Soil type regulates the divergent loss characteristics of sediment associated carbon and nitrogen in different size classes during rainfall erosion on cultivated lands.

Sediment associated carbon and nitrogen loss under rainfall, an important cause of soil quality degradation and water eutrophication, strongly depends on the intrinsic properties of original soil types. Relative to total loss, the transport behaviors of organic carbon and nitrogen among sediment size classes and response to soil types remain poorly understood. The concentrations of organic carbon (OC) and total nitrogen (TN) in different sediment size classes (>1, 0.25-1, 0.10-0.25, and <0.10 mm) and their contributions to total sediment load during rainfall erosion were determined under field plot rainfall simulation (at 90 mm h-1) on three contrasting soil types (Luvisol, Alisol and Ferralsol) with increased aggregate stability. During rainfall erosion, the concentrations of OC and TN in total and different sized sediments decreased first and then reached a steady state. The variability of OC and TN concentrations (coefficient of variations in 4.2-53.1% and 6.6-41.9%) among sediment size classes decreased from Luvisol to Ferralsol. Compared to original soils, sediments exhibited larger C/N ratios for Luvisol, and smaller values for Alisol, indicating the more selective transport of labile organic matter for weaker aggregated soils. Among sediment size classes, fine particles (<0.10 mm) accounted 69-88% of total OC and TN losses for Luvisol, and decreased to 30-39% for Ferralsol; and the main transport mechanisms of sediment associated OC and TN shifting from suspension-saltation (<0.10 mm) to rolling (>0.25 mm) with increased aggregate stability. Among original soil properties, inorganic cementing agents (including amorphous iron oxides and clay minerals) showed closer relationships with sediment OC and TN losses (|r| = 0.61-0.89, p < 0.001) than organic matter properties (|r| = 0.55-0.87, p < 0.001), further implying the important role of soil aggregate stability across soil types. This study provides an in-depth understanding on soil carbon and nitrogen losses and their divergent characteristics among soil types deserves consideration in the development of erosion model and land management in agricultural systems.

Evaluation of long-term impact of cereal rye as a winter cover crop in Illinois.

Extensive tile drainage usage combined with excess nitrogen fertilization has triggered nutrient loss and water quality issues in Illinois, which over time endorsed the hypoxia formation in the Gulf of Mexico. Past research reported that the use of cereal rye as a winter cover crop (CC) could be beneficial in reducing nutrient loss and improving water quality. The extensive use of CC may aid in reducing the hypoxic zone in the Gulf of Mexico. The objective of this study is to analyze the long-term impact of cereal rye on soil water­nitrogen (N) dynamics and cash crops growth in the maize-soybean agroecosystem in the state of Illinois. A gridded simulation approach was developed using the DSSAT model for the CC impact analysis. The CC impacts were estimated for the last two decades (2001-2020) for two fertilization scheduling (FA-SD = Fall and side-dress N and SP-SD = Spring pre-plant and side-dress N) comparing between CC scenario (FA-SD-C/SP-SD-C) with no CC (NCC) scenario (FA-SD-N/SP-SD-N). Our results suggest that the nitrate-N loss (via tile flow) and leaching reduced by 30.6 % and 29.4 %, assuming extensive adaptation of cover crop. The tile flow and deep percolation decreased by 20.8 % and 5.3 %, respectively, due to cereal rye inclusion. The model performance was relatively poor in simulating the CC impact on soil water dynamics in the hilly topography of southern Illinois. Generalizing changes in the soil properties (due to cereal rye inclusion) from the field scale to whole state (regardless of soil type) could be one of the possible limitations in this research. Overall, these findings substantiated the long-term benefits of cereal rye as a winter cover crop and found the spring N fertilizer application reduced nitrate-N loss compared to fall N application. These results could be helpful in promoting the practice in the Upper Mississippi River basin.

[Effects of Fertilization and Straw Mulching on Nitrogen and Phosphorus Loss in Chengdu Plain].

