Soil Nutrient Stocks Research Articles

Soil nutrient stocks in areas where oiticica (Licania rigida Benth) occurs in the paraiba hinterland

The experiment was conducted in the municipalities of Catolé do Rocha and Pombal, both located in the state of Paraíba in northeastern Brazil. The areas are composed of Eutrophic Fluvic Neosols, with low-activity clay and high natural fertility in flat relief. The factorial arrangement was 2x2, with a completely randomized design, with two municipalities: Catolé do Rocha and Pombal and two soil sampling depths: 0–20 cm and 20–40 cm, selecting 10 matrices of oiticica, L. rigida Benth, representing 10 replicates. In the municipality of Catolé, soil analysis revealed higher SB and CTC with lower pH and MOS compared to the municipality of Pombal. The chemical characterization of the soil in the surface layers presents higher concentrations of nutrients than in the subsurface layers, mainly regarding the levels of MO, reflecting in higher levels of phosphorus, sum of bases and cation exchange capacity.

Afforestation of a floodplain system in Paraguay with eucalyptus: Effects on soil properties and nutrient stocks

The gramineous species Andropogon lateralis and Paspalum notatum dominate lowland habitats in Paraguay. These habitats include wetlands and aquifers that provide essential ecosystem services, such as soil C storage, biodiversity, water flow regulation and water quality. Large areas of these valuable natural ecosystems have been transformed into intensive agricultural systems, including sugarcane and eucalyptus plantations. The transformation potentially affects water flow and lake and stream recharge and threatens the native biodiversity of the ecoregion. The soils in these zones are characterised by high C stocks, high acidity, nutrient limitation (low cation exchange capacity and base saturation) and a sandy texture, and they may be sensitive to perturbations. This study aimed to assess the impact of eucalyptus plantations on soil properties and nutrient and C stocks in afforested lowland regions in a subtropical area and to generate information relevant to sustainable management. For this purpose, 62 eucalyptus plantations of ages between 2 and 10 years and 8 native grassland plots were selected for study. The experimental design enabled us to estimate the amounts of nutrients extracted throughout the plantation rotation and to evaluate the impacts on soil properties (at 0–40 cm depth) and on soil carbon and nutrient stocks. The eucalyptus biomass production amounted to 215 Mg ha−1 after 10 years. The significant loss of soil C, which had decreased to 40 % after a decade, was attributed to the initial soil preparation, intensive drainage and the lower input of organic remains than in the natural grasslands. The significant decreases in soil nutrient stocks (N, P, Ca, Mg, and K), reaching between 50 % and 60 % throughout the rotation, were attributed to uptake of these elements by the trees. The bulk density increased by up to 1.3 g cm−3. The data suggest that establishing eucalyptus plantations in these lowland habitats leads to soil degradation and may reduce the environmental services supplied by the ecosystems. Local authorities must develop and implement territorial land plans and silvicultural practices in order to prevent degradation of these critical ecosystems.

Long-term conventional cultivation after desert reclamation is not conducive to the improvement of soil carbon pool and nutrient stocks, a case study from northwest China

Reclamation in desert-oasis areas is effective for improving land productivity and ensuring food supply. However, the understanding of the sustainable productivity of soils under long-term conventional cultivation after desert reclamation is still poor. This study was conducted to determine soil structural properties, organic carbon stocks (SOCS) and nutrient stocks under four desert reclamation ages (0, 30, 60, and 100) in the arid region of northwest China, and evaluate the influence of long-term conventional cultivation on desert soil quality. The results indicated that soil structural stability index (SI) in topsoil improved after desert reclamation, but showed a slight downward trend after 60 years of cultivation, and farmland soil in the study area was still at serious risk of degradation (SI ≤ 5 %) overall. SOCS were enlarged by 4.2 times after desert reclamation, and nitrogen stocks (NS) and phosphorus stocks (PS) were increased by 1.2–6.5 times. However, the regression analysis showed that SOCS and NS in 0–40 cm soil layer and PS in topsoil stopped increasing after about 60-year conventional cultivation. Soil stoichiometry, pH and texture were the key factors affecting SOCS, NS and PS in oasis farmlands. In summary, our study emphasized that soil quality in arid areas was greatly improved after desert reclamation, however, long-term conventional agriculture management measures limited this improvement. Therefore, long-term conventional management of agricultural land in arid areas should introduce appropriate conservation measures to achieve sustainable soil productivity.

