Nutrient Stocks Research Articles

Wood nutrients: Underexplored traits with functional and biogeochemical consequences.

Resource storage is a critical component of plant life history. While the storage of nonstructural carbohydrates in wood has been studied extensively, the multiple functions of mineral nutrient storage have received much less attention. Here, we highlight the size of wood nutrient pools, a primary determinant of whole-plant nutrient use efficiency, and a substantial fraction of ecosystem nutrient budgets, particularly tropical forests. Wood nutrient concentrations also show exceptional interspecific variation, even among co-occurring plant species, yet how they align with other plant functional traits and fit into existing trait economic spectra is unclear. We review the chemical forms and location of nutrient pools in bark and sapwood, and the evidence that nutrient remobilization from sapwood is associated with mast reproduction, seasonal leaf flush, and the capacity to resprout following damage. We also emphasize the role wood nutrients are likely to play in determining decomposition rates. Given the magnitude of wood nutrient stocks, and the importance of tissue stoichiometry to forest productivity, a key unresolved question is whether investment in wood nutrients is a relatively fixed trait, or conversely whether under global change plants will adjust nutrient allocation to wood depending on carbon gain and nutrient supply.

Glacial interglacial variations in the natural iron fertilization during the low sea ice periods along the eastern continental margin of Antarctica

The Southern Ocean sequesters atmospheric CO2 through biological pumps, though its driving factors are debated. Modern productivity is regulated by natural iron fertilization from micronutrient influx through dust, regeneration, and Antarctic glaciers and sea ice melting (ice melt). The productivity along the eastern Antarctic continental margin was low during the last glacial period and gradually increased through the deglacial to Late Holocene, marked by distinct productivity peaks. The micronutrients also varied similarly, with reduced glacial influx and an increase in the Holocene, which may cause productivity peaks. Therefore, the coherence of enhanced productivity and micronutrient influx is considered as enhanced iron fertilization period. The productivity peaks declined within ∼1.5 kyr, mostly due to the Ekman transport and sea ice formation. Along with ice melt, the independent weathering pattern that responds with glacial- interglacial ice volume changes suggest the source of micronutrients is not terrigenous. Shelf interaction of oceanic currents can influence the water column nutrient stock significantly, while its utilization occurs during reduced ice periods (low sea ice and high glacier melting) for productivity. Therefore, enhanced natural iron fertilization periods are considered as ice low periods that occurred in a periodicity of 2 kyrs, at ∼7.5 kyr BP, ∼5.5 kyr BP, ∼4 kyr BP, ∼ 2.5 kyr BP, and ∼0.5 kyr BP, likely due to the combined effects of atmospheric and oceanographic factors driven by the high amplitude regional temperature variability during the mid to late Holocene.

Influence of altered freshwater discharge on the seasonality of nutrient distributions near La Grande River, northeastern James Bay, Québec

In subarctic marine environments, nutrient stocks are replenished through physical and biogeochemical processes in winter, largely setting an upper limit on new primary production for the next growing season. In spring, marine nutrient stocks are modified by freshwater-associated additions, especially in coastal areas. Hydroelectric development of the La Grande River (LGR) in northern Québec has shifted the timing of peak freshwater discharge from spring into winter, producing 10 times the natural winter discharge. Here, we considered salinity, oxygen isotope ratio (δ18O), and nutrient (nitrate, phosphate) data from coastal waters of northeast James Bay in different seasons of 2016 and 2017. We quantified two main freshwater sources, LGR and sea-ice melt, established by freshwater tracers, and their influence on coastal nutrient distributions. Our results show that LGR is the dominant source of freshwater to coastal waters throughout the year, especially during winter, and an important source of nitrate to nitrogen-limited coastal waters (winter concentrations of 4.53 μM versus 3.18 μM in ambient seawater). Despite being a poor phosphate source (0.11 μM versus 0.66 μM in ambient seawater), LGR provides the largest portion of the phosphate stock in surface waters near its mouth. LGR regulation has changed the pattern of natural fluvial nitrate inputs: what was observed in spring (pre-development) is now observed in winter (post-development). Thus, high winter surface nitrate stocks (22.5 mmol m−2) are available to support primary production, but are dispersed to offshore areas prior to the onset of the growing season, which begins only after the return of light. In northeast James Bay, the timing and magnitude of primary production, dependent on nutrients in the water column, is expected to have been impacted by altered freshwater input, reducing overall production in local areas and potentially increasing production further downstream with cascading effects on the marine ecosystem.

