Effects Of Agricultural Land Use Research Articles

Short‐ and long‐term legacies of carbon sequestration, and nutrient burial in floodplain wetlands of agricultural and forested catchments, Indiana, United States

AbstractSoil organic carbon (C) sequestration and nitrogen (N) and phosphorus (P) burial were measured in two floodplain wetlands' soils of the West Fork of the White River watershed (Indiana, United States) whose catchments differed in land use to better understand how land use practices affect wetland C and nutrient retention. The catchment of one floodplain, Upper West Fork, is dominated by row crop agriculture (61%) whereas the second catchment, Beanblossom Creek, is mostly forested (85%). Soils (0–30 cm) of the two floodplain wetlands had similar bulk density (1.23 g/cm3). Soil organic C and N were low in both floodplains but the percent organic C and N was two times greater (3.3% C, 0.22% N) in the agricultural floodplain than in the floodplain in the forested catchment (1.5% C, 0.14% N). Soil P was three times greater in the agricultural (1100 μg/g) than in the forested floodplain (350 μg/g). Recent soil accretion based on 137Cs which provides a historical record since 1964 (60 years), was two times greater in the agricultural floodplain (2.2 mm/year) than in the forested catchment (1.0 mm/year). Sediment deposition (2500 g/m2/year), C sequestration (90 g/m2/year), and N burial (7.5 g/m2/year) were three times greater in the agricultural floodplain and P burial was seven times greater (3.0 vs. 0.41 g/m2/year). Long‐term measurements (100 years) based on 210Pb did not show large differences in C sequestration and N burial between the two floodplains though soil accretion and sediment deposition were greater in the forested floodplain. We attribute these higher rates to greater erosion in the watershed before 1950 when the catchment had more agricultural land and before instruction on best management practices to reduce soil erosion. These findings confirm previously published studies that show that P enrichment and accumulation in floodplain soils represent legacy effects of agricultural land use in the catchment.

Agricultural land-use effects on the colonization dynamics of the benthic diatom assemblage of lowland streams

Agricultural land-use effects on the colonization dynamics of the benthic diatom assemblage of lowland streams

Effects of agriculture on river biota differ between crop types and organism groups

While the general effects of agricultural land use on riverine biota are well documented, the differential effects of specific crop types on different riverine organism groups, remain largely unexplored. Here we used recently published land use data distinguishing between specific crop types and a Germany-wide dataset of 7748 sites on the ecological status of macroinvertebrates, macrophytes and diatoms and applied generalized linear mixed models to unravel the associations between land use types, crop types, and the ecological status. For all organism groups, associations of specific crop types with biota were stronger than those of urban land use. For macroinvertebrates and macrophytes, strong negative associations were found for pesticide intensive permanent crops, while intensively fertilized crops (maize, intensive cereals) affected diatoms most. These differential associations highlight the importance of distinguishing between crop types and organism groups and the urgency to buffer rivers against agricultural stressors at the catchment scales and to expand sustainably managed agriculture.

Effects of agricultural land use on soil nutrients and its variation along altitude gradients in the downstream of the Yarlung Zangbo River Basin, Tibetan Plateau

Agricultural development in alpine ecosystems can cause significant changes in soil nutrients. With large altitude spans, the combined effect of the two is still unclear in existing research. To answer this problem, this study took the downstream of the Yarlung Zangbo River Basin (YZRB) as the study area, and designed a comparative soil sampling scheme along the altitude gradient. We compared soil nutrient characteristics facility agricultural land (FA) and field cultivated land (FC), using grassland (GL), the main source of agriculture expansion, as a reference. A total of 44 sampling areas were designed within an altitude range of 800–3500 m to reveal the effects of agricultural land development along the altitude gradient on soil nutrients. Research found that the FA significantly improved soil nutrient levels, with most nutrient indicators higher than those of FC and GL (P < 0.05), while the above indicators of FC were only slightly higher than GL. Moreover, the effects of agricultural development decreased with soil depth, and mainly occurred within the 0–30 cm soil layer (P < 0.05). With increasing altitude, most of soil nutrients first decreased and then increased and differences in soil nutrients among different land use modes first expanded and then shrank. This may be related to differences in farmland management methods, vegetation coverage, and temperature under different altitude gradient constraints. Especially in middle-altitude areas, the FA not only breaks through the low-temperature limitations of the plateau, but also has the advantage of large-scale development, which is suggested for future agricultural intensification in the plateau.

