scholarly journals Key predictors of soil organic matter vulnerability to mineralization differ with depth at a continental scale

2021 ◽  
Author(s):  
Tyler L. Weiglein ◽  
Brian D. Strahm ◽  
Maggie M. Bowman ◽  
Adrian C. Gallo ◽  
Jeff A. Hatten ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Field Capacity ◽  
Climate Feedbacks ◽  
Organic C ◽  
Continental Scale ◽  
Broad Array ◽  
The Relationship ◽  
Boruta Algorithm ◽  
Som Decomposition

AbstractSoil organic matter (SOM) is the largest terrestrial pool of organic carbon, and potential carbon-climate feedbacks involving SOM decomposition could exacerbate anthropogenic climate change. However, our understanding of the controls on SOM mineralization is still incomplete, and as such, our ability to predict carbon-climate feedbacks is limited. To improve our understanding of controls on SOM decomposition, A and upper B horizon soil samples from 26 National Ecological Observatory Network (NEON) sites spanning the conterminous U.S. were incubated for 52 weeks under conditions representing site-specific mean summer temperature and sample-specific field capacity (−33 kPa) water potential. Cumulative carbon dioxide respired was periodically measured and normalized by soil organic C content to calculate cumulative specific respiration (CSR), a metric of SOM vulnerability to mineralization. The Boruta algorithm, a feature selection algorithm, was used to select important predictors of CSR from 159 variables. A diverse suite of predictors was selected (12 for A horizons, 7 for B horizons) with predictors falling into three categories corresponding to SOM chemistry, reactive Fe and Al phases, and site moisture availability. The relationship between SOM chemistry predictors and CSR was complex, while sites that had greater concentrations of reactive Fe and Al phases or were wetter had lower CSR. Only three predictors were selected for both horizon types, suggesting dominant controls on SOM decomposition differ by horizon. Our findings contribute to the emerging consensus that a broad array of controls regulates SOM decomposition at large scales and highlight the need to consider changing controls with depth.

Maximum soil organic matter decomposition along temperature gradient in Colombian topsoils: Dry Forests

2021 ◽  
Author(s):  
Gerardo Ojeda ◽  
Hernando García ◽  
Susanne Woche ◽  
Jorg Bachmann ◽  
Georg Guggenberger ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Organic Carbon ◽  
Temperature Gradient ◽  
Soil Organic Carbon ◽  
Soil Respiration ◽  
Maximum Rate ◽  
Field Capacity ◽  
Total Carbon ◽  
Som Decomposition

<p><strong>Contextualization</strong>: In 2011, it was published a curious conundrum, which forms the basis of the present study: why, when organic matter is thermodynamically unstable, does it persist in soils, sometimes for thousands of years? The question challenges the idea that the recalcitrant or labile character of soil organic matter (SOM) is a sufficient argument to ensure SOM persistence. Temperature could play an important role in SOM decomposition, especially in tropics. Particularly, tropical dry forest (TDF) represents an important ecosystem with unique biodiversity and fertile soils in Colombia. At present, the increase in population density and consequently, in the demands of energy and arable land, have led to its degradation.</p><p> </p><p><strong>Knowledge gap</strong>: Although the mentioned question was formulated several years ago, it has still to be answered, hence limiting the development of new soil organic carbon (SOC) models or the quantification of its ecosystem services. A key point, in terms of soil carbon storage, is to determine the maximum rate of CO<sub>2</sub> emissions from soils (Rmax). Traditionally, it is considered that Rmax occurs at the 50% of field capacity. Unfortunately, information about the environmental conditions under which this maximum occurs is scarce.</p><p><strong> </strong></p><p><strong>Purpose</strong>: The main objectives of this study were: (a) determine the maximum rate of soil respiration or CO<sub>2</sub> emissions from soil in TDF soils and (b) to estimate the main environmental drivers of maximum SOM decomposition along a temperature gradient (20°, 30°, 40°C) in incubated soils.</p><p><strong> </strong></p><p><strong>Methodology</strong>: Soils pertained to permanent plots were sampled in six different TDF of Colombia. The evolution of CO<sub>2</sub> emissions (monitored by an infrared gas analyser), relative humidity and soil temperature were recorded in time on incubated soils samples. Temperature was maintained constant at 20°C, 30°C and 40°C during soil incubations under soil drying conditions. Additionally, elemental composition (Fe, Ca, O, Al, Si, K, Mg, Na) of SOM and chemical composition of soil organic carbon (SOC: aromatic-C, O-alkyl-C, Aliphatic-C, Phenolic and Ketonic-C) were determined by X-ray photoelectron spectroscopy (XPS).</p><p><strong> </strong></p><p><strong>Results and conclusions</strong>: The majority of TDF soil samples (90.7%) presented that its peak of CO<sub>2</sub> emissions occurs at soil-water contents higher than saturation (0 MPa), at 20°, 30° and 40°C. Clearly, to consider that the maximum soil respiration rate could be observed at the 50% of field capacity, underestimated the real maximum value of carbon mineralization (48-68%.) Globally, increases in the Rmax values corresponded to increases in electrical conductivity, soil desorption rates, total carbon and nitrogen contents, and decreases in bulk density (BD) and aggregate stability. Taking into account the temperature gradient, increments in calcium and aromatic carbon contents corresponded to decrements in Rmax values but only at 30°C and 40°C, respectively. Some authors indicated that at high soil moisture contents, iron reduction could be release protected carbon. However, no significant relation between Fe and Rmax was observed. Consequently, physical and chemical properties related to SOM accessibility and decomposability by microbial activity, were the main drivers and controls of maximum SOM decomposition rates.</p>

