Loss Of Soil Organic Matter Research Articles

Straw uses trade-off only after soil organic carbon steady-state

Soil organic matter (SOM) is the key for a healthy soil and a relevant property to achieve the sustainability on soil management. However, soils are still net exporters of organic matter. One example is the use of wheat straw residue for industrial and energy applications, which has gained attention in the last years. The offfarm use of this abundant and low cost resource should follow sustainability criteria to avoid soil degradation and SOM losses. Straw residue incorporation is recognized as a recommended management practice to control erosion and mitigate CO2 emissions by increasing SOM. The goal of this work was: i) to evaluate the steady-state carbon (C) level in relation to C input and estimate the minimum residue input needed to maintain this SOC level in a durum wheat-based cropping system in long-term experiment; and ii) estimate the potential availability of durum wheat straws for alternative use. Results showed that a C steady-state can be achieved after 3.4 years with an annual organic C input of 4.5 Mgha–1. Only after reaching a steady-state, straws can be used for trade-off, leaving 1.03 Mgha–1y–1 of C input remain in the soil.

Vulnerability of Physically Protected Soil Organic Carbon to Loss Under Low Severity Fires

Soil aggregate degradation during medium and high severity fires is often identified as the main mechanism that leads to loss of soil organic matter due to fire. Low severity fires, however, are considered not to cause aggregate degradation assuming that temperatures <250o C, as occurring during low-severity burns, have only limited effects on the stability of the soil organic binding agents. Recent studies suggest that low severity burns may cause soil aggregate degradation due to rapid vaporization of soil pore water that can induce pressure on the soil aggregates beyond their yield stress. Such pressure-driven degradation of soil aggregates may expose physically protected organic carbon to decomposition. Our study investigated the effect of a low-severity fire on soil organic matter, water extractable organic C and N as well as respiration for two initial soil moisture conditions undergoing three heating regimes using aggregates from a California forest and Nevada shrubland soil. We found that initially moist soil aggregates that were rapidly heated up degraded the most, showing increased cumulative carbon mineralization when compared to aggregates that were not heated, aggregates that were dry before being heated , and initially moist soil aggregates that were slowly heated. Our results suggest that exposure of previously physically protected organic carbon within the soil aggregates to oxidative conditions was the most likely cause of increased rates of decomposition of organic matter after low-intensity burns. Additionally, we show that for a shrubland soil, aggregates with relatively low organic carbon content, low severity burns increased cumulative carbon mineralization. We hypothesized that this was due to decomposition of cytoplasmic material from lysed microbes. Our results suggest that low severity burns can accelerate decomposition of soil organic carbon protected in soil aggregates.

Linkages between soil carbon, soil fertility and nitrogen fixation in Acacia senegal plantations of varying age in Sudan.

BackgroundOver the last decades sub-Saharan Africa has experienced severe land degradation and food security challenges linked to loss of soil fertility and soil organic matter (SOM), recurrent drought and increasing population. Although primary production in drylands is strictly limited by water availability, nutrient deficiencies, particularly of nitrogen (N) and phosphorus (P), are also considered limiting factors for plant growth. It is known that SOM (often measured as soil organic carbon (SOC)) is a key indicator of soil fertility, therefore, management practices that increase SOM contents, such as increasing tree cover, can be expected to improve soil fertility. The objectives of this study were to investigate the effect of Acacia senegal (Senegalia senegal) trees on soil nitrogen, phosphorus and potassium (K) in relation to SOC, the potential of A. senegal for N2 fixation, and to identify possible N and P ecosystem limitations.MethodsSoil nutrient (total N, P, K and available P and exchangeable K) concentrations and stocks were determined for the 0–10, 10–20,20–30 and 30–50 cm layers of A. senegal plantations of varying age (ranging from 7 to 24-years-old) and adjacent grasslands (reference) at two sites in semi-arid areas of Sudan. At both sites, three plots were established in each grassland and plantation. The potential of A. senegal for N2 fixation in relation to plantations age was assessed using δ15N isotopic abundances and nutrient limitations assessed using C:N:P stoichiometry.ResultsSoil concentrations of all studied nutrients were relatively low but were significantly and directly correlated to SOC concentrations. SOC and nutrient concentrations were the highest in the topsoil (0–10 cm) and increased with plantations age. Acacia foliage δ15N values were >6‰ and varied little with plantations age. Soil C:N and C:P ratios did not differ between grassland and plantations and only 0–10 cm layer N:P ratios showed significant differences between grassland and plantations.DiscussionThe results indicated that soil fertility in the Sahel region is strongly related to SOM contents and therefore highlighting the importance of trees in the landscape. The higher mineral nutrient concentrations in the topsoil of the plantations may be an indication of ‘nutrient uplift’ by the deeper roots. The high foliar δ15N values indicated that N2 fixation was not an important contributor to soil N contents in the plantations. The accretion of soil N cannot be explained by deposition but may be related to inputs of excreted N brought into the area annually by grazing and browsing animals. The soil C:N:P stoichiometry indicated that the plantations may be limited by P and the grasslands limited by N.

