Effect of tillage and rotation on organic carbon forms of chernozemic soils in Saskatchewan

The effects of selected tillage and rotation systems on soil organic carbon and its fractions were studied on Chernozemic soils in south‐western and east‐central Saskatchewan. After practicing a no‐till fallow unfertilized‐wheat rotation for 7 years on an Orthic Brown Chernozem in south‐western Saskatchewan, total soil organic carbon (TOC) in the 0 – 5 cm and 5 – 10 cm layers was slightly lower than the tillage fallow‐unfertilized wheat comparable treatment. However, light fraction of organic carbon (LFOC) was similar in the two treatments. Comparison of the tillage fallow‐unfertilized wheat to a treatment involving conversion to a fertilized continuous cropping system for 10 years showed TOC increased slightly in the two depths and LFOC increased by 24 % and 29 % in the 0 – 5 cm and 5 – 10 cm layer, respectively, of the continuous cropping treatment. Microbial biomass carbon (MB‐C) was increased significantly at the 5 – 10 cm depth. After conversion of fallow‐wheat to alfalfa as perennial forage for 10 years, TOC increased by 80 % and 27 %, LFOC by 245 % and 286 %, and HFOC by 63 % and 20 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to the tilled cereal‐fallow system. Meanwhile, water soluble organic carbon (WSOC) was not affected but MB‐C increased significantly. In an Orthic Black Chernozem in east‐central Saskatchewan, the depletion and restoration of organic carbon was observed when native sod was changed into cropland and then back to grassland. For example, the TOC of cropland under cereal‐fallow rotation for 62 years decreased by 42 % and 33 % at 0 – 5 cm and 5 – 10 cm depths, respectively, compared to native sod. The LFOC decreased by 79 % and 74 % in the layers, and reductions in WSOC and MB‐C were even greater. After cropland was re‐seeded to grassland for 12 years, the concentration of total organic carbon was increased by 16 % and 22 % while the mass of organic carbon was the same as the cropland in the two layers. The LFOC and MB‐C amounts in the grass seed‐down were double that of the cropped land, but the amounts of TOC, LFOC, and MB‐C in grass seed‐down were still significantly lower than the native sod.     

Soil organic matter status of Chernozem soil in North Kazakhstan: effects of summer fallow

In North Kazakhstan there is concern about the degradation of Chernozem soil and agricultural sustainability by the inclusion and frequency of summer fallows in crop rotations in terms of their influence on the changes of soil organic matter (SOM) quality and quantity. We examined five fallow-wheat (Triticum aestivum L.) cropping systems with different frequencies of the fallow phase in Chernozem soil of North Kazakhstan; continuous wheat (CW), 6-y rotation (6R), 4-y rotation (4R), 2-y rotation (2R) and continuous fallow (CF). Soil samples were collected from the two phases of each rotation, pre- and post-fallow, and analyzed for potentially mineralizable C (PMC) and N (PMN), ‘light fraction’ organic matter (LF-OM), C (LF-C) and N (LF-N). Potentially mineralizable C was inversely proportional to the frequency of fallow and was highest in CW. Mineral N (min-N) and PMN were more responsive to rotation phase than other indices of SOM. Mineral N was higher in the post-fallow phase while PMN was higher in the pre-fallow phase. Light fraction organic matter was negatively correlated to the frequency of fallow and was higher in the pre-fallow than in the post-fallow phase in a rotation. The results suggested that the yearly input of plant residue in a less frequently fallowed system built up more PMC, whereas PMN was closely correlated to recent inputs of substrate added with plant residues. We conclude that a frequent fallow system may deplete SOM via accelerated mineralization. Also that LF-OM, PMC and PMN are more sensitive to detect subtle changes in SOM quality than total SOM. Our results may provide prediction of SOM response to fallow frequency in wheat-based rotation systems in Chernozem soils of semi-arid regions.     

