Total Nitrogen Loss Research Articles

Warming and grazing enhance litter decomposition and nutrient release independent of litter quality in an alpine meadow

Abstract Warming and grazing, and litter quality jointly determine litter decomposition and nutrient releases in grazing ecosystems. However, their effects have previously been studied in isolation. We conducted a two factorial experiment with asymmetric warming using infrared heaters and moderate grazing in an alpine meadow. Litter samples were collected from all plots in each treatment, among which some subsamples were placed in their original plots and other samples were translocated to other treatment plots to test the relative effects of each treatment on litter decomposition and nutrient releases. We found that warming rather than grazing alone significantly increased total losses of litter mass, total organic carbon, total nitrogen (TN) and total phosphorus (TP) per unit area due to increases in both mass loss rates and litter biomass. However, grazing with warming did not affect their total mass losses because increased mass loss was offset by decreased litter biomass compared with the control. Seasonal mean soil temperature better predicted litter decomposition than litter lignin content or carbon to nitrogen ratio. There were interactions between warming and grazing, but there were no interactions between them and litter quality on litter decomposition. The temperature sensitivity of TN loss was higher than that of TP loss per unit area. Our results suggest that increased temperature has a greater effect on litter decomposition and nutrient release than change in litter quality, and that more N release from litter could result in greater P deficiency in the alpine meadow.

Surface flow–interflow-coupled nitrogen loss in gray fluvo-aquic farmland soils in the Anhui Section of the Huaihe River Basin, China

To reveal the characteristics of nitrogen loss and their coupling relations in the process of surface flow and interflow under various rainfall intensities in gray fluvo-aquic soil areas, the coupling loss characteristics of total nitrogen (TN), nitrate nitrogen (NO3−-N), and ammonium nitrogen (NH4+-N) in the surface flow and interflow under three rainfall intensities (60, 80, and 110 mm·h−1) at a slope of 5° were studied using an artificial rainfall simulation. The results showed that (1) runoff yield and TN concentration were proportional to the rainfall intensity, with higher runoff concentrations of TN in the initial stage, and (2) surface flow yield, which was the main output mode of farmland runoff, was higher than interflow yield under a range of rainfall intensities. The average concentration of NO3−-N in surface flow decreased with increasing rainfall intensity, whereas the opposite was true in interflow. The main loss path of NO3−-N was interflow, whereas the main loss path of NH4+-N was the surface flow; NO3−-N was the main form of TN loss. The surface flow was the main loss path of soil nitrogen loss in farmland, and the runoff yield was an important factor in controlling nitrogen loss.

Effects of Turning Frequency on Ammonia Emission during the Composting of Chicken Manure and Soybean Straw.

Here, we investigated the impact of different turning frequency (TF) on dynamic changes of N fractions, NH3 emission and bacterial/archaeal community during chicken manure composting. Compared to higher TF (i.e., turning every 1 or 3 days in CMS1 or CMS3 treatments, respectively), lower TF (i.e., turning every 5 or 7 days in CMS5 or CMS7 treatments, respectively) decreased NH3 emission by 11.42–18.95%. Compared with CMS1, CMS3 and CMS7 treatments, the total nitrogen loss of CMS5 decreased by 38.03%, 17.06% and 24.76%, respectively. Ammonia oxidizing bacterial/archaeal (AOB/AOA) communities analysis revealed that the relative abundance of Nitrosospira and Nitrososphaera was higher in lower TF treatment during the thermophilic and cooling stages, which could contribute to the reduction of NH3 emission. Thus, different TF had a great influence on NH3 emission and microbial community during composting. It is practically feasible to increase the abundance of AOB/AOA through adjusting TF and reduce NH3 emission the loss of nitrogen during chicken manure composting.

