Mario Kirchhoff, Tobias Romes, I. Marzolff, M. Seeger, Ali Aït Hssaine, J. Ries
Abstract. The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.
{"title":"Spatial distribution of argan tree influence on soil properties in southern Morocco","authors":"Mario Kirchhoff, Tobias Romes, I. Marzolff, M. Seeger, Ali Aït Hssaine, J. Ries","doi":"10.5194/soil-7-511-2021","DOIUrl":"https://doi.org/10.5194/soil-7-511-2021","url":null,"abstract":"Abstract. The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should\u0000be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"51 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88284384","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
B. Bartkowski, Stephan Bartke, N. Hagemann, B. Hansjürgens, C. Schröter‐Schlaack
Abstract. Governance of natural resources is inherently complex and requires navigating trade-offs at multiple dimensions. In this paper, we present and operationalize the “governance disruptions framework” (GDF) as a tool for holistic analysis of natural resource governance systems. For each of the four dimensions of the framework (target adequacy, object adequacy, instrument adequacy, and behavioural adequacy), we formulate guiding questions to be used when applying the framework to particular governance systems. We then demonstrate the use of GDF by applying it to the core of German agricultural soil policy. We show that for each framework dimension, the governance system exhibits deficits, particularly with respect to object adequacy and instrument adequacy. Furthermore, we use the GDF-based analysis to highlight research gaps. We find that stakeholder analyses are a central gap across GDF dimensions.
{"title":"Application of the governance disruptions framework to German agricultural soil policy","authors":"B. Bartkowski, Stephan Bartke, N. Hagemann, B. Hansjürgens, C. Schröter‐Schlaack","doi":"10.5194/SOIL-7-495-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-495-2021","url":null,"abstract":"Abstract. Governance of natural resources is inherently complex and requires\u0000navigating trade-offs at multiple dimensions. In this paper, we present and\u0000operationalize the “governance disruptions framework” (GDF) as a tool for\u0000holistic analysis of natural resource governance systems. For each of the\u0000four dimensions of the framework (target adequacy, object adequacy,\u0000instrument adequacy, and behavioural adequacy), we formulate guiding\u0000questions to be used when applying the framework to particular governance\u0000systems. We then demonstrate the use of GDF by applying it to the core of\u0000German agricultural soil policy. We show that for each framework dimension,\u0000the governance system exhibits deficits, particularly with respect to object\u0000adequacy and instrument adequacy. Furthermore, we use the GDF-based analysis\u0000to highlight research gaps. We find that stakeholder analyses are a central\u0000gap across GDF dimensions.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82074485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Zosso, N. Ofiti, J. Soong, E. Solly, M. Torn, A. Huguet, G. Wiesenberg, M. Schmidt
Abstract. The microbial community composition in subsoils remains understudied, and it is largely unknown whether subsoil microorganisms show a similar response to global warming as microorganisms at the soil surface do. Since microorganisms are the key drivers of soil organic carbon decomposition, this knowledge gap causes uncertainty in the predictions of future carbon cycling in the subsoil carbon pool (> 50 % of the soil organic carbon stocks are below 30 cm soil depth). In the Blodgett Forest field warming experiment (California, USA) we investigated how +4 ∘C warming in the whole-soil profile to 100 cm soil depth for 4.5 years has affected the abundance and community structure of microorganisms. We used proxies for bulk microbial biomass carbon (MBC) and functional microbial groups based on lipid biomarkers, such as phospholipid fatty acids (PLFAs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). With depth, the microbial biomass decreased and the community composition changed. Our results show that the concentration of PLFAs decreased with warming in the subsoil (below 30 cm) by 28 % but was not affected in the topsoil. Phospholipid fatty acid concentrations changed in concert with soil organic carbon. The microbial community response to warming was depth dependent. The relative abundance of Actinobacteria increased in warmed subsoil, and Gram+ bacteria in subsoils adapted their cell membrane structure to warming-induced stress, as indicated by the ratio of anteiso to iso branched PLFAs. Our results show for the first time that subsoil microorganisms can be more affected by warming compared to topsoil microorganisms. These microbial responses could be explained by the observed decrease in subsoil organic carbon concentrations in the warmed plots. A decrease in microbial abundance in warmed subsoils might reduce the magnitude of the respiration response over time. The shift in the subsoil microbial community towards more Actinobacteria might disproportionately enhance the degradation of previously stable subsoil carbon, as this group is able to metabolize complex carbon sources.