Carbon mineralization and microbial activity in a field site trial used for 14C turnover experiments over a period of 30 years

 Long-term experiments on different crop management systems provide essential information about turnover of soil organic matter and changes in microbial properties over a period of time. A long-term field site trial, which was established in 1967 near Vienna, Austria, to document the fate of ¹⁴C-labelled manure (straw and farmyard) under different crop management systems (crop rotation, spring wheat and bare fallow), was investigated. Soil samples were taken in 1997 and separated into size fractions (>250 μm, 250–63 μm, 63–2 μm, 2–0.1 μm and <0.1 μm) after aggregate dispersion using low-energy sonication. Organic C, total N and ¹⁴C content were measured in the bulk soil and the size fractions and microbial properties were analysed in the bulk soil. Additionally, C mineralization in bulk soil samples was monitored at 20 °C over a period of 28 days, and subsequently ¹⁴C-CO₂ content was analysed. The distribution of organic C and N within the size fractions was similar between crop rotation and spring wheat; the highest amounts of organic C and N were found in the clay-sized fraction. The amounts of C and N were significantly smaller in the bare fallow, which was depleted of organic matter in the coarse-sized fractions. ¹⁴C distribution differed significantly from unlabelled C distribution, labelled C was accumulated in the silt-sized fraction, indicating weak humification of the applied manure C. The highest rate of C mineralization was measured in the crop rotation and spring wheat, whereas the emission rate of the bare fallow was about 40% lower. The higher ¹⁴C:C ratio of the bulk soil in comparison to the emitted CO₂ indicated that labelled C compounds still remained mineralizable after a period of 30 years. Microbial properties showed a great difference between crop management systems and bare fallow, particularly regarding urease and xylanase activity. Received: 31 May 1999     

Natural 13C Abundance and Chemical Structure of Organic Matter of Haplic Chernozem under Contrasting Land Uses

Eurasian Soil Science - Natural 13C abundance and chemical structure of different organic matter (OM) pools of Haplic Chernozem in contrasting land use variants (steppe and long-term bare fallow)...     

The influence of 12 years of tillage and crop rotation on total and labile organic carbon in a sandy loam soil

Information on which management practices can enhance soil organic matter (SOM) content and quality can be useful for developing sustainable crop production systems. We tested the influence of 12 years of no-till (NT) versus conventional tillage (CT), and four crop sequences on the organic C pools of a Grey Luvisolic sandy loam soil in northwestern Alberta, Canada. The crop sequences were: continuous wheat (Triticum aestivum L.), field pea (Pisum sativum L.)–wheat–canola (Brassica rapa L.)–wheat, red clover (Trifolium pratense L.) green manure–wheat–canola–wheat/red clover and fallow–wheat–canola–wheat. Soil samples from 1992, when the study was initiated, and 1996, 2000 and 2004 were analyzed for total organic C (TOC), the light fraction (LF) and its C content, and water-soluble and mineralizable C. Total organic C in the top 15 cm of soil was higher in the red clover rotation than either the pea or fallow rotation by 1996. The tillage effect became significant only in 2004 with NT having a higher TOC than CT. The LF dry matter (DM) increased from 6.9 g kg⁻¹ soil in 1992 to a range of 10–13 g kg⁻¹ in 2000 and 2004. It was higher under NT than CT in 2 of 3 years and in the red clover rotation than the pea or fallow rotation in 1 of 3 years. The LF C content exhibited a similar trend as LF DM. The water-soluble and mineralizable C pools were not affected by tillage but decreased with time. Among crop rotations, the red clover rotation tended to result in higher levels of hot water-soluble and mineralizable C. It is concluded that tillage had a greater influence than crop rotation on the LF DM and LF C (as indicators of C storage), whereas the converse effect applied to mineralizable C and, to a lesser degree, hot water-soluble C (as indicators of SOM quality).     

Long‐term effects of cropped vs. fallow and fertilizer amendments on soil organic matter I. Organic carbon

A long‐term field experiment, conducted since 1962 in Gumpenstein (Austria) on a Dystric Cambisol, was used for the present investigation. We combined a physical fractionation procedure with the determination of natural abundance of ¹³C and FT‐IR spectroscopy to study the influence of fertilizer amendments (organic manure and mineral fertilizers) and management practices (fallow vs. cropped) on changes in organic carbon (OC) associated with different particle‐size fractions. The OC content in bulk soil decreased or was not affected by slurry+straw, PK, and NPK treatments in both fallow and cropped plots after 28 and 38 yr of treatment. However, OC in plots receiving organic manures increased depending on the quality of the organic manures applied. The ranking among the different treatments under both fallow and cropped plots was: animal manure (liquid) > animal manure (solid) > cattle slurry = slurry+straw = PK = NPK. Results showed that the two types of management practices, fallow (non‐tilled) vs. cropped (tilled) had effects on OC concentrations. Comparing the OC contribution of particle‐size fractions to the total OC amount revealed the following ranking: silt > clay > fine sand > coarse sand except in the plots receiving solid or liquid animal manure. Size fractions within treatments showed larger variations of ¹³C abundances than bulk samples between treatments. The natural abundances of ¹³C increased especially in cropped (and tilled) plots. It was shown by cluster analysis that FT‐IR spectra differentiated between the different treatments originating from different land management practices. The present study revealed that below‐ground C deposition by agricultural plants can hardly compensate the C losses due to tillage.     

