Ferralic Cambisol Research Articles

Soil organic carbon pools under long-term mineral and organic amendments: a multisite study

Soil organic carbon (SOC) has various pools with different stabilization mechanisms. It is unclear how these SOC pools respond to various mineral and organic amendments depending on a large climate-soil gradient. Here, we studied in three zonal soils: Ferralic Cambisol (subtropic), Calcaric Cambisol (warm-temperate) and Luvic Phaeozem (mid-temperate) under 23-year mineral, straw and manure amendments. Six SOC sub-pools were isolated: unprotected, physically, chemically, biochemically, physico-chemically and physico-biochemically protected pools. Compared to initial level, SOC and most sub-pools increased in the three soils under manure application (p < 0.05), but little under straw and mineral amendments. The Luvic Phaeozems had much higher sequestration efficiencies of bulk SOC (27%) and its five sub-pools (5–7%) more than the Calcaric Cambisol (9%, 1–2%) and Ferralic Cambisol (9%, 0.5–1%). In contrast, Ferralic Cambisol had highest sequestration efficiency of unprotected pool (7%). The Calcaric Cambisol had divergent patterns of the six SOC pools compared with Luvic Phaeozems and Ferralic Cambisol, due to the low clay content. With the build-up of bulk SOC, the building-up abilities of non-protected, physically-, chemically- and biochemically-protected pools depended on soil type, while the building-up abilities of physico-chemically- and physico-biochemically-protected pools were convergent (12–19%) among soils. In conclusion, the Luvic Phaeozems had much higher build-up ability of bulk SOC and most sub-pools than the other two soils. With the build-up of SOC, the physico-chemically- and physico-biochemically-protected pools (most stable) had convergent response rates among soils, while the other pools had divergent response rates.Graphical

Biochemical composition of soil organic matter physical fractions under 32-year fertilization in Ferralic Cambisol

Biochemical properties of soil organic matter (SOM) are fundamental for soil fertility and health. However, it is unclear how fertilization regime influences the biochemical compositions and oxidation states of SOM and physical fractions. In this study, this issue was studied under four 32-year amendment regimes: unfertilized control, urea (N), N + calcium dihydrogen phosphate + potassium chloride (NPK), and NPK plus manure (NPKM). Three physical fractions: coarse particulate (> 250 μm, cPOM), fine particulate (53–250 μm, fPOM) and mineral-associated OM (< 53 μm, MAOM) were separated and measured by pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Compared with the background in 1986, the SOM increased by 10.6%, 14.2%, 23% and 52% in unfertilized control, N, NPK, and NPKM, respectively. The red soil here had not reached carbon saturation, because of the low conversion efficiency (6.8%) from input-carbon to soil organic carbon (SOC). Physical size but not amendment type primarily regulated the SOM molecular composition, with relative selective retention of aromatics and lignin in both the cPOM and fPOM, whereas N-containing compounds (particularly amino-N) were enriched in MAOM due to their high abilities to adsorb soil minerals. The C oxidation state was also mainly dependent on physical size, with the highest value in fPOM. The sources of SOM and its fractions, dominated by microbial-derived compounds (60–90%), were independent of physical size and fertilization. In conclusion, physical size arrangement (proxy of microbial decomposition degree) played a more important role in regulating the SOM biochemical features than initial quality of various amendments.Graphical

Co‐amelioration of red soil acidity and fertility with pig manure rather than liming

