Mineralization of soil organic nitrogen in upland fields as determined by a 15nh4+ dilution technique, and absorption of nitrogen by maize

0038-0717/89 33.00 + 0.00

Soil Bid. Biochrm. Vol. 21. No. 5, pp. 661-665. 1989 Printed in Great Britain. All rightsreserved

Copyright C 1989Maxwell Pergamon Macmillan pk

MINERALIZATION OF SOIL ORGANIC NITROGEN IN UPLAND FIELDS AS DETERMINED BY A 15NH,+ DILUTION TECHNIQUE, AND ABSORPTION OF NITROGEN BY MAIZE T. NISHIO and T. FUJIMOTO Upland Farming Division, Hokkaido National Agricultural Experiment Station, Memuro, Kasai-gun, Hokkaido 082, Japan (Accepted I December 1988) Summary-Mineralization rates of soil N in Hokkaido upland fields, Japan. were determined in the laboratory using “NH: dilution technique at ambient temperatures. The soil samples were collected every month from fields of a Brown Andosol and an Ordinary Andosol from 21 May until 22 September 1984. The gross mineralization rates obtained ranged from 1.15 to 2.21 pg N g-’ day-’ for the Brown Andosol. and from 1.60 to 3.77 for the Ordinary Andosol. The rates were highest in July for both the soils. Assuming a topsoil thickness of 35 cm, the total amount of soil N mineralized during the growing season of maize was calculated to be 521 kg N ha-’ in the Brown Andosol and 808 in the Ordinary Andosol. Amounts of soil N absorbed by maize in the Brown Andosol were determined in the presence or absence of applied (1JNH4)rS04. The total amount of soil N absorbed was 56 kg N ha-’ in the plot applied with N-fertilizer, and 46 kg N ha-’ in the plot without N-fertilizer. The values corresponded to I I and 9%, respectively. of the total inorganic N mineralized during the growing season for maize.

INTRODUCTION

Using “N-fertilizer, we found that the total amounts of soil N absorbed by sugar beet and winter wheat in a Brown Andosol were 71 and 37 kg N ha-‘, respectively. The amounts accounted for, respectively, 37 and 5 I % of the total amount of N absorbed by these plants at harvest time. Information about to what extent the growth of crops is supported by mineralization of organic matter are of primary importance for the management of crop yields by controlling fertilizer application. Stanford and Smith (1972) estimated net mineralization of N in 39 widely differing soils from increase of inorganic N during incubation. They developed a kinetic procedure to analyze mineralization of soil N. Their method might be used to quantify the easily decomposable fraction of soil organic matter. However, their values represent, at best, N mineralization potential, because the soil samples were kept at a temperature (35’C) higher than the average temperatures in the field during 30 wk. Air-drying of the soil samples further enhances mineralization. Estimates of the supply of soil inorganic N under natural conditions cannot be obtained by their method. Moreover, no information can be obtained, by their method, about N immobilized by soil microorganisms. Microbial biomass in soil often acts as a major source of inorganic N. Jenkinson and Ladd (1980) suggested that the flux of N through microbial biomass in an unmanured plot of Rothamsted Experimental Station is of the same order as the annual offtake of N in grain and straw of wheat. Many soil scientists have tried to correlate the supply of soil N with the microbial biomass (Jenkinson and Powlson, 1976; Powlson, 1980; Marumoto ef s.llB 1, G-D

al., 1982; Carter and Rennie, 1984). However, the methods used to determine the flux of inorganic N from microbial biomass impose drastic stresses such as high temperature, drying, grinding and fumigation in order to detect measurable increases of ammonium or evolution of CO,. Therefore, the information obtained cannot be directly applied to the events occurring in the field. Kirkham and Bartholomew (1954, 1955) presented a mathematical model to estimate the rates of mineralization and immobilization on the basis of data obtained by the “NH, dilution technique. Nishio et al. (1985) simultaneously determined mineralization, immobilization and nitrification by applying this method to an aerobic soil. This method has the advantage that gross mineralization rate is determined under the least stress within a relatively short period. We used this method to estimate the gross mineralization of inorganic N from organic matter in volcanic ash soils. The rate of gross mineralization was compared to that of N absorption by maize, the latter being determined independently from the N content in the plant and incorporation of lSN from “N-fertilizer. MATERIALS AND METHODS

