Conventional tillage versus cover crops in relation to carbon fixation in Mediterranean olive cultivation

Background and Aims

For croplands, controversy persists concerning the adequacy of the soil use and the management of environmental problems such as soil erosion and fertility in a context of climate change. In this study, we used the RothC model to evaluate the capacity of carbon fixation by the soil in a Mediterranean olive grove for two different scenarios: the land-use change from native vegetation (NV) to conventional tillage (T) in the olive grove, and for the change in soil management from conventional tillage to cover crop (CC).

Methods

In three experimental olive groves in Andalusia (S Spain) two soil-management systems were sampled: T and CC. Areas of NV adjacent to the grove were also sampled as indicative of the initial state of the soil without olive trees. We measured the aboveground biomass production of the cover and the clay content, bulk density, and soil organic carbon (SOC) for 0–5, 5–15 and 15–30 cm depth.

Results

The removal of NV to implement T resulted in a significantly loss of SOC that depended mainly on the relief of the terrain. However, the use of CC increased the SOC because of greater inputs (above-and belowground plant inputs) to the soil. The final concentration at each location was related to the carbon inputs and the clay content. The CC resulted in carbon storage during the first year of 4.02?±?1.65 Mg C ha^?1, and a total carbon fixation by the soil of 5.91?±?2.06 Mg C ha^?1.

Conclusion

The use of cover crops in Mediterranean olive groves proved to be a suitable strategy to increase the carbon storage into the soil and then to decrease the CO₂ concentration in the atmosphere.     

Fertilization enhancing carbon sequestration as carbonate in arid cropland: assessments of long-term experiments in northern China

Aims

Soil inorganic carbon (SIC), primarily calcium carbonate, is a major reservoir of carbon in arid lands. This study was designed to test the hypothesis that carbonate might be enhanced in arid cropland, in association with soil fertility improvement via organic amendments.

Methods

We obtained two sets (65 each) of archived soil samples collected in the early and late 2000’s from three long-term experiment sites under wheat-corn cropping with various fertilization treatments in northern China. Soil organic (SOC), SIC and their Stable ¹³C compositions were determined over the range 0–100 cm.

Results

All sites showed an overall increase of SIC content in soil profiles over time. Particularly, fertilizations led to large SIC accumulation with a range of 101–202 g C m^?2 y^?1 in the 0–100 cm. Accumulation of pedogenic carbonate under fertilization varied from 60 to 179 g C m^?2 y^?1 in the 0–100 cm. Organic amendments significantly enhanced carbonate accumulation, in particular in the subsoil.

Conclusions

More carbon was sequestrated in the form of carbonate than as SOC in the arid cropland in northern China. Increasing SOC stock through long-term straw incorporation and manure application in the arid and semi-arid regions also enhanced carbonate accumulation in soil profiles.     

Effect of the replacement of tropical forests with tree plantations on soil organic carbon levels in the Jomoro district,Ghana

Background and aims

In the Jomoro district in Ghana, tree plantations were the first cause of deforestation in the past, drastically reducing the area occupied by primary forests. The aim of this study was to quantify soil organic carbon (SOC) losses due to a change in land use from primary forest to tree plantations (cocoa, coconut, rubber, oil palm) on the different substrates of the district. Secondary forests and mixed plantations were also included in the study.

Methods

Soils were sampled at different depths up to 100 cm along a series of chronosequences in each of the three substrates (Granite, Lower Birrimian and Tertiary Sands) present in the area.

Results

The highest SOC losses in the 0–30 cm layer were caused by the conversion of primary forests to tree plantations: cocoa ?61 % of the original SOC stock, coconut ?55 %, rubber ?35 % and oil palm 28 %, while mixed plantations and secondary forests showed a loss of 23 % and 21 % of the original SOC stock, respectively. C losses were less apparent from the entire profile (to a depth of 100 cm).

Conclusions

All conversions to tree plantations caused substantial SOC losses, comparable to the conversion of forests to agricultural systems. Secondary forests and mixed plantations were the only sustainable land uses that restricted SOC losses considerably.     