AbstractLime (calcium oxide), animal manure and crop straw soil treatments have been shown to ameliorate soil acidity, yet their effectiveness at concurrently enhancing soil fertility status and improving crop yields is less well understood. In this study, an acidic nutrient deficient red soil (Ferralic Cambisol) received these treatments at various dosage rates (% of DW soil) in pot experiments with maize plants. Lime was applied at four dosage rates (0.05%, 0.10%, 0.15% and 0.20%), pig manure at three rates (0.50%, 1.00% and 1.50%), maize straw or milk vetch at two rates (0.50% and 1.00%) and combinations of lime (0.10% or 0.15%) with maize straw (0.50%) and/or pig manure (0.50%). Soils treated with and without chemical fertilizers were also included as controls. Measurements of soil pH, exchangeable acidity, plant available nutrients and maize shoot biomass were recorded. Maize shoot biomass increased by 4.7–7.6 times under pig manure treatments, 1.1–1.6 times under milk vetch, 0.4–1.5 times under lime and 1.1–6.2 times under combination treatments, compared with the control. Soil pH increased by 0.5–0.9 units under lime, by 0.2–0.4 units under pig manure and by 0.7 pH units under the combination treatment relative to the control. Variance partitioning analysis showed that on an individual basis, soil acidity amelioration (pH, exchangeable H+ and Al3+) or nutrient input (C, N, P, K, Ca, Mg, Zn) explained only 4.3% and 5.6% of improved maize growth, respectively. Whereas, their interaction explained 85.9% of the variation. We also report that the over‐application of pig manure could lead to P saturation and negative impacts on aquatic systems in the wider environment. Therefore, we recommend a combination of lime, pig manure and straw provides an optimal solution for addressing soil acidity and limiting P saturation in acid soils.

The impact of alternate wetting and drying and continuous flooding on antimony speciation and uptake in a soil-rice system

The accumulation of trace elements in rice, such as antimony (Sb), has drawn special attention owing to the potential increased risk to human health. However, the effects of two common irrigation methods, alternate wetting and drying and continuous flooding, on Sb behaviors and subsequent accumulation in rice is unclear. In this study a pot experiment with various Sb additions (0, 50, 200, 1000 mg Sb kg−1) was carried out with these two irrigation methods in two contrasting paddy soils (an Anthrosol and a Ferralic Cambisol). The dynamics of Sb in soil porewater indicated that continuous flooding generally immobilized more Sb than alternate wetting and drying, concomitant with a pronounced reduction of Sb(V) in porewater. However, a higher phytoavailable fraction of Sb was observed under continuous flooding. The content of Sb in the rice plant decreased in the order of root > shoot > husk > grain, and continuous flooding facilitated Sb accumulation in rice root and shoot as compared with alternate wetting and drying. The differences of Sb content in root, shoot, and husk between the two irrigation methods was smaller in aboveground parts, and almost no difference in Sb was observed in grain between the two methods. The findings of this study facilitates the understanding of Sb speciation and behavior in soils with these common yet different water management regimes.

Chemistry and Oxidation State of Soil Organic Matter Fractions Under Long-Term Mineral and Manure Amendments in Ferralic Cambisol

Chemical properties of organic matter are fundamental for soil fertility. However it is unclear how physical size and fertilization regime shifts the chemical composition and oxidation state of soil organic matter (SOM). Here we studied this issue among three physical size classes under four 32-years amendments: control (unfertilized), urea (N), urea+Ca(H2PO4)2+KCl (NPK), and NPK + pig manure (NPKM). Coarse particulate (cPOM, >250 μm), fine particulate (fPOM, 53–250 μm) and mineral-associated OM (MAOM, <53 μm) fractions were separated and analyzed by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Over the 32-years, the SOM of control, N, NPK and NPKM increased by 10.6%, 14.2%, 23% and 52% compared with the initial level, respectively. The conversion efficiency from fertilization-induced input-C to soil organic carbon (SOC) was 6.8%. Physical size but not fertilization primarily regulated the molecular composition of SOM, with relative selective retention of aromatics and lignin in cPOM and fPOM, whereas N-containing compounds, especially amino-N, were enriched in MAOM because of their high chemical affinities to minerals. The C oxidation state was also mainly dependent on physical size, with the highest value in fPOM. The sources of SOM and its fractions, dominated by microbial-derived compounds (60-90%), were independent on physical size and fertilization. In conclusion, physical size, not amendment regime, primarily regulated the chemical composition and oxidation state of SOM, suggesting that physical fractionation (proxy of microbial decomposition degree) plays greater role in SOM chemistry than the quality of amendments.

