Effect of long term conservation agricultural practices on soil CO2 emissions in rainfed Alfisols of HyderabadD. Suma Chandrika, K.L.Sharma, Munnalal, T. Satish Kumar , K.Usha Rani

Central Research Institute for Dryland Agriculture, P.O. Saidabad, Santoshnagar, Hyderabad- 500059

Measurement of soil CO2 flux with LICOR-8100

Soil carbon is the largest carbon pool in terrestrial ecosystems, containing more than two-thirds of total carbon. Soil respiration (belowground respiration) is the major pathway of carbon transfer from soil to atmosphere, and a tiny amount of change in soil respiration rate may have profound impact on the atmospheric CO2 budget, thus understanding soil respiration is crucial for the carbon balance of terrestrial ecosystems and for the global carbon balance. The CO2 fixed in plant biomass through photosynthesis can be stored in soil as organic C by converting plant residue into soil organic matter after the residue is returned to the soil.

Management practices, such as tillage, can increase carbon mineralization and thus CO2 emission from soil by disrupting soil aggregates, incorporating plant residue, and oxidizing soil organic whereas no-tillage practices and increased root biomass contribution through cropping intensity can increase soil C storage. Reduced tillage is regarded as one of the most effective agricultural practices to reduce CO2 emission and sequester atmospheric C in the soil.

Increased tillage intensity increases CO2 emission by increasing aeration due to greater soil disturbance and by physical degassing of dissolved CO2 from the soil solution. The magnitude of soil CO2 flux, depends on the degree and time of soil disturbance as well as on the soil conditions, basically soil moisture and temperature. On the other hand, nitrogen fertilization and crop rotation may play a significant role in impacting soil C. The effects of N deposition on soil CO2 emissions have also been studied in forest and grassland ecosystems. Increased above and belowground biomass production of crops can increase the amount of residue returned to the soil, thereby increasing CO2 flux. Studies on the combined effect of tillage, residues and N levels on soil CO2 emissions are meagre. Hence, the present study was conducted.

Main Treatments: Tillage (T)1. Conventional Tillage (CT): Two ploughings before planting + one plough planting + harrowing + operation for top dressing.2. Minimum Tillage (MT): Weeding occasionally with blade harrow or chemical spray and only seeding with tractor drawn planter / farm plough depending upon the situation.Sub treatments: Residues1. Sorghum Stover (SS) @ 2 t ha-1 (surface application)2. Gliricidia Loppings (fresh loppings of N fixing shrub) (GL) @ 2 t ha-1 (surface application)3. No Residue (NR) Sub-sub treatments: Nitrogen levels: 0 (N0), 30 (N30), 60 (N60), 90 (N90) kg Nha-1 through urea P application uniformly @ 30 kg P2O5 through single super phosphate (SSP)

Measurement of CO2 flux : The soil CO2 flux was measured with dynamic closed chamber connected to LICOR-8100.

About LICOR-8100:This is an automated system (Li-Cor Lincoln, NE) made of a hydraulic 10 cm survey soil chamber (15,2×15,2×25,4 cm) controlled by an electronic system, and an IRGA measuring H2O and CO2 densities. An auxiliary sensor interface allows the additional temperature or moisture sensors. The operator selects the desired number and time of measurements with a field computer. This system is programmable to enable measurements at determined intervals over long periods.