Intermittent aeration reducing N2O emissions from bioreactor landfills with gas–water joint regulation

Landfills are important emission sources of atmospheric N2O, especially bioreactor landfills with leachate recirculation. In this study, N2O emissions were characterized in four bioreactor landfills with different ventilation methods, including intermittent (2-h aeration per 12 h or 4 h/d in continuous) and continuous aeration (20 h/d), in comparison to a traditional landfill without aeration. During the experiment, the N2O emissions from the landfill reactors with intermittent aeration were 7.48 and 7.15 mg, accounting for only 20.8% and 19.9% of those with continuous aeration, respectively. Continuous aeration was more favorable for the biodegradation of organic matter than intermittent aeration in the landfilled waste and leachate. Intermittent and continuous aeration could both effectively remove total nitrogen (TN) and NH4+-N with removal efficiencies above 64% in the leachate. In the experimental landfill reactors with gas–water joint regulation, the proportion of N2O-N to TN loss ranged from 0.02% to 0.75%. Luteimonas, Pseudomonas, Thauera, Pusillimonas and Comamonas were the dominant denitrifying bacteria in the landfill reactors. The denitrifying bacterial community in the landfilled waste was closely related to its degree of stabilization and nitrogenous compound concentrations in the landfilled waste and leachate. The NO3–-N and NO2–-N concentrations of leachate were the most important environmental factors affecting the succession of nirS-type and nirK-type denitrifying microbial communities in the landfilled waste. These findings indicated that intermittent aeration was an economical and effective way to accelerate the stabilization of landfilled waste and reduce the pollutants in leachate and N2O emissions during landfill mining and reclamation.

The Effects of Meteorological and Hydrological Conditions on Nutrient Losses from Agricultural Areas in Latvia

Abstract Water quality in any stream is affected by complex interactions between natural and anthropogenic factors in a given catchment area. Agriculture has been identified as a major contributor of nitrogen and phosphorus inputs to surface waters in the Baltic Sea region. Although decisions regarding agricultural management practices, e.g. crop rotation, tillage, fertilization, have a direct impact on likelihood and magnitude of nitrogen and phosphorus losses from agricultural areas to surface waters, natural factors such as meteorological and hydrological conditions have a triggering role in processes determining transformations, storage, uptake and losses of nutrients. In order to investigate the effects of meteorological (precipitation and air temperature) and hydrological (runoff) conditions on water quality (losses of total nitrogen (TN) and total phosphorus (TP)) the results of the Agricultural Runoff Monitoring Programme collected at three monitoring sites (Berze, Mellupite, and Vienziemite) during the time period of 1995–2020 were summarized and analysed. The pronounced differences in mean annual air temperature and annual precipitation were observed when the meteorological information representing the periods of twenty years was compared indicating for evidences of climate change. In addition, the relationships between seasonal precipitation and runoff was detected. As affected by the hydrological behaviour the losses of TN and TP in agricultural catchments had large variations depending on the intensity of agricultural production and site location. The changes in seasonal and annual patterns of precipitation, air temperature and runoff may increase the risks of nutrient losses from agricultural catchments in the future.