Effects of land-use intensity, grazing and fire disturbances on soil bacterial and fungal communities in subtropical wetlands

Bacteria and fungi are primary components in wetland soil microbial communities and provide essential ecosystem functions and services. Understanding responses of bacterial and fungal communities to multiple drivers of environmental change and their interactions is crucial for wetland conservation and management, particularly for those embedded in agricultural landscapes. Yet little is known about effect of agricultural land use and wetland management on soil microbial communities in subtropical seasonal wetlands. Here, we used a long-term whole-ecosystem wetland experiment to examine individual and interactive effects of upland land-use intensification, livestock grazing, and prescribed fire on soil bacteria and fungi. We asked: (1) How do land-use intensification, grazing and fire disturbances interact to alter taxonomic composition and functional potential of wetland soil bacterial and fungal communities? (2) To what extent would these management and disturbance effects on wetland microbial communities manifest through alterations in soil properties? Our results showed that both microbial taxonomic and functional composition are responsive to agricultural land use and wetland management. Upland land-use intensification was the strongest driver (as compared to fire and grazing) in shaping bacterial and fungal community composition. Specifically, land-use intensification increased functional richness of both bacteria and fungi, whereas grazing and fire only interactively affected bacterial functional richness. In addition, responses of bacterial and fungal species diversity to wetland management varied, where grazing and fire reduced fungal species diversity in wetlands embedded in low-intensity managed pastures, but none of these management practices altered bacterial species diversity. Further, we found that pH and secondary nutrients (i.e., Ca and Mg) availability were the most important soil properties that explain how agricultural land use and wetland management drive the composition of bacterial and fungal communities. Our findings suggest that integration of lime application into intensified land uses to neutralize soil pH could facilitate maintenance of microbial diversity and associated functions. Our results highlight the need to comprehensively assess management impacts on soil microorganisms, rather than using a single or few indicators, due to inconsistent responses of bacterial and fungal communities, as well as their varied taxonomic and functional responses.

Agricultural land use regulates the fate of soil phosphorus fractions following the reclamation of wetlands

Over half of the Earth's wetlands have been reclaimed for agriculture, leading to significant soil P destabilization and leaching risks. To evaluate the effects of agricultural land use on soil P stability, we used sequential P extraction to investigate the long-term effects of wetland cultivation for rice and soybean on soil P fractions, including labile and moderately labile inorganic/organic P (LPi, LPo, MPi, and MPo), and stable P in Northeast China. The results showed that soybean cultivation decreased the total P by 35.9 %, whereas rice cultivation did not influence the total P content (p < 0.05). Both the soybean and rice cultivations significantly increased LPi (p < 0.05). Soybean cultivation significantly decreased the LPo and MPo compared to rice cultivation, and the latter increased MPi by 309.28 % compared with the reference wetlands (p < 0.05). Redundancy analysis indicated that pH, poorly crystalline Fe (Feca), crystalline Fe (Fec), and total organic carbon (TOC) explained similar variations in P fractions during soybean and rice cultivation (54.9 % and 49.7 %, respectively). Similarly, during soybean or rice cultivation, pH negatively influenced LPo and MPo, while Feca positively influenced MPi and LPi. Furthermore, TOC showed a positive role in LPo, and MPo, but a negative effect on LPi and MPi during rice cultivation. Hence, we concluded that the cultivation of soybean or rice create contrasting modifications to wetland soil P fractionation by altering TOC, Feca, Fec, and pH. Our study indicates that agricultural land use can regulate the fate of wetland soil P fractionation, with potential benefits to both i) P risk management in cultivated wetlands and ii) potential approaches for future wetland restoration.

