• Authors:
    • Herrera, F.
    • Rasse, R.
    • Giuliante, A.
    • Donoso, L.
    • Perez, T.
    • Marquina, S.
  • Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
  • Volume: 101
  • Issue: 1
  • Year: 2015
  • Summary: The largest share of Latin American and Caribbean (LAC) anthropogenic greenhouse gases is derived from land use changes as well as forestry and agriculture, representing up to 67 % of the relative contribution from all sources. However, in spite of the rapid expansion of LAC tropical agriculture, little is known about its impact on atmospheric trace gases emissions, such as nitrogen oxides (NO (x) ), nitrous oxide (N2O) and carbon dioxide (CO2), which are produced in soils by microbial processes and also accelerated in tropical climates. This information is crucial for assessing mitigation strategies linked to agricultural practices to satisfy food demands for the region's future. We measured NO, N2O and CO2 soil emissions along with soil variables from corn fields under tillage (T) and no-tillage (NT) agriculture at two of the largest cereal-producing regions in Venezuela during the crop-growing season. We found statistically significant positive correlations between the logarithms of nitrogen gas emissions and soil inorganic nitrogen concentrations, soil water and clay contents. Average emissions of NO and CO2 were larger in T than NT sites, while N2O fluxes showed the opposite. CO2 emissions from T were 1.6 as much as those found in NT, whereas N2O was 0.5 of that found in NT. These results imply that NT practices more effectively mitigate climate change from these monoculture systems mainly because of CO2 emission reduction. We suggest then that agricultural mitigation actions for tropical monoculture systems should aim for the enhancement of NT management practices along with N fertilization rate reduction to compensate for the larger N2O emissions.
  • Authors:
    • Ferraudo, A. S.
    • Teixeira, D. D. B.
    • Panosso, A. R.
    • Padovan, M. P.
    • Moitinho, M. R.
    • La Scala, N., Jr.
  • Source: Soil and Tillage Research
  • Volume: 148
  • Year: 2015
  • Summary: CO2 production in soil is the result of biological processes, such as the decomposition of organic matter and the respiration of roots and soil organisms. It also depends on the physical, chemical and biological properties and their interactions. Such properties exhibit variability in space and time, which provides a high degree of complexity on soil CO2 emission (FCO2). However few studies discuss the spatial and temporal component of FCO2, jointly. The objective of this study was to characterize the spatial and temporal variability of FCO2 and its relationship to the edaphoclimatic properties of the soil in sugarcane fields. The LI-8100 system, which monitors changes in CO2 concentrations within a portable chamber, was used to assess the FCO2. The CO2 flux measurements, soil temperature (0-20cm, thermometer of LI-8100) and soil water content (0-12cm, TDR device) were evaluated concomitantly. Overall, the mean values for FCO2, soil temperature and soil water content were 2.8μmolm-2s-1, 19.48°C and 17.20m3m-3, respectively. The FCO2 was positively correlated with the soil organic matter content (SOM) (r=0.67, p<0.001), the air-filled porosity (AFP) (r=0.71, p<0.001) and the available phosphorus (r=0.28, p<0.05) but negatively correlated with the soil C/N ratio (r=-0.75, p<0.001) and soil water content (r=-0.29, p<0.05). The air-filled porosity was the last property added to the multiple regression model and explained 77% of the spatial variability in soil CO2 emission. The largest temporal variations in CO2 emissions over the study period were explained by changes in soil water content, especially after rainfall. Spatially, the CO2 emission is modeled by chemical (organic matter and soil C/N ratio) and physical (air-filled porosity) soil properties which are associated to production and transport of CO2 in soil.
  • Authors:
    • Ishak, C. F.
    • Hanif, A. H. M.
    • Goh, K. J.
    • Sung, C. T. B.
