Nitrogen Release Research Articles

Residual Effect of Direct Seeded and Transplanted Rice, Nutritional Approaches and Slow Release Nitrogen Sources on the Growth Parameters of Blackgram Crop

A study was conducted on nutrient management approaches in rice-blackgram cropping system under different ecosystems. The growth parameters were recorded at 30 DAS, 60 DAS and at harvest of blackgram crop. The results indicated that the plant height and number of branches had increased linearly as the crop attained maturity. The three way interaction of ecosystem, nutritional approaches and N sources (M x N x S) had proved that significantly taller plants of blackgram were associated with the residual effect of transplanted soils which possessed neem coated urea based on SSNM for yield target of 7 t ha-1 (M2N4S2) at all stages of crop growth and number of branches at 60 DAS and at harvest.

Impact of contrasting fertilizer technologies on N dynamics from subsurface bands of “pure” or blended fertilizer applications

Abstract. Enhanced efficiency fertilizer (EEF) technologies that employ product coatings to delay nitrogen (N) release or are chemically stabilized to inhibit key steps of N transformations in soil offer potential for improving N use efficiency (NUE) in agricultural systems. However, the dynamics of N release and transformation from single technologies may result in a spatial or temporal mismatch of N supply and demand during a growing season. This may be overcome by use of blends of different technologies, provided the reduction in the concentration of stabilizing products does not reduce effectiveness. Laboratory incubations quantified the N dynamics around bands of controlled-release fertilizer (CRF) and nitrification-inhibited (NI) urea and varying blends of these technologies and referenced this against conventional urea and biodegradable, plant-oil-coated urea (POCU) applied at the same rates in two contrasting soils over 60 d. Blends of NI urea (3,4-dimethylpyrazole phosphate, DMPP urea) and a CRF (polymer-coated urea, PCU) typically resulted in N concentrations and distribution that were intermediate to those of the constituent products in unblended applications. Changes in the proportions of each product were mirrored by urea nitrogen (urea-N) concentrations around the bands in both soils, while the proportions of DMPP urea in each blend were only related to the extent of nitrification inhibition in the Vertisol. A proportion of the POCU granules burst during the early stages of incubation, resulting in initially higher mineral N concentrations compared to PCU. However, both CRFs delayed N release and formation of nitrate nitrogen (NO3-N) relative to granular urea, and mineral N distribution was similar within each soil. Soil type had a significant impact on banded N dynamics. Where there was little effect of N-fertilizer treatment on NO3-N production in the Ferralsol, the higher impedance to solute transport in the Vertisol contributed to a significant inhibitory effect of NI urea on nitrification in both pure and blended DMPP urea treatments. Using NO3-N production as a benchmark for the risk of environmental loss, the efficacy of fertilizer treatments in this soil was of DMPP urea / PCU blends (higher ratio of PCU may offer small but insignificant benefit) > DMPP urea = PCU > urea. These findings highlight the importance of soil properties in determining the N dynamics from different banded EEF products. Insights into the efficacy of biodegradable alternatives to polymer coatings and the efficacy of blended EEF products can improve the reliability of N supply while reducing environmental impacts, therefore offering greater opportunities to sustainably improve fertilizer NUE in cropping systems.

Changes in Soil Nitrogen Availability as Influenced by Direct Seeded Rice and Transplanted Rice Ecosystem, Nutritional Approaches and Slow-release Nitrogen Sources

An experiment was conducted on nutrient management approaches using RDF, SSNM, STCR and nutrient expert under different rice ecosystem using slow release nitrogen sources viz., neem coated urea and urea supergranules. The initial and final soil N content was analyzed at active tillering, panicle initiation, milking stages and at harvest of direct seeded and transplanted rice. The three-way interaction (M x N x S) proved that a significantly higher value of available N content in soil was noticed in SSNM (6 t ha-1) treated plot with neem coated urea in transplanted rice (M2N3S2) at active tillering stage (245.96 kg ha-1) and at harvest (213.46 kg ha-1), respectively, while application of NCU through SSNM approach (7 t ha-1) in direct seeded rice (M1N4S2) obtained maximum available N content at panicle initiation stage (229.18 kg ha-1) and application of NCU through STCR approach for the yield target of 7 t ha-1 in direct seeded rice (M1N2S2) at milking stage (218.15 kg ha-1).