Effect of land use, time since deforestation and management on organic C and N in soil textural fractions

Deforestation and subsequent cultivation practices often result in loss of soil organic matter, in a degree depending on time since deforestation and soil and crop management. A land in North Greece was studied in order to check the influence of land use and management on soil organic C (SOC) and N. Cultivated soils with three dates since deforestation (25, 34 and 72 years) were compared to adjacent undisturbed forest soils. Two management systems were used in the cultivated soils: not irrigated wheat with superficial ploughing and irrigated cotton crop with deeper ploughing alternated with wheat every two years. Soil samples were separated in textural size fractions and organic C and N were analysed. In terms of land use, the most distinctive differences between agricultural and forest plots were found in coarse particulate organic matter (2.8 g kg−1 soil in agricultural land vs 14.8 g kg−1 soil in forest sites), and in the fine sand fraction SOC (8.6 g kg−1 soil in agricultural land vs 40.6 g kg−1 soil in forest sites), and N (1 g kg−1 soil in agricultural land vs 2.4 g kg−1 soil in forest sites), with minimal differences in the clay fraction (15.5 g kg−1 soil in agricultural land vs 21.2 g kg−1 soil in forest sites for SOC, and 2.2 g kg−1 soil in agricultural land vs 2.4 g kg −1 soil in forest sites for N). Time as a factor was significant for all the studied properties regarding the first years following deforestation. Management practices had an effect on SOC and, more pronounced, on N, with the wheat plots showing higher contents. Clay particles present the most stable behavior in terms of SOC (especially regarding time and management as factors) and N (especially regarding land use and time as factors) protection and maintenance.

Soil carbon stocks cultivated with coffee in the brazilian savana: Effect of cultivation time and use of organic compost

&lt;p&gt;Land-use change (LUC) is one of the main responsible for the loss of soil organic matter (SOM) in the form of CO&lt;sub&gt;2&lt;/sub&gt; to atmosphere. The aims of the present study were i) evaluate soil C stocks due to coffee cultivation time after LUC and ii) evaluate the use of the organic compost from the by-product of bean processing as a source of SOM. The study was performed in dystrophic red latosol in the municipality of Patrocínio, MG, Brazil. Two evaluations were performed; i) three coffee (&lt;em&gt;Coffea arabica &lt;/em&gt;L. var. Icatú Vermelho) growing areas with different implantation times (8, 15 and 37 years) in relation to Cerrado &lt;em&gt; stricto sensu &lt;em&gt; (reference); and ii) area cultivated with coffee (&lt;em&gt; C. arabica &lt;/em&gt; var. Bourbon Vermelho) that received organic compost for four years. Soil was sampled in layers 0-5, 5-10 and 10-20 cm. In the first study, the C stock (0-20 cm) was higher under native vegetation (67 Mg C ha&lt;sup&gt;-1&lt;/sup&gt;) in relation to the coffee growing (63 Mg C ha&lt;sup&gt;-1&lt;/sup&gt;), however, did not differ significantly and showed subtle loss rates of 0.12; 0.06 and 0.02 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; year&lt;sup&gt;-1&lt;/sup&gt; for 8, 15 and 37 years, respectively. In the second study, the organic compost applied to the soil increased the C stock (0-20 cm) to 4.6 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; and showed an accumulation rate of 1.15 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; year&lt;sup&gt;-1&lt;/sup&gt;. Thus, it is concluded that C stocks is reduced in the soil due to LUC, however, the application of organic compost increased the supply of organic material, favoring the maintenance and even increasing the stock in the soil.&lt;/em&gt;&lt;/em&gt;&lt;/p&gt;

Are Nitrogen Fertilizers Deleterious to Soil Health?