    • Moradi, A.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 145
  • Year: 2015
  • Summary: Mulching materials from oil palm residues such as pruned palm fronds (OPF), empty fruit bunches (EFB), and Eco-mat (ECO; a compressed EFB mat) are often the recommended soil and water conservation practices (CP) for oil palm plantations on hill slopes. Another recommended CP is the construction of silt pits or trenches (SIL) across the hill slope to capture runoff and then return the water and nutrients into the surrounding soil. Although these four CP are recommended practices, their relative effects on improving soil physical properties and on increasing the soil water content have never been compared with one another. Consequently, the objective of this study was to fill in this knowledge gap. A three-year field experiment was conducted in a non-terraced oil palm plantation, and soil samples from 0 to 0.15, 0.15 to 0.30, and 0.30 to 0.45. m depths were collected every three months and analyzed for their soil physical properties. Soil water content up to 0.75. m depth was also measured daily. EFB released the highest amount of organic matter and nutrients into the soil compared to OPF, ECO, and SIL. Hence, EFB was most effective to increase soil aggregation, aggregate stability, soil water retention at field capacity, available soil water content, and the relative proportion of soil mesopores. Due to these improved soil physical properties, EFB also gave the highest soil water content. Unlike ECO that concentrated more water in the upper soil layers, EFB distributed the soil water more uniformly throughout the whole soil profile, but SIL concentrated more soil water in the lower soil layers (>0.30. m) because the water levels in the pits were often below 0.30. m from the soil surface. The large opening area of the silt pits could have also caused large evaporative water losses from the pits. EFB mulching is recommended as the best CP, particularly for oil palm plantations on hill slopes. © 2014 Elsevier B.V.
  • Authors:
    • Yemefack, M.
    • Ngo-Mbogba, M.
    • Nyeck, B.
  • Source: Soil and Tillage Research
  • Volume: 150
  • Year: 2015
  • Summary: The common agricultural practice in the humid tropical forest zone of Cameroon is shifting cultivation, which leads to a landscape mosaic system characterized by a diversity of land cover types. Our objective was to evaluate soil properties and soil quality under these land cover types and to investigate on their interrelationships. Topsoil samples (0-20. cm) were collected at the same time from 8 different land cover types (bare soil with burned vegetation biomass (FR1), bare soil with unburned vegetation biomass (FR), Chromolaena odorata fallow (JC), bush ligneous fallow (JR), secondary forest (SF), primary forest (FC), Gilbertiodendron dewevrei forest (FG), and raffia and Uapacca forest (RA)) and analysed for routine laboratory determinations. A soil quality index (SQI) computed based on soil chemical properties, analysis of variance and multiple comparison tests were used to compare soils from different land cover types. Principal component analysis (PCA) was used to select the most appropriate indicators that control soil quality. Several soil properties showed high to very high coefficient of variation within the land cover types. Organic matter was significantly high under forested land cover types (FC, FG, RA) and under bare soil with burned vegetation (FR1). Soil quality differs significantly (. p=. 0.000) from one land cover to another and shows the following ranking: SQI_FR1. ». SQI_FG. >. SQI_RA. >. SQI_FR. >. SQI_FC. >. SQI_JC. >. SQI_FS. >. SQI_JR. Organic matter (OM), available P, calcium (Ca), and pHw combined, accounted for 88.5% of the variation of soil quality. The soil quality appeared to be highly influenced by ashes from burned vegetation biomass which temporally enriches soils with nutrient elements and by the organic matter supplied by forested land cover types.
  • Authors:
    • Lafond, J.
    • Paré, M. C.
    • Pageau, D.
  • Source: Soil and Tillage Research
  • Volume: 150
  • Year: 2015
  • Summary: In the northern agroecosystem of Saguenay-Lac-Saint-Jean, cash crops such as barley, canola, and field pea are gaining popularity over traditional perennial crops like alfalfa. However, very little information is available on the relatively long-term effect of different crop rotations and soil tillage practices on crop yields and soil quality parameters. This study was conducted at the Normandin Research Farm of Agriculture and Agri-Food Canada. Five rotation types [1: Canola-Barley-Barley-Pea (C-B-B-P); 2: Canola-Pea-Barley-Barley (C-P-B-B); 3: Canola-Barley-Pea-Barley (C-B-P-B); 4: Pea monoculture; and 5: Barley monoculture] and two soil tillage practices [1: Chisel plough (CP) and 2: Moldboard plough (MP)] were evaluated. Canola monoculture of was not included. The study began in 1999 on a former alfalfa field and ended in 2010 after three four-year rotation cycles. Barley monoculture decreased yields by 600kgha-1 in the last five years, whereas field pea monoculture decreased yields by about 1000kgha-1 in most years. Barley monoculture did not significantly reduce grain yields compared to C-B-B-P and C-P-B-B, highlighting the importance of alternate crops every year. Soil tillage (CP versus MP) did not significantly affect yields for all crops in most years; and when it did have an effect, it showed inconsistencies by either increasing or decreasing grain yields. Soil tillage also had insignificant impact regardless of the rotation type involved. Rotation type and soil tillage had insignificant effect on soil organic matter content, whereas CP increased nitrate and phosphorus content in the 0-20cm soil layer. Rotation type had insignificant impact on soil physical properties, whereas CP improved soil water conductivity by 0.03cmh-1 for C-B-B-P and barley monoculture. Compared to MP, CP improved soil macro-aggregate (2-6mm) stability to water as well as aggregate mean weight diameter by about 15% for most of the rotations.