Wood-derived bio-coating materials incorporating hydrophobic lignin and hierarchically porous biochar for high-efficiency coating slow-release fertilizers

Coating slow-release fertilizers (CSRFs) have gained significant attention for their potential to improve nutrient utilization efficiency and prevent environmental pollution through mitigating soil and water contamination. This study developed a novel wood waste-derived composition as a bio-coating material for urea slow-release by integrating modified lignin (PCL) and activated biochar (ABC). PCL was prepared by grafting palmitoyl chloride (PC) with hydrophobic groups to the lignin via an esterification reaction. ABC with a high surface area and hierarchically porous structure created rich channels for ion transportation. These results increased the water-retention ability with a reduced absorbing/expelling rate and confer an excellent Cr(VI) adsorption capacity to the PCL and ABC hybrid coating material (PCL/ABC). The as-prepared PCL/ABC-based CSRF (PCL/ABC-CSRF) showed improving fertilizer slow-release properties for real application (nitrogen release persistence for 40 days at soil). The rice (Oryza sativa L.) hydroponics study suggested that such novel PCL/ABC was conducive to the rice growth in micro metallic contaminated hydroponics by eliminating the accumulation of chromium metal in rice roots. Overall, this study provides an attractive platform for developing biodegradable, heavy-metal adsorbable, and high-efficient CSRFs and a feasible and effective way for functionalized utilization of wood waste.

The Impact of Sediment–Water Ratio and Hydraulic Residence Time on the Release of Inorganic Nitrogen from Sediments in the Pearl River Delta

Black-odorous water bodies in the Pearl River Delta have been treated. However, the re-release of nitrogen (N)-containing compounds in sediment can cause a relapse of black-odorous water bodies. Sediment–water ratio (SWR) and hydraulic residence time (HRT) influence pollutant release. Therefore, how to control SWR and HRT during the treatment process has become an urgent problem. This study focuses on the dynamic release of endogenous inorganic N from sediments into overlying water in a river channel of Dongguan City, Guangdong Province. Physicochemical parameters (dissolved inorganic nitrogen (DIN), NH4+-N, NO3−-N, NO2−-N, dissolved oxygen (DO), pH, oxidation-reduction potential (ORP), chemical oxygen demand (COD), Fe and total phosphorus (TP)) of overlying water were monitored under different SWRs (0.71, 0.38, and 0.16) and HRTs (13 days and 6.5 days), and the nitrogen release flux under different conditions was compared. Finally, the correlation and influence pathways among environmental factors were analyzed. The results showed that SWR significantly affected DO, pH, ORP, and sediment N release fluxes while prolonging HRT-promoted denitrification. DIN → NO2−-N → DO pathway had a total effect of 19.6%, and DIN may promote low DO concentration via NO2− oxidation. Maintaining reasonable SWR and HRT can reduce the release of inorganic N from sediment into the overlying water. This study provides a theoretical basis for controlling black-odorous water bodies.

Efficient methane production from anaerobic co-digestion of poultry litter with wheat straw in sequencing batch reactor: Effects of carbon-to-nitrogen ratio, total solids, and hydraulic retention time

This study performed co-digestion of poultry litter (PL) with wheat straw in the daily anaerobic sequencing batch reactor considering operation parameters of carbon-to-nitrogen ratio (C/N, 11.6 to 28.4), total solids (TS, 2.6 to 9.4%), and hydraulic retention time (HRT, 7.6 to 24.4d). The inoculum with a diverse microbial community structure included 2% of methanogens (Methanosaeta) was chosen. Experimental performance by central composite design showed continuous methane production with the highest biogas production rate (BPR) obtained at C/N = 20, TS = 6%, and HRT = 7.6d, being (1.18 ± 0.14 L/LR/d). A significant modified quadratic model (p < 0.0001) for predicting BPR was built (R2 = 0.9724). The operation parameters and process stability both affected the release of nitrogen, phosphorus, and magnesium in the effluent. The results provided new support for the novel reactor operations for efficient bioenergy production from PL and agricultural wastes.