Quantifying the Effects of Root and Soil Properties on Soil Detachment Capacity in Agricultural Land Use of Southern China

Unsustainable agricultural land use will lead to an increased risk of soil erosion and soil degradation. However, few studies have investigated impacts of changes in root and soil properties on the soil detachment process. Therefore, we investigated the effects of agricultural land use on the relative contribution of root and soil properties to soil detachment capacity. Soil samples were collected from six different land use types and subjected to flow scouring under six shear stresses ranging from 4.98 to 16.37 Pa. Agricultural land use influenced root distribution and soil properties in the soil surface layer. Root length density, root surface area density, and root volume density in orchards with no cover, orchards with grass cover, and farmland were less than those of grassland samples. Different land use types affected soil detachment capacity. Bare land, farmland, and orchards with no cover were more vulnerable to erosion, while forest, orchard with grass cover, and grassland showed little soil detachment. Soil detachment capacity decreased exponentially with increasing soil bulk density, aggregate stability, organic matter, and root mass density. The root mass density and aggregate stability had the greatest contribution to the soil detachment capacity. Agricultural land use increases the risk of soil erosion; a groundcover management strategy, such as planting grass in orchard, could effectively increase the fine root distribution and aggregate stability to control soil erosion.

Demographic and Trophic Analysis of Adult Grass Shrimp (Palaemonetes pugio) from Living Shoreline and Natural Tidal Marshes in the Chesapeake Bay

With extensive and ongoing human development in coastal areas, effective shoreline-protection strategies against erosion and rising sea level that also provide natural ecosystem services will become increasingly important. Constructed living shoreline marshes can serve as successful management solutions when implemented correctly, but studies comparing these created estuarine habitats to their natural marsh counterparts are needed to assess their ecological functionality. We compared adult Palaemonetes pugio (Daggerblade Grass Shrimp) population demographics and diets from 13 pairs of living shoreline and natural marsh sites in the southwestern portion of the Chesapeake Bay. No significant differences were observed in demographics including abundance, weight, length, number of gravid females, and egg abundance and quality. Gut-content analysis detected significantly more terrestrial debris in shrimp from living shorelines, but the omnivorous dietary needs appeared met in all marsh sites. Overall, shrimp populations differed more among site pairs from different shorescape settings than between created and natural marshes from the same settings, suggesting that living shorelines are approaching ecosystem functionality similar to natural marsh habitats. However, the observed negative effect of agricultural land use on shrimp abundance and the discovery of microplastics in gut contents from all sites sampled indicate the need for further consideration of human impacts in both constructed and natural coastal habitats.

Effects of agricultural land use on the differentiation of nitrifier communities and functional patterns from natural terrestrial ecosystems

Human activities severely affect the global nitrogen (N) cycle. Croplands receive intensive N fertilization; consequently, cropland and natural ecosystem differentiation often results in community and functional variation in N-transforming microbes, including nitrifiers, which perform nitrification central to N cycle. However, evidence of such variation is mostly limited to ammonia oxidizers (AO) in local fields, excluding soil heterogeneity and nitrite-oxidizing bacteria (NOB); the variation under diverse climatic and soil conditions is not comprehensively understood. We conducted a large-scale survey of 131 cropland and natural sites in China. The community patterns of ammonia-oxidizing bacteria (AOB) and NOB differed significantly between croplands and some natural ecosystems, whereas ammonia-oxidizing archaea (AOA) were not affected by ecosystem type. The AOB population and nitrification potential (NP) were significantly higher in agroecosystems than in natural systems except wetlands. Fewer co-occurrence interactions involving nitrifiers were observed in croplands than in natural ecosystems except forests, systematically indicating the ecological diversification of nitrifiers in potential microbial associations among these habitats. Ecosystem type, pH, organic matter (OM), total phosphorus (TP), mean annual temperature (MAT) and mean annual precipitation (MAP) were primary drivers of nitrifier community and functional shifts. This study provides the first large-scale evidence of overall nitrifier community (i.e., AOA, AOB and NOB) and potential functional shifts between agroecosystems and natural environments, enabling predictions of terrestrial N cycle under foreseeable natural land use conversions and global climate change.

