinän 134Cs-pitoisuutta, kun taas biotiitti pienensi sitä. Aktiivisuuspitoisuus oli pienempi heinällä, joka oli kasvanut runsaasti typ- peä ja biotiittia sisältävässä maassa kuin vähän typ- peä ja kokonaan ilman biotiittia kasvaneella heinäl- lä. Tulokset osoittivat, että eri korjuutapojen väliset erot kasvin radiocesiumpitoisuudessa olivat yleensä pieniä. Erot saattoivat johtua myös muista tekijöis- tä, kuten esim. sääoloista, joiden vaikutusta ei tutkit- tu. Vaikka ammoniumnitraatti lisäsi heinän radioce- siumpitoisuutta, sitä voidaan käyttää kohtuullisesti laskeumatilanteessa, kunhan maahan samalla lisätään riittävästi biotiittia tai K-lannoitetta. Title Introduction Material and methods Results Discussion Conclusions References SELOSTUS