Abstract
Although agriculture is a victim of environmental risk due to global warming, but ironically it also contributes to global greenhouse gas (GHG) emission. The objective of this experiment was to determine the influence of long-term conservation tillage and N fertilization on soil carbon storage and CO2 emission in corn-soybean rotation system. A factorial experiment was arranged in a randomized completely block design with four replications. The first factor was tillage systems namely intensive tillage (IT), minimum tillage (MT) and no-tillage (NT). While the second factor was N fertilization with rate of 0, 100 and 200 kg N ha-1 applied for corn, and 0, 25, and 50 kg N ha-1 for soybean production. Samples of soil organic carbon (SOC) after 23 year of cropping were taken at depths of 0-5 cm, 5-10 cm and 10-20 cm, while CO2 emission measurements were taken in corn season (2009) and soybean season (2010). Analysis of variance and means test (HSD 0.05) were analyzed using the Statistical Analysis System package. At 0-5 cm depth, SOC under NT combined with 200 kg N ha-1 fertilization was 46.1% higher than that of NT with no N fertilization, while at depth of 5-10 cm SOC under MT was 26.2% higher than NT and 13.9% higher than IT. Throughout the corn and soybean seasons, CO2-C emissions from IT were higher than those of MT and NT, while CO2-C emissions from 200 kg N ha-1 rate were higher than those of 0 kg N ha-1 and 100 kg N ha-1 rates. With any N rate treatments, MT and NT could reduce CO2-C emission to 65.2 %-67.6% and to 75.4%-87.6% as much of IT, respectively. While in soybean season, MT and NT could reduce CO2-C emission to 17.6%-46.7% and 42.0%-74.3% as much of IT, respectively. Prior to generative soybean growth, N fertilization with rate of 50 kg N ha-1 could reduce CO2-C emission to 32.2%-37.2% as much of 0 and 25 kg N ha-1 rates.
Highlights
In recent decade, global warming due to greenhouse gas (GHG) emission is receiving great attention (Rastogi et al 2002; Lal 2007)
Soil organic carbon (SOC) plays a significant role in agro-ecosystem, due to it is directly related to productivity (Lal 2007; Smith and Collins 2007)
The presence of plant residues in Conservation tillage (CT) will create better micro climate that can enhance soil biota activity (Lavelle 1984; Brito-Vega et al 2009). This in situ mulch can act as an effective insulator and precursor of soil organic matter, and serve as substrate as well that can be converted to microbial biomass (Blevins et al 1984; Wright and Hons 2004)
Summary
Global warming due to greenhouse gas (GHG) emission is receiving great attention (Rastogi et al 2002; Lal 2007). CO2 is the most important gas, accounting for 60% of global warming (Rastogi et al 2002). Intensive agriculture contributes to CO2 emission through direct use of fossil fuels. Tillage breaks down soil aggregates, helps in mixing soil and organic particles, and enhances gas diffusivity and air-filled porosity resulted in a higher CO2 production (Rastogi et al 2002). The higher CO2 emission in intensive tillage should be reduced, other wise it will decrease C storage in the soil and end up with the decrease of soil quality and soil productivity (Paustian et al 2004)
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