Effects of Agricultural Land Use Practices on Soil Organic Carbon Stocks, Total Nitrogen and Available Phosphorous in Smallholder Farms in Embu County, Kenya

A study was conducted to determine soil organic carbon stocks (SOCs), total nitrogen (TN) and available phosphorous (AP) changes in agricultural land use practices with a focus on maize and coffee based agricultural systems along Kapingazi river catchment in Embu County. Demarcation was done into four agro-ecological zones (AEZ) following the river downstream; Lower Highland Zone 1 LH1; Upper Midland Zone 1, UM1; Upper Midland Zone 2, UM2; Upper Midland Zone 3, UM3. Soil samples were obtained from two depths of 0-25 cm and 25-50 cm across slope positions. The soil organic carbon stocks were high in LH1 at 58.38 kg/m2 whereas UM3 had least amount at 29.48 kg/m2. The total nitrogen was higher in LH1 at 0.27% while least at UM3 with 0.07%. The LH1 had higher mean amount of available phosphorous at 19.44 ppm and least at UM3. The coffee agricultural system had more available phosphorous in LH1 at 23.75 ppm whereas maize had more in UM1, UM2 and UM3. The soil organic carbon stocks, available phosphorous and total nitrogen decreased across the AEZ. The Farm Foot Slope sampling point had high soil organic carbon stocks with the lowest amounts in the Farm Summit sampling point at both depths. The concentration of total nitrogen in coffee was high in all slope positions, whereas, available phosphorous was higher in maize. Therefore, it is concluded that topography and agriculture land use and management practices influence soil nutrient status.

Pesticide effects on macroinvertebrates and leaf litter decomposition in areas with traditional agriculture

Traditional forms of agriculture have created and preserved heterogeneous landscapes characterized by semi-natural meadows and pastures, which have high conversation value for biodiversity. Landscapes in Central and Eastern European countries with traditional agriculture are a stronghold for pollinators, butterflies and amphibians, which have declined in other parts of Europe. Despite different landscape structures, agriculture-associated pesticide exposure in streams can be similarly high as in Western Europe. This raises the question whether the heterogeneous landscape can buffer a temporary water quality decline by agriculture. We investigated the influence of landscape heterogeneity and water quality, in particular pesticide exposure, on macroinvertebrate communities in 19 small streams in Central Romania. We sampled the macroinvertebrate community, assessed the ecosystem function of leaf litter decomposition and analyzed the parasite prevalence in Baetis sp. and Gammarus balcanicus. No association between pesticide toxicity towards macroinvertebrates and several macroinvertebrate metrics was found. However, the level of pesticide toxicity was generally high, constituting a rather short gradient, and the pesticide indicator SPEARpesticides implied pesticide-driven community change in all sites. Landscape heterogeneity and forested upstream sections were among the most important drivers for the macroinvertebrate metrics, indicating increased dispersal and recolonization success. Agricultural land use in the catchment was negatively associated with vulnerable macroinvertebrate taxa such as Ephemeroptera, Plecoptera and Trichoptera. G. balcanicus dominated the shredder taxa and its abundance was positively associated with the pesticide indicator SPEARpesticides. Parasite prevalence in G. balcanicus increased with extensive land use (pastures and forests), whereas it decreased with arable land. Our results suggest that heterogeneous landscapes with structures of low-intensive land use may buffer the effects of agricultural land use and facilitate dispersal and recolonization processes of pesticide-affected macroinvertebrate communities.

