Soil carbon fluxes and balances and soil properties of organically amended no-till corn production systems

Geoderma 197–198 (2013) 177–185

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Soil carbon fluxes and balances and soil properties of organically amended no-till corn production systems Raj K. Shrestha ⁎, Rattan Lal, Basant Rimal Carbon Management and Sequestration Center, School of Environment and Natural Resources, The Ohio State University, Columbus, OH 43210, USA

a r t i c l e

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Article history: Received 28 March 2011 Received in revised form 18 December 2012 Accepted 15 January 2013 Available online 28 February 2013 Keywords: Soil amendments Soil quality Compost Greenhouse gas emission Manure

a b s t r a c t The addition of organic amendments is essential for sustainable soil fertility management and crop production, but can also increase greenhouse gas (GHG) emissions. Thus, understanding the impacts of organic soil amendments on gaseous emissions is pertinent to minimizing agricultural impacts on the net emissions of GHGs. A long-term field experiment was conducted to assess the impacts of continuous application of organic amendments (i.e. compost and farmyard manure) and cover crop [mixture of rye (Secale cereal), red fescue (Festuca rubra), and blue grass (Poa pratensis L.)] on selected soil properties, apparent carbon (C) budget (calculated from the difference of sum of all sources of C inputs and outputs), gaseous flux (i.e. carbon dioxide, CO2, and methane, CH4), and relationship with weather parameters under no-till (NT) corn (Zea mays L.) cultivation in an Alfisol of central Ohio, USA. Soil properties and gaseous fluxes were measured continuously for 2 years. Ten years of continuous application of soil amendments increased soil pH and electrical conductivity, enhanced soil C pool, and decreased bulk density especially in 0–5 cm depth than that with cover crop and control plots. Two years average, cattle manure, compost, fallow, and cover crop emitted 14.1, 10.2, 7.5, and 7.2 Mg CO2–C ha−1 yr−1, respectively. Methane emission was 10.7 kg CH4–C ha−1 yr−1 from cattle manure and 4.0 kg CH4–C ha−1 yr−1 from compost. However, fallow consumed 3.3 and cover crop 5.0 kg CH4–C ha−1 yr−1. These data suggest that long-term application of compost in NT corn decreased emissions of CO2 by 38% and of CH4 by 167% compared to application of manuring. In general, soil temperature, air temperature, and precipitation were positively correlated with CO2 emissions. Estimation of C budget indicated that amended soil under NT is a C-sink while a non-amended system is a C-source. The application of composted soil amendments in NT corn enhances soil quality and reduces net GHG emissions. Published by Elsevier B.V.

1. Introduction Soil management practices that increase carbon (C) sequestration include the application of organic amendments, conversion to conservation agriculture (CA), cover cropping, and residue retention. Organic amendments (i.e., compost, manure, cover crops) are a source of plant nutrients in addition to improving soil quality. Organic amendments improve soil quality by improving physical (increasing aggregate stability and reducing bulk density), chemical (increasing soil pH, electrical conductivity, and soil organic carbon — the main source of energy for soil microorganisms), and biological activity of soils (Diacono and Montemurro, 2011; Duong et al., 2012; Eghball et al, 2004). Improvement in soil quality increases crop yield in addition to playing a positive role in climate change mitigation by sequestering C. Accumulation of SOC in cropping systems occurs when C additions into soil (from crop residue and organic amendments) exceed C losses through decomposition, erosion, and leaching. However, depending on their composition and application methods, these amendments can also contribute to ⁎ Corresponding author. Tel.: +1 614 688 4937; fax: +1 614 292 7432. E-mail address: [email protected] (R.K. Shrestha). 0016-7061/$ – see front matter. Published by Elsevier B.V. http://dx.doi.org/10.1016/j.geoderma.2013.01.005

greenhouse gas (GHG) emissions (Abbas et al., 2012; Andraski et al., 2000; Ding et al., 2007; Heller et al., 2010; N'Dayegamiye and Angers, 1990). Agricultural emissions account for 13.5% of the total anthropogenic gaseous (i.e., CO2, CH4, and N2O) emissions (IPCC, 2007). USEPA (2010) estimated that U.S. agriculture contributes about 427.5 teragrams of CO2 equivalent (Tg CO2 Eq.) or 6% of total U.S. GHG emissions. Agricultural emissions of CO2 include microbial respiration in bulk soil and rhizosphere (Rochette et al., 1999), dissolution of carbonates in calcareous soils (Bertrand et al., 2007), burning of fossil fuels for agricultural purposes, and erosion induced emissions (Lal, 2003). Whereas CH4 is produced in agricultural soils mainly from manure management and rice (Oryza sativa L.) cultivation. The magnitude of GHG emission also depends on soil moisture and temperature regimes, soil type, land use, cropping pattern, and type and quantity of organic residues added (Chianese et al., 2009; Johnson et al., 2007; Shrestha et al., 2009). Animal manure provides readily available C for microbial activities, which can enhance CO2 emissions (Granli and Bockman, 1994; Rochette et al., 2004). The Rothamsted C turnover model indicated an increase in CO2 emissions with an increase in application rate of SOM in a highly weathered tropical soil in Hawaii (Abbas and Fares, 2009).