Organic amendments stimulate co-precipitation of ferrihydrite and dissolved organic matter in soils

Ferrihydrite-organic matter (OM) complexes in soil play a vital role in preserving soil organic carbon (C), either through adsorption (reaction of OM with existing ferrihydrite) or co-precipitation (neo-formation of ferrihydrite in the presence of OM). However, there is still limited understanding of the effects of long-term fertilization on the pathways for the formation of ferrihydrite-OM in soil. In this study, the dissolved OM (DOM) extracted from a Ferralic Cambisol under 25-year inorganic nitrogen (N), phosphorus (P) and potassium (K) (NPK) or NPK plus organic pig manure (NPKM) was used to synthesize adsorption complexes and co-precipitates. Compared with the adsorption, the co-precipitation of ferrihydrite and DOM resulted in higher C/Fe ratios in the solid products, particularly under NPKM. Analysis of the iron K-edge X-ray absorption near-edge fine structure (XANES) showed that there was a preference for DOM from soil under NPKM treatment to co-precipitate with ferrihydrite, whereas adsorption of ferrihydrite on DOM was more likely with the long-term NPK fertilized soil. Fourier-transform infrared (FTIR) spectra suggested that a higher intensity of Si-O functional groups, clay minerals, and aromatic groups in the DOM from the NPKM treatment played important roles in the co-precipitation process. Desorption of co-precipitated OM was lower than that of adsorbed OM in soils, indicating a higher chemical stability of OM in the co-precipitates. In summary, our results demonstrate that 25-year long-term NPK and NPKM fertilizations have contrasting effects on the formation pathway of ferrihydrite-OM complexes. Organic amendments can stimulate the co-precipitation of DOM and ferrihydrite in soil, leading to greater biological C preservation than the adsorption process, and a further enhancement of long-term SOC protection.

Post-agricultural restoration of soil organic carbon pools across a climate gradient

Post-agricultural natural restoration is a worldwide strategy for eco-environmental sustainability. However, it is unclear how it affects soil organic carbon (SOC) pools and composition among soil types across climate gradient. Here, we investigated 23-year post-agricultural restorations of SOC in three soils: Luvic Phaeozem, Calcaric Cambisol and Ferralic Cambisol typical for mid-temperate, warm-temperate and subtropical zones, respectively. Six SOC fractions with different protection mechanisms (non-protected, physically, chemically, biochemically, physico-chemically and physico-biochemically) were separated. Compared with pre-restoration in 1990, post-agricultural restoration rebuilt SOC similarly (+68–+91%) among the three soils despite of different SOC background. Compared with continuous cultivation, post-agricultural restoration increased total SOC pools in all the three soils (+33–+60%) mainly because of the increments of non-protected pool (coarse particulate organic C, cPOC). However, the pure physically, chemically, and biochemically protected SOC fractions were less sensitive to post-agricultural restoration. The physico-biochemically protected SOC was hampered by restoration in the two temperate soils but remained stable in the subtropical soil, suggesting a divergent self-restoring trend. Positive correlations of the total SOC and most fractions with wetness (precipitation/temperature ratio) demonstrated the climate dependency of SOC. In conclusion, post-agricultural natural restoration builds up SOC pool mainly due to the cPOC increment and shifts SOC composition towards more easily available C in three soils across the climatic gradient.

Striking a balance between N sources: Mitigating soil acidification and accumulation of phosphorous and heavy metals from manure

Manure amendment has been shown to effectively prevent red soil (Ferralic Cambisol) acidification from chemical nitrogen (N) fertilization. However, information is lacking on how much manure is needed to mitigate acidification and maintain soil productivity while preventing accumulation of other nutrients and heavy metals from long-term inputs. This study determined the effects of various combinations of manure with urea-N on acidification and changes in soil P, K, and heavy metals in a 9-year maize field experiment in southern China. Treatments included chemical N, P and K fertilization only (NPKM0), and NPK plus swine manure, which supplied 20% (NPKM20), 40% (NPKM40), and 60% (NPKM60) of total N at 225 kg N ha−1 year−1. Soil pH, exchangeable acidity, available P and K, and maize yield were determined annually from 2009 to 2018. Soil exchangeable base cations, total and phytoavailable Cr, Pb, As, Ni, Cd, Cu, and Zn were measured in 2018. A significant decrease in soil pH occurred under NPKM0 and NPKM20 from initial 4.93 to 4.46 and 4.71, respectively. Whereas, under NPKM40 and NPKM60 no change or a significant increase in soil pH (to 5.47) occurred, as well as increased exchangeable base cations, and increased yields. Manure application markedly increased soil available P (but not K) to 67.6–182.6 mg kg−1 and significantly increased total Pb, Cu, and Zn and available Cu and Zn in soil. The results indicate sourcing 40% or greater of total N from manure can prevent or reverse acidification of red soil, and provide all P required, however, additional K inputs are required for balanced plant nutrient supply. An integrated approach of increasing N use efficiency, reducing chemical input, and reducing heavy metal concentrations in animal feed are all necessary for sustainable use of manure in soil acidity and nutrient management as well as minimizing environmental risks.