赤红壤植蔗坡地坡面径流及溶解态氮磷流失特征

为探究南方高强度、高频次降雨下赤红壤区坡耕地土壤侵蚀及氮磷养分流失的特征，基于野外径流小区原位观测试验，通过测定自然降雨下赤红壤植蔗坡地坡面径流和溶解态氮磷流失量，探讨自然降雨下甘蔗种植对赤红壤坡面径流及溶解态氮磷流失的影响。结果表明：（1）2019年和2020年，径流量分别为1111.3 m³/hm²和3269.4 m³/hm²，硝态氮（NO₃^--N）流失量分别为1.39 kg/hm²和15.60 kg/hm²，铵态氮（NH₄⁺-N）流失量分别为0.37 kg/hm²和1.02 kg/hm²，可溶性磷流失量分别为0.20 kg/hm²和0.27 kg/hm²。2019年和2020年植蔗坡地径流及溶解态氮磷流失量均集中在6月份，占流失总量的45%以上，硝态氮（NO₃^--N）是径流氮素流失的主要形式，占79%以上。此外，2019年和2020年5月至8月，侵蚀性降雨场次分别为18次和23次，侵蚀性降雨量分别为407.8 mm和668.0 mm。（2）不同侵蚀性降雨条件下，植蔗坡地溶解态氮磷流失量及其浓度波动较大，甘蔗生长前期（5-6月）溶解态氮磷流失量及其浓度呈上升趋势，而生长后期（7-8月）则呈波动下降趋势。2019年和2020年观测期侵蚀性降雨的年内分布存在明显差异，均集中在6月份，占35%以上。（3）坡面径流量与降雨量和最大30 min降雨强度呈极显著的正相关关系，同时坡面径流量与径流中硝态氮、铵态氮及可溶性磷流失量均呈极显著正相关关系。研究结果有助于明晰南方赤红壤区蔗区坡面土壤侵蚀及养分流失特征。;The characteristics of soil loss and nutrient loss in sloping land are quitely different among different areas of China, and crop patterns also have significant impacts on these indicators. The objectives of this study were as follows:1) to explore the characteristics of soil erosion and nutrient loss in sloping land with planting sugarcane of lateritic soil; and 2) to analyze the impacts of sugarcane growing stage and natural rainfall characteristics on soil erosion and nitrogen and phosphorus loss characteristics. This research based on the in-situ observation test of runoff plot and measured the loss of runoff, dissolved nitrogen, and phosphorus in sloping land with planting sugarcane. The amounts and concentrations of nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP) under individual natural rainfall during May to August in 2019 and 2020 were observed. The results showed that:(1) in 2019 and 2020, the runoffs, nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP) loss were 1111.3 m³/hm² and 3269.4 m³/hm², 1.39 kg/hm² and 15.60 kg/hm², 0.37 kg/hm² and 1.02 kg/hm², 0.20 kg/hm² and 0.27 kg/hm², respectively. The runoff and its dissolved nitrogen and phosphorus loss in sloping land with planting sugarcane under 2019 and 2020 were both concentrated in June, which accounted for more than 45%, and NO₃^--N was the main form of nitrogen loss in runoff, which accounted for more than 79% of total nitrogen loss. Besides, the times of individual erosive rainfall were 18 and 23, and the erosive rainfall amounts were 407.8 and 668.0 mm from May to August in 2019 and 2020, respectively. (2) The amounts of dissolved nitrogen and phosphorus loss and their concentrations in sloping land with planting sugarcane showed great fluctuation under different erosive rainfalls and stages of sugarcane growth. There were obvious differences in the annual distribution of erosive rainfall between observation period of 2019 and 2020, which were both concentrated in June, which accounted for more than 35% of total rainfall. In the early stage of sugarcane growth (from May to June), the losses of dissolved nitrogen and phosphorus and their concentrations showed an upward trend, while in the late stage of sugarcane growth (from July to August), they showed a fluctuating downward trend. (3) There was a significantly positive correlation between runoff and rainfall and maximum 30 min rainfall intensity, meanwhile, there was a significantly positive correlation between runoff and the loss of nitrate nitrogen (NO₃^--N), ammonium nitrogen (NH₄⁺-N), and dissolved phosphorus (DP). The results can provide a theoretical basis for clarifying the soil erosion characteristics of sloping land with planting sugarcane in the lateritic soil region of southern China.

Modeling and assessing water and nutrient balances in a tile-drained agricultural watershed in the U.S. Corn Belt

Identifying the key processes and primary sources of water and nutrient losses is essential for water quantity and quality management in watersheds. This is especially true in the U.S. Corn Belt, which has been recognized as the primary region contributing nutrient loads to the Great Lakes and the Gulf of Mexico. A SWAT (Soil and Water Assessment Tool) model simulation was set up in an agricultural watershed with about 50% tile drainage area in the U.S. Corn Belt to study the water and nutrient balance components for the whole watershed and the corn-soybean rotation system. The SWAT model was improved to consider additional nitrogen and phosphorus loss paths from the soil. The model was comprehensively calibrated and validated for simulating monthly stream flow, total suspended solids (TSS), nutrient loads (including total Kjeldahl nitrogen (TKN), nitrate and nitrite nitrogen (NOx-N), total phosphorus (TP) and orthophosphate phosphorus (orthoP)), actual evapotranspiration (ETa), leaf area index (LAI) and annual crop yields in the watershed from 2011 to 2019. Results showed the model performance was very good for simulating the stream flow, TSS and ETa, and acceptable for nutrient loads, LAI and crop yields. ETa, surface runoff, lateral soil flow, tile drainage and percolation respectively accounted for 65%, 15%, 2%, 8% and 9% of the precipitation. Fertilizer was the main source of nitrogen and phosphorus input to the watershed, and harvested crops were the main paths removing nutrients. Surface runoff, tile drainage and percolation each contributed about 30% of total nitrogen losses to water, with surface runoff being dominated by organic nitrogen while tile drainage and percolation were dominated by nitrate nitrogen. Phosphorus losses were mainly through surface runoff, which resulted in 66% of the total losses and was dominated by organic phosphorus and soluble phosphorus. Representing about 49% of the watershed area, the corn-soybean rotation system contributed 83% and 88% of the total nitrogen and phosphorus inputs, respectively, to the watershed, as well as 64% and 46% of the nitrogen and phosphorus losses to the water system, respectively. The non-growing season (October to the next April) was identified as the critical period resulting in water and nutrient losses due to low evapotranspiration and plant uptake. Targeted management strategies for reducing nutrient loads in key hydrological paths were suggested.