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In the U.S., CH4 emissions from manure management increased by 54% between 1990 and 2008, from 29.3 Tg CO2 Eq. to 45.0 Tg CO2 Eq. (USEPA, 2010). A majority of this increase was from swine and dairy cow manure. There is a growing trend of using liquid manures, which produce greater CH4 emissions. Considerable CH4 efflux occurs in soils where methanogenesis is accentuated by anaerobic conditions caused by heavy precipitation and periodic flooding (Yang and Chang, 2001). A study conducted in a silty clay loam soil in West Lafayette, IN under continuous corn (Zea mays L.) showed that liquid swine manure, injected at a rate of 255± 24 kg N ha−1 yr−1 in the spring or the fall, was the net CH4 emitter (Hernandez-Ramirez et al., 2009). In another study, application of 42–45 Mg ha−1 yr−1 of beef cattle feedlot manure and composted dairy manure in a corn–soybean (Glycine max L.) rotation with complete corn-stover removal increased SOC concentration (Thelen et al., 2010). The net global warming potential (GWP) for the manure and compost amended cropping systems was − 934 and −784 g m−2 yr−1 compared to 52 g m−2 yr−1 for the non-manure amended synthetic fertilizer control (Thelen et al., 2010). In a sandy loam soil in East Lansing, MI, application of compost (16.3 Mg C ha−1) and manure (21.6 Mg C ha−1) resulted in a net GWP of −1811 and −1060 g equivalent CO2 m−2 yr−1, respectively (Fronning et al., 2008). However, four years after termination of applying organic amendments in Nebraska, residual effects of manure and compost on CO2, N2O, and CH4 emissions were minimal (Ginting et al., 2003). Composting and the use of composted products indirectly reduce GHG emissions by reducing demand for and application of mineral fertilizers and pesticides (Favoino and Hogg, 2008). Reduction in agricultural emissions is possible by adopting recommended management practices (RMPs) through enhancing C sequestration, increasing CH4 consumption, and reducing N2O emissions. Data from most field studies are based on measurements of GHG emissions after years of using organic amendments in NT systems. Limited studies have reported GHG emissions following long-term continuous application of amendments under NT systems. Thus, this study is based on the hypothesis that the application of compost to NT corn production systems can increase SOC pool and also reduce the net C loss compared to manuring. The objectives of this study were to: (1) quantify the effects of long-term continuous application of cow manure and compost on CO2 and CH4 emissions, (2) compute annual soil C budget, and (3) identify determinants of CO2 and CH4 under NT corn production systems. 2. Material and methods 2.1. Site description and experimental detail A long-term field experiment was established in 1997 at the Waterman Farm of the Ohio State University, Columbus, Ohio (Elevation 241 m.a.s.l., latitude 40°01′N, and longitude 83°02′W). The dominant soil series at this site is Crosby silt loam (Soil Taxonomy: fine, mixed, mesic Aeric Ochraqualf), a somewhat poorly-drained soil developed from glacial till. Located in the humid continental zone, Columbus, Ohio is characterized by a temperate climate. The climate is warm during the summer, when the average maximum temperature is 22 °C, and cold during winter when the average minimum temperature is − 1 °C (Fig. 1A). The warmest month is July with an average maximum temperature of 29.5 °C, and the coldest is January with an average minimum temperature of − 6.5 °C. The annual average precipitation is 81 cm. Rainfall is fairly evenly distributed throughout the year. The driest month is February with 5.6 cm of rainfall, and the wettest is July with 11.7 cm of rainfall. There were four treatments: compost (mixture hardwood mulch, straw, and horse manure), manure (cow manure), cover crop (no amendments, grasses including 50% perennial rye, 30% annual rye, 10% red fescue and 10% blue grass), and fallow (no amendments, weedy fallow). Compost and manure were applied every year. Cover crops were permanent and no

