nitrate-N Concentrations Research Articles

The interactive effects of soil disturbance and residue quality on soil nitrogen mineralisation in a tropical sandy soil

Soil conservation practices, such as reduced and no tillage, have been found to enhance soil nitrogen (N) sequestration through decreasing the rate of N mineralisation of added organic materials. Nitrogen mineralisation is not only affected by tillage, but also by the quality (chemical composition) of the organic residues. This study evaluated the interaction of residue quality and soil disturbance on N mineralisation in a sandy soil. A 112-day incubation experiment was conducted with two levels of soil disturbance (undisturbed and disturbed conditions) and five plant residue amendments of contrasting quality. The contrasting quality (N, lignin (L), and polyphenols (Pp)) (in g kg–1) amendments follow: (i) unamended; (ii) Sesbania grandiflora (N 44, L 173, Pp 9.2); (iii) Indigofera hirsuta (N 41, L 177, Pp 30); (iv) Dipterocarpus tuberculatus (N 8.2, L 203, Pp 71); and (v) Eucalyptus camaldulensis (N 9.7, L 126, Pp 110). Residues (ii) and (iii) were fresh legume leaves, while (iv) and (v) were non-legume leaf litter. Disturbance only significantly increased N mineralisation rates in the legume-residue treated soils (increases of 18.8% for S. grandiflora and 27.1% for I. hirsuta) during the early stage of decomposition (first 14 days). In the legume treatment, disturbance significantly increased the ammonification, but decreased nitrification in soil relative to undisturbed soils. The difference in patterns of ammonification and nitrification was more pronounced in the early than in the later period of decomposition. This indicated an inhibitory effect of soil disturbance on nitrification, which was particularly pronounced in the legume-treated soils. The Pp content of residues was the major quality parameter regulating the soil ammonium-N and nitrate-N concentrations. Minimum soil disturbance should be adopted under legume soil organic amendment so that both ammonification and nitrification components of N mineralisation process can occur normally, and nitrate-loving crops can take up N in the form of nitrate-N which will enhance their yields. Moreover, undisturbed conditions under legume organic amendments reduced N mineralisation, resulting in enhancing soil N sequestration.

Tile-Drain and Denitrification Bioreactor Water Chemistry for a Soybean (<i>Glycine max</i>(L.) Merr.)-Corn (<i>Zea mays</i> L.) Rotation in East-Central Missouri (USA)

Nitrogen transport from agriculture production fields raises the specter of environmental degradation of freshwater resources. Our objectives were to document and evaluate nitrate-N, ammonium-N, phosphorus and other nutrients emanating from a 40-ha controlled subsurface irrigation drainage technology coupled in series with a denitrification bioreactor. The intent of the denitrification bioreactor is to create an environment for anoxic microbial populations to support denitrification. We monitored the tile-drainage effluent and denitrification bioreactor water chemistry under a corn-soybean rotation to estimate the nutrient concentrations and the competence of the denitrification bioreactor to foster denitrification. Nitrate-N bearing tile drainage effluents ranged from less than 1.5 to 109 mg NO3- -N/L, with the nitrate concentration differences attributed primarily to the: 1) timing of nitrogen fertilization for corn, 2) soil mineralization and residue decomposition, and 3) intense rainfall events. The denitrification bioreactor was highly effective in reducing drainage water nitrate-N concentrations providing the rate of water flow through the denitrification bioreactor permitted sufficient time for equilibrium to be attained for the nitrate reduction reactions. The nitrate-N concentrations entering the denitrification bioreactor ranged from 0.4 to 103 mg NO3- -N/L in 2018, whereas the outlet nitrate concentrations typically ranged from 0.3 to 5.2 mg NO3- -N/L in 2018. Nitrate tile-drainage effluent concentrations in 2019 were marginal, given soybeans obtain nitrogen from biological nitrogen fixation. Nutrient uptake by corn reduced the soil nitrate leaching pool and created nitrogen-bearing biomass, features important for formulating best management practices.