Unexpected bulk density and microstructures response to long-term pig manure application in a Ferralic Cambisol Soil: Implications for rebuilding a healthy soil

Excessive applications of chemical fertilizers (e.g., nitrogen fertilizers) result in soil degradation, while organic manure application can alleviate soil degradation and rebuild a healthy soil. However, the effect of organic manure application on alleviating soil degradation over long-term fertilization remains poorly understood. Using soils (Ferralic Cambisol) that had been collected from a long-term fertilization experiment for 23 years (1990 − 2013) in subtropic South China, we showed that soil organic carbon (SOC) stocks increased by 2.5 times following 23 years of manure fertilizations (pig manure or a combination of manure and chemical fertilizers) or by 1.4 − 1.8 times following non-manure fertilizations, compared to the initial SOC stock in 1990. Strikingly, soil bulk density after 23 years fertilizations decreased in the order: 1.41 g cm−3 (manure) > 1.26 g cm−3 (no fertilizer) > 1.12 g cm−3 (chemical fertilizer), suggesting that long-term manure fertilization increased soil bulk density when compared to the non-manure treatments. The X-ray micro-computed tomography further demonstrated that compared to the non-manure treatments, manure fertilizations decreased the number of pores, throats and paths as well as porosity. In addition, the stock of oxalate-extractable Al and Fe increased by 2 times following 23 years of manure fertilizations, relative to the initial soil. In summary, this study for the first time showed that changes in mineral reactivity impact soil physical properties and the potential of soils to stabilize C, strengthening the possibility in alleviating soil degradation and rebuilding a healthy soil.

Decarboxylation of organic anions to alleviate acidification of red soils from urea application

Decarboxylation of organic anions in crop straw is recognized as one of the mechanisms for increasing pH in acidified soils. However, the effectiveness of specific compounds in alleviating soil acidification from nitrification has not been well determined. This study examined three organic anions commonly found in crop straws and their effect on soil acidity and N transformation processes following urea application to a red soil (Ferralic Cambisol). A 35-day incubation experiment was conducted using soil after receiving 26 years of two different nutrient treatments: (1) chemical nitrogen, phosphorus, and potassium fertilization (NPK, pH 4.30) and (2) NPK plus swine manure (NPKM, pH 5.88). Treatments included three rates (0.25, 0.5, and 1.0 g C kg−1) of calcium citrate, 0.5 g C kg−1 calcium oxalate, 0.5 g C kg−1 calcium malate, urea-only (control) soil, and a non-treated soil as a reference. Soil acidity, mineral N species, decarboxylation, and their correlations were determined. All three organic anions significantly increased pH in both soils and the effectiveness was positively correlated with application rate. The change in total exchangeable soil acidity was dominated by aluminum concentration in the NPK soil, but by proton concentration in the NPKM soil. At ≥ 0.5 g C kg−1, the anions decreased soil exchangeable acidity by 25–68% in NPK soil and by 63–88% in NPKM soil as compared with control. Oxalate was the most effective in increasing soil pH by 0.70 and 1.31 units and reducing exchangeable acidity by 3.79 and 0.33 cmol(+) kg−1 in NPK and NPKM soils, respectively, and also resulted in the highest CO2 production rate. Addition of organic anions led to a lower nitrification rate in NPKM soil relative to the NPK soil. These results imply that crop straws rich in organic anions, especially oxalate, would have a higher potential to alleviate soil acidification.

