Long-term management impacts on soil C, N and physical fertility: Part I: Broadbalk experiment

For many centuries manure application to the soil has been common practice. Organic amendments and fertiliser applications can increase crop yields and soil organic matter (SOM). However, the long-term impacts on soil physical fertility are often neglected. This study was carried out on the Broadbalk Wheat Experiment at Rothamsted, UK, established in 1843 on an Aquic/Typic Paleudalf soil. Application of farmyard manure (FYM), N fertiliser and wheat straw on total organic C (C_T), labile C (C_L) and non-labile C (C_NL), total N (N_T), mean weight diameter (MWD) and unsaturated hydraulic conductivity (K_unsat) were studied on wheat (Triticum aestivum) and adjacent woodland and pasture areas. Manure additions, N fertiliser and straw incorporation increased all C fractions, particularly the C_L fraction. The addition of 35 t ha⁻¹ year⁻¹ of FYM increased C_T to 2.5 times that of the control (no fertiliser) treatment and C_L to 5 times that of the control. With highest N application and straw returned, C_T increased by 1.3 times and C_L by 1.5 times that of the control treatment. There were linear relationships between rate of N fertiliser applied and all C fractions, with the rate of increase almost double with straw than straw removed. Manure application improved MWD, as did high N fertiliser additions with straw returned. Application of N fertiliser only increased MWD and K_unsat (at 10 mm tension) if straw was returned, while the addition of manure resulted in decreased K_unsat. The highest K_unsat rate was on the high N fertiliser, straw returned treatments. The uncropped areas all had high soil structural stability. Similar relationships occurred between all C fractions and N_T and MWD for the high C soils, but relationships were much stronger with C_L than the other C fractions in the low C soils. These results showed that soils with low C concentration are more reliant on C_L for structural stability.     

Long-term management impacts on soil C,N and physical fertility: Part II: Bad Lauchstadt static and extreme FYM experiments

Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha⁻¹ 2 year⁻¹) combined with P, K and N fertiliser application on total organic C (C_T), labile C (C_L), non-labile C (C_NL), total N (N_T), mean weight diameter (MWD) and unsaturated hydraulic conductivity (K_unsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha⁻¹ year⁻¹) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly C_L, where application of 30 t ha⁻¹ 2 year⁻¹ increased C_L by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while N_T increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased K_unsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha⁻¹ year⁻¹ of FYM increased concentrations of C_L by 173% and of C_NL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, N_T and MWD compared with the cropped site, while K_unsat (10 mm tension) was increased on the 0 and 50 t ha⁻¹ year⁻¹ treatments as a result of a recent tillage. There was no difference in K_unsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha⁻¹ year⁻¹. There were similar significant positive correlations of all C fractions and N_T with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and N_T with K_unsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and K_unsat was with C_L. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future.     

Long-term management impacts on soil C, N and physical fertility: Part III: Tamworth crop rotation experiment

Degradation of soil structure can lead to increased risk of run-off and soil erosion, and therefore, it is necessary to implement management practices that are more sustainable and will enhance and rehabilitate soils while increasing food production. The impact of small-grain rotations grown with legumes, fallow and continuously on total C (C_T), labile C (C_L), non-labile C (C_NL), total N (N_T), aggregation expressed as mean weight diameter (MWD) and infiltration determined as unsaturated hydraulic conductivity (K_unsat) were examined in a long-term rotation trial established in 1966 on a Black Earth (Pellic Vertisol) and a Red Clay (Chromic Vertisol) soil near Tamworth, in New South Wales, Australia. The results were compared with an adjacent uncropped pasture on each soil type. Cropping reduced all C fractions, N_T, MWD and K_unsat on both soils, which were further degraded when long fallowing was included in the rotation. C_L decreased by 70% with long fallow in the Red Clay and by 78% in the Black Earth compared with the adjacent pasture, while MWD decreased by 61% in the Red Clay and 91% in the Black Earth. Rotation of cereals with legumes resulted in smaller decreases in C fractions, N_T, MWD and K_unsat when compared with pasture. Rotation with lucerne (Medicago sativa) resulted in 41% higher C_L, 45% higher MWD and 87% higher K_unsat (10 mm tension) than long fallow on the Red Clay soil and 65, 126 and 43% higher on the Black Earth soil. There were strong positive correlations of soil C fractions and N_T with MWD for both soil types. Similar significant relationships were found for all C fractions and N_T with K_unsat (10 mm tension) for the Red Clay soil, but not for the Black Earth. Rotations with forage legumes can limit declines in C fractions, N_T, MWD and K_unsat when cropping these soils and has potential to increase soil sustainability.     