Soil is one of the most important natural resources and medium for plant growth. Anthropogenic interventions such as tillage, irrigation, and fertilizer application can affect the health of the soil. Use of fertilizer nitrogen (N) for crop production influences soil health primarily through changes in organic matter content, microbial life, and acidity in the soil. Soil organic matter (SOM) constitutes the storehouse of soil N. Studies with 15N-labelled fertilizers show that in a cropping season, plants take more N from the soil than from the fertilizer. A large number of long-term field experiments prove that optimum fertilizer N application to crops neither resulted in loss of organic matter nor adversely affected microbial activity in the soil. Fertilizer N, when applied at or below the level at which maximum yields are achieved, resulted in the build-up of SOM and microbial biomass by promoting plant growth and increasing the amount of litter and root biomass added to soil. Only when fertilizer N was applied at rates more than the optimum, increased residual inorganic N accelerated the loss of SOM through its mineralization. Soil microbial life was also adversely affected at very high fertilizers rates. Optimum fertilizer use on agricultural crops reduces soil erosion but repeated application of high fertilizer N doses may lead to soil acidity, a negative soil health trait. Site-specific management strategies based on principles of synchronization of N demand by crops with N supply from all sources including soil and fertilizer could ensure high yields, along with maintenance of soil health. Balanced application of different nutrients and integrated nutrient management based on organic manures and mineral fertilizers also contributed to soil health maintenance and improvement. Thus, fertilizer N, when applied as per the need of the field crops in a balanced proportion with other nutrients and along with organic manures, if available with the farmer, maintains or improves soil health rather than being deleterious.

Monitoring of Soil Contamination by Heavy Metals in the Impact Zone of Copper-Nickel Smelter on the Kola Peninsula

The results of landscape monitoring of the concentrations of acid-extractable Ni, Cu, Co, Mn, and Zn in soils of the local impact zone of the Severonikel industrial complex on the Kola Peninsula are discussed. The aim of monitoring studies was to reveal the spatial and temporal regularities of variation in the degree of soil contamination by heavy metals. In 2001–2011, the concentrations of acid-extractable compounds of the elements in the upper part of organic soil horizons around this plant exceeded their background concentrations by two orders of magnitude for Cu and Co and by three orders of magnitude for Ni. The degree of topsoil contamination with Ni, Cu, and Co generally corresponded to the distance of the plots from the contamination source and to the modern technogenic load. However, because of the long period of the emissions, their extreme amounts, and complex composition, indirect factors—the degree of technogenic soil degradation, the loss of soil organic matter, saturation of the surface soil layers by the contaminating metals, and competitive relationships between the elements—also affect soil contamination level. The concentrations of all the studied metals in the topsoil are characterized by considerable (1.5 to 7 times) variability in their long-term dynamics. The most important factors of this variability for Ni, Cu, and Co are the organic matter content of the samples and the amount of atmospheric precipitation in the year preceding the sampling. An inverse relationship between element concentrations in the soils and the amount of atmospheric precipitation attests to the dynamic nature and reversible character of the accumulation of heavy metals in the soils.

Initial Soil Organic Matter Content Influences the Storage and Turnover of Litter, Root and Soil Carbon in Grasslands

Grassland degradation is a worldwide problem that often leads to substantial loss of soil organic matter (SOM). To estimate the potential for carbon (C) accumulation in degraded grassland soils, we first need to understand how SOM content influences the transformation of plant C and its stabilization within the soil matrix. We conducted a greenhouse experiment using C3 soils with six levels of SOM content; we planted the C4 grass Cleistogenes squarrosa or added its litter to the soils to investigate how SOM content regulates the storage of new soil C derived from litter and roots, the decomposition of extant soil C, and the formation of soil aggregates. We found that with the increase in SOM content, microbial biomass carbon (MBC) and the mineralization of litter C increased. Both the litter addition and planted treatments increased the amount of new C inputs to soil. However, the mineralization of extant soil C was significantly accelerated by the presence of living roots but was not affected by litter addition. Accordingly, the soil C content was significantly higher in the litter addition treatments but was not affected by the planted treatments by the end of the experiment. The soil macroaggregate fraction increased with SOM content and was positively related to MBC. Our experiment suggests that as SOM content increases, plant growth and soil microbial activity increase, which allows microbes to process more plant-derived C and promote new soil C formation. Although long-term field experiments are needed to test the robustness of our findings, our greenhouse experiment suggests that the interactions between SOM content and plant C inputs should be considered when evaluating soil C turnover in degraded grasslands.

