Nutrient Mass Balance Research Articles

Watershed-scale spatial prediction of agricultural land phosphorus mass balance and soil phosphorus metrics: A bottom-up approach.

Analysis of nutrient balance at the watershed scale, including for phosphorus (P), is typically accomplished using aggregate input datasets, resulting in an inability to capture the variability of P status across the study region. This study presents a set of methods to predict and visualize partial P mass balance, soil P saturation ratio (PSR), and soil test P for agricultural parcels across a watershed in the Lake Champlain Basin (Vermont, USA) using granular, field-level data. K-means cluster analyses were used to group agricultural parcels by soil texture, average slope, and crop type. Using a set of parcels accounting for ∼21% of the watershed's agricultural land and having known soil test and nutrient management parameters, predictions of partial P mass balance, PSR, and soil test P for agricultural land across the watershed were made by cluster, incorporating uncertainty. This resulted in an average partial P balance of 5.5±0.2kg P ha-1year-1 and an average PSR of 0.0399±0.0002. Furthermore, approximately 30% of agricultural land had predicted soil test P values above optimum levels. Results were used to visualize areas with high P loss potential. Such data and visualizations can inform watershed P modeling and assist practitioners in nutrient management decision making. These techniques can also serve as a framework for bottom-up modeling of nutrient mass balance and soil metrics in other regions.

144 Assessing economic implications of thermal stress of Bos indicus and Bos taurus species during finishing in northern Colorado

Abstract The objective of this study was to determine the economic implications of thermal stress on climate adaptive capacity, resiliency, and impact of Bos indicus and Bos taurus finishing steers using common finishing systems. The experimental design was a completely randomized design, with a 2 by 2 factorial arrangement of finishing system (‘natural’ or ‘conventional’) and species of cattle (Bos indicus or Bos taurus). Steers [n = 200; body weight (BW) ~450 kg] were housed in 20 feedlot pens (10 steers/pen) for the first 84 d, where cattle were blocked by initial BW. For the remainder of the 180 d (96 d) finishing period, cattle were moved to four Climate Smart Research Pens (50 steers/pen, 1 pen/ treatment, and species combination). Within each Climate Smart Research Pen, five SmartFeed systems were used to evaluate individual animal feed intake, one GreenFeed emission measurement system was used to evaluate individual animal gas emissions flux of enteric CH4, O2, H2, and CO2, and were equipped for nutrient mass balance of carbon, nitrogen, and phosphorus. Animal BW were collected every 28 d for analysis of average daily gain (ADG) and feed efficiency. Thermal stress behaviors were evaluated by one trained personnel on a subset of 7 steers/treatment via the measurement of respiration rate, open mouth breathing, rumen temperature, number of daily water intake events, lying and standing behavior, and pen surface temperature for the last 96 d of the finishing period. At harvest, carcass characteristics, liver scores, and heart scores were collected. Economic analyses were conducted post-hoc to determine the profitability of each species based on economic implications, tradeoffs, carcass quality and quantity, and time to finish. Selection of cattle for climate adaptive features may involve production tradeoffs (e.g., depressed rate of gain, greater yield risk, lower technical efficiency) and adjustment costs (e.g., re-optimizing feed for a new breed), which affect the adoption of less common breeds into the US cattle supply chain. Adding to the complexity of this evaluation, consumers preferences may not adapt quickly, affecting the prospect of Bos indicus cuts of meat in the market. We also, therefore, explore the supply- and demand-side effects of climate change adaptation through breed selection in the beef industry.

Greenhouse gas emissions and nutrient use efficiency assessment of 6 New York organic dairies