Long-Term Mineral Fertilization Improved the Grain Yield and Phosphorus Use Efficiency by Changing Soil P Fractions in Ferralic Cambisol

Elevated mineral fertilization may change the composition and increase the availability of soil phosphorus (P) in subtropical paddy soils and thus affect long-term plant growth. However, an understanding of the response of soil P fractions to long-term nitrogen, phosphorus and potassium (NPK) additions remains elusive. This study aimed to explore the responses of soil P-fractions and their mobility to different long-term chemical fertilization rates under a double rice cropping system. The rates of nitrogen (N), phosphorus (P), and potassium (K) in the low NPK treatment (LNPK) were 90, 45, and 75 kg ha−1 year−1, respectively, and in the high NPK treatment (HNPK), they were 180, 90, and 150 kg ha−1 year−1, respectively. The results showed that the concentrations of soil organic matter (SOM), total P, Olsen P, total N, and mineral N were remarkably increased under HNPK by 17.46%, 162.66%, 721.16%, 104.42%, and 414.46%, respectively, compared with those under control (CT). Compared to the CT P fractions, HNPK increased the labile P fractions (i.e., NaHCO3-Pi and NaHCO3-Po) by 322.25% and 83.53% and the moderately labile P fractions (i.e., NaOH-Pi, NaOH-Po and HCl. dil. Pi) by 163.54%, 183.78%, and 3167.25% respectively, while the non-labile P was decreased by the HNPK addition. P uptake and grain yield were increased by LNPK and HNPK by 10.02% and 35.20%, respectively, compared with CT. P use efficiency indices were also higher under HNPK than under LNPK. There was a strong positive relationship between grain yield and P use efficiency (R2 = 0.97). A redundancy analysis (RDA) showed a strong correlation between soil chemical properties and the labile and moderately labile P pools. Structural equation modeling (SEM) revealed that SOM, mineral N, and available P strongly control the labile P pool. In conclusion, NPK additions under the paddy soils significantly influences the soil P fractions. The soil P dynamics and the mechanisms governing the interactions between plants and soil nutrients are clearly explained in this study.

Fertilizer types shaped the microbial guilds driving the dissimilatory nitrate reduction to ammonia process in a Ferralic Cambisol

Dissimilatory nitrate reduction to ammonia (DNRA) is one of the three processes of soil nitrate reduction. However, relationships between DNRA microbes and nutrient fertilization are poorly known. We studied the DNRA microbial community in a Ferralic Cambisol containing plots including control without fertilization, swine manure fertilization (M), chemical fertilization (NPK), and chemical/manure combined fertilization (MNPK) treatments. The abundance of DNRA microbes, represented by the nrfA gene abundance, ranged from 2 × 107 to 5.8 × 107 g−1 dry soil and was positively correlated with soil moisture and total phosphorus (TP) and negatively correlated with NH4+ and total potassium (TK). The potential DNRA rate ranged from 0.5 to 1.5 μg N g−1 dry soil h−1. The α-diversity of the DNRA bacteria increased in the M-treated plots, and the dominant DNRA bacterial OTUs were assigned to the phyla Proteobacteria, Verrucomicrobia and Acidobacteria. PCoA and redundancy analysis indicated that the composition of the DNRA bacteria was strongly impacted by the long-term fertilization regimes and was associated with pH, TN, TP and TC followed by moisture, NH4+ and C/NO3−. Interestingly, the composition of the DNRA bacterial community, the properties of the soil (TP, AK and C/N) and the interactions of these factors (soil properties × DNRA composition) explained the DNRA rate. Collectively, these data suggested that the DNRA potential in the Ferralic Cambisol is possibly controlled by the stoichiometry of macronutrient and the composition of DNRA microbes but not their total abundance.

Effects of Italian ryegrass residues as green manure on soil properties and bacterial communities under an Italian ryegrass (Lolium multiflorum L.)-rice (Oryza sativa L.) rotation