Carbon and nitrogen fractions in soil during maize growth under long-term fertilizer management practices to maize-wheat cropping

A field experiment was conducted to study the effect of long-term fertilizer management (viz. control, 100% N, 100% NP, 100% NPK and 100% NPK+FYM) on the carbon (C) and nitrogen (N) fractions in soils under maize-wheat cropping. Soil samples were collected from on-going experiment (started in 1971) during maize growing season in kharif 2011 to discern long-term effect of field treatments on changes in different pools of C and N viz. soil organic C (SOC), water soluble C (WSC) and KMnO₄ oxidizable C (KMnO₄-C) and ammonical-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) content. Soil samples were analyzed after 1, 3, 5, 7 and 9 weeks interval during maize growth period. The SOC, NO₃⁻-N and NH₄⁺-N concentration increased significantly with combined application of NPK+FYM as compared to the control. The concentration of SOC increased after 3 weeks, and was reached the highest at harvesting. However, the WSC and KMnO₄-C concentration increased up to 5ᵗʰ week after sowing and it decreased afterwards. The NO₃⁻-N and NH₄⁺-N concentration decreased with increased maize growth stage, and decreased to the lowest value at harvesting. The dry matter yield of maize at maturity correlated well with SOC, WSC, KMnO₄-C, NH₄⁺-N and NO₃⁻-N concentration. Crop yield of maize and N uptake increased with NPK+FYM application at all growth stages.

Comparison of three measurement models of soil nitrate-nitrogen based on ion-selective electrodes

Ion-selective electrode (ISE) is a quick and low-cost method of soil nitrate nitrogen (N) detection. The measurement models of soil nitrate-N based on ISEs includes the linear regression model, multiple linear regression model and BP neural network model, and so on. Three models were analyzed in theory, measurement experiments of validation samples and soil nitrate-N concentrations were carried out in this study, and the measurement accuracies of the three models were compared. The results showed that, in the measurement experiments of validation samples and soil nitrate-N concentrations, BP neural network model had the highest accuracy (the average relative errors between results of the BP neural network model and the reference values were 5.07% and 8.81%, respectively) among the three models, multiple linear regression model had the second highest accuracy (the average relative errors between results of the multiple linear regression model and the reference values were 7.70% and 10.51%, respectively), linear regression model couldn’t exclude the interference of chloride ions so that it had the lowest accuracy (the average relative errors between results of the linear regression model and the reference values were 11.16% and 12.28%, respectively) among the three models. The BP neural network model can effectively restrain the interference of chloride ions, and it has a high accuracy for the measurement of soil nitrate-N concentration, so that the BP neural network model can be used to measure soil nitrate-N concentration accurately. Keywords: ion-selective electrode, soil nitrate-nitrogen, measurement model, accuracy DOI: 10.25165/j.ijabe.20201301.3599 Citation: Du S F, Pan Q, Xu Y, Cao S S. Comparison of three measurement models of soil nitrate-nitrogen based on ion-selective electrodes. Int J Agric & Biol Eng, 2020; 13(1): 211–216.

Balancing indicators for sustainable intensification of crop production at field and river basin levels

Adequate tools for evaluating sustainable intensification (SI) of crop production for agro-hydrological system are not readily available. Building on existing concepts, we propose a framework for evaluating SI at the field and river basin levels. The framework serves as a means to assess and visualise SI indicator values, including yield, water-use efficiency and nitrogen-use efficiency (NUE), alongside water and nitrogen surpluses and their effects on water quantity and quality. To demonstrate the SI assessment framework, we used empirical data for both the field level (the Static Fertilization Experiment at Bad Lauchstädt) and the river basin level (the Selke basin, 463 km2) in central Germany. Crop yield and resource use efficiency varied considerably from 1980 to 2014, but without clear trends. NUE frequently fell below the desirable range (<50%), exposing the environment to a large N surplus (>80 kg N ha−1). For the catchment as a whole, the average nitrate-N concentration (3.6 mg L−1) was slightly higher than the threshold of 2.5 mg L−1 nitrate-N in surface water. However, weather and climate-related patterns, due to their effects on transport capacity and dilution, influenced water quantity and quality indicators more than agronomic practices. To achieve SI of crop production in the Selke basin, irrigation and soil moisture management are required to reduce yield variability and reduce N surpluses at field level. In addition, optimum application of fertiliser and manure could help to reduce the nitrate-N concentration below the set water quality standards in the Selke basin. In this way, there is scope for increase in yields and resource use efficiencies, and thus potential reduction of environmental impacts at basin level. We conclude that the framework is useful for assessing sustainable production, by simultaneously considering objectives related to crop production, resource-use efficiency and environmental quality, at both field and river basin levels.