Improving nutrient use efficiency and reducing GHG emissions are important environmental priorities for organic-certified dairy operations. The objectives of this research were to quantify annual nutrient use and GHG emissions in 6 organic New York dairy farms. Farm-gate nutrient mass balances (NMB) were estimated with the Cornell NMB calculator. Whole-farm GHG emissions were estimated using the Cool Farm Tool (CFT) and COMET. Farm-gate NMB were low, ranging from -6.5 to 19 kg N/ha for N1 (without legume N fixation), 26 to 71 kg N/ha for N2 (including N fixation), -2.4 to 8.2 kg P/ha for P, and 1.1 to 19.8 kg K/ha for K. Additional nutrient imports, coupled with nutrient management planning, adequate legume stands, and diet balancing may help improve P balances and ensure no N deficiencies in the system. Estimates of annual GHG emissions intensity ranged from 0.98 to 2.10 kg of CO2-equivalents (CO2-eq) per kilogram of fat- and protein-corrected milk (FPCM) estimated by CFT, and from 0.69 to 2.48 kg CO2-eq/kg FPCM estimated by COMET. Enteric fermentation, feed production, and fuel and energy use represented the largest sources of GHG. For farms with liquid manure storages, manure management was also a significant source. Estimates of soil carbon (C) stock changes from CFT were in agreement with or smaller than previous studies, and estimates from COMET were in agreement or greater. Variability and uncertainty in the results for soil C stock change indicate that more research and new protocols are needed. The effects of individual management changes on GHG emissions intensity were small, ranging from -8 to +7% in CFT, and -8% to +8% in COMET. The management changes that resulted in the largest reductions in GHG emissions intensity included increasing individual cow productivity and ratio of milk to total feed, and implementation of manure treatment systems.

Engaging secondary school students in sustainability assessments through farm nutrient mass balances

AbstractDecision‐support tools (DSTs) are increasingly used to collect, manage, and/or analyze growing amounts of data generated on farms. The whole‐farm nutrient mass balance (NMB) is an assessment with an associated DST (the Cornell NMB calculator) that measures farm nutrient management efficiency. Our main objectives were to (1) develop and implement a secondary school curriculum on NMB assessments; (2) evaluate its impact on student knowledge and perceptions of agricultural sustainability, nutrient management, careers in agriculture, awareness about data collection and use of DSTs, and analytical and quantitative skills; and (3) assess teacher experiences delivering the materials. The curriculum was implemented across 21 New York classrooms. Students completed one pre‐ and one post‐curriculum implementation questionnaire (n = 134). Teachers completed a post‐curriculum implementation questionnaire (n = 19). Results showed that the curriculum enhanced student knowledge of nutrient management and effectively conveyed the fundamentals of the NMB metrics. It also impacted student perceptions of the utilization of DSTs and need for mathematical skills and data management knowledge in agriculture. The curriculum did not influence student interest in pursuing agricultural careers but exposed them to aspects of farming that they were not previously familiar with. The math‐focused lessons were identified as challenging by many students and teachers. Teachers found the curriculum applicable to the real world, exposing students to new aspects of farming. We conclude that real‐world case‐study examples, carefully planned math‐focused lessons, appropriate support materials including widely installable and user‐friendly software, and training opportunities for teachers can help effective teaching of DST use and agriculture sustainability concepts.

A perceptual approach to address complex water management issues in lowland permeable catchments

Water quality management is a pressing global concern, and an increasingly complex issue due to climate and land-use change, legacy pollution, and the persistent release of well-known and emerging contaminants from diffuse and point sources. The increasing availability of high-frequency monitoring data is leading existing, often heuristic approaches, to be judged inadequate. Water managers frequently rely on simple qualitative and/or quantitative approaches for decision-making, but a lack of tangible improvement in freshwater quality outcomes is demanding new and innovative approaches that rely more on physical process understanding, rather than precedent. In this study, we drew upon local geological, hydrogeological, and hydrological data to infer a high-level perceptual model of surface/groundwater interactions in a chalk stream in Dorset, UK. We used the perceptual model to interrogate spatial and temporal trends in historical water quality data and to construct reach-scale nutrient mass balances. Through novel representation with Sankey diagrams, the perceptual model highlighted the relative importance of different hydrological features. Surface/groundwater interactions were found to occur predominantly by spring flow. We demonstrate that river flow accretion was dominated by the Chalk aquifer despite only occupying ca. 15 % of the surface bedrock area, and that spring sources, whilst vital to dilute treated sewage inputs in baseflow conditions, were also major sources of legacy nitrate. Nutrient mass balances showed that sewage treatment works contributed ca. 13 % to soluble reactive phosphorus load, with groundwater accounting for ca. 48 %. Thus, a determinand often associated with point-source pollution was shown to be diffuse dominated in this river. The study demonstrated how a multi-disciplinary approach to water management, based on a comprehensive perceptual modelling approach, could identify hitherto unknown sources and relative contributors to freshwater pollution and allow flow and load apportionment studies to provide useful decision-support to manage nutrient pollution. The novel application of perceptual modelling tools, such as the Sankey diagram, allows different source attributions to be presented in an accessible manner, and can be readily transferred to other study areas.