In recent years, the excessive application of nitrogen and phosphorus fertilizers has caused serious pollution and eutrophication, especially in paddy fields. Accordingly, a two-year (2018-2019) study was conducted at a rice paddy field under different fertilizer application rates and straw mulching in Chengdu Plain. N and P losses through the rainfall and surface runoff in the paddy field were measured under natural rainfall conditions. The results showed that nitrogen mainly existed in the form of ammonium nitrogen, and phosphorus mainly existed in the form of soluble phosphorus in the wet deposition. The wet deposition of nitrogen and phosphorus mainly occurred in June, July, and August. Surface runoff was positively correlated with rainfall, whereas surface runoff nitrogen concentration was inversely correlated with rainfall. The highest runoff losses of TN (4.75 kg·hm-2 in 2018 and 2.68 kg·hm-2 in 2019) were produced by TR3 practice and were 26.73% and 43.32% higher than that of the conventional practice. TN runoff loss was significantly decreased by reducing the rate of N fertilizer (P<0.05). Compared with that in the conventional practice TR1, TR4 reduced the N loss by 36.33% in 2018 and 26.74% in 2019, respectively. Optimized fertilizer TR2 and nitrogen reduction practice TR4 decreased P loss from surface runoff, and high intensity rainfall could reduce the content of granular phosphorus in surface runoff. The surface runoff occurring in July, August, and September contributed mostly to the total N loss, whereas the loss of total P mainly occurred before July. Consequently, the use of balanced fertilizer and decreased nitrogen fertilization amount might be effective strategies to attenuate non-point source pollution in the Chengdu Plain in the paddy fields.

Potential of crop straw incorporation for replacing chemical fertilizer and reducing nutrient loss in Sichuan Province, China.

Sichuan Province is rich in crop straw, yet little is known about its spatial distribution pattern, potential in replacing chemical fertilizer and mitigating nutrient loss. Based on the statistical data and literature review, the spatial distribution and potential of nutrient resources in crop straw for replacing chemical fertilizers was evaluated in this study. The nutrient loss with both crop incorporation and chemical fertilizer application were examined using a nutrient release coefficient method and compared. Results showed that Chengdu Plain, Northeast and South Sichuan produced more than 95% of the total straw nutrient resources during the period of 2016-2020. The potential of crop straw to substitute potassium (K), nitrogen (N) and phosphorus (P) fertilizer were K2O 33.08-285.95 kg hm-2, N 9.52-82.32 kg hm-2 and P2O5 4.91-28.71 kg hm-2, respectively. If chemical fertilizer was substituted by all the available straw nutrient resources, N and P loss can be decreased by 55.12% and 65.84% in average in Sichuan Province. 343.93 t of N loss and 20.05 t of P loss can be reduced in plain areas, 122.88 t of N loss and 46.29 t of P loss can be reduced in mountainous and hilly areas, and 5.65 t of t N loss and 3.54 t of P loss can be reduced in plateau areas. It can be concluded that there were rich crop straw nutrient resources in Sichuan Province with obvious spatial variability, solid consideration should be put on to the proper use of crop straw nutrient resources, with the aim of chemical fertilizer reduction, nutrient loss reduction and sustainable development.

Arbuscular mycorrhizal fungi reduce potassium, cadmium and ammonium losses but increases nitrate loss under high intensity leaching events.

BACKGROUND: Nutrients and heavy metals can be lost from soils via leaching, and arbuscular mycorrhizal fungi (AMF) can influence these events. Soil column experiments were carried out to examine whether leaching intensity and AMF can alter nutrient and Cd uptake in white clover plants and the extent of their losses through leaching. RESULTS: The presence of AMF significantly increased shoot and total biomass, as well as increased N, P, Cu and Zn uptake independent of water amount applied; while root P and Cu uptakes were promoted by AMF at any water amount treatments. Higher water amounts led to reductions in total N, K and Zn uptake for AMF-colonized plants in comparison to moderate water amount treatments. In the absence of AMF, white clover at low water amount treatment exhibited maximal root Cd uptake. At high water amount treatments, the presence of AMF significantly decreased leachate volumes and the amount of leached NH4+, K and Cd while AMF significantly increased the amounts of leached NO3-. CONCLUSIONS: Overall we found that AMF-colonized white clover plants reduced NH4+, K and Cd loss from soils but increased the risk of NO3- loss under high intensity leaching conditions.

Towards sustainability: Threat of water quality degradation and eutrophication in Usangu agro-ecosystem Tanzania.