Nitrogen losses from two contrasting agricultural catchments in Norway.

Nitrogen (N) losses from agricultural areas, especially into drinking water and marine environments, attract substantial attention from governments and scientists. This study analysed nitrogen loss from runoff water using long-term monitoring data (1994–2016) from the Skuterud catchment in southeastern Norway and the Naurstad catchment in northern Norway. Precipitation and runoff were lower in the Skuterud catchment than in the Naurstad catchment. However, in the Skuterud catchment, the annual total N (TN) losses ranged from 27 to 68 kg hm−2. High precipitation (1247 mm) in the Naurstad catchment resulted in substantial runoff water (1108 mm) but relatively low total TN losses ranged from 17 to 35 kg hm−2. The proportion of nitrate losses to TN loss was 51–86% and 28–50% in the Skuterud and Naurstad catchments, respectively. Furthermore, the monthly average TN concentrations and nitrate losses had two peaks, in April–May and October, in the Skuterud catchment; however, no significant fluctuations were found in the Naurstad catchment. The contributions of N and runoff water to TN and nitrate losses were calculated using multiple linear regression, and runoff water was the major contributor to TN loss in both catchments. Runoff water was the main factor in the Skuterud catchment, and the nitrate-N concentration was the main factor in the Naurstad catchment.

Under temperate climate, the conversion of grassland to arable land affects soil nutrient stocks and bacteria in a short term

Projected population growth and climate change will make it inevitable to convert neglected and marginal land into productive arable land. We investigate the influence of agricultural management practices on nutrient stocks and soil functions during the conversion of former extensively used grassland to arable land. Effects of grassland removal, tillage, intercropping with faba bean (Vicia faba) and its later incorporation were studied with respect to soil properties and bacterial community structure. Therefore, composite samples were collected with a core sampler from the topsoil (0–20 cm) in (a) the initial grassland, (b) the transitional phase during the vegetation period of V. faba, (c) after ploughing the legume in, and (d) untreated controls. In all samples, nitrate-N, ammonium-N, dissolved organic carbon (DOC) and total nitrogen bound (TNb) were analyzed and comparisons of the bacterial community structure after 16S-amplicon sequencing were performed to assess soil functions. Mineralization after grassland conversion followed by the biological nitrogen fixation of broad beans enhanced the nitrate-N content in bulk soil from 4 to almost 50 μg N g−1dw. Bacterial community structure on phylum level in bulk soil was dominated by Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Bacteroidetes and remained almost stable. However, alpha and beta-diversity analysis revealed a change of the bacterial composition at the final state of the conversion. This change was primarily driven by increasing abundances of the genera Massilia and Lysobacter, both members of the Proteobacteria, after the decay of the leguminous plant residues. Furthermore, increasing abundances of the family Gaiellaceae and its genus Gaiella fostered this change and were related to the decreasing carbon to nitrogen ratio. In short, gentle management strategies could replace the input of mineral fertilizer with the aim to contribute to future sustainable and intensified production even on converted grassland.

