External Nutrient Inputs Research Articles

Assessing Impacts of Changes in External Nutrient Loadings on a Temperate Chinese Drinking Water Reservoir

The safety of drinking water is constantly being evaluated. In the last few decades, however, many drinking waters sources in the world, including in China, have undergone serious eutrophication and consequently water quality deterioration due to anthropogenic induced stressors such as elevated external nutrient inputs. In this study, we used the state-of-the-art complex, dynamic, mechanistic model GOTM-FABM-PCLake (a coupled one-dimensional hydrodynamic-lake ecosystem model) to quantitatively assess the impacts of external nutrient loading on the temperate Jihongtan reservoir in Shandong Province, China. Simulated values of all variables targeted in calibration (water temperature, dissolved oxygen, total nitrogen, total phosphorus, and chlorophyll a) agreed well with observations throughout the entire calibration and validation period and generally mimicked seasonal dynamics and inter-annual variations as found in the monitoring data. A series of scenarios, representing changed external nutrient loadings (both increasing and decreasing compared to the current nutrient load), were set up to quantify the effects on the reservoir water quality. Changes relative to the current external nutrient load had a significant effect on the simulated TN and TP concentrations in the reservoir. Our impact assessment indicate that TN will meet the Chinese water quality requirements of the water source (Class III) when the external nitrogen load is reduced by 70%, whereas TP will meet the requirements even if the external phosphorus load is increased by 100% relative to current loads. The model predicts progressively higher summer and autumn phytoplankton biomasses in the scenarios with increasing external phosphorus loading and potential toxic cyanobacteria will become more dominant at the expense of diatoms and other algae. Strict control of the external nutrient loading is therefore needed to maintain good drinking water quality in the reservoir.

Regenerative Agriculture: An agronomic perspective.

Agriculture is in crisis. Soil health is collapsing. Biodiversity faces the sixth mass extinction. Crop yields are plateauing. Against this crisis narrative swells a clarion call for Regenerative Agriculture. But what is Regenerative Agriculture, and why is it gaining such prominence? Which problems does it solve, and how? Here we address these questions from an agronomic perspective. The term Regenerative Agriculture has actually been in use for some time, but there has been a resurgence of interest over the past 5 years. It is supported from what are often considered opposite poles of the debate on agriculture and food. Regenerative Agriculture has been promoted strongly by civil society and NGOs as well as by many of the major multi-national food companies. Many practices promoted as regenerative, including crop residue retention, cover cropping and reduced tillage are central to the canon of ‘good agricultural practices’, while others are contested and at best niche (e.g. permaculture, holistic grazing). Worryingly, these practices are generally promoted with little regard to context. Practices most often encouraged (such as no tillage, no pesticides or no external nutrient inputs) are unlikely to lead to the benefits claimed in all places. We argue that the resurgence of interest in Regenerative Agriculture represents a re-framing of what have been considered to be two contrasting approaches to agricultural futures, namely agroecology and sustainable intensification, under the same banner. This is more likely to confuse than to clarify the public debate. More importantly, it draws attention away from more fundamental challenges. We conclude by providing guidance for research agronomists who want to engage with Regenerative Agriculture.

Response of planktonic communities to environmental stress in the eutrophic waters of Xiaoping Island in China

Phytoplankton blooms were affected by external environmental nutrient input, while the interspecific interactions in plankton (phytoplankton and mesozooplankton) under the nutrient pollution gradient remain largely unknown. Here, we systematically collected samples for 9 months (from April to December 2018) in the coastal waters of Xiaoping Island in China to analyze the planktonic community structure and identify the main driving environmental factors along the nutrient gradient from the sewage outlet to the open sea. The results indicated that there existed obvious seasonal and spatial variations in the planktonic community. Procrustes test analysis showed that temperature, transparency, dissolved oxygen, nitrate (NO3–N), phosphate (PO4–P), and silicate (SiO3–Si) significantly affected the community compositions and diversity of plankton (p < 0.05). Co-occurrence network showed that seasons and nutrients pollution had an important influence on the inter-specific interactions between phytoplankton and mesozooplankton. In different nutrient pollution gradients, diatom was the most associated with Copepods in Section 1 (9.38%), Section 2 (9.84%), and Section 3 (5.38%), respectively, and it was also associated with Planktonic larva in Section 1 (7.81%), followed by in Section 3 (4.30%) and 2 (1.64%). Dinoflagellates were associated with Chaetognatha only in Section 1 (4.69%). This study may provide new insights into the plankton dynamics and facilitate nearshore environmental management.