The agrochemicals and nutrient losses from farming areas such as paddy farming significantly dictate quality and eutrophication of the freshwater resource. However, how farming and land use pattern affect water qualities and eutrophication remain poorly understood in most African agro-ecosystems. The present study characterized how paddy farming influences water qualities and eutrophication in 10 irrigation schemes in Usangu agro-ecosystem (UA). About 42 water samples were sampled from intakes, channels, paddy fields, and drainages and analyzed for EC, Cl, P, NH4-N, NO3-N, TN, Zn, Cu, Ca, and Mg. We observed water pH ranging from 4.89 to 6.76, which was generally below the acceptable range (6.5-8.4) for irrigation water. NH4-N concentration was in a range of 10.6-70.0 mg/L, NO3-N (8.4-33.9 mg/L), and TN (19.1-21,104 mg/L). NH4-N increased along sampling transect (sampling points) from intakes (5.7-29.1 mg/L), channels (19-20 mg/L), fields (12.9-35.8 mg/L), and outflow (10.6-70.0 mg/L), the same trend were found for NO3-N and TN. The TP determined in water samples were in the range of 0.01 to 1.65 mg/L; where some sites had P > 0.1 mg/L exceeding the allowable P concentration in freshwater resource, thus indicating P enrichment and eutrophication status. The P concentration was observed to increase from intake through paddy fields to drainages, where high P was determined in drainages (0.02-1.65 mg/L) and fields (0.0-0.54 mg/L) compared to channels (0.01-0.13 mg/L) and intakes (0.01-0.04 mg/L). Furthermore, we determined appreciable amount of potentially toxic elements (PTEs) such as Cu, Pb, Cd and Cr in studied water samples. The high N, P, and PTEs in drainages indicate enrichment from agricultural fields leading to water quality degradation and contaminations (eutrophication). The study demonstrates that water quality in UA is degrading potentially due to paddy rice farming and other associated activities in the landscape. Thus, the current study recommends starting initiatives to monitor irrigation water quality in UA for better crop productivity, and improved quality of drainage re-entering downstream through the introduction of mandatory riparian buffer, revising irrigation practices, to include good agronomic practices (GAP) to ensure water quality and sustainability.

How climate change and land-use evolution relates to the non-point source pollution in a typical watershed of China.

The water quality of Le 'an River Watershed (LRW) is crucial to the water environmental safety of Poyang Lake, especially the concentration of nitrogen and phosphorus. The effect of climate and land use change on watershed water quality has always been under the attention of local managers. More importantly, the lack of detailed studies on climate and land use impact on river water quality has prevented sustainable water security management in the LRW. Therefore, this study aimed to quantify the weight of climate and land use on nutrient loss in the LRW, respectively. We divided the historical period (1990-2020) into six scenarios and a baseline scenario. TN and TP losses in the watershed were simulated using Soil and Water Assessment Tool (SWAT), and the weight of climate and land use were quantified in overall, by period, and by region. The results showed that the weight of climate was greatly higher than land use with values around 90%. However, the weight of land use had a positive cumulative effect in a certain period, and its influence could not be neglected. The climate in all scenarios led to a reduction in nutrient loss, while land use was found to slightly increase the nutrient loss yield. In addition to, unique regional topographic features, urbanization rates, and climatic conditions could cause spatial heterogeneity in the climatic and land use weights.

Arbuscular mycorrhizae: natural modulators of plant-nutrient relation and growth in stressful environments.

The human population is increasing by 0.96% annually and is estimated to reach from 7.3 to 9 billion in 2050 and 11 billion in 2100. The world's agriculture is under pressure to produce more food and ensure food security. On the other hand, around 40% of the cultivable land is already degraded due to various factors including urbanization, soil sealing, soil acidification, salinization, soil erosion, and contamination. Arbuscular mycorrhizal fungi (AMF) constitute a unique group of root obligate symbiont that exchange mutual benefits with about 90% of terrestrial plants and represents a key link between plants and soil mineral nutrients. Literature is scanty on the studies on massive inoculation of AMF in food crops in agronomic settings, and thereby achieving efficient uptake and minimization of the major soil nutrients, eventually meeting our food demand under increasing and inevitable stressed environments. Given above, this review aimed to (i) introduce agricultural soil-contamination, and the relation of soil microbiome with the health of soils and plants; (ii) briefly overview AMF; (iii) highlight AMF role as a bioinoculant, and enhancer of efficient uptake and loss-minimization of nutrients; (iv) appraise literature available on AMF role in the regulation of growth and nutrition mainly in vegetable, horticultural crops and fruit trees; (v) enlighten the role and major mechanisms underlying AMF-mediated regulation of plant growth and nutrition under major biotic and abiotic stresses; (vi) highlight AMF role in the minimization of greenhouse gas emissions; and (vii) list major aspects so far unexplored in the current context.