Green manure shows promise for the relief of the environmental pressure caused by successive farming and excessive applications of fertilizers. Soil microbes play an important role in the decomposition of green manure. However, few studies focused on the relationship between the release of nutrients and bacterial community diversity when different rates of green manure are applied. The aim of this study was to evaluate the dynamic changes in soil bacterial communities and nutrient release during the decomposition of the green manure Italian ryegrass (Lolium multiflorum L.) residues in a new type Italian ryegrass-rice (Oryza sativa L.) rotation (IRR) system in South China. Six different rates (P0–P5) of Italian ryegrass were added to rice-growing red soil (Ferralic Cambisol) and allowed to decompose for 40 d (sampled every 10 d). Nutrient release and soil properties were determined during the decomposition and Illumina reads of the 16S rRNA gene amplicons were used to analyse changes in the bacterial communities. The addition of residues increased both nutrient concentrations (e.g., total nitrogen, available nitrogen and available potassium) and the relative abundance of microbes involved in nutrient cycling (e.g., Proteobacteria, Bacteroidetes, Acidobacteria, and Gemmatimonadetes). Italian ryegrass residues had much faster rates of decomposition at 1–10 d, 11–20 d, and 21–30 d (from 183.2 to 238.1 g kg–1, on average) than that (45.6 g kg–1) at 31–40 d. Overall, the high green manure decomposition rates were accompanied by high similarities in bacterial community structures during decomposition. The nutrient cycle efficiency and bacterial community diversity were higher when the soils were treated with 40,170–44,895 kg ha–1 (P3–4) of green manure than other treatments. The average Shannon index values following the 44,895 kg ha–1 (P4) treatment were the highest among the different rates of residue application, and they were 6.42 at 10 d, 6.37 at 20 d, 6.29 at 30 d, and 6.53 at 40 d. The highest soil total nitrogen concentrations of 1.4–2.0 g kg–1 were obtained following the 40,170 kg ha–1 (P3) treatment, and seedling biomass increased the most under P3 treatment. In addition, soil total nitrogen and available potassium concentrations were significantly correlated with rice seedling biomass. This study demonstrates that the management of green manure application based on the IRR system facilitates rice growth by improving bacterial communities (composition and diversity) and soil fertility, and it provides a new perspective on the links between potential microbial community functions and organic agro-ecosystems.

A new strategy for assessing the binding microenvironments in intact soil microaggregates

Adsorption to soil minerals and occlusion within soil aggregates are two critical mechanisms to shield soil organic carbon (SOC) from microbial decomposition. Here, we combined the synchrotron radiation based Fourier transform infrared (SR-FTIR) spectroscopy, synchrotron radiation based micro X-ray fluorescence microscopy (μ-XRF) and two-dimensional correlation spectroscopy (2DCOS) analysis to in situ visualize the interiors of intact microaggregates from a typical Ferralic Cambisol in China, which had endured 25-year organic fertilization. Results showed that the spatial distribution and correlation between clay clusters and biopolymers were heterogeneous and significant, and also demonstrated that clay clusters were associated as nuclei with the potential of binding carbon at the submicron scale. Furthermore, the combination of SR-FTIR mapping and 2DCOS analysis could explore the strategy of identifying overlapped spectra and quantifying the sequestration reactivity for the first time. Specifically, carbon retention correlated as the binding sequence orders: 3630 cm−1 > 3610 cm-1, 985 cm-1 > 898 cm-1, indicating that Fe/Al oxyhydroxides and phyllosilicates could regulate the organic matter sequestration without the influence of spatial perturbations. Together, we conclude a combined methodology to assess the heterogeneous binding microenvironments between the mineral assemblages and biopolymers, which could also contribute to understand the process of carbon sequestration interrestrial ecosystems.

Strategy for Microscale Characterization of Soil Mineral‐Organic Associations by Synchrotron‐Radiation‐Based FTIR Technology

Core Ideas The spatial arrangements of soil MOAs are highly heterogeneous. The processes of carbon binding in different soil types are different. Combination of SR‐FTIR mapping and 2DCOS could in situ characterize the sequences of MOAs. Direct characterization of spatial distribution and binding environments of soil mineral‐organic associations (MOAs) are imperative for understanding the mechanism of C storage. Here, we propose a new strategy of synchrotron‐radiation‐based Fourier transform‐infrared (SR‐FTIR) technology and two‐dimensional FTIR correlation spectroscopy (2DCOS) analysis to simultaneously characterize the MOAs extracted from two types of soil, which one is classiðed as Ferralic Cambisol and another is Typic Hapludoll. This study successfully showed the spatial heterogeneity by SR‐FTIR mapping, which illustrated that the different soil types had different spatial arrangements at the microscale scale. Moreover, the overlapped one‐dimensional (1D) SR‐FTIR spectra and various sequence orders in two types of soil were demonstrated by 2DCOS analysis. The results showed that the intra hydrogen bonds in clay‐OH minerals and Si‐O‐metal bonds were more highly reactive in the Ferralic Cambisol soils than that in the Typic Hapludoll soils, which was critical for understanding the binding processes in soil micro‐environments.

