خاکورزی و اثر مدیریت زهکشی در انتشار گاز خاک

Subsurface drainage influences the gaseous exchange in soils and improves crop productivity. Thus, gas diffusivity were monitored on a long-term drainage/tillage experiment established in 1994 at the Waterman Farm of The Ohio State University, Columbus, OH, USA. Specific objectives of the present study were to compare the gas diffusion and physical properties (bulk density and water retention) of soils managed under no-till (NT) and chisel-tillage (CT) systems with subsurface drainage management. Soils of the experimental site are classified as Crosby silt loam (Fine, mixed, mesic, Aeric Ochraqualf; fine, mixed, mesic, Typic Argiaquall). Treatments included: NT with tile drainage (NT-D), NT with no-drainage (NT-ND), CT with drainage (CT-D), and CT with no-drainage (CT-ND). The research site has been under continuous corn (Zea mays L.) cropping system since the start of the experiment. Intact core samples (n = 36) from 0–10, 10–20, and 20–30 cm depths were collected during November 2011 in three replicated plots of NT and CT systems under D and ND treatments. Results from this study showed that drainage treatments significantly influencing the relative gas diffusion (Dp/D0), is defined as the ratio of the soil gas diffusion coefficient to that in free air. The Dp/D0 for NT soils (23.1 × 10−3) were 26% higher than those for CT (18.3 × 10−3). Similarly, the ratio was 22% higher for soils under D (25.0 × 10−3) compared with those under ND (20.5 × 10−3). The tillage by drainage interaction was also significant for the Dp/D0 at the 0–10 cm depth. Corn yield was positively correlated with relative gas diffusion (R2 = 0.36). It can be concluded from this study that NT system under drainage management can improve the gas diffusivity, enhance the soil structure and increase crop yield.

No-till (NT) system is a useful technology for soil and water conservation, increases the soil organic carbon (SOC) pool, and serves as a sink of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (NO2) (Six et al., 2004 and Triplett and Dick, 2008). The NT system also decreases labor input and increasing profitability. In 2007, more than 26 million ha (Mha) of total crop land in the U.S., representing about 16% of total cropland areas, was under NT management production of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), wheat (Triticum aesitivum L.), and cotton (Gossypium hirsutum L.) ( Derpsch et al., 2010 and Kassam et al., 2012). The NT system is spreading globally, but especially in South America ( Derpsch and Friedrich, 2009). In general, the NT system improves soil properties, increases nutrient retention, enhances carbon (C) cycling, and moderates the flux of water and air ( Blanco-Canqui and Lal, 2007). However, the soil physical environments and GHG emissions may not always be improved under NT ( Arshad et al., 2004). Further, several questions remain about processes for improvement of soil quality and emissions of GHGs ( Blanco-Canqui et al., 2004). For a wide acceptance of NT agricultural system, therefore, it is crucial to understand and evaluate soil physical properties and emissions of GHGs. Globally, 146 Mha of arable land has poorly drained soils and is in need of some drainage management to improve soil physical properties (e.g., soil aeration, water retention, aggregation) and decrease soil erosion (Randall and Iragavarapu, 1995). The low water infiltration rate, high ground water level, snow melt and heavy rains in the spring accentuate the need for drainage management to increase and sustain high agronomic productivity. If excessively wet crop land soils are not drained, crop growth is adversely affected by the lack of aeration, reduced concentration of O2 and increased concentration of CO2 and CH4 (Lal and Taylor, 1969). Thus, drainage management is important to improving soil physical quality, reducing emission of GHGs, and improving crop growth. However, research data on the effects of drainage management on soil physical properties and emission of GHGs, especially under the NT agricultural system, are scanty (Abid and Lal, 2008 and Abid and Lal, 2009). Thus, it is critical to understand the impact of NT farming and drainage management on soil physical properties. Good soil aeration and favorable diffusivity are essential to alleviating soil-related constraints in poorly drained soils (Allaire et al., 2008), and to moderate GHG emissions (Pingintha et al., 2010). Plant roots and soil biota need O2 for respiration which is exchanged by gaseous movement, particularly gaseous diffusion and exchange. Otherwise plants and microbes could not thrive in anaerobic soils due to the lack of O2 and low respiration. In addition, gaseous diffusion is a crucial factor for a favorable composition of soil air and decomposition and transformation of soil organic carbon (SOC) and nitrogen (N) (Pingintha et al., 2010). The results of these processes affect emission of GHGs from cropland under NT management. Therefore, the gaseous movement in soils needs to be well understood to optimize the potential of agricultural practices (e.g., NT, minimum tillage, and tile drainage) and to reduce emissions of GHGs. Gaseous diffusion is one of the main processes associated with gaseous movement in soils (Marshall, 1959, Moldrup et al., 2004, Osozawa and Kubota, 1987, Taylor and Abrahams, 1953 and Werner et al., 2004). Gaseous movement is affected by soil structure (e.g., soil texture, clay mineral, macro and micro pores, bulk density, total porosity, aggregation, and pore size distribution), and water content (Ball et al., 1988, Moldrup et al., 2001, Schjonning et al., 2003 and Tuli et al., 2005). Further, gaseous diffusion depends on the continuity of soil porous media through the gas exchange process, more directly than any other soil physical properties (Ball et al., 1997). Yet, there has been little research conducted under field conditions on these issues. Schjonning (1989) and Kessavalou et al. (1998) studied the relationship between soil pore characteristics by gas diffusivities on long-term reduced tillage experiments (Kessavalou et al., 1998, Schjonning, 1989 and Schjonning and Rasmussen, 1989). Yet, the effects of soil gas diffusion in NT managed cropland soils must be thoroughly understood because relative gas diffusivity is an indicator of aerobic microbial activity (Schjonning et al., 2003). Thus, the overall goal of this research was to assess differences in soil gas diffusion over a range of NT and drainage managements. Specific objective of this study was to quantify the impacts of the NT and drainage management systems on gaseous diffusivity in soil. The hypothesis tested in this study was that NT treatment and subsurface drainage of poorly drained soils improve gaseous diffusion, decrease bulk density, improve soil structure, increase SOC concentration, and increase crop productivity.

The hypothesis that NT and D treatment under poorly-drained soils can improve gaseous diffusivity, decrease soil BD and improve crop productivity is proven. The data also support following conclusions: Soil bulk density was lower under NT than CT, and also under D than ND treatment. In contrast, therefore, total porosity of soil was higher under NT and D than CT and ND treatments. Drainage treatment significantly influenced the relative gas diffusion at pF 2.0 in 0–10 cm depth. The tillage × drainage interaction was also significant in terms of the relative gas diffusion. Tillage and drainage treatments significantly influenced the relative gas diffusion under field conditions but only for 0–10 cm depth. Drainage treatments significantly affected permanent wilting point for 0–10 cm and available water capacity for 10–20 cm depth. Relatively higher SOC concentration in 0–10 cm layer may have improved soil water retention under ND than D treatment. There were positive and significant correlations between the relative gas diffusion and grain and stover yields. Overall, NT and D treatments improved gas diffusivity and soil structure, and also enhanced corn yields.