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《Soil & Tillage Research》2007,92(1-2):217-226
The one-compartment C model is being long used to simulate soil organic C (SOC) stocks. Ct is the SOC stock at the time t; C0, the initial SOC stock; k2, the annual rate of SOC loss (mainly mineralization and erosion); k1, the annual rate to which the added C is incorporated into SOC; and A, the annual C addition. The component expresses the decay of C0 and, for a time t, corresponds to the remains of C0 (C0 remains). The component refers, at time t, to the stock of SOC derived from C crops (Ccrop). We herein propose a simple method to estimate k1 and k2 coefficients for tillage systems conducted in long-term experiments under several cropping systems with a wide range of annual C additions (A) and SOC stocks. We estimated k1 and k2 for conventional tillage (CT) and no-till (NT), which has been conducted under three cropping systems (oat/maize −O/M, vetch/maize −V/M and oat + vetch/maize + cowpea −OV/MC) and two N-urea rates (0 kg N ha−1 −0 N and 180 kg N ha−1 −180 N) in a long-term experiment established in a subtropical Acrisol with C0 = 32.55 Mg C ha−1 in the 0–17.5 cm layer. A linear equation (Ct = a + bA) between the SOC stocks measured at the 13th year (0–17.5 cm) and the mean annual C additions was fitted for CT and NT. This equation is equivalent to the equation of the model , so that and . Such equivalences thus allow the calculation of k1 and k2. NT soil had a lower rate of C loss (k2 = 0.019 year−1) than CT soil (k2 = 0.040 year−1), while k1 was not affected by tillage (0.148 year−1 under CT and 0.146 year−1 under NT). Despite that only three treatments had lack of fit (LOFIT) value lower than the critical 5% F value, all treatments showed root mean square error (RMSE) lower than RMSE 95% indicating that simulated values fall within 95% confidence interval of the measurements. The estimated SOC stocks at steady state (Ce) in the 0–17.5 cm layer ranged from 15.65 Mg ha−1 in CT O/M 0 N to 60.17 Mg ha−1 in NT OV/MC 180 N. The SOC half-life (t1/2 = ln 2/k2) was 36 years in NT and 17 years in CT, reflecting the slower C turnover in NT. The effects of NT on the SOC stocks relates to the maintenance of the initial C stocks (higher C0 remais), while increments in Ccrop are imparted mainly by crop additions. 相似文献
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Earthworms can enhance plant productivity by promoting nitrogen (N) mineralization in N-limited agroecosystems and may also enhance the risk of N2O emissions and leaching in N-enriched agroecosystems. However, direct evidence demonstrating the enhancement by earthworms of N2O emissions and leaching in the field is scarce, particularly in intensively managed systems. In addition, the interaction of earthworm feeding strategies and organic amendment may profoundly modulate N cycling. We examined these impacts using two earthworm species with distinct ecological strategies (epigeic Eisenia foetida and endogeic Metaphire guillemi) in combination with two manure application methods (surface mulch and incorporation into the soil) in a field experiment. Our results demonstrated that earthworm addition significantly increased the crop yield by 18%–47% and cumulative N2O emissions by 19%–25% largely regardless of earthworm species and manure application methods, respectively. However, earthworms did not significantly increase the leachate concentration. Earthworm-induced N2O emissions were primarily attributed to increased soil N availability ( and microbial biomass N) and carbon (C) availability (dissolved organic C). In contrast, a stepwise regression revealed that an earthworm-promoted soil macroaggregation exerted negative effects on N2O emissions. Irrespective of earthworm species and manure application methods, earthworms had no stimulatory effects on the yield-scaled N2O–N because the promotion of crop productivity counteracted the extent of N2O increase. In conclusion, understanding the trade-off between earthworm services and dis-services will contribute to the development of environmentally justified soil management by allowing the full utilization of biological resources. 相似文献
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Apolline Auclerc Johanne Nahmani Pierre Huguier Yvan Capowiez Delphine Aran François Guérold 《Pedobiologia》2011