English

Soil water deficit is a major production-limiting factor in the predominantly rainfed agriculture of the Ruzizi plain, eastern Democratic Republic of Congo (DRC). Appropriate soil and water conservation (SWC) practices would be a valuable option for maximizing water uptake by plants in the context of water demand and supply unbalance. This study assessed the efficiency of selected SWC practices in improving water and nutrient (nitrogen and phosphorus) balances along the slope gradients in Ruzizi plain using a three-season field experiment. The SWC practices, tied ridges and Zaï pits, improved the cumulative soil water balance by 148.7 and 21.1%, respectively, compared to conventional tillage. In the same order, the maize (Zea mays L.) yield performance significantly varied with SWC practices: tied ridges (2.16 t ha-1) out performed the Zaï pits (1.48 t ha-1) and conventional tillage (1.58 t ha-1).  Besides, the tied ridges reduced the total nitrogen losses by 34.4–49.8%, compared to conventional tillage. However, SWC practices were only reliable when daily rainfall amounts were at reasonable threshold (>10 mm) and on low slope gradients (<8%). Therefore, tied ridges provide an opportunity as a component of an integrated soil water and nutrient management strategy to sustain the rainfed maize production in Ruzizi plain. Key words: Tied ridges, Zaï pits, rainfall variability, slope gradient, dryland, Zea mays L.

Non-point source pollution loads estimation in Three Gorges Reservoir Area based on improved observation experiment and export coefficient model.

The non-point source (NPS) pollution has become an important limitation to the sustainable development of the Three Gorges Reservoir Area (TGRA) water resources. NPS load estimation research has theoretical and realistic significance for water environment security and water pollution control. Therefore, the TGRA was chosen to be the study area, and the export coefficients of different land-use type were calculated through literature consultation method combined with improved observation experiment. The load of total nitrogen (TN) and total phosphorus (TP) of NPS from different pollution sources including farmland, decentralized livestock and poultry breeding and domestic pollution sources were estimated. The results are shown as follows: the order of TN load of different sources in the TGRA from high to low was land use, livestock and poultry breeding, rural life; the TN from land use was 372% higher than that of rural; the order of TP load of different sources in the TGRA from high to low was livestock and poultry breeding, rural life, land use; the TP from livestock and poultry breeding was 114.5% higher than that of land use. Therefore, control of livestock and poultry sewage discharges was the key practice to limit the TP loss, while the optimization of agricultural management was the key practice to control the loss of TN.

Different Effects of Thermophilic Microbiological Inoculation With and Without Biochar on Physicochemical Characteristics and Bacterial Communities in Pig Manure Composting.

This study evaluated the effects of thermophilic microbiological inoculation alone (TA) and integrated with biochar (TB) on the physicochemical characteristics and bacterial communities in pig manure (PM) composting with wheat straw. Both TA and TB accelerated the rate of temperature increase during the PM composting. TA significantly reduced total nitrogen loss by 18.03% as opposed to TB which significantly accelerated total organic carbon degradation by 12.21% compared with the control. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were the major phyla in composting. Variation of the relative abundance of genera depended on the composting period and treatment. The genera Lactobacillus (26.88–46.71%) and Clostridium_sensu_stricto (9.03–31.69%) occupied a superior position in the temperature rise stage, and Bacillus (30.90–36.19%) was outstanding in the cooling stage. Temperature, total nitrogen (TN), and ammonium nitrogen significantly influenced the bacterial phyla composition. TN, water content, and nitrite nitrogen were the main drivers of the bacterial community genera. Furthermore, our results demonstrated that microbiological consortia were resistant to high temperatures and could fix nitrogen for enriched Pseudomonas; however, when interacted with biochar, total organic carbon (TOC) degradation was accelerated for higher bacterial richness and diversity as well as overrepresented Corynebacterium.