Pedotransfer Functions in the Assessment of Fragile Mountainous Areas: Carbon and Nitrogen Stocks in Mountains in Southeastern Brazil

Objective: This study aimed to obtain the Bd of organic constitution horizons through PTFs and evaluate the C and N stocks of different soil classes found in the upper part of the INP. Theoretical framework: The evaluation of bulk density (Bd) depends on the method used to obtain the sample and presents great spatial variability, especially in mountainous regions such as the upper part of Itatiaia National Park (INP), Brazil. Techniques can be used for this purpose, including those of pedotransfer functions (PTFs) allowing the quantification of nutrients such as C and N in soils. Methodology: The research was conducted within the Itatiaia National Park (INP), situated in the Mantiqueira Mountains of southeastern Brazil. Soil samples were collected from the upper portion of the INP, specifically targeting soil profiles containing hystic horizons (O or H). The study employed pedotransfer functions (PTFs) established by Beutler et al. (2017) to estimate the soil bulk density (Bd) of organic horizons. Based on these assessments, stocks of carbon (C) and nitrogen (N) were calculated. The standard depth for these calculations was 30 cm. In total, 47 profiles were selected, 26 of which belonged to the order Histosols, 15 to Cambisols, and 6 Leptosols & Regosols. Results and conclusion: In general, a high C content, between 5 and 15 g kg-1, and N contents greater than 1.0 g kg-1 were observed. For Bd an increase in depth occurred, with values close to 0.50 Mg m-3 in the superficial horizons and > 0.75 Mg m-3 in depths greater than 30 cm. The area occupied by soil profiles presenting hystic horizons corresponds to 16403.69 ha (hectares) with 315645.7 Mg of C and 20043.0 Mg of N. Of this total, 10254.44 ha were Cambisols that store approximately 205282.1 Mg of C and 13121.8 Mg of N. Histosols occupied an area of 4148.38 ha and stored 90698.4 Mg of C and 5576.0 Mg of N. The area occupied by Leptosols & Regosols was 1347.74 ha and they stored 19665.1 Mg of C and 1345.1 Mg of N. For the Cambisols, the average values of C and N stocks were lower than those quantified in the Histosols, but considering the area occupied, the total C stock was more than twice the amount quantified in the Histosols. Research implications: Soils with organic horizons complicate Bd determination due to costly and unrepresentative collection methods. Additionally, converting soil masses to volume for nutrient stock measurements (e.g., C and N) is problematic. Due to limited accessibility in certain areas, obtaining undisturbed soil samples for evaluation can be challenging. In such cases, pedotransfer functions (PTFs) play a crucial role in assessing and modeling soil phenomena. Indirect quantification of Bd using PTFs has become essential for addressing these issues. Originality/value: This study utilizes pedotransfer functions (PTFs) to estimate soil bulk density (Bd) and, consequently, nutrient stocks in fragile mountainous soils, enabling monitoring of these environments.

Spatial Variability and Statistical Analysis of Soil Properties in the Rice Wheat-Based Systems of North-West India