Microbial biomass in soils of Russia under long-term management practices

 Non-tilled and tilled plots on a spodosol (C_org 0.65–1.70%; pH 4.1–4.5) and a mollisol (C_org 3.02–3.13%, pH 4.9–5.3), located in the European region of Russia, were investigated to determine variances in soil microbial biomass and microbial community composition. Continuous, long-term management practices, including tillage and treatment with inorganic fertilizers or manure, were used on the spodosol (39 years) and mollisol (22 years). Total microbial biomass (C_mic), estimated by the substrate-induced respiration (SIR) method, and total fungal hyphae length (membrane filter technique) were determined seasonally over a 3-year period. Long-term soil management practices (primarily tillage and fertilizer application) led to decreases in total microbial biomass (80–85% lower in spodosol and 20–55% lower in mollisol), decreases in the contribution of C_mic to C_org (2.3- to 3.5-fold lower in spodosol and 1.2- to 2.3-fold lower in mollisol), and 50–87% decreases in total fungal hyphae length compared to non-tilled control plots. The contribution of fungi to total SIR in virgin mollisol and fallow spodosol plots was approximately 30%. However, the contribution of fungi to SIR was approximately two times greater in tilled spodosol plots compared to a fallow plot. In contrast, the contribution of fungi to SIR in tilled plots of mollisol was less (1.4–4.7 times) than for a virgin plot. In summary, long-term soil management practices such as tillage and treatment with organic or inorganic fertilizers are important determinants of soil microbial biomass and the contribution of fungi to total SIR. Received: 28 April 1998     

Evaluating biodegradability of soil organic matter by its thermal stability and chemical composition

The stability of soil organic matter (SOM) as it relates to resistance to microbial degradation has important implications for nutrient cycling, emission of greenhouse gases, and C sequestration. Hence, there is interest in developing new ways to quantify and characterise the labile and stable forms of SOM. Our objective in this study was to evaluate SOM under widely contrasting management regimes to determine whether the variation in chemical composition and resistance to pyrolysis observed for various constituent C fractions could be related to their resistance to decomposition. Samples from the same soil under permanent pasture, an arable cropping rotation, and chemical fallow were physically fractionated (sand: 2000-50 μm; silt: 50-5 μm, and clay: <5 μm). Biodegradability of the SOM in size fractions and whole soils was assessed in a laboratory mineralization study. Thermal stability was determined by analytical pyrolysis using a Rock-Eval pyrolyser, and chemical composition was characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the C and N K-edges. Relative to the pasture soil, SOM in the arable and fallow soils declined by 30% and 40%, respectively. The mineralization bioassay showed that SOM in whole soil and soil fractions under fallow was less susceptible to biodegradation than that in other management practices. The SOM in the sand fraction was significantly more biodegradable than that in the silt or clay fractions. Analysis by XANES showed a proportional increase in carboxylates and a reduction in amides (protein) and aromatics in the fallow whole soil compared to the pasture and arable soils. Moreover, protein depletion was greatest in the sand fraction of the fallow soil. Sand fractions in fallow and arable soils were, however, relatively enriched in plant-derived phenols, aromatics, and carboxylates compared to the sand fraction of pasture soils. Analytical pyrolysis showed distinct differences in the thermal stability of SOM among the whole soil and their size fractions; it also showed that the loss of SOM generally involved preferential degradation of H-rich compounds. The temperature at which half of the C was pyrolyzed was strongly correlated with mineralizable C, providing good evidence for a link between the biological and thermal stability of SOM.     