The soil CO2 flux measurements were taken at weekly intervals and at maturity (at the time of harvest during the crop growing season). Tillage, residues and N levels significantly influenced the CO2 emissions at all stages of measurement. The CO2 flux rate increased from 232nd Julian day (August) to 259th Julian day while a decline was observed at the time of maturity (at harvest) of the crop (292nd day of the year) (October) (Fig.1). Conventional tillage recorded significantly higher soil CO2 flux (531 mg CO2 m-2 hr-1) followed by minimum tillage (284 mg CO2 m-2 hr-1) when averaged over residues and N levels on 232nd Julian date. The CO2 flux rates also increased with the application of residues in all the Julian dates (232nd -292nd Julian days). Significantly higher soil CO2 flux was observed with application of sorghum stover (525 mg CO2 m-2 hr-1) followed by Gliricidia loppings (368 mg CO2 m-2 hr-1) which was 58% and 11.2% higher over no residue application on 232nd Julian day.The increased higher CO2 flux with application of sorghum stover is attributed to higher C:N ratio as well as higher microbial respiration owing to more biomass (substrate) availability. Al-Kaisi and Yin (2005) found CO2 emissions after 20 days to be 41% lower with NT and 26% lower with strip tillage (ZT at 10-cm depth) than CT in a Typic Haludoll in Iowa. Root respiration is a contributor to soil CO2 fluxes and this contribution can be from 10 to 90%, depending on vegetation type and time during the growing season; in annual crops it is suggested that the root contribution to soil respiration is higher during the growing season but low in dormant periods (Hanson et al., 2000). Application of N @ 90 kg ha-1 recorded significantly higher (454 mg CO2 m-2 hr-1) soil CO2 flux compared to no nitrogen application (362 mg CO2 m-2 hr-1). Addition of N strongly stimulated the soil CO2 losses in the fertilization plots (N @ 90 kg ha-1) which was to the extent of 30% over control under conventional tillage on 232nd Julian day.Higher CO2 fluxes due to nitrogen application could be attributed to more rapid decomposition by the microbial community, greater root respiration, or both (Fig.2). Russell et al. (2005) found that 90 kg N ha-1 increased SOC in continuous corn-corn rotation but had no effect on SOC in a corn–soybean rotation. Other researchers have found that increased N fertilizer rates can increase SOC content in long-term corn and wheat cropping systems (Liang and Mackenzie, 1992; Halvorson et al., 2002).

At maturity: On the 292nd Julian day, the soil CO2 flux declined across all the treatments and it varied from 332 mg CO2 m-2 hr-1 to 150 mg CO2 m-2 hr-1 . Conventional tillage (299.90 mg CO2 m-2 hr-1) recorded significantly higher CO2 flux than minimum tillage (259.5 mg CO2 m-2 hr-1). Loss of carbon through CO2 emissions from the soil was significantly higher with application of sorghum stover (327.88 mg CO2 m-2 hr-1) followed by application of Gliricidia loppings (300.9 mg CO2 m-2 hr-1) (Fig.3). Similarly, fertilizer N application also had a significant effect on soil CO2 flux (306 mg CO2 m-2 hr-1) over no nitrogen application (315 mg CO2 m-2 hr-1).

The loss of C in the form of CO2 evolved from the soil surface was significantly higher with conventional tillage compared to minimum tillage. Management practices like application of residues and N fertilizer also significantly influenced soil CO2 emissions. Application of sorghum stover recorded higher CO2 fluxes compared to Gliricidia application. N fertilizer @ 90 kg ha-1 significantly increased the CO2 flux rates from soil. From the present study, it was observed that conservation agricultural practices like minimum tillage, residue application can minimise carbon losses from semi arid Alfisol soils. Hence, there is a need to minimise soil CO2

losses by adopting suitable conservation agricultural practices for sustainable crop production.However, long term studies are needed to determine the effects of management practices on CO2 flux and soil C levels under various soil, climatic, and environmental conditions in semi arid tropics.

CONCLUSION

INTRODUCTION MATERIALS AND METHODS:

RESULTS AND DISCUSSIONS

General View of Sorghum crop

References: Al-Kaisi, M.M., and X. Yin. (2005). Tillage and crop residue effects on soil carbon and carbon dioxide emission in corn-soybean rotation. J. Environ. Qual. 34:437–445. Halvorson, A.D., Wienhold, B.J., Black, A.L.(2002). Tillage, nitrogen, and cropping system effects on soil carbon sequestration. Soil Sci Soc Am J. 66:906–912.Liang, B.C., Mackenzie, (1992). Changes in soil organic carbon and nitrogen after six years of corn production. Soil Sci. 153, 307–313. Russell, A.E., Laird, D.A., Parkin, T.B., Mallarino, A.P.(2005). Impact of nitrogen fertilization and cropping system on carbon sequestration in Midwestern mollisols. Soil Sci. Soc. Am. J. 69, 413–422.Sainju U.M., Jabro J.D., Stevens, W.B. (2008). Soil carbon dioxide emission and carbon sequestration as influenced by irrigation, tillage, cropping system, and nitrogen fertilization. Journal of Environmental Quality 37, 98-106.

Fig 1: Soil CO2 flux (mg CO2 m-2 hr-1) as influenced by tillage from 232-292 Julian Days in Sorghum crop

Fig 2: Soil CO2 flux (mg CO2 m-2 hr-1) as influenced by tillage X N levels from 232-292 Julian Days in Sorghum crop

Fig: 3 Soil CO2 flux (mg CO2 m-2 hr-1) as influenced by tillage X residues from 232-292 Julian Days in Sorghum crop