{"title":"Whole-soil warming decreases abundance and modifies the community structure of microorganisms in the subsoil but not in surface soil","authors":"C. Zosso, N. Ofiti, J. Soong, E. Solly, M. Torn, A. Huguet, G. Wiesenberg, M. Schmidt","doi":"10.5194/SOIL-7-477-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-477-2021","url":null,"abstract":"Abstract. The microbial community composition in subsoils remains understudied, and it is largely unknown whether subsoil microorganisms show a similar response to global warming as microorganisms at the soil surface do. Since microorganisms are the key drivers of soil organic carbon decomposition, this knowledge gap causes uncertainty in the predictions of future carbon cycling in the subsoil carbon pool (> 50 % of the soil organic carbon stocks are below 30 cm soil depth). In the Blodgett Forest field warming experiment (California, USA) we investigated how +4 ∘C warming in the whole-soil profile to 100 cm soil depth for 4.5 years has affected the abundance and community structure of microorganisms. We used proxies for bulk microbial biomass carbon (MBC) and functional microbial groups based on lipid biomarkers, such as phospholipid fatty acids (PLFAs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs). With depth, the microbial biomass decreased and the community composition changed. Our results show that the concentration of PLFAs decreased with warming in the subsoil (below 30 cm) by 28 % but was not affected in the topsoil. Phospholipid fatty acid concentrations changed in concert with soil organic carbon. The microbial community response to warming was depth dependent. The relative abundance of Actinobacteria increased in warmed subsoil, and Gram+ bacteria in subsoils adapted their cell membrane structure to warming-induced stress, as indicated by the ratio of anteiso to iso branched PLFAs. Our results show for the first time that subsoil microorganisms can be more affected by warming compared to topsoil microorganisms. These microbial responses could be explained by the observed decrease in subsoil organic carbon concentrations in the warmed plots. A decrease in microbial abundance in warmed subsoils might reduce the magnitude of the respiration response over time. The shift in the subsoil microbial community towards more Actinobacteria might disproportionately enhance the degradation of previously stable subsoil carbon, as this group is able to metabolize complex carbon sources.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86717490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Reichenbach, P. Fiener, G. Garland, M. Griepentrog, J. Six, S. Doetterl
Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.
{"title":"The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils","authors":"M. Reichenbach, P. Fiener, G. Garland, M. Griepentrog, J. Six, S. Doetterl","doi":"10.5194/soil-7-453-2021","DOIUrl":"https://doi.org/10.5194/soil-7-453-2021","url":null,"abstract":"Abstract. Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to\u0000contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical\u0000African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley\u0000positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil\u0000and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of\u0000regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms\u0000together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization\u0000mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in\u0000the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC\u0000dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic\u0000carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 ± 13.2 % of total SOC stock\u0000in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased\u0000strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression\u0000models, considering depth intervals of 0–10, 30–40 and 60–70 cm, showed that variables affiliated with soil weathering, parent material\u0000geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and\u0000Δ14C. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with\u0000microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material\u0000leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization\u0000mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils\u0000investigated.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"94 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85498865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Elad Levintal, Y. Ganot, G. Taylor, P. Freer-Smith, K. Suvočarev, H. Dahlke
Abstract. The use of wireless sensor networks in the measurement of soil parameters represents one of the least invasive methods available to date. Wireless sensors pose the least disturbance to soil structure and having fewer aboveground cables reduce the risk of undesired equipment damage and potential data loss. However, implementing wireless sensor networks in field studies usually requires advanced and costly engineering knowledge. This study presents a new underground, wireless, open-source, low-cost system for monitoring soil oxygen, temperature, and soil moisture. The process of system design, assembly, programming, deployment, and power management is presented. The system can be left underground for several years without the need for changing the battery. Emphasis was given on modularity so that it can be easily duplicated or changed if needed, and deployed without previous engineering knowledge. Data from this type of system have a wide range of applications, including precision agriculture and high-resolution modelling.