ABSTRACT There are limited reports about the impacts of long-term rice wheat cropping system (RWCS) on soil properties and nutrient stocks under smallholder farmer’s conditions in developing counties. The study was carried out in RWCS in Haryana (10 districts) of North-West India in order to map out some soil properties and assess their variability within the area. From the study area, a total of 150 surface soil samples (15 samples each district) were collected using Global Positioning System (GPS) after harvest of wheat crop. Then, soil properties, that is, pH, electrical conductivity (EC), soil organic carbon (SOC), carbonate content, cation exchange capacity (CEC), salinity content (Na+, K+, Ca2+ + Mg2+) soil available nutrients (NPK, Fe & Zn), and micronutrient fractions were measured in the laboratory. All soil properties significantly changed under RWCS, except for bulk density, SOC, and SAR variables. The SOC stock varied significantly among the majority of RWCS in north-western India but was not significantly different in total nitrogen (TN) stocks. After log-transformation of data, classical statistics were used to describe the soil properties, and one-way analysis of variance. The PCA chosen soil properties explained 81.37% of the soil quality variability among the RWCS. Such soil properties and nutrient stock variability among the RWCS suggested the introduction of suitable management practices that sustain the soil system of the RWCS with poor properties and nutrients. On the basis of the linear function, soil chemical properties (44.65%) contributed more to soil quality index (SQI) than physical ones.

Increasing complexity of agroforestry systems benefits nutrient cycling and mineral-associated organic carbon storage, in south-eastern Brazil

Agroforestry systems are often promoted as solutions to address land degradation and climate change. However, agroforestry is an umbrella term for a large variety of systems and it is not clear how their degree of complexity influences their provision of soil-based ecosystem services, such as soil organic carbon (SOC) storage and nutrient cycling. Furthermore, a knowledge gap remains whether agroforestry systems perform equally well on all soil types. The objectives of this study were 1) to assess the links between agroforestry complexity, nutrient cycling and SOC fractions, and 2) to assess how soil texture influences these relationships in Brazilian agroforestry systems. We sampled 59 agroforestry plots across 30 sites in Sao Paulo state, Brazil, and 8 monocrop sites (6 pastures and 2 crop monocultures). The 38 sites represented a soil textural gradient, ranging from very sandy to very clayey (clay content range 25 – 620 g kg−1). An Agroforestry Complexity Index (ACI) was defined based on tree species richness, stem density and pruning management. Nutrient (N, P, K, Ca, Mg) and C contents were determined in litter and soil (0–30 cm depth) samples, and mineral-associated organic C (MAOC) and particulate organic C (POC) in soil samples were assessed as well. ACI was positively associated with C, N, P, Ca and Mg stocks in litter, and these litter nutrients were in turn positively associated with the corresponding soil nutrient stocks. Associations between soil nutrients and MAOC were stronger on sandy soils than on clayey soils, particularly for P, Ca and Cation Exchange Capacity (CEC). For POC, robust relationships with nutrients were only found on sandy soils. Structural Equation Models indicated causal relationships between agroforestry complexity, P and Ca cycling, and MAOC and POC stocks in topsoils. Our results indicate that nutrients effectively cycle from in situ mulch into plant-available soil pools and highlight the synergies between nutrient cycling and stable C stocks that can be achieved in complex agroforestry systems. These synergies seem to be particularly strong on sandy soils (<15 % clay).

Changes in Soil Chemistry and Soil Nutrient Stocks after 30 Years of Treated Municipal Wastewater Land Disposal: A Natural Experiment

The benefits and risks of irrigation with treated municipal wastewater (TMW) on soil quality and crop production have been largely investigated. However, there is a lack of knowledge on the effect of plant species on the interaction between soil quality and TMW. We leveraged a natural experiment investigating the effect of 30 years of TMW irrigation at a rate of 4 m y−1 (eq. 1860 kg N ha−1 y−1, and 264 kg P ha−1 y−1) on a sandy soil under pine plantation and pasture, compared with soil under New Zealand native Kunzea robusta. There was a consistent increase in soil P with irrigation under both pasture (Olsen P in topsoil 40 mg kg−1 vs. 74 mg kg−1) and pine (18 mg kg−1 vs. 87 mg kg−1), which was significant down to 2 m deep. The pH, electrical conductivity, total organic C and N, inorganic N and Na were affected by both irrigation and vegetation type. Beyond P soil accumulation, there was no evidence of soil degradation by Na or trace element accumulation. Estimations of nutrient mass balance indicated that 80% and 60% of the total applied P was lost under pine and pasture, respectively. This percentage increased to 96% and 83% for N, respectively. Although plant species had a significant effect on soil quality and N and P losses from TMW-irrigated areas, adjusting irrigation rates to levels that can be managed by plants is the only way to design sustainable TMW irrigation schemes.