Effects of Different Fertilization Patterns on Nitrogen Leaching Loss from Paddy Fields Under Reduced Nitrogen

Nitrogen leaching loss in paddy fields is one of the main ways of farmland non-point source pollution. To explore the suitable fertilization of rice fields in the Erhai Lake Basin and reduce the nitrogen loss from paddy fields, a field experiment was conducted by setting single applications of chemical or organic fertilizer, combined organic and inorganic application, and single application of controlled release fertilizer under reduced nitrogen conditions. The results showed that, compared with the conventional fertilization treatment(CF), there was no significant difference in rice grain and straw yield between the single chemical fertilizer treatment(T1) and the organic-inorganic combined treatment(T3); the single organic fertilizer treatment(T2) decreased the rice grain yield by 13.0%, and decreased straw yield by 17.1%; single application of controlled-release fertilizer(T4) increased rice grain and straw yield by 15.7% and 21.0%, respectively. Further, compared with CF, the single application of chemical fertilizer(T1), organic fertilizer(T2), and organic-inorganic combined application(T3) reduced the total nitrogen leaching loss at 30 cm depths by 26.9%, 18.0%, and 33.9%, respectively. The loss of ammonia nitrogen leaching with T1, T2, and T3 decreased by 24.4%, 36.9%, and 36.6%, respectively, and the loss of nitrate nitrogen leaching decreased by 40.2%, 4.8% and 46.4%. The total nitrogen leaching at 60 cm soil depths was reduced by 34.2%, 26.3%, and 42.1%, the loss of ammonia nitrogen leaching was reduced by 31.4%, 35.7%, and 46.6%, and the loss of nitrate nitrogen leaching was reduced by 8.0%, 10.1%, and 23.9% for T1, T2, and T3, respectively. The total nitrogen loss at 30 and 60 cm depths increased by 41.6% and 14.0% in the single application of controlled release fertilizer(T4) treatment. Considering factors such as agronomic and environmental benefits of different fertilization modes, T1 and T3 are suitable environmentally friendly alternative fertilization modes.

Comprehensive quantification of global cropland ammonia emissions and potential abatement

Ammonia (NH3) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH3 emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH3 emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH3 emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8–31.2 Tg N yr−1 during 1996–2013 with the increase rate of 1.6% yr−1. Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH3 emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH3 emissions will decline by 26% from 2010 to 2100 given a 0.5% yr−1 decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH3 emissions by up (71%, 17.6 Tg N yr−1) at an abatement cost of US$524 billion. Our findings indicate that cropland NH3 emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH3 abatement strategies.

Modified bentonite as a conditioning agent for stabilising heavy metals and retaining nutrients in sewage sludge for agricultural uses.

The management and disposal of excess sludge are emerging issues owing to the high costs associated with treatment. In this study, the viability of a modified bentonite was investigated as a conditioning agent for the stabilisation of heavy metals (i.e., Cu, Zn, Cr, Pb, and Cd) and the retention of nutrient species (i.e., total nitrogen (TN), total phosphorus (TP), available nitrogen (available N), and Olsen-phosphorus (Olsen-P)) in sewage sludge for agricultural use. Five grams of modified bentonite resulted in the highest stabilisation rate of heavy metals and strongly contributed to the stabilisation of heavy metals. However, increased amounts of modified bentonite might increase the TN, available N, and TP losses in the conditioned sewage sludge. Through the analytic hierarchy process modelling, optimal concentrations of nutrient species and heavy metals remaining in the conditioned sewage sludge were achieved when the ratio of bentonite to sewage sludge was 1:12.5 (4 g bentonite : 50 g sludge). Moreover, the optimal mixing ratio of the conditioned sewage sludge to the soil (1:2) was suggested for agricultural use. Based on these observations, modified bentonite allowed the sewage sludge to be used as a fertiliser in agriculture by stabilising heavy metals and retaining nutrient species.

