Pedosphere最新文献

Iron (Fe) minerals are commonly used to remove phosphorus (P) from waste streams, producing P-loaded Fe(III) oxides or Fe(II) phosphate minerals (e.g., vivianite). These minerals may be used as fertilizers to enhance P circularity if solubilized in soil. Here, we tested the P fertilizer value of recycled Fe phosphates (FePs) in a pot trial and in an incubation experiment, hypothesizing that P release from FePs is possible under Fe(III)-reducing conditions. First, a pot trial was set up with rice (Oryza sativa) in all combinations of soil flooding or not, three P-deficient soils (acid, neutral, and calcareous), and six FePs (three Fe(III)Ps and three Fe(II)Ps) referenced to triple superphosphate (TSP) or zero amendments. Shoot P uptake responded to TSP application in all treatments but only marginally to FePs. The redox potential did not decrease to -200 mV by flooding for a brief period (13 d) during the pot trial. A longer incubation experiment (60 d) was performed, including a treatment of glutamate addition to stimulate reductive conditions, and P availability was assessed with CaCl₂ extraction of soils. Glutamate addition and/or longer incubation lowered soil redox potential to < -100 mV. On the longer term, Fe(III) minerals released P, and adequate P was reached in the calcareous soil and in the neutral soil amended with Fe(III)P-sludge. It can be concluded that prolonged soil flooding and organic matter addition can enhance the P fertilizer efficiency of FePs. Additionally, application of FeP in powder form may enhance P availability.

Different pore sizes present different pore shrinkage capacities in a nonrigid soil. However, the shrinkage capacities of different pore sizes and their influencing factors are not clear. We aimed to quantify the shrinkage capacities of different pore sizes (large pores, > 50 μm; medium pores, 0.2–50 μm; fine pores, < 0.2 μm) and determine how soil properties impact soil shrinkage capacity at the regional scale. Two sampling transects from west to east (360 km long, 35 samples) and from north to south (190 km long, 29 samples) were selected to investigate soil shrinkage capacity and physicochemical properties of at 0–20 cm depth in the Vertisol (locally known as Shajiang black soil) region of the North China Plain. The results showed that soil total shrinkage capacity, indicated by the coefficient of linear extensibility (COLE), had a mean value of 0.041–0.051 in the west-east and north-south transects. Large pores had higher pore shrinkage index (PSI) values (0.103–0.109) than medium (0.077–0.096) and fine (0.087–0.091) pores. The PSI of fine pores showed a fluctuating increasing trend from northwest to southeast, and the fine pore shrinkage capacity determined the COLE (r² = 0.789, P < 0.001). The PSI of large pores had a significant relationship with soil bulk density (r = 0.281, P < 0.05) and organic carbon (r = -0.311, P < 0.05), whereas those of medium and fine pores were correlated with soil clay content (r = 0.381 and 0.687, respectively, P < 0.001). In addition, the PSI of fine pores was also correlated with montmorillonite content (r = 0.387, P < 0.01). It can be concluded that the PSI of large pores is related to anthropogenically influenced soil properties with low stability, whereas those of medium and fine pores are related to pedogenic properties. The high variability in anthropogenic and pedogenic factors explains the spatial pattern of Vertisol shrinkage capacity on the North China Plain.

Nitrogen (N) priming is a microbially mediated biochemical process as affected by different incorporation practices. However, little information is known about the microbial mechanisms driving the response of N priming to co-operation of Chinese milk vetch (CMV, Astragalus sinicus L.) and different rates of chemical fertilizers in paddy soils in South China. Here, an anaerobic incubation experiment was conducted to study N priming effects (PE) and their relationships with soil microbial functional genes after CMV incorporation alone (M), co-incorporation of CMV with 100% (normal dosage) chemical fertilizers (MC100), and co-incorporation of CMV with 80% chemical fertilizers (MC80). Co-incorporation of CMV and chemical fertilizers enhanced the short-time scale (the first 20 d of incubation) positive PE of N, while no significant differences existed among the three treatments on day 60 or 90 of incubation (P > 0.05). Compared with the M treatment, gross priming effect (GPE) in the MC100 and MC80 treatments significantly increased by 34.0% and 31.3%, respectively, and net priming effect (NPE) increased by 47.7% and 47.8%, respectively, during the first 20 d of incubation (P < 0.05). This was likely attributed to soil nutrient availability and added substrate quality. The MC100 and MC80 treatments increased the gdhA gene abundance by 5.0% and 9.8%, increased the gdh2 gene abundance by 12.7% and 45.7%, and increased the nasB gene abundance by 9.5% and 41.4%, respectively, in comparison with the M treatment on day 20 of incubation. Correlation analyses indicated that soil microbial functional genes involved in N mineralization (gdhA and gdh2), assimilatory nitrate reduction (nasB), and nitrification (amoB) were significantly correlated with N priming under different incorporation practices during the incubation period (P < 0.05). Thus, co-incorporation of CMV and chemical fertilizers can regulate soil microbial community functional gene structure, which may accelerate mineralization and assimilatory nitrate reduction and inhibit nitrification, thereby increasing the short-term positive PE of N in the present study.