The interactions between biochar and earthworms, and their influence on soil properties and clover growth: A 6-month mesocosm experiment

A six-month mesocosm experiment was conducted to investigate the joined effect of biochar and earthworms on soil properties and plant (white clover) growth in two contrasting soils – a dystric Cambisol and a sil-andic Andosol, both soils with pH-H2O < 6. Treatments were (i) biochar amendment (1% weight basis), (ii) a positive control (lime added at the liming equivalence of the biochar application), and (iii) a negative control (no amendment). Each treatment had two variants: with or without earthworms (Aporrectodea caliginosa). Soil chemical and biological properties were measured before the start of the experiment and after 6 months of incubation. Earthworms were associated with higher ammonium-N and nitrate-N concentrations, lower pH, higher fungi:bacteria ratio, higher abundance of Collembola, and higher clover biomass in mesocosms. The influence of biochar on plant productivity was overshadowed by earthworm activity, yet a significant positive effect of biochar on clover biomass was observed in the absence of earthworms; this effect was not related to the liming potential of biochar. Synergistic effects of biochar and earthworms were observed for increasing abundance of Collembola and soil fungal biomass. The interaction between biochar and earthworms was soil-type specific – for example, on their own, biochar and earthworms increased clover growth more in the Cambisol, while the positive synergistic effect of biochar and earthworms on soil biochemical processes and clover growth was more evident in the Andosol. Combined use of biochar and earthworms has good productivity potential for acidic soils, and can be part of sustainable soil management.

Monitoring wheat nitrogen requirement and top soil nitrate for nitrate residue controlling in drylands

Abstract Nitrogen (N) fertilizer application is an essential way to keep the high yielding crop production, but nitrate-N residue in agricultural soils has attracted wide attentions due to its various environmental effects. Understanding the yield formation and its relation to the N uptake and requirement are urgently needed to reduce the nitrate-N residue for plastic mulched wheat production in drylands. A three-year location-fixed field experiment with five N rates was carried out to test the grain yield formation and N use characteristics of wheat and soil nitrate-N response to no mulch (NM) and plastic film mulch (PM) cultivations. Obtained results showed that the PM promoted the wheat growth and had higher maximum grain yield and biomass at the similar N rate, compared to the NM. Although wheat took up much more N from the soils under the PM, its N requirement for 1000 kg grain formation (NR) showed no significant difference from that of the NM, and for management of N fertilization, the same NR can be used for both cultivations in dryland. Nitrate-N content in 0–20 cm top soil (SNC) was found lower under NM than that under PM, but nitrate-N residue in 0–100 cm soil (SNR) showed no significant difference between these two cultivations. The SNR was significantly and linearly correlated with the SNC under both cultivations, and thus the SNC is able to be used to predict the SNR. Therefore, the present work provides a feasible way or an idea to use the top soil nitrate content, wheat grain yield and its N requirement to optimize the N application rates and N fertilizer recommendation for wheat production and soil nitrate-N residue control in dryland.

Mitigating the risk of atrazine exposure: Identifying hot spots and hot times in surface waters across Nebraska, USA

Atrazine, one of the most widely used herbicides in the world, threatens human health along with terrestrial and aquatic biota. Recent reports have found atrazine in drinking water to be associated with increased birth defects and incidences of Non-Hodgkin's Lymphoma, with higher levels of significance from exposure to both atrazine and nitrate-N. The Midwest region of the United States, which includes Nebraska, is one of the leading regions for high nitrate-N concentrations and agrochemicals, including atrazine, in surface waters. Therefore, the objective of this study was to provide a case study for completing an environmental risk analysis for the potential exposure of atrazine and nitrate-N to ecosystems and humans through interaction with surface waters using two approaches: (1) Identify watersheds across Nebraska that were at risk for exceeding atrazine and nitrate-N maximum contaminant limits (MCLs) in surface water; and (2) Determine the specific times of year where risks were greatest. Factors were then analyzed using Geographic Information System (GIS) software to identify areas of high risk. Impairments for both nitrate-N and atrazine in the surface water were found predominately during the early growing season in the southeastern region of Nebraska, in watershed areas with the highest amount of corn production and annual precipitation. Further, the methodology developed in this study has the potential for application in regions with higher dependency on surface water to determine multiple agrochemical load influxes from upstream regions and evaluate other surface water contaminants during the same time periods.