Effects of burrowing crabs on coastal sediments and their functions: A systematic meta‐analysis

AbstractBurrowing ecosystem engineers, such as termites, crabs, marmots, and foxes, can profoundly affect the biological structure and ecosystem functions of their environments. However, the relative importance of the effects of burrowing engineers on sediments are challenging to predict and are expected to be influenced by engineer density, engineer functional traits (e.g., burrow morphology), and environmental conditions (e.g., geomorphology, vegetation presence). To develop robust hypotheses predicting the impacts of burrowing ecosystem engineers, we conducted a systematic meta‐analysis evaluating the effects of burrowing crabs on sediment properties, nutrient stocks, and ecosystem functions in soft‐sediment coastal habitats (e.g., salt marshes, mangrove forests, tidal flats). Additionally, we tested the impacts of crab burrow density, burrowing crab superfamily (a proxy for crab burrow morphology and diet), and biotic conditions (i.e., vegetation) on the effects of burrowing crab engineers on coastal sediments. Burrowing crabs rework and oxygenate sediments and accelerate rates of nutrient cycling (i.e., nitrification and CO2 flux). However, the magnitude and direction of burrowing crab effects depend on burrowing crab superfamily, the presence of vegetation, and their interaction. Crab burrow density did not consistently predict burrowing engineer effects on sediments. Future efforts need to focus on implementing rigorous manipulative experiments to assess crab ecosystem engineering effects, since methodological variation has hindered efforts to generalize their effects. Our findings suggest that crab engineering effects are predictable across environmental contexts, and understanding the context dependency of crab engineering effects may promote the management and restoration of the critical ecosystem services that are mediated by crab engineers.

Vegetation patterns associated with nutrient availability and supply in high-elevation tropical Andean ecosystems

Abstract. Plants absorb nutrients and water through their roots and modulate soil biogeochemical cycles. The mechanisms of water and nutrient uptake by plants depend on climatic and edaphic conditions, as well as the plant root system. Soil solution is the medium in which abiotic and biotic processes exchange nutrients, and nutrient concentrations vary with the abundance of reactive minerals and fluid residence times. High-altitude ecosystems of the tropical Andes are interesting for the study of the association between vegetation, soil hydrology, and mineral nutrient availability at the landscape scale for different reasons. First of all, because of low rock-derived nutrient stocks in intensely weathered volcanic soils, biocycling of essential nutrients by plants is expected to be important for plant nutrient acquisition. Second, the ecosystem is characterized by strong spatial patterns in vegetation type and density at the landscape scale and hence is optimal to study soil-water–vegetation interactions. Third, the area is characterized by high carbon stocks but low rates of organic decomposition that might vary with soil hydrology, soil development, and geochemistry, all interconnected with vegetation. The páramo landscape forms a vegetation mosaic of bunch grasses, cushion-forming plants, and forests. In the nutrient-depleted nonallophanic Andosols, the plant rooting depth varies with drainage and soil moisture conditions. Rooting depths were shallower in seasonally waterlogged soils under cushion plants and deeper in well-drained soils under forest and tussock grasses (>100 cm). Vegetation composition is a relevant indicator of rock-derived nutrient availability in soil solutions. The soil solute chemistry revealed patterns in plant-available nutrients that were not mimicking the distribution of total rock-derived nutrients nor the exchangeable nutrient pool but clearly resulted from strong biocycling of cations and removal of nutrients from the soil by plant uptake or deep leaching. Soils under cushion plants showed solute concentrations of Ca, Mg, and Na of about 3 times higher than forest and tussock grasses. Differences were even stronger for dissolved Si with solute concentrations that were 16 times higher than forest and 6 times higher than tussock grasses. Amongst the macronutrients derived from lithogenic sources, P was a limiting nutrient with very low solute concentrations (<1 µM) for all three vegetation types. In contrast K showed greater solute concentrations under forest soils with values that were 2 to 3 times higher than under cushion-forming plants or tussock grasses. Our findings have important implications for future management of Andean páramo ecosystems where vegetation type distributions are dynamically changing as a result of warming temperatures and land use change. Such alterations may lead not only to changes in soil hydrology and solute geochemistry but also to complex changes in weathering rates and solute export downstream with effects on nutrient concentrations in Andean rivers and high-mountain lakes.