{"title":"An underground, wireless, open-source, low-cost system for monitoring oxygen, temperature, and soil moisture","authors":"Elad Levintal, Y. Ganot, G. Taylor, P. Freer-Smith, K. Suvočarev, H. Dahlke","doi":"10.5194/SOIL-2021-72","DOIUrl":"https://doi.org/10.5194/SOIL-2021-72","url":null,"abstract":"Abstract. The use of wireless sensor networks in the measurement of soil parameters represents one of the least invasive methods available to date. Wireless sensors pose the least disturbance to soil structure and having fewer aboveground cables reduce the risk of undesired equipment damage and potential data loss. However, implementing wireless sensor networks in field studies usually requires advanced and costly engineering knowledge. This study presents a new underground, wireless, open-source, low-cost system for monitoring soil oxygen, temperature, and soil moisture. The process of system design, assembly, programming, deployment, and power management is presented. The system can be left underground for several years without the need for changing the battery. Emphasis was given on modularity so that it can be easily duplicated or changed if needed, and deployed without previous engineering knowledge. Data from this type of system have a wide range of applications, including precision agriculture and high-resolution modelling.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81958375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Tamale, R. Hüppi, M. Griepentrog, L. Turyagyenda, M. Barthel, S. Doetterl, P. Fiener, O. van Straaten
Abstract. Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40 m×40 m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 d after fertilization; p<0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p=0.05) and background (p=0.01) CH4 consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO2 fluxes in the transitory phase (p=0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p<0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO2 effluxes. However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P availability over these biomes.
{"title":"Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda","authors":"J. Tamale, R. Hüppi, M. Griepentrog, L. Turyagyenda, M. Barthel, S. Doetterl, P. Fiener, O. van Straaten","doi":"10.5194/SOIL-7-433-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-433-2021","url":null,"abstract":"Abstract. Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40 m×40 m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO2 fluxes were\u0000partitioned into autotrophic and heterotrophic components through a root\u0000trenching treatment. In addition, soil temperature, soil water content, and\u0000nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 d after fertilization; p<0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p=0.05) and background (p=0.01)\u0000CH4 consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO2 fluxes in the transitory phase (p=0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p<0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO2 effluxes. However, neither heterotrophic nor autotrophic\u0000respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P\u0000availability over these biomes.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"65 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83946513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. Wilken, P. Fiener, M. Ketterer, K. Meusburger, Daniel Muhindo, K. Van Oost, S. Doetterl
Abstract. Due to the rapidly growing population in tropical Africa, a substantial rise in food demand is predicted in upcoming decades, which will result in higher pressure on soil resources. However, there is limited knowledge on soil redistribution dynamics following land conversion into arable land in tropical Africa that is partly caused by infrastructure limitations for long-term landscape-scale monitoring. In this study, fallout radionuclides 239+240Pu are used to assess soil redistribution along topographic gradients at two cropland sites and at three nearby pristine forest sites located in the DR Congo, Uganda and Rwanda. In the study area, a 239+240Pu baseline inventory is found that is higher than typically expected for tropical regions (mean forest inventory 41 Bq m−2). Pristine forests show no indication of soil redistribution based on 239+240Pu along topographical gradients. In contrast, soil erosion and sedimentation on cropland reached up to 37 cm (81 Mg ha−1 yr−1) and 40 cm (87 Mg ha−1 yr−1) within the last 55 years, respectively. Cropland sites show high intra-slope variability with locations showing severe soil erosion located in direct proximity to sedimentation sites. This study shows the applicability of a valuable method to assess tropical soil redistribution and provides insight into soil degradation rates and patterns in one of the most socio-economically and ecologically vulnerable regions of the world.