Fifty years after deep‐ploughing: Effects on yield, roots, nutrient stocks and soil structure

AbstractDeep‐ploughing far beyond the common depth of 30 cm was used more than 50 years ago in Northern Germany with the aim to break root‐restricting layers and thereby improve access to subsoil water and nutrient resources. We hypothesized that effects of this earlier intervention on soil properties and yields prevailed after 50 years. Hence, we sampled two sandy soils and one silty soil (Cambisols and a Luvisol) of which half of the field had been deep‐ploughed 50 years ago (soils then re‐classified as Treposols). The adjacent other half was not deep‐ploughed and thus served as the control. At all the three sites, both deep‐ploughed and control parts were then conventionally managed over the last 50 years. We assessed yields during the dry year 2019 and additionally in 2020, and rooting intensity at the year of sampling (2019), as well as changes in soil structure, carbon and nutrient stocks in that year. We found that deep‐ploughing improved yields in the dry spell of 2019 at the sandy sites, which was supported by a more general pattern of higher NDVI indices in deep‐ploughed parts for the period from 2016 to 2021 across varying weather conditions. Subsoil stocks of soil organic carbon and total plant‐available phosphorus were enhanced by 21%–199% in the different sites. Root biomass in the subsoil was reduced due to deep‐ploughing at the silty site and was increased or unaffected at the sandy sites. Overall, the effects of deep‐ploughing were site‐specific, with reduced bulk density in the buried topsoil stripes in the subsoil of the sandy sites, but with elevated subsoil density in the silty site. Hence, even 50 years after deep‐ploughing, changes in soil properties are still detectable, although effect size differed among sites.

Above- and belowground composition and diversity of subtropical plantations and their relationships with soil nutrient stocks

Above- and belowground composition and diversity of subtropical plantations and their relationships with soil nutrient stocks

Effect of land use on carbon-, nitrogen- and silica soil stocks in the South African bushveld

Anthropogenic land use alters soil properties and influences biological transformations in the root zone, thereby affecting the distribution and supply of soil nutrients. It is generally acknowledged that human land-use activities such as intensive cattle farming and cultivation of citrus products lead to a homogenization of soil nutrients. This research aims at investigating the heterogeneity in soil nutrient stocks and BSi stocks (a beneficial plant element) within the Savannah biome of South Africa. In this study, C-N-Si stocks and their ratios were quantified in the soil of five different land use types, common in South Africa. The five different land use types are i) bush savannahs, ii) mopane-dominated woodlands, iii) annually burned land, iv) communal grazing land and v) citrus orchards. Empirical research however could not fully validate this hypothesis. In particular fire management and game farming (natural land use type) led to more variability in nutrient pools, with occasional occurrences of C-N-Si hotspots. Our results suggest that when ecosystem analysis of soil nutrient and carbon stocks is handled as a homogeneous unit potentially large mistakes are made, even in anthropogenic landscapes previously hypothesized with uniform nutrient distributions.

Variation in Soil Properties and Nutrient Stocks Under Different Forest Tree Species with Altitude, Aspect and Soil Depths