Carbon and nitrogen mineralization in soil treated with chloride and phosphate salts

1999 ◽  
Vol 79 (3) ◽  
pp. 427-429 ◽  
Author(s):  
D. Curtin ◽  
H. Steppuhn ◽  
C. A. Campbell ◽  
V. O. Biederbeck
Keyword(s):  
Organic Matter ◽  
Field Capacity ◽  
Organic C ◽  
Treated Soil ◽  
Carbon And Nitrogen ◽  
Inhibition Of Nitrification ◽  
Chloride Sulfate ◽  
C And N ◽  
Phosphate Salts ◽  
The Relationship

This study was undertaken to characterize the response of organic matter mineralization to soluble electrolyte concentration. We added salts (either KCl or KH2PO4) to a non-saline Black Chernozem at rates of 0 to 64 mmol kg−1 and measured the amounts of C and N mineralized in a 40 d incubation (21 °C and field capacity). Precipitation of calcium phosphate in KH2PO4-treated soil resulted in electrical conductivity (EC), measured in a 1:2 soil:water extract, being lower than in KCl-treated soil. Dissolved organic C (DOC) was increased (up to twofold) by KH2PO4 addition but KCl had little effect. The relationship between C mineralization and EC appeared to be independent of salt type. Mineralization decreased sharply (by 50%) when EC increased from 0.5 dS m−1 (check value) to 1.3 dS m−1. Inhibition of nitrification was not detected until EC increased to about 2 dS m–1. Key words: Mineralization, organic matter, salinity, chloride, sulfate

The long-term effect of biochar on composition of soil organic matter 

2021 ◽  
Author(s):  
Sandra Pärnpuu ◽  
Karin Kauer ◽  
Henn Raave
Keyword(s):  
Organic Matter ◽  
Nmr Spectroscopy ◽  
Soil Organic Matter ◽  
Soil Samples ◽  
Bulk Soil ◽  
Organic C ◽  
Native Soil ◽  
Soil Hydrophobicity ◽  
Som Decomposition