Insight into the roles of hematite iron oxide nanoparticles on microalgae growth, urban wastewater treatment and bioproducts generation: Gompertz simulation, nutrient mass balance and gene expression

In this study, the effect of α-Fe2O3 nanoparticles spiking in urban wastewater (UWW) on growth rate, wastewater treatment ability and bioproducts generation of C. vulgaris and Spirulina was investigated and compared with pure cultivation system. The biomass concentration of C. vulgaris and Spirulina improved by 20 % and 39 % at 10 and 15 mg/L α-Fe2O3, respectively while the both microalgae growth pattern fitted better with Gompertz simulation after treatment with α-Fe2O3. The nutrients mass balance revealed that 1 g of treated C. vulgaris and Spirulina could uptake more COD, TN and TP in comparison to the untreated cells. The lipid generation increased remarkably (C. vulgaris: 45 % and Spirulina: 72 %) after α-Fe2O3 treatment. While, the addition of α-Fe2O3 showed no significant impact on the protein and carbohydrate productivity. Overall, this study evangelize the role of nanoparticles on promoting microalgae applications as a sustainable approach for UWW treatment and promising feedstock for biofuel production.

Modeling ammonia emissions from manure in conventional, organic, and grazing dairy systems and practices to mitigate emissions

Almost 60% of all ammonia (NH3) emissions are from livestock manure. Understanding the sources and magnitude of NH3 emissions from manure systems is critical to implement mitigation strategies. This study models 13 archetypical conventional (5 farms), organic (5 farms), and grazing (3 farms) dairy farms to estimate NH3 emissions from manure at the barn, storage, and after land application. Mitigation practices related to management of the herd, crop production, and manure are subsequently modeled to quantify the change in NH3 emissions from manure by comparing archetypical practices with these alternative practices. A mass balance of nutrients is also conducted. Emissions per tonne of excreted manure for the manure system (barn, storage, and land application) range from 3.0 to 4.4 g of NH3 for conventional farms, 3.5 to 4.4 g of NH3 for organic farms, and 3.4 to 3.9 g of NH3 for grazing farms. For all farm types, storage and land application are the main sources of NH3 emissions from manure. In general, solid manures have higher emission intensities due to higher pH during storage (pH = 7.4 for liquid, 7.8 for slurry, and 8.5 for solid manure) and lower infiltration rates after land application when compared with slurry and liquid manures. The most effective management practices to reduce NH3 emissions from manure systems are combining solid-liquid separation with manure injection (up to 49% reduction in NH3 emissions), followed by injection alone, and reducing crude protein in the dairy ration, especially in organic and grazing farms that have grazing and forages as the main component of the dairy ration. This study also shows that the intensity of NH3 emissions from manure depends significantly on the functional unit and presents results per manure excreted, total solids in excreted manure, animal units, and fat- and protein-corrected milk.

Biochar from animal manure: A critical assessment on technical feasibility, economic viability, and ecological impact

AbstractAnimal manure has been used to manage soil fertility since the dawn of agriculture. It provides plant nutrients and improves soil fertility. In the last decades, animal husbandry has been significantly expanded globally. Its economics were optimized via the (international) trade of feed, resulting in a surplus of animal manure in areas with intensive livestock farming. Potentially toxic elements (PTEs), pathogenic microorganisms, antibiotic residues, biocides, and other micropollutants in manure threaten animal, human, and environmental health. Hence, manure application in crop fields is increasingly restricted, especially in hotspot regions with intensive livestock activities. Furthermore, ammonia volatilization and greenhouse gas (GHG) emissions during manure storage, field application, and decomposition contribute to air pollution and climate change. Conventional manure management scenarios such as composting and anaerobic digestion partially improve the system but cannot guarantee to eliminate sanitary and contamination risks and only marginally reducing its climate burden. Hence, this review discusses the potential of pyrolysis, the thermochemical conversion under oxygen‐limited conditions as an alternative treatment for animal manure providing energy and biochar. Manure pyrolysis reduces the bioavailability of PTEs, eliminates pathogenic microorganisms and organic micropollutants, and reduces GHG emissions. Pyrolysis also results in the loss of nitrogen, which can be minimized by pretreatment, that is, after removing soluble nitrogen fraction of manure, for example, by digestion and stripping of ammonia–nitrogen or liquid–solid separation. However, conclusions on the effect of manure pyrolysis on crop yield and fertilization efficiencies are hampered by a lack of nutrient mass balances based on livestock unit equivalent comparisons of manure and manure biochar applications. Hence, it is essential to design and conduct experiments in more practically relevant scenarios and depict the observations based on the amount of manure used to produce a certain amount of biochar.