Assessing the Accuracy of Farmers' Nutrient Loss Risk Perceptions.

Use of nutrient management practices to reduce nutrient loss from agriculture and its associated water quality consequences, including hypoxia and eutrophication, is widely encouraged. However, little is known about which factors influence farmers' risk perceptions associated with nutrient loss, and thus possibly influence their decisions to adopt such practices. To determine which factors were associated with relative "accuracy" of nutrient loss-associated risk perceptions, specific farm field management information was used as inputs to a Soil and Water Assessment Tool model of the study watershed to produce water quality outputs for each modeled farm field. This information was paired with farmers' risk perceptions associated with nutrient loss on their farm to assess relative "accuracy" of each farmer's perceptions compared to the rest of the farmers in the study. We then investigated characteristics of the farm and farmer that are associated with comparative "overprediction" and "underprediction" of risk, and found that characteristics of the individual (conservation identity, prior conservation practice adoption, efficacy beliefs, and perceived seriousness of the consequences of nutrient loss) are more important in determining whether farmers are likely to "overpredict" or "underpredict" risk than is the objective (modeled) vulnerability of their land to nutrient loss.

[Tracing the sources of sedimentary organic matter in Nanyue small watershed based on 13C, 15N and C/N]. / 基于13C、15N和C/N识别南岳小流域沉积有机质的来源.

Losses of organic matter in agricultural watersheds result in eutrophication and land degra-dation, which not only threaten water quality and food security, but also lead to environmental problems such as the greenhouse gases emission. We used 13C, 15N and C/N as fingerprint markers to trace the sources of sedimentary organic matter at the outlet in the Nanyue small watershed. We analyzed the spatial distribution in watershed sedimentary organic matter and soils of typical land use types, including forest, paddy field, and vegetable fields. The Bayesian stable isotope mixing model was used to quantitatively estimate the contribution of different sources. The results showed that there was significant spatial variation of δ13C. The δ13C of sediment organic matter (-22.6‰±0.53‰) and forest soil (-23.13‰±1.71‰) was significantly higher than that of paddy soil (-25.24‰±1.4‰). The differences of δ15N among the sources were not significant, with sediment having the maximum (4.37±0.83)‰ and forest soil having the minimum (2.38±1.97)‰. Forest soil had the highest C/N of 16.66±7.18, while paddy soil had the lowest C/N of 11.95±0.92. The results of the Bayesian stable isotope mixture model showed that the contribution rates of forest land, paddy fields and vegetable fields to the organic matter deposited at the outlet in the watershed were 19.6%, 15.7%, and 64.7%, respectively. Paddy filed and vegetable field had a combined contribution rate of 80.4%. It was concluded that, soils of agricultural land were the main sources of organic matter deposited in the Nanyue small watershed, and that nutrient loss in the watershed would be effectively controlled by optimizing farmland management.

Impact of harvesting methods and forest floor displacement on nutrient stock of Scots pine ecosystems in the Central Anatolia Region of Turkey.

