FERTILIZER NITROGEN IN SOIL Armi Kaila University of Helsinki, Department of Agricultural Chemistry Pentti Hänninen Agricultural Research Centre, Central Finland Agricultural Experiment Station Received May 8, 1961 Soluble nitrogen fertilizers are usually applied as a surface dressing. It is sup- posed that the salts are rapidly dissolved by the soil moisture and carried down- wards to the layers where the plant roots are able to take up their ions. Parti- cularly the nitrate ion is assumed to be very easily movable in the soil. This, however, may not always be the case. Cunningham and Cooke (1) found that nitrate was not easily removed from the surface layer of a heavy soil by summer rainfalls sufficient to be detectable in drainage. Gasser (2) showed that leaching of nitrate in a light soil was effective only in prolonged wet periods. Some observations in Finland also indicate that in dry summers a large part of the nitrate nitrogen applied as a surface dressing may remain in the top inch (6). In order to study this problem more thoroughly under the conditions of arable land in Finland, samples were regularly collected from field trials in which calcium nitrate or ammonium nitrate limestone were applied at various rates. The distribu- tion of ammonium and nitrate nitrogen was followed through two growing periods. In one experiment, also the distribution of fertilizer nitrogen in a non-cropped soil was studied. Material and methods The field trials were carried out in 1959 and 1960 in Viikki, the experimental farm of Helsinki University, and in the experimental fields of Agricultural Research Centre in Central Finland. The experimental crop was oats. The yield results are reported elsewhere (4). In 1959, in the trials of V 1 and V 2 in Viikki, and K 1 and K 2 in Central Finland, ammonium nitrate limestone or calcium nitrate were applied as the surface dressing at rates corresponding to 0, 25, and 50 kg/ha of nitrogen. In 1960, in trials V 4 in Viikki and K 5 in central Finland heavier dress- ings were used: 75 and 100 kg/ha of nitrogen. In trial V 4 the treatments were applied to cropped and non-cropped plots. 2 https://www.c-info.fi/en/info/?token=dRyTVlJDw4PUJRK7.XpipfW7khgvUjutqNQ0frg.rfz-VT_3FrejjRDyYY183jVKV-XUwRKkcbAE0mDE5bBBAVvnrYbKIwLmYnxRLotDCXQ1vKD0_Az8sbm5b8JyB7MeDG5zn9xcYlWLwXAw6GmXOI3-64J88q123lrsn5C7_13bnQ3bESUDegNeUgq4ULi1fIAGnvwQmJpUJ48UX86qFnTp8JcpwVqce46z4x6dlw 170 The soil samples were collected every fourteenth day starting about one week after the fertilizers had been applied to the seeded plots. A special core sampler (3) was employed which allows rapid sampl- ing of each successive layer of one inch down to 4 inches. An additional sample from 4 inches to about 6 inches was taken with another auger. Further samples were taken for moisture determination in each trial. In order to avoid disturbing of the stands to beharvested, a special sampling area of 0.4 m breadth was reserved in each plot. At each sampling, ten cores were taken per plot, and samples from the same layer of the plot were bulked. The holes were filled with soil and a top layer of sand in order to prevent a new sampling from the same place. The samples were collected systematically, with a distance of 0.8 meter between the spots. Since it was not possible to arrange the analyzing of the soil samples immediately after collecting, the samples were air-dried at room temperature and ground. The four replicate samples were separately analyzed. Ammonium nitrogen and nitrate nitrogen were extracted with 0.5 N K 2S0 4 in the ratio of 1:10. The time of extraction was 2 hours. The ammonium nitrogen was determined from an aliquote of the filtrate by steam distillation into boric acid according to the procedure recommended by Lyndersen and Opem (5). The nitrate nitrogen was determined from the filtrate by the phenol disulphonic acid method. The ammonium fixing capacity of the experimental soils was determined by an unpublished method proposed by Prof. Dr. P, Schachtschabel. 5g of soil was mixed with 50 ml of N NH 4CI in a decanter and let stand for one day with occasional stirring. The clear solution was decanted and the soil washed first with N CaCl 2 and then four times with 0.2 N CaCl2. Finally it was twice washed with me- thylated spirits, dried at 105°C, and ground. 4.0 g of the treated sample and 4.0 g of an untreated one were boiled in 20 ml of concentrated H 2S04 for three hours, and the ammonium nitrogen distilled into boric acid. The difference between the amounts of ammonium nitrogen in the treated and untreated samples is presumed to represent the ammonium fixing capacity of the soil. Experimental soils Some characteristics of the experimental soils are recorded in Table 1. The trials in Central Fin- land, K 1, K 2, and K 5 were on silt or loam soils low in organic matter and only slightly acid. The clay content of the experimental soils in Viikki, in trials V 1, V 2, and V 4. is markedly higher as is also the case with content of organic matter in these soils. The silt clay soils of trials V 1 and V 4 are acid, the fine sand clay of trial V 2 is less acid and somewhat lower in organic matter than the other two soils in Viikki. Table 1. Soils Org. C Weight Mechanical Analysis, % Trial pH % of Clay Silt Fine sand Sand volume