An investigation of submarine groundwater discharge and related fluxes in parts of the southeast coast of India: Combined radon and nutrients mass balance approach

An investigation of submarine groundwater discharge and related fluxes in parts of the southeast coast of India: Combined radon and nutrients mass balance approach

Key nitrogen and phosphorus performance indicators derived from farm-gate mass balances on dairies

Efficient management of N and P on dairy farms is critical for farm profitability and environmental stewardship. Annual farm-gate nutrient mass balance (NMB) assessments can be used to determine the nutrient-use efficiency of farms, set efficiency targets, and monitor the effect of management changes with minimal inputs required. In New York, feasible N and P balances have been developed as benchmarks for dairy farm NMB, alongside key performance indicators (KPI) that serve as predictors for high NMB. Here, 3 yr of NMB data from 47 farms were used to evaluate the main drivers of N and P balances and identify additional KPI. From the 141 farm records, 26% met both the feasible N balances per hectare and per megagram of milk produced. For P, 53% of the records met both benchmarks. Imports, rather than exports, drove NMB primarily by feed and fertilizer purchases, consistent with earlier findings. Linear regression analysis showed that a selection of KPI currently used, particularly animal density, nutrient-use efficiency, and the amount of home-grown feed, explained a large portion of variation in NMB. Heifer-to-cow ratio and the relative proportion of various forage crops may provide further insight into the drivers of feed and fertilizer imports and ultimately farm-gate NMB. This study provides avenues toward a better assessment of whole-farm nutrient management and means for farms to communicate progress to stakeholders and consumers.

Retraction Note: Nutrient mass balance of a large riverine reservoir in the context of water residence time variability.

Retraction Note: Nutrient mass balance of a large riverine reservoir in the context of water residence time variability.

Evaluation of the effects of wood-sourced biochar as a feedlot pen surface amendment on manure nutrient capture.

Feedstuffs utilized in U.S. feedlot finishing rations incorporate high concentrations of N and P, with less than 15% of fed N and P retained by the animal. The remaining N and P are excreted in the manure, where the opportunity for manure N loss via ammonia (NH3) volatilization from the feedlot pen surface is a risk to the environment and lowers the value of manure as a fertilizer. Two nutrient mass balance experiments were conducted during the winter and summer seasons to evaluate the effects of spreading unprocessed Eastern red cedar biochar onto the feedlot pen surface on manure nutrient capture and cattle performance. A 186-d feedlot finishing experiment was conducted from December to June (WINTER) and a subsequent 153-d finishing experiment was conducted from June to November (SUMMER). The WINTER experiment evaluated three treatments (5 pens per treatment; 10 steers per pen), including biochar spread on pen surface during the feeding period (1.40 kg biochar/m2; 17.6 m2/steer soil surface of the pen), hydrated lime spread on pen surface at end of feeding period (1.75 kg/m2) and control (no treatment applied). The SUMMER experiment evaluated biochar treatment (1.40 kg biochar/m2; 5 pens per treatment; 8 steers per pen; and 22 m2/steer soil surface of the pen) against control. There were no differences in N and P intake, retention, or excretion (P ≥ 0.38) between WINTER treatments. Steer performance (P ≥ 0.10) and carcass characteristics (P ≥ 0.50) were not impacted by pen treatment in WINTER. Nitrogen and P intake and excretion (P ≥ 0.35) were not different between treatments in SUMMER and retention of N and P was significantly greater for the biochar treatment (P ≤0.04) due to greater ADG (P = 0.05). There was no difference in DMI (P = 0.48) in SUMMER, steers on biochar pen treatment had heavier HCW (P = 0.05) and greater ADG, resulting in a tendency for greater feed efficiency (P = 0.08). In both experiments, biochar addition to the pen surface tended (P = 0.07) to increase manure N as a percent of manure DM, but this increase in N concentration did not impact kg of N removed from the feedlot pens (P ≥ 0.15) or N losses (P ≥ 0.68). The addition of red cedar biochar to the feedlot pen surface did not increase manure nutrient capture of N or P and did not reduce N losses associated with soil-based feedlot pens.