fertilizer or soil amendments were applied. Weed growth in the weedy fallow plot was similar to cover crop. The experimental design was a randomized complete block (RCBD) with four replications. Plot size was 6.1 × 6.1 m. Compost was applied manually at the rate of 44 Mg ha −1 in early April. Cow manure was applied in December at the rate of 29 Mg ha−1 using a manure spreader (Kuhn Knight ProTwin Slinger). Carbon concentrations in manure and compost were 408 and 395 g kg−1, and nitrogen concentrations were 8.8 and 6.7 g kg−1 soil, respectively. No chemical fertilizers (N, P, K) were applied to the amended plots. Amended plots were planted to NT corn (variety Steyer 1104 RR). Corn was seeded during the last week of April to early May at the rate of 76,000 seeds ha−1 using a NT drill (model 900, CASE IH), and row to row spacing of 75 cm. Urea-N fertilizer was broadcasted manually in the fallow and the cover crop plots at the rate of 148 kg N ha−1 at the time of corn emergence in amended plots. Atrazine (2-chloro-4ethylamino-6-isopropylamino-s-triazine) was sprayed before planting corn at the rate of 4.68 l per ha. Glycophosate [N-(phosphonomethyl) glycine] was applied at the rate of 2.34 l per ha when corn plants were 20 cm high. A tractor-mounted sprayer (Huskee 200 gal) was used to apply pesticides. Corn was harvested in early October by using a 6-row grain harvester (International 1440 Combine). Residues (i.e., stover, cobs, and husks) were left in the field. 2.2. Soil sampling, processing, and analyses Soil and core samples were obtained from the plots at 0–5, 5–15, and 15–30 cm depths in December, 2006. Three soil samples, obtained from each plot, were bulked depth-wise, to make composite samples for each replication. The composite soil samples were air-dried under shade. Large clods were gently crushed, stones removed, and soil sieved through a 2-mm sieve. The sieved soil was used to measure pH in 1:1 soil/water extract using a thermo Scientific Orion StarTM Series Meter (Thermo Fisher Scientific Inc., Beverly, MA), and electrical conductivity in 1:5 soil/water extracts (Rhoades, 1996). Soil texture was determined by the hydrometer method (Gee and Or, 2002). About 10 g of a composite subsample (b 2 mm) was further ground using a ball mill and sieved through a 250-μm sieve for the determination of total C and N concentrations by the dry combustion method using a vario MAX CN analyzer (Elementar, Hanau, Germany). The carbonate test with 1 M HCl was negative. Therefore, total C was assumed to be equal to the SOC. Soil bulk density (ρb) was determined on intact soil cores from all three depths at the same location from where the composite samples were collected (Grossman and Reinsch, 2002). Cores with the dimension of 5.3 cm in diameter and 3 cm in length were used for 0 to 5 cm depth, and 5.3 cm in diameter and 6 cm in length for 5 to 15, and 15 to 30 cm depths. Core samples were collected from the middle of each depth increment to represent ρb for the depth, and soil moisture content was measured by drying at 105 °C for 48 h. Soil sample inside the core was recovered and passed through a 2-mm sieve to determine the gravel content. Soil ρb data was reported in Mg m−3 after making correction for the gravel content >2 mm (Page-Dumroese et al., 1999). Soil samples were collected again in December 2008 at 0–5, 5–15, and 15–30 cm depths and analyzed for C concentration to compute C budget. Carbon concentrations in the experimental site ranged from 31 to 53 mg g−1, clay content 167 to 219 g kg−1, and bulk density 0.82 to 1.26 Mg m −3 (Table 1). 2.3. Gas flux measurements and calculations The GHG fluxes were measured using the manual closed static chamber technique. The details about the size and shape of chambers and lids are discussed by Shrestha et al. (2009). Chambers, made of polyvinyl chloride (PVC), were installed one month before the flux measurement to avoid the effects of soil disturbances and potential

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Fig. 1. Daily (A) average air-temperature and precipitation, (B) carbon dioxide (CO2), and (C) methane (CH4) fluxes during March, 2007 to February, 2009. Vertical bars represent LSD (0.05) values for treatment comparison within given sampling date at P b 0.05.

changes in CO2 and CH4 fluxes. Chambers were inserted 10 cm into the ground, leaving 15 cm above ground. Two gas chambers were installed in each plot, giving a total of 6 replications (three replications× two chambers per replication). Fluxes of CO2 and CH4 were measured by collecting soil–air samples about bi-weekly from March 20, 2007 to February 26, 2009. Less frequent measurements were made during the dormant winter season. Chambers were left open in the field for the entire two year sampling period to mimic the natural environment, except during the farm operations. Chambers were kept free of any plants for the entire two year period, and therefore, CO2 fluxes represent soil respiration. A lid, also made of PVC material, was used to close the chamber at the time of soil–air sampling. Immediately after covering with the lid, soil–air samples were withdrawn from each chamber headspace with a 20 ml syringe and were labeled as zero-minute samples. Subsequent soil-air samples were collected 30- and 60-minutes after replacing the lid. They were then transferred to the crimp-sealed pre-evacuated (b 0.05 kPa) 10 ml vials. Soil–air samples were also collected from outside of the chamber, immediately after zero minute sampling from the chamber, to correct the impact of the chamber, if any. They were obtained between 11:00 and 15:00 h, when the diurnal temperature variation is minimal (Bajracharya et al., 2000; Benasher et al., 1994). The sequence of the gas sampling was randomized every time to avoid bias caused by changes in air temperature during the sampling period. Samples were analyzed for CO2 and CH4 concentration using a Shimadzu GC-14A gas chromatograph equipped with a thermal conductivity detector (TCD, at 100 °C for CO2 detection) and a flame ionization detector (FID, at 150 °C for CH4 detection). Helium was used as the

carrier gas at the flow rate of 20 mL min−1. The gas chromatograph was calibrated using standard gas obtained from Alltech (Deerfield, IL). Daily fluxes of CO2 (F, g CO2–C m − 2 d − 1) and CH4 (F, mg CH4–C m − 2 d − 1) were computed using the Eq. (1): F¼