Converting paddy fields to Lei bamboo (Phyllostachys praecox) stands affected soil nutrient concentrations, labile organic carbon pools, and organic carbon chemical compositions

Background and aims

Land-use change often markedly alters soil carbon (C) and nitrogen (N) pool sizes with implications for climate change and soil sustainability. The objective of this research was to study the effect of converting paddy fields to Lei bamboo (Phyllostachys praecox) stands on soil C and N and other nutrient pools as well as the chemical structure of soil organic C (SOC) in the soil profile.

Methods

Soils (Anthrosols) from four adjacent paddy field–bamboo forest pairs with a known land-use history were sampled from Lin’an County, Zhejiang Province. Soil water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water soluble organic N (WSON), and other soil chemical and physical properties were determined. Soil organic C functional group compositions were determined by ¹³C-nuclear magnetic resonance (NMR).

Results

Concentrations of soil available P, available K, and different N forms increased (P?<?0.05) by the land-use conversion. Higher concentrations of SOC and total N (TN) were observed in the subsoil (20–40 and 40–60 cm soil layers) but not in the topsoil (0–20 cm layer) in the bamboo stands than in the paddy fields. The storage of SOC and TN in the entire soil profile (0–60 cm) increased by 56.7 and 70.7 %, respectively, after the land-use change. The increases in the SOC stock of the three soil layers were 11.0, 14.3, and 9.5 Mg C ha^?1, respectively. The conversion decreased WSOC concentrations in the subsoil but increased the ROC concentration in the topsoil. Solid-state NMR spectroscopy of soil samples showed that the conversion increased (P?<?0.05) the O-alkyl C content while decreased the aromatic C content, alkyl C to O-alkyl C ratio (A/O-A), and aromaticity of SOC.

Conclusions

Conversion of paddy fields to bamboo stands increased soil nutrient availability, and SOC and TN stocks. Effects of land-use change on C pools and C chemistry of SOC varied among different soil layers in the profile. The impact of the land-use conversion on soil organic C pools was not restricted to the topsoil, but changes in the subsoil were equally large and should be accounted for.     

Soil Carbon Storage by Switchgrass Grown for Bioenergy

Life-cycle assessments (LCAs) of switchgrass (Panicum virgatum L.) grown for bioenergy production require data on soil organic carbon (SOC) change and harvested C yields to accurately estimate net greenhouse gas (GHG) emissions. To date, nearly all information on SOC change under switchgrass has been based on modeled assumptions or small plot research, both of which do not take into account spatial variability within or across sites for an agro-ecoregion. To address this need, we measured change in SOC and harvested C yield for switchgrass fields on ten farms in the central and northern Great Plains, USA (930 km latitudinal range). Change in SOC was determined by collecting multiple soil samples in transects across the fields prior to planting switchgrass and again 5 years later after switchgrass had been grown and managed as a bioenergy crop. Harvested aboveground C averaged 2.5?±?0.7 Mg C ha^?1 over the 5 year study. Across sites, SOC increased significantly at 0–30 cm (P?=?0.03) and 0–120 cm (P?=?0.07), with accrual rates of 1.1 and 2.9 Mg C ha^?1 year^?1 (4.0 and 10.6 Mg CO₂ ha^?1 year^?1), respectively. Change in SOC across sites varied considerably, however, ranging from ?0.6 to 4.3 Mg C ha^?1 year^?1 for the 0–30 cm depth. Such variation in SOC change must be taken into consideration in LCAs. Net GHG emissions from bioenergy crops vary in space and time. Such variation, coupled with an increased reliance on agriculture for energy production, underscores the need for long-term environmental monitoring sites in major agro-ecoregions.     

Effect of conventional versus mechanized sugarcane cropping systems on soil organic carbon stocks and labile carbon pools in Mauritius as revealed by 13C natural abundance

Aims

Maintenance of adequate levels of soil organic carbon (SOC) is crucial for the biological, chemical and physical functioning of soils. This study was conducted (i) to determine the impact of long-term sugarcane monoculture on total SOC stocks and on its labile fractions and (ii) to quantify the loss of original SOC and the accretion of sugarcane-derived C following the adoption of new management practices namely de-rocking/land grading and mechanized harvesting.