Soil microbial community dynamics indicate disruption of nitrogen cycling by pollution in vegetation buffer zones

Hongfeng Lake is one of the largest artificial freshwater lakes on the Karst plateau of China, and the control of external nutrient input into the lake by a vegetation buffer zone is key to mitigating its eutrophication. Although soil microbial communities play key roles in nitrogen pollutant interception and in maintaining ecosystem stability, few studies have investigated these communities in lake vegetation buffer zone soils. In this study, the effects of seasonal and human disturbances on soil microbial communities of the vegetation buffer zones of Hongfeng Lake were determined by high-throughput sequencing and community profiling. BIOENV analysis revealed that soil redox potential was the primary factor associated with soil microbial community composition during the wet season, while Total nitrogen better explained variation in the dry season microbial communities. The relative abundances of Cyanobacteria were significantly higher in vegetation buffer zone soils that were polluted by upstream livestock and domestic sewage. Further, analysis of microbial community network topological features indicated that the soil microbial communities of the vegetation buffer zone markedly differed between wet and dry seasons. Specifically, wet season community networks suggested that the proliferation of Cyanobacteria, E. coli, and Panaeolus papilionaceus inhibited the growth of microorganisms capable of nitrification and denitrification, thereby contributing to increased risk of nitrogen loss to surface waters. Based on these results, we suggest that discharge of domestic sewage and livestock wastewater should be prohibited along Hongfeng Lake tributaries. Moreover, vegetation should be artificially managed to improve the mitigation of non-point source pollution into the lake via vegetation buffer zones.

Role of external inputs of nutrients to aquatic ecosystems in determining prevalence of nitrogen vs. phosphorus limitation of net primary productivity

Whether net primary productivity in an aquatic ecosystem is limited by nitrogen (N), limited by phosphorus (P), or co-limited by N & P is determined by the relative supply of N and P to phytoplankton compared to their elemental requirements for primary production, often characterized by the “Redfield” ratio. The supply of these essential nutrients is affected by both external inputs and biogeochemical processes within the ecosystem. In this paper, we examine external sources of nutrients to aquatic systems and how the balance of N to P inputs influences nutrient limitation. For ocean subtropical gyres, a relatively balanced input of N and P relative to the Redfield ratio from deep ocean sources often leads to near co-limitation by N and P. For lakes, the external nutrient inputs come largely from watershed sources, and we demonstrate that on average the N:P ratio for these inputs across the United States is well above that needed by phytoplankton, which may contribute to P limitation in those lake that experience this average nutrient loading. Watershed inputs are also important for estuaries and coastal marine ecosystems, but ocean sources of nutrients are also significant contributors to overall nutrient loads. The ocean-nutrient sources of N and P are very often at or below the Redfield ratio of 16:1 molar, and can be substantially so, particularly in areas where the continental shelf is wide. This large input of coastal ocean nutrients with a low N:P ratio is one factor that may make N limitation more likely in many coastal marine ecosystems than in lakes.

A Multi-Objective Model Exploration of Banana-Canopy Management and Nutrient Input Scenarios for Optimal Banana-Legume Intercrop Performance