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.

Negative effects of human disturbance and increased aridity on root biomass and nutrients along the regeneration of a tropical dry forest in the context of slash-and-burn agriculture

Biomass is an important indicator of the ability of tropical forests to deliver ecosystem services, but little attention has been given to belowground biomass and its drivers in human-modified landscapes. Here, we investigated the belowground biomass and nutrient concentration/stocks (C, P, and N) across regenerating forest stands with varying ages (10–76 years old) and old-growth forests in the Caatinga dry forest (northeastern Brazil) in the context of slash-and-burn agriculture. Belowground biomass ranged from 1.89 ± 0.33 Mg ha−1 to 17.53 ± 2.28 Mg ha−1 (mean ± SE) across regenerating forest stands and averaged 8.33 ± 1.59 Mg ha−1, with no differences compared to old-growth stands. However, regenerating stands exhibited a higher root/shoot ratio with biomass concentrated in the superficial soil layer and in large-sized roots, regardless of the successional stage. Root nutrient concentration and stocks were highly variable across forest stands with fine roots supporting a higher concentration of N and P, while regenerating stands supported lower nutrient stocks as compared to old-growth forests. Finally, precipitation and chronic disturbance emerged as the most important drivers of belowground biomass and nutrient concentrations/stocks, while aboveground biomass played a negligible role. Our results indicate that, in human-modified landscapes of tropical dry forests, belowground biomass and nutrients play important roles in ecosystem functions in regenerated forests after slash-and-burn agriculture. Forest resilience and provision of ecosystem services (e.g., nutrient cycling) appear to be very sensitive to increased aridity and exploitation of forest resources.

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.

Carbon and nutrient cycling in cocoa agroforests under organic and conventional management

In cocoa agroforestry systems, cycling of leaves, pods, and branches are key for organic matter sustenance. We investigated annual total litterfall, annual nutrient stocks in total litterfall, cocoa pods and beans, as well as cocoa leaf decomposition rates in cocoa agroforestry systems under conventional and organic management in Suhum Municipality, Eastern Region of Ghana. The study was conducted using six cocoa agroforests for each management selected from a total of four villages. Litterfall was collected monthly using litterboxes and a litterbag technique was employed to study the rates of leaf decomposition and nutrient release for 12 months. In June and July, total litterfall in organic farms were 94% and 65%, respectively, higher than in conventional farms, but management had no effect on average annual total litterfall of 8.8 t ha−1 yr−1 litterfall. Due to the trees’ reduced transpiration, 61% of the annual total litterfall occurred during the dry season. Whereas average leaf litter nitrogen (N) concentration was 17% higher in the rainy season than dry season, potassium (K) concentration was 38% higher during the dry season than rainy season. This likely reflected the contribution of N rich green leaves to litterfall in the rainy season and plant coping strategy to drought leading to K accumulation. Cocoa leaf decomposition was not affected by management. Annual potassium (K) and calcium (Ca) stocks in cocoa pod husk were four and nine-fold, respectively, higher than in cocoa beans. We conclude that organic versus conventional management had no effect on litterfall and cocoa leaf decomposition rather season influenced litterfall quantity and chemistry. Irrespective of management the spreading of cocoa pod husk after harvest will improve internal nutrient cycling in cocoa agroforestry systems.