Soil microbial populations and activities as influenced by legume green fallow in a semiarid climate

Tilled fallow-wheat (Triticum aestivum L.) (F-W) is the most commonly used cropping system in the semiarid Canadian prairie. However, because frequent fallowing degrades soil, a partial fallow with annual legumes as green manure [i.e. ‘green fallow’ (GF)] has been proposed as a soil conserving and more bio-resource efficient alternative to bare fallow. We conducted a 6-year study to compare the influence of four GF-W, a F-W and a continuous W (Cont. W) system, on soil microbial communities, microbial biomass (MB) and activities in an Orthic Brown Chernozem, silt loam (Aridic Haploboroll) at Swift Current, Sask., Canada. The four GF legumes used were black lentil (Lens culinaris Medikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.) and feedpea (Pisum sativum L.). They were grown to full bloom and then incorporated with a tandem disk. Analysis of soil taken from 0 to 10 cm depth after growing wheat in the sixth year of the experiment (i.e. 15 months after the most recent legume GF had been turned under) showed that most of the soil biochemical and microbiological attributes assessed were significantly improved (compared to F-W) by increasing cropping intensity (Cont. W), and even more by using the GF systems. The average improvement gained from the four GF legumes relative to F-W, was 385% for number of bacteria, 210% for filamentous fungi, 170% for MB-C, 191% for MB-N, 205% for cumulative C mineralization in 30 days at 21 °C, 202% for dehydrogenase, 171% for phosphatase, and 287% for arylsulfatase activity. The biologically active C and N, when expressed as ratios of MB-C or MB-N to total soil C or N, increased from 1.6 and 2.0% in F-W to 1.9 and 2.6% in Cont. W and to an average of 2.4 and 3.5% in GF-W. A sensitivity analysis (ratio of other treatment values to value for F-W) showed that Cont. W, and the GF-W systems even more, increased all major soil biological attributes tested. Among the GF systems, lentil-W consistently increased sensitivity the most, while Tangier flatpea-W usually increased it the least. The dynamic direct and indirect microbiological attributes were more sensitive indicators of changes in soil productivity than total organic C or N. The sensitivity of the attributes decreased in the sequence: Bacteria>Arylsulfatase>Filamentous fungi≈Cumulative C mineralization≈Dehydrogenase>MB-N>Phosphatase≈MB-C. Compared to the earlier published sensitivities of select physical and chemical attributes of soil quality to these same agronomic treatments, the microbiological attributes proved to be far more sensitive and more responsive to the beneficial influence of legume green fallowing in this semiarid loam.     

Moisture regime of typical chernozems under the mown Steppe and plowland of Kursk oblast under the anomalous weather conditions of the last decades

The analysis of long-term (since 1947) data on the water content of the upper 3-m-thick layer in the Streletskaya Steppe chernozems under annual mowing showed that the weather changes during the last decades (from 1972–1973 to 2005–2006) resulted in an increase in the soil wetting depth during the fall-winter-spring period and the frequency of the percolation, a decrease in the water consumption from the 150- to 300-cm layer during the growing season, and a decrease in the water deficit in the fall. Therefore, the total water content of the steppe chernozems increased, although to a significantly lesser degree than that found for the steppe plot with a succession of woody-shrub vegetation. In a perennial fallow, the water content of the soil layer also increased. The water supply of the 0- to 160-cm layer of chernozems under winter wheat and corn underwent no significant changes.     

不同地表覆盖栽培对旱地土壤有机碳、无机碳和轻质有机碳的影响

通过田间长期定位试验,分层采集冬小麦-休闲种植体系0—40 cm土层的土样,研究了常规、地表覆膜和覆草栽培对土壤有机碳、无机碳和轻质有机碳的影响。结果表明,覆膜或覆草可以显著增加地上部小麦生物量和子粒产量。不同地表覆盖对0—40 cm土层的无机碳含量和分布无显著影响,但与常规栽培相比,地表覆膜使0—5 cm土层的有机碳含量显著降低,0—40 cm各土层轻质有机碳表现出明显降低趋势,平均降低 C 6.1~74.5 mg/kg;地表覆草却表现出明显增加土壤轻质有机碳的趋势,0—5,5—10,10—20 cm土层的轻质有机碳含量分别增加C 235.2、190.0和144.9 mg/kg,相当于常规的38.7%,32.9%和34.5%。同时,覆草栽培还表现出降低0—10 cm土层轻质有机质含碳量的趋势,并使0—20 cm土层轻质有机碳占有机碳的比例显著高于常规栽培和地表覆膜处理。可见,地表长期覆膜不利于旱地土壤有机碳累积,覆草不仅可以增加表层土壤的轻质有机碳累积,还可改善土壤碳氮组成。     