Methods

Five study sites representing the five major soil groups under sugarcane in Mauritius were selected with a classical “paired-plot” design adopted. In this design, two sites with similar initial conditions were developed in different ways over time. One represents the reference soil (virgin land with predominantly C₃ type vegetation) and the other represents one of the following cropping treatments: (i) fields continuously cultivated with sugarcane for more than 25 or 50 years without de-rocking or land grading, (ii) fields under long-term sugarcane but having undergone de-rocking and land grading for mechanized harvesting in the last 3 years. Soil samples were taken to a depth of 50 cm and analysed for total organic C, labile C, ¹³C natural abundance, bulk density and stone content.

Results

Changes in SOC stock in the 0–50 cm profile following >50 years of cane cropping were not significant (P?>?0.05) compared to virgin land at any site. Soil δ¹³C values revealed that long-term sugarcane cultivation resulted in a depletion of original SOC by 34 to 70 %. However, this loss was fully compensated by C input from sugarcane residues at all sites studied resulting in no net change in SOC stock. Adoption of mechanized harvest did not have any detrimental effect on SOC stocks due to C inputs from crop residues. However, long-term sugarcane cultivation resulted in significant decline in a labile C (KMnO₄-oxidizable) fraction.

Conclusion

Despite the large losses of original C following conversion from forest to sugarcane, long-term sugarcane cultivation resulted in sequestration of sugarcane-derived C which adequately compensated these losses. Moreover, intensive de-rocking and land grading preceding mechanized harvesting did not have any detrimental effect on SOC stocks. However, the quality of sugarcane soils, as indicated by a decline in labile C, could be degraded.     

Effect of wildfires on soil respiration in three typical Mediterranean forest ecosystems in Madrid, Spain

Background and Aims

Mediterranean forests are vulnerable to numerous threats including wildfires due to a combination of climatic factors and increased urbanization. In addition, increased temperatures and summer drought lead to increased risk of forest fires as a result of climate change. This may have important consequences for C dynamics and balance in these ecosystems. Soil respiration was measured over 2 successive years in Holm oak (Quercus ilex subsp. ballota; Qi); Pyrenean Oak (Quercus pyrenaica Willd; Qp); and Scots pine (Pinus sylvestris L.; Ps) forest stands located in the area surrounding Madrid (Spain), to assess the long term effects of wildfires on C efflux from the soil, soil properties, and the role of soil temperature and soil moisture in the variation of soil respiration.

Methods

Soil respiration, soil temperature, soil moisture, fine root mass, microbial biomass, biological and chemical soil parameters were compared between non burned (NB) and burned sites (B).

Results

The annual C losses through soil respiration from NB sites in Qi, Qp and Ps were 790, 1010, 1380 gCm^?2?yr^?1, respectively, with the B sites emitting 43 %, 22 % and 11 % less in Qi, Qp and Ps respectively. Soil microclimate changed with higher soil temperature and lower soil moisture in B sites after fire. Exchangeable cations and the pH also decreased. The total SOC stocks were not significantly altered, but 6–8 years after wildfires, there was still measurably lower fine root and microbial biomass, while SOC quality changed, indicated by lower the C/N ratio and the labile carbon and a relative increase in refractory SOC forms, which resulted in lower Q₁₀ values.

Conclusions

We found long term effects of wildfires on the physical, chemical and biological soil characteristics, which in turn affected soil respiration. The response of soil respiration to temperature was controlled by moisture and changed with ecosystem type, season, and between B and NB sites. Lower post-burn Q₁₀ integrated the loss of roots and microbial biomass, change in SOC quality and a decrease in soil moisture.     

Ozone pollution influences soil carbon and nitrogen sequestration and aggregate composition in paddy soils

Background and aims

Much attention has focused on the effects of tropospheric ozone (O₃) on terrestrial ecosystems and plant growth. Since O₃ pollution is currently an issue in China and many parts of the world, understanding the effects of elevated O₃ on soil carbon (C) and nitrogen (N) sequestration is essential for efforts to predict C and N cycles in terrestrial ecosystems under predicted increases in O₃. Thus the main objective of this study was to determine whether an increases in atmospheric O₃ concentration influenced soil organic C (SOC) and N sequestration.