Impact of aridity rise and arid lands expansion on carbon-storing capacity, biodiversity loss, and ecosystem services.

Drylands, comprising semi-arid, arid, and hyperarid regions, cover approximately 41% of the Earth's land surface and have expanded considerably in recent decades. Even under more optimistic scenarios, such as limiting global temperature rise to 1.5°C by 2100, semi-arid lands may increase by up to 38%. This study provides an overview of the state-of-the-art regarding changing aridity in arid regions, with a specific focus on its effects on the accumulation and availability of carbon (C), nitrogen (N), and phosphorus (P) in plant-soil systems. Additionally, we summarized the impacts of rising aridity on biodiversity, service provisioning, and feedback effects on climate change across scales. The expansion of arid ecosystems is linked to a decline in C and nutrient stocks, plant community biomass and diversity, thereby diminishing the capacity for recovery and maintaining adequate water-use efficiency by plants and microbes. Prolonged drought led to a -3.3% reduction in soil organic carbon (SOC) content (based on 148 drought-manipulation studies), a -8.7% decrease in plant litter input, a -13.0% decline in absolute litter decomposition, and a -5.7% decrease in litter decomposition rate. Moreover, a substantial positive feedback loop with global warming exists, primarily due to increased albedo. The loss of critical ecosystem services, including food production capacity and water resources, poses a severe challenge to the inhabitants of these regions. Increased aridity reduces SOC, nutrient, and water content. Aridity expansion and intensification exacerbate socio-economic disparities between economically rich and least developed countries, with significant opportunities for improvement through substantial investments in infrastructure and technology. By 2100, half the world's landmass may become dryland, characterized by severe conditions marked by limited C, N, and P resources, water scarcity, and substantial loss of native species biodiversity. These conditions pose formidable challenges for maintaining essential services, impacting human well-being and raising complex global and regional socio-political challenges.

Plant root mechanisms and their effects on carbon and nutrient accumulation in desert ecosystems under changes in land use and climate.

Deserts represent key carbon reservoirs, yet as these systems are threatened this has implications for biodiversity and climate change. This review focuses on how these changes affect desert ecosystems, particularly plant root systems and their impact on carbon and mineral nutrient stocks. Desert plants have diverse root architectures shaped by water acquisition strategies, affecting plant biomass and overall carbon and nutrient stocks. Climate change can disrupt desert plant communities, with droughts impacting both shallow and deep-rooted plants as groundwater levels fluctuate. Vegetation management practices, like grazing, significantly influence plant communities, soil composition, root microorganisms, biomass, and nutrient stocks. Shallow-rooted plants are particularly susceptible to climate change and human interference. To safeguard desert ecosystems, understanding root architecture and deep soil layers is crucial. Implementing strategic management practices such as reducing grazing pressure, maintaining moderate harvesting levels, and adopting moderate fertilization can help preserve plant-soil systems. Employing socio-ecological approaches for community restoration enhances carbon and nutrient retention, limits desert expansion, and reduces CO2 emissions. This review underscores the importance of investigating belowground plant processes and their role in shaping desert landscapes, emphasizing the urgent need for a comprehensive understanding of desert ecosystems.

Stoichiometry of arable black soil on the Ukrainian Western forest steppe

ABSTRACT Luvic Greyzemic Phaeozems have been farmed for centuries in Western Ukraine. We investigate their stocks of major nutrients and stoichiometry under arable crops receiving conventional NPK fertilisation and an unfertilised control. Total carbon stocks increase only with parallel increases in total N, P, Ca and Mg. Likewise, total N increases along with parallel increases in total Ca and Mg, P and Ca, P and C. Under winter barley, application of the background fertilisation (N23P60K60) + N97 (urea) before sowing, with or without nitrapyrin as a nitrogen stabiliser, improved the status of C, N, Ca and Mg to P in the 0–20 cm soil layer. The best ratio of total C, N, Ca and Mg to P and the best C:N, C:P, N:P, and Ca:N ratios were achieved with the background fertilisation plus nitrapyrin and urea or ammonium nitrate. The system cannot hold onto nutrients, nitrogen in particular, applied in excess of the harmonic stoichiometry.