摘要由于热带非洲人口的迅速增长，预计未来几十年粮食需求将大幅增加，这将对土壤资源造成更大的压力。然而，对热带非洲土地转化为耕地后土壤再分配动态的了解有限，部分原因是长期景观尺度监测的基础设施限制。在这项研究中，使用放射性沉降物239+240Pu来评估位于刚果民主共和国、乌干达和卢旺达的两个农田和三个附近原始森林遗址沿地形梯度的土壤再分布。在研究区域，发现a239+240Pu的基线库存高于热带地区的典型预期(平均森林库存41 Bq m−2)。在239+240Pu的基础上，原始森林没有土壤沿地形梯度再分布的迹象。与此相反，在过去55年中，农田的土壤侵蚀和沉积分别达到37 cm (81 Mg ha−1 yr−1)和40 cm (87 Mg ha−1 yr−1)。农田场地表现出较高的坡内变异性，直接靠近沉积场地的地点显示出严重的土壤侵蚀。这项研究显示了一种评估热带土壤再分配的有价值方法的适用性，并提供了对世界上最社会经济和生态脆弱地区之一土壤退化率和模式的见解。
{"title":"Assessing soil redistribution of forest and cropland sites in wet tropical Africa using 239+240Pu fallout radionuclides","authors":"F. Wilken, P. Fiener, M. Ketterer, K. Meusburger, Daniel Muhindo, K. Van Oost, S. Doetterl","doi":"10.5194/SOIL-7-399-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-399-2021","url":null,"abstract":"Abstract. Due to the rapidly growing population in tropical Africa, a substantial rise\u0000in food demand is predicted in upcoming decades, which will result in higher\u0000pressure on soil resources. However, there is limited knowledge on soil\u0000redistribution dynamics following land conversion into arable land in\u0000tropical Africa that is partly caused by infrastructure limitations for\u0000long-term landscape-scale monitoring. In this study, fallout radionuclides 239+240Pu are used to assess soil redistribution along topographic\u0000gradients at two cropland sites and at three nearby pristine forest sites\u0000located in the DR Congo, Uganda and Rwanda. In the study area, a\u0000239+240Pu baseline inventory is found that is higher than typically\u0000expected for tropical regions (mean forest inventory 41 Bq m−2).\u0000Pristine forests show no indication of soil redistribution based on 239+240Pu along topographical gradients. In contrast, soil erosion and\u0000sedimentation on cropland reached up to 37 cm (81 Mg ha−1 yr−1)\u0000and 40 cm (87 Mg ha−1 yr−1) within the last 55 years,\u0000respectively. Cropland sites show high intra-slope variability with\u0000locations showing severe soil erosion located in direct proximity to\u0000sedimentation sites. This study shows the applicability of a valuable method\u0000to assess tropical soil redistribution and provides insight into soil\u0000degradation rates and patterns in one of the most socio-economically and\u0000ecologically vulnerable regions of the world.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73621081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Kirsten, R. Mikutta, D. Kimaro, K. Feger, K. Kalbitz
Abstract. Aggregation affects a wide range of physical and biogeochemical soil properties with positive effects on soil carbon storage. For weathered tropical soils, aluminous clays (kaolinite and gibbsite) and pedogenic Fe (oxyhydr)oxides (goethite and hematite; termed “Fe oxides”) have been suggested as important building units for aggregates. However, as aluminosilicates, aluminum hydroxides, and Fe oxides are part of the clay-sized fraction it is hard to separate how certain mineral phases modulate aggregation. In addition, it is not known what consequences this will have for organic carbon (OC) persistence after land-use change. We selected topsoils with unique mineralogical compositions in the East Usambara Mountains of Tanzania under forest and cropland land uses, varying in contents of aluminous clay and Fe oxides. Across the mineralogical combinations, we determined the aggregate size distribution, aggregate stability, OC contents of aggregate size fractions, and changes in aggregation and OC contents under forest and cropland land use. Patterns in soil aggregation were rather similar across the different mineralogical combinations (high level of macroaggregation and high aggregate stability). Nevertheless, we found some statistically significant effects of aluminous clay and pedogenic Fe oxides on aggregation and OC storage. An aluminous clay content > 250 g kg−1 in combination with pedogenic Fe contents < 60 g kg−1 significantly promoted the formation of large macroaggregates > 4 mm. In contrast, a pedogenic Fe content > 60 g kg−1 in combination with aluminous clay content of < 250 g kg−1 promoted OC storage and persistence even under agricultural use. The combination with low aluminous clay and high pedogenic Fe contents displayed the highest OC persistence, despite conversion of forest to cropland causing substantial disaggregation. This indicates that aggregation in these tropical soils is modulated by the mineralogical regime, causing moderate but significant differences in aggregate size distribution. Nevertheless, aggregation was little decisive for overall OC persistence in these highly weathered soils, where OC storage is more regulated by direct mineral–organic interactions.