Sampling of soils and maize

Topsoils (0-20cm) of a Brown Andosol and an Ordinary Andosol in Hokkaido, Japan, were used. The chemical properties of the soils were described by Nishio et al. (1988). Two experimental plots were set up for each soil. One plot was set up in a non-fertilized fallow (6.4 x 5 m) and the other in an adjacent area (cropped plot 1; 10.4 x 5 m) where maize was grown with the application of mixed fertilizer includ661

T. NISHI~and T. FVJIMOT~

662

ing ~~~n~~rn sulfate. The fertilizer was band-applied in the row at the rates of 150 kg N ha-‘. An additionaf plot (cropped plot 2; IO.4 x 5 mf where no N fertihzer was applied was selected in the cropped Brown Andosol field. The date of seeding and fertilizer application was 16 May 1984. Soil samples were taken every month from the non-fertilized fallow. The samples were taken to a depth of 2Ocm at random from several areas using a trowel. The samples collected from each plot of the non-fertilized fallow were mixed uniformly. The soil in cropped plot 2 was collected on 14 August from 30 x 25 cm of quadrats (two areas), so arranged as to foeate the stem of a maize plant at its center. The whole soil in the quadrats was coheeted to depth of 5Ocm segmented by tOcm depth intervals. The co&&d soils were sieved (~2 mm), and stored at 3°C. Using a portion of the sieved sample, percentage moisture was determined by weight loss upon drying at 105°C for 24 h. Assays of mineralization were begun under field-moist conditions within 2 days from field collection To measure N absorption by maize, several 65 x 50 cm quadrats with galvanized metal barriers (25 cm deep) was established in cropped plot I of the Brown Andosol field (Fig. 1). The fertilizer containing ‘JN-labeled ammonium sulfate (3.08 atm% rsN) was applied on 16 May 1984 to the quadrats at the same rate as to the field. At dates indicated, maize pfants including roots were collected (8 plants pfot-’ ) and the roots were washed to remove soil. Dry matter was weighed and all analyses done on plant material dried at 70°C for 2 days. Assays of mineralization

Sieved soil samples (1OOg dry wt) were placed in SO0ml flasks. To half of the flasks, a 5 ml of solution containing 2 mg N of “N-labeled ammonium sulfate (20.6 atm% “N) was added. No additions were made to the rest of the flasks. The flasks were stoppered, and held at the constant temperature. In order to estimate the seasonal changes of mineraiization rate, the soils were incubated at average temperature in each season, which was obtained for the last 3 yr from a IOcm depth in the Brown Andosot field (cf. Fig. 2). Every treatment was duplicated, and incubation was

0

0 -

P

I

o--maize

0

0

0

65cm 0

t

0

Skm

Zfcm d

0

f

o

t+ 0

O-

Fig.

0

65cm -0

0

a

I. Siting of a quadtat (65 x SOcm) made of galvanized metal barriers in the cropped plot.

Fig. 2. Seasonal changes in mineratization rates and soil temperature in the non-fertilized fallow of the Brown Andosol and the Ordinary Andosol. The values of the mineralization rates are the mean of two determinations. --Q-, Gross mineralization in the Brown Andosol: -+--, gross mineralization in the Ordinary Andosol; ---O---. net mineralization in the Brown Andosol; ---+--. net mineralization in the Ordinary Andosol; -+ --, average sail

temperature at a 1Ocm of depth as estimated from the records before and after IO days of the indicated dates taken over the last 3yr.

for 4 days where ammonium sulfate had been added, or 8 days where ammonium sulfate had not been added. Twenty grams of the soii was removed from each flask every day (or every 2 days), and inorganic N in the soil sample was extracted with 10% (W/W) KCI solution. Changes in concentrations of ammonium, nitrate and “N-ammonium were determined, and the rate of gross mineralization was calculated (Nishio et al., 1985). The rate of net mineralization was determined by the mass balance of inorganic N in the soils without the addition of ammonium sulfate.