Methods

A free-air O₃ enrichment (O₃-FACE) experiment was started in 2007 and used continuous O₃ exposure from March to November each year during crop growth stage in a rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation field in the Jiangsu Province, China. We investigated differences in SOC and N and soil aggregate composition in both elevated and ambient O₃ conditions.

Results

Elevated atmospheric O₃ (18–80 nmol mol^?1 or 50 % above the ambient) decreased the SOC and N concentration in the 0–20 cm soil layer after 5 years. Elevated O₃ significantly decreased the SOC concentration by 17 % and 5.6 % in the 0–3 cm and the 10–20 cm layers, respectively. Elevated O₃ significantly decreased the N concentration by 8.2–27.8 % in three layers at the 20 cm depth. In addition, elevated O₃ influenced the formation and transformation of soil aggregates and the distribution of SOC and N in the aggregates across soil layer classes. Elevated O₃ significantly decreased the macro-sized aggregate fraction (16.8 %) and associated C and N (0.5 g kg^?1 and 0.32 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (61 %) and associated C (1.7 g kg^?1) in the 0–3 cm layer. Elevated O₃ significantly decreased the macro-sized aggregate fraction (9.6 %) and associated C and N (1.4 g kg^?1 and 0.35 g kg^?1, respectively), and significantly increased the silt+ clay-sized aggregate fraction (41.8 %) and decreased the corresponding associated N (0.14 g kg^?1) in the 3–10 cm layer. Elevated O₃ did not significantly effect the formation and transformation of aggregates in the 10–20 cm layer, yet it did significantly increase the C concentration in the macro-sized fraction (1 g kg^?1) and decrease the N concentration in the macro- and micro-sized fractions (0.24 g kg^?1 and 0.16 g kg^?1, respectively).

Conclusion

Long-term exposure to elevated atmospheric O₃ negatively affected the physical structure of the soil and impaired soil C and N sequestration.     

Plant growth regulator and nitrogen fertilizer effects on soil organic carbon sequestration in creeping bentgrass fairway turf

The objective of this study was to determine the effects of plant growth regulator (PGR) (no PGR, trinexapac-ethyl, and paclobutrazol) and N fertilizer (zero N, an average of 37 kg N ha^?1 month^?1, 6 and 12 kg N ha^?1 week^?1) on soil organic C (SOC) and soil N in creeping bentgrass (Agrostis stolonifera L.) fairway turf. After 4 years of field experiments soil samples were obtained from soil depths of 0–2.5, 2.5–5, 5–7.5, 7.5–10, 10–15, 15–20, and 20–30 cm. Soil bulk density, SOC, total N, NO ₃ ^? –N, and NH ₄ ⁺ –N concentrations were determined. Paclobutrazol and trinexapac-ethyl application increased SOC. The 37 kg N ha^?1 month^?1 application increased SOC at the 0–2.5 cm depth with both PGRs. When paclobutrazol was used, N fertilizer always increased SOC; however, the greatest increase was observed with the 12 kg N ha^?1 week^?1 application when compared to other rates, inversely related to the NH ₄ ⁺ –N concentration. Nitrogen application increased soil total N and NO ₃ ^? –N in the upper three depths. The application of PGRs and N fertilizer to creeping bentgrass fairway turf is an effective strategy for promoting C sequestration.     

Zinc fertilizer placement affects zinc content in maize plant

Background and aims

Adequate zinc (Zn) in maize (Zea mays L.) is required for obtaining Zn-enriched grain and optimum yield. This study investigated the impact of varying Zn fertilizer placements on Zn accumulation in maize plant.

Methods

Two pot experiments with same design were conducted to investigate the effect of soil Zn heterogeneity by mixing ZnSO₄·7H₂O (10 mg Zn kg^?1 soil on an average) in 10–15, 0–15, 25–30, 0–30, 30–60 and 0–60 cm soil layers on maize root growth and shoot Zn content at flowering stage in experiment-1, and assessing effects on grain Zn accumulation at mature stage in experiment-2.

