Guiding the landscape patterns evolution is the key to mitigating river water quality degradation.

Consensus has emerged that landscape pattern evolution significantly impacts the river environment. However, there remains unclear how the landscape pattern evolves possible to achieve a balance between land resource use and water conservation. Thus, simulating future landscape patterns under different scenarios to predict river eutrophication level is critical to propose targeted landscape planning programs and alleviate river water quality degradation. Here, we coupled five water quality parameters (TOC, TN, NO3--N, NH4+-N, TP), collected from October 2020 to September 2021, to construct the river eutrophication index (EI) to assess river water quality. Meanwhile, based on redundancy analysis, patch-generating land use simulation model, and stepwise multiple linear regression model comprehensively analyze the Fengyu River watershed landscape patterns evolution and their impact on river eutrophication. Results indicated that current rivers reach eutrophic levels, and EI reaches 40.7. The landscape patterns explain 88.2 % of river eutrophication variation, while the LPI_Con metric is critical and individually explained 21.5 %. Furthermore, eutrophication in the watershed will increase in 2040 under the natural development (ND) scenario, and the EI will reach 44.4. In contrast, farmland protection (FP) scenarios and environmental protection (EP) scenarios contribute to mitigating eutrophication, the EI values are 38.2 and 38.1, respectively. The results provide a potential mechanistic explanation that river eutrophication is a consequence of unreasonable landscape pattern evolution. Guiding the landscape patterns evolution based on critical driver factors from a planning perspective is conducive to mitigating river water quality degradation.

Enhancing rice production sustainability and resilience via reactivating small water bodies for irrigation and drainage.

Rice farming threatens freshwater resources, while also being increasingly vulnerable to drought due to climate change. Rice farming needs to become more sustainable and resilient to climate change by improving irrigation drainage systems. Small water bodies, used to store drainage water and supply irrigation in traditional rice farming systems have gradually been abandoned in recent decades. This has resulted in a higher water footprint (WF) associated with rice farming due to increased freshwater usage and wastewater release, also leaving rice production more vulnerable to extreme weather events. Here, we propose how protecting and reactivating small water bodies for rice irrigation and drainage can decrease rice production WF in China by 30%, save 9% of China's freshwater consumption, increase irrigation self-sufficiency from 3% to 31%, and alleviate yield loss in dry years by 2-3%. These findings show that redesigning rice irrigation drainage systems can help meet water scarcity challenges posed by climate change.

Fate of 15N-labelled urea as affected by long-term manure substitution.

Quantifying the fate of fertilizer nitrogen (N) is essential to develop more sustainable agricultural fertilization practices. However, the fate of chemical fertilizer N, particularly in long-term manure substitution treatment regimes, is not fully understood. The present study aimed to investigate the fate of 15N-labelled urea in a chemical fertilizer treatment (CF, 240 kg 15N ha-1) and N manure 50 % substitution treatment (1/2N + M, 120 kg 15N ha-1 + 120 kg manure N ha-1) in two continuous crop seasons, based on a 10-year long-term experiment in the North China Plain (NCP). The results showed that manure substitution greatly enhanced 15N use efficiency (15NUE) (39.9 % vs. 31.3 %) and suppressed 15N loss (6.9 % vs. 7.5 %) compared with the CF treatment in the first crop. However, the N2O emissions factor in the 1/2N + M treatment was increased by 0.1 % (0.5 kg 15N ha-1 for CF vs. 0.4 kg 15N ha-1 for 1/2N + M) compared with the CF treatment, although N leaching and NH3 volatilization rates decreased by 0.2 % (10.8 kg 15N ha-1 for CF vs. 5.1 kg 15N ha-1 for 1/2N + M) and 0.5 % (6.6 kg 15N ha-1 for CF vs. 2.8 kg 15N ha-1 for 1/2N + M), respectively. In which, only NH3 volatilization presented significantly difference between treatments. It is important to note that in the second crop, the residual 15N in soil (0-20 cm) remained mostly in the soil for the CF (79.1 %) and the 1/2N + M treatment (85.3 %), and contributed less to crop N uptake (3.3 % vs. 0.8 %) and leached losses (2.2 % vs. 0.6 %). This proved that manure substitution could enhance the stabilization of chemical N. These results suggested that long-term manure substitution effectively increases NUE, suppresses N loss, and improves N stabilization in soil, but negative impacts such as N2O emissions due to climate change should be investigated further.