Horizontal Well Test for Simulating the In Situ Remediation of Nitrate Contaminated Groundwater by Microbial Denitrification

An in situ horizontal well (IHW) fan-shaped test tank was constructed in the laboratory. And nitrate removal rates were analyzed under different hydraulic loads. When the initial concentration of groundwater nitrate-N was 25 mg/L and the hydraulic load increased from 0.78 to 3.90 m3/(m2 day), the results show that the nitrate-N concentration was less than 1.25 mg/L after the denitrification process stabilized. Additionally, the nitrate-N removal rate was over 95%. The concentration of nitrite-N was still below 1 mg/L, and the level of ammonia-N was between 0.5 and 1.00 mg/L. No increase in nitrite-N and ammonia-N concentration occurred during the test. The hydraulic conductivity of the medium in the horizontal well showed little variation, ranging from 34.09 to 31.64 m/day, indicating that there was no blockage caused by microbial growth in the IHW during the test. In addition, no ethanol was detected in the test tank except for the horizontal well, revealing that ethanol did not diffuse into the surrounding aquifer. Therefore, when the concentration of groundwater nitrate contamination is 25 mg/L, the hydraulic load under the IHW test tank condition is 3.90 m3/(m2 day). The IHW test tank had a stable and good biological denitrification effect, and it can provide certain reference significance for in situ remediation of nitrate-contaminated groundwater.

Interactive Effects of Water and Fertilizer on Yield, Soil Water and Nitrate Dynamics of Young Apple Tree in Semiarid Region of Northwest China

Exploring the interactive effect of water and fertilizer on yield, soil water and nitrate dynamics of young apple tree is of great importance to improve the management of irrigation and fertilization in the apple-growing region of semiarid northwest China. A two-year pot experiment was conducted in a mobile rainproof shelter of the water-saving irrigation experimental station in Northwest A&amp;F University, and the investigation evaluated the response of soil water and fertilizer migration, crop water productivity (CWP), irrigation water use efficiency (IWUE), partial factor productivity (PFP) of young apple tree to different water and fertilizer regimes (four levels of soil water: 75%–85%, 65%–75%, 55%–65% and 45%–55% of field capacity, designated W1, W2, W3 and W4, respectively; three levels of N-P2O5-K2O fertilizer, 30-30-10, 20-20-10 and 10-10-10 g plant−1, designated F1, F2 and F3, respectively). Results showed that F1W1, F2W1 and F3W1 had the highest average soil water content at 0~90 cm compared with the other treatments. When fertilizer level was fixed, the average soil water content was gradually increased with increasing irrigation amount. For W1, W2, W3 and W4, high levels of water content were mainly distributed at 50~80 cm, 40~70 cm, 30~50 cm and 10~30 cm, respectively. There was no significant difference in soil water content at all fertilizer treatments. However, F1 and F2 significantly increased soil nitrate-N content by 146.3%~246.4% and 75.3%~151.5% compared with F3. The highest yield appeared at F1W1 treatment, but there was little difference between F1W1 and F2W2 treatment. F2W2 treatment decreased yield by 7.5%, but increased IWUE by 11.2% compared with F1W1 treatment. Meanwhile, the highest CWP appeared at F2W2 treatment in the two years. Thus, F2W2 treatment (soil moisture was controlled in 65–75% of field capacity, N-P2O5-K2O were controlled at 20-20-10 g·tree−1) reached the best water and fertilizer coupling mode and it was the optimum combinations of water and fertilizer saving.

Prediction of nitrate accumulation and leaching beneath groundwater irrigated corn fields in the Upper Platte basin under a future climate scenario