Soil organic carbon loss decreases biodiversity but stimulates multitrophic interactions that promote belowground metabolism.

Soil organic carbon (SOC) plays an essential role in mediating community structure and metabolic activities of belowground biota. Unraveling the evolution of belowground communities and their feedback mechanisms on SOC dynamics helps embed the ecology of soil microbiome into carbon cycling, which serves to improve biodiversity conservation and carbon management strategy under global change. Here, croplands with a SOC gradient were used to understand how belowground metabolisms and SOC decomposition were linked to the diversity, composition, and co-occurrence networks of belowground communities encompassing archaea, bacteria, fungi, protists, and invertebrates. As SOC decreased, the diversity of prokaryotes and eukaryotes also decreased, but their network complexity showed contrasting patterns: prokaryotes increased due to intensified niche overlap, while that of eukaryotes decreased possibly because of greater dispersal limitation owing to the breakdown of macroaggregates. Despite the decrease in biodiversity and SOC stocks, the belowground metabolic capacity was enhanced as indicated by increased enzyme activity and decreased enzymatic stoichiometric imbalance. This could, in turn, expedite carbon loss through respiration, particularly in the slow-cycling pool. The enhanced belowground metabolic capacity was dominantly driven by greater multitrophic network complexity and particularly negative (competitive and predator-prey) associations, which fostered the stability of the belowground metacommunity. Interestingly, soil abiotic conditions including pH, aeration, and nutrient stocks, exhibited a less significant role. Overall, this study reveals a greater need for soil C resources across multitrophic levels to maintain metabolic functionality as declining SOC results in biodiversity loss. Our researchers highlight the importance of integrating belowground biological processes into models of SOC turnover, to improve agroecosystem functioning and carbon management in face of intensifying anthropogenic land-use and climate change.

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.

Decision-tree-based ion-specific dosing algorithm for enhancing closed hydroponic efficiency and reducing carbon emissions.

The maintenance of ion balance in closed hydroponic solutions is essential to improve the crop quality and recycling efficiency of nutrient solutions. However, the absence of robust ion sensors for key ions such as P and Mg and the coupling of ions in fertilizer salts render it difficult to effectively manage ion-specific nutrient solutions. Although ion-specific dosing algorithms have been established, their effectiveness has been inadequately explored. In this study, a decision-tree-based dosing algorithm was developed to calculate the optimal volumes of individual nutrient stock solutions to be supplied for five major nutrient ions, i.e., NO3, K, Ca, P, and Mg, based on the concentrations of NO3, K, and Ca and remaining volume of the recycled nutrient solution. In the performance assessment based on five nutrient solution samples encompassing the typical concentration ranges for leafy vegetable cultivation, the ion-selective electrode array demonstrated feasible accuracies, with root mean square errors of 29.5, 10.1, and 6.1 mg·L-1 for NO3, K, and Ca, respectively. In a five-step replenishment test involving varying target concentrations and nutrient solution volumes, the system formulated nutrient solutions according to the specified targets, exhibiting average relative errors of 10.6 ± 8.0%, 7.9 ± 2.1%, 8.0 ± 11.0%, and 4.2 ± 3.7% for the Ca, K, and NO3 concentrations and volume of the nutrient solution, respectively. Furthermore, the decision tree method helped reduce the total fertilizer injections and carbon emissions by 12.8% and 20.6% in the stepwise test, respectively. The findings demonstrate that the decision-tree-based dosing algorithm not only enables more efficient reuse of nutrient solution compared to the existing simplex method but also confirms the potential for reducing carbon emissions, indicating the possibility of sustainable agricultural development.