Concern about the negative effects of logging residue extraction on the sustainability of forest ecosystems has been rising recently. Tree residues, including leaves, branches, bark and roots, left in the forest after logging may supply most of the nutrients for tree growth. The aim of this study was to (i) determine the carbon and nutrient stocks in different components and (ii) model the carbon and nutrient stocks in tree biomass of a mature Scots pine forest. The study site was located on the Turkmen mountain range in the Central Anatolia Region of Turkey. In sample plots, stand measurements were made, and samples collected from trees, soil and the forest floor for analysis of carbon and nutrients and the stock of each nutrient per unit area were calculated. Data were analysed using analysis of variance and regression analysis. Significant differences were found in carbon and nutrient concentrations and stocks between ecosystem components. C, Ca, Mg, Na, Fe, Cu and Mn stocks were higher in wood; the N stock was higher in needles, and P, K, S and Zn stocks were higher in roots. In the ecosystem, trees had the highest C stock; the soil had the highest N, P, K, Ca, Mg, Na, Cu, Zn and Mn stocks, and the forest floor had the highest Fe and S stocks. Therefore, it is critical that the forest floor is protected as it is an important element of the ecosystem nutrient cycle and source of Fe and S stocks. Maximum attention should be paid to leaving behind needles, bark, roots and thin branches with low economic value to minimise carbon and nutrient loss in the nutrient-limited forests. Equations predicting carbon and nutrient stocks through stem volume can be used for estimation of nutrient loss due to biomass removed from the system through interventions, contributing to sustainable forest management.

Nutrient loss by runoff from rice-wheat rotation during the wheat season is dictated by rainfall duration.

Clarifying the properties/features of nutrient loss from farmland surface runoff is essential for the mitigation of nutrient losses. Plough pan formation underneath topsoil is a common feature of long-term paddy soils that significantly affects water movement and nutrient runoff loss, especially during the upland season of paddy-upland rotation. To characterize the nutrients that are lost from wheat fields of paddy-wheat rotation with runoff, a field experiment was conducted in a wheat field using a simulated rainfall system from November 2019 to May 2020 in Nanjing, China. The aim of this study was to investigate the temporal characteristics of nitrogen (N) and phosphorus (P) loss under different rainfall intensities (low, 30 mm h-1; middle, 60 mm h-1; high, 90 mm h-1). The results showed that the time interval from the beginning of rain to the occurrence of runoff (time to runoff, Tr) was negatively correlated with "rainfall intensity" (Ri) (P＜0.01) but unaffected by soil moisture. Different rainfall intensities had no effect on the runoff coefficient (the ratio of the runoff volume over the precipitation, 0.14-0.17). The N and P loss concentrations in the nutrient discharge followed a power-function relationship that decreased over time (P＜0.01), and the peak nutrient concentration appeared during the initial runoff period (0-5 min). The N and P loss rates were the highest during the middle-to-late discharge period (15-30 min) for all intensities. In terms of cumulative nutrient losses, the amounts of TN lost were similar for all rainfall intensities, while TP significantly increased with intensity. The results revealed that nitrate-nitrogen (NOX--N) and particulate phosphorus (PP) were the predominant forms of N and P losses. Overall, during the initial runoff period, nutrient concentration peaks, whereas the nutrient loss rate is the highest during the middle-late phase of the phenomenon.

National estimates of environmental thresholds for upland soil phosphorus in China based on a meta-analysis.

The environmental threshold for upland soil phosphorus (P) content (ETSP, i.e., inflection point of soil P content leading to enhanced P loss) provides an important metric for guiding agricultural nonpoint source P pollution control. This study achieved the first meta-analysis to determine ETSP values for upland soils in China. The estimated national-level ETSP based on 472 field experimental observations of Olsen-P content and P loss rate was 30.1 ± 4.0 mg P kg-1, which was lower than the average ETSP value (52.1 ± 5.0 mg P kg-1) but higher than the average agronomic threshold values (16.0 ± 6.4 mg P kg-1) previously reported. Lower upland ETSP values occurred in acidic soils and soils having higher organic matter content (SOM), precipitation and slope (ETSP: 30.5 for pH < 7.0 versus 46.1 for pH ≥ 7.0; >56.4 for SOM < 2%, 49.9 for SOM = 2%-3%, and <3 for SOM > 3%; 33 for precipitation < 1000 mm yr-1, 27.5 for precipitation = 1000-1200 mm yr-1 and <5 for precipitation > 1200 mm yr-1; and 39.8 for slopes < 5° versus <9 for slopes ≥ 5°). A multiple regression model that incorporates SOM, pH, precipitation and slope was developed to predict upland ETSP values (R2 = 0.73, p < 0.01). The model estimated national upland ETSP values ranging from ~0 to 100 mg P kg-1 with an areal-weighted average of 60.6 mg P kg-1 and 15% of national upland soils having ETSP values <30 mg P kg-1. Upland soil P contents in Guangdong, Fujian and Zhejiang provinces largely exceeded their corresponding ETSP values by 1-22 mg P kg-1, indicating high P loss risks. Controlling upland P loss requires integrated management of soil P content, SOM, pH and erosion control. This study provides the first national estimate of upland soil ETSP, providing critical quantitative information for designing management practices to attenuate agricultural nonpoint source P pollution.