Ammonium and nitrate in the KC! extracts were determined by the methods of Solorzano (1969) and Wood et al. (1967), respectively. The N content of maize was determined by the Kjeldahi method, using salicylic acid ta include nitrate. The lSN isotope-ratio of ammonium was analyzed by the method of Kano et al. (1974). RESULTS

Seasonal changes in the rate of gross mineralization in the soils collected from the non-fertilized fatlow and the average soit temperatures are shown in Fig. 2. The gross mineralization rate in both soils was highest in July. The tendency of the seasonal changes in the gross mineralization rate was consistent with that of soil temperature except for June. The gross mineralization rate of the Ordinary Andosol were always higher than that of the Brown Andosol. The broken lines in Fig. 2 represent the net mineralization rate. If the gross mineralization of organic N is not modified by the addition of 20 c(g N g-t of ammonium, the immobilization of N can be esti-

Mineralization of soil nitrogen and absorption by maize Table 1. Vertical distribution of N and mi~~tioa Inorganic N NH; NO,

Depth (cm)

0.7 0.7 0.9 0.7 1.4

1.3 1.3 1.6 I:

rate in the Brown Attdoeol f&d’

Organic N (mgNg_‘)

(ngNg-‘)

O-10 IO-20 20-30 3&40 40-50

663

Mineralization rate @gNg-‘day“)

2.12 2.11 2.11 I .89 0.77

Moi?rture content (W

2.08 I .78 I .86 I.41 0. I7

31.9 33.1 33.6 36.8 33.2

‘The soils were collected on 14 August from cropped plot 2. Mineralization rate was detcmined at 20°C. The values are the mean of two determinations except for organic N and moisture content (single determination).

mated from the difference between the gross mineralization and net minerali~tion. A net increase of inorganic N was invariably observed for the Ordinary Andosol. while little net increase was detected in the Brown Andosol. Changes in the gross mineralization rate with depth in the Brown Andosol field are shown in Table 1 together with the vertical distribution of N. In the Brown Andosol, the subsoil was present at a depth of 35 cm and the organic N content was almost constant down to 35 cm. Although the value of the layer between 0-IOcm was highest, the gross mineralization rate did not decrease much at 35cm. Figure 3 shows the gross mineralization rate as a function of moisture content of the Brown Andosol; the lower the moisture content the lower the mineralization rate. The moisture content in soils collected from both fields is shown in Table 2. Table 3 shows changes with time in N absorption by maize in the Brown Andosol field. The total amount of N absorbed at harvest time was I50 kg N ha-’ in cropped plot 1, and 46 in cropped plot 2. N assimilated by maize is divided into soil N and fertilizer N; soil N is derived from mineralization of organic N in the soil. The ratio of soil N to total N absorbed by the maize was calculated from the 15N abundance in the maize (Fig. 4). The ratio of soil N to the total was below 20% in June and Juiy, but it

Table 2. Moisture content of the aoil collected’ Sampling date 21 I9 23 27 22 26

BrOWI

Ordinary

Andosol

Andosol

34.2 30.9 36.0 34.3 35.4 36.9

31.7 30.3 34.9 34.7 34.2 35.5

May June July Aun s&i Dct

‘The moisture content of the toil is cxpreaaed in percent by weight of soil (single dcterminalion). Table 3. Changes with time in the yield of maim dry matter and N absorption by maize N added as fertilizer Plot

fnrn 3

I

I5

2

0

Sampling date 18 June 6 July 23 July 8 Aug 19 Sept I8 6 23 8 I9

June July July Aug scm

Yictd of maize dry matter’ (gm-t) S.lS(O.S5) 57.1 (8.7) 274(31) 530 (56) 1310(120) 2.22 19.8 I03 337 619

N removed in maim (ita-‘) 0.20 (0.03) 2.17(0.21) 7.71 (1.11) 7.87 (0.74) 15.02(1.57) 0.05 0.48 I .96 3.45 4.67

‘The values arc the mean of at least two determinations except when the SDS are given in parenthems, where four rcplicatea are used.

increased with the growth of maize, and finally reached 37% (Fig. 4). The soil N absorbed during August and September was calculated, from the data given in Table 3 and Fig. 4 to be about 70% of the total soil N absorbed.

i 0.6 0

DISCUSSION

Q

0.6 -

The gross mineralization rate both in the Brown Andosol and the Ordinary Andosol were highest in

0.4 . 0.2 -

0

ratio

0.02,

39 43 13 moisture

28

content

1

34

18 June

WI

f-1

PI.1

Fig. 3. The gross mineralization rate as a function of moisture content in the Brown Andosol. The soil sample was collected on 14 April from the uncropped bare area, and were incubated at 20°C. Moisture content of the soil was originally 32%. and adjusted by a&hying or adding water up to the indicated contents. The values arc the mean of two determinations.