Bananas on smallholder farmers in the African Great Lakes region are often pruned to illuminate shorter understory intercrops, reducing overall farm profitability. The impact of this practice on environmental and nutritional indicators are not known. This study determined the effect of this practice on operating profit, protein yield, soil organic matter (SOM) balance, and nitrogen input; and the management options for optimal performance of the intercrops. Alternative scenarios for improving soil nutrient balances of the system were also explored. Data from an experiment intercropping bush beans with banana at three leaf pruning levels (i.e., retaining all, seven, and four leaves) was used as the input for the multi-objective optimization FarmDESIGN model. Retention of four functional leaves mimicked a worst-case scenario observed on farms. Banana and bush bean monocrops served as controls. The model maximized operating profit, protein yield, and SOM, and minimized nitrogen input. Nutrient input scenarios in which (i) farmyard manure was only applied at planting (business as usual (‘BaU’)); and ‘BaU’, was combined with (ii) hedges, (iii) inorganic fertilizers, (iv) hedges and goat manure, (v) hedges and inorganic fertilizers, (vi) inorganic fertilizers and goat manure, and (vii) hedges, inorganic fertilizers, and goat manure, were also explored. Severe banana leaf pruning reduced profitability, SOM, and protein yield, although it’s less nutrient demanding. In contrast, the “un-pruned banana-bush bean intercrop” and “sole banana crop” had a higher profitability, SOM balance, and protein yield, whereas they demand more soil nutrients. No profound improvements in operating profit, SOM balance, and protein yield occurred for ‘BaU’, while hedges resulted in mild improvements. Profound improvements in all objectives occurred with the addition of the inorganic fertilizers, while goat manure resulted in a high SOM balance and N input. For ‘BaU’ and hedges, “severely pruned banana-bush bean intercrop” dominated the optimal solution set for improving farm performance. In contrast, when the inorganic fertilizers and/or goat manure was introduced, “un-pruned banana-bush bean intercrop” and/or “sole un-pruned banana crop” were the optimal solutions. The study confirms severe leaf pruning to negatively impact profitability, while the more profitable un-pruned crop options are unsustainable without external input of nutrients. Thus, investments in external inputs are crucial for a sustainable banana-intercrop system. The FarmDESIGN model made the trade-offs and synergies in this complex intercrop system explicit, thus was also helpful for field-level decision making.

Contributions of external nutrient loading and internal cycling to cyanobacterial bloom dynamics in Lake Taihu, China: Implications for nutrient management

AbstractHarmful cyanobacterial blooms (CyanoHABs) are linked to increasing anthropogenic nitrogen (N) and phosphorus (P) inputs. However, CyanoHABs in many large lakes continue despite extensive abatement efforts, mostly focused on external P loading. Internal nutrient cycling can modify nutrient availability and limitation; thus, understanding the relative importance of external vs. internal nutrient loading is essential for developing effective mitigation strategies for CyanoHABs. We estimated long‐term nutrient budgets for Lake Taihu, China, from mass balance models using extensive monitoring of input and output nutrient data from 2005 to 2018 to quantify contributions from internal nutrient loading. The nutrient mass balance showed that 9% and 63% of annual external N and P inputs, respectively, were retained in the lake. Denitrification removed 54% of external N loading and can thus help explain rapid decreases in lake N concentrations and summer N limitation. Water columnregeneration can help sustain CyanoHABs over the short term and contributed 38–58% of potentialdemand for summer‐fall,Microcystis‐dominated blooms. Internal P release contributed 23–90% of CyanoHABs P demand, although Taihu was a net P sink on an annual scale. Our results show that internal nutrient cycling helps sustain CyanoHABs in Taihu, despite reductions in external nutrient inputs. Furthermore, N is leaving the lake faster than P, thereby creating persistent N limitation. Therefore, parallel reductions in external N loading, along with P, will be most effective in reducing CyanoHABs and accelerate the recovery process in this and other large, shallow lakes.

Canopy modification of base cations deposition in a subtropical broadleaved forest: Spatial characteristics, canopy budgets and acid neutralizing capacity