Effect of Environmental Factors on Soil Nutrient Loss under Conditions of Mining Disturbance in a Coalfield

Underground coal mining can result in land deformation (e.g., land subsidence and ground fissures), and may consequently change the soil nutrients. Soil organic matter (SOM), total nitrogen (TN), and available phosphorus (AP) are critical indicators of soil fertility and eco-restoration in mining areas. In this study, soil samples (depth: 0–20 cm) were collected twice from 20 sampling points in pre-mining and post-mining in the No.12 panel of Caojiatan coalfield, in the Loess Plateau of China. SOM, TN, and AP in soil samples were measured, and the nutrient loss was evaluated. Ten environmental factors affecting soil nutrient loss were identified from a 5-m resolution digital elevation map (DEM). The paired t-test was utilized to evaluate the differences between SOM, TN, and AP in pre-mining and post-mining soil. The mechanisms of the effects of environmental factors on soil nutrient loss were revealed based on multiple linear regression, redundancy analysis (RDA), and the random forest algorithm (RF). Ordinary kriging and RF were utilized to predict and optimize the spatial distribution of the soil nutrient loss. The results showed that significant differences existed between the SOM, TN, and AP in the pre-mining and post-mining soil. The model established by RF provided a higher accuracy in terms of fitting the correlation between soil nutrient loss and environmental factors compared to the model established by multiple linear regression, and the feature importance obtained by RF showed that profile curvature, distance to working panel margin, and surface roughness were the most significant factors affecting the loss of SOM, TN, and AP, respectively. This study provides a theoretical reference for eco-restoration, as well as soil and water conservation, in subsided lands in coalfields.

Effect of Geobacillus toebii GT-02 addition on composition transformations and microbial community during thermophilic fermentation of bean dregs

Bean dregs can be prepared into organic fertilizer by microbial fermentation. Geobacillus toebii GT-02, which has promoting effect on bean dregs fermentation, was isolated from horse dung and it grows within a range of 40–75 °C and pH 6.50–9.50. The effectiveness of GT-02 addition on composition transformations and the microbial community in bean dregs thermophilic fermentation at 70 °C for 5 days was investigated (T1). Fermentation of bean dregs without GT-02 served as control (CK). The results showed that T1 (the germination index (GI) = 95.06%) and CK (GI = 86.42%) reached maturity (defined by GI ≥ 85%) on day 3 and day 5, respectively. In addition, the total nitrogen loss of T1 (18.46%) on day 3 was lower than that in CK (24.12%). After thermophilic fermentation, the total organic carbon and dry matter loss of T1 (53.51% and 54.16%) was higher than that in CK (41.72% and 42.82%). The mean microbial number in T1 was 4.94 × 107 CFUs/g dry matter, which was 5.37 times higher than that in CK. 16S rDNA sequencing identified Bacillus, Geobacillus and Thermobacillus as dominant in CK, while Bacillus, Ammoniibacillus and Geobacillus were dominant in T1. A canonical correspondence analysis showed that Geobacillus and Ammoniibacillus were positively correlated with the GI. Thus, thermophilic fermentation with GT-02 can promote the maturity of bean dregs, which indicated the potential application value of GT-02 in thermophilic fermentation.

Runoff and nutrient losses in alfalfa (Medicago sativa L) production with tied-ridge-furrow rainwater harvesting on sloping land