Effectiveness of crop straws, and swine manure in ameliorating acidic red soils: a laboratory study

Crop straws and animal manure have the potential to ameliorate acidic soils, but their effectiveness and the mechanisms involved are not fully understood. The aim of this study was to evaluate the effectiveness of two crop (maize and soybean) straws, swine manure, and their application rates on acidity changes in acidic red soils (Ferralic Cambisol) differing in initial pH. Two red soils were collected after 21 years of the (1) no fertilization history (CK soil, pH 5.46) and (2) receiving annual chemical nitrogen (N) fertilization (N soil, pH 4.18). The soils were incubated for 105 days at 25 °C after amending the crop straws or manure at 0, 5, 10, 20, and 40 g kg−1 (w/w), and examined for changes in pH, exchangeable acidity, N mineralization, and speciation in 2 M KCl extract as ammonium (NH4+) and nitrate plus nitrite (NO3− + NO2−). All three organic materials significantly decreased soil acidity (dominated by aluminum) as the application rate increased. Soybean straw was as effective (sometimes more effective) as swine manure in raising pH in both soils. Soybean straw and swine manure both significantly reduced exchangeable acidity at amendment rate as low as 10 g kg−1 in the highly acidic N soil, but swine manure was more effective in reducing the total acidity especially exchangeable aluminum (e.g., in the N soil from initial 5.79 to 0.50 cmol(+) kg−1 compared to 2.82 and 4.19 cmol(+) kg−1 by soybean straw and maize straw, respectively). Maize straw was less effective than soybean straw in affecting soil pH and the acidity. The exchangeable aluminum decreased at a rate of 4.48 cmol(+) kg−1 per pH unit increase for both straws compared to 6.25 cmol(+) kg−1 per pH unit from the manure. The NO3− + NO2− concentration in soil increased significantly for swine manure amendment, but decreased markedly for straw treatments. The high C/N ratio in the straws led to N immobilization and pH increase. While swine manure continues to be effective for ameliorating soil acidity, crop straw amendment has also shown a good potential to ameliorate the acidity of the red soil. Thus, after harvest, straws should preferably not be removed from the field, but mixed with the soil to decelerate acidification. The long-term effect of straw return on soil acidity management warrants further determination under field conditions.

Manure amendment increases the content of nanomineral allophane in an acid arable soil

Natural nanoparticles are of central importance in the environment, e.g. sorption of soil organic carbon (SOC) and contaminants. A large number of study have focused on the metal binding, transport and ecotoxicity of nanoparticles. Fertilizer amendments are routinely applied to arable soils and induce changes in soil chemical, physical and biological properties. However, the effects of fertilizer amendments on natural nanoparticles are still unknown. In this study, soil nanoparticles were separated from acid red soil (Ferralic Cambisol) including long-term (26 years) treatments of unfertilized control (CK), chemical nitrogen, phosphorus and potassium fertilizers (NPK) and raw pig manure (M). The results from high-resolution transmission electron microscopy (HRTEM) and Fourier-transformed infrared (FTIR) spectroscopy indicated that nanoparticles in red soil were heterogeneous organo-mineral associations with irregular shapes, regardless of fertilization history. In addition, kaolinite and allophane occurred in the soil nanoparticles. Intriguingly, we found the content of allophane under M treatment (0.64 g kg−1) was much higher than under CK and NPK treatments. However, the CK (0.27 g kg−1) and NPK (0.21 g kg−1) had similar allophane concentrations. Our study may indicate long-term organic manure amendment initializes positive feedback loop for further SOC sequestration. However, the mechanisms for the enhancement of nanomineral allophane by manure amendment deserve further investigation.