Çalışma toprak makro (C, N, P, K, Ca, Mg) ve mikro (Fe, Mn, Na, Cu, Zn, Al) besin stoklarına, yükselti, bakı ve ağaç türlerinin etkisini araştırmak için Kastamonu ili Daday ilçesi ormanlarında gerçekleştirilmiştir. Çalışmada, dört ağaç türünde (sarıçam, karaçam, kayın ve meşe) ve üç toprak derinliğinden (0-10, 10-20, 20-30 cm) olmak üzere iki bakı (güneşli ve gölgeli) ve iki yükselti basamağında (1189 m ve 871 m) örnek alanlar seçilmiştir. Sonuçlara göre, türler arasında en yüksek C (57.7 ton/ha), N (3.32 ton/ha) ve P (0.181 ton/ha) stoku kayın, en düşük meşede (39.7-ton C ha-1; 2.37-ton N ha-1, 0.115-ton P ha-1) bulunmuştur. Ağaç türleri arasında ortalama değerlere göre en yüksek kalsiyum stoku karaçamda (3.64 ton/ha) ve meşede (2.41 ton/ha), en düşük sarıçam (0.73 ton/ha) ve kayında (0.67 ton/ha) tespit edilirken, en yüksek potasyum stoku sarıçamda (3.60 ton/ha), sonrasında kayında (2.92 ton/ha), karaçamda (2.16 ton/ha) ve en düşük meşede (1.03 ton/ha) tespit edilmiştir. Makro besin stoklarının yükselti ile bakıya bağlı olarak önemli değişiklik gösterdiği, fakat değişikliğin yönünün ağaç türü ve besin elementine göre farklılık gösterdiği belirlenmiştir. Mikro besin stoklarında farklılıklar genel olarak aynı yönde değişim göstermiştir. Mikro besin stokları üst rakım ve güneşli bakılarda daha yüksek, türler arasında ise sarıçam ve kayında, karaçam ve meşeden daha fazla bulunmuştur.

Effects of fragmentation and shifting cultivation on soil carbon and nutrients: A case study in Sitapahar forest, Bangladesh

The consequences of converting primary forests to agriculture and pasture on soil carbon (C) and nutrient stocks are important, although they are little known in tropical forests. In the Sitapahar forest of Bangladesh, we evaluated soil C and nutrient concentrations and stocks among intact, fragmented, and shifting cultivation sites. We also investigated whether there are any correlations between nutrient stocks and tree species diversity or soil C stock. We measured and identified the trees in 30 main plots (20 m × 20 m), 10 in each of the three sites. Four subplots (1 m × 1 m each) were used to measure the physical and chemical characteristics of the soil at depths of 0–10, 10–20, and 20–30 cm. Results show that during shifting cultivation as compared to intact sites, soil C stock was 50% lower whereas soil P stock was 26% greater. When compared to the other two sites, the soil N and K stocks under the shifting cultivation site were 57% and 27% greater, respectively. Soil Mg stock in the intact site was up to 155% higher compared to the other two sites. In all sites, soil C stock was positively correlated with N stock, but negatively correlated with the P stock. Tree species diversity was positively correlated with K stock, but negatively correlated with N stock in the shifting cultivation site. Sustainable management of the sites should focus on the understanding of soil-plant interactions and the protection of soil C, nutrients, and species diversity.

Fine earth soil bulk density at 0.2 m depth from Land Use and Coverage Area Frame Survey (LUCAS) soil 2018

AbstractSoil Bulk Density (BD) is an extremely important variable because it is an important site characterization parameter, and it is highly relevant for policy development because it is mandatory for calculating soil nutrient stocks. BD can influence soil chemical properties, land‐use planning and agronomic management. The 2018 Land Use and Coverage Area Frame Survey (LUCAS) saw the unprecedented collection of BD core analysis in a subset of the locations in Europe and the United Kingdom where soil physical and chemical properties were analysed in the 2009 and the 2015 sampling campaigns. Here, we integrated the LUCAS 2018 BD sampling campaign with the mass fraction of coarse fragments previously determined in LUCAS 2009–2015 in order to provide a dataset of the volume fraction of coarse fragments and the BD of the fine earth and improve soil organic carbon (SOC) stock estimation accuracy for topsoil. BD data sampled at 0–10 and 10–20 cm were averaged to harmonize the BD with the mass fraction of coarse fragments measured in 2009, 2012 and 2015. Samples were from cropland, grassland and woodland soils, which accounted for 41%, 21% and 30%, respectively, of the total number of selected sites (n = 6059); ‘bareland’, and ‘shrubland’ accounted for 3% of the sites each, whereas ‘artificial land’ accounted for &lt;1%. Only six samples were classified as ‘wetland’. The dataset was produced assuming the mass density of the coarse fraction to be constant across all LUCAS soil samples. We also estimated the SOC stocks associated with LUCAS 2018 BD and SOC content measurements and showed that correcting the BD by the coarse mass fraction instead of the coarse volume fraction generates SOC stock underestimation. We found the highest deviations in woodlands and shrublands. We showed that, when SOC stock is computed with coarse mass fraction, the error compared with the computation by volume may vary depending on the SOC and coarse mass fraction. This may imply a SOC stock underestimation for European soils. This dataset fits into the big framework of LUCAS soil properties monitoring and contributes both to soil awareness and soil research and assessments, which are two important objectives of the Soil Strategy and the European Soil Observatory (EUSO).