 Δg V k Δt A

ð1Þ

where, Δg/Δt is the linear change in soil–air concentration inside the chamber (i.e. g CO2–C m−3 min−1 or mg CH4–C m−3 min−1), V is the chamber volume (m3), A is the surface area covered by the chamber (m2), and k is the time conversion factor (1440 min day−1). Changes in headspace gas concentration with time were tested for nonlinearity as suggested by Rochette and Eriksen-Hamel (2008) and Kroon et al. (2008). Cumulative soil fluxes were calculated by summing the averaged product of the two neighboring fluxes, multiplied by number of days of sampling interval. Annual fluxes were calculated by summing the weighted daily fluxes over a year. The negative fluxes of GHG indicate the uptake of a given gas by soil and positive fluxes indicate the net emissions from soil. 2.4. Collection of weather data and measurement of soil moisture and temperature Soil temperatures at 10 and 20 cm soil depths were monitored near each chamber simultaneously with gas sampling using a thermocouple Thermometer (YO-91210-45, Cole-Parmer ®). Gravimetric

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Table 1 Effects of cover crop, compost and manure on soil pH, electrical conductivity (EC), bulk density (BD), sand and silt content, Nov. 2006. Soil properties

pH

Treatment

Fallow Cover crop Compost Manure LSD 0.05 EC (μS cm−2) Fallow Cover crop Compost Manure LSD 0.05 −1 Carbon concentration (mg g ) Fallow Cover crop Compost Manure LSD (0.05) −1 Carbon pool (Mg ha ) Fallow Cover crop Compost Manure LSD (0.05) C/N Fallow Cover crop Compost Manure LSD (0.05) −3 BD (Mg m ) Fallow Cover crop Compost Manure LSD 0.05 −1 Sand (g kg ) Fallow Cover crop Compost Manure LSD 0.05 Clay (g kg−1) Fallow Cover crop Compost Manure LSD 0.05

Soil depth (cm)

LSD 0.05

0–5

5–15

15–30

6.4 5.6 6.9 6.8 0.6 89 57 185 166 54 28.9 35.1 53.0 46.9 5.9 18.0 21.0 22.2 24.5 3.8 11.3 11.6 13.4 10.9 0.5 1.26 1.21 0.82 1.05 0.21 418 430 462 457 132 197 219 167 217 80

6.3 5.7 6.2 6.4 0.9 64 33 55 70 50 24.6 26.7 28.7 29.4 5.5 34.0 35.5 39.5 40.6 7.4 11.5 11.1 11.4 10.9 0.9 1.40 1.34 1.40 1.40 0.08 426 376 409 437 166 212 253 231 257 107

6.6 0.4 6.1 0.4 6.5 0.6 6.4 0.4 0.7 53 34 33 13 40 66 49 14 36 22.1 2.9 24.8 5.4 23.6 11.4 24.8 5.6 6.5 46.3 7.8 48.3 12.1 50.5 12.2 51.4 14.4 11.7 11.8 1.7 11.0 0.6 11.0 0.9 11.0 2.8 1.7 1.41 0.13 1.35 0.12 1.48 0.19 1.42 0.16 0.08 397 114 426 29 416 101 403 24 29 253 15 259 18 239 43 247 65 110

years between initial and final soil C pool measurement. Carbon budget was calculated using the following Eq. (2). C budget ¼

X

Cinputs −

X

Coutputs :

ð2Þ

Amount of the amendment applied was estimated using a 0.5 m × 0.5 m metal frame. The samples were collected from three frames within each plot and weighed to determine the total fresh weight. Six random sub-samples were collected for moisture determination after drying them in an oven at 50 °C to a constant weight in order to compute the dry weight of the amendment applied. Dried compost and manure samples were ground and sieved through a 250-μm sieve for the determination of the C and N concentrations using a vario MAX C-N analyzer. Three random weed and cover crop biomass samples were also collected from each plot using a 0.5 × 0.5 m metal frame. These samples were dried in an oven at 50 °C to calculate the dry biomass weight of weeds and cover crops. The gaseous loss of C from different treatments was estimated by monitoring CO2 and CH4 fluxes throughout the two year period, as discussed earlier, and cumulative annual C loss as CO2 and CH4, assumed to be respiratory C loss was estimated. Corn residues were returned back to soil. Therefore, only corn grains were considered as an output. Ground grain samples were used for the determination of C concentrations using a vario MAX CN analyzer (Nelson and Sommers, 1973). 2.6. Statistical analysis The daily, annual, and cumulative CO2 and CH4 fluxes and soil moisture and temperature regimes for each sampling date were analyzed using the GLM procedure available in SAS 9.2 for Windows (2002–2008 by SAS Institute Inc., Cary, NC, USA.) to detect the effects of the amendment applications. Similarly, C balance and selected physical and chemical properties of soil were also analyzed using the PROC GLM test at 95% confidence level. Means were separated using the least square significance test. Soil temperature and moisture regimes in each treatment were correlated with CO2 and CH4 fluxes for each treatment. Precipitation and air-temperature were also correlated with CO2 and CH4 fluxes for each individual treatment. 3. Results and discussion

soil moisture content was also determined by collecting soil samples close to the chambers at 0–10 cm depth. Soil samples for moisture content and air and soil temperature measurements were made biweekly for two years in conjunction with soil–air sampling. The weather data on daily rainfall and daily average temperature were recorded at a nearby weather station at the Waterman farm (~400 m), which was compiled by the Ohio Agricultural Research and Development Center (OARDC). Rainfall and temperature data from 9/12/2007 to 3/5/2009 were obtained from OARDC Weather System (2011). Missing data from 3/1/2007 to 9/11/2007, not available in OARDC Weather System, were obtained from the National Climatic Data Center (2011).