Fig. 4. Relative contribution of soil N and fertilizer N to the total N absorbed by maize in the Brown Andosol field. The values are the mean of two determinations.

T. NISHM) and

664

fable 4. Estimates of N mineralization in topsoils and N absorption by maize (kg ha - ’ ) Brown Andosol Amount of mineralized N’ (10 May-20 September) Content of organic N’ Absorption by maize (crop9pc;~ 1; NlMkgha-‘fFertilizer N’ (crop@ plot 2: KOkghae’)* Soil N

Ordinary Andosol SOB

521 6140

14.000

, 56 94

-

46

-

‘The values calculated by assuming a topsoil depth of 35 cm. :Application rate of N-fertilizer. ‘Estimated from “N abundance and total N al harvest time.

July (Pig. 2). This indicates that the rates are controlled primarily by temperature. The lower mineralization rates observed in June can be attributed to the reduced moisture contents of the soils (Fig. 3, Table 2). The gross minerali~tion rate in the topsoils (35 cm) of the Brown Andosol does not vary substantially with depth (Table I). Since the roots of maize extend to at least 35 cm below the soil surface, we can assume that maize absorbs soil N from the top 35 cm layer. The supply of inorganic N from the subsoil is probably of minor importance. Assuming a further bulk density of the soil of 0.7, we estimated the gross mineralization during the growing season of maize. The gross mineralization is 521 kg N ha-’ for the Brown Andosol, and 808 for the Ordinary Andosol (Table 4). The contents of organic N in the topsoils are roughly calculated to be 6140 kg N ha-’ for the Brown Andosol, and 14,000 for the Ordinary Andosol. We can, therefore, infer that approx. 8.5% of the organic N is mineralized during the maize growing season in the Brown Andosol and 5.8% in the Ordinary Andosol. Dead microbial biomass has been suggested to form the main pool of mobile organic N (Powlson, 1980; Marumoto er al.. 1982). Ahmad et al. (1973) indicated that the immobilized N is much more susceptible to mineralization than is the native-organic N when the soil is treated with air-drying or oven-drying. The relativeiy high values for the gross mineralization obtained suggests the occurrence of N recycling through microbial biomass. The ratio of N absorbed by maize to inorganic N mineralized was I I % for cropped plot 1, and 9% for cropped plot 2. These values were much lower than the availability of chemical fertilizer to maize (63%). There is a possibility that the gross mineralization is overestimated because of the inevitable modification of environmental conditions associated with experimental processes. The mineralization is probably enhanced by the addition of water (nutrient solution) by at least 10% (Fig. 3), and the mineralization in deeper layers might also be somewhat accelerated by the changes in soil structure and other physical and chemical properties. Even if the effects described above are taken into account our results still suggest, however, that N produced by the mineralization of organic matter in the soils is not effectively utilized by maize. The following reasons can be considered.

T. FUJIM~TO 1. During the initial growth of maize, the roots of maize do not extend sufficiently. The major part of inorganic N produced is immobilized by microorganisms or lost by leaching before the maize can utilize it. Actually, the availability of the inorganic N mineralized in August and September by maize is calculated to be 20% if the data shown in Table 3 and Fig. 4 are used. 2. Inorganic N is transported to the root surface by diffusion and mass flow, with the latter dominating where concentrations of inorganic N in soil solution are high. Fertilizer N may be mainly supplied to the plant roots by mass flow because the concentration of inorganic N in the soil solution is very high at the site where fertilizer is applied. However, the concentration of inorganic N produced by the mineralization of soil organic matter is too low to be transported to the root surface by mass flow. Most of the soil inorganic N absorbed by maize would be produced in close proximity to the roots. 3. The roots of crops exhibit localized development at the site where fertilizer is supplied. Drew and Saker (1975) observed that a combination of increased lateral root growth and increased rate of nitrate uptake from within the enriched zone appears to compensate for the deficient supply of nitrate to the remainder of the root system when nitrate is supplied at an appropriate concentration to only part of the root system of barley. Other crops probably respond in a similar manner. The concentration of inorganic N produced from soil organic matter is too low to induce such a response. Plants and soil microorganisms probably compete with each other for nitrogenous nutrients mineralized in the close proximity of the root. Smith (1979) and Riha et al. (1985) have presented kinetic models of competition for ammonium among soil heterotrophs, nitrifiers and plant roots. A fuller knowledge of the process of competition for soil N among microorganisms and roots is critically needed for a greater understanding of the dynamic aspects of soil organic N and its real functions. Acknowledgement-We

thank

Professor

A.