Coupling loss characteristics of N-P-C through runoff and sediment in the hilly region of SE China under simulated rainfall.

Soil total carbon (TC), phosphorus (P), and nitrogen (N) exports from the weathered granite slopes are greatly influenced by the complex hydrological processes and terrain factors. In this study, the coupling loss characteristics of N-P-C via runoff and sediment were studied with two soil tanks under simulated rainfalls. Three soils respectively derived from the tillage layer (T-soil), laterite layer (L-soil), and sand layer (S-soil) were employed to determine the interactions of hydrology and topography on N-P-C exports under three rainfall intensities (1.5, 2.0, and 2.5 mm/min). The erosion degree of different soils displayed an order of S-soil > L-soil > T-soil. The results showed that surface flow was the main runoff form for L- and T-soil, while underground flow was predominant for S-soil. There was a linear correlation between sediment and surface flow (R2 > 0.78). Surface flow was the dominant pathway of P loss via runoff with underground flow being an important supplementation, and the main P loss pattern switched between dissolved phosphorus (DP) and particle phosphorus (PP) during the experiment. However, P lost via eroded sediment accounted for more than 94% of the TP loss amount. N presented an opposite trend to P and was mainly lost via underground flow. The main N loss form in surface and underground flow was NO3--N. Underground flow was the predominant total nitrogen (TN) loss pathway for S- and L-soil, followed by sediment and surface flow. For T-soil, TN lost via runoff was much greater than that carried by eroded sediment. TC for S-soil was mainly lost via underground flow while that for L- and T-soil was mostly lost via surface flow. Both N-P loss loads in surface flow and P loss load in underground flow were positively correlated with TC loss load (p < 0.05), indicating that the presence of organic matter brings about more nutrient losses. These results expand our understanding of the combined effects of rainfall intensity and erosion degree on runoff and sediment yields as well as N-P-C losses from the bare weathered granite slopes of SE China.

Effect of Ridge Height, Row Grade, and Field Slope on Nutrient Losses in Runoff in Contour Ridge Systems under Seepage with Rainfall Condition.

Seepage plays a key role in nutrient loss and easily occurs in widely-used contour ridge systems due to the ponding process. However, the characteristics of nutrient loss and its influential factors under seepage with rainfall condition in contour ridge systems are still unclear. In this study, 23 seepage and rainfall simulation experiments are arranged in an orthogonal rotatable central composite design to investigate the role of ridge height, row grade, and field slope on Nitrate (NO3--N) and Orthophosphate (PO4+3-P) losses resulting from seepage in contour ridge systems. In total, three types of NO3--N and PO4+3-P loss were observed according to erosion processes of inter-rill-headward, inter-rill-headward-contour failure, and inter-rill-headward-contour failure-rill. Our results demonstrated that second-order polynomial regression models were obtained to predict NO3--N and PO4+3-P loss with the independent variables of ridge height, row grade, and field slope. Ridge height was the most important factor for nutrient loss, with a significantly positive effect and the greatest contribution (52.35-53.47%). The secondary factor of row grade exerted a significant and negative effect, and was with a contribution of 19.86-24.11% to nutrient loss. The interaction between ridge height and row grade revealed a significantly negative effect on NO3--N loss, whereas interactions among the three factors did not significantly affect PO4+3-P loss. Field slope only significantly affected NO3--N loss. The optimal design of a contour ridge system to control nutrient loss was obtained at ridge height of 8 cm, row grade of 2°, and field slope of 6.5°. This study provides a method to assess and model nutrient loss, and improves guidance to implement contour ridge systems in terms of nutrient loss control.

Nutrient dynamics in water and soil under conventional rice cultivation in the Vietnamese Mekong Delta.