<p>Biochar has been described as relatively stable form of C with long mean residence time due to its predominantly aromatic structure. Addition of biochar can sequester C in the soil, albeit the effect of biochar on native soil organic C decomposition, whether it stimulates or reduces the decomposition of native soil organic matter, requires further understanding. The aim of this research was to study the long-term impact of biochar (BC) on the composition of soil organic matter (SOM) in Fragi-Stagnic Albeluvisol. The work was compiled on the basis of field experiment, set up on a production field in 2011. The experiment was drawn up of two treatments and four replicates, where on half of the replicates slow-pyrolysis hardwood BC (51.8% C, 0.43% N) produced at 500-600 °C was applied 50 Mg ha<sup>-1</sup>. The soil samples were collected from 0-10 cm soil layer in autumn 2020. The air-dried samples were sieved through a 2-mm sieve and divided into two fractions: the particulate organic matter (POM) fraction (soil particles larger than 0.063 mm) and the mineral-associated organic matter (MAOM) (<0.063 mm) by density fractionation method. The soil organic carbon (SOC) and total nitrogen (Ntot) concentrations of bulk soil and fractions were measured. The chemical composition of SOM was studied using <sup>13</sup>C nuclear magnetic resonance (NMR) spectroscopy. Bulk soil samples and fractions were pretreated with 10% HF solution before NMR spectroscopy analysis. Two indices were calculated: the ratio of alkyl C/O-alkyl C, which describes the degree of SOM decomposition and soil hydrophobicity (HI): (aromatic-C+alkyl-C)/O/N-Alkyl-C.</p><p>The addition of BC to the soil increased the SOC concentration but did not influence the Ntot concentration and the soil C/N ratio increased from 11.6 to 16.7. The distribution of POM and MAOM was not affected by the BC and POM proportion accounted for an average of 57–58%. The SOC concentrations of POM and MAOM fractions were higher in the BC variant. The BC increased the proportion of aromatic-C in the SOM, as the proportion of aromatic-C in initial BC was high (almost 92%). Initially the BC is inherently highly hydrophobic and increased the HI of bulk soil, POM, and MAOM fractions. The HI increased in line: MAOM<bulk<POM (1.51<1.67<1.97). An increase in HI inhibits the decomposition of SOM and it was also confirmed by a decreased ratio of alkyl-C/O-alkyl-C after the BC addition. The decomposition degree was lowest in POM fraction where SOC concentration was more than doubled due to BC. The suppressed decomposition was caused by the limitation of soil Ntot concentration and increased C/N ratio.</p><p>In conclusion, the effect of BC on the composition of SOM was still evident after 10 years of increasing SOC concentration and soil hydrophobicity and decreasing SOM decomposition degree promoting C sequestration to the soil.</p><p>This work was supported by the Estonian Research Council grant PSG147.</p>

scholarly journals Chemical and Spectroscopic Parameters Are Equally Sensitive in Describing Soil Organic Matter Changes After Decades of Different Fertilization

Agriculture ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 422
Author(s):  
Tomáš Šimon ◽  
Mikuláš Madaras
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Field Experiments ◽  
Climatic Conditions ◽  
Hot Water ◽  
Organic C ◽  
The Czech Republic ◽  
Spectral Detection ◽  
Total Organic C ◽  
Som Decomposition

The composition and dynamics of soil organic matter (SOM) are decisive factors in soil quality. In this work, total organic C (Ctot), hot water extractable C (Chwl), and aliphatic and aromatic SOM components detected by Fourier transform infrared (FTIR) spectroscopy were determined to evaluate SOM quantity and quality in soil samples taken between 2004 and 2017 from 13 field experiments established in different soil and climatic conditions of the Czech Republic. In addition, the C pool index (CPI), lability index (LI), C management index (CMI), and SOM decomposition index (DI) were assessed. Treatments were selected as follows: Unfertilized control (Nil), mineral fertilized treatment (NPK), farmyard manured treatment (FYM), and organic and mineral fertilized treatment (FYM+NPK). Both organic and combined fertilization significantly increased soil Ctot, Chwl, CPI, LI, CMI, and labile aliphatic SOM components (FTIRaliph) in most of the experiments compared to unfertilized treatments (p ≤ 0.05). In contrast, the highest content of recalcitrant aromatic SOM components (FTIRarom) and increased DI were determined in majority of unfertilized soils. Our results show that: (1) fertilization regimes increased both labile and total C pools; the highest increase was nearly uniformly observed for NPK+FYM treatment; (2) SOM chemical and FTIR spectral detection had equal sensitivity to the changes; and (3) none of the parameters or indices tested can be used as a stand-alone SOM quality descriptor.

scholarly journals Fractionation of Heavy Metals in Multi-Contaminated Soil Treated with Biochar Using the Sequential Extraction Procedure