In digital soil mapping (DSM), a fundamental assumption is that the spatial variability of the target variable can be explained by the predictors or environmental covariates. Strategies to adequately sample the predictors have been well documented, with the conditioned Latin hypercube sampling (cLHS) algorithm receiving the most attention in the DSM community. Despite advances in sampling design, a critical gap remains in determining the number of samples required for DSM projects. We propose a simple workflow and function coded in R language to determine the minimum sample size for the cLHS algorithm based on histograms of the predictor variables using the Freedman-Diaconis rule for determining optimal bin width. Data preprocessing was included to correct for multimodal and non-normally distributed data, as these can affect sample size determination from the histogram. Based on a user-selected quantile range (QR) for the sample plan, the densities of the histogram bins at the upper and lower bounds of the QR were used as a scaling factor to determine minimum sample size. This technique was applied to a field-scale set of environmental covariates for a well-sampled agricultural study site near Guelph, Ontario, Canada, and tested across a range of QRs. The results showed increasing minimum sample size with an increase in the QR selected. Minimum sample size increased from 44 to 83 when the QR increased from 50% to 95% and then increased exponentially to 194 for the 99% QR. This technique provides an estimate of minimum sample size that can be used as an input to the cLHS algorithm.

Agriculture has a close relationship with nature, but it can also be the source of negative and permanent environmental effects. The use of pesticides in modern agriculture is a common practice, but their side effects on the environment cannot be disregarded. In this study, we evaluated a combination of solarization and ozonation techniques for the elimination of six amide pesticides (boscalid, chlorantraniliprole, cyflufenamid, fluopyram, napropamide, and propyzamide) in soil. Initial experiments were performed with four different soils to assess the efficiency of this methodology at different soil temperatures and ozone dosages under laboratory conditions, and then a greenhouse pot experiment was conducted under controlled conditions during summer. Fifty days after the onset of the experiments, higher degradation percentages of amide pesticides were observed in ozonized soils than in other treated soils, particularly when ozone was applied at 10 cm soil depth. The results show that the utilization of ozonation, along with solarization, represents a valid method for degrading residues of the studied pesticides and suggest that this combined technology may be a promising tool for remediating pesticide-polluted soils.

Vegetable soils with high nitrogen input are major sources of nitrous oxide (N₂O) and nitric oxide (NO), and incorporation of the nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) into soils has been documented to effectively reduce emissions. However, the efficiency of DMPP in terms of soil N₂O and NO mitigations varies greatly depending on soil temperature and moisture levels. Thus, further evaluations of DMPP efficiency in diverse environments are required to encourage widespread application. A laboratory incubation study (28 d) was established to investigate the interactive effects of DMPP, temperature (15, 25, and 35 °C), and soil moisture (55% and 80% of water-holding capacity (WHC)) on net nitrification rate, N₂O and NO productions, and gene abundances of nitrifiers and denitrifiers in an intensive vegetable soil. Results showed that incubating soil with 1% DMPP led to partial inhibition of the net nitrification rate and N₂O and NO productions, and the reduction percentage of N₂O production was higher than that of NO production (69.3% vs. 38.2%) regardless of temperature and soil moisture conditions. The increased temperatures promoted the net nitrification rate but decreased soil N₂O and NO productions. Soil moisture influenced NO production more than N₂O production, decreasing with the increased moisture level (80%). The inhibitory effect of DMPP on cumulative N₂O and NO productions decreased with increased temperatures at 55% WHC. Conversely, the inhibitory effect of DMPP on cumulative N₂O production increased with increased temperatures at 80% WHC. Based on the correlation analyses and automatic linear modeling, the mitigation of both N₂O and NO productions from the soil induced by DMPP was attributed to the decreases in ammonia-oxidizing bacteria (AOB) amoA gene abundance and NO₂^--N concentration. Overall, our study indicated that DMPP reduced both N₂O and NO productions by regulating the associated AOB amoA gene abundance and NO₂^--N concentration. These findings improve our insights regarding the implications of DMPP for N₂O and NO mitigations in vegetable soils under various climate scenarios.