Susceptibility of soil organic matter fractions to soil erosion under potato-legume intercropping systems in central Kenya

Soil organic matter (SOM) losses due to soil erosion may be considered low in continuous potato (<i>Solanum tuberosum</i> L.) cropping systems, but cumulated over time may cause considerable soil degradation. A field study was conducted in Kabete, Kenya, during the 2014 to 2015 rainy seasons to determine the effect of sediment particle size distribution on SOM losses and to assess the SOM fractions most susceptible to soil erosion under potato-legume intercropping systems. The treatments comprised of bare soil, pure potato stand (sole potato), potato + garden pea (<i>Pisum sativa</i>), potato + climbing bean (<i>Phaseolus vulgaris</i>), and potato + dolichos lablab (<i>Lablab purpureus</i>). A combined aggregate size and density fractionation was used to separate the sediment in size classes of aggregates 53 to 250 μm and in the sieve fraction &lt;−53 μm, while SOM was fractionated into particulate organic matter with a density of 1.65 to 1.85 g cm⁻³ and mineral-associated SOM with a density of 2.60 g cm⁻³. Sediment and organic matter enrichments varied significantly (<i>p</i> &lt; 0.05) among the cropping systems and were consistently highest under sole potato and lowest under potato + dolichos. Soil particles were transported mainly as aggregates, with those in the &lt;53 μm size fraction containing primary silt and clay particles. Stable fractions of SOM related positively with silt plus clay particles (<i>r</i> = 0.89; <i>p</i> &lt; 0.01) and accounted for 95% of the total SOM losses. Vegetal cover (β = −0.10508; <i>p</i> = 0.001603), splash detachment (β = 0.00323; <i>p</i> = 0.039403), and their interactive effect (β = −0.27327; <i>p</i> = 0.027224) influenced the amount and composition of SOM fractions at the aggregate level. Dolichos lablab ensured continuity of effective groundcover and protected the organic matter against soil erosion, thus demonstrating the need to integrate indeterminate legume cover crops into potato cropping systems.

The effects of burning and grazing on soil carbon dynamics in managed Peruvian tropical montane grasslands

Abstract. Montane tropical soils are a large carbon (C) reservoir, acting as both a source and a sink of CO2. Enhanced CO2 emissions originate, in large part, from the decomposition and losses of soil organic matter (SOM) following anthropogenic disturbances. Therefore, quantitative knowledge of the stabilization and decomposition of SOM is necessary in order to understand, assess and predict the impact of land management in the tropics. In particular, labile SOM is an early and sensitive indicator of how SOM responds to changes in land use and management practices, which could have major implications for long-term carbon storage and rising atmospheric CO2 concentrations. The aim of this study was to investigate the impacts of grazing and fire history on soil C dynamics in the Peruvian montane grasslands, an understudied ecosystem, which covers approximately a quarter of the land area in Peru. A density fractionation method was used to quantify the labile and stable organic matter pools, along with soil CO2 flux and decomposition measurements. Grazing and burning together significantly increased soil CO2 fluxes and decomposition rates and reduced temperature as a driver. Although there was no significant effect of land use on total soil C stocks, the combination of burning and grazing decreased the proportion of C in the free light fraction (LF), especially at the lower depths (10–20 and 20–30 cm). In the control soils, 20 % of the material recovered was in the free LF, which contained 30 % of the soil C content. In comparison, the burnt–grazed soil had the smallest recovery of the free LF (10 %) and a significantly lower C content (14 %). The burnt soils had a much higher proportion of C in the occluded LF (12 %) compared to the not-burnt soils (7 %) and there was no significant difference among the treatments in the heavy fraction (F) ( ∼ 70 %). The synergistic effect of burning and grazing caused changes to the soil C dynamics. CO2 fluxes were increased and the dominant temperature driver was obscured by some other process, such as changes in plant C and N allocation. In addition, the free LF was reduced when these two anthropogenic activities took place on the same site – most likely a result of reduced detritus being incorporated into the soil. A positive finding from this study is that the total soil C stocks were not significantly affected and the long-term (+10 years) C storage in the occluded LF and heavy F were not negatively impacted. Possibly this is because of low-intensity fire, fire-resilient grasses and because the grazing pressure is below the threshold necessary to cause severe degradation.