Background The evaluation of nutrient variability plays a crucial role in accessing soil potentials and practical intervention responses in rice production systems. Synthetic fertilizer applications and cultivation practices are considered key factors affecting nutrient dynamics and availability. Here, we assessed the nutrient dynamics in surface, subsurface water and soil under local water management and conventional rice cultivation practices in the Vietnamese Mekong Delta. Methods We implemented a field experiment (200 m 2) in the 2018 wet season and the 2019 dry season in a triple rice-cropping field. Eight samples of surface water, subsurface water (30-45 cm), and topsoil (0-20 cm) were collected and analysed during the rice-growing seasons. Results The results showed that N-NH 4 +, P-PO 4 3- and total P peaks were achieved after fertilizing. Irrespective of seasons, the nutrient content in surface water was always greater than that of subsurface water ( P < 0.001), with the exception of N-NO 3 -, which was insignificant ( P > 0.05). When comparing the wet and dry seasons, nutrient concentrations exhibited minor differences ( P > 0.05). Under conventional rice cultivation, the effects of synthetic fertilizer topdressing on the total N, soil organic matter (SOM), and total P were negligible in the soil. Higher rates of N fertilizer application did not significantly increase soil N-NH 4 +, total N, yet larger P fertilizer amounts substantially enhanced soil total P ( P < 0.001). Conclusions Under conventional rice cultivation, N-NH 4 +, P-PO 4 3- and total P losses mainly occur through runoff rather than leaching. While N-NO 3 - loss is similar in surface water and subsurface water. Notably, nutrient content in soil was high; whilst SOM was seen to be low-to-medium between seasons. Future work should consider the nutrient balance and dynamic simulation in the lowland soil of the Vietnamese Mekong Delta's paddy fields.

Quantifying the Effects of Vegetation Restorations on the Soil Erosion Export and Nutrient Loss on the Loess Plateau.

The transport of eroded soil to rivers changes the nutrient cycles of river ecosystems and has significant impacts on the regional eco-environment and human health. The Loess Plateau, a leading vegetation restoration region in China and the world, has experienced severe soil erosion and nutrient loss, however, the extent to which vegetation restoration prevents soil erosion export (to rivers) and it caused nutrient loss is unknown. To evaluate the effects of the first stage of the Grain for Green Project (GFGP) on the Loess Plateau (started in 1999 and ended in 2013), we analyzed the vegetation change trends and quantified the effects of GFGP on soil erosion export (to rivers) and it caused nutrient loss by considering soil erosion processes. The results were as follows: (1) in the first half of study period (from 1982 to 1998), the vegetation cover changed little, but after the implementation of the first stage of the GFGP (from 1999 to 2013), the vegetation cover of 75.0% of the study area showed a significant increase; (2) The proportion of eroded areas decreased from 41.8 to 26.7% as a result of the GFGP, and the erosion intensity lessened in most regions; the implementation significantly reduce the soil nutrient loss; (3) at the county level, soil erosion export could be avoided significantly by the increasing of vegetation greenness in the study area (R = -0.49). These results illustrate the relationships among changes in vegetation cover, soil erosion and nutrient export, which could provide a reference for local government for making ecology-relative policies.

End-Stage Renal Disease Patients Lose a Substantial Amount of Amino Acids during Hemodialysis.