[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 to mitigate nitrogen emissions from paddy runoff: A microbiological perspective.

Ditches and ponds are the basic units of agroecosystems that serve irrigation and drainage and also perform the natural ecological function of reducing nitrogen (N) emissions. To better enhance the design and advance management strategies in the paddy field ecosystem to minimize N emission, the N cycling microorganism in the paddy field ecosystem including interconnected fields with rice-wheat rotation, ditches, and ponds in central China was investigated by metagenomic techniques. Our results showed that ditches and ponds may be N removal hotspots by microorganisms in the rice and wheat seasons respectively. Given seasonal variation, the abundance of N-related microorganisms was high during the rice season. However, the Shannon and Simpson indices were lower and the microbial co-occurrence network was destabilized, which could make microbes in the rice season fragile and sensitive. Phytoplankton as key environmental factors affecting the N cycling microbial could promote more stable microbial communities through maintaining a good mutualistic symbiosis. While high algae concentration significantly promotes the abundance of norB than nosZ (P < 0.05), which may result in more N2O production. To trade off N removal and N2O emission, the algae concentration needs to be controlled. Our findings provide a systematic profile of N-related microorganisms in the paddy field ecosystem, and it would benefit in developing effective strategies for limiting N pollution in agriculture.

Managing landscape patterns at the riparian zone and sub-basin scale is equally important for water quality protection.

Widespread attention has been given to understanding the effect of the landscape pattern on river water quality. However, which spatial scale (riparian zone versus sub-basin) has the greater impact on water quality has long been controversial, since the key metrics that affect water quality varied with spatial scale. Thus, quantifying the spatial scale effects of key landscape metrics on water quality is critical to clarifying which scale of landscape pattern is more conducive to water quality conservation. Here, we adopted variation partitioning analysis (VPA) and random forest models to quantify the landscape pattern impact on water quality at northern Erhai Lake during the 2019 rainy season (early, mid, and late), and comprehensively analyze the key landscape metrics on different scales. The results revealed that the riparian zone and sub-basin scale landscape patterns explained similar water quality variations (difference only 0.9%) in the mid (August) and late rainy season (October), but exhibited a large difference (24.1%) during the early rainy season (June). Furthermore, rivers were primarily stressed by nitrogen pollution. Maintaining the Grassland_ED > 27.99 m/ha, Grassland_LPI > 4.19%, Farmland_LSI < 3.2 in the riparian zone, and Construction_ED < 1.69 m/ha, Construction_LSI < 2.46, Farmland_PLADJ < 89.0% at the sub-basin scale could significantly reduce the TN concentration in the stream. Meanwhile, managing of these metrics can effectively prevent rapid increases of TN in rivers. Moreover, due to the low phosphorus concentration in the rivers, none of the landscape metrics significantly explained the variation in TP. This study explored the spatial scale effect of landscape patterns on water quality and revealed the driving factors of nutrient variation. This study will provide a scientific basis for aquatic environmental management in plateau watersheds.

Rice-crayfish pattern in irrigation-drainage unit increased N runoff losses and facilitated N enrichment in ditches.