Biodiversity of nematodes biological indicators of soil quality in the agroecosystems

ABSTRACT: Nematodes can be associated with the soil ecological condition, thus being associated with this sustainability condition of agricultural production. Studies of their diversity can be applied with the purpose of using them as bioindicators of environmental changes and the productive impacts. However, these organisms have been neglected in the agroecosystems, only assuming status of pathogen when their population is very high, with considerable losses in productivity. It is estimated that approximately 10% of the nematodes cause damage to plants, 25% are nematodes grouped into trophic levels of fungivores or fungal feeders, bacterivorous, and omnivores, according to the type of their food. In many cases it is not known the ratio of population level of the nematode with the level of damage in plants. For this reason, the use of pesticides and fertilizers is still part of the most common practices by farmers, causing loss of soil organic matter, soil erosion and groundwater contamination, in addition to an imbalance in the microbiote. The objective of this work was to make a brief review about the diversity of nematodes in the soil in the agroecosystems that can be used in studies of sustainability, as soil quality bioindicators. Several species of nematodes have the potential to be used as biological indicators of soil quality. In this sense, the knowledge and use of bioindicators by rural producers are important, in order to encourage practices of sustainable management systems that do not cause the soil biodiversity imbalance.

Erosion-induced losses of carbon, nitrogen, phosphorus and heavy metals from agricultural soils of contrasting organic matter management

Water erosion on agricultural land preferentially carries away fine particles. Due to the generally high specific density of sorption sites of these particles, their displacement can be associated with substantial particle-bound transfer also of nutrients and pollutants with low solubility. Organic matter amendments can reduce soil erosion, but to what extent they affect the erosion-induced element losses has not been studied much. Here, we carried out field rainfall experiments on three pairs of soil plots (1.5×0.75m) after incorporating a mixture of wheat straw and grass (2.12gC per kg soil) as organic amendment into the topsoil (0–5cm depth) of one plot in each pair (OI treatment). The other plot was prepared in the same way but without incorporation of the amendment (NI treatment). Artificial rainfall (49.1mmh−1) was simultaneously applied on each pair of plots for approximately 2h, and sediment samples were collected at designated time steps for the analyses of C, N, P, Cu, Zn and stable carbon isotope ratios. The organic amendment substantially reduced element losses, but to a lesser extent than soil loss, as the element concentrations were higher in the exported sediments in the OI than in the NI treatment. With and without organic amendment, the concentrations of the studied elements were consistently higher in the exported sediments than in the bulk soil. They were always maximal at the onset of discharge and then continuously decreased towards the values of the bulk soil. The δ13C values revealed that the eroded C was preferentially derived from the fresh organic residue added to the soil. Pairwise correlations between elements and sediment size indicate that the export of N, Cu and Zn was primarily associated with soil organic matter loss, whereas P export was more associated with mineral fractions.

Conservation agriculture improves yield and reduces weeding activity in sandy soils of Cambodia

The years of intensive tillage in Cambodia have caused significant decline in agriculture’s natural resources that could threaten its future of agricultural production and sustainability. Conventional tillage could cause rapid loss of soil organic matter, leading to a high potential for soil degradation and decline of environmental quality. Hence, a better and comprehensive process-based understanding of differential effects of tillage systems and crop management on crop yield is critically needed. A study was conducted in 10 farmer’s fields to evaluate the effect of conservation agriculture and conventional tillage on yield of selected crops and weeding activity in two villages of Siem Reap, Cambodia. The experiment was laid out following a 2 × 2 factorial treatment combination in randomized complete block design. Each treatment was replicated five times. Each farmer’s field was divided into four plots and was randomly assigned with production management and irrigation treatments, respectively. We demonstrated that our results supported the overall premises of conservation agriculture. Average yields of selected crops were significantly (≤ 0.001) improved in plots with conservation agriculture (17.1 ± 6.3 to 89.3 ± 40.2 Mg ha−1) compared with conventional tillage (18.8 ± 6.4 to 63.8 ± 27.7 Mg ha−1). Our results showed that manual weeding in all cropping seasons was significantly reduced by about 35% in conservation agriculture (169 ± 23 to 125 ± 18 man-day ha−1), which can be attributed to existing cover crops and surface mulch. Overall, our results suggest that in smallholder commercial household farms, adoption of conservation agriculture had a profitable production management system, which could save natural resources, improve yield, and reduce labor. We proved for the first time that in Cambodian smallholder commercial household farms, adoption of conservation agriculture saves natural resources, improves yield, and reduces labor. Additional studies are encouraged to further test the conservation agriculture system for a longer period of time, with repeated cropping sequences.