Oxic-anoxic cycling promotes coupling between complex carbon metabolism and denitrification in woodchip bioreactors.

Denitrifying woodchip bioreactors (WBRs) are increasingly used to manage the release of non-point source nitrogen (N) by stimulating microbial denitrification. Woodchips serve as a renewable organic carbon (C) source, yet the recalcitrance of organic C in lignocellulosic biomass causes many WBRs to be C-limited. Prior studies have observed that oxic-anoxic cycling increased the mobilization of organic C, increased nitrate (NO3 - ) removal rates, and attenuated production of nitrous oxide (N2 O). Here, we use multi-omics approaches and amplicon sequencing of fungal 5.8S-ITS2 and prokaryotic 16S rRNA genes to elucidate the microbial drivers for enhanced NO3 - removal and attenuated N2 O production under redox-dynamic conditions. Transient oxic periods stimulated the expression of fungal ligninolytic enzymes, increasing the bioavailability of woodchip-derived C and stimulating the expression of denitrification genes. Nitrous oxide reductase (nosZ) genes were primarily clade II, and the ratio of clade II/clade I nosZ transcripts during the oxic-anoxic transition was strongly correlated with the N2 O yield. Analysis of metagenome-assembled genomes revealed that many of the denitrifying microorganisms also have a genotypic ability to degrade complex polysaccharides like cellulose and hemicellulose, highlighting the adaptation of the WBR microbiome to the ecophysiological niche of the woodchip matrix.

Study on Physicochemical Properties of Biocomposite Films with Spent Coffee Grounds as a Filler and Their Influence on Physiological State of Growing Plants.

The aim of the study was to plasticize corn starch with two selected urea (U)-rich plasticizers: choline chloride (CC):U or betaine (B):U eutectic mixtures at a molar ratio of 1:5 with a presence of spent coffee grounds as a filler. The biomaterials were prepared via a solventless one-step extrusion method and then extrudates were thermoformed using compression molding into sheets. The materials were characterized using mechanical and sorption tests, TGA, DMTA and FTIR. Additionally, a study on the biodegradation and remaining nitrogen content in soil was conducted. For the first time, an influence on physiological state of growing plants of the materials presence in soil was investigated. The addition of the coffee filler slightly increased the mechanical properties and decreased the swelling degree of the materials. The DMTA results indicated that biocomposites were easily thermoformable and the high filler addition (20 pph per polymer matrix) did not affect the processability. According to the biodegradation test results, the materials disappeared in soil within ca. 70 days. The results from this study on the physiological state of growing plants revealed that the materials, especially plasticized with CCU, did not exhibit any toxic effect on the yellow dwarf bean. The percentage of total nitrogen in the soil substrate in comparison with the control increased indicating an effective release of nitrogen from the TPS materials into the substrate.

Effects of fungal agents and biochar on odor emissions and microbial community dynamics during in-situ treatment of food waste

The effects of the co-addition of fungal agents and biochar on physicochemical properties, odor emissions, microbial community structure, and metabolic functions were investigated during the in-situ treatment of food waste. The combined addition of fungal agents and biochar decreased cumulative NH3, H2S, and VOCs emissions by 69.37%, 67.50%, and 52.02%, respectively. The predominant phyla throughout the process were Firmicutes, Actinobacteria, Cyanobacteria, and Proteobacteria. Combined treatment significantly impacted the conversion and release of nitrogen from the perspective of the variation of nitrogen content between different forms. FAPROTAX analysis revealed that the combined application of fungal agents and biochar could effectively inhibit nitrite ammonification and reduce the emission of odorous gases. This work aims to clarify the combined effect of fungal agents and biochar on odor emission and provide a theoretical basis for developing an environmentally friendly in-situ efficient biological deodorization (IEBD) technology.