Atmospheric deposition of base cations in contact with the canopy alters their chemical characteristics and plays a vital role in offsetting soil acidification and nutrient imbalance by replenishing the base cationic pool in forest ecosystems. However, the effects of site characteristics on deliveries of base cations fluxes via throughfall (TF) and stemflow (SF) across topographic gradients within a watershed remain less understood. Here, we examined the concentrations and fluxes of base cations (potassium (K+), calcium (Ca2+), magnesium (Mg2+) and sodium (Na+)), acid neutralizing capacities (ANC) and alkalinity (ALK) in bulk precipitation (BP), TF and SF in an upper slope plot (UP) and a lower slope plot (LP) in a subtropical broadleaved montane forest, Southeast China. In addition, a canopy budget model was applied to distinguish the relative contributions of dry deposition (DD) and canopy exchange (CE) to net TF + SF (NTF) flux. Results showed that annual volume weighted mean concentrations of base cations in TF and SF were significantly higher than those in BP in both UP and LP. Annual fluxes of TF or SF base cations had no significant differences between UP and LP, resulting in a comparable of the NTF fluxes. However, the relative contributions of DD and CE to NTF were different at the two slope plots. NTF K+ flux was dominated by CE regardless of slope position. Unlike K+, NTF Ca2+ and Mg2+ fluxes were dominated by DD in UP, while CE in LP. In addition, ANC and ALK of TF and SF were significantly higher compared to BP, suggesting rainwater beneath the canopy became less acidic and may mitigate in part the risk of soil acidification, especially in the dormant season. This study can provide insights into the spatial variability of chemical characteristics of base cations, and improve our understanding of the quantities and controls of external and internal nutrient inputs occurring within the canopy in forest watershed.

The use of nutrient budget approach for informing eutrophication management in urbanised shallow coastal lakes: A case study from Lake Nokoué in Benin

Lake Nokoué in Benin supports the livelihoods of more than 500.000 people through fish production and sand mining. However, its health is jeopardised by eutrophication and excessive growth of the invasive water hyacinth, which dies off and sink to sediment during dry seasons when the lake's salinity increases due to tidal intrusion. Water-hyacinth constitutes then a potential source of internal nutrient loading through the decomposition of detritus and therefore can exacerbate eutrophication problems. An important management question is whether the removal of water hyacinth before it dies would significantly reduce eutrophication problems through the removal of nutrients. To compare the amount of nutrients removed by water-hyacinth biomass to the amount of nutrients transported into the Lake, mass-balance approach has been taken. Nutrient concentrations, water hyacinth cover, and hydrological inflows were measured over a 12 month period from November 2016 to October 2017. Water-hyacinth biomass estimation was based on a calibrated NDVI and field measurement relationship. In total the hyacinth covered up to 18 km2 (10%) of the lake, corresponding to 80,000 tonnes of dry weight which sink to the bottom each year when salinity rise. The potential internal nutrient loaded from hyacinth to the system was estimated to 1021 tonnes of nitrogen (8% of external input) and 231 tonnes of phosphorus (40% of external input). Considering that the tidal nutrient output compensates almost all the external nutrient inputs (about 70%), part of the nutrient available for eutrophication must come from internal sources, likely through the decomposition of sediment detritus.

Lake warming intensifies the seasonal pattern of internal nutrient cycling in the eutrophic lake and potential impacts on algal blooms

Lake warming induced by climate change has constituted a particular challenge for the restoration of eutrophic lakes. However, a quantitative analysis about impacts of lake warming on the internal nutrient cycling in eutrophic lakes is limited. In this study, monthly nutrient monitoring data set in 2015-2016 in eutrophic Lake Chaohu, China, revealed a regular seasonal pattern of nutrient concentration. A process-based water quality model was established to quantify contributions from internal loadings on seasonal nutrient variations and predict responses under climate change scenarios. Results indicated that internal nutrient loading was responsible for the intra-annual variations of nutrient concentrations in the lake, and the internal loadings fluctuated much more between different seasons than the external nutrient inputs. We predicted that lake warming might probably result in stronger seasonal fluctuations of internal loading and create conditions beneficial for longer duration of cyanobacteria blooms in the year. Evidence derived from this study could help water managers to rethink the existing mitigation strategies in the restoration of eutrophic lakes and emphasize the potential interactions among lake warming, eutrophication and internal nutrient cycling in the future.

Satellite Estimation of Dissolved Carbon Dioxide Concentrations in China's Lake Taihu.

