Increase In Soil Organic C Research Articles

Long-term management impacts on soil carbon and nitrogen dynamics of grazed bermudagrass pastures

Managed pastures have potential for C and N sequestration in addition to providing forage for livestock. Our objectives were to investigate changes in soil organic C (SOC) and soil organic N (SON) concentrations and mineralizable C and N in cattle (Bos indicus) grazed bermudagrass [Cynodon dactylon (L.) Pers.] pastures up to 32 y after establishment. Management included low- and high-grazing intensity, fertilization, and winter overseeding with annual ryegrass (Lolium multiflorum Lam.) and clover (Trifolium sp.). Soil (0–15cm) was sampled 7, 15, 26, and 32 y after establishment of Coastal and common bermudagrass pastures. No significant differences in SOC or SON concentrations were observed between Coastal and common bermudagrass pastures. Grazing strategies played important roles in C and N sequestration, as high-grazing intensity resulted in a lower increase in SOC and SON concentrations over time compared to low-grazing intensity. Increases in SOC were observed up to 26 y, while increases in SON were observed up to 32 y after establishment of bermudagrass pastures. Soil organic C increased 67 and 39% from 7 to 26 y at low-grazing intensity for bermudagrass+ryegrass and bermudagrass+clover pastures, respectively. SOC and SON concentrations did not increase beyond 15 y after bermudagrass establishment at high-grazing intensity. An exception was the Coastal bermudagrass+ryegrass pastures, which exhibited higher SON at 32 y than at 7 y at both grazing intensities. By 32 y, SON increased 83 and 45% in Coastal bermudagrass+ryegrass pastures at low- and high-grazing intensity, respectively, compared to 7 y. The introduction of clover to pastures decreased SOC and SON relative to ryegrass at high- but not at low-grazing intensity. Potentially mineralizable C increased from 7 to 15 y, while mineralizable N increased from 7 to 32 y. Potentially mineralizable N was also greater for bermudagrass+clover than bermudagrass+ryegrass pastures. Long-term increases in SOC and SON concentrations suggest that managed and grazed pastures have strong potential for C and N sequestration.

Physical and Hydrological Characteristics of Reclaimed Minesoils in Southeastern Ohio

Reclamation of disturbed soils is done with the primary objective of restoring the land. Therefore, measurement of physical and chemical properties of reclaimed minesoils (RMS) is essential for understanding the process of soil restoration. This study was designed to assess soil quality of two reclaimed sites and two nearby undisturbed sites in Jackson and Vinton counties, Ohio. Three different rates of fertilizers applied annually to the RMS at Jackson and Vinton County sites from 1979–1994 were: no fertilizer (FL1), 112‐25‐46 kg NPK ha−1 (FL2), and 224‐50‐92 kg NPK ha−1 (FL3). Bulk and core samples were obtained for only 0‐ to 10‐cm depth for undisturbed (unmined) soil (UMS) and for 0 to 10 and 10 to 20 cm for RMS. A comparison within UMS and RMS showed that water‐stable aggregation and mean weight diameter of aggregates (MWDs) were significantly higher for UMS than RMS for both sites (P < 0.05). Apart from soil bulk density (ρb) for Vinton, no significant differences were observed in ρb, electrical conductivity (EC), pH, saturated hydraulic conductivity and water infiltration for the 0‐ to 10‐cm depth among fertility treatments in RMS and UMS for both Jackson and Vinton County sites. Average soil organic C (SOC) 5 yr after reclamation in 1981 was 14.2 Mg ha−1 for Jackson and 15.1 Mg ha−1 for Vinton site for the 0‐ to 10‐cm depth. In 2001, average SOC was 28.7 Mg ha−1 for Jackson and 30.24 Mg ha−1 for Vinton site. A two‐fold increase in SOC was obtained at both sites between 1981 and 2001. Soil pH was >6.4 and was favorable for root development and biomass production at both reclaimed sites. No significant differences in several soil properties between UMS and RMS showed that fertility treatments improved the soil quality of RMS.

Long-term effects of fertilization on soil organic carbon changes in continuous corn of northeast China: RothC model simulations.

Soil organic C (SOC) content can increase by managing land use practices in which the rates of organic C input exceed those of organic C mineralization. Understanding the changes in SOC content of Black soils (mainly Typic Halpudoll) in northeast China is necessary for sustainable using of soil resources there. We used the RothC model to estimate SOC levels of Black soils under monoculture cropping corn in a long-term fertilization trial at Gongzhuling, Jilin Province, China. The model outputs for the changes in SOC were compared with measured data in this long-term fertilization/manure trial. The sound performance of model in simulating SOC changes suggests that RothC is feasible with Black soils in the temperate climatic region of northeast China. The modeled and measured results indicated that the treatment without fertilizer/farmyard manure (FYM) addition led to a continuous decline in SOC during the study period and N and NPK fertilization were inadequate to maintain the SOC levels in the plow layer (upper 20 cm) unless FYM was added under the current conventional management associated with no above-ground crop residues returning into the soil. Soil organic carbon could follow the same path of decline if the same management practices are maintained. Model results indicate that returning above-ground crop residues to the soil from 2002 to 2022 would increase SOC by 26% for the treatment without fertilization addition, 40% for N treatment, 45% for NPK treatment, and 38% and 46% for N and NPK treatments with FYM addition, compared to the levels in the corresponding treatments in 2002. The simulation results suggest that the RothC model is a feasible tool to assess SOC trend under different management practices, and returning above-ground crop residues into the soil would lead to a remarkable increase in SOC of Black soils in the region.