2.5. Apparent carbon budget Apparent carbon budget was calculated from the difference in sum of all sources of C inputs and outputs (Eq. (2)). Inputs included C added from compost, manure, cover crops, and weeds in fallow plot and the antecedent soil C pool. Outputs included C loss as CO2–C, C harvested in grains, and any change in the final soil C pool. Carbon gain or loss as CH4–C was insignificant and therefore not included in the budget calculations. Initial and final soil C pools were estimated to a depth of 30 cm. Carbon sequestration rates were calculated by subtracting initial soil C pool from final and dividing by number of

3.1. Effects of soil amendment application 3.1.1. Changes in soil properties after ten years Continuous application of soil amendments (compost and manure) for ten years to NT corn significantly affected soil properties (Table 1). Application of compost and manure significantly increased soil pH towards neutral compared to cover crop. However, increase in pH was significant only in the 0–5 cm depth. Soil EC was two to three times higher in compost (185 μS cm −2) and manure (166 μS cm −2) applied corn treatments than in fallow (89 μS cm −2) and cover crop (57 μS cm −2). Other studies (Ouédraogo et al., 2001) have also reported similar increase in soil pH and electrical conductivity with compost application. At 0–5 cm depth, the SOC concentration in compost increased by 58–71% compared to fallow and cover crop. Similarly at 0–5 cm depth, bulk density decreased by 35% because of compost application than without compost. Similar observation of a decrease in bulk density with compost application was also made by D'Hose et al. (2012). Manuring increased SOC pool in the 0– 30 cm depth by 29% compared with weedy fallow. However, a significant increase in SOC pool at all depths was observed only with manure application. Although C concentration was high in 0–5 cm depth of compost applied soil, the SOC pool did not differ from those under fallow and cover crop because of a drastic decrease in ρb. The SOC pool in 30 cm depth of manure (119 Mg ha −1) applied

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corn was 30% higher than that under fallow (92 Mg ha −1) and 16% higher than that under compost (103 Mg ha −1). Application of compost increased SOC pool by 12% compared to that under fallow. Improvement in SOC sequestration and decrease in ρb with compost application was also observed in a gravelly-clay soil in Hawaii (Abbas and Fares, 2009) and silty clay loam soil of China (Li et al., 2012). 3.1.2. Carbon dioxide flux Soil CO2 flux differed among seasons, increasing gradually from early spring, reaching maxima during late spring to early summer at the peak of corn growth, gradually declining in the fall, and reaching minima during winter (Figs. 1B). Two sources of CO2 flux are decomposition of SOM and root respiration. Averaging the two year's worth of data from all treatments, 49% of the total annual CO2 emission occurred during spring, 32% during summer, 11% during winter, and 9% during fall. Fluxes of CO2 increased with increase in soil- and air-temperatures during spring (Figs. 1B and 2) and with corn growth. Flux of CO2 was low from late fall through early spring when the ground was mostly frozen. Although fluxes were generally low during frozen conditions in winter, fluxes from amendment applied soils in 2007–2008 were significantly higher than those from non-amended soil. Soil microorganisms maintain both catabolic (CO2 production) and anabolic processes (biomass synthesis) under frozen conditions (Drotz et al., 2010). Thus, gaseous exchange between the atmosphere and soil does not stop even under frozen soil, resulting in the accumulation of CO2 during winter and its release into

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the atmosphere during spring thaw events (Burton and Beauchamp, 1994). The amount of amendment-induced CO2 flux varied among years, with the most notably large flux measured in 2007–2008. Continuous application of soil amendments increased soil CO2 flux compared to un-amended because of the readily decomposable C substrate from organic amendments (Rochette et al., 2006). For most of the sampling throughout a 2-yr study period, daily soil CO2 fluxes were significantly high with manure application. The average daily CO2 flux was the highest in manure (3.81 g CO2–C m −2 d−1), followed by that in compost (2.79 g CO2–C m−2 d−1), cover crop (2.16 g CO2–C m−2 d−1), and fallow (2.07 g CO2–C m−2 d−1) treatment. A possible explanation for the higher CO2 flux observed in manure plot compared to compost plot may be due to a higher carbon concentrations in the former (408 g kg−1 soil) than in the latter (395 g kg−1 soil). The largest CO2 flux recorded during the monitoring period occurred in manure (16.7 g CO2–C m−2 d −1) applied plot followed by the compost (10.5 g CO2–C m −2 d−1) treatment on June 4, 2007. This flux rate is similar to the largest CO2 flux (17.9 g CO2–C m−2 d−1) reported by Adviento-Borbe et al. (2010). In both years, cumulative soil CO2 fluxes were higher for cattle manure followed by compost, fallow, and cover crop treatments (Fig. 3). Cumulative CO2 fluxes from compost application were significantly lower than those from manure treatment. The cumulative CO2 flux in 2007–2008 was higher than in 2008–2009, which was due to a large peak of 16.7 g CO2–C m−2 d −1 from manure applied soil and 10.5 g CO2–C m −2 d−1 from compost treatment on June 4, 2007. Long-term applications of soil amendments significantly