Lakes play an important role in the global carbon cycle; however, there are still large uncertainties in the estimation of global lake carbon emission due to the limitations in conducting field surveys at large geographic scales. Using long-term Moderate-Resolution Imaging Spectroradiometer (MODIS) imagery and field observation data in eutrophic Lake Taihu, we developed a novel approach to estimate the concentration of dissolved carbon dioxide (cCO2) in lakes. Based on the MODIS-derived chlorophyll-a concentration, lake surface temperature, diffuse attenuation coefficient of photosynthetically active radiation, and photosynthetically active radiation, a spatially explicit cCO2 model was developed using multivariate quadratic polynomial regression (coefficient of determination (R2) = 0.84, root-mean-square error (RMSE) = 11.81 μmol L-1, unbiased percent difference (UPD) = 22.46%). Monte Carlo simulations indicated that the model is stable with relatively small deviations in cCO2 estimates caused by input variables (UPD = 26.14%). MODIS data from 2003 to 2018 showed a significant declining trend (0.42 μmol L-1 yr-1, p < 0.05) in the annual mean cCO2. This was associated with a complex balance between the increasing algae biomass and decreasing external inputs of inorganic carbon, nutrients, and organic matter. The high spatiotemporal variabilities in cCO2 were attributed to river inputs and seasonal changes in temperature and algae biomass. The study shows that satellite remote sensing can play an important role in the field of inland water carbon cycling, providing timely much-needed insights into the drivers of the spatial and temporal changes in dissolved CO2 concentrations in inland waters.

An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

Abstract. State-of-the-art global nutrient deposition fields are coupled here to the Pelagic Interactions Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemistry model to investigate their effect on ocean biogeochemistry in the context of atmospheric forcings for pre-industrial, present, and future periods. PISCES, as part of the European Community Earth system model (EC-Earth) model suite, runs in offline mode using prescribed dynamical fields as simulated by the Nucleus for European Modelling of the Ocean (NEMO) ocean model. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P into the global ocean account for ∼ 40 Tg N yr−1, ∼ 0.28 Tg Fe yr−1, and ∼ 0.10 Tg P yr−1. Pre-industrial atmospheric nutrient deposition fluxes are lower compared to the present day (∼ 51 %, ∼ 36 %, and ∼ 40 % for N, Fe, and P, respectively). However, the overall impact on global productivity is low (∼ 3 %) since a large part of marine productivity is driven by nutrients recycled in the upper ocean layer or other local factors. Prominent changes are, nevertheless, found for regional productivity. Reductions of up to 20 % occur in oligotrophic regions such as the subtropical gyres in the Northern Hemisphere under pre-industrial conditions. In the subpolar Pacific, reduced pre-industrial Fe fluxes lead to a substantial decline of siliceous diatom production and subsequent accumulation of Si, P, and N, in the subpolar gyre. Transport of these nutrient-enriched waters leads to strongly elevated production of calcareous nanophytoplankton further south and southeast, where iron no longer limits productivity. The North Pacific is found to be the most sensitive to variations in depositional fluxes, mainly because the water exchange with nutrient-rich polar waters is hampered by land bridges. By contrast, large amounts of unutilized nutrients are advected equatorward in the Southern Ocean and North Atlantic, making these regions less sensitive to external nutrient inputs. Despite the lower aerosol N : P ratios with respect to the Redfield ratio during the pre-industrial period, the nitrogen fixation decreased in the subtropical gyres mainly due to diminished iron supply. Future changes in air pollutants under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario result in a modest decrease of the atmospheric nutrients inputs into the global ocean compared to the present day (∼ 13 %, ∼ 14 %, and ∼ 20 % for N, Fe, and P, respectively), without significantly affecting the projected primary production in the model. Sensitivity simulations further show that the impact of atmospheric organic nutrients on the global oceanic productivity has turned out roughly as high as the present-day productivity increase since the pre-industrial era when only the inorganic nutrients' supply is considered in the model. On the other hand, variations in atmospheric phosphorus supply have almost no effect on the calculated oceanic productivity.

Factors controlling accumulation of organic carbon in a rift-lake, Oligocene Vietnam