The rice-crayfish (RC) integrated pattern has been developed vigorously in China, but how it affects the nitrogen (N) runoff loss and distribution status during rice production is still poorly studied. Based on this, we selected two types of irrigation and drainage units (IDUs), which adopted the traditional rice-wheat (RW) rotation pattern and burgeoning RC rotation pattern separately, to investigate the effect of the RC pattern on N runoff loss, inorganic N distribution and N balance of the IDU. The results showed that there was a 241 kg ha-1 yr-1 and 135 kg ha-1 yr-1 N surplus achieved under RW and RC, respectively. Among these, the N surplus of RC was 53 % lower than that of RW during the rice growing season and was 37 % lower at other times. The NH4+-N contents of paddy field soils, rice yields and productive traits were not affected by rotation patterns. Nevertheless, the total nitrogen (TN), dissolved organic nitrogen (DON) and NH4+-N concentrations of RC field water were significantly higher (P < 0.01), and the N runoff losses of the RC pattern increased by 103 % to 855 % compared with the RW pattern. In addition, the NH4+-N reserved in RC ditch sediments substantially increased regardless of the dynamic changes during the rice growing season or from the vertical distribution at depths of 0-40 cm. Our results indicated that the RC pattern was beneficial for decreasing the N surplus without impacting the rice yield. However, larger N runoff losses and more available N flowing into crayfish farming ditches still pose great environmental risks. Therefore, more efficient and cleaner measures should be applied for the N management of IDU under the RC pattern.

Improved estimation of nitrogen dynamics in paddy surface water in China.

Paddy surface water is the direct source of artificial drainage and surface runoff leading to N loss from rice paddy fields. Quantifying the N dynamics in paddy surface water on a large scale is challenging because of model deficiencies and the limitations of field measurements. This study analyzed the N dynamics and the influencing factors in paddy surface water in the three main Chinese rice-growing regions: Northeast Plain, Yangtze River Basin, and Southeast Coast. An improved first-order kinetic model was proposed to evaluate the total nitrogen (TN) dynamics at a countrywide scale by improving the calculation method of the initial TN concentration (C0) and providing the optimum value of attenuation coefficient (k). The results show that: (1) the average reduction rate of TN concentration on the 7th day after fertilization increased with the growth period (85%, 90%, and 95% during the basal, tillering, and panicle fertilization periods, respectively); (2) the attenuation coefficient k for the growth periods was ranked as follows: panicle fertilization period > tillering fertilization period > basal fertilization period. The Yangtze River Basin had the highest average k value (0.31-0.34), followed by the Southeast Coast (0.24-0.41) and Northeast Plain (0.22-0.30); and (3) the improved first-order kinetic model performed well in the N dynamics estimation (R2 > 0.6). High TN concentration with high fertilizer application amounts and precipitation caused the Yangtze River Basin to have a high N runoff loss risk. The proposed universal model realizes the simulation of N dynamics from a single site to multi-sites while greatly saving multi-site monitoring costs. This study provides a basis for effectively optimizing N management and preventing N loss in rice paddies.

Restriction of biosolids returning to land: Fate of antibiotic resistance genes in soils after long-term biosolids application.

Although the utilization of biosolids in agricultural lands is widely considered as an effective way to improve resource reuse, the presence of antibiotic resistance genes (ARGs) severely restricts biosolids returning to fields. A 12-year long-term experiment with different biosolids application rates (from 0 to 36 t ha-1 yr-1) was conducted to study the effect of biosolids application on shaping ARGs in soil. Biosolids application significantly increased ARGs abundance in the soil, except for MBS treatment (9 t ha-1 yr-1 biosolids application). The abundance of ARGs in soil did not increase linearly with the dose of biosolids applied, but they were significantly (P < 0.05) positively correlated. A total of 173 subtypes were detected, among them mobile genetic elements (MGEs), aminoglycoside, and multidrug resistance genes were the most dominant types. Except for MBS treatment, most of the ARGs detected were enriched in amended soils after long-term continuous biosolids application. Specifically, tetPA, sul1, mefA, and IS6100 were highly enriched in all amended soils. In addition, biosolids application increased soil nutrients and heavy metals, and changed the soil microbial community, all of which affected ARGs formation. But MGEs may be a greater factor for shaping ARGs profiles than soil properties. Overall, controlling the rate of biosolid application is the key to reducing the accumulation and horizontal transfer of ARGs in soils.