Results

In experiment-1, Zn placements created a large variation in soil DTPA-Zn concentration (0.3–29.0 mg kg^?1), which induced a systemic and positive response of root growth within soil layers of 0–30 cm; and shoot Zn content was increased by 102 %–305 % depending on Zn placements. Supply capacity of Zn in soil, defined as sum of product of soil DTPA-Zn concentration and root surface area at different soil layers, was most related to shoot Zn content (r?=?0.82, P?<?0.001) via direct and indirect effects according to path analysis. In experiment-2, Zn placements increased grain Zn concentration by up to 51 %, but significantly reduced the grain Zn harvest index from 50 % by control to about 30 % in average.

Conclusion

Matching the distribution of soil applied Zn with root by Zn placement was helpful to maximize shoot Zn content and grain Zn concentration in maize.     

Ecosystem carbon storage and soil organic carbon stability in pure and mixed stands of Cunninghamia lanceolata and Michelia macclurei

Background and aims

Across the world, about 264 million ha forest plantations are monospecific. This practice has been found to cause site productivity and soil fertility decline in the regions where forests have been harvested several times. To mitigate these problems, mixed-species plantations, especially with broadleaved and coniferous species, are preferred. Understanding the effects of introducing broadleaved tree in monospecific coniferous plantation on ecosystem carbon (C) storage and soil organic C (SOC) stability is critical to improve our understanding of forest C sequestration and C cycle.

Methods

Plots were established in subtropical plantations with a randomized block design to examine the influence of introducing Michelia macclurei trees into pure Cunninghamia lanceolata plantation on biomass C storage, SOC storage of total, labile, and recalcitrant fractions (0–40 cm depth), and SOC stability.

Results

Introducing M. macclurei trees increased biomass C by 17.9 % and 14.2 % compared with monospecific C. lanceolata and M. macclurei plantations, respectively. Storage of different SOC fractions was not significantly different between monospecific C. lanceolata and mixed plantations. SOC stability in bulk soils was not affected, although it differed in 10–20 cm and 20–40 cm soil depth among three plantations.

Conclusions

Mixed species plantations can increase C sequestration, and in the subtropical forest ecosystem examined this was mainly attributed to an increase in biomass C.     

Coupled response of soil carbon and nitrogen pools and enzyme activities to nitrogen and water addition in a semi-arid grassland of Inner Mongolia

Background and aims

Previous studies have demonstrated positive net primary production effects with increased nitrogen (N) and water availability in Inner Mongolian semi-arid grasslands. However, the responses of soil carbon (C) and N concentrations and soil enzyme activities as indicators of impacts of long-term N (urea) and water addition are still unclear. We tested the effect of 7 years of a N and water addition experiment on soil C, N, and specific soil-bound enzymes in a semi-arid grassland of Inner Mongolia.

Methods

We determined concentrations of soil organic carbon (SOC) and soil total nitrogen (TN) in both the 0–10 and 10–20 cm soil layers. Concentrations of labile carbon (LC) and inorganic nitrogen (nitrate and ammonium), and soil pH were measured. Additionally, soil dehydrogenase (DHA), β-glucosidase (BG) and acid and alkaline phosphomonoesterase (PME) enzyme activities were determined in the 0–10 cm soil layer.

Results

SOC concentration in the 0–10 cm soil layer showed no response to N addition or N plus water addition, but increased with water addition alone by 0.3–15.7 %. N addition significantly increased nitrate by 46.0–138.4 % and ammonium by 19.0–73.3 % in the 0–10 cm soil layer, whereas water addition did not affect them. The activities of DHA and alkaline PME enzymes, as well as soil pH, in the 0–10 cm layer decreased with N addition, however water addition alone caused these enzyme activities to increase. Unlike the surface soil (0–10 cm), the lower soil layer (10–20 cm), was responsive to N and water addition in that SOC and TN concentrations decreased with N addition and increased with water addition.