Nitrogen mobility, ammonia volatilization, and estimated leaching loss from long-term manure incorporation in red soil

Nitrogen (N) loss from fertilization in agricultural fields has an unavoidable negative impact on the environment and a better understanding of the major pathways can assist in developing the best management practices. The aim of this study was to evaluate the fate of N fertilizers applied to acidic red soil (Ferralic Cambisol) after 19 years of mineral (synthetic) and manure fertilizer treatments under a cropping system with wheat-maize rotations. Five field treatments were examined: control (CK), chemical nitrogen and potash fertilizer (NK), chemical nitrogen and phosphorus fertilizer (NP), chemical nitrogen, phosphorus and potash fertilizer (NPK) and the NPK with manure (NPKM, 70% N from manure). Based on the soil total N storage change in 0–100 cm depth, ammonia (NH3) volatilization, nitrous oxide (N2O) emission, N plant uptake, and the potential N leaching loss were estimated using a mass balance approach. In contrast to the NPKM, all mineral fertilizer treatments (NK, NP and NPK) showed increased nitrate (NO3−) concentration with increasing soil depth, indicating higher leaching potential. However, total NH3 volatilization loss was much higher in the NPKM (19.7%) than other mineral fertilizer treatments (≤4.2%). The N2O emissions were generally low (0.2–0.9%, the highest from the NPKM). Total gaseous loss accounted for 1.7, 3.3, 5.1, and 21.9% for NK, NP, NPK, and NPKM treatments, respectively. Estimated N leaching loss from the NPKM was only about 5% of the losses from mineral fertilizer treatments. All data demonstrated that manure incorporation improved soil productivity, increased yield, and reduced potential leaching, but with significantly higher NH3 volatilization, which could be reduced by improving the application method. This study confirms that manure incorporation is an essential strategy in N fertilization management in upland red soil cropping system.

Long-term organic-inorganic fertilization ensures great soil productivity and bacterial diversity after natural-to-agricultural ecosystem conversion

Natural ecosystems comprise the planet's wild plant and animal resources, but large tracts of land have been converted to agroecosystems to support the demand for agricultural products. This conversion limits the number of plant species and decreases the soil biological diversity. Here we used high-throughput 16S rRNA gene sequencing to evaluate the responses of soil bacterial communities in long-term converted and fertilized red soils (a type of Ferralic Cambisol). We observed that soil bacterial diversity was strongly affected by different types of fertilization management. Oligotrophic bacterial taxa demonstrated large relative abundances in chemically fertilized soil, whereas copiotrophic bacterial taxa were found in large relative abundances in organically fertilized and fallow management soils. Only organic-inorganic fertilization exhibited the same local taxonomic and phylogenetic diversity as that of a natural ecosystem. However, the independent use of organic or inorganic fertilizer reduced local taxonomic and phylogenetic diversity and caused biotic homogenization. This study demonstrated that the homogenization of bacterial communities caused by natural-to-agricultural ecosystem conversion can be mitigated by employing rational organic-inorganic fertilization management.

Swine manure and quicklime have different impacts on chemical properties and composition of bacterial communities of an acidic soil

Red soil is a kind of Ferralic Cambisol. Good hydrothermal resources but usually acidic and low base saturation make it very easy to be acidified under unreasonable fertilizer managements in agricultural area. In 1990, a series of fertilizer applications were established on a homogeneous field to investigate the soil fertility changes under different fertilizations in Hunan province, among them, long-term chemical nitrogen fertilization (NPK) induced severe soil acidification, whereas long-term chemical plus swine manure fertilization (NPKM) exhibited an overwhelming advantage in terms of nutrient concentration and bacterial diversity. In 2010, to investigate the effect of short-term quicklime and swine manure applications on the acid red soil, a remediation experiment was established on the NPK treatment. Quicklime (CaO) and swine manure (the same as the swine manure in NPKM) applications on NPK soil had different effects on remediating the soil acidification: short-term quicklime application (NPK+Ca) increased soil pH and bacterial diversity more rapidly, whereas short-term swine manure application (NPK+M) improved soil nutrient concentration more effectively. Alteration of environmental conditions caused significant changes of bacterial community: oligotrophic groups were in greater relative abundances with quicklime treatment, whereas copiotrophic groups were in greater relative abundances with swine manure treatment. This study provides insights into the two major remediation approaches for an acidic red soil; these insights are important for soil remediating and improving fertility. Taken together, we recommended short-term quicklime application to increase the soil pH quickly and long-term swine manure fertilization to improve soil fertility.