Biomolecules ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 448
Author(s):  
Mahrous Awad ◽  
Zhongzhen Liu ◽  
Milan Skalicky ◽  
Eldessoky S. Dessoky ◽  
Marian Brestic ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Ph ◽  
Contaminated Soil ◽  
Contaminated Soils ◽  
Extraction Procedure ◽  
Sequential Fractionation ◽  
Relationship Of ◽  
The Relationship

Heavy metals (HMs) toxicity represents a global problem depending on the soil environment’s geochemical forms. Biochar addition safely reduces HMs mobile forms, thus, reducing their toxicity to plants. While several studies have shown that biochar could significantly stabilize HMs in contaminated soils, the study of the relationship of soil properties to potential mechanisms still needs further clarification; hence the importance of assessing a naturally contaminated soil amended, in this case with Paulownia biochar (PB) and Bamboo biochar (BB) to fractionate Pb, Cd, Zn, and Cu using short sequential fractionation plans. The relationship of soil pH and organic matter and its effect on the redistribution of these metals were estimated. The results indicated that the acid-soluble metals decreased while the fraction bound to organic matter increased compared to untreated pots. The increase in the organic matter metal-bound was mostly at the expense of the decrease in the acid extractable and Fe/Mn bound ones. The highest application of PB increased the organically bound fraction of Pb, Cd, Zn, and Cu (62, 61, 34, and 61%, respectively), while the BB increased them (61, 49, 42, and 22%, respectively) over the control. Meanwhile, Fe/Mn oxides bound represents the large portion associated with zinc and copper. Concerning soil organic matter (SOM) and soil pH, as potential tools to reduce the risk of the target metals, a significant positive correlation was observed with acid-soluble extractable metal, while a negative correlation was obtained with organic matter-bound metal. The principal component analysis (PCA) shows that the total variance represents 89.7% for the TCPL-extractable and HMs forms and their relation to pH and SOM, which confirms the positive effect of the pH and SOM under PB and BB treatments on reducing the risk of the studied metals. The mobility and bioavailability of these metals and their geochemical forms widely varied according to pH, soil organic matter, biochar types, and application rates. As an environmentally friendly and economical material, biochar emphasizes its importance as a tool that makes the soil more suitable for safe cultivation in the short term and its long-term sustainability. This study proves that it reduces the mobility of HMs, their environmental risks and contributes to food safety. It also confirms that performing more controlled experiments, such as a pot, is a disciplined and effective way to assess the suitability of different types of biochar as soil modifications to restore HMs contaminated soil via controlling the mobilization of these minerals.

Soil stripping and replacement for the rehabilitation of bauxite-mined land at Weipa. I. Initial changes to soil organic matter and related parameters

Soil Research ◽  
2000 ◽  
Vol 38 (2) ◽  
pp. 345 ◽  
Author(s):  
G. D. Schwenke ◽  
D. R. Mulligan ◽  
L. C. Bell
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Field Experiments ◽  
Surface Soil ◽  
Soil Disturbance ◽  
Microbial Biomass C ◽  
Low Grade ◽  
Double Pass ◽  
Organic C ◽  
The Difference

At Weipa, in Queensland, Australia, sown tree and shrub species sometimes fail to establish on bauxite-mined land, possibly because surface-soil organic matter declines during soil stripping and replacement. We devised 2 field experiments to investigate the links between soil rehabilitation operations, organic matter decline, and revegetation failure. Experiment 1 compared two routinely practiced operations, dual-strip (DS) and stockpile soil, with double-pass (DP), an alternative method, and subsoil only, an occasional result of the DS operation. Other treatments included variations in stripping-time, ripping-time, fertiliser rate, and cultivation. Dilution of topsoil with subsoil, low-grade bauxite, and ironstone accounted for the 46% decline of surface-soil (0–10 cm) organic C in DS compared with pre-strip soil. In contrast, organic C in the surface-soil (0–10 cm) of DP plots (25.0 t/ha) closely resembled the pre-strip area (28.6 t/ha). However, profile (0–60 cm) organic C did not differ between DS (91.5 t/ha), DP (107 t/ha), and pre-strip soil (89.9 t/ha). Eighteen months after plots were sown with native vegetation, surface-soil (0–10 cm) organic C had declined by an average of 9% across all plots. In Experiment 2, we measured the potential for post-rehabilitation decline of organic matter in hand-stripped and replaced soil columns that simulated the DS operation. Soils were incubated in situ without organic inputs. After 1 year’s incubation, organic C had declined by up to 26% and microbial biomass C by up to 61%. The difference in organic C decline between vegetated replaced soils (Expt 1) and bare replaced soils (Expt 2) showed that organic inputs affect levels of organic matter more than soil disturbance. Where topsoil was replaced at the top of the profile (DP) and not ploughed, inputs from volunteer native grasses balanced oxidation losses and organic C levels did not decline.