Long-term management impacts on soil C,N and physical fertility: Part III: Tamworth crop rotation experiment

Degradation of soil structure can lead to increased risk of run-off and soil erosion, and therefore, it is necessary to implement management practices that are more sustainable and will enhance and rehabilitate soils while increasing food production. The impact of small-grain rotations grown with legumes, fallow and continuously on total C (C_T), labile C (C_L), non-labile C (C_NL), total N (N_T), aggregation expressed as mean weight diameter (MWD) and infiltration determined as unsaturated hydraulic conductivity (K_unsat) were examined in a long-term rotation trial established in 1966 on a Black Earth (Pellic Vertisol) and a Red Clay (Chromic Vertisol) soil near Tamworth, in New South Wales, Australia. The results were compared with an adjacent uncropped pasture on each soil type. Cropping reduced all C fractions, N_T, MWD and K_unsat on both soils, which were further degraded when long fallowing was included in the rotation. C_L decreased by 70% with long fallow in the Red Clay and by 78% in the Black Earth compared with the adjacent pasture, while MWD decreased by 61% in the Red Clay and 91% in the Black Earth. Rotation of cereals with legumes resulted in smaller decreases in C fractions, N_T, MWD and K_unsat when compared with pasture. Rotation with lucerne (Medicago sativa) resulted in 41% higher C_L, 45% higher MWD and 87% higher K_unsat (10 mm tension) than long fallow on the Red Clay soil and 65, 126 and 43% higher on the Black Earth soil. There were strong positive correlations of soil C fractions and N_T with MWD for both soil types. Similar significant relationships were found for all C fractions and N_T with K_unsat (10 mm tension) for the Red Clay soil, but not for the Black Earth. Rotations with forage legumes can limit declines in C fractions, N_T, MWD and K_unsat when cropping these soils and has potential to increase soil sustainability.     

Long-term management impacts on soil carbon and nitrogen dynamics of grazed bermudagrass pastures

Managed pastures have potential for C and N sequestration in addition to providing forage for livestock. Our objectives were to investigate changes in soil organic C (SOC) and soil organic N (SON) concentrations and mineralizable C and N in cattle (Bos indicus) grazed bermudagrass [Cynodon dactylon (L.) Pers.] pastures up to 32 y after establishment. Management included low- and high-grazing intensity, fertilization, and winter overseeding with annual ryegrass (Lolium multiflorum Lam.) and clover (Trifolium sp.). Soil (0-15 cm) was sampled 7, 15, 26, and 32 y after establishment of Coastal and common bermudagrass pastures. No significant differences in SOC or SON concentrations were observed between Coastal and common bermudagrass pastures. Grazing strategies played important roles in C and N sequestration, as high-grazing intensity resulted in a lower increase in SOC and SON concentrations over time compared to low-grazing intensity. Increases in SOC were observed up to 26 y, while increases in SON were observed up to 32 y after establishment of bermudagrass pastures. Soil organic C increased 67 and 39% from 7 to 26 y at low-grazing intensity for bermudagrass+ryegrass and bermudagrass+clover pastures, respectively. SOC and SON concentrations did not increase beyond 15 y after bermudagrass establishment at high-grazing intensity. An exception was the Coastal bermudagrass+ryegrass pastures, which exhibited higher SON at 32 y than at 7 y at both grazing intensities. By 32 y, SON increased 83 and 45% in Coastal bermudagrass+ryegrass pastures at low- and high-grazing intensity, respectively, compared to 7 y. The introduction of clover to pastures decreased SOC and SON relative to ryegrass at high- but not at low-grazing intensity. Potentially mineralizable C increased from 7 to 15 y, while mineralizable N increased from 7 to 32 y. Potentially mineralizable N was also greater for bermudagrass+clover than bermudagrass+ryegrass pastures. Long-term increases in SOC and SON concentrations suggest that managed and grazed pastures have strong potential for C and N sequestration.     