Loss of Soil Organic Matter, Lignocellulose and Microbial Population in Oil Palm Plantations Located at Different Slopes

Loss of soil organic matter can be caused by erosion triggered by soil compaction and high rainfall. The aims of the study were to determine (1) the loss of soil organic matter, lignocellulose, and soil microbial population due to erosion and (2) the contribution of organic matter from oil palm fronds. In the current study, the erosion plots were built on the accessible inter-row (gawangan hidup) and inaccessible inter-row (gawangan mati) of oil palm plantations located at the slope of 6-10% and &gt;10%. Soil organic matter, lignin, cellulose, and hemicellulose contents and total soil microbial populations were measured in the sediments collected from the erosion plots. The results showed that the loss of organic matter was higher in the accessible inter-row than that in the inaccessible inter-row. The addition of lignin, cellulose, and hemicellulose from oil palm fronds into the soil are 2.06 Mg ha-1 yr-1, 1.13 Mg ha-1 yr-1 and 1.02 Mg ha-1 yr-1, respectively. Total bacterial population in the sediments taken from the accessible inter-row was higher than that from the inaccessible inter-row, while the total fungal population in the sediments from the inaccessible inter-row was higher than that from the accessible inter-row.

Development of a composite soil degradation assessment index for cocoa agroecosystems in southwestern Nigeria

Abstract. Cocoa agroecosystems are a major land-use type in the tropical rainforest belt of West Africa, reportedly associated with several ecological changes, including soil degradation. This study aims to develop a composite soil degradation assessment index (CSDI) for determining the degradation level of cocoa soils under smallholder agroecosystems of southwestern Nigeria. Plots where natural forests have been converted to cocoa agroecosystems of ages 1–10, 11–40, and 41–80 years, respectively representing young cocoa plantations (YCPs), mature cocoa plantations (MCPs), and senescent cocoa plantations (SCPs), were identified to represent the biological cycle of the cocoa tree. Soil samples were collected at a depth of 0 to 20 cm in each plot and analysed in terms of their physical, chemical, and biological properties. Factor analysis of soil data revealed four major interacting soil degradation processes: decline in soil nutrients, loss of soil organic matter, increase in soil acidity, and the breakdown of soil textural characteristics over time. These processes were represented by eight soil properties (extractable zinc, silt, soil organic matter (SOM), cation exchange capacity (CEC), available phosphorus, total porosity, pH, and clay content). These soil properties were subjected to forward stepwise discriminant analysis (STEPDA), and the result showed that four soil properties (extractable zinc, cation exchange capacity, SOM, and clay content) are the most useful in separating the studied soils into YCP, MCP, and SCP. In this way, we have sufficiently eliminated redundancy in the final selection of soil degradation indicators. Based on these four soil parameters, a CSDI was developed and used to classify selected cocoa soils into three different classes of degradation. The results revealed that 65 % of the selected cocoa farms are moderately degraded, while 18 % have a high degradation status. The numerical value of the CSDI as an objective index of soil degradation under cocoa agroecosystems was statistically validated. The results of this study reveal that soil management should promote activities that help to increase organic matter and reduce Zn deficiency over the cocoa growth cycle. Finally, the newly developed CSDI can provide an early warning of soil degradation processes and help farmers and extension officers to implement rehabilitation practices on degraded cocoa soils.