Conclusions

The accumulation of SOC and TN in N and water addition plots may be caused by the input of plant biomass exceeding SOC decomposition. Decrease in microbial activity, derived from decreased DHA and alkaline PME activities might result from suppression effects of lower pH and decreased microbial N supply. Water availability is proved to be more important than N availability for soil C and N accumulation in this semi-arid grassland.     

Soil Greenhouse Gas Emissions and Carbon Dynamics of a No-Till,Corn-Based Cellulosic Ethanol Production System

Crop residues like corn (Zea mays L.) stover perform important functions that promote soil health and provide ecosystem services that influence agricultural sustainability and global biogeochemical cycles. We evaluated the effect of corn stover removal from a no-till, corn-soybean (Glycine max (L.) Merr) rotation on soil greenhouse gas (GHG; CO₂, N₂O, CH₄) fluxes, crop yields, and soil organic carbon (SOC) dynamics. We conducted a 4-year study using replicated field plots managed with two levels of corn stover removal (none; 55 % stover removal) for four complete crop cycles prior to initiation of ground surface gas flux measurements. Corn and soybean yields were not affected by stover removal with yields averaging 7.28 Mg ha^?1 for corn and 2.64 Mg ha^?1 for soybean. Corn stover removal treatment did not affect soil GHG fluxes from the corn phase; however, the treatment did significantly increase (107 %, P?=?0.037) N₂O fluxes during the soybean phase. The plots were a net source of CH₄ (～0.5 kg CH₄-C ha^?1 year^?1 average of all treatments and crops) during the generally wet study duration. Soil organic carbon stocks increased in both treatments during the 4-year study (initiated following 8 years of stover removal), with significantly higher SOC accumulation in the control plots compared to plots with corn stover removal (0–15 cm, P?=?0.048). Non-CO₂ greenhouse gas emissions (945 kg CO₂-eq ha^?1 year^?1) were roughly half of SOC (0–30 cm) gains with corn stover removal (1.841 Mg CO₂-eq ha^?1 year^?1) indicating that no-till practices greatly improve the viability of biennial corn stover harvesting under local soil-climatic conditions. Our results also show that repeated corn stover harvesting may increase N loss (as N₂O) from fields and thereby contribute to GHG production and loss of potential plant nutrients.     

Effect of long-term tillage and mineral phosphorus fertilization on arbuscular mycorrhizal fungi in a humid continental zone of Eastern Canada

Aims

Evidence shows that tillage modifies soil properties, especially phosphorus (P) dynamics. Our objective was to disentangle long-term effects of P-fertilization and tillage on arbuscular mycorrhizal fungal (AMF) proliferation and community structure.

Methods

Changes in the community structure of AMF and in the density of their hyphae and spores induced by moldboard plow (MP) or no till (NT), and fertilization with 0, 17.5, or 35 kg?P?ha^?1 were sought in the 0–15 cm and 15–30 cm soil layers after soybean harvest, at a long-term (17 years) experimental site in a humid continental zone of eastern Canada. The relationships among AMF, soil and plant attributes were examined.

Results

The 0–15 cm and 15–30 cm soil layers had different properties under NT, but were similar under MP, after 17 years, and MP increased soil available P levels. Phosphorus fertilization increased P levels in soil and in soybean. Treatment effects on AMF spore and hyphal density at 0–15 cm were greater than that at 15–30 cm, whereas effects on AMF community structure did not change with soil depths. At 0–15 cm, P-fertilization increased AMF spore density and reduced AMF hyphal density, and MP reduced AMF spore density. A total of eight AMF phylotypes were detected. Phosphorus fertilization reduced AMF phylotype richness and Shannon diversity index. Soil P availability increased under MP and hence the influence of P-fertilization treatments on the frequency of AMF phylotype detection varied with tillage system; it declined with P-fertilization under MP, but increased under NT.

Conclusions

Phosphorus fertilization shifts resource partitioning in AMF propagules rather than in their hyphae, and degrades the genetic diversity of AMF in soil; tillage increases soil P availability and hence aggravates the impact of P-fertilization.     