Organic matter turnover in soil physical fractions following woody plant invasion of grassland: Evidence from natural C and N

Soil physical structure causes differential accessibility of soil organic carbon (SOC) to decomposer organisms and is an important determinant of SOC storage and turnover. Techniques for physical fractionation of soil organic matter in conjunction with isotopic analyses (δ¹³C, δ¹⁵N) of those soil fractions have been used previously to (a) determine where organic C is stored relative to aggregate structure, (b) identify sources of SOC, (c) quantify turnover rates of SOC in specific soil fractions, and (d) evaluate organic matter quality. We used these two complementary approaches to characterize soil C storage and dynamics in the Rio Grande Plains of southern Texas where C₃ trees/shrubs (δ¹³C=−27‰) have largely replaced C₄ grasslands (δ¹³C=−14‰) over the past 100-200 years. Using a chronosequence approach, soils were collected from remnant grasslands (Time 0) and from woody plant stands ranging in age from 10 to 130 years. We separated soil organic matter into specific size/density fractions and determined their C and N concentrations and natural δ¹³C and δ¹⁵N values. Mean residence times (MRTs) of soil fractions were calculated based on changes in their δ¹³C with time after woody encroachment. The shortest MRTs (average=30 years) were associated with all particulate organic matter (POM) fractions not protected within aggregates. Fine POM (53-250 μm) within macro- and microaggregates was relatively more protected from decay, with an average MRT of 60 years. All silt+clay fractions had the longest MRTs (average=360 years) regardless of whether they were found inside or outside of aggregate structure. δ¹⁵N values of soil physical fractions were positively correlated with MRTs of the same fractions, suggesting that higher δ¹⁵N values reflect an increased degree of humification. Increased soil C and N pools in wooded areas were due to both the retention of older C₄-derived organic matter by protection within microaggregates and association with silt+clay, and the accumulation of new C₃-derived organic matter in macroaggregates and POM fractions.     

Organic matter addition, N, and residue burning effects on infiltration, biological, and physical properties of an intensively tilled silt-loam soil

Seventy years of different management treatments have produced significant differences in runoff, erosion, and ponded infiltration rate in a winter wheat (Triticum aestivum L.)–summer fallow experiment in OR, USA. We tested the hypothesis that differences in infiltration are due to changes in soil structure related to treatment-induced biological changes. All plots received the same tillage (plow and summer rod-weeding). Manure (containing 111 kg N ha⁻¹), pea (Pisum sativum L.), vine (containing 34 kg N ha⁻¹), or N additions of 0, 45 and 90 kg ha⁻¹ were treatment variables with burning of residue as an additional factor within N-treatments. We measured soil organic C and N, water stability of whole soil, water stable aggregates, percolation through soil columns, glomalin, soil-aggregating basidiomycetes, earthworm populations, and dry sieve aggregate fractions. Infiltration was correlated (r = 0.67–0.95) to C, N, stability of whole soil, percolation, and glomalin. Basidiomycete extracellular carbohydrate assay values and earthworm populations did not follow soil C concentration, but appeared to be more sensitive to residue burning and to the addition of pea vine residue and manure. Dry sieve fractions were not well correlated to the other variables. Burning reduced (p < 0.05) water stability of whole soil, total glomalin, basidiomycetes, and earthworm counts. It also reduced dry aggregates of 0.5–2.0 mm size, but neither burning nor N fertilizer affected total C or total N or ponded infiltration rate. Water stability of whole soil and of 1–2-mm aggregates was greater at 45 kg N ha⁻¹ than in the 0 and 90 kg N ha⁻¹ treatments. Zero N fertilizer produced significantly greater 0.5–2.0 mm dry aggregate fractions. We conclude that differences in infiltration measured in the field are related to relatively small differences in aggregate stability, but not closely related to N or residue burning treatments. The lack of an effect of N fertilizer or residue burning on total C and N, along with the excellent correlation between glomalin and total C (r = 0.99) and total N (r = 0.98), indicates that the major pool of soil carbon may be dependent on arbuscular mycorrhizal fungi.     