Long-term tillage and cropping effects on microbiological properties associated with aggregation in a semi-arid soil

Little is known about the long-term tillage and cropping management effects on the microbiologically derived factors that influence macroaggregates in semi-arid soil. We tested the hypothesis that differences in macro-aggregation are due to changes in soil structure related to management treatment-induced microbiological changes. In an experiment, microbiological factors consisting of aggregate stability, glomalin, russuloid basidiomycete fungi, uronic acids, total organic C (TOC), and total N (TN) were quantified in macroaggregate-size classes ranging from 4.75 to 0.25 mm, collected at 0–5 cm depth for the following treatments: (1) 12th year of fallow phase after 11 years of conventional- and no-tilled spring wheat-fallow (CTF and NTF), (2) 12th year of lentil phase after 11 years of conventional- and no-tilled spring wheat-lentil (CTL and NTL), (3) 12 years no-tilled continuous spring wheat (NTCW), and (4) 16 years uncultivated pasture (P) used as a baseline treatment. Immunoreactive easily extractable glomalin concentration was five to six times greater under P, NTCW, or NTL in the 2.00–1.00- and 1.00–0.50-mm macroaggregate-size classes than the other treatments and these results corroborated well with the results from aggregate stability assays. Russuloid basidiomycetes were highest in all NTCW macroaggregate-size classes, suggesting that annual input of lignin-containing wheat residues may influence the growth and survival of these fungi. Uronic acid amounts were highest in P but did not differ among the other treatments. In all macroaggregate-size classes, TOC content was greater in NTCW compared to CTF, and TN was about three times higher in NTL than NTF or CTF. In conclusion, 12 years of NTCW management in semi-arid soil has resulted in higher macroaggregate stability, glomalin concentration, russuloid basidiomycete populations, and TOC in macroaggregates compared to alternate-year fallow. Lentil can be used to replace fallow in dryland wheat rotation under no-till to enhance TN content and improve soil macro-aggregation.     

Influence of fallow, wheat and subterranean clover on pH within an initially mixed surface soil in the field

 To ascertain the cause of the decrease in pH with depth through the surface 15 cm of moderately acidic soils, pH was monitored in layers of an initially mixed surface soil (to a nominal depth of 10 cm) during two consecutive seasons under fallow, wheat, and subterranean-clover plots. Variation of pH-influencing processes within soil layers to 15 cm depth was measured during the first season. Initially, soil pH was relatively uniform within the surface 7.5 cm, although there was an average 0.53 unit decrease of pH from 0–2.5 cm to 10–15 cm depth. Under all plots, residual lime reaction, net organic anion association and oxidation, net manganese oxidation and reduction, and particularly net N mineralisation and subsequent nitrification, tended to decrease with depth through the surface 15 cm of soil. In wheat and subterranean-clover plots, the alkalinity added with the return of 3.9–4.7 t ha^–1 of plant residue dry matter was predominantly released within the surface 2.5 cm of soil. The dominant pH-influencing processes were net N mineralisation and subsequent nitrification, and the return of alkaline plant residues. In the fallow plots, the surface 10 cm of soil tended to acidify due to nitrification. However in wheat and clover plots, alkalinity added to the surface 2.5 cm of soil from plant residues exceeded acidification resulting from nitrification at this depth. The magnitude of the pH gradient through 0–15 cm depth was therefore maintained under wheat, increased under clover, and decreased under fallow. Received: 11 October 1999     

Total and labile soil organic nitrogen as influenced by crop rotations and tillage in Canadian prairie soils

Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha^–1year^–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha^–1year^–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha^–1 year^–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha^–1year^–1 to 28 kg N ha^–1year^–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha^–1year^–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha^–1year^–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.     

减氮配施有机物质对麦田土壤性质和小麦产量的影响

探究氮肥减量配施有机物质的情况下对氮素利用状况及土壤肥力和小麦产量的影响,为我国华北平原区小麦生产中提高氮肥利用效率、实现节肥增效提供理论基础.通过田间试验,设置5个处理:不施氮肥(CK)、农民习惯施氮肥(FN)、减氮20％(80％FN)、减氮20％+生物有机肥(80％FN+OM)、减氮20％+生物炭(80％FN+BC...     