摘要团聚体广泛影响土壤的物理和生物地球化学性质，对土壤碳储量有积极影响。对于热带风化土壤，铝质粘土(高岭石和三水石)和成土铁(氧合)氧化物(针铁矿和赤铁矿);被称为“氧化铁”)被认为是聚集体的重要组成单位。然而，由于硅酸盐铝、氢氧化铝和氧化铁是粘土大小的部分，很难分离出某些矿物相是如何调节聚集的。此外，目前尚不清楚这对土地利用变化后有机碳(OC)持久性的影响。我们在坦桑尼亚东部usambara山脉的森林和农田土地利用下选择了具有独特矿物学成分的表土，其铝粘土和铁氧化物的含量各不相同。在不同的矿物学组合中，我们确定了团聚体粒度分布、团聚性、团聚体粒度组分的有机碳含量，以及森林和农田土地利用下团聚体和有机碳含量的变化。不同矿物学组合的土壤团聚模式相当相似(高水平的大团聚和高团聚稳定性)。然而，我们发现了一些统计上显著的铝粘土和成土铁氧化物对聚集和OC储存的影响。铝矾土含量> 250 g kg - 1，富铁含量4 mm。相反，当土壤铁含量> 60 g kg - 1和铝质粘土含量< 250 g kg - 1时，即使在农业使用下，土壤中碳的储存和持久性也得到了提高。低铝质粘土和高成土铁含量的组合显示出最高的有机碳持久性，尽管森林转化为农田导致了大量的分解。这表明这些热带土壤中的团聚体受矿物学制度的调节，导致团聚体大小分布的适度但显著的差异。然而，在这些高度风化的土壤中，聚集性对总体有机碳持久性没有决定性作用，在这些土壤中，有机碳储存更多地受到直接矿物-有机相互作用的调节。
{"title":"Aluminous clay and pedogenic Fe oxides modulate aggregation and related carbon contents in soils of the humid tropics","authors":"M. Kirsten, R. Mikutta, D. Kimaro, K. Feger, K. Kalbitz","doi":"10.5194/SOIL-7-363-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-363-2021","url":null,"abstract":"Abstract. Aggregation affects a wide range of physical and biogeochemical soil\u0000properties with positive effects on soil carbon storage. For weathered\u0000tropical soils, aluminous clays (kaolinite and gibbsite) and pedogenic Fe\u0000(oxyhydr)oxides (goethite and hematite; termed “Fe oxides”) have been\u0000suggested as important building units for aggregates. However, as\u0000aluminosilicates, aluminum hydroxides, and Fe oxides are part of the\u0000clay-sized fraction it is hard to separate how certain mineral phases\u0000modulate aggregation. In addition, it is not known what consequences this\u0000will have for organic carbon (OC) persistence after land-use change. We\u0000selected topsoils with unique mineralogical compositions in the East\u0000Usambara Mountains of Tanzania under forest and cropland land uses, varying\u0000in contents of aluminous clay and Fe oxides. Across the mineralogical\u0000combinations, we determined the aggregate size distribution, aggregate\u0000stability, OC contents of aggregate size fractions, and changes in\u0000aggregation and OC contents under forest and cropland land use. Patterns in\u0000soil aggregation were rather similar across the different mineralogical\u0000combinations (high level of macroaggregation and high aggregate stability).\u0000Nevertheless, we found some statistically significant effects of aluminous\u0000clay and pedogenic Fe oxides on aggregation and OC storage. An aluminous\u0000clay content > 250 g kg−1 in combination with\u0000pedogenic Fe contents < 60 g kg−1 significantly\u0000promoted the formation of large macroaggregates > 4 mm. In\u0000contrast, a pedogenic Fe content > 60 g kg−1 in\u0000combination with aluminous clay content of < 250 g kg−1\u0000promoted OC storage and persistence even under agricultural use. The\u0000combination with low aluminous clay and high pedogenic Fe contents displayed\u0000the highest OC persistence, despite conversion of forest to cropland causing\u0000substantial disaggregation. This indicates that aggregation in these\u0000tropical soils is modulated by the mineralogical regime, causing moderate\u0000but significant differences in aggregate size distribution. Nevertheless,\u0000aggregation was little decisive for overall OC persistence in these highly\u0000weathered soils, where OC storage is more regulated by direct\u0000mineral–organic interactions.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79644022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. O. Hounkpatin, J. Stendahl, Mattias Lundblad, E. Karltun
Abstract. The status of the soil organic carbon (SOC) stock at any position in the landscape is subject to a complex interplay of soil state factors operating at different scales and regulating multiple processes resulting either in soils acting as a net sink or net source of carbon. Forest landscapes are characterized by high spatial variability, and key drivers of SOC stock might be specific for sub-areas compared to those influencing the whole landscape. Consequently, separately calibrating models for sub-areas (local models) that collectively cover a target area can result in different prediction accuracy and SOC stock drivers compared to a single model (global model) that covers the whole area. The goal of this study was therefore to (1) assess how global and local models differ in predicting the humus layer, mineral soil, and total SOC stock in Swedish forests and (2) identify the key factors for SOC stock prediction and their scale of influence. We used the Swedish National Forest Soil Inventory (NFSI) database and a digital soil mapping approach to evaluate the prediction performance using random forest models calibrated locally for the northern, central, and southern Sweden (local models) and for the whole of Sweden (global model). Models were built by considering (1) only site characteristics which are recorded on the plot during the NFSI, (2) the group of covariates (remote sensing, historical land use data, etc.) and (3) both site characteristics and group of covariates consisting mostly of remote sensing data. Local models were generally more effective for predicting SOC stock after testing on independent validation data. Using the group of covariates together with NFSI data indicated that such covariates have limited predictive strength but that site-specific covariates from the NFSI showed better explanatory strength for SOC stocks. The most important covariates that influence the humus layer, mineral soil (0–50 cm), and total SOC stock were related to the site-characteristic covariates and include the soil moisture class, vegetation type, soil type, and soil texture. This study showed that local calibration has the potential to improve prediction accuracy, which will vary depending on the type of available covariates.