Evaluation of a simple model to describe carbon accumulation in a Brown Chernozem under varying fallow frequency

Soil organic C (SOC) is readily influenced by crop management practices, such as summerfallowing. On the Canadian prairies, the area summerfallowed has decreased significantly in recent years. Our objectives were to determine the influence of fallow frequency on the rate of change in SOC in an Orthic Brown Chernozem, and to test the effectiveness of an empirical equation developed in an earlier study for estimating SOC changes in these rotations over 33-yr period. The rotations, which were initiated in 1967, all received adequate N and P fertilizers. They were (i) fallow-spring wheat (Triticum aestivum L.) (F-W), F-W-W, F-W-W-W-W-W and W-lentil (Lens culinaris L.) (W-Lent). Soil organic C was measured in the 0- to 15-cm and 15- to 30-cm depths in 1976, 1981, 1984, 1990, 1993, 1996 and 1999. No measurements of SOC were made in 1967; we estimated SOC starting values to be 30.5 Mg ha–1 in the 0- to 15-cm depth. In the period 1967 to 1990, when growing season precipitation was near normal for this semiarid region, SOC in the four rotations approached a steady state. However, a decade of much more favourable growing season precipitation in the 1990s increased C inputs, which resulted in a marked increase in SOC in the treatments. The empirical equation suggests, and the F-W and W-Lent rotations appear to confirm, that these rotations are approaching a new steady state at a higher level of SOC, reflecting the decade of favourable precipitation. Measured SOC levels were quite variable, emphasizing the difficulty of relying on measurements made over short time frames (e.g., 5-6 yr) when quantifying SOC changes. The equation effectively simulated the trends in SOC changes in all rotations, but consistently underestimated SOC levels in the W-Lent rotation by about 2 Mg ha–1. Estimates of difference in SOC between treatments were generally similar whether expressed on a mass/fixed depth or a mass/equivalent depth basis. Based on the estimates derived by the empirical equation, we estimated rates of SOC sequestration during the 1967-1990 period to be 0.03 Mg ha–1 yr–1 for F-W, 0.10 Mg ha–1 yr–1 for F-W-W, and 0.15 Mg ha–1 yr–1 for W-Lent. If we include the decade of more favourable precipitation (1967-1999), the rates were between 0.05 Mg ha–1 yr–1 for F-W and 0.20 Mg ha–1 yr–1 for W-Lent. These values are much higher than those estimated by others using the CENTURY model. We concluded that (i) simple models, such as that used in this study, are very useful for estimating management effects on SOC changes, and (ii) we must be cautious in extrapolating C sequestration estimates based on data from short-term experiments because future weather conditions are not easily predicted and weather can have an important impact on C sequestration. Key words: C sequestration, cropping frequency, crop rotations, wheat, lentil, flax, oats

Quantifying short-term effects of crop rotations on soil organic carbon in southwestern Saskatchewan

Crop management practices can have a major influence on soil fertility and soil organic C (SOC) sequestration. We need to accurately measure and estimate changes in SOC in the short term (<20 yr). A 10-yr crop rotation experiment, conducted on a medium-textured Orthic Brown Chernozem at Swift Current, in southwestern Saskatchewan, was sampled in 1990 (3 yr after initiation of the study) and in 1993 and 1996, to measure SOC changes under nine crop rotation treatments. Minimum tillage practices were used. The stubble was cut high to enhance snow trap and N and P fertilizer applied based on soil tests. Grain and straw yields of the cereals, and hay yields of the crested wheatgrass (CWG) [Agropyron cristatum (L.) Gaeertn.] were measured annually. An empirical equation which uses two simultaneous first order kinetic expressions, one to estimate crop residue decomposition and the other to estimate soil humus C mineralization was used, together with crop residue (straw and estimated root) C inputs, to estimate SOC changes over the 1987 to 1996 period. The estimated SOC values for the 1990 to 1996 period were generally similar to the measured values (r2 = 0.64, P < 0.0001). Significant (P < 0.10) changes in SOC were not observed below 15 cm depth, perhaps because shallow tillage (10- to 12.5-cm depth) is practiced. A change from cropland to CWG did not increase SOC, and this treatment, chemical fallow-winter wheat (Triticum aestivum L.)-spring wheat (F-WW-W), and F-high-yielding (Hy) Canada Prairie Spring (CPS) wheat-Hy (F-Hy-Hy) rotations, had the lowest SOC gains among the rotations. The CPS wheat had a higher harvest index (0.46) than hard red spring (HRS) wheat (0.39), but it increased SOC less than the comparable HRS wheat rotation between 1990 and 1996 indicating that higher grain yields do not always equate to higher SOC. Weather conditions were favourable for cereals from 1990 to 1996 and we measured significant increases in SOC (up to 5.5 Mg ha−1 in 6 yr). This is encouraging for producers who may be contemplating participating in "C trading", although this also suggests that periods of less favourable weather will limit gains in SOC. Summerfallowing once in 4 yr in this semiarid environment did not reduce SOC gains compared to continuous wheat (Cont W). For example, a F-W-W-W rotation gained 4.88 Mg C ha−1 in 6 yr while continuous wheat gained 5 Mg ha−1. Growing Indianhead lentil (Lens culinaris Medikus) as a legume green manure crop (GM) with wheat in a GM-W-W rotation did not increase SOC more than F-W-W. The efficiencies of conversion of residue C to SOC were high, ranging between 9% for frequently fallowed systems to 29% for continuously cropped systems, likely due to the favourable weather conditions experienced. Key words: Carbon sequestration, legume green manure, crested wheatgrass, harvest index effect, C conversion efficiencies

