Search

Macropores resulting from soil pedogenesis, biological activity, and agricultural practices play important roles in soil water, chemical and gas transport; however, seldom studies focus on the effect of soil macropores on CO2 behavior. In this study, a 150-day soil column incubation experiment was conducted to investigate the CO2 behavior in a homogeneous soil column and a soil column with an artificial macropore, which have the same total porosity. The results showed that the cumulative CO2 fluxes observed in the soil with a macropore (57.2 g m−2) were higher than those in the homogeneous soil (52.7 g m−2). The soil cumulative CO2 fluxes measured using column incubation can fit the kinetic model, and a higher carbon mineralization rate in the soil with the macropore was found. The results of the incubation experiment also suggest that macropore increased the gas diffusivities, and thus decreased the CO2 concentrations in the soil profile. This study proposed a simulation experiment and quantified the effect of macropore on soil CO2 behavior, which could help to understand the mechanism of CO2 emission from soil with macropores especially caused by agricultural practices.

Accurate quantification of soil gas diffusion is essential to understand the gas transport mechanism in soils, especially for soil greenhouse gas emissions. To date, the performance of soil gas diffusivity (Dp/D0, where Dp is the soil gas diffusion coefficient and D0 is the diffusion coefficient in free air) models has seldom been evaluated for no-tilled and tilled volcanic ash soils. In the present study, six commonly used models were evaluated for volcanic ash soils under two treatments by comparing the predicted and measured soil gas diffusivities at water potentials of pF 1.3–3. The Buckingham-Burdine-Campbell (BBC), soil-water-characteristic-dependent (SWC-dependent), and two-region extended Archie’s Law (2EAL) models showed better performance for both no-tilled and tilled volcanic ash soils, which is likely because porosity and pore size parameters of bimodal soils were taken into consideration in these models. Since the BBC model showed better accuracy than the SWC-dependent and 2EAL models...

Agricultural management plays an important role in the storage of carbon in soils. The behavior of soil CO2 in an Andisol in two different tillage systems (no tillage and tillage) was studied. Soil-column incubation experiments were performed for a period of 150 days to conduct this study. Soil CO2 flux, under no-tillage and tillage treatments, was observed to be 0.557 and 0.616 gCO2-C m−2 d−1, respectively. The cumulative CO2 flux under tillage treatment was observed to be higher than that under no-tillage treatment, but no distinct difference in the soil carbon stock was observed between both treatments. The soil CO2 concentration under no-tillage treatment was clearly much higher than that under tillage treatment, except at a depth of 2.5 cm. Tillage decreased soil dry bulk density and enhanced soil air-filled porosity. Soil gas diffusivity, which depends on air-filled porosity, was increased by tillage at a depth of 0–15 cm, which contributed to their lower soil CO2 concentration. CO2 flux through the soil profile, calculated from the CO2 concentration, decreased with depth. Compared to the deep soils, the surface soil (0–5 cm) showed greater variation in CO2 flux. The CO2 production at depths of 0–10 cm accounted for 62.2 and 51.7 % of the whole CO2 production of the 0–30-cm soil profile for no-tillage and tillage treatments. CO2 production was higher for soil under no tillage at depths of 0–10 cm, but contrary results were observed for soil at depths of 10–30 cm.

Water-saving rice-winter crop rotation systems were repeated for 4 cycles from 2000 to 2004 in an urban area, Nishitokyo, Japan, to assess the effects of water-saving (i.e. non-flooded vs. flooded) on grain yield of rice (Oryza sativa L.) and chemical constituents of percolating water. The effects of pre-rice winter cropping compared with fallow on rice yield were also examined. The pre-cultivated crops were wheat (Triticum aestivum L.), italian ryegrass (Lolium multiflorum Lam.) or spinach (Spinacea oleracea L.) with their above-ground parts removed, chinese milk vetch (Astragalus sinicus L.) or rapeseed (Brassica napus L.) with their above-ground parts incorporated before rice transplanting. Neither winter cropping effects nor its interaction with water-saving were significant for rice yield, although the yield after rapeseed incorporation tended to be 9 % higher than that after fallow. In 2001, 2003 and 2004, when more than 70% of irrigation water was saved in the non-flooded trial, average yield in non-flooded trial was 58 % of flooded trial, but water productivity increased (from 0.10 to 0.16 kg m-3). Among the 3 years, yield in non-flooded trial was highest in 2004 when the amounts of irrigation and total water supply was larger, the frequency of dry spells was the lowest, and 2 seedlings were transplanted per hill. The nitrate and nitrite concentrations in the percolating water were far below the environmental standard values by WHO. The study showed that incorporation of winter crops had no negative effects on water-saving rice production at least for the first 4 years, and that under extreme water-saving, irrigation and planting methods could minimize yield reduction.

A Deep Root System May Be A Desirable Plant Characteristic In Upland Rice Because It Improves The Plant’s Water Extraction Capacity. The Objective of The Present Study Was To Assess The Deep Root Development of Rice Cultivars In Relation To Soil Moisture Change and Plant Water Status Under Upland Conditions With Moderate Water Deficits In The Field and In Simple Lysimeter Experiments. We Used One Upland Cultivar (‘Yumeno-Hatamochi [Yhm]) and Two Lowland Cultivars (‘Lemont’ [Lmt] and 'Nipponbare’ [Npb]) In The Field Experiment, With No Supplemental Water From 88 To 106 Days After Sowing (Das) and 116 To 145 Das. In The Lysimeter Experiment, We Used Yhm and Npb and Imposed Two Water Stress Periods During The Late Vegetative Stages (71 To 104 Das and 88 To 104 Das). In The Lysimeter Experiment, A Higher Deep-Root Length Ratio (Proportion of The Length of Deep Roots To The Total Root Length) In Yhm Was Associated With A Greater Deep-Root Length Than In Npb. The Difference In Deep Root Development Was Associated With Change In Soil Water Content At The Depths of 45 To 70 Cm Between The Two Cultivars Under The Above Conditions. The Drought In The Field Experiment Was Less Intense Than In The Lysimeter Experiment, and We Observed Greater Varietal Differences In Total Aboveground Biomass Than In Root System Development; This Was Associated With The Change In Soil Water Content During The Initial Drought Period. Lmt, With Smaller Shoots, Tended To Save Water and Maintain Higher Leaf Water Potential and Lower Diffusion Resistance As The Drought Progressed. Our Results Suggest That Deep Root Development of Rice Was Primarily Advantageous For Soil Water Extraction and Plant Water Status Under Moderate Water Stress In Uplands, But That The Advantage of A Deep Root System Was Affected By Total Aboveground Biomass, Which Had Strong Effects On Plant Water Status Under These Conditions.