Introducing hydroxyl-containing POSS to liquefaction of biomass: An alternative route to bio-based polyurethane nanocomposites for coated fertilizers

A new route, introducing POSS-OH to liquefaction of biomass, is developed for bio-based polyurethane nanocomposites and applied in the controlled release of chemicals. The effect of POSS-OH on the chemical structures and properties of biopolyols and their coatings was characterized by GC–MS, FTIR and others. The results indicated that after adding POSS-OH to liquefaction of starch, the hydroxyl content of the biopolyol synthesized was higher than that of the biopolyol from sole starch, and the resultant nanocomposite owned good thermal stability, water resistance and, importantly, non-toxicity to plants. Meanwhile, after coating the urea granules, the controlled release ability of the nanocomposite coating with 3% POSS-OH was the best, and in comparison with the coating without POSS-OH the nitrogen release duration was prolonged by a month. Overall, POSS-OH was used not only as both co-liquefier of biomass instead of the commonly used glycerol to affect the liquefaction process, but also as filler for bio-based polyurethane nanocomposite to improve the interaction. Thus, the substitution of petroleum-based polyols can be expected in synthesizing the green and bio-based coatings for controlled release of chemicals.

Impact of Urea-Intercalated-Biochar on N-Release in Soil and Humified Soil Organic Matter

This research investigated the impact of urea-intercalated-biochar (ICB) on nitrogen release as well as on humified soil organic matter (SOM) distribution in highly weathered soil. Incubation studies were performed with a typical dystrophic red Ultisol and with 10 treatments: soil without amendment (control, CON), soil with three doses of biochar (BC75, BC145, and BC 290), and soil with ICB doses (ICB75, ICB145 and ICB 290). BC and ICB were characterized by 13C Nuclear Magnetic Resonance 13C-NMR CP/MAS spectroscopy and elemental analyses. N-extractable forms were periodically determined by Kjeldahl method and humic substances (HS) distribution was analyzed on the 28th day after incubation begins (DAI). Intercalation of urea in BC increased sample N content from 2.7 to 22 %, whereas that of C decreased from 40 % to 28 %. As a consequence, C: N decreased from 14.9 to 1.3. The 13C NMR spectra of BC and ICB were similar but relative abundance of major organic functional groups differs, for example, ICB presented a greater proportion of C=O groups due to the carbonyl group of urea and a greater proportion of N/O alkyl C, O-alkyl C, and anomeric C groups due to the addition of starch. There was a significant increase in the concentration of extractable N-NH4+ by addition of urea from the onset of incubation down late period and a significant difference (P &amp;gt; 0.05) was obtained between the ICB and BC over time. This could be as a result of the less accessible form of N in the biochar materials due to the pyrolysis process. There was no evidence of extractable N-NO3- ion until 14 DAI, significant difference in N-NH4+ concentrations at 28 DAI between the ICB and control was observed over time and the highest value recorded from ICB treated pots at 145 and 290 kg N ha-1.

Release Pattern of Nitrogen and Potassium from Controlled Release Fertilizer (CRF) in the Soil

Nitrogen (N) and potassium (K) are macronutrients that plants need for better growth and yield. However, they are readily lost from the soil through volatilization, denitrification, and leaching, aside from being absorbed by plant roots. Thus, a Controlled Release Fertilizer (CRF) may be formulated and applied to maximize the beneficial effects of N and K fertilization. This study aimed to describe the release pattern of ammonium nitrogen (NH4 -N), nitrate nitrogen (NO3 -N), and K from CRF through the laboratory incubation method. Two types of CRF - CRF A (16-16-16) and CRF B (30-6-8), with a non-CRF (Mutiara NPK16-16-16) as Control – were used. Each fertilizer was tested at 600 and 1200 kg ha-1 doses. The results showed that the NH4 -N release was very high at 40 – 60% but declined to almost 0% after 14 weeks. The NO3 -N release rate was 17 – 40% during the first week, followed by a steady increase to nearly 100% by the 14th incubation week. Potassium release ranged from 20% to 30% in the first week, then rose to 30 – 70% at Week 14. Overall, CRF (30-6-8) at a dose of 1200 kg ha-1 showed the slowest rate of nitrogen release.

