Enhancing Carbon Sequestration

Soil Carbon Storage

At the long-term plot, the highest soil C storage after 23 years of cropping at 0–20 cm depth was obtained by treatment combining NT with a higher N rate, while the lowest soil C strorage was in IT with 0 kg N/ha as shown in Fig. 4.3, left. No-tillage and MT resulted in soil C storage 43 % and 20 % higher than IT, respectively. The initial carbon storage at 0–20 cm depth in 1987 (when this long-term plot was established) was 32.0 Mg ha−1(Utomo et al. 2010a). Thus, during 23 years of cropping, NT had sequestered as much as 4.4 Mg C ha−1of carbon, amounting to a carbon sequestration rate of 0.2 Mg C ha−1 year−1. In contrast, IT had depleted 6.6 Mg C ha−1 of carbon, yielding with carbon depletion rate of 0.3 Mg C ha−1 year−1. The higher C sequestration of CT than business as usual practice was attributed to addition of previous plant residues, and a lower rate of soil organic matter decomposition with respect to CT. Every season, the average weight of crop residue applied to the NT soil surface was 6–13 Mg ha−1 season−1 with a C-N ratio of around 32 (Utomo et al. 2010a).

Fig. 4.3 Soil carbon storage at 0–20 cm depth after 23 years of conservation tillage (left) and farmers'fields (right); Agrft = agroforest, IT = intensive tillage, MT = minimum tillage, NT = notillage and CT = conservation tillage ( Utomo et al. 2010b)

Table 4.1 Carbon balance of corn (during a single season)

Treatment

Root

Stalk

Grain

Total C-biomass (Mg C ha−1)

Emission

Net sequestration

Intensive tillage

1.2

3.6

2.5

7.3

2.0

5.3

Minimum tillage

1.6

3.4

4.5

9.5

1.5

8.0

No-tillage

2.1

5.3

5.0

12.4

1.0

11.4

Note: With optimum fertilization (Utomo et al. 2011)

This higher soil carbon sequestration is also reflected in improved soil quality and crop productivity with respect to CT. Utomo et al. (2013) recently reported that compared to the IT corn field, the CT corn field after 23 years of cropping had higher soil moisture, soil exchange bases, and soil microbial biomass. The corn yield of long-term CT was also 31.8 % higher than that of IT.

At the farmer's fields, that finding was confirmed by soil C storage at 0–20 cm depth under the different land use systems presented in Fig. 4.3, right. Soil C storage under CT farming was 138 % higher than under IT farming and 48 % higher than under rubber agroforest. The significant increase in soil C storage was attributable to the decomposition of previous crop residues and less soil erosion with respect to CT and rubber forest (Utomo et al. 2010b).

Carbon Sequestration of Corn Crops

Carbon sequestration of corn biomass was measured at harvest time. Through photosynthesis, plants fix CO2 from the air and convert it into organic carbon compounds that are used to grow plant tissues or biomass (Luo and Zhou 2006). The total carbon of NT corn biomass was 12.4 Mg C ha−1, 31 % higher than MT and 70 % higher than IT. With a better micro-climate and soil quality (Utomo et al. 2013), CT sequestered carbon in biomass at a higher level than other tillage systems, as reported by Lal (1997), Wright and Hons (2004), and Smith and Collins (2007). As shown in Table 4.1, NT's potential net sequestration reached 11.4 Mg C ha−1, or 115 % and 43 % higher than IT and MT, respectively.

Dispite the fact that tillage systems generated CO2 emissions, howevr, all tillage systems also seqestered carbon at a rate higher than their CO2 emissions (Table 4.1). Thus, CT corn is not in fact a net CO2 emitter, but instead is a net sinker. In the final analysis, therefore, it is evident that CT farming using RMP can mitigate CO2 emission in a rain-fed tropical agro-ecosystem.

Conclusions and Policy Implication

In tropical rainfed agro-ecosystems, long-term conservation tillage of corn reduced CO2 emission and increased carbon sequestration both in biomass and soil. Long-term conservation tillage of corn was also an effective net sinker of carbon.

However, further research is needed to improve the capacity of conservation tillage technology to mitigate greenhouse gas emissions in other crops and in different agro-ecosystems.

The policy implication of this strategic finding is that conservation tillage should be promoted by farmers, policy makers, and politicians as a recommended management practice for halting environmental degradation, reducing greenhouse gas emission, and strengthening food security.

Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

 
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