Leached phosphorus apportionment and future management strategies across the main soil areas and cropping system types in northern China.

Excess phosphorus (P) leached from high fertiliser input cropping systems in northern China is having detrimental effects on water quality. Before improved management can be directed at specific soils and cropping system types estimates of P leached loss apportionment and mitigation potentials across the main soil (fluvo-aquic soil, FAS; cinnamon soil, CS; black soil, BS) areas and cropping systems (protected vegetable fields, PVFs; open vegetable fields, OVFs; cereal fields, CFs) are needed. The present study designed and implemented conventional fertilisation and low input system trials at 75 sites inclusive of these main soils and cropping system types in northern China. At all sites, a uniform lysimeter design (to 0.9 m depth) enabled the collection and analysis of leachate samples from 7578 individual events between 2008 and 2018. In addition, site-specific static and dynamic activity data were recorded. Results showed that annual total phosphorus (TP) leached losses across the main soil areas and cropping systems were 4.99 × 106 kg in northern China. A major finding was PVFs contributed to 48.5% of the TP leached losses but only accounted for 5.7% of the total cropping areas. The CFs and OVFs accounted for 40.3% and 11.2% of the TP leached losses, respectively. Across northern China, the TP leached losses in PVFs and OVFs were greatest in FAS areas followed by CS and BS areas. The higher TP leached losses in FAS areas were closely correlated with greater P fertiliser inputs and irrigation practices. From a management perspective in PVFs and OVFs systems, a decrease of P inputs by 10-30% would not negatively affect yields while protecting water quality. The present study highlights the importance of decreasing P inputs in PVFs and OVFs and supporting soil P nutrient advocacy for farmers in China.

The impact of immersed liquid circulation on anaerobic digestion of rice straw bale and methane generation improvement.

Immersed liquid circulation is assumed to improve solid-state anaerobic digestion (SS-AD) with digestate flow convection on the surface of solid-state bed (SSB), which depends on SSB concentration and circulation rate (CR). In this study, the impact of CR on rice straw SS-AD was investigated within a 30 L pilot digester. Results showed that SSB threshold concentration for efficient biogas conversion was 10%-12% TS, achieving the methane yield of 185.3 mL/g VS. Within the threshold, methane production progress and VFAs release could be enhanced simultaneously by rational CR increasing, but no significant methane yield improvement was observed; above, the rapid and stable biogas generation could be acquired with a competitive methane yield of 174.7 mL/g VS (150% CR). No matter within or above the threshold, efficient lingo-cellulosic degradation was always accompanied by the moderate CR for effective methane generation. SSB was proposed to be above threshold for industrial application.

Effects of biochar application with fertilizer on soil microbial biomass and greenhouse gas emissions in a peanut cropping system.

This study investigated the effects of biochar application with organic or mineral fertilizers on soil microbial biomass, and associated emissions of CO2 and CH4 under field settings planted with peanut. The results indicated that physicochemical properties of soil were improved under biochar application. Soil microbial biomass carbon (MBC) was significantly increased with the application of biochar plus organic fertilizer compared to that of organic fertilizer only, but no significant difference of MBC was found between the treatment under biochar application plus mineral fertilizer and that under mineral fertilizer only. Biochar application did not affect the amount of microbial biomass nitrogen (MBN) with either mineral or organic fertilizer. The cumulative CO2 emission did not change under biochar application, while the cumulative CH4 emission was significantly decreased (p < 0.05) by 68.67% on average with the application of organic fertilizer plus biochar compared to that of organic fertilizer only. When biochar was applied in combination with either mineral or organic fertilizer, both the net global warming potential (GWP) and the greenhouse gas intensity (GHGI) were significantly decreased compared to that without biochar amendment. In all, biochar can improve soil quality, and enhance soil carbon sequestration as well as peanut yields.

