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A controlled environmental facility is necessary for investigation of the interaction between above-ground and below-ground components in microcosm experiments. The Earthtron is a simple computer-controlled chamber simulating natural environments: diurnal light/dark cycles, and separately controlled soil and air temperature, humidity and CO2 concentration. In soil core incubation experiments, the Earthtron was able to simulate the dynamics of soil temperature field conditions. Environmental control also affects the dynamics of soil water and distribution patterns of nutrients in the microcosm, linking to the distribution of plant roots and soil biota. The Earthtron can not only reproduce field conditions but also predict the effects of global climatic change on terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Natural abundance of radiocarbon (14C) has been applied to estimate the turnover time of soil carbon (C) across different climate regions. However, despite the important functional role played by soil animals in decomposition processes, little is known about variation in their 14C concentrations across different climate regions. In this study, we measured 14C concentrations of earthworms collected in three forests in Japan. In addition, we also reviewed 14C data on earthworms that were previously reported. We used these data to test whether the diet ages (defined as time elapsed since C in the diet of earthworms was fixed from atmospheric CO2 by photosynthesis) differed according to feeding habits and across study sites in various climate regions ranging from cool temperate forest to tropical savanna. Multiple regression analysis showed that the diet ages of earthworms were significantly affected by both feeding habits and study sites. The diet ages of endogeic (soil-feeding) earthworms (8.3±0.4 years, mean±SE) were significantly older than those of epigeic (litter-feeding) earthworms (2.6±0.5 years), with anecic (litter-/soil-feeding) earthworms (5.7±0.9 years) having intermediate diet ages. When mean diet age was compared for each feeding habit, only that of endogeic earthworms differed significantly across the sites. However, it did not necessarily become younger in warmer climate regions. These results either suggest that the degree of decomposition of soil organic matter used by earthworms differs among the study sites, or that the difference in the turnover time of soil organic C used by earthworms across the sites is relatively small and variable due to factors other than temperature, such as soil texture and vegetation. [Copyright &y& Elsevier]

Agricultural practices often lead to a decrease in soil carbon (C), which often begins shortly after a natural system is converted to arable land. Conservation agriculture practices, such as no-till farming and weed mulching (NWM), may help maintain soil C. Increases in plant biomass through fertilization can also increase soil C. However, there is limited knowledge of the initial C dynamics following land conversion followed by conservation agriculture and fertilizer application, and of the soil biological and physical processes associated with these dynamics. Here, we studied the effects of two tillage practices (conventional tillage and NWM), fertilizer, and their interaction on earthworm abundance, soil aggregates, and soil C at two years after land conversion from grassland to agricultural land. We conducted a 2 × 2 factorial experiment (tillage/NWM and fertilized/not fertilized) in an experimental field in central Japan. We found that soil bulk densities and C concentrations at 0–5 cm depth were lower and higher, respectively, in the NWM plots than in the tillage plots at two years after the start of land conversion. After two years, earthworms were found only in the NWM plots. The percentage of macroaggregates (> 2 mm) was higher, and larger amounts of C were stored, in macroaggregates in NWM plots than in tillage plots. Amounts of crop biomass, roots, and plant residues were larger in the fertilized NWM plots. In the long term, such organic matter could accumulate in the form of macroaggregates, thereby further increasing soil C stock. Overall, we found that the soil biological and physical parameters that potentially control soil C responded to agricultural practices within a short period. The maintenance of biological activities by NWM and increased organic matter input by crop residues through fertilization can enhance soil C accumulation, which could have significant consequences for sustainable crop yields. [ABSTRACT FROM AUTHOR]

The response of the soil food web structure to soil quality changes during long-term anthropogenic disturbance due to farming practices has not been well studied. We evaluated the effects of three tillage systems: moldboard plow/rotary harrow (MP), rotary cultivator (RC), and no-tillage (NT), three winter cover-crop types (fallow, FL; rye, RY; and hairy vetch, HV), and two nitrogen fertilization rates (0 and 100 kg N ha −1 for upland rice, and 0 and 20 kg N ha −1 for soybean production) on changes in nematode community structure. Sixty-nine taxa were counted, total nematode abundance (ALL), bacterial feeders (BAC), predators (PRD), omnivores (OMN), and obligatory root feeders (ORF) were more abundant in NT than in MP and RC, but fungal feeders and facultative root feeders (FFR) were more abundant in RC than in NT and MP. Cover crop also influenced nematode community structure; rye and hairy vetch were always higher in ALL, BAC, FFR, ORF, and OMN than fallow. Seasonal changes in nematode community structure were also significant; in particular, as soil carbon increased, nematode abundance also increased. The relationship between nematode indices and soil carbon was significant only in NT, but not in MP and RC. In NT, with increasing soil carbon, enrichment index and structure index (SI) were positive and significant and channel index was negative. Bulk density was significantly negatively correlated with FFR and ORF. Seasonal difference in nematode community between summer and autumn was larger in an upland rice rotation than in a soybean rotation. Over the nine-year experiment, SI increased not only in NT but also in MP and RC, suggesting that repeated similar tillage inversions in agroecosystems may develop nematode community structures adapted to specific soil environmental conditions. Because NT showed the highest values of both SI and soil carbon, the increase of soil carbon in NT is expected to have a great impact on developing a more diverse nematode community structure. [ABSTRACT FROM AUTHOR]