Soil fertility differences across a land-use intensification gradient in the highlands of Chiapas,Mexico

In the highlands of Chiapas, southern Mexico, soil texture and soil chemical properties were measured in 70 agricultural fields covering a range of slope positions and managements. Fields represented four corn cropping systems: long fallow, short fallow, pasture–cultivation rotation, and annual continuous cultivation, in addition to fallow at rest (forest, shrubland, and pastures). Fields were located in four slope positions (upper, middle, and lower slopes, and doline floor) in a karst landscape developed on limestone with additions of acid volcanic ashes. Distribution of clays and sands were related to the toposequence and the percentage of clay fraction increased from upper slope to doline floor. Sand presented a reverse pattern. Some soil chemical properties also vary in a characteristic way along the toposequence. Exchangeable Ca²⁺ and Mg²⁺ effective cation exchange capacity (ECEC) and pH were higher in the doline floor than in the other slope positions. Soil organic matter and total N contents were 30.4 and 35.2% higher under long fallow than under annual continuous cultivation. Soil Olsen P was greater under cultivation than under fallow (irrespective of the cropping system), with the highest values under annual continuous cultivation (16.2±8.3 mg kg⁻¹) and the lowest in the forest (5.3±2.5 mg kg⁻¹). Exchangeable K⁺ was 74 and 51% higher in cultivated plots of the long and the short fallow than under forest and shrubland, respectively. Exchangeable Ca²⁺ and Mg²⁺ and ECEC did not vary significantly among the cropping systems. Inputs of basic cations through burning of tree and shrub vegetation increased the soil pH. These results indicate that land use intensification is leading to a decline in soil organic matter and total N, whereas Olsen P increased with intensification due to the continuous application of P fertilizers and sheep manure as soil conditioners in intensively cultivated fields.     

Chemical stabilization of organic carbon pools in particle size fractions in no-till and meadow soils

The knowledge about the relevance of physical and chemical fractionation methods to soil organic carbon (SOC) stabilization mechanisms is fragmentary but needed to manage the SOC pool. Therefore, our objective was to compare the C contents of the particle size fractions coarse and fine sand, silt, and clay of the two uppermost horizons of a soil under three different management systems (meadow; no-till corn, NT; no-till corn with manure, NTm). The mineral composition was dominated by silt (48–60%). However, coarse sand and clay showed the highest enrichment of C compared to the bulk soil. In spite of an enrichment factor below 1, the high proportion of silt made this fraction the main C store. In the upper 30 cm, this fraction amounted to 27.1 Mg C ha⁻¹ in NTm and progressively less in NT (15.5 Mg C ha⁻¹), and meadow (14.9 Mg C ha⁻¹), representing 44%, 39%, and 39% of the total SOC pool, respectively. The C in the isolated particle size fractions was further investigated by an oxidizing treatment with Na₂S₂O₈ and a treatment with HF to solubilize the mineral phases. The pools of oxidizable C were comparable among particle size fractions and pedons, as indicated by Na₂S₂O₈ treatment. The pools of C preferentially associated with soil minerals were also comparable among pedons, as indicated by HF treatment. However, NTm stored the largest pool (12.6 Mg ha⁻¹) of mineral-associated C in 0–30 cm depth. The silt-associated and mineral-bound SOC pool in NTm was greater compared to NT due to increased organic matter (OM) input. Thus, the silt particle size fraction at the North Appalachian Experimental Watershed (NAEW) has the potential for SOC sequestration by stabilizing OM inputs. Mineralogical and molecular level analyses on a larger set of fractions obtained from entire rooted soil profiles are required, however, to compare the SOC sequestration capacity of the land uses.     