Fig. 2. Effects of compost, cover crop and manure on (A) soil temperature at 10 cm depth (B) 20 cm depth, and (C) soil gravimetric moisture content at 0–10 cm depth. Bars represent LSD values at 0.05 confidence level for each sampling date.

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Fig. 3. Cumulative carbon dioxide and methane fluxes affected by compost, cattle manure, cover crops, and fallow in no-till corn from 2007 to 2009.

and consistently increased CO2 emissions during both 2007–2008 and 2008–2009 compared to un-amended treatments (Fig. 3). Higher CO2 flux from organically amended versus non-amended treatment may be attributed to the combined effects of available C substrate (Adu and Oades, 1978), soil temperature and moisture regimes (Howard and Howard, 1993; Smith et al., 2003), aeration and gas diffusivity (Fang and Moncrieff, 1999; Gregorich et al., 2006), and increased microbial activity (Rochette et al., 2000). The data from the present study indicate that application of soil amendments increased soil moisture content (annual average 340–370 g kg−1) and decreased soil temperature (annual average 12.7–14.6 °C) compared to un-amendment treatments (240–260 g kg−1, 14.8–15.2 °C) (Fig. 2). Annual CO2 emission in 2007–2008 was significantly higher (46.8%) from manure-applied soil than that from the compost treatments. High SOC pool in manure (119 Mg ha−1) applied soil compared to compost (103 Mg ha−1) treatment may be one of the factors leading to high CO2 emissions. Mean annual CO2 emissions were 14.1, 10.2, 7.5, and 7.2 Mg ha−1 yr−1, and mean seasonal (corn growing season: the last week of April to the first week of October) CO2 emissions were 10.8, 8.3, 6.4, and 6.0 Mg ha−1 season−1 from cattle manure, compost, fallow, and cover crop treatment, respectively. Adviento-Borbe et al. (2010) reported CO2 emission of 9.4 Mg C ha−1 growing season−1 for corn that received liquid dairy manure in silt loam soil. Annual CO2 emission of 9.7 Mg CO2–C ha−1 yr−1 was reported from corn treated with pasteurized chicken manure at the rate of 10 Mg ha−1 yr−1 in sandy loam soil (Heller et al., 2010), and 13.3–15.3 Mg CO2–C ha−1 yr−1 that received cattle manure at the rate of 20 Mg ha−1 (fresh weight) in sandy soil (Matsumoto et al., 2008). However, Ding et al. (2007) reported a much lower annual emission of 4.01 Mg CO2–C ha − 1 yr − 1 for corn and wheat cropping systems that received composted manure in a sandy loam soil. High annual emissions in the present study may be due to a higher C input from compost (17 Mg ha − 1) and manure (12 Mg ha − 1) than that applied by Ding et al. (2007) (2.8 Mg ha − 1).

3.1.3. Methane flux Both CH4 production and consumption were observed during the 2-yr measurement period. This (Fig. 1C) and other studies (HernandezRamirez et al., 2009; Jarecki and Lal, 2006; Shrestha et al., 2009; Yao et al., 2009) show that CH4 fluxes are characterized by a high temporal variability. Therefore, there are no clear trends in cropland soils in CH4 fluxes (non-waterlogged). Because of the high variability in CH4 flux, differences between treatments are mostly insignificant. A positive CH4 flux (emissions) dominated in the amended soils and negative (consumption) in the un-amended treatment. Of the 30 sampling dates, CH4 emissions were recorded for 20 sampling dates in manure and 16 in compost-amended soils. Similar trends were reported by Jarecki et al. (2008). Long-term application of manure inhibits CH4 consumption and increases its production. Inhibition of CH4 oxidation is due to the presence of NH4 that is toxic to CH4-oxidizing bacteria (Hutsch, 2001). Additionally, increase in CH4 production in amended soils is also due to the availability of substrate (acetate) from fermentation of organic matter (Meixner and Eugster, 1999). Of 30 sampling dates, CH4 consumption in un-amended soils was recorded for 19 sampling dates in cover crop and 21 in the fallow treatment. The rate of CH4 oxidation in soil is influenced by diffusion of the gas to the microorganisms. Daily methane fluxes ranged from −3.57 to 6.91 mg CH4–C m−2 d−1 in manure, −2.44 to 4.63 mg CH4–C m−2 d−1 in compost,−4.48 to 2.49 mg CH4–C m−2 d−1 in cover crop, and −6.90 to 2.32 mg CH4–C m−2 d−1 in the fallow treatment. Cumulative CH4 emissions were observed until the fall of 2007–2008 and during all of the 2008–2009 year in manured treatment (Fig. 3), but consumption was observed only during 2007– 2008 in compost-amended plots. Also during 2008–2009, CH4 emissions were observed in compost-applied field but insignificantly less quantities than those from the manured treatment. In non-amended cover crop and fallow soils, cumulative CH4 consumptions were observed throughout the 2-year study period. The data of annual net flux for both years showed that amended soils have net CH4 emissions and non-amended soils have net