Understanding of the processes of petroleum source rock (SR) accumulation in lacustrine rift basins and the behavior of lake systems as long-term carbon sinks is fragmentary. Investigation of an 800 m thick (500 m core and ~ 300 m outcrop), deep-lacustrine, Oligocene section in Vietnam, provides a rare insight into the controls and deposition of organic carbon (OC) and SR formation in continental rift basins. A multidisciplinary dataset, combining elemental data, inorganic and organic geochemistry with sedimentology, shows that the richest alginite-prone, sapropelic SR developed during periods of relative tectonic quiescence characterized by moderate primary productivity in a mainly dysoxic lacustrine basin. Increased rift activity and further development of graben morphology intensified water column stratification and anoxia, which hindered nutrient recycling. Sapropelic organic matter (OM) continued to accumulate, but with increasing amorphous OM content and decreasing total OC values. Periods of increased seasonality were characterized by thermocline weakening, enhanced mixing of water columns, increased primary productivity and diatom blooming. The results suggest that a change from dysoxia towards anoxia or extreme primary productivity does not necessarily enhance OC burial and SR quality. External nutrient input from a phosphate-rich hinterland is sufficient for sapropel formation, whereas the main limiting factor is methanogenesis.

Cyanobacteria dynamics and phytoplankton species richness as a measure of waterbody recovery: Response to phosphorus removal treatment in a tropical eutrophic reservoir

External nutrient inputs account for the main cause of eutrophication of aquatic systems and intensification of toxic cyanobacteria blooms. But internal loads from sediments significantly contribute to environmental degradation. In-lake treatments may therefore be combined to accelerate the restoration process. A tropical, eutrophic reservoir with persistent cyanobacteria blooms was subjected to applications of a lanthanum-enriched clay (Phoslock®) designed to control internal phosphorus loading. This study aimed to evaluate if the treatment could lead to cyanobacteria reduction and improvement of the phytoplankton community and environmental status. Data were obtained during the application and post-application months, and compared with pre-treatment datasets. Significant decrease in phosphorus concentration occurred, but only in the second treatment year. Cyanobacteria responded after five months of applications, reducing biomass with a 4-fold increase in water transparency, but blooms were able to re-establish. However, by the end of the second year and until the interruption of the treatment, cyanobacteria dominance was significantly reduced and replaced by a more diverse phytoplankton community rarely seen in this environment. At this time, the number of species belonging to groups other than cyanobacteria increased, characterizing more than 80% of the total of species. While pointing to the system resilience and the treatment limitations, this study also indicated that under a long-term control of phosphorus load, lakes could be restored and their aquatic communities recover. Decrease of cyanobacteria biomass and increase in non-cyanobacteria biodiversity were key factors to evaluate the treatment success. The study reinforces the importance of species and communities as sentinels of a healthier ecosystem.

Urban soil health: A city-wide survey of chemical and biological properties of urban agriculture soils

The integration of urban green spaces into modern city planning is seen as a promising tool to offset the drawbacks of ever-expanding cities. Urban agriculture is a common method to implement such strategies and to increase urban sustainability with a special focus on food security. Due to their location, urban farms are highly influenced by past and present anthropogenic activities which can threaten both soil health and food safety. This study includes 12 urban agriculture sites in the metropolitan area of Adelaide, Australia. It is the first of its kind to focus on soil health in urban agriculture systems with a further emphasis on mycorrhizal fungi. Descriptive information about each site, the biodiversity of the selected plots and soil samples from different depths and locations were collected and analysed for chemical and biological parameters. Seven metals, total and plant-available (Colwell) phosphorus and available nitrogen were measured in soils. A glasshouse bioassay was also conducted to determine the abundance of beneficial arbuscular mycorrhizal fungi in the soils and the change of root colonization after inoculation with the mycorrhizal fungus Rhizophagus irregularis. Results showed a generally high biodiversity of plants that correlated with site activity (commercial or community garden) and which could potentially be used for urban biodiversity conservation. Metal concentrations in soils were below national guidelines levels for all samples, although sites with previous industrial history showed elevated levels when compared to sites without industrial history. The use of raised beds with introduced soils eliminated differences in previous land-use history, thereby providing a good option to support cleaner production. Gardening soils were considered highly fertile, with plant-available (Colwell) P concentrations exceeding recommended levels for most horticultural crops, while soils were adequately supplied with nitrogen. Most plant nutrients were derived from freely available urban waste streams and integrated via composting. Various urban waste streams could be used to counter-act imbalanced soil nutrients. Arbuscular mycorrhizal fungi were present in all sites, indicating that the practiced soil management is sustainable from a microbial perspective. Given their important role in supporting plant nutrition, and potential to reduce the need for external nutrient inputs, they provide an important focal point for achieving clean and sustainable urban food production. The results were incorporated into a framework for the management of urban soil health.