Hattori, Re-

search Institute for Information and Knowledge, Kanagawa University, for helpful comments. REFERENCES

Ahmad Z., Yahiro Y., Kai H. and Harada T. (1973) Factors affecting immobili~tion and release of nitrogen in soil and chemical characteristics of the nitrogen newly immobilized. IV. Chemical nature of the organic nitrogen becoming decomposable due to the drying of soil. Soil Science and P1an1 Nutrition 19, 287-298. Barber S. A. (1977) Nutrients in soil and their flow to plant roots. In The Belowground Ecosystem: A Synthesis of Plant-Associated Processes (J. K. Marshall, Ed.). DO. 161-170. Range Science Department Science Series ‘ho. 26. Colorado&ate University, Fort Collins. Carter M. R. and Rennie D. A. (1984) Dynamics of soil microbial biomass N under zero and.shallow tillage for spring wheat. using rJN urea. Rant and Soil 76, 157-164. Drew M. C. and Saker L. R. (19751 Nutrient SUDO~Y and the growth of the seminal rootsystem in barley II~I&aIii, compensatory increases in lateral root growth and rates of nitrate uptake when nitrate supply is restricted to only part of the root system. lournal 01 Experimenfal Botany 26, 79-90.

Mineralization of soil nitrogen and absorption by maize Jenkinson 0. S. and Ladd J. N. (1980) Microbial biomass in soil: measurement and turnover. In Soil Biochemistry 5, (Pa ’ E. A. and Ladd J. N., Eds), pp. 415+71. Marceil-Dekker, New York. Jenkinson 0. S. and Powison 0. S. (1976) The effects of biocidai treatments on metabolism in soil. V. A method for measuring sioi biomass. Soil Biology & Biochernisrry 8, 209-213. Kano H., Yoneyama T. and Kumazawa K. (1974) Determination of N-15 by emission spectrometty (in Japanese). Journal of rhe Science of Soif and Manure. Jaaan 45. W-559. Kirkham D. and Bartholomew W. V. (1954) Equations for following nutrient transformations in soil, utilizing tracer data. Soil Science Society of America Proceedings 18, 33-34. Kirkham D. and Bartholomew W. V. (1955) Equations for following nutrient transfo~ations in soil, utilizing tracer data. II. Soil Science Society of America Proceedings 19, 189-192. Marumoto T., Anderson J. P. E. and Domsch K. H. (1982) Mineralization of nutrients from soil microbial biomass. Soil Biology & Biochemisrry 14. 469-475. Nishio T., Kanamori T. and Fujimoto T. (1985) Nitrogen transformations in an aerobic soil as determined by a “NH: dilution technique. Soil Biology & B~ochem~zry 17, 149-1.54.

665

Nishio T., Kanamori T. and Fujimoto T. (1988) Effects of organic matter, moisture content and other environmental factors on de~t~~~tion in top-&s of an upland tieid. sOi/ Science and PIam Nurririon 34, 97-105. Powlson 0. S. (1980) The effects of grinding on microbial and non-microbial organic matter in soil. lournol of Soil Science 31, 77-85. Riha S. J., Campbell G. S. and Wolfe J. (1986) A model of competition for ammonium among heterotrophs, nitriftets. and roots. Soil Science Society ofAmerica Journal 50.1463-1466. Smith 0. L. (1979) An analytical model of the decomposition of soil organic matter. Soil Biology c( Biochemistry 11, 58-6. Soiorzano L. (1969) Determination of ammonia in natural waters by the phenoihypochiorite method. Limnology and Oceanography 14. 799-80 I. Stanford G. and Smith S. J. (1972) Nitrogen ~nerali~tion potentials of soils. Soii Science Sociery of America Proceedings 36, 465172. Wood E. 0.. Armstrong F. A. and Richards F. A. (1967) Determination of nitrate in sea water by cadmium-copper reduction to nitrite. Journal of Marine Bioiogicai Association of Unired Kingdom 47, 23-71.