CARBON AND NITROGEN CYCLING IN CONSERVATION TILLAGE
SYSTEMS
Charles W. Rice
Professor of Soil Microbiology
Department of Agronomy
Kansas State University
Manhattan, KS 66506-5501
During the last 30 years there has been a conversion from moldboard plowing to
conservation tillage systems. Plant residues left on the soil surface protect the
soil from soil erosion. No-tillage is one practice of conservation tillage that
minimizes soil disturbance and leaves all the residues on the soil surface.
Conservation tillage systems also conserve soil water (Phillips et al., 1980;
Unger and McCalla, 1980; Schertz, 1988). As a result of improved water
resources, crop yields often increase with a reduction in tillage intensity (Blevins
et al., 1984; Dick and Van Doren, 1985; Dick et al., 1991).
However, reduction in tillage soil C and N, microbial activity and nutrient
dynamics are altered (Carter and Rennie, 1982; Follett and Peterson, 1988;
Carter, 1991; Salinas-Garcia et al., 1997). The change in C and N is partly
attributed to a change in the microbial environment. Maintaining residues on the
surface modifies the soil environment for the soil microorganisms (Doran, 1980).
Physical Environment
To understand how various tillage systems affect C and N dynamics it is
necessary to consider the changes in the physical properties of the soil. These
changes are summarized in Table 1. Thermal insulation by surface mulch
reduces the fluctuations in temperatures at the soil surface. The mulch
decreases the maxim soil temperature. In cooler climates this reduction in soil
temperature may slow microbial activity, but in tropical environments a reduction
in temperatures may be beneficial to soil organisms. Conservation tillage,
particularly no-tillage, usually results in greater soil water contents as a result of
reduce evaporation and increased infiltration (Phillips et al., 1980). Under
drought conditions, higher soil water is beneficial to crops and microorganisms.
However under wet conditions, the soil may become prone to anaerobic
conditions, which may slow decomposition and increase N loss. Another
physical property affected by tillage systems is bulk density. Higher bulk
densities commonly observed in conservation tillage systems affect water
infiltration and aeration. The change in soil aeration will alter microbial activity.
Organic Carbon
Reducing tillage intensity can slow or prevent the loss of organic C in the soil
(Dick, 1983; Havlin et al., 1990; Kern and Johnson, 1993). In continuous notillage systems, plant residues from the previous crops accumulate on the soil
surface. The lack of tillage results in redistribution and greater accumulation in
no-tillage soils. For soils previously cultivated, soil organic matter levels increase
when converted to no-tillage (Gilliam and Hoyt, 1987). Soils originating from
grass generally show a slower decline in soil organic matter with no-tillage
compared with tilled soils (Blevins et al., 1983; Bauer and Black, 1981; Rice et
al., 1986). Research in Kansas has shown no-tillage can increase soil organic
matter by xx % (Havlin et al., 1990). After 5 y, no-till maize resulted in 15%
increase in soil organic C in the surface 5 cm with no differences below 5 cm
(Fig. 1). (Espinoza et al., 1998). After 34y of crop rotation and tillage, Dick and
Durkalski (1997) measured soil organic C and N in the upper 60 cm of the soil
profile was significant between systems (Fig. 2). There was a significant
interaction between tillage and rotation both for C (P>0.06) and N (P> 0.03).
These results are consistent with other studies (Blevins et al., 1977; Havlin et al.,
1990; Franzluebbers et al., 1995).
Conservation management systems, such as no-tillage, also increase the size of
the active fractions of soil organic matter (Rice et al., 1986; Franzluebbers et al.,
1995; Salinas-Garcia, 1997). After 5 y of tillage treatments we have not detected
increases on the active fraction of soil organic C (Espinoza et al., 1998).
However the microbial biomass had increased by 25 % with no-till compared with
chisel/disk.
Organic Nitrogen
As with organic C, organic N in the soil increases with a reduction in tillage
intensity (REF). In our 5 y study with tillage and N source, no-tillage resulted in a
significant (P>0.05) increase in soil organic N in the surface 5 cm compared with
chisel/disk (Espinoza, 1997) (Fig. 3). There were no significant differences below
5 cm between tillage systems. Microbial biomass N was 30% greater (P>0.05)
under no-till compared with chisel/disk.