Ridge-furrow rainwater harvesting (RFRH) is known to be effective in controlling water loss and soil erosion, and increasing soil moisture and crop yield in semiarid regions. However, it can cause waterlogging, ridge overtopping, and harvest failure if not properly designed. A four consecutive-year field trial was carried out to assess the impacts of various slope gradients and tillage practices on soil moisture, runoff, sediment yield, associated soil nutrient losses, fodder yield, and water use efficiency (WUE) of alfalfa in the Loess Plateau, China. The trial adopted a split-plot design, taking slope gradient (5° and 10°) as main plot treatment and tillage practice (traditional tillage, open-ridging, and tied-ridging) as split-plot treatment, from 2015 to 2018. There were greater variations in runoff, sediment yield, and associated soil nutrient losses than in fodder yield and WUE. Tied-ridging and open-ridging resulted in decreased runoff and reduced sediment transport and associated soil nutrient losses, and increased soil moisture, fodder yield, and WUE. Runoff, sediment transport, and associated soil nutrient losses inclined with increasing slope; while fodder yield and the WUE declined. For slopes of 5° and 10°, the average decrease in runoff, sediment yield, total nitrogen, total phosphorus, and organic matter losses for open-ridging were 47.7–56.2%, 91.0–92.7%, 90.4–93.1%, 90.1–92.2%, and 88.9–90.2%, respectively, while these for tied-ridging were 62.4–68.4%, 94.5–96.4%, 93.6–95.5%, 93.9–95.9%, and 93.0–94.9%, over 4 years as compared with traditional tillage. The mean annual runoff, sediment, total nitrogen, total phosphorus, and organic matter losses for slopes of 10° were 1.31, 1.96, 1.87, 1.99, and 1.64 times greater than the corresponding values for slopes of 5°, respectively. The increase of fodder yield and WUE for open-ridging and tied-ridging was 40.1–45.6% and 16.0–17.5%, and 3.66–5.99 and 1.35–2.50 kg ha−1 mm−1, respectively, for slopes of 5° and 10°. The average fodder yield and WUE for slopes of 5° were 1.19 and 1.23 times greater than corresponding values for slopes of 10°, respectively. The disparities in fodder yield and WUE of alfalfa between slopes of 5° and 10° were not clear in dry years, but were evident in wet years. Tied-ridging was recommended for water and soil conservation, while open-ridging was recommended for increase of fodder yield and WUE of alfalfa. The implementation of RFRH in crop production should be evaluated by the use of a model in accordance with climatic conditions, soil type, and plant species.

Gaseous Nitrogen Emission from Soil After Application of NH4+-N Loaded Biochar

To safely and effectively transfer NH4+-N from eutrophic water to soil, biochar was applied to adsorb NH4+-N from wastewater, and this NH4+-N loaded biochar (N-BC) was subsequently used as a soil amendment. Understanding the influence of N-BC on N2O-N emission and NH3-N volatilization is important for both decreasing the application of chemical fertilizers and reducing gaseous nitrogen loss from soil. In this study, experiments were conducted in soil columns with four treatments, namely CK (no fertilizer), NPK (chemical fertilizer), N-BC+PK (NH4+-N loaded biochar+chemical fertilizer), and BC+NPK (biochar+chemical fertilizer). Compared to both the NPK and BC+NPK treatments, N-BC+PK significantly reduced the cumulative N2O-N emissions and NH3-N volatilization, as well as the total gaseous nitrogen loss from the soil (P<0.05). Relative to NPK and BC+NPK, cumulative N2O-N emissions decreased by 33.62% and 24.64%, cumulative NH3-N volatilization decreased 70.64% and 79.29%, and the cumulative total gaseous nitrogen loss decreased by 64.97% and 73.75%. In particular, BC+NPK significantly enhanced the cumulative NH3-N volatilization. Furthermore, the N2O-N emission flux and NH3-N volatilization rate were significantly positively correlated with the NH4+-N concentration, NO3--N concentration, and pH of soil (P<0.01). Overall, using NH4+-N loaded biochar can significantly decrease N2O-N emissions and NH3-N volatilization, relative to the traditional application combining biochar and chemical fertilizer. This research provides solid theoretical support and data for the application of NH4+-N loaded biochar in soil, to reduce gaseous nitrogen loss.

The Effect of Soil Conservation Measures on Runoff, Soil Erosion, TN, and TP Losses Based on Experimental Runoff Plots in Northern China

Total nitrogen (TN) and total phosphorous (TP) are the main pollutants affecting the water quality of the Miyun Reservoir, Beijing. However, few studies have been conducted on their responses to implemented soil conservation measures at a slope scale in northern China. To explore the impact of soil conservation measures on TN and TP losses, field monitored data from 18 runoff plots under natural rainfalls were used to analyze the changing characteristics of runoff, soil loss, and nutrient losses during 2014–2019. The results indicated that runoff, soil erosion, as well a TN and TP losses from the plots varied significantly, depending on land use and soil conservation measures. Bare plots suffered the highest soil, TN, and TP losses, followed by cultivated plots without soil conservation measures, cultivated plots with contour tillage, and other plots. Event-averaged runoff and soil loss rates ranged from 0 to 7.9 mm and from 0 to 444.4 t km−2 yr−1, and event-averaged TN and TP losses from cultivated plots were the highest, with values of 39.8 and 3.0 kg km−2, respectively. Bare and cultivated plots were the main sediment and nutrient sources. Among the cultivated plots, the terraced plot had the lowest soil and nutrient losses. The vegetated plots had insignificantly lower soil and nutrient losses. Most TN and TP were lost in particulate status from the plots, especially from the plots with soil conservation measures. Soil conservation measures can effectively prevent TN and TP losses. To guarantee water resource use, contour tillage is preferred for the bare and cultivated lands in the study region.

