Soil Science Society of America Journal 64:738-745 (2000)
© 2000 Soil Science Society of America
DIVISION S-6-SOIL & WATER MANAGEMENT & CONSERVATION
Cultivation Effects on Soil Carbon and Nitrogen Contents at Depth in the Russian Chernozem
E.A. Mikhailovaa,
R.B. Bryanta,
I.I. Vassenevb,
S.J. Schwagerc and
C.J. Posta
a Cornell Univ., Dep. of Soil, Crop, and Atmospheric Sci., Bradfield Hall, Ithaca, NY 14853 USA
b Russian Inst. of Agronomy and Soil Erosion Control, K. Marx St., 70B, Kursk, Russia 305021
c Cornell Univ., Dep. of Biometrics, 434 Warren Hall, Ithaca, NY 14853 USA
em10{at}cornell.edu
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ABSTRACT
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Little is known about changes in soil organic C (SOC) and total N with depth and with land use. We conducted this study to determine the depth of changes in SOC and total N under different management regimes in the chernozem soil. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50-yr continuous-fallow field, a yearly cut hay field in the V.V. Alekhin Central-Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine-silty, mixed, frigid Pachic Hapludolls. Soil organic C, total N contents, and bulk densities with depth were compared. Significant reductions in SOC and total N concentrations were detected to a depth of 120 to 130 cm in the 50-yr continuous-fallow field and to a depth of 80 cm in the continuously cropped field. Highest reductions were observed in the top 10 cm of soil, where reduction in SOC ranged from 38 to 43% and reduction in total N ranged from 45 to 53%. Significant losses of SOC and total N per equivalent soil mass on an area basis were observed to a depth of 60 cm in the continuously cropped field and to a depth of 100 cm in the 50-yr continuous-fallow field.
Abbreviations: CNAL, Cornell Nutrient Analysis Laboratory • SOC, soil organic carbon
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INTRODUCTION
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CHERNOZEM SOILS, which occupy 6586470 ha (49.6% of total agricultural lands) in Russia alone (Russian State Committee on Land Resources and Land-Use, 1997) and contain 
130 to 160 t ha-1 of organic matter in the top 20 cm, are a huge source and sink of CO2 gas (Orlov and Birukova, 1995; Kudeyarov et al., 1995). Located primarily in the breadbasket regions of Russia, these soils have great agricultural significance and have been extensively studied (Dokuchaev, 1967; Afanasyeva, 1966). The Kursk area is one region with predominantly chernozem soils where intensive cultivation has led to changes in soil properties (Scherbakov and Ruday, 1983; Kuznetsova et al., 1993; Sorokina and Kogut, 1997). Scherbakov and Vassenev (1996) made a thorough review of the Russian literature on the subject since Dokuchaev's research. Unfortunately, it is not always clear what statistical methods of comparison were used in the analysis of SOC and N inventories and how many replicated samples were used. Lack of good worldwide data, especially on bulk density and SOC content with depth, complicates the estimation of changes in SOC inventories following cultivation of previously untilled soils (Duxbury, 1991; Davidson and Ackerman, 1993). Often research is concentrated on evaluating SOC loss in the top soil layers (A and upper B horizons), thereby underestimating the full potential of SOC and total N losses (Tiessen et al., 1982; Duxbury, 1991; Davidson and Ackerman, 1993). Such estimates are necessary to evaluate the impact of agriculture on CO2 emissions into the atmosphere. Currently, researchers are attempting to create and maintain worldwide databases with data from long-term field studies, which would allow the prediction of possible rates and directions of change in SOC (Powlson et al., 1996; Paul et al., 1997). Lack of data on changes in SOC with depth and land use was identified as one of the major knowledge gaps in soil science (Lal et al., 1998, p. 602).
This research encompasses a long-term field study conducted in the V.V. Alekhin Central-Chernozem Biosphere State Reserve, where a combination of a native grassland site, not cultivated for at least 300 yr, and a 50-yr continuous-fallow field allows monitoring of the C inventory at the extreme event of cultivation (long-term continuous fallow). Although SOC and total N contents were measured for the plowed field with no cropping in earlier studies (Ponomareva and Nikolaeva, 1965), the lack of data on the variability of these measurements did not allow a valid statistical comparison of changes in SOC contents and total N over time.
The objectives of this study were to evaluate statistically the long-term cultivation effects on soil bulk density, SOC, and total N contents in the Russian Chernozem, within and below the plow layer.