Impact of crop management systems on soil nematode communities in South Brazil

The analysis of nematode communities allows inferring consequences of management practices on the soil food web. We studied the taxonomic structure of nematode communities in preserved areas of the Atlantic forest (native forest = NF) in Ponta Grossa, Paraná State, Brazil, and in three different agroecosystems in neighboring areas to assess the effect of agricultural land use on nematode assemblages. Agroecosystems were located in a red latosol cropped during 30 years under conventional tillage (CT), no-tillage (NT), and minimal tillage (MT). We collected ten composite soil samples in each area in the summer. Nematodes were extracted by Baermann funnel and fixed with formalin. Subsequently, individuals were classified into taxonomic groups and counted on a Peters slide to determine densities of each taxon. Plant-parasitic and free-living nematodes were classified at the genus level. Data were analyzed with the parameters abundance, Bray & Curtis, Shannon-Weaver, and Simpson indexes. We recorded 35 genera and abundance of nematodes in MT and NT areas was more similar. Higher richness was observed in NF in relation to cropped areas, especially under NT and CT. The PCA and clustering analyses from both nematode communities and soil chemical characteristics showed that MT and CT were more similar and NT was clustered near NF. The replacement of native vegetation by cropping systems caused a reduction of nematode diversity, demonstrating the influence of agricultural practices on nematode communities.

Agricultural land use affects the heterogeneity of Odonata communities in the Brazilian Pampa

Farming expansion has negative impacts on freshwater biodiversity. However, the effects of agricultural land use are not similar across taxa and depend on local context. For instance, the impacts of agricultural expansion are understudied in the Neotropics (one of the leading regions in cropland expansion). Knowledge of the effects of agricultural land use on aquatic insects from South American subtropical grasslands (Pampa) is even more incipient. We tested whether landscape modification related to increased agricultural land use was associated with taxonomic homogenization in odonate communities in waterbodies in the Brazilian Pampa. Odonates were collected in waterbodies differing in the main land-use class in their surroundings (cropland or grassland). Cropland and grassland sites differed with respect to their abiotic conditions (water chemistry) and species composition of Odonata. Additionally, we found higher variation in the composition of Odonata (and suborders Anisoptera and Zygoptera separately) in grassland than cropland sites. We found an interplay between agricultural and grassland land uses and the variation in the composition of odonate communities in the Brazilian Pampa. Specifically, landscape modification by agriculture modified the abiotic conditions in the waterbodies, which may have favored species able to establish as larvae under harsher environmental conditions. We suggest that the maintenance of mixed-grassland and cropland land uses in the fields adjacent to waterbodies can limit the negative effects of agricultural encroachment on Odonata communities with respect to biotic homogenization in the Brazilian Pampa.

Effects of Agricultural Stressors on Growth and an Immune Status Indicator in Wood Frog (Lithobates sylvaticus) Tadpoles and Metamorphs.

Like many amphibians, wood frog (Lithobates sylvaticus) populations have likely declined or experienced local extirpations as a result of habitat alterations. Despite this, wood frogs are still present and breeding in altered landscapes, like the agricultural Prairie Pothole Region of central Canada, and are exposed to a variety of anthropogenic impacts. As tadpoles, water contamination can have negative effects on growth, development, and immune systems. To investigate the potential effects of agricultural land use on tadpole growth and immune system stress, we used boosted regression trees to model body mass, body condition, and neutrophil to lymphocyte ratios, a measure of immune stress, against 32 variables including water quality, wetland habitat, and landscape-level measures. Developmental stage strongly influenced all 3 endpoints, and body mass was negatively influenced by higher levels of total dissolved solids (>600-700 mg/L) and at the first sign of pesticide detection (>0.01 proportion pesticides detected of those screened). While correlative, these data suggest that tadpoles developing in agricultural environments may experience survival and reproductive disadvantages if they metamorphose at smaller body sizes. Given the potential impacts this can have on adult frogs and frog populations, these results provide an impetus for further field-based investigation into the effects that pesticides, and especially total dissolved solids, may have on tadpoles. Environ Toxicol Chem 2021;40:2269-2281. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Riparian Forest Cover Modulates Phosphorus Storage and Nitrogen Cycling in Agricultural Stream Sediments.