Nitrogen release from different polymer‐coated urea fertilizers in soil is affected by soil properties

AbstractThe use of urea as nitrogen (N) fertilizer in agriculture needs to consider environmental, economic and resource conservation aspects because of low N‐use efficiency (NUE). Polymer‐coated urea (PCU) offers an effective way to improve the NUE of urea and to reduce its environmental trade‐offs. However, we lack information on the impact of climate and soil properties on N release from PCU. Therefore, this study was performed to quantify the effects of soil texture, moisture and temperature on the release kinetics of N from PCU. We designed a test system for soil incubation experiments and investigated three fertilizers with different release patterns, five topsoils, three moisture levels and two temperatures over 48 days. We analysed the concentrations of inorganic N ( and ) in the soil and estimated N release rates using the unified Richards model. Soil texture did not change the N release patterns, but release rates varied significantly among the investigated soils. Changes in soil moisture for a given soil had no effect on N release from PCU and urea when fertilizers were incorporated into the soil at conditions supportive of crop growth. Lowering soil temperatures, however, decreased N release rates from PCU by 16%–49% but only in silt loam and not in sandy loam. We conclude that PCU improves the N residence time in soil, but predictions on N release from PCU must be adapted to the prevailing environmental conditions and cannot be generalized across differently textured soils.

Simultaneous immobilization of ammonia and phosphorous by thermally treated sediment co-modified with hydrophilic organic matter and zeolite

The use of calcined sediments (CS) for thin-layer capping is an environment-friendly technology for controlling nitrogen (N) or phosphorus (P) release. However, the effects of CS derived materials and efficiency in controlling the sedimentary N/P ratio have not been thoroughly investigated. While zeolite-based materials have been proven efficient to remove ammonia, it is limited by the low adsorption capacity of PO43−. Herein, CS co-modified with zeolite and hydrophilic organic matter (HIM) was synthesized to simultaneously immobilize ammonium-N (NH4+-N) and remove P, due to the superior ecological security of natural HIM. Studies on the influences of calcination temperature and composition ratio indicated that 600 °C and 40% zeolite were the optimal parameters leading to the highest adsorption capacity and lowest equilibrium concentration. Compared with doping with polyaluminum chloride, doping with HIM not only enhanced P removal but also achieved higher NH4+-N immobilization efficacy. The efficiency of zeolite/CS/HIM capping and amendment in prohibiting the discharge of N/P from sediments was assessed via simulation experiments, and the relevant control mechanism was studied at the molecular level. The results indicated that zeolite/CS/HIM can reduce 49.98% and 72.27% of the N flux and 32.10% and 76.47% of the P flux in slightly and highly polluted sediments, respectively. Capping and incubation with zeolite/CS/HIM simultaneously resulted in substantial reductions in NH4+-N and dissolved total P in overlying water and pore water. Chemical state analysis indicated that HIM enhanced the NH4+-N adsorption ability of CS owing to its abundant carbonyl groups and indirectly increased P adsorption by protonating mineral surface groups. This research provides a novel strategy to control sedimentary nutrient release by adopting an efficient and ecologically secure remediation method to rehabilitate eutrophic lake systems.

