JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND 406 Maataloustieteellinen A ikakauskirja Vol. 49:406-414, 1977 Effect of fertilizers, lime and cadmium added to soil on the cadmium content of spring wheat Antti Jaakkola Agricultural Research Centre, Department of Agricultural Chemistry and Physics 01300 Vantaa 30. Abstract. In a pot experiment the cadmium content of wheat grain grown on acid (pHCcadj 5.5) loam and clay soils was increased from 55 to 440 540 /«g/kg by addition of 1 mg of cadmium per kg of soil. Raising of NPK fertilization increased the cadmium content of grain in general. The effect of liming varied. In field experiments the cadmium contents of wheat grain and straw were increased by cadmium addition on loam much more than on clay. Wheat grown on the loam suffered from severe drought. Cadmium application of 100 g/ha raised the cadmium contents in grain 10—6O and in straw 10—9O fig/kg. The contents were initially in the range 39 —69 («g/kg. In an experiment in which fertilizers with various cadmium contents because of different raw materials were compared, not even the highest addition of cadmium, 49 g/ha, caused a significant change in the cadmium contents of grain or straw. Introduction The injurious effect of cadmium depends mainly on its ability to accumulate in certain human and animal organs, particularly in the liver and kidneys. In consequence even a moderate amount of cadmium in food may prove serious if the food in question forms the major part of the diet. The cadmium content of cereal grain is therefore particularly interesting, although there are a number of plants that normally contain much more cadmium. The aim of this study was to collect data on the effect of fertilizers and lime on the cadmium content of spring wheat and on its response to added cadmium. Material and methods The experiments consisted of pot and field experiments. The pot experiment was performed using soils taken from theplough layer of two experimental fields. In addition to these experiments made in 1973, a third field trial was performed in the following year. The pot experiment was established with two soils: clay % org. C, % pHCaci 2 Loam 22 4.9 4.6 Clay 48 3.7 5.4 https://www.c-info.fi/en/info/?token=crPSTdpiJrRT3bZN.F7vEokhI_pIxwidz5AWmHg.7jHU0Ak2XGQij25bKqc3oT9D8b0uPsjGUdzmlwXYNLSPZ7Mrh6XRe7Y6OjgYHtxZiwC6vWSB5Eq28pqDSZ3FPmXsq-QBa9X5e-k4iu1wBbTsfpblrqLjfeV7aIDFENKVyAX5LTRRLF3f_8xIrOIIEbf1ukvnrMy4BS-OvA 407 The treatments in four replicates consisted of three factors with the follow- ing levels: L lime application L 0 no lime Lj 10 gof Ca(OH) 2 per pot L 2 20 » » » * » F fertilizer rate Fj N 0.7, P 0.45, K 0.6 g per pot = low F 2 N 1.4, P 0.9 , K 1.2 » » » = high Cd cadmium addition Cd0 no cadmium Cd 1 0.5 mg of Cd per pot as Cd(NO3) 2 Cdjy » » » » » »in NPK fertilizer Cd 10 5.0 » » » » »as Cd(NOa) 2 The Cdly treatment was given as cadmium chloride treated compound fertilizer containing 15 % N, 8.7 % P, and 12.4 % K. Combined with treatment F x the fertilizer (5 g/pot) contained 100 mg/kg of Cd and with F 2 (10 g/pot) 50 mg/kg of Cd. The cadmium treatment of the fertilizer was performed by Kemira Co. In the other cadmium treatments (Cd o, Cd2 and Cd 10) the N, P and K were given as analytical grade chemicals. The fertilizers, including, in addition to the above-mentioned nutrients, adequate amounts of Mg, Mn, Cu, Zn and B, and cadmium nitrate weighed for each pot, were mixed with 5.0 kg of air-dry soil. The soils in the pots were moistened approximately to field capacity with deionized water. Spring wheat, variety Ruso, was sowed 26—27. 3. 1973. After sprouting the plants were thinned to twenty per pot. The pots were kept in glasshouse over the whole period of growth. They were watered when necessary to keep the moisture near field capacity. The crop was harvested after a growing time of 92 days at full grain maturity. After threshing, the grain of each pot was weighed and analysed for cadmium. At the end of the experiment the soil pH in 0.01 M CaCl2 sus- pension was determined. The two field experiments from whose plough layer the soils for the pot experiment had been taken were located in southern Finland, one in Hausjärvi (loam soil) and the other in Tuusula (clay soil). In both places a split plot ex- periment was established. The treatments in the main plots were: L 0 no lime Lj 10 t/ha of ground limestone There were four replicates arranged in separate blocks. In each block the treatments were randomized. The main plots were divided into three subplots having the following randomized treatments: Cd0 no cadmium added Cd, 100 g/ha of cadmium added in NPK fertilizer Cd2 200 g/ha » » » » » »» » » » The subplots were two square metres in size. The lime was distributed in the spring of the experimental year. It was mixed with the soil to a depth of 408 ca. 15 cm by harrowing. For fertilization 1000 kg/ha of a compound fertilizer containing 15 % N, 8.7 % P and 12.4 % K was used. The fertilizers used for the cadmium treated plots had been coated with cadmium chloride by Kemira Co. The cadmium contents of the fertilizers were 100 mg/kg (Cd x ) or 200 mg/kg (Cd 2). The fertilizer was placed to a depth of 8 cm. Spring wheat, variety Ruso, was sowed 7.5. (clay soil) and 23. 