Interactions between N fertilization, grass clipping addition and pH in turf ecosystems: Implications for soil enzyme activities and organic matter decomposition

Turf has been acknowledged as an important ecosystem with potential for soil C sequestration. As a major process dictating soil C storage, organic matter decomposition has received little attention in turf systems. Given that soil enzyme-catalyzed biochemical reactions are the rate limiting steps of organic matter decomposition, we examined the activities of oxidative and hydrolytic soil enzymes and their relations with soluble organic compounds and soil C and N mineralization in two turf chronosequences with contrasting soil pH and in response to N fertilization and grass clipping addition. In comparison with turf ecosystems under acidic soil, phenol oxidase activity was about two-fold greater in turf ecosystems under alkaline soil and positively correlated to about two-fold differences in soluble phenolics and dissolved organic C between alkaline and acidic soils. However, the activities of hydrolytic enzymes including cellulase, chitinase, and glucosidase were lower in alkaline soil. It appears that the high concentration of soluble phenolics inhibited the activities of hydrolytic enzymes that in turn limited the decomposition of dissolved organic C and resulted in its accumulation in alkaline soil. Nitrogen mineralization was comparable between alkaline and acidic soils, but CO₂ evolution was about two-fold greater in alkaline soil, possibly due to considerable abiotic carbonate dissolution. We observed that mineral N input at 60 mg N kg⁻¹ soil had very minor negative effects on the activities of both phenol oxidase and hydrolytic enzymes. Grass clipping addition did not affect the activity of phenol oxidase, but increased the activities of soil chitinase, cellulase, glucosidase, and glucosaminidase by up to 20% and also soluble phenolics in soil by about 10%. Our results suggest that soil phenol oxidase might regulate the activities of hydrolytic soil enzymes via its control on soluble phenolics and function as an ‘enzymatic latch’ to hold soil organic C in highly managed turf ecosystems. While soil pH is important to affect phenol oxidase activity and therefore decomposition, management practices, i.e., N fertilization and grass clipping addition may indirectly affect the decomposition through enhancing turfgrass productivity and thus soil C input.     

免耕对旱作燕麦田耕层土壤微生物生物量碳、氮、磷的影响

2005～2008年,在内蒙古清水河县研究了免耕留低茬(NL)、免耕留高茬(NH)、免耕留低茬覆盖(NLS)、免耕留高茬覆盖(NHS)和常规耕作(T)5种耕作方式对旱坡地燕麦田耕层土壤微生物生物量碳、氮、磷的影响。结果表明:各处理土壤微生物生物量碳、氮、磷含量在不同年际间的变化趋势一致。土壤微生物生物量碳、氮含量均呈双峰曲线变化,其中,NHS和NLS处理土壤微生物生物量碳的峰值出现在拔节期和灌浆期,NH、NL和T处理的土壤微生物生物量碳的峰值出现在孕穗期和灌浆期,而土壤微生物生物量氮的峰值则出现在苗期和灌浆期。土壤微生物生物量磷呈单峰曲线变化,各处理的峰值均出现在灌浆期。不同年份间、不同生育期间,土壤微生物生物量碳、氮、磷含量的大小顺序为:NHS>NLS>NH>NL>T。其中,免耕各处理的燕麦产量相对常规耕作呈先降低后增加的趋势,以2008年为例,NHS、NLS、NH、NL燕麦产量分别较T增加了22%、17%、11%、5%。综上所述,免耕有利于提高土壤微生物生物量碳、氮、磷含量,而且可有效地增加作物产量,尤其是NHS和NLS处理比较明显。     

Tillage and drainage impact on soil quality: I. Aggregate stability, carbon and nitrogen pools