Soil functional microbial taxa and extracellular enzymes are involved in a variety of biogeochemical cycling processes. Although many studies have revealed the vertical change patterns of microbial communities along soil profile, the general understanding of the coupling changes in the functional gene abundances (FGAs) and extracellular enzyme activities (EEAs) in soil profiles is still limited, which hinders us from revealing soil ecosystem processes. Herein, we comparatively investigated the FGAs and EEAs in the diagnostic A, B, and C horizons of soil profiles obtained from two suborders of Isohumosols (Mollisols), Ustic and Udic Isohumosols, in Northeast China based on quantitative real-time polymerase chain reaction and standard fluorometric techniques, respectively. The distribution patterns of both FGAs and EEAs significantly distinguished by the two soil suborders and were also separated from A to C horizon. Additionally, the variations of EEAs and FGAs were greater in Udic Isohumosols compared to Ustic Isohumosols along soil profiles, and greater changes were observed in C horizon than in A horizon. Both FGAs and EEAs correspondently decreased along the soil profiles. However, when normalized by soil organic carbon, the specific EEAs significantly increased in deep soil horizons, suggesting that microorganisms will input more resources to the production of enzymes to ensure microbial nutrient requirements under resource scarcity. More importantly, we revealed that soil microbial nutrient demands were limited by carbon (C) and phosphorus (P), and the C and P limitations significantly increased along soil profiles with a greater C limitation observed in Ustic Isohumosols than in Udic Isohumosols. Overall, our findings provided solid evidence showing the links between FGAs, EEAs, and microbial nutrient limitations, which would be helpful for a better understanding of the ecosystem processes in soil profiles.

Estimation of the plant-available water capacity (PAWC) of soils at a regional scale helps in adopting better land use planning, developing suitable irrigation schedules for crops, and optimizing the use of scarce water resources. In the current study, 72 soil profiles were sampled from the Barossa region of South Australia to estimate pedo-transfer functions deduced from easily estimated soil properties. These functions were then used to estimate the fixed (10 and 33 kPa) and dynamic pressure head (h_fc) water contents at field capacity (FC) for minimum drainage flux (0.01 and 0.001 cm d^-1), which serves as the upper boundary for plant-available water in soils. The estimated residual water content was corrected for subsoil constraints, especially the exchangeable sodium percentage (ESP). The results showed that the mean values of h_fc in sand-dominated light and medium textured soils (i.e., sand, loamy sand, sandy loam, and loam) varied in a narrow range (15.8–18.2 kPa), whereas those in the clay-dominated heavy textured soils (i.e., clay loam) showed a wide range (11.3–49.3 kPa). There were large differences in PAWC for dynamic FC (PAWC_fc) and fixed FC at 10 kPa (PAWC₁₀), 33 kPa (PAWC₃₃), and a mix of 10 and 33 kPa (PAWC_{10, 33}) pressure heads depending on soil texture. Normally, the difference between PAWC at 10 kPa and h_fc (ΔPAWC₁₀) was positive, whereas that between 33 kPa and h_fc (ΔPAWC₃₃) was negative across all sites. Nevertheless, the estimation of PAWC assuming a fixed FC at 10 and 33 kPa pressures (i.e., PAWC_{10, 33}) for sandy, clay, and silty soils reduced the difference between fixed and dynamic pressure PAWCs to < 10% across the region. The estimation of PAWC was improved by incorporating the impact of subsoil constraints, such as high ESP, which was more pronounced for clay and silty soils. These findings demonstrate the inherent inconsistencies between static pressure and flux-based dynamic FC estimations in soils. Soil heterogeneity, intra-texture variability, subsoil constraints, and swell-shrink clays can have great impacts on the water retention capacity in response to dynamic and fixed pressure FC values.

Continuous cropping is a common pattern of modern agriculture that takes regional advantages for crop yield profits. Along the progress of mono-cropping continuously supported by intensive fertilizer inputs, such a cropping pattern often undergoes serious problems with low fertilizer use efficiencies and unsustainable crop production. In this study, we dealt with a > 25-year continuous garlic cropping system as an example for a problem-solving investigation. These garlic cropping soils underwent problems characterized by loss of soil organic matter, dramatic retention of NH₄⁺-N, and excess accumulation of phosphate and potash chemicals. Through hydroponic simulations, we revealed that the presence of NH₄⁺-N inhibited the root uptake of NO₃^--N and K by 68% and 88%, respectively. Despite the traditionally emphasized importance of K, we observed the negative effect of high K on the growth of garlic roots. Further field experiments demonstrated that P and K applications can be reduced by 60% and 50%, respectively, without loss of yield. We thus developed a high-performance fertilization strategy by integrating a recomposed NPK fertilizer formulation to reduce unnecessary P and K inputs, a supplementary application of long-lasting C of woody peat to compensate for the soil C loss, and a foliar K approach to strengthen the stomatal function improvement with K. This strategy allowed a 15% increase of garlic yield and a seasonal soil C profit of ca. 1.8 Mg ha^-1 even at ca. 30% lower fertilizer cost. This study would be helpful in managing garlic fertilization and developing compound fertilizers, with broader significance for other long-term cropping soils.