Understanding the impacts of future climate change on soil hydrological processes and solute transport is crucial to develop appropriate strategies to minimize the adverse impacts of agricultural activities on groundwater quality. To evaluate the direct effects of climate change on the transport and accumulation of nitrate-N, we developed an integrated modeling framework combining climatic change, nitrate-N infiltration in the unsaturated zone, and groundwater level fluctuations. The study was based on a center-pivot irrigated corn field at the Nebraska Management Systems Evaluation Area (MSEA) site. Future groundwater recharge (GR) and actual evapotranspiration (ETa) rates were predicted via an inverse vadose zone modeling approach by using climatic data generated by the Weather Research and Forecasting (WRF) climate model under the RCP 8.5 scenario, which was downscaled from the global CCSM4 model to a resolution of 24 km by 24 km. A groundwater flow model was first calibrated on the basis of historical groundwater table measurements and then applied to predict the future groundwater table in 2057–2060. Finally, the predicted future GR rate, ETa rate, and groundwater level, together with future precipitation data from the WRF climate model, were used in a three-dimensional (3D) model to predict nitrate-N concentrations in the subsurface (saturated and unsaturated parts) from 2057 to 2060. The future GR was predicted to decrease in the study area, as compared with the average GR data from the literature. Correspondingly, the groundwater level was predicted to decrease (30 to 60 cm) over the 5 years of simulation in the future. The nitrate-N mass in the simulation domain was predicted to increase but at a slower rate than in the past. Sensitivity analysis indicated that the accumulation of nitrate-N is sensitive to groundwater table elevation changes and irrigation rates.

Growth and nutrient and nitrate accumulation of lettuce under different regimes of nitrogen fertilization

For plant growth and composition, the effects of fertilizers including blood meal (BLO), cottonseed meal (CSM), dehydrated cow manure (COW), and urea (UREA) factored with lettuce (Lactuca sativa L.) of different morphological phenotypes including iceberg, romaine, loose head, and loose leaf were studied in a greenhouse. Lettuce growth increased with increasing nitrogen (N) applications from 0 to 800 mg N/pot (kg), but the top application of BLO, CSM, or UREA suppressed yields. Lettuce grown with BLO, CSM, or UREA had higher concentrations of N than with COW. Nitrate-N concentration in leaves of all varieties exceeded some standards at high application of organic fertilizer or urea except for COW. In general, increasing N application resulted in higher concentration of NH4-N in lettuce with increases in applications of fertilizers. Organic fertilizers and urea were equally effective in supporting growth and affecting nutrient accumulation in lettuce if sufficient N was supplied.

Characterising the soil ecosystem phenotype associated with relatively low nitrate-N concentrations

In agricultural systems, elevated concentrations of soil nitrate (NO3−-N) pose an environmental risk. Nitrate is highly mobile, and can be transported through soil into aquatic ecosystems resulting in eutrophication. Furthermore, under anaerobic conditions nitrate-N can undergo microbial denitrification. This latter process is a significant source of N2O, a potent greenhouse gas. The goal of this research is to determine (1) if there are soils, from under live-stock grazed (pastoral) land use, that contain lower than expected (anomalous) nitrate-N per total N content, and (2) characterise the phenotypes of these soils based on physicochemical and microbial attributes. Using a set of 50 soils that have been fully characterised based on edaphic properties, and for which GeoChip environmental functional microarray data is available, the ratio of nitrate-N to total N, an expected value was determined for the 50 soils. Using a ‘leave one out’ prediction strategy, soils anomalously high (n = 13) or low (n = 14) in nitrate-N were determined. The phenotypes of these two groups were characterised based on the edaphic and molecular (functional gene and associated phylogenetic association) data. Significant (permutation p < 0.05) variation in mid-level carbon (C) and nitrogen (N) cycling gene categories were evident between groups of soil with relatively low or high nitrate N levels. Low nitrate-N soils were characterised by increased abundance of genes involved in reductive acetyl CoA pathway, acetyl-CoA carboxylase, glyoxylate cycling, starch and chitin degradation, and nitrogen reduction (denitrification). Furthermore, the increased occurrence of these metabolic pathways was associated with increased abundance of Classes of Firmicute, Actinobacteria, and some groups of Proteobacteria and fungal taxa. In the group of soils with anomalously low nitrate-N, changes in the function and composition of the microbial community occurred with increased ratios of C:P, C:N, and C:S., and lower sulphate-S contents. These results indicate that a general widening of the stoichiometry of C with other nutrients maybe an important driver, or associative factor, linked with changes in the microbial community function. Opportunities to shift soil ecosystems to a low nitrate-N phenotype may be best achieved through alteration of C inputs to soil or changing C-cycling ecophysiology. This maybe achieved through selection of plants for specific (quantitative and qualitative) rhizosphere C allocation profiles.