Changes in soil organic carbon and nutrient pools in aggregate‐sized fractions along a chronosequence of wolfberry (Lycium barbarum L.) plantations in arid areas of Northwest China

AbstractDifferent land use and management actions can affect soil aggregates (SAs) and nutrient stocks, which are crucial for sustainable agriculture. The impacts of various chrono‐sequences on the soil aggregate structure, soil organic carbon (SOC) and nutrients associated with aggregate fractions in wolfberry (Lycium barbarum L.) plantations are still not fully understood. This study examined the composition and stability of SAs, SOC, total nitrogen (TN), available phosphorus (AP) and exchangeable cations (K+, Na+, Ca2+ and Mg2+) in bulk soil and various aggregate‐size fractions from five wolfberry plantations with varying ages (1, 4, 6, 10 and 13 years) and a corn field (0 years) in the arid region of northwest Ningxia in China. The results indicated that silt–clay (&lt;53 μm) fractions were dominant in the soil, accounting for 51%–66%, under different plantation ages. The proportion of the macro‐aggregates (&gt;250 μm) increased significantly, by 40%–47%, over the 4 years of wolfberry plantation. Likewise, the soil aggregate stability was improved, and total exchangeable bases (TEB) along with numerous cations concentrations (K+, Na+, Ca2+ and Mg2+) in SAs were significantly reduced as the wolfberry plantings became older. Both concentrations of SOC and TN in the soil aggregates peaked in the 13th year. The silt–clay fractions stored a considerable amount of SOC and nutrients. However, short‐term (under 6 years) cultivation of wolfberry reduced the stocks of SOC, TN and AP in the soil, while long‐term (over 10 years) cultivation increased them, particularly in macro‐aggregates. These findings indicated that long‐term wolfberry farming had several advantages, such as enhancing soil structure, accumulating SOC and nutrients and ameliorating alkaline soils, especially after 10 years, in the arid northwest of China.

Effective Striga control and yield intensification on maize farms in western Kenya with N fertilizer and herbicide-resistant variety.

Maize production in western Kenya is limited by the spread of parasitic weed Striga hermonthica and depletion of soil nutrient stocks. Nitrogen (N) fertilizer and imidazolinone resistant (IR) maize are key elements in the agronomic toolbox to control infestations and enhance yields. The circumstances under which their use, individually or combined, is most effective on farmer fields have not been well documented. Inappropriate management decisions and low returns on investments arise from this knowledge gap, causing hunger and poverty in smallholder communities to persist. Experiments were carried out on 60 fields in three different agroecosystems of western Kenya using full-factorial treatments with non-herbicide treated maize (DH) and herbicide treated maize (IR), and N fertilizer omission and application. Trials were stratified on a field with low and high soil fertility within individual farms and repeated over two seasons. Cultivating IR maize instead of DH maize decreased the emergence of Striga with 13 shoots m-2 on average while applying N fertilizer on DH maize led to a reduction of 5 shoots m-2 on average. Decreases of Striga by use of IR maize and N fertilizer were between 6 and 23 shoots m-2 larger at the site with high levels of infestation than at the sites with medium or low emergence. Input of N fertilizer increased grain harvests by 0.59 ton ha-1 on average while use of IR maize enhanced the productivity with 0.33 ton ha-1 on average. Use of N fertilizer had similar yield effects in all three sites, whereas use of IR maize at the site with high Striga emergence increased maize production by 0.26-0.39ton ha-1 more than at the sites with medium or low emergence. The greater Striga responses to IR maize and the greater yield responses to N fertilizer demonstrate their use could be optimized according to field conditions and management goals. Combining IR maize and N fertilizer has larger added yield benefits where their individual effects on grain productivity are smaller. Findings from this study indicate that farmers in western Kenya require guidance on how to align the use of herbicide resistant maize and inorganic N inputs with the level of Striga infestation and maize yield on their fields for effectively controlling the pernicious weed and enhancing food production.