Modeling daily surface runoff, sediment and nutrient loss at watershed scale employing Arc-APEX model interfaced with GIS: a case study in Lesser Himalayan landscape

The present study was carried out to evaluate performance of Agricultural Policy Environmental eXtender (APEX) integrated with GIS as ArcAPEX model in simulating surface runoff, sediment and nutrients loss from a watershed located in lesser Himalayan region in Uttarakhand state, India. Daily surface runoff, sediment and nutrient loss data measured at watershed level for the year 2010–2011. Measurement at watershed revealed average daily sediment loss in range of 1.0–1.32 t ha−1 was measured with peak of 3.04 t ha−1 on daily time-step. The loss of total carbon (TC) and total nitrogen (TN) were estimated from 0.49 to 0.58 kg ha−1 and 0.16 to 01.7 kg ha−1, respectively from the watershed on daily basis for the rainfall considered for the modelling. A total of 40 rainy days surface runoff and sediment data were collected and of which half of the events data were used for calibration and remaining for validation. The calibration was done by changing the sensitive parameters. Analysis showed that SCS CN number was found most sensitive to runoff, followed by saturated hydraulic conductivity, available water-holding capacity, CN retention parameter and C factor whereas erosion control practice (P) factor was found to be most sensitive, followed by C factor, sediment routing coefficient, average upland slope and soil erodibility (K) factor for the sediment and nutrient loss. APEX model calibrated for the watershed and it predicted quite well for the surface runoff (r = 0.92, NSE = 0.50), sediment loss (r = 0.88, NSE = 0.61 and nutrients of total carbon (r = 0.78, NSE = 0.59) and fairly for total nitrogen (r = 0.77, NSE = 0.19). The calibration and validation results indicate that APEX model can be satisfactorily used for predicting runoff, sediment and nutrient (TC) loss at watershed scale on daily time-step. The landscape is prone landslips/ collapse of field terraces etc. occurring at high rainfall events was not accounted by the model that may be a reason for under prediction of sediment loss by the model. The study suggests to incorporate landslips/collapse of field terraces, etc., processes in future improved versions of APEX for improving sediment yield prediction in the Himalayan landscape.

Impacts of rainfall and soil conservation measures on soil, SOC, and TN losses on slopes in the black soil region, northeastern China

Water erosion significantly affects the productive black soils in Northeastern China. The aim of this study was to analyze the impacts of rainfall characteristics, slope, and soil conservation measures on soil, soil organic carbon (SOC), and total nitrogen (TN) losses and thus to help implement a rational soil loss control strategy. The present study was conducted using sampled soil, runoff, and soil loss data from the plots in the years 2014, 2015, and 2020 when the rainfall characteristics varied greatly. Studies found that soil, SOC, and TN losses on the 18 plots differed greatly, depending on soil conservation measures, slope and rainfall characteristics. Bare and up-downslope (UD) cultivated plots suffered the highest loss rates of soil, SOC, and TN. In 2014, annual loss rates of soil, SOC, and TN on the UD plots reached 5849, 88.55, and 6.84 t km−2 yr−1, respectively. In 2015, soil loss rate (SLR) on the UD plots approached 434.88 t km−2 yr−1 with SOC and TN loss rates of 5.83 and 0.44 t km−2 yr−1. In 2020, the mean SLR on the UD plots was 637.96 t km−2 yr−1 which was lower than that (i.e., 1385.61 t km−2 yr−1) on the bare plots. Annual loss rates of soil, SOC, and TN presented an increasing trend with increasing slope degree. The soil, SOC and TN control efficiencies of contour tillage and hedgerow planting on the 3° and 5° plots were around 90%. The mean SLR on the 53-m terraced plots was two times the tolerable value (i.e., 200 t km−2 yr−1). The size of terrace on steep slopes should be reconsidered, and slope length should be reduced. Bare and UD slopes must be implemented with rational soil conservation measures to control soil, TN, and SOC losses in the black soil region of northeastern China.