Evaluation of Sodium Omadine for Short-Term Preservation of Nitrate-N and Orthophosphate in Water Samples

Maintaining nitrate-N and orthophosphate (dissolved reactive phosphorus) concentrations in a water sample over time is critical for water quality research. This study investigated the ability of current preservation methods to maintain nitrate-N and orthophosphate concentrations in environmental water samples over a period of up to 14 days. The United States Environmental Protection Agency (US EPA) currently recommends adding sulfuric acid for nitrate-N and filtering the water sample at the time of collection for orthophosphate. This study compared these recommended methods to baseline control concentrations in subsurface tile drainage water, pond water, and stream water. In addition, sodium omadine was tested as a potential alternative preservative. Across the three sources of water tested, sulfuric acid was the most reliable preservation method for both nitrate-N and orthophosphate, with percent changes from the baseline concentrations on Day 14 ranging from 2.30–3.27% for nitrate-N and 1.94–8.48% for orthophosphate. The control samples also maintained the baseline concentrations quite well, with percent changes on Day 14 ranging from 0.09–6.68% for nitrate-N and 2.63–11.87% for orthophosphate. When sodium omadine was added to the water samples, the nitrate-N concentrations had percent changes of 0.13–6.10% from the baseline concentration on Day 14. In contrast, sodium omadine was less effective for maintaining orthophosphate concentrations, with percent changes of 8.86–13.06% from the baseline concentration on Day 14. However, there were no significantly different orthophosphate concentrations when sodium omadine was added to stream water, showing a promising alternative for this scenario. Depending on the objective, researchers may need to consider the source water and length of storage of water samples to determine what, if any, preservative is necessary.

The effect of forestry management activities on stream water quality within a headwater plantation Pinus radiata forest

Many long-term forestry water quality studies focus on the impact of the harvesting phase of forestry operations. As a result, the water quality impacts of other activities such as forest (re)planting, thinning and fertilising are less well understood. Here we report the results from 23 years of monthly water quality monitoring from a steep headwater catchment within the Waikato region, New Zealand. Three experimental sub-catchments were planted in different proportions of Pinus radiata (PW2 = 100%, K-Pine 57%; PW3 = 36%). PW2 and PW3 were historical pastoral sites in the first rotation of plantation forestry and K-Pine was harvested and subsequently planted in a second rotation of forestry. All sites underwent two phases of stand thinning six and eight years after planting. The most significant effect of forestry was the increase in nitrate-N (NO3-N) and total nitrogen (TN) concentrations in response to both stand planting and stand thinning operations. Planting resulted in significant increases in NO3-N, TN and DRP over a four-year planting period at PW2. Significant increases in NO3-N and TN were detected over a four-year thinning period, at all three experimental sites. We propose that stream NO3-N and TN concentrations increased in response to stand planting at PW2 because of the change in physical conditions (e.g. increased stream shading, proliferation of nitrogen fixing weeds and decreased spatial extent of seepage wetlands) caused by the change in land use. Increasing nitrogen concentrations due to decreasing stream runoff could also be contributing a factor. Any decrease in NO3-N and TN concentrations in response to increased uptake by the rapidly growing P. radiata appears to have been masked by these other factors. However, the increase in NO3-N and TN concentrations in response to stand thinning at all three experimental sites suggests that NO3-N uptake by growing trees is an important process. Over the entire forestry period, median NO3-N concentrations at PW2 (first rotation site) increased by a factor four (400–1590 µg l−1). The median NO3-N during the post-thinning period was also one order of magnitude higher than those measured at K-Pine (second rotation site) during the post-thinning period. We attribute these differences to the NO3-N legacy within soil and/or groundwater of the previous sheep and beef cattle grazing land use. Long-term use of the PW2 catchment for forestry may eventually reduce NO3-N concentrations to the lower levels measured at K-Pine. Therefore, while NO3-N concentrations and loads may increase in response to the establishment of plantation forestry we envisage that these will decline if plantation forestry continues beyond the first rotation. This research highlights: (i) the complex nature of the response of stream water quality to catchment land use changes, and (ii) the value of studies that monitor the impact of land use/cover change over the long-term.