{"title":"Predicting the spatial distribution of soil organic carbon stock in Swedish forests using a group of covariates and site-specific data","authors":"K. O. Hounkpatin, J. Stendahl, Mattias Lundblad, E. Karltun","doi":"10.5194/SOIL-7-377-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-377-2021","url":null,"abstract":"Abstract. The status of the soil organic carbon (SOC) stock at any position in the landscape is subject to a complex interplay of soil state factors operating at different scales and\u0000regulating multiple processes resulting either in soils acting as a net sink or net source of carbon. Forest landscapes are characterized by high spatial variability, and key drivers of SOC stock might be specific for sub-areas compared to those influencing the whole landscape. Consequently, separately calibrating models for sub-areas (local models) that collectively cover a target area can result in different prediction accuracy and SOC stock drivers compared to a single model (global model) that covers the whole area. The goal of this study was therefore to (1) assess how global and local models differ in predicting the humus layer, mineral soil, and total SOC stock in Swedish forests and (2) identify the key factors for SOC stock prediction and their scale of influence. We used the Swedish National Forest Soil Inventory (NFSI) database and a\u0000digital soil mapping approach to evaluate the prediction performance using\u0000random forest models calibrated locally for the northern, central, and\u0000southern Sweden (local models) and for the whole of Sweden (global model).\u0000Models were built by considering (1) only site characteristics which are\u0000recorded on the plot during the NFSI, (2) the group of covariates (remote sensing, historical land use data, etc.) and (3) both site characteristics and group of covariates consisting mostly of remote sensing data. Local models were generally more effective for predicting SOC stock after\u0000testing on independent validation data. Using the group of covariates\u0000together with NFSI data indicated that such covariates have limited\u0000predictive strength but that site-specific covariates from the NFSI showed\u0000better explanatory strength for SOC stocks. The most important covariates\u0000that influence the humus layer, mineral soil (0–50 cm), and total SOC\u0000stock were related to the site-characteristic covariates and include the\u0000soil moisture class, vegetation type, soil type, and soil texture. This study showed that local calibration has the potential to improve prediction\u0000accuracy, which will vary depending on the type of available covariates.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87599229","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ming Lu, D. Powlson, Yi Liang, D. Chadwick, Shengbi Long, Dunyi Liu, Xin-ping Chen
Abstract. Within the context of sustainable development, soil degradation driven by land use change is considered a serious global problem, but the conversion from growing cereals to vegetables is a change that has received limited attention, especially in subtropical regions. Here, we studied the effects of the conversion from paddy rice to an oilseed rape rotation to vegetable production in southwestern China on soil organic carbon (SOC), total nitrogen (TN), the C/N ratio, pH, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) based on face-to-face farmer surveys and soil analysis. In the vegetable cropping system, fertilizer application often exceeds the crop demand or levels recommended by the local extension service several times over. Thus, the crop use efficiency of N, P, K, Ca, and Mg was only 26 %, 8 %, 56 %, 23 %, and 28 %, respectively. In the vegetable cropping system studied, SOC, C stock, TN, and N stock were decreased significantly due to low organic inputs from crop residues and high tillage frequency. Furthermore, the soil C/N ratio decreased slightly; available P (AP) in the topsoil increased by 1.92 mg kg−1 for every 100 kg ha−1 of P surplus, and the critical levels of AP and CaCl2-soluble P in P leaching were 104 and 0.80 mg P kg−1. Besides, compared to the current paddy–rape rotation system, a clear trend of soil acidification was observed in the vegetable fields. However, increasing the contents of soil Ca and Mg significantly alleviated topsoil acidification, with the effect increasing over time. Given our findings, the potential benefits of conservation agricultural practices, integrated soil–crop system management strategies, and agricultural technology services for recovering the degraded soil and improving the vegetable productivity are discussed here.