Effects of Broad-Leaf Crop Frequency in Various Rotations on Nitrate Nitrogen and Extractable Phosphorus in a Black Chernozem Soil

In the Canadian prairies, current recommendations allow growing of canola or pea once every 4 years on a particular field to effectively mange diseases, insects, and weeds, but producers are interested in increasing frequency of these crops to optimize economic returns. A 4-year (from 1999 and 2002) field experiment, with treatments consisting of rotations of monoculture canola and pea to rotations that contained these crops every 2, 3, and 4 years with wheat and flax, was conducted on a Black Chernozem (Udic Boroll) silty clay at Melfort, Saskatchewan, to determine the impact of frequency of broad-leaf crops canola and pea in various crop rotations on accumulation and distribution of nitrate nitrogen (N) and extractable phosphorus (P) in the soil profile after 4 years. Two cultivars of canola, an herbicide-tolerant blackleg- resistant variety (hybrid) and a conventional (not herbicide tolerant) open-pollinated, blackleg-susceptible variety (OP), were included. Mean effects of crop rotation or rotation length on soil nitrate N were not significant, though the amount of soil nitrate N in different soil layers tended to be greatest with monocultures and least in the 4-year rotation with flax. Effects of crop phase (i.e., individual crops that make up the rotation)?×?crop rotation interactions on soil nitrate N were significant for all layers in the soil profile. The amounts of nitrate N in soil after canola, especially hybrid canola, were lowest in most crop rotations, suggesting the importance of canola in minimizing downward movement of nitrate N in the soil profile. Soil extractable P in the 0- to 15-cm layer was least with monocultures and greatest in the 4-year rotation with flax. There was a significant effect of crop phase on soil extractable P, but soil P levels varied with crop phase in different rotations. In conclusion, residual nitrate N in soil can be reduced by extending crop rotations and using high-yielding disease-resistant canola cultivars, most likely by improving crop yields.     

Long-term straw management and N fertilizer rate effects on quantity and quality of organic C and N and some chemical properties in two contrasting soils in Western Canada

Crop residue and fertilizer management practices alter some soil properties, but the magnitude of change depends on soil type and climatic conditions. Field experiments with mainly barley (and canola, wheat, triticale, or pea in a few years) under conventional tillage were conducted from 1983 to 2009 at Breton (Gray Luvisol (Typic Haplocryalf) loam) and Ellerslie (Black Chernozem (Albic Argicryoll) clay loam), Alberta, Canada, to determine the effects of straw management (straw removed (S _Rem) and straw retained (S _Ret)) and N fertilizer rate (0, 25, 50, and 75 kg N ha⁻¹) on total organic C (TOC) and N (TON), light fraction organic C (LFOC), and N (LFON) in the 0–7.5 and 7.5–15 cm, pH in the 0–7.5, 7.5–15, and 15–20 cm and extractable P, ammonium-N, and nitrate-N in the 0–15, 15–30, 30–60, and 60–90 cm soil layers. The S _Ret and N fertilizer treatments usually had higher mass of TOC, TON, LFOC, and LFON in soil at Breton, but only of LFOC and LFON in soil at Ellerslie compared with the corresponding S _Rem and zero-N control treatments. The responses of soil organic C and N to management practices were more pronounced for N fertilization than straw management. There were significant correlations among most soil organic C or N fractions, especially at Breton. Linear regressions between crop residue C or N input, or rate of fertilizer N applied and soil organic C or N were significant in most cases at Breton, but only for LFOC and LFON at Ellerslie. At Breton, compared with zero-N rate, the C sequestration efficiency of additional crop residue C input was 5.8%, 20.1%, and 20.4% in S _Ret and 17.2%, 28.0%, and 30.1% in S _Rem treatments at the 25, 50, and 75 kg N ha⁻¹ rates, respectively. The effects of crop residue management and N fertilization on chemical properties were generally similar for both contrasting soil types. There was no effect of crop residue management on soil pH, extractable P and residual nitrate-N. Extractable P and pH in the top 0–15 cm soil decreased significantly with N application in both soil types. Residual nitrate-N (though quite low in Breton soil) increased with application of N and also indicated some downward movement in the soil profile up to 90 cm depth in Ellerslie soil. There was generally no effect of any treatment on ammonium-N in soil. In conclusion, straw retention and N application improved organic C and N in soil, and generally differences were more pronounced for light fraction than total organic C and N, and between the most extreme treatments (S _Rem0 vs. S _Ret75). Application of N fertilizer reduced extractable P and pH in the surface soil, and showed accumulation and downward leaching of nitrate-N in the soil profile.     

Chemical Structure of the Organic Matter of Water-Stable Structural Units in Haplic Chernozem under Contrasting Land Uses: Solid-State CP-MAS 13C-NMR Spectroscopy

Eurasian Soil Science - The chemical structure of different soil organic matter (OM) pools in water-stable macro- and free microaggregates isolated from the surface horizons of Haplic Chernozem in...