BACKGROUND: Poor nutritional status is frequently observed in end-stage renal disease patients and associated with adverse clinical outcomes and increased mortality. Loss of amino acids (AAs) during hemodialysis (HD) may contribute to protein malnutrition in these patients. OBJECTIVE: We aimed to assess the extent of AA loss during HD in end-stage renal disease patients consuming their habitual diet. METHODS: Ten anuric chronic HD patients (mean ± SD age: 67.9 ± 19.3 y, BMI: 23.2 ± 3.5 kg/m2), undergoing HD 3 times per week, were selected to participate in this study. Spent dialysate was collected continuously and plasma samples were obtained directly before and after a single HD session in each participant. AA profiles in spent dialysate and in pre-HD and post-HD plasma were measured through ultra-performance liquid chromatography to determine AA concentrations and, as such, net loss of AAs. In addition, dietary intake before and throughout HD was assessed using a 24-h food recall questionnaire during HD. Paired-sample t tests were conducted to compare pre-HD and post-HD plasma AA concentrations. RESULTS: During an HD session, 11.95 ± 0.69 g AAs were lost via the dialysate, of which 8.26 ± 0.46 g were nonessential AAs, 3.69 ± 0.31 g were essential AAs, and 1.64 ± 0.17 g were branched-chain AAs. As a consequence, plasma total and essential AA concentrations declined significantly from 2.88 ± 0.15 and 0.80 ± 0.05 mmol/L to 2.27 ± 0.11 and 0.66 ± 0.05 mmol/L, respectively (P < 0.05). AA profiles of pre-HD plasma and spent dialysate were similar. Moreover, AA concentrations in pre-HD plasma and spent dialysate were strongly correlated (Spearman's ρ = 0.92, P < 0.001). CONCLUSIONS: During a single HD session, ∼12 g AAs are lost into the dialysate, causing a significant decline in plasma AA concentrations. AA loss during HD can contribute substantially to protein malnutrition in end-stage renal disease patients. This study was registered at the Netherlands Trial Registry (NTR7101).

Using vegetation correction coefficient to modify a dynamic particulate nutrient loss model for monthly nitrogen and phosphorus load predictions: a case study in a small loess hilly watershed.

Vegetation is an important factor affecting nutrient enrichment ratio in runoff sediments but few studies have been examined in the effects of different vegetation scenarios on the monthly evolutions of particulate nitrogen (N) and phosphorus (P) loss. In this study, a vegetation correction coefficient was innovatively embedded in a dynamic particulate nutrient loss model to evaluate the monthly trends of particulate N and P loss in a small highly erodible watershed. Results indicate that (i) the monthly sediment yield from June to August 2013 accounted for the dominant percentage in this extreme hydrological year, which was consistent with the monthly trends of rainfall erosivity. The largest monthly sediment yield rate under four different vegetation scenarios all occurred in July with the values of 530.56, 258.09, 579.69, and 370.74 t km-2. (ii) Particulate N and P loss from April to September changed significantly under different vegetation scenarios, and they were mainly concentrated in June and July 2013; only the N and P loss loads in July accounted for > 70% of annual load. However, the loads in January, February, March, October, November, and December were considered as zero because there was no erosive rainfall during the above 6 months. (iii) The reduction efficiency of particulate N and P loss by scenario 1 was about 1.7 times higher than scenario 3, which shows that forestland in sediment reduction was stronger than grassland and cropland in Zhifanggou Watershed. Results provide the underlying insights needed to guide vegetation reconstruction and soil conservation planning in loess hilly regions.

Riparian leaf litter decomposition on pond bottom after a retention on floating vegetation.

Allochthonous (e.g., riparian) plant litter is among the organic matter resources that are important for wetland ecosystems. A compact canopy of free-floating vegetation on the water surface may allow for riparian litter to remain on it for a period of time before sinking to the bottom. Thus, we hypothesized that canopy of free-floating vegetation may slow decomposition processes in wetlands. To test the hypothesis that the retention of riparian leaf litter on the free-floating vegetation in wetlands affects their subsequent decomposition on the bottom of wetlands, a 50-day in situ decomposition experiment was performed in a wetland pond in subtropical China, in which litter bags of single species with fine (0.5 mm) or coarse (2.0 mm) mesh sizes were placed on free-floating vegetation (dominated by Eichhornia crassipes, Lemna minor, and Salvinia molesta) for 25 days and then moved to the pond bottom for another 25 days or remained on the pond bottom for 50 days. The leaf litter was collected from three riparian species, that is, Cinnamomum camphora, Diospyros kaki, and Phyllostachys propinqua. The retention of riparian leaf litter on free-floating vegetation had significant negative effect on the carbon loss, marginal negative effects on the mass loss, and no effect on the nitrogen loss from leaf litter, partially supporting the hypothesis. Similarly, the mass and carbon losses from leaf litter decomposing on the pond bottom for the first 25 days of the experiment were greater than those from the litter decomposing on free-floating vegetation. Our results highlight that in wetlands, free-floating vegetation could play a vital role in litter decomposition, which is linked to the regulation of nutrient cycling in ecosystems.