Joint analytical hierarchy and metaheuristic optimization as a framework to mitigate fertilizer-based pollution.

The emission of nitrogenous pollution from agricultural lands in form of ammonia volatilization, leaching, runoff, N2O emissions, etc. is still a serious challenge to which agricultural sector faces. In this context, a vast number of decision support systems have been developed and tested to find the best nitrogen application rate. These models are highly dependent on crop simulation models, mathematical and regression models, evolutionary algorithms and artificial intelligent, GIS-based models, etc., while in most cases have ignored to be interfered with regional and national regulations established by experts in the field. In this study, a new framework combining analytical hierarchy (AHP)/modified AHP methods (MAHP) plus metaheuristic optimization techniques has been suggested to find the best nitrogen application rate considering regional capacities and requirements. To reach the objectives of the present study a three yield field experiment was conducted upon which crop yield, nitrogen use efficiency, nitrogen uptake, soil nitrate, ammonia volatilization, N2O emissions, and N leaching were monitored or measured. Using the results from the field experiments and a survey from local experts, the models were developed. AHP-assisted optimization model could cause some biases in the final results due to its intrinsic nature which avoids direct pairwise comparison among indicators (so called sub-criteria) under two different main-criteria. On the contrary, MAHP-assisted model could well reflect the concerns of experts and notably decrease hotspot pollution. Such decision support system can satisfy both farmers and environmentalists' need because of the created high profit and low environmental pollution, while saving resources and ensuring a sustainable production system.

[Emission Characteristics of Nitrogen and Phosphorus in a Typical Agricultural Small Watershed in Tuojiang River Basin].

The emission of nitrogen and phosphorus via non-point source pollution from a small watershed has become the main pollution source of river waters, while climatic conditions and human activities directly affect the changes in rainfall-runoff and types of land use that are closely related to nitrogen and phosphorus pollution. In this study, we explore the runoff loss, nitrogen and phosphors concentration, and nitrogen and phosphorus emission in Huajiaogou small watershed on the upper reaches of Yangtze River. The rainfall, runoff, and temporal changes of nitrogen and phosphorus were analyzed using the continuous position monitoring data. The results showed that:① the runoff volumes were 10.05×105 m3 and 3.34×105 m3 from July 1st to September 30th, accounting for 76.58% and 56.51% in 2012 and 2013, respectively, and they were positively correlated to rainfall. The peak concentrations of ammonia nitrogen (NH4+-N) from April 1st to June 30th were 11.51 mg ·L-1 and 4.44 mg ·L-1in 2012 and 2013, respectively. ② The NH4+-N emission risk period was from July 1st to September 30th, accounting for 78.45% and 62.24% in 2012 and 2013, respectively. The peak concentration and emission risk period of total nitrogen (TN) and nitrate nitrogen (NO3--N) were from July 1st to September 30th, and NO3--N was the main form of the total nitrogen emission. The peak concentration of NO3--N was 6.06 mg ·L-1 and 11.43 mg ·L-1in 2012 and 2013, respectively, and the loss in NO3--N from July 1st to September 30th accounted for 88.74% and 65.55% in 2012 and 2013, respectively. ③The emission risk period of total phosphorus (TP), dissolved total phosphorus (DTP), and particulate phosphorus (PP) was also from July 1st to September 30th, and the particulate phosphorus was the main form of the total phosphorus emission. The particulate phosphorus emission from July 1st to September 30th accounted for 36% and 68% in 2012 and 2013, respectively, and the ration of particle phosphorus to total phosphorus was easily affected by rainfall.

How long-term excessive manure application affects soil phosphorous species and risk of phosphorous loss in fluvo-aquic soil.