Soil, water, nutrients and soil organic matter losses by water erosion as a function of soil management in the Posses sub-watershed, Extrema, Minas Gerais, Brazil

Knowledge of the quantity and quality of the material lost by soil erosion due to soil management is a basic need to identify land management zones in catchments. The aim of this study was to investigate the influence of soil management on the quantity and quality of soil material lost by erosion in the Posses sub-watershed, Municipality of Extrema, State of Minas Gerais, Brazil. Water and sediments lost by natural rainfall erosion were sampled from erosion plots located on a Red-Yellow Argisol (PVA) under the following systems: bare soil, subsistence farming (maize/beans/pumpkin/jack-beans/fallow), degraded pasture, well-managed pasture, and reforestation set up in 2013; and in a Litholic Neosol (RL): reforestation set up in 2008, bare soil, and native forest. Ca, Mg, K, P, N and soil organic matter (SOM) contents were determined in sediment and soil samples (at 0-5 cm depth) for the determination of the runoff enrichment ratios. Management influences soil losses more so than water losses. Minor losses were found in reforestation set up in 2013 (soil); in well-managed pasture (water); and in reforestations (nutrients and SOM). These losses tend to stability with time. The general sequence of nutrient losses was N &gt; Ca &gt; Mg &gt; K &gt; P in PVA; and N &gt; Ca &gt; K &gt; Mg &gt; P in RL. Loss rates of SOM and N followed the order: bare soil &gt; subsistence farming &gt; degraded pasture &gt; well-managed pasture &gt; reforestation, in PVA; and bare soil &gt; native forest &gt; reforestation, in RL. Reforestation and well-management pasture are effective conservation strategies in order to lower the erosion process in the Posses sub-watershed. Soil losses, as well as nutrients and organic matter losses were more influenced by soil management than water losses. The safeguarding native forest under Litholic Neosol is essential to the conservation of this pedoenvironment, especially in steep slopes.

Carbon saturation drives spatial patterns of soil organic matter losses under long-term bare fallow

Spatial controls of soil organic carbon (SOC) turnover are not well understood. We hypothesized that spatial patterns of SOC turnover are related to carbon (C) saturation rather than to the size of measurable SOC-pools such as particulate organic matter (POM), determined as SOC in particle-size fractions. Therefore, we repeatedly grid-sampled a field after one, three, seven, and eleven years under bare fallow management, which revealed a spatial gradient from high to low degrees of C saturation. We measured the contents of SOC and the contents of SOC in coarse sand-size (2000–250μm, POM1), fine sand-size (250–53μm, POM2), silt-size (53–20μm, POM3), and fine silt to clay-size fractions (nonPOM, <20μm), calculated the degree of C saturation from textural properties and nonPOM contents, and related these parameters to SOC losses. In the first year of bare fallow, the soil contained on average 12.1g SOC kg−1, of which 0.6gkg−1, 1.7gkg−1, and 2.1gkg−1 were lost after three, seven, and eleven years of bare fallow, respectively. The SOC losses within eleven years were spatially variable and varied between 1% and 46% relative to the initial SOC content. In support of our hypothesis, SOC losses were largest at subsites with largest degrees of C saturation (R2=0.83). Although the POM fractions declined most drastically, they only comprised 4 to 9% of bulk SOC, and they did neither correlate with nor explain spatial patterns of SOC losses. We conclude that the concept of C saturation is superior to conventional physical fractionation approaches for predicting spatio-temporal patterns of SOC turnover at sites with a high degree of C saturation.

Response of sedimentary organic matter source to rainfall events using stable carbon and nitrogen isotopes in a typical loess hilly-gully catchment of China

Understanding the information on sedimentary organic matter (SOM) source is of great importance for better understanding biogeochemical cycling and terrestrial carbon sequestration on the Earth’s surface. Such information, especially during field rainfall process, however, is unavailable or difficult to assemble. In order to further study the dynamic variation of sedimentary organic matter source during rainfall process, suspended sediment were sampled manually at the outlet of two paired typical hilly-gully watersheds of Loess Plateau in China [Qiaozi East watershed (QEW) and Qiaozi West watershed (QWW)], and source materials included subsoil (i.e., soils from channel bank and gully bank) and topsoil (i.e., surface soils from different slope positions in land uses), along with C3 and C4 plants. In this study reported, natural stable isotopes (13C and 15N) and elemental compositions (TOC and TN), combined with a isotope mixing model (stable isotope analysis in R, SIAR) were successfully used to assemble this information. The results showed that the response of source contributions to SOM displayed difference significantly during different rainfall processes, showing fluctuation with flow. Subsoil was the main source of SOM pool for two similar small watersheds (accounting for 38.50% for QWW and 35.63% for QEW). Minor contribution was sourced from the C3 and C4 plants (< 25%), but only 10% for the C4 plants, indicating that the C3 plants dominated the input of organic matter in superficial soils of this study region. The source of sedimentary organic matter transported by erosion showed different contribution proportions from potential sources in two similar small watersheds with different management practices, indicating that management practice could decrease the soil organic matter loss by reducing the sediment transportation and flow during rainfall process in the Loess Plateau of China.