The MANAGE Drain Concentration database: A new tool compiling North American drainage nutrient concentrations

Artificially drained agricultural systems can be a primary contributor of non-point source nitrogen (N) and phosphorus (P) pollution to ground and surface waters; therefore, it is imperative to understand the mechanisms responsible for nutrient transport from this land use. Here, 79 drainage nutrient-related studies were used to compile 1564 site-years of agricultural drainage N and P concentrations (annual mean flow-weighted and annual arithmetic average) into a major database to aid in assessment of factors leading to nutrient loss through drainage systems. This new Drain Concentration table in the MANAGE (Measured Annual loads from AGricultural Environments) database is a publicly available resource (https://www.ars.usda.gov/plains-area/temple-tx/grassland-soil-and-water-research-laboratory/docs/manage-nutrient-loss-database). Probability of exceedance values were calculated using a Weibull distribution, and across the database, there was a 69% probability a drainage site-year would exceed an annual nitrate-N (NO3-N) concentration of 10 mg/L, the US Environmental Protection Agency Maximum Contaminant Level for drinking water, but only a 27% probability a reported site-year would exceed 0.0375 mg/L dissolved reactive phosphorus, which is a critical total P concentration to avoid freshwater eutrophication. While a surprising number of reported annual means were arithmetic averages rather than flow-weighted averages (27 vs. 71%), reporting of arithmetic means in peer-reviewed literature has decreased over time. We encourage further contributions to and analysis with the MANAGE database, so it can remain a resource for new efforts to better understand and mitigate nutrient losses from agricultural systems.

Manipulating Nutritional Conditions and Salinity-Gradient Stress for Enhanced Lutein Production in Marine Microalga Chlamydomonas sp.

Marine microalgae has great potential for lutein production with the advantage of saving fresh water resource. Thus, marine microalga Chlamydomonas sp. JSC4 is investigated as a potential lutein producer in this study. The medium types, nitrate-N and sea salt concentration are individually investigated to promote the cell growth rate and lutein production of JSC4. In Modified Bold Basal 3N medium, cell growth and lutein content are optimal at the nitrate-N concentration of 1000 mg L-1 and sea salt concentration of 2%. In addition, an innovative salinity-gradient strategy is operated to dramatically enhance biomass productivity (560 mg/L/d) and lutein content (3.42 mg g-1 ), resulting in the optimal lutein productivity (1.92 mg/L/d). Overall, this study clearly demonstrates that salinity is a significant inducer of lutein accumulation by strain JSC4 and that lutein production can be successfully optimized using the salinity-gradient strategy, which is beneficial for the outdoor large-scale lutein production in the future.

Nutrient patches are transient and unpredictable in an unproductive mountain grassland

While plant roots respond consistently to nutrient availability under experimental conditions, our understanding of the role of such response in the field is hindered by poor knowledge of size and duration of nutrient patches there. In particular, knowledge of patch duration is critically important for understanding types of root response. We determined spatial and temporal variations in phosphate-P, nitrate-N and ammonium-N concentrations, and pH in an unproductive mountain meadow for which extensive data on fine-scale root distribution exist. We sampled soil solution weekly over 2.5 growing seasons using suction cups to in a hierarchical spatial design with the smallest grain of 3.3 cm. Overall concentrations of all studied nutrients were fairly low with occasional and short-term, but large-in-magnitude peaks, with no pronounced spatial or temporal structure at any scale. Temporal variation was much stronger than spatial variation, with both interannual differences and within-season differences playing a role. Phosphate-P was consistently highest in spring, whereas ammonium-N increased during summers. The ammonium-N, the major nitrogen source at the site, was negatively correlated with phosphate-P. Our data suggest that repeated sampling of soil solution in fixed positions is necessary to cover the entire extent of nutrient variation in the field. It shows that there are no stable nutrient patches at the fine scale, and the duration and size of nutrient patches are smaller than usual growth responses of roots. This implies that under such conditions, the best rooting strategy is homogeneous space occupation linked with fast physiological response to varying nutrient concentrations.