The excessive application of manure has caused a high load of phosphorus (P) in the North China Plain. Having an understanding of how manure application affects soil P changes and its transport between different soil layers is crucial to reasonably apply manure P and reduce the associated loss. Based on our 28-year field experiments, the compositions and changes of P species and the risk of P loss under excessive manure treatments were investigated, i.e., no fertilizer (CK), mineral fertilizer NPK (NPK), NPK plus 22.5 t ha-1 yr-1 swine manure (LMNPK), and NPK plus 33.75 t ha-1 yr-1 swine manure (HMNPK). Manure application increased the content of orthophosphate and myo-inositol hexaphosphate (myo-IHP), especially the orthophosphate content exceeded 95%. The amount of orthophosphate in manure and the conversion of organic P to inorganic P in soil were the main reasons for the increased soil orthophosphate. Compared with NPK treatment, soil microbial biomass phosphorus and alkaline phosphatase activity in LMNPK and HMNPK treatments significantly increased. Compared with NPK treatment, a high manure application rate under HMNPK treatment could increase the abundance of organic P-mineralization gene phoD by 60.0% and decrease the abundance of inorganic P-solubilization gene pqqC by 45.9%. Due to the continuous additional manure application, soil P stocks significantly increased under LMNPK and HMNPK treatments. Furthermore, part of the P has been leached to the 60-80 cm soil layer. Segmented regression analysis indicated that CaCl2-P increased sharply when Olsen-P was higher than 25.1 mg kg-1, however the content of Olsen-P did not exceed this value until 10 years after consecutive excessive manure application. In order to improve soil P availability and decrease the risk of P loss, the manure application rate should vary over time based on soil physicochemical conditions, plants requirements, and P stocks from previous years.

Plastic pollution in croplands threatens long-term food security.

Plastic pollution is a global concern given its prevalence in aquatic and terrestrial ecosystems. Studies have been conducted on the distribution and impact of plastic pollution in marine ecosystems, but little is known on terrestrial ecosystems. Plastic mulch has been widely used to increase crop yields worldwide, yet the impact of plastic residues in cropland soils to soil health and crop production in the long term remained unclear. In this paper, using a global meta-analysis, we found that the use of plastic mulch can indeed increase crop yields on average by 25%-42% in the immediate season due to the increase of soil temperature (+8%) and moisture (+17%). However, the unabated accumulation of film residues in the field negatively impacts its physicochemical properties linked to healthy soil and threatens food production in the long term. It has multiple negative impacts on plant growth including crop yield (at the mean rate of -3% for every additional 100 kg/ha of film residue), plant height (-2%) and root weight (-5%), and soil properties including soil water evaporation capacity (-2%), soil water infiltration rate (-8%), soil organic matter (-0.8%) and soil available phosphorus (-5%) based on meta-regression. Using a nationwide field survey of China, the largest user of plastic mulch worldwide, we found that plastic residue accumulation in cropland soils has reached 550,800 tonnes, with an estimated 6%-10% reduction in cotton yield in some polluted sites based on current level of plastic residue content. Immediate actions should be taken to ensure the recovery of plastic film mulch and limit further increase in film residue loading to maintain the sustainability of these croplands.

The reactive nitrogen loss and GHG emissions from a maize system after a long-term livestock manure incorporation in the North China Plain.