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consumption (Fig. 3). Net annual CH4 fluxes did not differ among treatments in 2007–2008, but did in 2008–2009. Net annual emissions were 10.7 kg CH4–C ha − 1 yr − 1 from manure-amended and 4.0 kg CH4–C ha − 1 yr − 1 from compost-amended treatments. Net annual consumptions were 3.3 kg CH4–C ha − 1 yr − 1 in cover crop and 5.0 kg CH4–C ha − 1 yr − 1 in the fallow treatment. Similarly, Hernandez-Ramirez et al. (2009) also reported emissions (0.16 to 0.33 kg ha − 1 yr − 1) from a soil amended with liquid swine manure, and CH4 consumption (−0.13 to −0.18 kg ha−1 yr−1) in non-amended silt loam soils. When soil under CA system (consisting of non-inversion in-row sub-soiling and winter cover crops) was amended with dairy manure (at a rate of 10 Mg ha−1), it emitted 2.7 kg CH4–C ha−1 yr−1 (Gacengo et al., 2009).

3.1.4. Carbon budget After ten years of continuous soil amendment application, SOC pools in 0–15 cm soil depth were 65, 62, 56, and 52 Mg C ha −1 in manure, compost, cover crop, and fallow treatments, respectively. We also calculated SOC pools for the same 0–15 cm depths based on equivalent soil mass approach (Ellert and Bettany, 1995) and which were 80, 78, 69 and 61 Mg ha −1. Trend was similar with both approach but the amount was higher with equivalent soil mass approach by 17 to 22%. C sequestration rates for manure, compost, cover crop and fallow plots were 1.2, 1.0, 0.9 and 0.8 Mg C ha−1 yr−1, respectively (Table 2). Although treatment comparison of relative CO2 flux measurement using the static chamber method is valid and frequently used (Adviento-Borbe et al., 2010; Bender and Wood, 2007; Gao et al., 2001; Thornton and Valente, 1996), there is some degree of uncertainty in the absolute values measured. The magnitude of the calculated annual CO2 flux in this study (7.3 to 14.1 Mg ha−1 yr−1) is within the range of the published annual flux (2.0 to 18.5 Mg ha−1 yr−1) (Adviento-Borbe et al., 2010; Gacengo et al., 2009; Hernandez-Ramirez et al., 2009). Annual C loss as CO2 was 3.8, 2.8, 2.0, and 2.1 Mg C ha−1 (average of two years) in manure, compost, cover crop, and fallow plots, respectively. Annual soil C gain or loss as CH4 was insignificant, and therefore not included in the C budget calculations. The C budget estimations indicated that there was a positive balance in amended soils, indicating a net gain of C, and a negative balance in non-amended soils, indicating a net loss. However, Duiker and Lal (2000) reported negative C budget even for the crop residue-C applied plot (6.61 Mg ha−1). The positive budget observed in the present study may be due to high amendment-C applied as compost (17 Mg C ha−1 yr−1) and manure (12 Mg C ha−1 yr−1). These results also show that, even after accounting for the grain harvest, amended NT corn ecosystem is a net C-sink of 10.5 Mg C ha −1 yr−1 for compost and 3.7 Mg C ha−1 yr−1 for manured treatments. The large input of compost-C and smaller loss through respiration (as CO2) contribute to the large C sink in compost-amended systems (Table 2). However, non-amended systems are a C-source of 1.3 Mg C ha−1 yr−1 for cover crop and 1.5 Mg C ha −1 yr−1 for fallow, which does not correspond with the measured SOC content with a C sequestration rate of 0.9 Mg C ha −1 yr−1 for the cover crop and 0.8 Mg C ha−1 yr−1 for

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the fallow treatment. Bono et al. (2008) reported a C balance at equilibrium for un-amended NT loamy soil in semiarid region in Argentina. The approach in the present study of estimating C budget does not account for any effects of earthworm feeding and burrowing activities, and depths of soil sampled for estimating the SOC pool. It is assumed that the gain or loss of C through earthworm activities may not have any significant impact, and a soil depth of 30 cm is appropriate to estimating the C pool in amended soils. Hollinger et al. (2005) reported that, accounting for 100% grain harvest, NT corn ecosystem was a net sink of 1.84 Mg C ha −1 yr−1 while soybean crop was a net source of 0.94 Mg C ha −1 yr−1. A lower C-sink in corn and a C-source in soybean in Hollinger et al. (2005)'s report in comparison with the present study may be due to the absence of C input from amendments in the former experiment.