Differential soil organic carbon storage at forb- and grass-dominated plant communities, 33 years after tallgrass prairie restoration

Background and aims

Dominance of C₄ grasses has been proposed as a means of increasing soil organic carbon (SOC) sequestration in restored tallgrass prairies. However, this hypothesis has not been tested on long time scales and under realistic (e.g. N-limited) environmental conditions. We sampled a restoration in southern Illinois 33 years after establishment to determine the effects of varying plant communities on SOC sequestration in the top 50 cm of soil.

Methods

SOC, total nitrogen (TN), and the stable isotopic composition of SOC (δ¹³C) were used to calculate SOC sequestration rates, N storage, and the relative contributions of C₃ vs. C₄ plant communities as a function of soil depth.

Results

While both a forb-dominated and a mixed forb-grass plant community showed positive sequestration rates (0.56?±?0.13 and 0.27?±?0.10 Mg C ha^?1 yr^?1, respectively), a C₄ grass-dominated community showed SOC losses after 33 years of restoration (?0.31?±?0.08 Mg C ha^?1 yr^?1). Soil δ¹³C values were significantly more negative for forb-dominated plant communities, increasing the confidence that plant communities were stable over time and an important contributor to differences in SOC stocks among transects.

Conclusion

These results suggest that functional diversity may be necessary to sustain sequestration rates on the scale of decades, and that dominance of C₄ grasses, favored by frequent burning, may lead to SOC losses over time.     

Nitrogen dynamics following field application of biochar in a temperate North American maize-based production system

Background and aims

Biochar additions to tropical soils have been shown to reduce N leaching and increase N use efficiency. No studies exist verifying reduced N leaching in field experiments on temperate agricultural soils or identifying the mechanism for N retention.

Methods

Biochar derived from maize stover was applied to a maize cropping system in central New York State at rates of 0, 1, 3, 12, and 30 t?ha^-1 in 2007. Secondary N fertilizer was added at 100, 90, 70, and 50 % of the recommended rate (108 kg N ha^-1). Nitrogen fertilizer enriched with ¹⁵?N was applied in 2009 to the 0 and 12 t?ha^-1 of biochar at 100 and 50 % secondary N application.

Results

Maize yield and plant N uptake did not change with biochar additions (p?>?0.05; n?=?3). Less N (by 82 %; p?<?0.05) was lost after biochar application through leaching only at 100 %?N fertilization. The reason for an observed 140 % greater retention of applied ¹⁵?N in the topsoil may have been the incorporation of added ¹⁵?N into microbial biomass which increased approximately three-fold which warrants further research. The low leaching of applied fertilizer ¹⁵?N (0.42 % of applied N; p?<?0.05) and comparatively high recovery of applied ¹⁵?N in the soil (39 %) after biochar additions after one cropping season may also indicate greater overall N retention through lower gaseous or erosion N losses with biochar.

Conclusions

Addition of biochar to fertile soil in a temperate climate did not improve crop growth or N use efficiency, but increased retention of fertilizer N in the topsoil.     

Crop Residue Mass Needed to Maintain Soil Organic Carbon Levels: Can It Be Determined?

Corn’s (Zea mays L.) stover is a potential nonfood, herbaceous bioenergy feedstock. A vital aspect of utilizing stover for bioenergy production is to establish sustainable harvest criteria that avoid exacerbating soil erosion or degrading soil organic carbon (SOC) levels. Our goal is to empirically estimate the minimum residue return rate required to sustain SOC levels at numerous locations and to identify which macroscale factors affect empirical estimates. Minimum residue return rate is conceptually useful, but only if the study is of long enough duration and a relationship between the rate of residue returned and the change in SOC can be measured. About one third of the Corn Stover Regional Partnership team (Team) sites met these criteria with a minimum residue return rate of 3.9?±?2.18 Mg stover ha^?1 yr^?1, n?=?6. Based on the Team and published corn-based data (n?=?35), minimum residue return rate was 6.38?±?2.19 Mg stover ha^?1 yr^?1, while including data from other cropping systems (n?=?49), the rate averaged 5.74?±?2.36 Mg residue ha^?1 yr^?1. In broad general terms, keeping about 6 Mg residue ha^?1 yr^?1 maybe a useful generic rate as a point of discussion; however, these analyses refute that a generic rate represents a universal target on which to base harvest recommendations at a given site. Empirical data are needed to calibrate, validate, and refine process-based models so that valid sustainable harvest rate guidelines are provided to producers, industry, and action agencies.     