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Materials and methods
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Field Sites
Four sites were sampled in the Kursk region of Russia in the summers of 1997 and 1998: a native grassland, a 50-yr continuous-fallow field, a yearly cut hay field, and a continuously cropped field. The region has a temperate climate, which is moderately cold, with a mean annual precipitation of 587 mm and a mean annual air temperature of 5.4°C (V.V. Alekhin Central-Chernozem Biosphere State Reserve, 1947–1997). The topography of the sampled area is nearly level (<2% slope gradient) with a few shallow circular depressions (<2 m deep and 10 m in diam.) that are common in the area (Tselicheva and Daineko, 1966). These depressions are formed as a result of loess compression when water accumulates in the low areas of the landscape, causing more intensive leaching than in the upper areas of the landscape (Gavrik, 1968). Small mole hills in the soil provide visible evidence of active faunalpedoturbation, as defined by Fanning and Fanning (1989)(p. 54).
The first three fields (native grassland, 50-yr continuous-fallow field, and yearly cut hay field) are located in the Streletskyi section of the V.V. Alekhin Central-Chernozem Biosphere State Reserve at 51° N, 36° E, about 18 km south of the city of Kursk (Vinogradov, 1984). Elevation of these sites is 264 m above mean sea level (Ryabov, 1979). According to Alekhin (1934), plant species richness can reach as high as 77 species per m2 and 120 species per 100 m2. Dominant species include meadow bromegrass (Bromus riparius Rehm.), wild oats (Stipa pennata L.), narrow-leaved meadow grass (Poa angustifolia L.), intermediate wheatgrass [Elytrigia intermedia (Host) Nevski], meadowsweet rose (Filipendula vulgaris Moench), and green strawberry (Fragaria viridis Duch.).
The four sampled sites are as follows:
- The native grassland field is located in the Streletskyi section of the V.V. Alekhin Central-Chernozem Biosphere State Reserve. No agricultural activity, hunting, burning, or gathering of plants has been allowed on this site since 1935. Before 1935, this land was used as a pasture for at least 300 yr (Maleshin and Zolotuhin, 1994).
- The 50-yr continuous-fallow field is located about 50 m from the native grassland site. This field (0.8 ha) has been continuously plowed since 1947, but no crops have ever been planted during this period. Weed growth has been controlled by periodic plowing with the disk cultivator to 20-cm depth. The plowing takes place once or twice a month as needed, depending on weed emergence.
- The yearly cut hay field is located 1000 m from the native grassland field. Originally a native grassland, this field has been used for yearly hay collection for at least 50 yr.
- The continuously cropped field is located within the territory of the Experimental Station of the Russian Institute of Agronomy and Soil Erosion Control, which is adjacent to the Biosphere Reserve. This site has been continuously cropped for at least 100 yr. Table 1
presents information from agronomic records for this field for the past 10 yr. Plowing depth is 30 cm.
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Table 1 Cropping and management characteristics of the continuously cropped field for the past 10 yr (Agronomy records of the experimental station)
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Sampling Procedure
The native grassland and 50-yr continuous-fallow fields were sampled on a radial grid with a distance of 5 m between sampling points (Fig. 1)
. The orientation of the grid was determined by randomly selecting an angle from 360°. Deep soil cores were obtained at the center and at 20 m from the center at all four sites. The sampling scheme was modified in that only deep soil cores were collected for the continuously cropped and yearly cut hay fields. All samples were obtained to a depth of 2 m or more using a 5-cm diam. hand probe. Soil cores were dissected into 10-cm increments, and the following data were recorded in the field: upper and lower boundary of soil horizon, moist and dry color (Munsell color chart), reaction to 10% HCl, and presence of carbonate accumulations.
A separate sampling was conducted to determine bulk density of the soil at each site. Samples for the bulk density determination were obtained with a 5-cm diam. hand probe and an inserted 5-cm high metal ring. In close proximity to the deep soil cores, bulk density was determined for soil at 5-cm, 19-cm, 33-cm, and 47-cm depths (mid-points of the height of the metal ring during the soil probing). In close proximity to the shallow soil cores, bulk density was determined at the 19-cm and 33-cm depths. Oven-dry bulk densities were determined for each sampled depth.