Watershed land cover affects in-stream water quality and sediment nutrient dynamics. The presence of natural land cover in the riparian zone can reduce the negative effects of agricultural land use on water quality; however, literature evaluating the effects of natural riparian land cover on stream sediment nutrient dynamics is scarce. The objective of this study was to assess if stream sediment phosphorus retention and nitrogen removal varies with riparian forest cover in agricultural watersheds. Stream sediment nutrient dynamics from 28 sites with mixed land cover were sampled three times during the growing season. Phosphorus dynamics and nitrification rates did not change considerably throughout the study period. Sediment total phosphorus concentrations and nitrification rates decreased as riparian forest cover increased likely due to a decline in fine, organic material. Denitrification rates were strongly correlated to surface water nitrate concentrations. Denitrification rate and denitrification enzyme activity decreased with an increase in forest cover during the first sampling period only. The first sampling period coincided with the greatest connectivity between the watershed and in-stream processing, indicating that riparian forest cover indirectly decreased denitrification rates by reducing the concentrations of dissolved nutrients entering the stream. This reduction in load may allow the sediment to maintain greater nitrogen removal efficiency, because bacteria are not saturated with nitrogen. Riparian forest cover also appeared to lessen the effect of agriculture in the watershed by decreasing the amount of fine material in the stream, resulting in reduced phosphorus storage in the stream sediment.

Improving the representation of cropland sites in the Community Land Model (CLM) version 5.0

Abstract. The incorporation of a comprehensive crop module in land surface models offers the possibility to study the effect of agricultural land use and land management changes on the terrestrial water, energy, and biogeochemical cycles. It may help to improve the simulation of biogeophysical and biogeochemical processes on regional and global scales in the framework of climate and land use change. In this study, the performance of the crop module of the Community Land Model version 5 (CLM5) was evaluated at point scale with site-specific field data focusing on the simulation of seasonal and inter-annual variations in crop growth, planting and harvesting cycles, and crop yields, as well as water, energy, and carbon fluxes. In order to better represent agricultural sites, the model was modified by (1) implementing the winter wheat subroutines following Lu et al. (2017) in CLM5; (2) implementing plant-specific parameters for sugar beet, potatoes, and winter wheat, thereby adding the two crop functional types (CFTs) for sugar beet and potatoes to the list of actively managed crops in CLM5; and (3) introducing a cover-cropping subroutine that allows multiple crop types on the same column within 1 year. The latter modification allows the simulation of cropping during winter months before usual cash crop planting begins in spring, which is an agricultural management technique with a long history that is regaining popularity as it reduces erosion and improves soil health and carbon storage and is commonly used in the regions evaluated in this study. We compared simulation results with field data and found that both the new crop-specific parameterization and the winter wheat subroutines led to a significant simulation improvement in terms of energy fluxes (root-mean-square error, RMSE, reduction for latent and sensible heat by up to 57 % and 59 %, respectively), leaf area index (LAI), net ecosystem exchange, and crop yield (up to 87 % improvement in winter wheat yield prediction) compared with default model results. The cover-cropping subroutine yielded a substantial improvement in representation of field conditions after harvest of the main cash crop (winter season) in terms of LAI magnitudes, seasonal cycle of LAI, and latent heat flux (reduction of wintertime RMSE for latent heat flux by 42 %). Our modifications significantly improved model simulations and should therefore be applied in future studies with CLM5 to improve regional yield predictions and to better understand large-scale impacts of agricultural management on carbon, water, and energy fluxes.

Stoichiometry of carbon, nitrogen, and phosphorus in soil: Effects of agricultural land use and climate at a continental scale

Agricultural land use profoundly alters soil carbon (C), nitrogen (N), and phosphorus (P) contents, impacting crop productivity, environmental quality, and soil C sequestration. However, how the soil C:N:P stoichiometry is affected by upland and paddy cropping over broad geographical scale remains largely unknown. The objective of this study is to examine the soil C:N:P stoichiometry in woodland (as control), agricultural upland and paddy from four climate zones (tropics, subtropics, warm temperate, and mid-temperate) across eastern China. 720 surface soil samples were collected from 240 sites with adjacent woodland, upland, and paddy at a depth of 0–15 cm. Total C, N, and P contents and their ratios were determined. Among climate zones, C and N contents and C:N ratios decreased in the order of mid-temperate > tropics > subtropics > warm temperate, whereas C:P and N:P ratios followed the order of subtropics > mid-temperate and tropics > warm-temperate. Compared to woodland, upland agriculture decreased the C content by 4.0–6.4 g kg−1, but increased P content by 0.2–0.5 g kg−1, resulting in the decreases of C:N, C:P, and N:P ratios by 1.4–5.1, 3.4–91.5, and 1.6–4.1, respectively. Hence, uplands are relatively limited by C and N but enriched with P, particularly in warm temperate zone. By contrast, the C, N, and P contents in paddy soils were all increased compared to woodland soils, but larger N and P increase leads to the decreases in C:N and C:P ratios. The higher P content, and consequently lower C:N:P ratios in both agricultural soils are the consequences of intensive fertilization. As a whole, the direction of soil C, N, and P contents and their stoichiometric ratios in response to agricultural use was similar in the four climate zones: P increased, but C:N:P ratios decreased. The more intensive agricultural practices and stronger biological and geochemical processes with higher temperature and precipitation in warmer and wetter zones lead to more pronounced differences of soil C, N, and P contents and their stoichiometric ratios among land-use types than those in cooler and drier climates.