Two laboratory experiments were carried out to determine the potential effects of lime application on the behavior of earthworms inoculated in an acidified forest soil from Vosges Mountains. Several field soils were studied: (i) a non-limed soil that had received decades of atmospheric acid depositions , (ii) an in situ limed soil that had been limed 6 years before at 2.5 t ha?1 and (iii) in vitro limed soils composed of non-limed soil mixed with several lime amounts in the laboratory corresponding to field rates of 1, 2.5, 5, 10 and 20 t ha?1. Firstly, we adapted the earthworm avoidance test (ISO, 2006) by using Eisenia fetida as the model organism and Lumbricus castaneus, a local species, to determine earthworm preference between non-limed and limed soils. Secondly, a cast production (CP) study was performed according to Capowiez et al. (2009) with Lumbricus terrestris, in seven different treatments (non-limed soil, in situ limed and five in vitro limed soils with pH from 5 to 6.3). Both species avoided the non-limed soil in favour of in situ and in vitro limed soils for both species. Results of the CP bioassay showed that the bioturbation behavior of L. terrestris significantly increased with the increase of soil pH, following a dose–response curve. However, in the long term (>6 years), the application of lime was insufficient to significantly improve soil conditions for enhancing earthworm activity. In conclusion, we may recommend this kind of earthworm laboratory tests with field soils to assess any changes in soil quality over time due to liming application. 相似文献
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Competition for nutrients between plants and microbes is an important determinant for plant growth, biodiversity and carbon cycling. Perturbations such as drought affect the availability of nitrogen (N) and phosphorus (P), and may cause shifts in uptake of N and P between plants and microbes. Competitiveness for these nutrients may depend on how flexible plants and microbes are in taking up N and P. We used a novel dual isotope labelling technique (15N and 32P) to assess short-term uptake of N and P by plants and microbes affected by drought in two different plant–soil systems. Mesocosms were extracted from two grassland sites differing in soil nutrient availability and plant species. Half of the mesocosms were subjected to drought one week prior to injection of 15N (as KNO3) and 32P (as H3PO4) tracers. Uptake rates of and P in plants and microbes were estimated based on average source pool enrichment during the labelling period and on plant and microbial recovery of 15N and 32P measured after 4 days of labelling. Overall competition for N and P was reduced with drought as less and P was taken up in plants and microbes. However, plant uptake of was more sensitive to drought than microbial uptake, while microbial P uptake was more sensitive than plant P uptake. These different sensitivities to drought by plants and microbes may decouple the N and P cycle with increased drought conditions. 相似文献
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Isotopic CO2 measurements of soil respiration over conventional and no-till plots in fall and spring
Soils and vegetation are the second largest global carbon reservoir. Carbon storage in soil can be increased by increasing carbon inputs and/or reducing decomposition rates. Reduced tillage practices have the potential to increase soil carbon storage by reducing decomposition of soil organic matter and/or crop residue. Isotope values (C) of soil respiration can help infer the contribution of soil carbon pools to the soil CO2flux, providing insight into the effects of tillage on residue decomposition. The objectives of this paper were to: (1) measure the isotope signatures of respired CO2 from conventional tillage and no-till plots; (2) compare and contrast the two treatments in the fall and in the following spring before planting; and (3) compare the C of soil respiration of the experimental plots with the surrounding region. Isotope soil CO2 fluxes were measured using tunable diode laser spectroscopy and micrometeorological methods in a field experiment in Ontario, Canada. Measurements were made in fall following corn (a C4 plant) harvest and again in spring prior to soybean emergence. Data were used to compute the C value of respired CO2 using both the flux ratio and Keeling plot methods. The large concentration footprint prevented the Keeling plots from discerning the treatment effect. In the conventional till plots, the respired C value showed a stronger C4 signature () compared to the no-till field () which had no soil incorporation of above-ground crop residue. This indicates more rapid decomposition of the ‘new’ residue in the conventional tillage treatment. Both treatments showed a decrease in the isotope ratio during the spring measurements ( and for the conventional and no-till plots, respectively) which shows a depletion of the labile C4 substrate and a shift in respired substrate towards the soil C3 organic matter over the fall to spring period. For the fall, we estimate that 57 and 25% of the CO2 flux originated from crop residue for the conventional and no-till systems, while in the spring the proportions had decreased to 22 and 0%, respectively. 相似文献