Nutrient mass balance for improved traditional coastal shrimp ponds of Bangladesh

Three category of tidal water exchange system depended ponds have been selected for the experiments which were canal connected, river connected and pond connected pond. Present study was undertaken to estimate the nutrient balance into the coastal shrimp ponds of Cox’s Bazar coastal region. It was found that mineral fertilizer, organic fertilizer, feed, fish and shrimp fry, water supply and rainfall are the nutrient input and crop product (fish, shrimp, crab), crop residues, denitrification, water discharge and sedimentation are the nutrient output for shrimp pond. Estimation of overall nutrient mass balance per hector basis indicates that fertilizer was the highest nutrient contributor as followed by the supplementary feed into the experimental ponds. The total inputs of nitrogen and phosphorus were 78.87 kgha-1cycle-1 and 42.85 kgha-1cycle-1 respectively. Among the input only 34.6 % of nitrogen and 7.20 % of phosphorus were removed as harvested shrimp, fish and crab. A large portion, 38.58 % of N and 91.38 % of P were remained in the sediments and unaccounted for. From the investigation on nutrient balance for 3 categories of shrimp ponds it was concluded that Reuse water or pond connected pond system for coastal shrimp ponds should not be practiced anywhere in Bangladesh
 

210 Evaluation of the Effects of Wood-Sourced Biochar as a Feedlot Pen Surface Amendment on Manure Nutrient Capture

Abstract Two nutrient mass balance experiments were conducted during winter and summer seasons to evaluate the effects of spreading unprocessed Eastern red cedar biochar onto the feedlot pen surface on manure nutrient capture and cattle performance. A 186-d feedlot finishing experiment was conducted from December to June (WINTER) and a subsequent 153-d feedlot finishing experiment was conducted from June to November (SUMMER). The WINTER experiment evaluated 3 treatments, including biochar spread to the pen surface during the feeding period (24 kg/steer; 10 steers per pen), hydrated lime spread to pen surface at end of feeding period (31 kg/steer), and control (no treatment applied). The SUMMER experiment evaluated biochar treatment (31 kg/steer; 8 steers per pen) against control. There was no difference in N and P intake, retention, or excretion (P ≥ 0.38) between WINTER treatments. Steer performance (P ≥ 0.10) and carcass characteristics (P ≥ 0.50) were not impacted by pen treatment in WINTER. Nitrogen and P intake and excretion (P ≥ 0.35) were similar between treatments in SUMMER and retention of N and P was significantly greater for the biochar treatment (P = 0.04) due to greater ADG. There was no difference in DMI (P = 0.48) in SUMMER, steers on biochar pen treatment had heavier HCW and increased ADG (P = 0.05), resulting in improved feed efficiency (P = 0.08). In both experiments, biochar addition to the pen surface tended (P = 0.07) to increase manure N as a percent of manure DM, but this increase in N concentration did not impact kg of N removed from the feedlot pens (P ≥ 0.15) or N losses (P ≥ 0.68). The addition of unprocessed red cedar biochar to the feedlot pen surface did not improve manure nutrient capture of N or P and did not reduce N losses associated with soil-based feedlot pens.

A dynamic nutrient mass balance model for optimizing waste treatment in RAS and associated IMTA system

The combination of a Recirculation Aquaculture System (RAS) and Integrated Multi-trophic Aquaculture (IMTA) aims to optimize the utilization of nutrient input by recycling aquaculture wastes through use as food resources for co-cultured species. The coupling of RAS and IMTA also allows the development of new aquaculture products, potentially increasing economic return. A dynamic nutrient mass balance model was developed for a seawater-based RAS system with a hypothetical IMTA component. The model incorporated a three-dimensional trophic food web (Atlantic salmon, Ulva lactuca and an invertebrate grazing species) alongside traditional mechanical and biological (nitrification) filtration processes. The model simulated different waste treatment methods using biological and mechanical filtration only and further incorporating macroalgae filtration. Simulations showed that RAS in combination with macroalgae IMTA could reduce dissolved inorganic nitrogen (DIN) by 66% and dissolved inorganic phosphorus (DIP) by 31% compared with just RAS biological filtration. Using an optimal harvesting strategy, DIN and DIP waste removal rose to 94% and 45% respectively, and an increase in by-products biomass of 41%. The dynamic nutrient mass balance model provides a quantitative tool to better understand the fate of nutrients, and to optimize the design of the system. Although the commercial-scale development of this type of aquaculture system will depend on feasibility and profitability, the concept of combining RAS and IMTA provides important potential for sustainable aquaculture in the future.