Short-term cultivation limiting soil aggregate stability and macronutrient accumulation associated with glomalin-related soil protein in Eucalyptus urophylla × Eucalyptus grandis plantations

The relationship between glomalin-related soil protein (GRSP) and soil aggregation has been a hot topic of research for its close link to soil stability and quality. However, the short-term cultivation of Eucalyptus poses serious threats to soil stability and nutrient stocks, and the effects of GRSP on soil aggregate stability and macronutrient accumulation remain unclear. The aim is to clarify the potential mechanisms affecting soil aggregate stability and macronutrient accumulation in short-term Eucalyptus plantations. Five Eucalyptus urophylla × Eucalyptus grandis plantations with different cultivation periods (1–5 years) in this study were investigated, and a native evergreen broadleaf forest (0 year) was selected as control. The mean weight diameter index increased in the first 3 years and then significantly decreased during 5 years cultivation of Eucalyptus. Soil organic carbon (SOC) and total nitrogen also decreased after planting Eucalyptus for 3 years, but variation in total phosphorus was not obvious. The relative abundance of Glomeraceae and Claroideoglomeraceae decreased in the 5-year-old Eucalyptus plantations and was positively correlated with GRSP content. In pathway modeling, nutrient-acquisition enzyme activities positively affected GRSP and macronutrient content. Total GRSP (T-GRSP) had higher total effects than easily extractable GRSP on soil aggregate stability, and positively correlated with SOC in macroaggregates. Both T-GRSP and SOC had positive and direct effects on soil aggregate stability. Variance partitioning analysis further explained the contribution of GRSP and SOC to aggregate stability, particularly in >2 and 2–0.25 mm macroaggregates. Our results suggested that GRSP was directly associated with SOC content and soil aggregate stability, and was a potential key factor affecting soil aggregate stability in Eucalyptus plantations. Improving T-GRSP and SOC are efficient approaches for preventing the gradual deterioration of soil aggregate stability. Short-term cultivation should be carefully used in Eucalyptus plantations, and a new cultivation period is needed.

Spatial and temporal sampling strategy connecting NEON Terrestrial Observation System protocols

AbstractThe National Ecological Observatory Network Terrestrial Observation System (NEON TOS) produces open‐access data products that allow data users to investigate the impact of change drivers on key “sentinel” taxa and soils. The spatial and temporal sampling strategy that coordinates implementation of these protocols enables integration across TOS products and with products generated by NEON aquatic, remote sensing, and terrestrial instrument subsystems. Here, we illustrate the plots and sampling units that make up the physical foundation of a NEON TOS site, and we describe the scales (subplot, plot, airshed, and site) at which sampling is spatially colocated across protocols and subsystems. We also describe how moderate resolution imaging spectroradiometer‐enhanced vegetation index (MODIS‐EVI) phenology data are used to temporally coordinate TOS sampling within and across years at the continental scale of the observatory. Individually, TOS protocols produce data products that provide insight into populations, communities, and ecosystem processes. Within the spatial and temporal framework that guides cross‐protocol implementation, the ability to draw inference across data products is enhanced. To illustrate this point, we develop an example using R software that links two TOS data products collected with different temporal frequencies at both plot and site spatial scales. A thorough understanding of how TOS protocols are integrated with each other in space and time, and with other NEON subsystems, is necessary to leverage NEON data products to maximum effect. For example, a researcher must understand the spatial and temporal scales at which soil biogeochemistry data, soil microbe biomass data, and plant litter production and chemistry data may be combined to quantify soil nutrient stocks and fluxes across NEON sites. We present clear links among TOS protocols and across NEON subsystems that will enhance the utility of NEON TOS data products for the data user community.