Influence of soil organic matter on sulfate retention in two Podzols in Quebec, Canada

1999 ◽  
Vol 79 (1) ◽  
pp. 103-109 ◽  
Author(s):  
F. Courchesne ◽  
J.-F. Laberge ◽  
A. Dufresne
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Ammonium Oxalate ◽  
X Ray Diffraction ◽  
Weighted Mean ◽  
Fine Silt ◽  
Mineral Horizon ◽  
Organic C ◽  
X Ray

The role of soil organic matter (OM) on SO4 retention was investigated by comparing OM content, SO4 retention, and the distribution of Fe, Al and Si compounds in OM-poor (Grands-Jardins, PGJ) and OM-rich (Hermine, HER) Podzols from Québec, Canada. At both sites, four pedons were sampled by horizon; soil pH in H2O, organic C, phosphate-extractable SO4 and, sodium pyrophosphate, acid ammonium oxalate and dithionite-citrate-bicarbonate (DCB) extractable Fe, Al and Si were measured for each mineral horizon. The mineralogy of the clay (<2 µm) and fine silt (2–20 µm) fractions of selected horizons was determined by X-ray diffraction (XRD) and infrared spectroscopy (IR). Weighted mean organic C and pyrophosphate extractable Fe and Al contents were significantly higher in the HER than in the PGJ sola, while the PGJ soils were richer in amorphous inorganic Al. No trends were observed for inorganic Fe compounds. Chemical dissolution and IR allowed the identification of short-range ordered aluminosilicates, probably allophane, in the OM-poor and slightly acidic to neutral PGJ soils. These materials were absent from the OM-rich and acidic HER soils. Phosphate extractions showed that the weighted mean native SO4 content was five times higher in the PGJ than in the HER soil. Finally, native SO4 was strongly related to inorganic Fe, Al and Si (associated with allophane) at PGJ but only to inorganic Fe at HER. These results indicate that OM indirectly affects SO4 sorption through the influence organic substances exerts on the nature and distribution of pedogenic Fe, Al and Si compounds, such as allophane, in Podzolic profiles. Key words: Organic matter, sulfate, imogolite, allophane, silica, Podzol

scholarly journals Growing Food with Garbage: Effects of Six Waste Amendments on Soil and Vegetable Crops

HortScience ◽  
2017 ◽  
Vol 52 (6) ◽  
pp. 896-904 ◽  
Author(s):  
Rebecca J. Long ◽  
Rebecca N. Brown ◽  
José A. Amador
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Quality ◽  
Organic Waste ◽  
Sweet Corn ◽  
Mineral Fertilizer ◽  
Plant Nutrients ◽  
Chicken Manure ◽  
Organic C ◽  
Yard Waste