Predicting nitrogen and phosphorus balance in beef open lots

Our objectives were to evaluate nutrient mass balance in feedlots and to determine climactic and management factors affecting nutrient recovery in manure, and to understand sources of variability. Data from 15 summer- and winter-feeding periods at the Eastern Nebraska Research and Education Center feedlot, including 416 independent pen measurements, were summarized for nutrient mass balance and used to determine sources of variability affecting nitrogen (N) and phosphorus (P) using linear regression. The quantity of manure N collected was less ( P < 0.01) for summer- than winter-feeding periods, averaging 54 (CV = 50%) and 92 (CV = 33%) g/steer daily, respectively, compared with the ASABE (2014) standard of 88.5 g/steer daily. Likewise, the quantity of manure P collected for summer was less than winter ( P < 0.01), averaging 17 (CV = 55%) and 28 (CV = 45%) g/steer daily, respectively, compared with the ASABE standard of 37 g/steer daily ( ASABE, 2014 ). The season (summer vs. winter) cattle were fed affected manure nutrient retention and loss. Additionally, feed N intake partially predicted manure N (R 2 = 0.22, P < 0.01) and N lost (R 2 = 0.54, P < 0.01) in the summer, but offered less explanation during winter-feeding periods. Manure OM was a moderately strong predictor of manure N for feeding periods in both summer (R 2 = 0.85, P < 0.01) and winter (R 2 = 0.70, P < 0.01). Our analysis identifies challenges associated with planning based on standard methods for estimating manure characteristics. Nutrient composition based on seasonal specific manure analysis is critical. If not available, timing of seasonal feeding period and dietary nutrient concentration may assist with adjusting standardized estimates.

Addressing Nutrient Depletion in Tanzanian Sisal Fiber Production Using Life Cycle Assessment and Circular Economy Principles, with Bioenergy Co-Production

Nutrient depletion in Tanzanian sisal production has led to yield decreases over time. We use nutrient mass balances embedded within a life cycle assessment to quantify the extent of nutrient depletion for different production systems, and then used circular economy principles to identify potential cosubstrates from within the Tanzanian economy to anaerobically digest with sisal wastes. The biogas produced was then used to generate bioelectricity and the digestate residual can be used as a fertilizer to address the nutrient depletion. Life cycle assessment was used in a gate-to-gate assessment of the anaerobic digestion options with different cosubstrates. If no current beneficial use of the cosubstrate was assumed, then beef manure and marine fish processing waste were the best cosubstrates. If agricultural wastes were assumed to have a current beneficial use as fertilizer, then marine fish processing waste and human urine were the best cosubstrates. The largest reduction in environmental impacts resulted from bioelectricity replacing electricity from fossil fuels in the national electricity grid and improved onsite waste management practices. There is significant potential to revitalize Tanzanian sisal production by applying circular economy principles to sisal waste management to address soil nutrient depletion and co-produce bioenergy.

How will the next-generation of sensor-based decision systems look in the context of intelligent agriculture? A case-study

The development of cost-effective, digitally based decision support systems is a key challenge in the optimization of farm management. Yet, the majority of sensor-based decision tools which support fertiliser management have relied on simplistic mechanistic frameworks normally informed by a single sensor. This study used a 20-year nitrogen (N) experiment on winter wheat ( Triticum aestivum L.) to test a range of approaches for N decision support systems, including commercial sensor-based options and a novel, multivariate, data-driven approach. The latter was based on a non-mechanistic framework in which various digital variables were trained directly against optimum N application rates using machine learning. It was hypothesized that such a method would enhance our ability to handle system complexity, resulting in higher accuracy for the decision, as compared to current farm management or to available sensor-based options, both of which are normally underpinned by mechanistic methods. Results showed that the proposed approach was able to predict the optimal N rate with an RMSE of 16.5 kg N ha –1 (R 2 = 0.79). This method was also the only one that was statistically superior (p < 0.05) to the control scenario (the application of the historical average optimal N rate; RMSE =38.0 kg N ha –1 ). This proposed approach used a multivariate digital input including a spectral vegetation index (normalized difference vegetation index, NDVI), weather and soil moisture data and information from on-farm experimentation (the in-situ N response using a ‘N-rich’ strip) to guide the decision. When similar data input and modelling techniques were used to predict yield potential to then derive an N recommendation through a mechanistic decision framework – a nutrient mass balance – the recommendation error (RMSE) increased to 26.0 kg N ha −1 (R 2 = 0.51). In summary, by forcing the input data through the mechanistic framework, the decision error increased. This study challenges the ideas that farm decisions should follow pre-established agronomic mechanistic frameworks and that digital technologies must necessarily be used to estimate specific crop and soil attributes so as to enable deployment of current decision systems at scale and site-specifically.