  • Authors:
    • Zhang, Y. Z.
    • Zhou, H.
    • Yan, X.
    • Peng, X.
    • Sun, H.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 146
  • Issue: Pt. A
  • Year: 2015
  • Summary: In tropical and subtropical soils, sesquioxides and soil organic matter (SOM) are major binding agents for aggregates. However, the biotic and abiotic contributions to aggregation are often difficult to distinguish. In this study, we attempted to assess their contributions to aggregation separately, as indicated by aggregate size distribution and specific surface area (SSA). Our objectives were (i) to determine aggregate size distribution and SSA before and after removal of sesquioxides and SOM, and (ii) to assess the contributions of sesquioxides and SOM to soil aggregation. An oxide-rich Ultisol under long-term fertilization was extracted by water as a control, oxalate, dithionite-citrate-bicarbonate (DCB), or by H2O2 in the absence of any physical disturbance. The aggregate size distribution, Fe/Al oxides, soil organic C (SOC), and SSA of the soil before and after extraction were determined. Our results showed that the DCB and oxalate solutions broke down the sand-sized aggregates most intensively, whereas the H2O2 treatment disrupted 0.25-2.0mm aggregates intensively, indicating that SOM is the major binding agent for aggregates of this size. A slight change either in SOC stock after removal of Fe/Al oxides by DCB and oxalate or in Fe/Al oxides after removal of SOC by H2O2 indicated that organo-mineral complexes are a minor binding mechanism of aggregation in the soil studied. The SSA was reduced by 72-84% in the soil extracted by DCB, followed by 32.0-35.9% after the oxalate extraction, whereas the removal of SOM increased SSA by 3.8-12.6%. Our results showed that Fe/Al oxides played a major role in aggregation in the Ultisols studied. The difference in the major binding agent for different aggregate size classes is another reason to explain why the hierarchy aggregate concept is not applicable to oxide-rich soils. This study, however, could not assess their contributions to soil aggregation precisely, because of the difficulty in tracing aggregate dynamics. To better understand the mechanisms of soil aggregation we need more works in the future.
  • Authors:
    • Townsend, C. R.
    • Lear, G.
    • Salis, R. K.
    • Piggott, J. J.
    • Matthaei, C. D.
  • Source: GLOBAL CHANGE BIOLOGY V
  • Volume: 21
  • Issue: 1
  • Year: 2015
  • Summary: Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.
  • Authors:
    • Don, A.
    • Poeplau, C.
  • Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
  • Volume: 200
  • Year: 2015
  • Summary: A promising option to sequester carbon in agricultural soils is the inclusion of cover crops in cropping systems. The advantage of cover crops as compared to other management practices that increase soil organic carbon (SOC) is that they neither cause a decline in yields, like extensification, nor carbon losses in other systems, like organic manure applications may do. However, the effect of cover crop green manuring on SOC stocks is widely overlooked. We therefore conducted a meta-analysis to derive a carbon response function describing SOC stock changes as a function of time. Data from 139 plots at 37 different sites were compiled. In total, the cover crop treatments had a significantly higher SOC stock than the reference croplands. The time since introduction of cover crops in crop rotations was linearly correlated with SOC stock change (R2=0.19) with an annual change rate of 0.32±0.08Mgha-1yr-1 in a mean soil depth of 22cm and during the observed period of up to 54 years. Elevation above sea level of the plot and sampling depth could be used as explanatory variables to improve the model fit. Assuming that the observed linear SOC accumulation would not proceed indefinitely, we modeled the average SOC stock change with the carbon turnover model RothC. The predicted new steady state was reached after 155 years of cover crop cultivation with a total mean SOC stock accumulation of 16.7±1.5Mgha-1 for a soil depth of 22cm. Thus, the C input driven SOC sequestration with the introduction of cover crops proved to be highly efficient. We estimated a potential global SOC sequestration of 0.12±0.03PgCyr-1, which would compensate for 8% of the direct annual greenhouse gas emissions from agriculture. However, altered N2O emissions and albedo due to cover crop cultivation have not been taken into account here. Data on those processes, which are most likely species-specific, would be needed for reliable greenhouse gas budgets.