Nitrogen Fertilization Effects on Soil Carbon and Nitrogen in a Dryland Cropping System

No‐till (NT) increases the potential to crop more frequently in the Great Plains than with the conventional‐till (CT) crop–fallow farming system. More frequent cropping requires N input to maintain economical yields. We evaluated the effects of N fertilization on crop residue production and its subsequent effects on soil organic C (SOC) and total soil N (TSN) in a dryland NT annual cropping system. Six N rates (0, 22, 45, 67, 90, and 134 kg N ha−1) were applied to the same plots from 1984 through 1994, except 1988 when rates were reduced 50%, on a Weld silt loam (fine, smectitic, mesic Aridic Argiustoll). Spring barley (Hordeum vulgare L.), corn (Zea mays L.), winter wheat (Triticum aestivum L.), and oat (Avena sativa L.)–pea (Lathyrus tingitanus L.) hay were grown in rotation. Crop residue production varied with crop and year. Estimated average annual aboveground residue returned to the soil (excluding hay years) was 2925, 3845, 4354, 4365, 4371, and 4615 kg ha−1, while estimated annual contributions to belowground (root) residue C were 1060, 1397, 1729, 1992, 1952, and 2031 kg C ha−1 for the above N rates, respectively. The increased amount of crop residue returned to the soil with increasing N rate resulted in increased SOC and TSN levels in the 0‐ to 7.5‐cm soil depth after 11 crops. The fraction of applied N fertilizer in the crop residue decreased with increasing N rate. Soil bulk density (Db) in the 0‐ to 7.5‐cm soil depth decreased as SOC increased. The increase in SOC with N fertilization contributes to improved soil quality and productivity, and increased efficiency of C sequestration into the soil. Carbon sequestration can be enhanced by increasing crop residue production through adequate N fertility.

Soil Organic Matter Pools during Early Adoption of Conservation Tillage in Northwestern Canada

AbstractChanges in soil organic matter (SOM) pools during adoption of reduced (RT) or zero tillage (ZT) can influence soil physical properties, nutrient cycling, and CO2 flux between soil and atmosphere. We determined soil organic C (SOC), soil microbial biomass C (SMBC), basal soil respiration (BSR), and mineralizable N to a depth of 200 mm at the end of 3, 5, and 6 yr after implementation of tillage management on a Falher clay (fine, montmorillonitic, frigid Typic Natriboralf) near Rycroft, Alberta, in a canola (Brassica campestris L.)‐wheat (Triticum Aestivum L.)‐barley (Hordeum vulgare L.)‐fallow cropping system. At the end of 6 yr, SOC was not different among tillage regimes and averaged 8.6 kg m−2. At the end of 3 and 5 yr, SMBC was not significantly different among tillage regimes, but at the end of 6 yr SMBC was 7% greater in RT and 9% greater in ZT than in conventional tillage (CT). Basal soil respiration and mineralizable N at the end of 6 yr were not different among tillage regimes following barley and averaged 2.7 g CO2‐C m−2 d−1 and 5.0 g inorganic N m−2 24 d−1, respectively. However, BSR following fallow was 2.2, 2.5, and 2.6 g CO2‐C m−2 d−1 in CT, RT, and ZT, respectively. Mineralizable N following fallow was 5.8 g inorganic N m−2 (24 d)−1 in RT and ZT and 7.3 g inorganic N m−2 (24 d)−1 in CT. At 0 to 50 mm, there was no significant increase in SOC at the end of 6 yr, a 17 to 36% increase in SMBC, and a 12 to 69% increase in BSR with ZT compared with CT, depending on rotation phase. Relatively small changes in SOM pools with adoption of conservation tillage may be attributable to the large amount of SOM initially present and the cold, semiarid climate that limits SOM turnover.