5. 1973 (loam soil). After 95 (clay soil) and 84 (loam soil) days 1.5 m 2 of the subplots were harvested by cutting the plants ca. 5 cm above the soil surface. When threshed, the grain and straw were weighed and samples were taken for chemical analyses. To get an idea of the practical importance of cadmium containing fertilizers, and in order to compare fertilizers differing in their cadmium sources, a further field experiment was laid out. In this experiment common methods used in practical farming were applied as far as possible. The fertilizer was placed to a depth of 8 cm into every second 12 cm space between the sowing rows. The treatments consisted of fertilizations performed with compound fertilizers (15 % N, 8.7 % P and 12.4 % K) differing in their cadmium content and source of cadmium. In all treatments the fertilizer rate was 600 kg/ha. The treatments were: 1. NPK fertilizer for which Kola apatite was used as phosphorus source, cadmium content of the fertilizer 1.5 mg/kg. 2. NPK fertilizer, made by the Kemira fertilizer manufacturing company in a pilot plant using Kola apatite as phosphorus source. Sulphuric acid used in the process was contaminated with cadmium. Cadmium content 30 mg/kg. 3. NPK fertilizer, made in the pilot plant of Kemira using cadmium con- taining rock phosphate from Taiba, cadmium content of the fertilizer 57 mg/kg. 4. NPK fertilizer, made in the pilot plant of Kemira using cadmium con- taining rock phosphate from Taiba as phosphorus source. Extra cadmium was added as chloride. Cadmium content 81 mg/kg. 5. Mixture of fertilizers used for treatments 1 and 3 (49: 51), cadmium con- tent 30 mg/kg. 6. Mixture of fertilizers used for treatments 1 and 4 (65: 35), cadmium con- tent 30 mg/kg. Each treatment had four replicates situated in separate blocks. The 24 plots were 60 m 2 in size. Spring wheat, variety Ruso, was sowed 16. 5. 1974 and harvested with a combine harvester 8.9. The straw of each plot was baled. After weighing the yields samples were taken of grain and straw for determina- tions of moisture, cadmium and some nutrients. Analytical methods For cadmium determination the plant material was digested by dry ashing at 450° C. The ash was dissolved in 4 N HCI. The solution was evaporated to dryness. The residue was dissolved in nitric acid. The cadmium was determined in this solution by flameless atomic absorption (equipment Varian Techtron, CRA-63). For determination of some mineral nutrients in plant material, dry 409 ashing at 520° C was applied as digestion method. K, Ca and Mg were determined by atomic absorption and P colorimetrically (vanadate method) in acid extract of the ash. The analysis of variance was applied for the statistical testing of the results. In order to compare individual treatment means Tukey’s test (Steel and Torrie 1960) was used. Results The pot experiment The grain yield of spring wheat was not affected by cadmium addition to the soil. Consequently only the mean yields over the four cadmium treatments are given in Table 1. In the loam soil the pH of which was rather low, both liming and raising of fertilizer application increased the yield. The yield in- crease due to higher fertilization was not clearly dependent on the liming. In the clay soil the only significant effect of the lime was a decrease of yield at the rate of 10 g/pot, however, only at lower fertilization. Heavier liming raised the yield to the initial level again. Higher fertilization led to a higher yield. The cadmium content of grain in pots given 5 mg of cadmium varied much more than the content in other pots. For this reason the statistical analysis was performed in separate groups. Table 1. Yields and cadmium contents of spring wheat grain in the pot experiment. Treatment Yield Cadmium content, figlg in D.M. Ca(OH) a NPK g/pot No Cd Cd added, milligrams per pot g/pot rate of D.M. added "a 5 0.5 in NPK 5.0 1. Loam soil 0 low 33.7 A 59" 119b <: 117** 508 n^ high 39.1 B 49» 132" i 5580 10 low 39.5BC 57» 118fc 150" i 444°/? high 42.4BC 86»» 140=d 213 e 8617 20 low 39.0 B 54» 90»* 