Potassium release characteristics, potassium balance, and fingermillet (Eleusine coracana G.) yield sustainability in a 27- year long experiment on an Alfisol in the semi-arid tropical India

Aims

In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978–2004) years of cropping fingermillet (Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India.

Methods

Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha^?1 farm yard manure (FYM), 10 Mg ha^?1 FYM +50 % NPK, 10 Mg ha^?1 FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO₃ (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl₂ (mild extracting solution).

Results

Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions.

Conclusion

For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity.     

Mitigation of greenhouse gas emissions from reed canary grass in paludiculture: effect of groundwater level

Background and aims

Combination of rewetting and wetland crop cultivation (paludiculture) is pursued as a wider carbon dioxide (CO₂) mitigation option in drained peatland. However, information on the overall greenhouse gas (GHG) balance for paludiculture is lacking. We investigated the GHG balance of peatlands grown with reed canary grass (RCG) and rewetted to various extents.

Methods

Gas fluxes of CO₂, methane (CH₄) and nitrous oxide (N₂O) were measured with a static chamber technique for 10 months from mesocosms sown with RCG and manipulated to ground water levels (GWL) of 0, ?10, ?20, ?30 and ?40 cm below the soil surface. Gross primary production (GPP) was estimated from the above ground biomass yield.

Results

The mean dry biomass yield across all water table treatments was 6 Mg ha^?1 with no significant differences between the treatments. Raising the GWL to the surface decreased both the net ecosystem exchange (NEE) of CO₂ and N₂O emissions whereas CH₄ emissions increased. Total cumulative GHG emissions (for 10 months) corresponded to 0.08, 0.13, 0.61, 0.68 and 0.98 kg CO₂ equivalents m^?2 from the GWL treatments at 0, ?10, ?20, ?30 and ?40 cm below the soil surface, respectively.

Conclusions

The results showed that a reduction in total GHG emission can be achieved without losing the productivity of newly established RCG when GWL is maintained close to the surface. Further studies should address the practical constrains and long-term productivity of RCG cultivation in rewetted peatlands.     

Causes of variation in mineral soil C content and turnover in differently managed beech dominated forests

Background and aims

Forest soils are important carbon stores and considered as net CO₂ sinks over decadal to centennial time scales. Intensive forest management is thought to reduce the carbon sequestration potential of forest soils. Here we study the effects of decades of forest management (as unmanaged forest, forest under selection cutting, forest under age class management) on the turnover of mineral associated soil organic matter (MOM) in German beech (Fagus sylvatica L.) dominated forests.

Methods

Radiocarbon contents were determined by accelerator mass spectrometry (AMS) in 79 Ah horizon MOM fractions of Cambisols (n?=?13), Luvisols (n?=?51) and Stagnosols (n?=?15). Mean residence times (MRTs) for soil organic carbon (SOC) were estimated with a 2-pool model using the litter input derived from a forest inventory.

Results

MOM fractions from Ah horizons contained 64?±?8.8 % of the bulk SOC. The radiocarbon content of MOM fractions in Ah horizons, expressed as Δ¹⁴C, ranged between ?2.8?‰ and 114?‰ for the three soil groups. Almost all samples contained a detectable proportion of ‘bomb’ carbon fixed from the atmosphere since 1963. Under the assumption that depending on the soil texture between 19 % and 24 % of the SOC from the labile pool is transferred to the stable SOC pool, the corresponding MRTs ranged between 72 and 723 years, with a median of 164 years.

Conclusions

Our results indicate that the MOM fraction of Ah horizons from beech forests contained a high proportion of young carbon, but we did not find a significant decadal effect of forest management on the radiocarbon signature and related turnover times. Instead, both variables were controlled by clay contents and associated SOC concentrations (p?<?0.01). This underlines the importance of pedogenic properties for SOC turnover in the MOM fraction.