A century of change: Reconstructing the biogeochemical history of Hubbard Brook

AbstractEcosystems constantly adjust to altered biogeochemical inputs, changes in vegetation and climate, and previous physical disturbances. Such disturbances create overlapping ‘biogeochemical legacies’ affecting modern nutrient mass balances. To understand how ‘legacies’ affected watershed‐ecosystem (WEC) biogeochemistry during five decades of studies within the Hubbard Brook Experimental Forest (HBEF), we extended biogeochemical trends and hydrologic fluxes back to 1900 to provide an historical framework for our long‐term studies. This reconstruction showed acid rain peaking at HBEF in the late 1960s‐early 1970s near the beginning of the Hubbard Brook Ecosystem Study (HBES). The long‐term, parabolic arc in acid inputs to HBEF generated a corresponding arc in the ionic strength of stream water, with acid inputs generating increased losses of H+ and soil base cations between 1963 and 1969 and then decreased losses after 1970. Nitrate release after disturbance is coupled with previous N‐deposition and storage, biological uptake, and hydrology. Sulfur was stored in soils from decades of acid deposition but is now nearly depleted. Total exports of base cations from the soil exchange pool represent one of the largest disturbances to forest and associated aquatic ecosystems at the HBEF since the Pleistocene glaciation. Because precipitation inputs of base cations currently are extremely small, such losses can only be replaced through the slow process of mineral weathering. Thus, the chemistry of stream water is extremely dilute and likely to become even more dilute than pre‐Industrial Revolution estimates. The importance of calculating chemical fluxes is clearly demonstrated in reconstruction of acid rain impacts during the pre‐measurement period. The aggregate impact of acid rain on WEC exports is far larger than historical forest harvest effects, and even larger than the most severe deforestation experiment (Watershed 2) at HBEF. A century of acid rain had a calcium stripping impact equivalent to two W2 experiments involving complete deforestation and herbicide applications.

High-Frequency Monitoring Reveals Multiple Frequencies of Nitrogen and Carbon Mass Balance Dynamics in a Headwater Stream

The uptake of aquatic nutrients can represent a major pathway for their removal from river ecosystems and is a key control on nitrogen and carbon export from watersheds. Our understanding of temporal variability in nutrient mass balance is incomplete as conventional methods for estimating uptake rates are suited to low-frequency analysis. Here, we utilised hourly streamflow, nitrate (NO3--N) and dissolved organic carbon (DOC) to generate near-continuous estimates of nutrient uptake along a 1 km reach in a headwater catchment with a history of agricultural activity. We identified variability in nutrient mass balance at multiple frequencies. Over seasonal timescales, a shift from nitrate release during spring to uptake during autumn was apparent. In contrast, consistent uptake of DOC was observed across the whole monitoring period (i.e., spring—autumn). Both DOC and nitrate uptake were related significantly to environmental variables (river discharge) and antecedent discharge conditions. DOC:nitrate stoichiometry appeared to be a key control on nitrate uptake rates, yet this coupling weakened from summer to autumn as DOC became more abundant and physical controls become more important. Daily cycles in nutrient uptake were evident and at times the investigated reach acted as a net sink of DOC during the day and a source at night. Short-term impacts of storm events on uptake rates varied seasonally but no consistent changes were observed between pre- and post-event conditions, suggesting aquatic communities were resilient to short-term flow disturbances. For the duration of our study, the reach acted as net sink from the water for DOC (−1.7% of upstream flux) and a net source for nitrate (+2.6%). Even during autumn, when uptake was greatest, mass removal represented &amp;lt;3% of nitrate exported downstream. Our results facilitate new insights into multi-timescale patterns and drivers of stream ecosystem processes, which are essential for developing effective catchment-scale management strategies.