3.2. Effects of soil temperature, soil moisture, precipitation, and air temperature on CO2 and CH4 fluxes In general, soil temperatures at 10 and 20 cm depths were positively correlated with CO2 fluxes (Table 3; P = b 0.01, n = 120). A similar positive relationship between CO2 fluxes and soil temperatures was also observed in earlier studies in central Ohio (Duiker and Lal, 2000; Jarecki and Lal, 2006; Shrestha et al., 2009) and elsewhere (Adviento-Borbe et al., 2010; Ding et al., 2007; Fortin et al., 1996; Hernandez-Ramirez et al., 2009; Rochette and Gregorich, 1998). However, Alluvione et al. (2010) did not observe a significant impact of soil temperature on CO2 fluxes at Turin, Italy, probably due to a narrow range of soil temperatures (between 20 and 30 °C). In the present study, the relationship between soil temperatures and CO2 fluxes was strong in compost-amended treatments (P = b0.01, n = 30, R 2 = 0.317), weak in cover crop (P = b0.05, n = 30, R 2 = 0.128) and fallow (P = b0.05, n = 30, R 2 = 0.165) treatments, and nonexistent in manure-amended treatments. Increase in CO2 flux with increase in soil temperature in compost-amended treatment may be due to increase in root growth and enhanced decomposition of SOM. In contrast to CO2 flux, soil temperatures have no impact on CH4 fluxes, possibly because of a large variability in CH4 fluxes. Furthermore, CO2 and CH4 fluxes were not related to seasonal variation in soil moisture at 0–10 cm depth. In general, soil moisture content influenced CO2 flux during the corn growing season (April to October) (Pb 0.01, R = 0.303, n = 76), but not in the dormant season (November to March). In contrast, Matsumoto et al. (2008) observed that CO2 emissions were correlated with soil moisture content during the dormant season but not during the corn-growing season. The present study also shows that precipitation and air temperatures, averaging data from three days before flux measurement, are positively correlated with the CO2 flux. Borken et al. (2003) also observed the effect of rainfall events on gaseous emissions because increasing soil temperature and rainfall stimulates microbial activities (Kirschbaum, 1995). However, CH4 fluxes from manure-amended soil were positively correlated with precipitation (Pb 0.05).

Table 2 Apparent carbon budget affected by soil management. Treatment

Input

a

a

C from treatment

Final soil C

2006

2007/2008

2008/2009

2008

2007/2008

2008/2009

2007

2008

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

(Mg ha−1)

98.3 104.8 112.2 116.5

1.5 1.6 17.0 12.0

1.4 1.7 17.0 12.0

99.9 106.7 114.2 119.0

2.37 2.13 3.41 4.99

1.72 1.88 2.15 2.69

0.00 0.00 3.12 3.44

0.00 0.00 2.28 2.94

Initial soil C

Fallow Cover crops Compost Manure

C budget (input–output) (Mg ha−1 yr−1)

Output a

Soil C pool is for 0–30 cm depths.

Annual C loss as CO2

C in harvested grain

−1.5 −1.3 10.5 3.7

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Table 3 Correlation coefficient (R2) of precipitation, air temperature, soil temperature and moisture with carbon dioxide and methane fluxes for different treatments. C flux in different treatments

Soil temperature Compost

CO2

CH4

a

Compost Manure Cover crop Fallow Compost Manure Cover crop Fallow

Manure

Soil moisture Cover crop

Fallow

Compost

Manure

Cover crop

0.098 0.128* −0.012

0.165* 0.023

0.001 0.003

0.005 0.018

Air temperaturea

0.142* 0.276** 0.190** 0.440** 0.068 0.161* −0.008 −0.095

0.361** 0.141* 0.159* 0.198** 0.005 0.010 0.006 0.002

Fallow

−0.107

0.317**

Precipitationa

0.026 0

Precipitation and air-temperature values averaged for flux sampling days plus three days early * and ** significant at P = b0.05 and P = b0.01, respectively.

4. Conclusions Application of soil amendments under no-till systems significantly impacted the soil carbon budget and gaseous emissions. Long-term application of soil amendments improved soil quality by increasing pH, raising electrical conductivity, enhancing soil carbon concentration, and decreasing bulk density. It also accentuated CO2 and CH4 emissions. Increase in CO2 and CH4 emissions was large in manured treatments compared to those receiving compost. Soils receiving compost and manure were C-sinks, and others were C-sources. Compost-amended soils had a large net C balance in no-till corn due to less gaseous loss of C as CO2 and CH4 compared to that of manure-amended systems. The data suggests that manuring a no-till corn field may accentuate gaseous emissions.

Acknowledgments This project was partly funded by the US Department of Energy through the Midwest Regional Carbon Sequestration Partnership project led by Battelle Columbus, OH. The authors would like to thank Nicholas Johnson, Research Assistant and Colin Waldman, Student Assistant for field and laboratory assistance.

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