  • Authors:
    • Zhu, X. D.
    • Zhuang, Q. L.
    • Qin, Z. C.
  • Source: GLOBAL CHANGE BIOLOGY BIOENERGY Volume: 7 Issue: 1 Pages: 25-39 DOI:
  • Volume: 7
  • Issue: 1
  • Year: 2015
  • Summary: This study estimated the potential emissions of greenhouse gases (GHG) from bioenergy ecosystems with a biogeochemical model AgTEM, assuming maize ( Zea mays L.), switchgrass ( Panicum virgatum L.), and Miscanthus ( Miscanthus * giganteus) will be grown on the current maize-producing areas in the conterminous United States. We found that the maize ecosystem acts as a mild net carbon source while cellulosic ecosystems (i.e., switchgrass and Miscanthus) act as mild sinks. Nitrogen fertilizer use is an important factor affecting biomass production and N 2O emissions, especially in the maize ecosystem. To maintain high biomass productivity, the maize ecosystem emits much more GHG, including CO 2 and N 2O, than switchgrass and Miscanthus ecosystems, when high-rate nitrogen fertilizers are applied. For maize, the global warming potential (GWP) amounts to 1-2 Mg CO 2eq ha -1 yr -1, with a dominant contribution of over 90% from N 2O emissions. Cellulosic crops contribute to the GWP of less than 0.3 Mg CO 2eq ha -1 yr -1. Among all three bioenergy crops, Miscanthus is the most biofuel productive and the least GHG intensive at a given cropland. Regional model simulations suggested that substituting Miscanthus for maize to produce biofuel could potentially save land and reduce GHG emissions.
  • Authors:
    • Daniel, H.
    • Lockwood, P. V.
    • Wilson, B. R.
    • Rabbi, S.
    • Young, I. M.
  • Source: SOIL & TILLAGE RESEARCH
  • Volume: 146
  • Issue: Pt. B
  • Year: 2015
  • Summary: The conventional model of aggregate formation suggests a hierarchy where micro-aggregates with lower porosity and therefore reduced soil organic carbon (SOC) mineralization form inside macro-aggregates. This model has however been questioned for highly weathered Oxisols where inconclusive results regarding the presence of aggregate hierarchy have been obtained to date. We hypothesized that in Oxisols (i) an aggregate hierarchy would be present (ii) the porosity of micro-aggregates would be lower than that of macro-aggregates and (iii) pore geometry of aggregates would influence SOC mineralization. We collected topsoils from Oxisols in northern New South Wales, Australia from which macro-aggregates (>250µm), micro-aggregates (53-250µm) and <53µm fractions were isolated from bulk soil by wet sieving. 3D images of macro- and micro-aggregates were produced using X-ray computed tomography (µCT) showing the presence of micro-aggregates inside macro-aggregates, which confirmed the presence of an aggregate hierarchy in the Oxisols studied. Macro-aggregates were more common and SOC in higher concentrations in forest systems compared with agricultural (the cultivation or pasture) land-uses, but aggregate geometry differed little between the land-uses studied. The porosity of macro-aggregates (4%) was significantly lower than micro-aggregates (5.5%). Despite the differences in pore geometry between macro- and micro-aggregates, SOC mineralized (SOCmin) during a 2-month incubation (at 25°C) was similar in macro- (3% of SOC concentration) and micro-aggregates (2.8% of SOC concentration). We conclude that although aggregate hierarchy exists in these soils and that aggregate geometry did differ between aggregate size classes, there was no evidence to support the porosity exclusion principle and the assumption that SOC is preferentially stabilized within micro-aggregates in these soils.