Biochar alters nitrogen and phosphorus dynamics in a western rangeland ecosystem

Application of biochar to soils has been proposed as a novel approach to managing wood residuals, enhancing soil carbon (C) storage and improving soil fertility; however, the majority of biochar studies have been conducted in agricultural systems that rely on tillage and nutrient inputs associated with annual cropping schemes. Few studies have evaluated the influence of biochar on soil processes in semi-natural rangeland ecosystems that feature more complex plant communities, lack deep soil disturbance, and have relatively few external nutrient inputs. In August 2018, biochar produced using wood waste from a lumber mill in Columbia Falls, MT, USA was applied to surface soils in replicated plots at an experimental ranch in western Montana to test the impact of biochar on soil C storage and nutrient management. A series of soil biochemical properties including total soil C and nitrogen (N), microbial N functional genes, available phosphorus (P) and the net accumulation of nutrients below surface soil layer were evaluated over a one-year period following biochar addition with or without a poultry litter based organic fertilizer. Biochar used alone slightly reduced soil NH4+, significantly increased soil nitrification potential, increased the relative abundance of the bacterial amoA gene, and increased the soil nitrate (NO3−) pool size, while having no net effect on soil inorganic N accumulation below surface soil. By contrast, biochar charged with poultry litter (termed “charged biochar”) had no effect on NH4+ availability, but had a positive effect on amoA abundance. Charged biochar significantly reduced NH4+ accumulation below 25 cm depth compared to poultry litter alone. Biochar additions led to a shift towards a more fungal dominated community and a general increase in P availability. However, biochar alone also contributed to a greater amount of soluble P collected below surface soil, an effect slightly attenuated when biochar was applied with poultry litter. Soil pH increased from 5.7 to 6.9 in response to biochar addition and was one of the dominant factors governing the observed changes in soil processes. Charged biochar helped retain soil nutrients and promoted soil C storage in this semi-natural rangeland system over one growing season. Changes in these soil pools and fluxes may influence various trophic groups affecting ecosystem functioning over time.

Interactions of nitrogen and phosphorus cycling promote P acquisition and explain synergistic plant-growth responses.

Plant growth is often co-limited by nitrogen (N) and phosphorus (P). Plants might use one element to acquire another (i.e., trading N for P and P for N), which potentially explains synergistic growth responses to NP addition. We studied a 66-yr-old grassland experiment in South Africa that consists of four levels of N addition with and without P addition. We investigated the response of aboveground net primary production (ANPP) to N and P addition over the last 66yr. Further, we tested whether phosphatase activity and plant P uptake depend on N availability, and vice versa, whether non-symbiotic N2 fixation and plant N uptake depend on P availability. We expected that the interaction of both elements promote processes of nutrient acquisition and contribute to synergistic plant growth effects in response to NP addition. We found synergistic N and P co-limitation of ANPP for the period from 1951 to 2017 but the response to N and P addition diminished over time. In 2017, aboveground P stocks, relative rRNA operon abundance of arbuscular mycorrhizal fungi, and soil organic P storage increased with N fertilization rate when N was added with P compared to the treatment in which only N was added. Further, N addition increased phosphatase activity, which indicates that plants used N to acquire P from organic sources. In contrast, aboveground N stocks and non-symbiotic N2 fixation did not change significantly due to P addition. Taken together, our results indicate that trading N for P likely contributes to synergistic plant-growth response. Plants used added N to mobilize and take up P from organic sources, inducing stronger recycling of P and making the plant community less sensitive to external nutrient inputs. The latter could explain why indications of synergistic co-limitation diminished over time, which is usually overlooked in short-term nutrient addition experiments.

Potential yield challenges to scale-up of zero budget natural farming.