Effects of two tillage treatments, tillage (T) with chisel plough and no-till (NT), were studied under un-drained and drained soil conditions. Soil physical properties measured were bulk density (ρ_b), total porosity (ƒ_t), water stable aggregates (WSA), geometric mean diameter (GMD), mean weight diameter (MWD), organic carbon (OC) and total N concentrations in different aggregate size fractions, and total OC and N pools. The experiment was established in 1994 on a poorly drained Crosby silt loam soil (fine mixed, mesic, Aeric Ochraqualf) near Columbus, Ohio. In 2007, soil samples were collected (0–10, 10–20, and 20–30 cm) from all treatments and separated into six aggregate size classes for assessing proportions of macro (5–8, 2–5, 1–2, 0.5–1, 0.25–0.5) and micro (<0.25 mm) aggregates by wet sieving. Tillage treatments significantly (P ≤ 0.05) influenced WSA, MWD, and GMD. Higher total WSA (78.53 vs. 58.27%), GMD (0.99 vs. 0.68 mm), and MWD (2.23 vs. 0.99 mm) were observed for 0–10 cm depth for NT than T treatments. Relative proportion of macro-aggregates (>0.25-mm) was also more in NT than T treatment for un-drained plots. Conversely, micro-aggregates (<0.25-mm) were more in T plots for both drained and un-drained treatments. The WSA, MWD and GMD decreased with increase in soil depth. The OC concentration was significantly higher (P ≤ 0.05) in NT for un-drained (P ≤ 0.01) treatment for all soil depths. Within macro-aggregates, the maximum OC concentrations of 1.91 and 1.75 g kg⁻¹ in 1–2 mm size fraction were observed in NT for un-drained and drained treatments, respectively. Tillage treatments significantly (P < 0.01) affected bulk density (ρ_b), and total porosity (f_t) for all soil depths, whereas tillage × drainage interaction was significant (P < 0.01) for 10–20 and 20–30 cm depths. Soil ρ_b was negatively correlated (r = −0.47; n = 12) with OC concentration. Tillage treatments significantly affected (P ≤ 0.05) OC pools at 10–20 cm depth; whereas drainage, and tillage × drainage significantly (P ≤ 0.05) influenced OC pools for 0–10 cm soil layer. The OC pool in 0–10 cm layer was 31.8 Mg ha⁻¹ for NT compared with 25.9 Mg kg⁻¹ for T for un-drained treatment. In comparison, the OC pool was 23.1 Mg ha⁻¹ for NT compared with 25.2 Mg ha⁻¹ for T for the drained plots. In general, the OC pool was higher in NT system, coupled with un-drained treatment than in drained T plots. The data indicate the importance of NT in improving the OC pool.     

Assessing management impacts on soil organic matter quality in subtropical Australian forests using physical and chemical fractionation as well as C NMR spectroscopy

Successful soil organic matter (SOM) quality assessment is needed to improve our ability to manage forest soils sustainably. Our objective was to use a multivariate data set to determine whether the land use conversion from native forest (NF) to hoop pine plantation and the following rotation and site preparation practices had altered SOM quality at three adjacent sites of NF, first (1R) and second rotation (2R, including tree planting row (2R-T) and windrow of harvest residues (2R-W)) of hoop pine plantations in southeast Queensland, Australia. Cross-polarization magic angle spinning ¹³C nuclear magnetic resonance (CPMAS ¹³C NMR) spectroscopy and sequential hot water and acid hydrolysis were conducted on SOM fractions separated by wet-sieving and density fractionation procedures to characterize SOM quantitative and qualitative relevant parameters, including carbon (C) functional groups, C and nitrogen (N) contents, C/N ratios, and C and N recalcitrant indices. Analysis of variance (ANOVA) and principal component analysis (PCA) of these multivariate parameters together indicated a complicated interaction between physical protection and biochemical recalcitrance, making the land use and management induced changes of SOM quality more complex. Knowledge of PCA based on the refined set of 41 SOM quantitative and qualitative parameters identified that principal component 1 (PC1), which explained 55.7% of the total variance, was most responsible for the management induced changes in soil processes. This was reflected by the dynamics of SOM regarding the aspects of total stock, soil basal and substrate induced respirations, gross and net N mineralization and nitrification, and microbial biomass, microbial diversity of C utilization patterns. Further, the macroaggregates (F_{250-2000 μm}) and the C/N ratio of acid extracts of SOM physical fractions, which represented the most informative and unique variables loading on PC1, might be the most promising physical and chemical measures for SOM quality assessment of land use and management impacts in subtropical Australian forests.     