Temporal Dynamics of Soil Microbial Communities below the Seedbed under Two Contrasting Tillage Regimes.

Agricultural productivity relies on a wide range of ecosystem services provided by the soil biota. Plowing is a fundamental component of conventional farming, but long-term detrimental effects such as soil erosion and loss of soil organic matter have been recognized. Moving towards more sustainable management practices such as reduced tillage or crop residue retention can reduce these detrimental effects, but will also influence structure and function of the soil microbiota with direct consequences for the associated ecosystem services. Although there is increasing evidence that different tillage regimes alter the soil microbiome, we have a limited understanding of the temporal dynamics of these effects. Here, we used high-throughput sequencing of bacterial and fungal ribosomal markers to explore changes in soil microbial community structure under two contrasting tillage regimes (conventional and reduced tillage) either with or without crop residue retention. Soil samples were collected over the growing season of two crops (Vicia faba and Triticum aestivum) below the seedbed (15–20 cm). Tillage, crop and growing stage were significant determinants of microbial community structure, but the impact of tillage showed only moderate temporal dependency. Whereas the tillage effect on soil bacteria showed some temporal dependency and became less strong at later growing stages, the tillage effect on soil fungi was more consistent over time. Crop residue retention had only a minor influence on the community. Six years after the conversion from conventional to reduced tillage, soil moisture contents and nutrient levels were significantly lower under reduced than under conventional tillage. These changes in edaphic properties were related to specific shifts in microbial community structure. Notably, bacterial groups featuring copiotrophic lifestyles or potentially carrying the ability to degrade more recalcitrant compounds were favored under conventional tillage, whereas taxa featuring more oligotrophic lifestyles were more abundant under reduced tillage. Our study found that, under the specific edaphic and climatic context of central Belgium, different tillage regimes created different ecological niches that select for different microbial lifestyles with potential consequences for the ecosystem services provided to the plants and their environment.

Effects of aeolian processes on soil nutrient loss in the Gonghe Basin, Qinghai–Tibet Plateau: an experimental study

The Gonghe Basin of northeastern Qinghai–Tibet Plateau is threatened by aeolian processes, soil nutrient loss, and desertification, where human activities have greatly increased over recent decades. However, the interactions between aeolian processes and soil nutrient loss remain poorly understood. Therefore, in this study, we employed a wind tunnel to simulate aeolian processes and soil nutrient loss affected by human activities such as tillage and trampling by livestock. Field investigations, wind tunnel experiments, and experimental analyses were conducted to assess the impacts of human activity (wholesale destruction of vegetation) and aeolian processes on soil nutrient loss and desertification in the Gonghe Basin. After grassland soil surface was disaggregated, sediments removed by high aeolian intensity (≥16 m s−1) ranged from 294.02 to 1012.73 g m−2, and wind erosion depths varied from 4.09 to 11.27 mm. High wind velocities resulted in losses of total soil organic matter (SOM) and total nitrogen (TN) by 7.56 and 0.38 kg ha−1, respectively. Under very high wind velocities (≥22 m s−1), losses of SOM and TN were 26.99 and 1.41 kg ha−1, respectively. Wind tunnel experiments indicate that in the Gonghe Basin, there were no significant correlations between wind velocity and the removal of SOM and TN; however, positive correlations were observed between wind velocity and total phosphorus (TP) and total potassium (TK). Aeolian processes remove TK and TP from the soil surface, which has a potential impact on vegetation because that K and P are essential nutrients for plant growth. In addition, most nutrients are enriched within fine particle fraction of soil. Nutrient loss caused by aeolian processes may therefore result in the degradation of farmland and grassland, which consequently may have triggered desertification in the Gonghe Basin.