Microbial Transformations of Nitrogen
Immobilization
The build up of organic of organic C and N in conservation tillage systems can
impact plant N availability. The redistribution of plant residues in no-tillage
results in higher C:N ratio of organic matter at the surface. Surface applied N
fertilizers may show significant N immobilization (Table 2) (Rice and Smith,
1984). For maize with a rye cover crop, immobilization may be as much as 41%
compared with 11% for tilled soils Rice and Smith, 1984).
In fact N
immobilization may be a greater significance than N lost be denitrification and
leaching in determining N availability.
Mineralization
The increase of soil organic N in conservation tillage systems my lead to an
improved N supplying capacity of the soil. In one study, after 10 y, increase
organic N in no-tillage resulted in that N mineralization was greater than with full
tillage (Fig. 4) (Rice et al., 1986). Nitrogen mineralization is dependent on soil
water and drainage of the soil. Rice et al. (1987) reported greater mineralization
from no-tillage in well-drained soils. As drainage decreased plowing the soil
increase N mineralization relative to no-tillage (Table 3).
Added organic N as cover crops or manure can increase the amount of N
mineralized. Several studies have shown the value of cover crops, particularly
legumes, for supplying N to a subsequent grain crop (Ebelhar et al., 1984; Varco
et al., 1993). Manure also can be a source of N. Manure in combination with notillage resulted in a significant increase in potential and actual N mineralization
(Table 4).
Denitrification
Denitrification has been extensively studies in conservation tillage systems. The
higher soil water contents in no-tillage soils provide conditions conducive for
denitrification. Numbers of denitrifiers and its potential activity are greater in notill soils compared with tilled soil (Doran, 1980, Rice and Smith, 1982, Madison et
al., 1994, Kocyigit, 1998). (Fig. 5). However, in semi-arid environments, actual
losses of N due to conservation tillage are likely to be minimal (Madison et al.,
1994).
In summary, conservation tillage systems result in increased levels of soil organic
C and N. This improves the quality of the soil by positive impacts on soil
physical, chemical and biological properties. Reduction in tillage intensity can
increased sequestration of atmospheric CO2. However increased soil C the
associated microbial activity can change N availability. However with proper N
management, crop N availability can be maintained and even increased as the
productive capacity of the soil improves.
References
Bauer, A., and A.L. Black. 1981. Soil carbon, nitrogen and bulk density
comparisons in two cropland tillage systems after 25 years and in virgin
grassland. Soil Sci. Soc. Am. J. 45:1166-1170.
Blevins, R.L., G.W. Thomas, and P.L Cornelius. 1977. Influence of no-tillage
and nitrogen fertilization on certain soil properties after five years of continuous
corn. Agron. J. 69:383-386.
Blevins, R.L., G.W. Thomas, M.S. Smith, W.W. Frye, P.L. Cornelius. 1983.
Changes in soil properties after ten years continuous non-tilled and
conventionally tilled corn. Soil Tillage Res. 3:135-146.
Blevins, R.L. 1984. Soil adaptability for no-tillage. P. 42-65. In S.H. Phillips
and R.E. Phillips (eds) No-tillage agriculture: Principles and practices. Van
Nostrand Reinhold, New York, NY.
Carter, M.R. 1991. the influence of tillage on the proportion of organic carbon
and nitrogen in the microbial biomass of medium textured soil in a humid climate.
Biol. Fert. Soils 11:135-139.
Carter, M.R., and D.A. Rennie. 1982. Changes in soil quality under zero tillage
farming systems: Distribution of microbial biomass and mineralizable C and N
potentials. Can. J. Soil Sci. 62:587-597.
Dick, W.A., and D.M Van Doren, Jr. 1985. Continuous tillage and rotation
combination effects of corn, soybean and oat yields. Agron. J. 77:459-465.
Dick, W.A., E.L. McCoy, S.M. Edwards, and R. Lal.
application of no-tillage to Ohio soils. Agron. J. 77:65-73.
1991.
Continuous
Dick, W.A., and J.T. Durkalski. 1997. No-tillage production agriculture and
carbon sequestration in a typic fraguidalf soil of northeastern Ohio. p. 59-71. In
R. Lal (eds) Advances in Soil Sciences: Management of Carbon Sequestration in
Soil. Boca Raton, FL.