稻田系统管理措施对微生物生物量C、N、P的长期影响

A 12-year field experiment was conducted to investigate the effect of different tillage methods and fertil-ization systems on microbial biomass C,N and P of a gray fluvo-aguic soil in rice-based cropping system .Five fertilization treatments were designed under conventional tillae(CT) or on tillage(NT) system:no fertilizer(CK) ; chemical fertilizer only(CF) ; combining chemical fertilizer with pig manure(PM); combining chemical fertilizer with crop straw (CS) and fallow (F). The results showed that biomass C,N and P were enriched in the surface layer of no-tilled soil,whereas they distributed relatively evenly in the tilled soil,which might result from enrichment of crop resdue,organic manure and mineral fertilzer,and surficial developent of root systems under NT.Under the cultivation system NT had slightly greater biomass C,N and P at 0-5 cm depth ,significantly less biomass C,N and P at 5-15 cm depth ,less microbial biomass C,N and equivalent biomass P at 15-30 cm depth as compared to CT,indicating hat tillage was beneficial for the multiplication of organims in the plowed layer of soil.Under the fallow system,biomass C,N and P in the surface layer were significantly greater for NT than CT while their differences between the two tillage methods were neligible in the deeper layers.In the surface layer,biomass C,N and P in the soils amended with oranic manure combined with mineral fertilizers were significantly greater than those of the treatments only with mineral fertilizers and the control.Soils without fertilzer had the least biomass nutrient contents among the five fertilization treatments.Obviously,the long-term application of organic manure could maintain the higher activity of microorganisms in soils.The amounts of biomass C,N and P in the fallowed soils varied with the tillage methods;they were much greater under NT than under CT,especially in the surface layer,suggesting that the frequent plowing could decrease the content of organic matter in the surface layer of the fallowed soil.     

Impacts of 22-year organic and inorganic N managements on soil organic C fractions in a maize field,northeast China

Impacts of 22-year organic and inorganic N managements on total organic carbon (TOC), water-soluble organic C (WSOC), microbial biomass C (MBC), particulate organic C (POC) and KMnO₄ oxidized organic C (KMnO₄-C) concentrations, C management index (CMI), and C storage in surface soil (0–20 cm) were investigated in a maize (Zea may L.) field experiment, Northeast China. The treatments included, CK: unfertilized control, M: organic manure (135 kg N ha^− 1 year^− 1), N: inorganic N fertilizer (135 kg N ha^− 1 year^− 1) and MN: combination of organic manure (67.5 kg N ha^− 1 year^− 1) and inorganic N fertilizer (67.5 kg N ha^− 1 year^− 1). TOC concentration and C storage were significantly increased under the M and MN treatments, but not under the inorganic N treatment. The organic treatments of M and MN were more effective in increasing WSOC, MBC, POC and KMnO₄-C concentrations and CMI than the N treatment. The M treatment was most effective for sequestrating SOC (10.6 Mg ha^− 1) and showed similar increase in degree of grain yield to the N and MN treatments, therefore it could be the best option for improving soil productivity and C storage in the maize cropping system.     

Twenty years of intensive fertilization and competing vegetation suppression in loblolly pine plantations: Impacts on soil C, N, and microbial biomass

Silvicultural treatments of fertilization (F) and competing vegetation suppression (H) have continued to increase as demands for forest products have grown. The effects of intensive annual F and H treatments on soil C, N, microbial biomass, and CO₂ efflux were examined in a two-way factorial experiment (control, F, H, FxH) in late-rotation (20+ years) loblolly pine stands. This study is unique in testing the cumulative effects of continual H and repeated F treatments for the first 20 years of stand growth, an uncommon operational practice, and in having treatments replicated upon four different soil types in the state of Georgia, USA. Annual fertilization included applications of N, P, K and periodic additions of micronutrients while competing vegetation suppression was maintained for all non-pine vegetation with herbicides throughout the rotation. Measurements included total O-horizon (forest floor) organic matter, C, and N, and 0-10 cm mineral soil pH, C, N, microbial biomass C and N, and surface CO₂ efflux. Sample collections and analyses were conducted seasonally for 1.5 yrs. Competing vegetation suppression was associated with a decrease of total soil C, soil microbial biomass C and N, and soil surface CO₂ efflux, while increasing O-horizon C:N. The fertilization treatment greatly reduced soil microbial biomass C and N, soil pH, and O-horizon C:N, while increasing O-horizon mass, N content, and soil carbon. No significant interactions between F and H were found. The combination of F and H treatments acted additively to achieve the greatest loss of soil microbial biomass, which may possibly have negative implications for long-term soil fertility.     