Using organic wastes as agricultural amendments is a productive alternative to disposal in landfills, providing nutrients for plant growth and carbon to build soil organic matter. Despite these benefits, a large fraction of organic waste is sent to landfills. Obstacles to the adoption of wastes as sources of plant nutrients include questions about harmful effects to crops or soils and the wastes’ ability to produce satisfactory yields. We compared six organic waste amendments with a mineral fertilizer control (CN) to determine effects on soil quality, soil fertility, crop quality, and crop yield in 2013 and 2014. Waste amendments were applied at a rate sufficient to supply 10,000 kg organic C/ha over two seasons, and mineral fertilizer was applied to control plots to provide 112 kg-N/ha/yr. The experiment was laid out in a randomized block design with four replicates and three crops: sweet corn (Zea mays L. cv. Applause, Brocade, and Montauk), butternut squash (Cucurbita moschata Duchesne cv. JWS 6823), and potatoes (Solanum tuberosum L. cv. Eva). Amendment with biosolids/yard waste cocompost (BS), dehydrated restaurant food waste (FW), gelatin manufacturing waste (GW), multisource compost (MS), paper fiber/chicken manure blend (PF), and yard waste compost (YW) did not have a negative impact on soil moisture, bulk density, electrical conductivity (EC), or the concentration of heavy metals in soil or plant tissue. Our results indicate potential uses for waste amendments including significantly raising soil pH (MS) and increasing soil organic matter [OM (YW and BS)]. The carbon-to-nitrogen ratio (C:N) of waste amendments was not a reliable predictor of soil inorganic N levels, and only some wastes increased potentially mineralizable nitrogen (PMN) levels relative to the control. Plots amended with BS, FW, and GW produced yields of sweet corn, butternut squash, and potatoes comparable with the control, whereas plots amended with YW, PF, and MS produced lower yields of sweet corn, squash, or both, although yields for potatoes were comparable with the control. In addition, the marketability of potatoes from PF plots was significantly better than that of the control in 2014. None of the wastes evaluated in this study had negative impacts on soil properties, some provided benefits to soil quality, and all produced comparable yields for at least one crop. Our results suggest that all six wastes have potential to be used as sources of plant nutrients.

Impact of long-term cultivation on the status of organic matter and cadmium in soil

2001 ◽  
Vol 81 (3) ◽  
pp. 349-355 ◽  
Author(s):  
D. F. E. McArthur ◽  
P M Huang ◽  
L M Kozak
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Significant Positive Correlation ◽  
Soil Organic C ◽  
Organic C ◽  
Total Soil ◽  
Total Organic C ◽  
Soil Cd ◽  
Cultivated Soils

Research has suggested a link between the bioavailability of soil Cd and total soil organic matter. However, some research suggested a negative relationship between total soil organic matter and bioavailable soil Cd while other research suggested a positive relationship. This study investigated the relationship between soil Cd and both the quantity and quality of soil organic matter as influenced by long-term cultivation. Two Orthic Chernozemic surface soil samples, one from a virgin prairie and the other from an adjacent cultivated prairie, were collected from each of 12 different sites throughout southern Saskatchewan, Canada. The samples were analyzed for total organic C, total Cd, Cd availability index (CAI), and pH. The nature of the soil organic matter was investigated with 13C Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy (13C CPMAS NMR). The total soil Cd, CAI, and total soil organic C of the cultivated soils were significantly lower than those of the virgin soils whereas the opposite trend was observed for the soil pH and the aromaticity of the organic C. The reduced CAI in the cultivated soils was related to the increase in both the soil pH and the aromaticity of the organic C. No relationship was found between the CAI and the soil organic C content, but a significant positive correlation was found between total organic C and total Cd in both the virgin and the cultivated soils. As well, a significant positive correlation was found between the fraction of total Cd removed from the soil after long-term cultivation and the corresponding fraction of organic C removed. Key words: Long-term cultivation, soil organic matter, 13C CPMAS NMR, cadmium

Changes in soil carbon under long-term maize in monoculture and legume-based rotation

2001 ◽  
Vol 81 (1) ◽  
pp. 21-31 ◽  
Author(s):  
E G Gregorich ◽  
C F Drury ◽  
J A Baldock
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Magnetic Resonance ◽  
Soil Carbon ◽  
Crop Residues ◽  
Cropping Systems ◽  
Natural Abundance ◽  
Organic C ◽  
Soil C

Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha-1. The effects of fertilization on soil C were small (~6 Mg C ha-1), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha-1 in the fertilized and 14 Mg ha-1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha-1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legume-based rotation tend to be more “preservative” of residue C inputs, particularly from root inputs, than soils under monoculture. Key words: Soil carbon, 13C natural abundance, 13C nuclear magnetic resonance, maize cropping, legumes, root carbon

Sign in / Sign up

Export Citation Format

Share Document