179d 332" high 43.4C 75» b 141cd 258 e 545/^ 2. Clay soil 0 low 28.9BC 55»» 113bc ° 180 d<" 240' 616"5 10 low 24.2 A 38» 72» bc 80»"° 254 aP high 33.1 D 72»"= 134"»' 194»' 6675 20 low 28.3 B 37» 105»"c 127»cd 189° high 32.4D 62»" 143««« 176<>e' 405^Y Yields and their cadmium contents on each soil followed by a common letter do not differ significantly (P = 0.05) according to Tukey’s test. 410 No statistically significant differences were observed in grain cadmium contents between the treatments without cadmium addition to the soil. However, a tendency of highsr fertilization to increase the content was obvious. The addition of 0.5 mg of cadmium per pot apparently increased the grain cadmium content in general. However, the differences were not significant in all fertilizing and liming treatments. In the limed loam the cadmium in the commercial NPK fertilizer was more efficient than the same amount added separately. This appeared to be generally so in spite of the significance lacking in the othar cases. At the higher fertilizer application, the grain contained more cadmium than at the lower one, however, not always significantly. The cad- mium given in NPK fertilizer to the loam warmore efficient when the soil was heavily limed. The addition of 5 mg of cadmium per pot increased the grain cadmium content very clearly. On the limed soils, higher fertilization led to a larger increase of cadmium content in the grain. On the loam, at the high fertilizer rate, the smal- ler amount of calcium hydroxide (10 g/pot) raised the grain cadmium content, but the double amount lowered it again to the initial level. On the clay soil liming brought about a decrease in grain cadmium, more clearly at the lower than at the higher fertilizer rate. The pH of the soil measured after the harvest was affected by liming only, not by other treatments. The following values were observed: 10 g/pot 20 g/pot no lime Ca(OH) 2 Ca(OH) 2 Loam 4.8 5.6 6.2 Clay 5.5 6.5 7.1 Field experiments In the experiments performed in 1973 with the small-plot technique, liming affected neither the grain or straw yields nor the elements determined in them. The means over the lime treatments are presented in Table 2. Table 2. Yields and cadmium contents of spring wheat grain and straw in the small-plot field experiments. Yield Cadmium content, fig/g in D.M. kg/ha No Cd Cd added, g/ha of D.M. added 100 200 1. Loam soil Grain 990 69» 120 b 184» Straw 1100 51 k 151' 231 m 2. Clay soil Grain 2290 39» 67 b 65 b Straw 2680 43k 66k 65k Cadmium contents on each soil followed by a common letter do not differ significantly (P = 0.05) according to Tukey’s test. 411 The grain and straw yields of wheat grown on the loam soil were very low because of severe drought which ripened the crop too early. Nor were the yields in the other experiment on the clay soil high. However, it is obvious that the mineral composition was not highly abnormal as can be seen from the following average contents in grain and straw harvested from the field experiments: P mg/g K mg/g Ca mg/g Mg mg/g Loam (1973), grain 4.4 3.9 0.6 1.2 l straw 1.6 12.1 1.8 0.8 Clay (1973), grain 3.2 3.3 0.6 1.2 » straw 1.2 9.1 1.4 0.6 Fine sand (1974), grain 3.9 4.7 I straw 1.1 12.8 Neither grain nor straw yields were affected by the cadmium treatments. There- fore, only the yield means are given in Table 2. The cadmium contents of wheat grain and straw were clearly increased by cadmium addition. The contents seemed to increase almost linearly with in- creasing amounts of cadmium. On the clay soil theresponse to cadmiumaddition was much more restricted, and in the case of straw it was not evens ignificant because of wide variation. The fertilizers containing cadmium in various amounts deriving from diffe- rent sources did not cause any clear differences in the cadmium contents of wheat grain or straw (Table 3). However, the grain of the wheat given the fertilizer in which the cadmium derived from sulphuric acid, seemed to contain somewhat more cadmium than other grain. It is, however, not certain whether the cadmium treatment is the primary cause, for the yield of this grain was also high. The cadmium content of straw seemed to follow the cadmium supply in the fertilizer in a logical order, but because of wide variation the differences were not significant. On the basis of the results the most probable increase in the cadmium up- take of the crop due to 49 g/ha of cadmium in fertilizer was estimated to be 50 mg/ha or 0.1 per cent of the supply. Table 3. Yields and cadmium contents of spring wheat grain and straw in the field experiment in 1974. Amount of Yield, kg/ha Cadmium content. No1 ) Source of P C