Organic C and N stabilization in a forest soil: Evidence from sequential density fractionation

In mineral soil, organic matter (OM) accumulates mainly on and around surfaces of silt- and clay-size particles. When fractionated according to particle density, C and N concentration (per g fraction) and C/N of these soil organo-mineral particles decrease with increasing particle density across soils of widely divergent texture, mineralogy, location, and management. The variation in particle density is explained potentially by two factors: (1) a decrease in the mass ratio of organic to mineral phase of these particles, and (2) variations in density of the mineral phase. The first explanation implies that the thickness of the organic accumulations decreases with increasing particle density. The decrease in C/N can be explained at least partially by especially stable sorption of nitrogenous N-containing compounds (amine, amide, and pyrrole) directly to mineral surfaces, a phenomenon well documented both empirically and theoretically. These peptidic compounds, along with ligand-exchanged carboxylic compounds, could then form a stable inner organic layer onto which other organics could sorb more readily than onto the unconditioned mineral surfaces (“onion” layering model).To explore mechanisms underlying this trend in C concentration and C/N with particle density, we sequentially density fractionated an Oregon andic soil at 1.65, 1.85, 2.00, 2.28, and 2.55 g cm⁻³ and analyzed the six fractions for measures of organic matter and mineral phase properties.All measures of OM composition showed either: (1) a monotonic change with density, or (2) a monotonic change across the lightest fractions, then little change over the heaviest fractions. Total C, N, and lignin phenol concentration all decreased monotonically with increasing density, and ¹⁴C mean residence time (MRT) increased with particle density from ca. 150 years to >980 years in the four organo-mineral fractions. In contrast, C/N, ¹³C and ¹⁵N concentration all showed the second pattern. All these data are consistent with a general pattern of an increase in extent of microbial processing with increasing organo-mineral particle density, and also with an “onion” layering model.X-ray diffraction before and after separation of magnetic materials showed that the sequential density fractionation (SDF) isolated pools of differing mineralogy, with layer-silicate clays dominating in two of the intermediate fractions and primary minerals in the heaviest two fractions. There was no indication that these differences in mineralogy controlled the differences in density of the organo-mineral particles in this soil. Thus, our data are consistent with the hypothesis that variation in particle density reflects variation in thickness of the organic accumulations and with an “onion” layering model for organic matter accumulation on mineral surfaces. However, the mineralogy differences among fractions made it difficult to test either the layer-thickness or “onion” layering models with this soil. Although SDF isolated pools of distinct mineralogy and organic-matter composition, more work will be needed to understand mechanisms relating the two factors.     

Changes in C and N fractions with composted manure plus chemical fertilizers applied in apple orchard soil: an in‐situ field incubation study on the Loess Plateau,China

We investigated the effects of compost (CM ), made from poultry and cattle manure with spent mushroom substrate, plus chemical fertilizers (CF s) on soil organic carbon (C) and nitrogen (N) fractions in silty loam soil of the Loess Plateau. Eight fertilizer practices were applied in a 7‐year‐old ‘Red Fuji’ apple (Malus domestica Borkh.) orchard for 360 days. Compared to CM alone, CM –CF s decreased slightly soil total organic C but increased total N by 4.3–11.6%. Notably, CM –CF s increased soil microbial biomass C (MBC ) by 2.7–26.5% and microbial biomass N (MBN ) by 7–13.7%. Soil water‐soluble carbon (WSC ) was increased by 20.7% and 19.2% when 2% CM plus N and phosphorus (P) (2%M–NP ) and 4% CM plus N and P (4%M–NP ) were applied, respectively. Whereas 0.5% CM plus N and P (0.5%M–NP ) increased WSC by 9.3% on day 30 but decreased it by 7.2% from 30–360 days. Hot water‐soluble C increased by 13.1–14.6% from 0–180 day, but thereafter, the effect disappeared. Compared to CF s, CM –CF s increased MBN by 35.1–115.6%, and increased alkali‐hydrolyzable‐N by 3.5–55.8% over 180–360 days of incubation. Additionally, CM –CF s promoted N mineralization, increasing NH ₄‐N and NO ₃‐N contents. Based on the changes in C and N fractions and available nutrients, 2%M–NP (45 t/ha of CM plus 450 kg/ha of N and 157.5 kg/ha of P) may be the optimal fertilizer strategy for stimulating soil microbial growth and activity, and enhancing nutrient cycling for apple growth.     