Doran, J.W. 1980. Soil microbial and biochemical changes associated with
reduced tillage. Soil Sci. Soc. Am. J. 44:765-771.
Ebelhar, S.A., W.W. Frye, and R.L. Blevins. 1984. Nitrogen from legume cover
crops for no-tillage corn. Agron. J. 76:51-55.
Espinoza, Y. 1997. Availability of nitrogen to corn after five years of manure
and fertilizer application under tillage and no-tillage systems. Kansas State
University, Manhattan.
Espinoza, Y., C.W. Rice, and R.E. Lamond. 1998. Effects of nitrogen source
and tillage on soil organic matter. p. 105-106. In R.E. Lamond (ed) Kansas
Fertilizer Research, 1997. Rept. Of Progress No. 800. Kansas Ag. Exp. Stn.,
Manhattan, KS.
Follett, R.F., and G.A. Peterson. 1988. Surface nutrient distribution as affected
by wheat-fallow tillage system. Soil Sci. Soc. Am. J. 52:141-147.
Franzluebbers, A.J., F.M. Hons, and D.A. Zuberer. 1995. Soil organic carbon,
microbial biomass, and mineralizable carbon and nitrogen in sorghum. Soil Sci.
Soc. Am. J. 59:460-466.
Gilliam, J.W. and G.D. Hoyt. 1987. Effect of conservation tillage on fate and
transport of nitrogen. p. 217-240. In T.J. logan et al. 9eds) Effects on
conservation tillage on groundwater quality: Nitrates and pesticides. Lewis
Publ., Inc., Chelsea, MI.
Havlin, J.L., D.E. Kissel, L.D. Maddux, M.M. Claassen, and J.H. Long. 1990.
Crop rotation and tilaage effects on soil organic carbon and nitrogen
management. Soil Biol. Biochem. 28:733-738.
Kern, J.S. and M.G. Johnson, 1993. Conservation tillage impact on national soil
and atmospheric carbon levels. Soil Sci. Soc. Am. J. 57:200-210.
Kocyigit, Rasim. 1998. Response of denitrifiers to tillage systems and nitrogen
sources.
MS Thesis. Kansas State Univ., Manhattan.
Madison, C.E., C.W. Rice, J.G. Harris, and R.E. Lamond. 1995. Nitrogen source
and tillage effects on corn grain yield, soil nitrogen and denitrification. P. 97-99
In R.E. Lamond (ed) Kansas Fertilizer Research, 1994. Rept. Of Progress No.
719. Kansas Ag. Exp. Stn., Manhattan, KS.
Phillips, R.E., R.L. Blevins, G.W. Thomas, W.W. Frye, and S.H. Phillips. 1980.
No-tillage agriculture. Sci. 208:1108-1113.
Rice, C.W., and M.S. Smith. 1982. Denitrification in no-till and plowed soils.
Soil Sci. Soc. Am. 46:1168-1173.
Rice, C.W., and M.S. Smith. 1984. Short-term immobilization of fertilizer
nitrogen at the surface of no-till and plowed soils. Soil Sci. Soc. Am. J. 48:295297.
Rice, C.W., M.S. Smith, and R.L. Blevins. 1986. Soil nitrogen availability after
long-term continuous no-tillage and conventional tillage corn production. Soil
Sci. Soc. Am. J. 50:1206-1210.
Rice, C. W., J. H. Grove, and M. S. Smith. 1987. Estimating soil net nitrogen
mineralization as affected by tillage and soil drainage due to topographic
position. Can. J. Soil Sci. 67:513-520.
Salinas-Garcia, J.R., F.M. Hons, and J.E. Motocha. 1997. Long-term effects of
tillage and fertilization on soil organic matter dynamics. Soil Sci. Soc. Am. J.
61:152-159.
Schertz, D.L. 1988. Conservation tillage: An analysis of acreage projections in
the United States. J. Soil Water Conserv. 43:256-259.
Unger, P.W., and T.M. McCalla. 1980. Conservation tillage system. Adv. Agron.
33:1-58.
Varco, J.J., W.W. Frye, M.S. Smith, and C.T. MacKown. 1993. Tillage effects on
legume decomposition and transformation of legume and fertilizer nitrogen-15.
Soil Sci. Soc. Am. J. 57:750-756.