Abstract: Soil carbon (C) is crucial for maintaining soil functions, and it increases after conversion of an agricultural field from conventional tillage management to no-tillage management due to decreasing human-induced soil disturbance and the modification of soil structure through ecosystem engineers such as earthworms. To improve soils and prevent degradation, understanding the effects of no-tillage management over time in changing water stable aggregates (WSA) and soil C is important. We investigated the changes in WSA and soil C at a site in Akame, Mie, Japan, operating a no-tillage with weed mulch management (NWM) system over a chronosequence from 0 to 17years after conversion from conventional tillage practices (NWM for 0, 5, 10, 15, and 17years). We measured weed aboveground biomass, litter accumulation, and root and earthworm density and biomass, and analyzed the WSA and C of bulk soil and each WSA size fraction. Weed aboveground biomass increased with site age, while litter accumulation, root biomass (soil depth of 0–4cm), and earthworm density and biomass did not appear to be related to site age. Endogeic earthworm density and biomass tended to increase at year 5 of NWM compared to year 0. The WSA >2mm and soil C stock in WSA of >2mm increased over time under NWM at a soil depth of 0–15cm, while the soil C stock of 0.25–1-mm WSA decreased at soil depths of 0–5cm. The total soil C accumulation rate was 60gCm−2 yr−1 at a soil depth of 0–25cm over the NWM chronosequence. Therefore, our results indicated that by adopting NWM, C inputs to the soil from weed aboveground biomass, as well as increases in the WSA of >2mm, might be responsible for soil C sequestration. [Copyright &y& Elsevier]

Highlights: [•] We examine changes of soil organic carbon contents in Andosol. [•] No tillage increased SOC by 10.2MgCha−1 for 9 year experiment. [•] Cover crops also increased SOC 13.4 and 8.6Mgha−1 for rye in the same period. [•] Soybean rotation increased SOC compare with field rice rotation. [•] No tillage with rye cover crop enhances carbon sequestration in Kanto, Japan. [Copyright &y& Elsevier]

Abstract: Soil aggregates are known to increase under no-tillage management (NT). We hypothesized that earthworm activity increase soil carbon (C), and investigated the effect of earthworm activity on soil aggregate size (>1mm: L, <1mm: S) and C accumulation patterns under NT by analyzing the water stable aggregate (WSA) and radiocarbon contained in surface soil (0–2cm). The study was conducted at two NT sites (Andosols), at Ami town, Ibaraki, Japan, which were both converted from conventional tillage: one with a winter cover crop and no earthworms (NT control for 6 years: NC) and the other with no weeding and a high earthworm density (natural farming for 11 years: NF) in 2009. Total C concentrations at NC and NF were 5.0% and 8.1%, respectively. The L fraction was more abundant at NF than that at NC. Total C concentrations in both the L and S fractions were significantly higher at NF than at NC. WSA (>1mm) composed approximately 80% of the total soil, reflecting NT and accumulation of earthworm casts (>1mm). The winter cover crop Secale cereale L. at NC and earthworms and weeds Digitaria ciliaris (Retz.) Koel at NF had Δ14C values of 30.1‰, 35.3‰, and 41.9‰, respectively. Earthworms incorporated C recently fixed by plants, whereas all soil samples showed negative Δ14C values (<0‰), indicating that a significant part of soil C was composed of “pre-bomb” C (before the 1960s). The earthworm community in NF was dominated by epigeic Magascolecidae, which feed on both soil and plant residue. Earthworms were estimated to translocate at least 2.8 and 1.3tCha−1 from S and plant residues to L, respectively, within 11 years, and they consumed S soil and plant residues at a weight ratio of 9:1. Epigeic earthworm increased soil C by incorporating fresh C fractions in WSA. [Copyright &y& Elsevier]