The use of livestock manure as a substitution for synthetic nitrogen (N) fertilizers is recommended to improve the sustainable use of manure nutrients and alleviate the adverse impacts of synthetic N fertilizers on the environment. A thorough understanding of how such substitutions affect reactive N losses and greenhouse gas (GHG) emissions in cereal production systems in the North China Plain (a main livestock production region in China), is needed to achieve an environmental friendly and sustainable production. Based on a long-term field experiment, different manure/chemical fertilizer treatments were designed, i.e., non-fertilization control (CK), chemical fertilizers alone (NPK), and manure substitution for chemical N fertilizers (with equivalent N rate; NPKP, 50% N from pig manure; NPKC, 50% N from chicken manure). Crop yield, nitrogen use efficiency (NUE), soil fertility, N losses, and GHG emissions were chosen as prominent indicators to evaluate the consequences of manure substitutions for N-based fertilizers. The replacement of synthetic fertilizers by livestock manure decreased NO3-N leaching and NH3 volatilization by 46.2% and 5.61-22.2%, respectively, while sustained the crop yields and improved NUE. However, both NPKP and NPKC treatments did not have any impact on N2O and CO2 mitigation. Compared with NPK, NPKC and NPKP meaningfully increased SOC by 9.56% and 19.6%, respectively. More specifically, NPKC increased TN content by 14.7% (P < 0.05) compared to NPK treatment. The results showed that 50% substitution of manure for synthetic N fertilizers is a potential option in maize production systems to decrease N losses (including NH3, N2O emissions and N leaching) by approximately 45% (42.8-48.1%). However, only 1.81% of the total farmers surveyed (i.e., 16,595) have being applied livestock manure for maize cultivation in the North China Plain. Therefore, famers in this plain should be encouraged to use manure to improve ecological aspects of cereal cultivation and decrease the associated environmental pollutions.

Potential nutrient removal function of naturally existed ditches and ponds in paddy regions: Prospect of enhancing water quality by irrigation and drainage management.

Conventionally, paddy fields are regarded as important non-point sources of nutrient pollution, while ecological ditches and ponds are developed to reduce or retain nutrient export from agricultural fields. To quantify the potential nutrient removal function of ditches and ponds that naturally existed in rice growing regions, a representative paddy irrigation and drainage unit (IDU) composed of fields, ditches and a pond in the one-season rice region of the middle Changjiang River basin, China was monitored for two years. With data and knowledge gained, a Water Quantity and Quality Model for Paddy IDUs (WQQM-PIDU) is developed and applied for 30 years simulation to produce a general view. The monitored and modelled results showed that nutrient concentration peaks after fertilization was delayed and lowered in ditches and ponds, compared to those in paddy fields. Concentrations of runoff from the IDU outlet were generally lower than from the field during the whole rice growing season except the transplanting period. If fully utilized as temporary reservoirs, ditches and ponds naturally existed in a typical paddy IDU would reduce 39% nitrogen loads from field edges with a range of 17%-93% and 28% phosphorus loads with a range of 12%-92%. Although typical paddy IDUs discharge fewer nutrient loads than the content input into them, the discharge concentrations may be risky to surface waters. For their nutrient removal function, natural ditches and ponds are recommended to be included into irrigation and drainage management with accurate water level management during drainage, which is a promising and cost-effective approach to enhance surface water quality in rice growing regions.

Impact of human activities on phosphorus flows on an early eutrophic plateau: A case study in Southwest China.

The net anthropogenic phosphorus inputs (NAPI) model has been used extensively to assess changes in phosphorus (P) inputs and cycling in the environment. However, temporary populations have generally been unconsidered in these assessments. In this study, the NAPI model was used to estimate P loads from the 16 towns and villages in the Erhai Lake Basin (ELB), Southwest China and to evaluate the potential impact from temporary residents (tourism). The results showed that the average value P inputs in the basin (estimated at 2384 kg P km-2 year-1) were 5 times the national average level, and that temporary residents contributed 1%. Agriculture accounted for most of the net P, with chemical fertilizers (55% of the inputs) as the main source, followed by food and animal feed. Only 9.54% of the P inputs to the basin were exported. River water quality and NAPI were significantly correlated (P < 0.01). Tourism industry contributes significantly to regional economic growth and prosperity, but its beneficial effects on the economy does not equate with the adverse impact on environment. This study illustrates what is happening in Southwest China and provides scientific evidence that shows we need to find novel ways to reduce nutrients.