Nitrogen release dynamics and carbon sequestration by legume and non-legume cover crops under pure and mixed planting conditions

Abstract Synchronizing crop residue decomposing and releasing nitrogen with subsequent cash crop needs provides benefits for ecosystems, but it is difficult to carry out. This study aimed to investigate the trend of decomposition of vetch (Vicia sativa), rye (Secale cereale) and mixed (rye + vetch) cover crop residues as well as nitrogen release after incorporating them into the soil during 12 weeks of the potato growth season by using the mesh bag method. Vetch residues decomposed very quickly in the spring and their nitrogen is released due to their higher nitrogen content and consequently a lower Carbon/Nitrogen (C/N) ratio. However, rye residues decomposed at a slower rate compared to mixed treatment, and their nitrogen content was immobilized mainly due to a higher C/N ratio. A better understanding of cover crops residues decomposition dynamics leads to maximizing the cover crop effects and higher nutrient uptake by subsequent main crops. The results of this study showed that the input level of nitrogen fertiliser can be reduced by implementing management strategies in farming potatoes and using cover crops, which will reduce the harmful environmental effects and increase the economic benefit for farmers.

A modelling approach for the assessment of energy recovery and impact on the water line of sludge pre-treatments

A simple, easy-to-use, first-order model was elaborated to predict the methane production and the release of ammoniacal nitrogen (N–NH3) to the digestate in full-scale anaerobic digestion (AD) processes. The study used long-term, semi-continuous AD tests, carried out with samples of primary sludge (PS), raw waste activated sludge (WAS), WAS after a thermo-alkali pre-treatment (90 °C, 90 min, 4 g NaOH/100 g TS) and mixed sludge (PS/treated WAS), to calibrate and validate the model. The results of both the experimental activities and the phase of model tuning demonstrated that the proposed model was capable to provide reliable information to completely characterize the AD process, thus overcoming the limitations due to discontinuity of experimental tests. Furthermore, it was demonstrated that low-temperature thermo-alkali pre-treatments could increase the values of the model parameters, namely methane production after an infinite time (B0, +70%) and hydrolysis constant (k, +450%), and made them comparable to those obtained by the application of commercial, high-energy demanding treatments (e.g. Cambi). Finally, the issue concerning the release of N–NH3 to digestate was deemed to be very worthy to being investigated because, after pre-treatments, the cost for nitrogen removal in the water line, through the traditional processes of nitrification – denitrification, could increase even by 140%.

Canopy Gaps Control Litter Decomposition and Nutrient Release in Subtropical Forests

The formation of a canopy gap results in changes to the microenvironment which, in turn, affect litter decomposition and nutrient release. However, the mechanisms underlying these effects in differently sized gaps and non-gaps remain poorly understood. To address this gap in knowledge, we selected three large gaps (above 150 m2), three medium gaps (50–100 m2), three small gaps (30–50 m2), and three non-gaps with basically the same site conditions. We then used the litter bag method to investigate leaf and branch litter decomposition over a year in a Castanopsis kawakamii natural forest with the aim of characterizing the litter mass remaining and the nutrient release in canopy gaps and non-gaps. Our results revealed that the remaining litter mass of leaf and branch litter was lower in medium gaps compared to other gaps, and leaf litter decomposed faster than branch litter. Environmental factors were identified as the primary drivers of total carbon and nitrogen release during litter decomposition. Gap size (canopy openness), taxonomic Margalef index, the Brillouin index of soil microbes, soil total nitrogen content, soil pH value, and average air temperature were identified as the main factors driving carbon and nitrogen release from branch litter. In the late decomposition stage, the taxonomic Pielou index, soil total potassium content, soil water content, and average relative air humidity were the main drivers of nutrient release from branch litter. The soil water content and average relative air humidity were also found to be the main factors affecting the nutrient release from leaf litter throughout the different stages of decomposition. Overall, our study highlights the impact of canopy gaps on microenvironmental variation, taxonomic community diversity, and soil microbial functional diversity and how these factors ultimately influence litter decomposition and nutrient release. Our findings provide an important foundation for further research into soil nutrient cycling in subtropical natural forests.