Laboratory Methods
Soil samples from each 10-cm depth increment were air-dried, manually crushed, and passed through a 2-mm sieve. One soil profile was randomly selected from each of the sampled fields and particle-size distribution was determined for each of the 10-cm depth increments by the pipette method after pretreating for removal of carbonates with 1 M NaOAc (adjusted to pH 5). Additional pretreatments included organic matter removal with 30% H2O2, and soluble salt removal by ceramic candle filtering and repeated washing with deionized water (Gee and Bauder, 1986). Samples from the same soil profiles were used for chemical analysis. Soil pH was measured from a 1:1 soil/water suspension (McLean, 1982). Exchange acidity was determined using BaCl2–triethanolamine buffered at pH 8 according to Method S1840 of the Cornell Nutrient Analysis Laboratory (CNAL) (Greweling and Peech, 1965). Exchangeable cations were extracted with 1 M NH4OAc at pH 7.0 using a Zero-Max E2 vacuum extractor (Zero-Max, Minneapolis, MN) as described in Method S2030 of the CNAL (McClenahan and Ferguson, 1989). Cation-exchange capacity was determined by summation of cations. Exchangeable Al was extracted with 1 M KCl and analyzed by inductively coupled argon emission plasma (ICAEP), JY70 Type II (Instruments S.A., Edison, NJ) using Method S2510 of the CNAL (McClenahan and Ferguson, 1989). Carbonate content in the bulk soil and clay fraction was determined by the pressure-calcimeter method (Nelson, 1982).
Total N, SOC, and 
13C were determined by dry-combustion–mass spectrometry using a Robo-prep-Tracemass system (Europa Scientific, Cheshire, UK). Samples that reacted to 10% HCl were treated with 4 M HCl for carbonate removal before analysis.
All statistical calculations in this study were performed using the Minitab statistical software program (State College, PA) (Ryan and Joiner, 1994).
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Results and discussion
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All sampled soils were developed on deep loess deposits and were classified as fine-silty, mixed, frigid Pachic Hapludolls (Soil Survey Staff, 1998). Selected physical and chemical characteristics of the typical soil profiles sampled at each field are shown in Tables 2 and 3
, respectively. Interpretation of these data demonstrates the similarity between studied soils, except when comparing SOC and total N contents.
Soil organic C and total N contents were measured in earlier studies for the continuous-fallow field (Ponomareva and Nikolaeva, 1965). Figure 2
incorporates these earlier results and indicates that there may be some changes in SOC and total N with time and depth. Unfortunately, no definitive conclusions can be drawn because of the lack of data on variability of these measurements. Although earlier measurements of SOC were conducted by Tyurin's method (Bel'chikova, 1954), they seem to be comparable to measurements obtained by today's more commonly used dry-combustion techniques (Sorokina and Kogut, 1997). Tyurin's method tends to underestimate SOC concentration compared with dry-combustion methods, and a factor of 1.13 is used to convert the Tyurin's measurement to the dry-combustion equivalent in the Kursk chernozems (Kogut, 1993, p. 63).
Dominant plant species in the native grassland are C3 type, as indicated by 13C values of -25
(Table 4)
. C3–type plants have 13C values of about -27, compared with the standard (Raven et al., 1986, p. 111).
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Table 4 Comparison of soil organic C and N contents between native grassland field, yearly cut hay field, continuously cropped field, and 50-yr continuous-fallow field
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Table 5
presents a statistical comparison of values for SOC and total N concentrations among the sites sampled in this study. Soil organic C and total N contents are not significantly different between the native grassland and the yearly cut hay field. The most dramatic decreases in SOC and total N occurred after 50 yr of continuous fallow, with losses occurring down to the 120- to 130-cm depth (Table 4). Highest reductions of SOC and total N concentrations were observed in the top 10 cm of soil, ranging from a 38 to 43% loss of SOC and from a 45 to 53% loss of total N. There are significant changes in soil organic C and total N in the cropped field down to the 70- to 80-cm depth. This implies that there is insufficient input from plant material to compensate for the lost SOC.
Evaluation of management-induced changes in SOC and total N contents are influenced by the method used to calculate such changes. Several authors documented the importance of comparing SOC and total N on volume basis (Tiessen et al., 1982; Ellert and Bettany, 1995; Doran and Parkin, 1996). Table 6
presents calculations of SOC and total N contents and losses based on the equivalent soil mass approach described by Ellert and Bettany (1995). This approach was adapted to include the soil below the surface horizons and a statistical comparison of volume-based estimates per equivalent soil mass, which takes into account variability in soil bulk density, SOC, and total N measurements.