Under current trends, 60% of India's population (>10% of people on Earth) will experience severe food deficiencies by 2050. Increased production is urgently needed, but high costs and volatile prices are driving farmers into debt. Zero budget natural farming (ZBNF) is a grassroots movement that aims to improve farm viability by reducing costs. In Andhra Pradesh alone, 523,000 farmers have converted 13% of productive agricultural area to ZBNF. However, sustainability of ZBNF is questioned because external nutrient inputs are limited, which could cause a crash in food production. Here, we show that ZBNF is likely to reduce soil degradation and could provide yield benefits for low-input farmers. Nitrogen fixation, either by free-living nitrogen fixers in soil or symbiotic nitrogen fixers in legumes, is likely to provide the major portion of nitrogen available to crops. However, even with maximum potential nitrogen fixation and release, only 52-80% of the national average nitrogen applied as fertilizer is expected to be supplied. Therefore, in higher-input systems, yield penalties are likely. Since biological fixation from the atmosphere is possible only with nitrogen, ZBNF could limit the supply of other nutrients. Further research is needed in higher-input systems to ensure that mass conversion to ZBNF does not limit India's capacity to feed itself.

Simulating Nutrient Uptake Dynamics in Plankton Models: a Case Study for the Cilician Basin Marine Ecosystem

The primary productivity in the Cilician Basin is severely constrained by phosphorus limitation due to high N:P ratios in the external nutrient inputs. Therefore, special attention is required when the dynamics of plankton is modelled. Acknowledging that mathematical formulation of nutrient uptake by phytoplankton in ecosystem models is crucial as it determines the degree of realism of the representation of biogeochemical dynamics, a plankton model was developed by utilising two widely adopted approaches; i) Monod nutrient uptake kinetics, and ii) Droop nutrient uptake kinetics, to delineate the seasonality of phytoplankton in an attempt to establish a mechanistic biogeochemical model of the Cilician Basin. The model was validated against field data from Erdemli Time Series stations in the region and differences between the approaches were compared. The model successfully simulated the phosphorus limitation in the basin; however, the scenario with Droop kinetics had a better fit to the field data. Both scenarios reproduced the primary productivity in the region. Overall, the results indicated that implementation of Monod kinetics generally sufficed to represent the seasonality of phytoplankton, whereas in environments with severe temporal nutrient scarcity, i.e. the Cilician Basin, implementation of Droop kinetics is required to represent the phytoplankton dynamics more realistically.

Integrated Effects of Vermi-compost and NPS Fertilizer Rates on Soil Chemical Properties and Maize Production in Bedele District, Western Oromia

Integrated plant nutrient management is the application of inorganic fertilizer in combination with organic fertilizer to maintain soil fertility and balance nutrient supply in order to boost up the crop yield per unit area. A study was conducted in Bedele District on farmers' fields to find out the combined effects of vermi-compost (organic fertilizer) and NPS (inorganic fertilizer) rates on soil chemical properties and maize production. The treatments consisted of three levels of vermi-compost (0, 1.5 and 3 t ha-1) and three levels of NPS fertilizer (0, 100 and 200 kg ha-1). The experiment was laid out in RCBD design in factorial combination with three replications. laboratory analysis results of composite soil samples collected before sowing showed deficiency in soil chemical properties. However, analysis of variance of post harvest composite soil samples collected from each plot indicated significant differences on soil available P, OC, TN and CEC while, soil pH and exchangeable acidity showed positive improvement as compared to initial soil sample. The analysis of variance among the treatments showed significant differences (P ≤ 0.05) on almost all the maize characters tested. The highest and lowest maize grain yield (7932.1 kg ha-1) and (1944.4 kg ha-1) were obtained from the treatment combination of 3 t ha1 vermi-compost with 200 kg ha-1 NPS and 92 kg ha-1 N, and control plot, respectively. However this combination was statically at par with the treatment combination of 1.5 t ha-1 vermi-compost with 200 kg ha-1 NPS and 92 kg ha-1 N, which gave maize grain yield (7577.2 kg ha-1). Therefore, the present study showed that combined fertilization of vermi-compost and NPS fertilizer enhanced maize productivity and soil fertility status in the study area; indicated that maize productivity in the study sites were reduced due to high demand for external nutrient inputs. Hence combined fertilization of 1.5 t ha1 vermi-compost with 200 kg ha-1 NPS and 92 kg ha-1 N could improve maize productivity and soil chemical properties, and recommended for the study area (Bedele District) and similar agro-ecology. The result also showed that the soils of the study sites had poor chemical fertility and integrated soil fertility management practices can improve the current situation.