M IHÄLY SZÜ CS
NITRATE MOVEMENT IN THE SOIL
Department o f Chemistry and Soil
Pannonian University o f Agricultural Sciences, M osonmagyarovar
INTRODUCTION
The investigation of the nitrate ion movement in the soil is justified by its role in plant nutrition and environmental pollution.
As out soils do not adsorb any considerable quantity of nitrate, their movement can be connected primarily with the soil-water regime.
Many experiments have proved that during the movement of a solution contai ning nitrate a concentration distribution is attained, which can be described roughly by normal distribution [9]. It has been proved also that the movement and speed of the chloride ion are practically the same as those of nitrate [1]. Computer simulation models have been made to describe this important transformation process [3, 5].
According to some investigation in Hungary [2, 4] the quantity of leached nitrate ion is influenced mainly by plant cover, the texture of the soil and the amount of pre cipitation.
Most of the above mentioned experiments were carried out using unstructured soils or sand under laboratory conditions, so our attempt was made to establish the real situation on the fields of large-scale farms and then to investigate the speed of ni trate movement in plot experiments. Some details about the field investigations were published earlier [8].
M ATERIAL A N D METHODS
The fact-finding investigation on soils of large-scale farms at sampling 540 soil profiles in 9 farms in the north-west part of the country were carried out in 1974-1976. The brown forest soils comprised 43%, the meadow soils 38%, and the chernozems 16% of the investigated profiles. All the profiles were sampled to the depth of 150 cm and divided into 30-cm parts for the determination of the nitrate and chloride contents. The movement of nitrate and chloride ion was followed according to the miscible displacement theory [6] by the transfer of the distribution peak point position [7]. This was possible, as the sampling dates as well as the time of fertiliza tion were known. The small number of measuring points in each profile did not ena
1 1 6 M. Szücs
ble us to fit normal distribution, so a square equation was put to every distribution whose peak could be demonstrated. The place of the peak can be calculated from the first differential coefficient, and the width of the distribution zone from the solution of the equation. Knowing the function by the help of a definite integral, the amount of the nitrate ion in the distribution zone can be calculated.
The 110 kg N per ha of fertilizers used as a mean on ploughed land in the early seventies has not been changed much so far. So the conclusions can be real in our days, too.
The second part of investigations was started in 1983 on an unfertilized field in the form of a special field plot experiment on the calcareous alluvial soil. Plots of 100 rrT were fertilized with 230 kg N per ha of ammonium nitrate. Every plot was fertilized only once and then regularly sampled at every 10 cm to the depth of 150 cm. NO3-N content in samples of the fertilized and unfertilized plots was compared.
This method allowed to separate the fate of the fertilizer-caused NO3 from the natural
one, which was not possible in case of large-scale farm investigations.
RESULTS A N D D ISCU SSIO N
The mean content of the NO3-N in the sampled 540 profiles of the large-scale
farm fields was 102 kg/ha. In the upper 30 cm layer 43 kg NO3-N per ha was found,
in the 30-60 cm zone 18 kg/ha, and in the others 13-14 kg/ha. It means that the nitrate content at of the boundary of the arable layer decrease rapidly, and after that the dec line is very slow. The mean quantity of NO3-N in a profile under the upper layer is
59 kg/ha. Examining the profiles one by one we have found that an average NO3-N
content in every layer covers a wide variation range. Some profiles have no nitrate below the upper 30 cm layer, and others have accumulation zones at different depths (Fig. 1). Some profiles have more than one accumulation zone, and the width of a zo
ne was about 60-80 cm. Only 44% of the profiles investigated had NO3 accumulation
zones below the upper layer, 81% of the profiles had chloride accumulation zones under the surface layer which is attributed to the influence of the regularly used KC1 fertilizer. The difference can be explained by the more intensive plant uptake, the im mobilization process and the denitrification losses of the nitrate ion in the soil.
The place of accumulation zones was described by the peak point position depth. The date shows (Fig. 2) that these zones could be found at every depth, but the di stribution frequency of them was a little greater at the depths of 40 cm and 80 cm. These can be the most frequent yearly movements of these ions. Plot experiment re sults show (Fig. 3) that the concentration distribution under real circumstances does not match completely the normal distribution curve, nevertheless the peak can be fo und.
The native N O3 was considerable, but it could be separated from the fertilizer- born amount. Paying attention only to the peak point position depth (Fig. 4) we can find that the movement to the 40 cm depth occurs very easily, especially at the spring time start. In case of drought to the end of summer an upward movement can be ob served. The yearly leaching depth is the resultant of the two opposite movements. In dry years there may be no leaching at all, but in case of most precipitation in winter and early spring it can attain 80 cm.
T h e s e c o n d d e g r e e p o l y n o m a l T h e n o r m a l d i s t r i b u t i o n c u r v e * D e r i v e d f r o m m e a s u r e m e n t s
Fig. 1. Distribution of the nitrate and chloride content in a soil profile (Bana 1)
CO NC LUSION S
1. Investigations of more than 500 soil profiles in the north-west part of Hungary
have proved that the highest nitrate concentration occurs in the upper arable layer of
Fig. 2. Frequency distribution of accumulation peak point at different depths
During the yearly movements there are considerable transformation losses of ni trate, and if fertilizing is made with doses not exceeding the plant uptake, the lea ching losses would be small.
118 M. Szücs
Fig. 4. Movement of the peak point of the nitrate zone resulting from the NH4NO3 fertilizer (220 kg N per ha) application at 1st Nov. 1983
the soils, but in 44% of cases there are elevated nitrate concentration zones moving down in the soil.