Change in soil carbon, nitrogen, and phosphorus after timber harvesting in northern hardwood forests

AbstractQuantifying changes in soil carbon (C) and nutrient stocks after timber harvesting is needed to inform C management and to ensure that forest productivity is sustained over time. Our objective was to assess changes in soil C, nitrogen (N), and phosphorus (P) 1 year after timber harvesting in temperate northern hardwood forests. We established permanent plots in forest stands for measuring forest attributes before and after harvesting. We collected soils from quantitative soil pits, which were associated with permanent plots, to determine total C, total N, and extractable P stocks and concentrations. Mean post‐harvest fine fraction organic (O) horizon C was less than the pre‐harvest stock, but we did not detect a statistically significant change in total O horizon or mineral soil C stocks. For the fine fractions of the O horizon and mineral soil from the 0–5 and 5–30 cm depth increments of the B horizon, total N and extractable P stocks were positively correlated with total C stocks. For all of these soil components, extractable P stocks and concentrations declined over time, which could be related to post‐harvest stand conditions that favored microbial activity and immobilization of available P. These findings indicate that P availability could be a concern in these forests and that long‐term monitoring is needed to consider potential management actions for ensuring that forest productivity is sustained.

The sustainability of timber and biomass harvest in perspective of forest nutrient uptake and nutrient stocks

The sustainability of tree harvest is questioned since harvest results in increased nutrient losses which may reduce nutrient stocks in forest soils, particularly in forests on acidified and poor soils with low base saturation. We used a new forest experiment to quantify nutrient stocks and nutrient uptake rates in mature forest stands, and to assess the forest nutrient balance in relation to different forest management scenarios: clearcutting, shelterwood and thinning; and whole-tree harvest (WTH), stem-only harvest (SOH) and wood only harvest (WOH, with on-site bark stripping). Forests were dominated by trees of Fagus sylvatica, Pseudotsuga Menziesii or Pinus sylvestris, all situated on poor, acidified soils.We measured forest biomass and nutrient stocks based on destructive sampling of fifteen mature trees per species and by using new, calibrated allometric relationships. Aboveground stocks of N, P, S, K, Ca, Mg, Mn, Cu, Fe and Zn were calculated for foliage, branches, stem bark and stem wood. Annual forest growth and nutrient uptake were determined using tree ring measures and allometric relationships. Organic layer nutrient stocks and available nutrients in the mineral soil were determined following intensive soil sampling.Stands of beech, Douglas fir and Scots pine differed in aboveground biomass and nutrient stocks, with highest biomass stocks in Douglas fir. However, beech stands had the highest aboveground nutrient stocks, nutrient uptake rates and nutrient losses following harvest, followed by Scots pine. Organic layer nutrient stocks generally exceeded aboveground nutrient stocks, except for the base cations and Mn. Compared to SOH, WTH increased nutrient export between 66% (Douglas fir) up to 100% (Scots pine), while WOH decreased the nutrient export between 23% (beech) up to 41% (Douglas fir).High aboveground base cation and Mn stocks indicate potential long-term threats to forest nutrition if trees are harvested. However, in Douglas fir stands, nutrient losses through SOH may fully recover when using rotation periods of 80 years. Contrary, negative Ca balances are predicted when applying SOH in beech and Scots pine, since Ca stocks are potentially depleted within 2 final fellings. WTH poses, regardless of the species, potential threats for sustainable biomass harvest as nutrients cannot be recovered using common rotation periods. WOH conserves nutrients within the forest posing opportunities for sustainable biomass harvest. For similar temperate forest on acidified, sandy soils, we therefore recommend to limit tree harvest depending on the tree species, and to avoid WTH and consider WOH to better conserve critical nutrients required for long-term forest recovery.

Potential Overestimation of Soil Organic Carbon and Nutrient Stocks in Soils with Abundance of Coarse Fragments

Potential Overestimation of Soil Organic Carbon and Nutrient Stocks in Soils with Abundance of Coarse Fragments