摘要在可持续发展的背景下，土地利用变化导致的土壤退化被认为是一个严重的全球性问题，但从种植谷物到种植蔬菜的转变受到的关注有限，特别是在亚热带地区。本研究基于面对面农户调查和土壤分析，研究了中国西南水稻轮作油菜轮作蔬菜对土壤有机碳(SOC)、全氮(TN)、C/N、pH、磷(P)、钾(K)、钙(Ca)和镁(Mg)的影响。在蔬菜种植系统中，肥料施用通常超过作物需求量或当地推广服务建议的水平数倍以上。因此，氮、磷、钾、钙、镁的作物利用效率分别只有26%、8%、56%、23%和28%。在研究的蔬菜种植系统中，由于作物残茬有机投入少和耕作频率高，土壤有机碳储量、全氮储量和氮储量显著减少。土壤碳氮比略有下降;每增加100 kg ha - 1磷肥，表层土壤速效磷(AP)增加1.92 mg kg - 1，磷淋溶中AP和钙溶性磷的临界水平分别为104和0.80 mg P kg - 1。此外，与目前的水田-旱作系统相比，菜田土壤酸化趋势明显。增加土壤Ca和mg含量显著缓解了表层土壤酸化，且随时间的增加效果逐渐增强。基于我们的研究结果，本文讨论了保护性农业实践、土壤-作物系统综合管理策略和农业技术服务对恢复退化土壤和提高蔬菜生产力的潜在效益。
{"title":"Significant soil degradation is associated with intensive vegetable cropping in a subtropical area: a case study in southwestern China","authors":"Ming Lu, D. Powlson, Yi Liang, D. Chadwick, Shengbi Long, Dunyi Liu, Xin-ping Chen","doi":"10.5194/SOIL-7-333-2021","DOIUrl":"https://doi.org/10.5194/SOIL-7-333-2021","url":null,"abstract":"Abstract. Within the context of sustainable development, soil degradation driven by land use change is considered a serious global problem, but the conversion from growing cereals to vegetables is a change that has received limited attention, especially in subtropical regions. Here, we studied the effects of the conversion from paddy rice to an oilseed rape rotation to vegetable production in southwestern China on soil organic carbon (SOC), total\u0000nitrogen (TN), the C/N ratio, pH, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) based on face-to-face farmer surveys and soil analysis. In the vegetable cropping system, fertilizer application often exceeds the crop demand or levels recommended by the local extension service several times over. Thus, the crop use efficiency of N, P, K, Ca, and Mg was only 26 %, 8 %, 56 %, 23 %, and 28 %, respectively. In the vegetable cropping system studied, SOC, C stock, TN, and N stock were decreased significantly due to low organic inputs from crop residues and high tillage frequency. Furthermore, the soil C/N ratio decreased slightly; available P (AP) in the topsoil increased by 1.92 mg kg−1 for every 100 kg ha−1 of P surplus, and\u0000the critical levels of AP and CaCl2-soluble P in P leaching were 104\u0000and 0.80 mg P kg−1. Besides, compared to the current paddy–rape\u0000rotation system, a clear trend of soil acidification was observed in the\u0000vegetable fields. However, increasing the contents of soil Ca and Mg\u0000significantly alleviated topsoil acidification, with the effect increasing\u0000over time. Given our findings, the potential benefits of conservation\u0000agricultural practices, integrated soil–crop system management strategies,\u0000and agricultural technology services for recovering the degraded soil and\u0000improving the vegetable productivity are discussed here.\u0000","PeriodicalId":22015,"journal":{"name":"Soil Science","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91159456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"农林科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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