2. The width of the high nitrate concentration zones below the surface layer was found about 60 cm, and the peak point position depth transfer was accepted for mea suring of movement.
3. Plot experiments have confirmed the results of farm field estimations. It has been concluded, that the yearly leaching is a resultant of downward and upward mo vements.
4. The yearly nitrate downward movement was found between 40 and 80 cm, but in some dry years there was no movement at all.
5. Calcareous soils, if they were tilled would have a considerable amount of ni trate even without fertilizers.
REFERENCES
[1] C a m e r o n K . C . , W i l d A. Comparative rates of leaching of chloride, nitrate and tritiated water under field conditions. J. Soil Sei. 1982, 33: 649-657.
[2] D e b r e c z e n i B. , D e b r e c z e n i K. A tâpanyagés vizellâtas kapcsolata. Mezögazd. Kiadó. Buda pest 1983.
[ 3 ] F r i s s e l M. J . , V a n V e e n J. A. Simulation of nitrogen behaviour of soil-plant systems. Centre for Agricultural Publishing and Documentation, Wageningen 1981.
[4] G y ö r i D . A talaj termékenysége. Mezögazd. Kiadó. Budapest 1984.
[5] H a g i n J. et al . Outlines of a computer simulation model on residual and added nitrogen changes and transport in soils. Z. Pflanzenern. Bodenk. 1976,4: 443-455.
[6] N i e l s e n D . R . , B i g g a r J . W. Miscible displacement: III. Theoretical considerations. Soil Sei. Amer. Proc. 1962,26: 216-221.
[7] R o s e C . W . , H o g a r t h W . L . , D a y a n a n d a W. A. Movement of peak solute concentration position by leaching in a nonsorbing soil. Aus. J. Soil Res. 1982, 20: 23-36.
[8] S z ü c s M . Distribution of nitrate in soils of large-scale farms. CIEC 9th Fertilizer Congress Procee dings. Budapest 1984, 2:193-196.
[ 9 ] T e r r y D . L . , M c C a n t s D . Quantitative prediction of leaching in field soils. Soil Sei. Soc. Amer. Prod. 1979,34: 271-276. М .С Ю Ч ПЕРЕДВИЖЕНИЕ НИТРАТНОГО АЗОТА В ПОЧВЕ Паннонский аграрный университет, Сельскохозяйственный факультет, з. Мошонмадьяровар, Венгрия Р е з ю м е Для определения распределения нитратного азота в производственных условиях по почвенному профилю было изучено более 500 разрезов, заложенных на полях хозяйств. Анализ содержания нитратов был произведен до глубины 150 см. Самое больш ое содерж ание нитратов в среднем, как это ожидалось, было в пахотном горизонте почв, однако в 44%-ном количестве разрезов наблюдалоць наличие аккумуляционной зоны нитратов ниже пахотного горизонта. Толщина этих зон была в среднем около 60 см, а концентрационный профиль в них описывался закономерностью нормального распределения. Глубину аккумуляционной зоны выражали о д ним числом, расстоянием места максимального содержания нитрата от поверхности, что однов ременно явилось серединой зоны. Аккумуляционные зоны можно было найти на разных глубинах, но самая большая частота их нахождения была на глубине 40 и 80 см. В полевых опытах эти наблюдения были подтверждены. Кроме того установлено, что ср ед н ее годовое передвижение нитратной зоны составляет 60 см. Нисходящее движение имеет м е сто в конце зимы и весной, а подтягивание нитратного слоя в сторону поверхности осенью. П оэтому вымывание нитратов зависит от соотношения этих двух движений. В некоторые сухие годы эти движения взаимно уравновешиваются.
120 M. Szücs M.SZÜCS
RUCH A ZO TAN ÓW W GLEBIE
Pannoński Uniwersytet Rolniczy, Mosonmagyarôvàr, Węgry S t r e s z c z e n i e
Dla określenia rozmieszczenia azotanów w profilu gleb oznaczono ich zawartość w przeszło 500 profilach gleb pól produkcyjnych do głębokości 150 cm. Jak należało oczekiwać, średnio najwięcej azo tanów występowało w warstwie ornej gleby. Jednakże aż 44% profilów miało strefy akumulacji poniżej warstwy ornej. Miąższość tych stref akumulacji wynosiła około 60 cm, a rozkład koncentracji dał się opi sać krzywą rozkładu normalnego. Głębokość akumulacyjnej strefy można było wyrazić jedną liczbą, a mianowicie odległością miejsca maksymalnej zawartości azotanów od powierzchni, która jest równocze śnie środkiem strefy. Akumulacyjne strefy znajdowano na różnych głębokościach, ale najczęściej na głę bokości 40 i 80 cm.
Te obserwacje były potwierdzone w polowych doświadczeniach. Oprócz tego wykazano, że średni roczny ruch azotanów ku dołowi wynosił 60 cm i następował z końcem zimy i wiosną. W niektórych la tach posusznych zauważono pod koniec jesieni znaczny ruch azotanów ku górze. Wymywanie azotanów było w ięc wypadkową tych dwóch przeciwnych ruchów. W niektórych suchych latach te dwa przeciw stawne ruchy równoważyły się i wówczas nie stwierdzano wymywania azotanów.
Dr M. Szücs Praca wpłynęła do redakcji w marcu 1991 r.
Department of Chemistry and Soil Sciences University of Agricultural Science Mosonmagyarôvàr, Lucsony u. 15-15 Hungary — Węgry