Agricultural Land-Use Effects on Soil Cation Exchange Capacity, Organic Carbon and Total Nitrogen in Soil Aggregate Sized Fractions in Ile-Ife, Nigeria

Agricultural Land-Use Effects on Soil Cation Exchange Capacity, Organic Carbon and Total Nitrogen in Soil Aggregate Sized Fractions in Ile-Ife, Nigeria

Depth-dependent soil organic carbon dynamics of croplands across the Chengdu Plain of China from the 1980s to the 2010s.

Agricultural soils have tremendous potential to sequester soil organic carbon (SOC) and mitigate global climate change. However, agricultural land use has a profound impact on SOC dynamics, and few studies have explored how agricultural land use combined with soil conditions affect SOC changes throughout the soil profile. Based on a paired soil resampling campaign in the 1980s and 2010s, this study investigated the SOC changes of the soil profile caused by agricultural land use and the correlations with parent material and topography across the Chengdu Plain of China. The results showed that the SOC content increased by 3.78gC/kg in the topsoil (0-20cm), but decreased in the 20-40cm and 40-60cm soil layers by 0.90 and 1.26gC/kg respectively. SOC increases in topsoil were observed for all types of agricultural land. Afforestation on former agricultural land also caused SOC decreases in the 20-60cm soil layers, while SOC decreases only occurred in the 40-60cm soil layer for agricultural land using a traditional crop rotation (i.e. traditional rice-wheat/rapeseed rotation) and with rice-vegetable rotations converted from the traditional rotations. For each agricultural land use, SOC decreases in deep soils only occurred in high relief areas and in soils formed from Q4 (Quaternary Holocene) grey-brown alluvium and Q4 grey alluvium that had a relatively low soil bulk density and clay content. The results indicated that SOC change caused by agricultural land use was depth dependent and that the effects of agricultural land use on soil profile SOC dynamics varied with soil characteristics and topography. Subsoil SOC decreases were more likely to occur in high relief areas and in soils with low soil bulk density and low clay content.

Intensive agriculture alters the biomass size spectrum and body-mass of benthic insects: evidence from a reciprocal transfer experiment

The aim of this study was to test the effects of agricultural land use on benthic insect population body-mass and community biomass size spectrum. Agricultural land use effects were assessed by conducting a reciprocal transfer experiment between two stream reaches exposed to differing intensities of row crop and livestock agricultural activity representing best attainable and highly developed agricultural land use scenarios. We found that transferred insect communities showed no change in richness, abundance, distribution or biomass, indicating that exposure to increased agricultural intensity did not have selective lethal effects on transferred benthic insect communities. However, populations of Ephemerellidae and Hydropsyche demonstrated an increase and decrease, respectively, in body-mass following the transfer to the best attainable agriculture site. Furthermore, the community biomass size spectrum at the best attainable agriculture site contained large, predatory insects not found at the intensive agriculture site. Our findings suggest that taxon-specific body-mass and biomass size spectra have the potential to detect environmental effects prior to long-term community changes. Further research is needed to explore the mechanisms by which changes in the biomass size spectrum link agricultural intensity to shifts in benthic insect community structure.