Post-dredging nitrogen dynamics at the sediment–water interface: the shallow, eutrophic Mogan Lake, Turkey

The sedimentation and resuspension of various forms of nitrogen in wetlands determines the direction of the nitrogen dynamics. Mogan Lake, in the Gölbaşı Special Environmental Protection Area, is one of the most important Ramsar-nominated wetlands in Turkey. Lake management applications have been performed by the local managers since 2008, including sediment cleaning activities such as dredging. In this context, the aim was to quantitatively predict the nitrogen dynamics (ammonium and nitrate release/ uptake in the positive and/or negative direction) at the sediment–water interface, which has not been addressed in the eutrophication and sediment-related studies conducted to date on the lake in question. Sediment ammonium and nitrate flux were estimated to be between -9.16 and 0.36 µg m-2 d-1 and between -67.2 and 35.16 µg m-2 d-1, respectively. The estimations for sediment nitrogen flux in Mogan Lake did not show a regular seasonal or spatial fluctuation. Our results demonstrate that low nitrogen release levels in Mogan Lake do not pose a threat to its nutrient level. In conclusion, both monitoring and reducing external loading is still the top priority for a long-term recovery of water quality in the process of freshwater ecosystems.

Nutrient controlled release performance of bio-based coated fertilizer enhanced by synergistic effects of liquefied starch and siloxane

The porous structure and hydrophilicity of coating shells affect the nutrient controlled-release performance of castor oil-based (CO) coated fertilizers. In order to solve these problems, in this study, the castor oil-based polyurethane (PCU) coating material was modified with liquefied starch polyol (LS) and siloxane, and a new coating material with cross-linked network structure and hydrophobic surface was synthesized, and used it to prepare the coated controlled-release urea (SSPCU). The results demonstrated that the cross-linked network formed by LS and CO improved the density and reduced the pores on the surface of the coating shells. The siloxane was grafted on the surface of coating shells to improve its hydrophobicity and thus delayed water entry. The nitrogen release experiment indicated that the synergistic effects of LS and siloxane improved the nitrogen controlled-release performance of bio-based coated fertilizers. Nutrient released longevity of SSPCU with 7 % coating percentage reached >63 days. Moreover, the nutrient release mechanism of coated fertilizer was further revealed by the analysis of the release kinetics analysis. Therefore, the results of this study provide a new idea and technical support for development of efficient and environment-friendly bio-based coated controlled-release fertilizers.

A method for researching the eutrophication and N/P loads of plateau lakes: Lugu Lake as a case

Lugu Lake is one of the best plateau lakes in China in terms of water quality, but in recent years the eutrophication of Lugu Lake has accelerated due to high nitrogen and phosphorus loads. This study aimed to determine the eutrophication state of Lugu Lake. Specifically, the spatio-temporal variations of nitrogen and phosphorus pollution during the wet and dry seasons were investigated in Lianghai and Caohai, and the primary environmental effect factors were defined. Adopting the endogenous static release experiments and the exogenous improved export coefficient model, a novel approach (a combination of internal and external sources) was developed for the estimation of nitrogen and phosphorus pollution loads in Lugu Lake. It was indicated that the order of nitrogen and phosphorus pollution in Lugu Lake was Caohai > Lianghai and dry season > wet season. Dissolved oxygen (DO) and chemical oxygen demand (CODMn) were the main environmental factors causing nitrogen and phosphorus pollution. Endogenous nitrogen and phosphorus release rates in Lugu Lake were 668.7 and 42.0 t/a, respectively, and exogenous nitrogen and phosphorus input rates were 372.7 and 30.8 t/a, respectively. The contributions of pollution sources, in descending order, were sediment > land-use categories > residents and livestock breeding > plant decay, of which sediment nitrogen and phosphorus loads accounted for 64.3 % and 57.4 %, respectively. Regulating the endogenous release of sediment and obstructing the exogenous input from shrubland and woodland are emphasized for the management of nitrogen and phosphorus contamination in Lugu Lake. Thus, this study can serve as a theoretical foundation and technical guide for eutrophication control in plateau lakes.