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Table 6 Contents and losses of soil organic C (SOC) and total N based on equivalent soil mass in native grassland field, yearly cut hay field, continuously cropped field, and 50-yr continuous-fallow field within 130 cm of soil
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Soil bulk density measurements for the top 0 to 50 cm were obtained in the summer of 1997. Bulk density was significantly greater in the 50-yr continuous-fallow field, yearly cut hay field, and continuously cropped field than in the native grassland field down to a depth of 33 cm (Table 5). This increase can be explained by the duration and intensity of cultivation. It was not possible to obtain bulk density values below 50 cm because no excavation of soil profiles is permitted within the V.V. Alekhin State Biosphere Reserve.
Average values for bulk density measurements in the native grassland and the continuous-fallow field below the 50-cm depth were provided by Afanasyeva (1966), but corresponding standard deviations were not reported by the author. On the basis of Table 5, it was concluded that bulk density measurements below the 50-cm depth were not significantly different between the native grassland field, yearly cut hay field, continuously cropped field, and 50-yr continuous-fallow field, and it was assumed that bulk density did not change since 1966.
To obtain the estimate of variability in bulk density data below 50 cm, it was assumed that two sets of data (native grassland and continuous-fallow fields) constitute replicate observations at each depth level, which are normally distributed and independent. Based on these assumptions, a standard deviation of 0.04 was obtained and used for bulk densities below 50 cm. Standard deviations for area-based estimates per equivalent soil mass were calculated by the method of statistical differentials (Kendall and Stuart, 1969, p. 231; Kotz et al., 1988, p. 646–647). Area-based estimates per equivalent soil mass were compared between treatments using the Tukey method of multiple comparisons (Neter et al., 1990, p. 581).
Results reported in Table 6 support the finding that management-induced changes in SOC and total N can extend beyond the plow layer. These results are not as dramatic as when reported on the concentration basis (Table 4) because of considerable variation in soil bulk density measurements. Calculations made on the equivalent soil mass may be more valid and ecologically relevant (Doran and Parkin, 1996) because they take into account changes in soil mass that are reflected by increased bulk density values. As with concentration data, there is no loss in SOC and total N in the yearly cut hay field, compared with the native grassland field. Significant losses in SOC and total N extend to 60 cm in the continuously cropped field and to a 100-cm depth in the 50-yr continuous-fallow field. Changes in SOC and total N at depth may be explained by decaying roots of native grassland species, which can extend to a depth of 200 cm in the native grassland; the amount of roots (Gertsyk, 1959; Afanasyeva, 1966); leaching of organic compounds (Kokovina, 1967); faunalpedoturbation, as defined by Fanning and Fanning (1989)(p. 54); and warmer soil temperatures as a result of continuous fallow.
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Conclusions
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This study found a significant decline in soil organic matter beyond the plow depth with long-term continuous cultivation with and without cropping. Comparison of SOC and total N losses on a concentration and area basis yielded similar results, but the depth of changes was less distinct in the area-based comparison because of considerable variability in bulk density measurements. Results showed that it is important to sample the entire soil profile to assess the total losses of SOC and total N. Measurement of cultivation effects on the SOC and total N only in the plowed horizons significantly underestimates the total losses in SOC and total N from the soil profile.
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ACKNOWLEDGMENTS
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We wish to acknowledge the many people and organizations in Russia who have contributed to this study. We would like to thank the V.V. Alekhin Central-Chernozem Biosphere State Reserve, especially N.A. Maleshin, N.I. Zolotuhin, and O.S. Boiko; and the Russian Institute of Agronomy and Soil Erosion Control in Kursk, and its director, V.M. Volodin. The authors greatly appreciate field assistance by E.K. Daineko, Kathy Bryant, and Aleksei Ivanov. This research was supported by the Mario Einaudi Center for International Studies; the Cornell University Agricultural Experiment Station; the Cornell University Biogeochemistry Minigrant Program; and the Cornell University Department of Soil, Crop, and Atmospheric Sciences. The authors are grateful to Dr. J.M. Duxbury and Dr. J.M. Galbraith for their technical advice and comments.
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NOTES
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Contribution from the Dep. of Soil, Crop, and Atmospheric Sci., Cornell Univ., Ithaca, NY 14853.
Received for publication February 19, 1999.
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TOP
ABSTRACT
INTRODUCTION