Identifying agroforestry characteristics for enhanced nutrient cycling potential in Brazil

Tropical soils are prone to rapid degradation if not managed well, and agroforestry systems have the potential to restore degraded soils and support agricultural production together with other ecosystem services. In Brazil, an increasing number of pioneering farmers are establishing agroforestry systems on previously cleared farmland. However, while there are a wide range of agroforestry systems, this diversity has hardly been quantified, and it is not clear how these systems differ in their capacity for nutrient cycling to reverse soil degradation. The objectives of the study were to assess innovative agroforestry systems in terms of taxonomic and functional diversity, spatial structure and management, and to assess how these systems differ in terms of structural complexity and their potential for nutrient cycling. We assessed a LiDAR-derived stand structural complexity index (SSCI), interrow spacing, stem density, tree species richness and diversity, community weighted means (CWM) of foliar nitrogen and wood density, livestock density, pruning and mowing regimes in 30 agroforestry systems in the state of São Paulo, Brazil. We used N, P, K, Ca and Mg stocks in litter as a proxy for nutrient cycling. The agroforestry systems could be broadly categorized into silvopastures, multistrata and successional agroforestry systems. These types spanned a gradient of structural complexity, and this complexity was positively associated with tree species richness and planting density. Litter nutrient stocks were positively associated with pruning and mulching, and negatively associated with CWM of wood density, indicating the importance of pioneer trees. Overall, our results suggest that densely planted, pruned agroforestry systems that contain high species richness, including pioneer trees, contain relatively high amounts of N, P, K, Ca and Mg in their litter. These findings provide insight in the key characteristics of agroforestry systems to support nutrient cycling, and can inform the design of agroforestry systems for the regeneration of degraded agricultural land.

Soil fertility in silvopastoral systems integrating tree legumes with signalgrass (Urochloa decumbens Stapf. R. Webster)

Silvopastoral Systems (SPS) can increase overall productivity and generate continuous income in order to stimulate simultaneous growth and development of trees, forage and livestock. Moreover, the SPS with tree legumes would be important for add nutrients to the system, mainly N, and ensure the soil health and quality. Soil properties were assessed in two SPS, implanted in 2011, using tree legumes and Urochloa decumbens Stapf. R. Webster (Signalgrass). Treatments were Signalgrass + Mimosa caesalpiniifolia Benth (Sabia) and Signalgrass + Gliricidia sepium (Jacq.) Kunth ex Walp. (Gliricidia), and they were allocated in a randomized complete block design, with three replications. Soil was sampled in 2013, 2017, and 2018, at 0, 4, and 8 m along transects perpendicular to tree double rows, from 0- to 20- and 20- to 40-cm layers. Soil chemical properties included pH, P, K+, Ca2+, Mg2+, Al3+, H++Al3+, cation exchange capacity (CEC), and base saturation. In addition, light fraction of soil organic matter (LF-SOM), soil basal respiration (SBR), and natural abundance of 13C of the respired CO2 (δ13C-CO2) were analyzed. Soil pH (5.3, 5.2, 5.1), P (11.3, 7.2, 3.6 mg dm-3), and CECeffective (5.8, 5.1, 5.0 cmolc dm-3) decreased (P < 0.05) along the years 2013, 2017, and 2018, respectively. In 2018, the LF-SOM and δ13C-CO2 was greater in Sabia (1.1 g kg-1 and -16.4‰) compared to Gliricidia (0.7 g kg-1 and -18.2‰). Silvopastoral systems reduced soil fertility regardless of the tree legume species used as result of biomass nutrient stock, without maintenance fertilization. Sabia had greater deposition of LF-SOM, without increasing SBR, providing potential for microbial C use efficiency. Enriched C-CO2 isotope composition shows an efficient SOM oxidize in SPS with Gliricidia or Sabia. This information can contribute to the assessments related to CO2 balance and C retention. Both SPS contribute to C sequestration.

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.