Long-term effects of lantana (Lantana spp. L.) residue additions on soil physical properties under rice–wheat cropping: I. Soil consistency, surface cracking and clod formation

Poor soil tilth is a major constraint in realizing optimum yield potential of wheat (Triticum aestivum L.) in rice (Oryza sativa L.)–wheat cropping system. The effect of long-term additions of lantana (Lantana spp. L.) biomass, a wild sage, on physical properties of a silty clay loam soil under rice–wheat cropping was studied in north-west India. Lantana was added to soil 10–15 d before puddling at 10, 20 and 30 Mg ha⁻¹ yr⁻¹ (fresh weight). At the end of 10th rice crop, liquid limit, plastic limit, shrinkage limit and plasticity index of soil increased significantly with lantana additions. The friability range of lantana-treated soil decreased from 8.9 to 7.8–8.2% gravimetric-moisture content, but soil became friable at relatively higher moisture content. Soil cracking changed from wide, deep cracks in hexagonal pattern to a close-spaced network of fine cracks. The cracks of sizes <5 mm increased, 10–20 mm and wider decreased, while 5–10 mm remained almost unchanged with lantana additions. The volume density of cracks decreased by 36–76% and surface area density by 19–37% compared with control. The clods of sizes <2 cm diameter increased, while 2–4 cm and 4–6 cm diameter decreased with lantana additions. The MWD of clods varied between 2.15 and 2.34 cm in lantana-treated soil as against 2.83 cm in the control. The bulk density and breaking strength of soil clods were lower in lantana-treated soil by 4–9% and 29–42% than in the control. About 23–47% less energy was required to prepare seed-bed in lantana-treated than in the control soil.     

Competition between invasive earthworms (Amynthas corticis, Megascolecidae) and native North American millipedes (Pseudopolydesmus erasus, Polydesmidae): Effects on carbon cycling and soil structure

Invasive earthworms can have significant impacts on C dynamics through their feeding, burrowing, and casting activities, including the protection of C in microaggregates and alteration of soil respiration. European earthworm invasion is known to affect soil micro- and mesofauna, but little is known about impacts of invasive earthworms on other soil macrofauna. Asian earthworms (Amynthas spp.) are increasingly being reported in the southern Appalachian Mountains in southeastern North America. This region is home to a diverse assemblage of native millipedes, many of which share niches with earthworm species. This situation indicates potential for earthworm-millipede competition in areas subject to Amynthas invasion.In a laboratory microcosm experiment, we used two ¹³C enriched food sources (red oak, Quercus rubra, and eastern hemlock, Tsuga canadensis) to assess food preferences of millipedes (Pseudopolydesmus erasus), to determine the effects of millipedes and earthworms (Amynthas corticis) on soil structure, and to ascertain the nature and extent of the interactions between earthworms and millipedes. Millipedes consumed both litter species and preferred red oak litter over eastern hemlock litter. Mortality and growth of millipedes were not affected by earthworm presence during the course of the experiment, but millipedes assimilated much less litter-derived C when earthworms were present.Fauna and litter treatments had significant effects on soil respiration. Millipedes alone reduced CO₂ efflux from microcosms relative to no fauna controls, whereas earthworms alone and together with millipedes increased respiration, relative to the no fauna treatment. CO₂ derived from fresh litter was repressed by the presence of macrofauna. The presence of red oak litter increased CO₂ efflux considerably, compared to hemlock litter treatments.Millipedes, earthworms, and both together reduced particulate organic matter. Additionally, earthworms created significant shifts in soil aggregates from the 2000-250 and 250-53 μm fractions to the >2000 μm size class. Earthworm-induced soil aggregation was lessened in the 0-2 cm layer in the presence of millipedes. Earthworms translocated litter-derived C to soil throughout the microcosm.Our results suggest that invasion of ecosystems by A. corticis in the southern Appalachian Mountains is unlikely to be limited by litter species and these earthworms are likely to compete directly for food resources with native millipedes. Widespread invasion could cause a net loss of C due to increased respiration rates, but this may be offset by C protected in water-stable soil aggregates.