Phosphorus Losses In Runoff Research Articles

Spatiotemporal variations of cropland phosphorus runoff loss in China

Quantitative assessment of cropland phosphorus (P) loss via surface runoff is essential for developing effective pollution mitigation strategies. In this study, we compiled 812 datasets from 114 peer-reviewed papers for cropland P loss across China. We then developed machine learning (ML) approaches to estimate temporal and spatial variations in P runoff loss across China from 1990 to 2020. Four prevalent ML models were considered, namely, multiple linear regression (MLR), random forest (RF), classification and regression trees (CART), and boosted regression trees (BRT). Among these four models, RF exhibited the highest predictive accuracy for both uplands (calibration: R2 = 0.86, n = 293; validation: R2 = 0.61, n = 96) and paddy fields (calibration: R2 = 0.88, n = 137; validation: R2 = 0.60, n = 44). According to RF, China’s croplands are estimated to have lost an average of 148 ± 27 Gg P yr−1 from 1990 to 2020, with uplands and paddy fields contributing 114 ± 26 Gg P yr−1 and 34 ± 4 Gg P yr−1, respectively. There was a significant increase in upland TP runoff loss over the study period (p < 0.001), whereas paddy field TP loss remained relatively constant. Regions in southern, eastern, and southwestern China, notably in Hainan, Guangxi, and Fujian provinces, were identified as hotspots of cropland TP runoff loss. Improved cropland management scenarios were predicted to reduce TP runoff loss by 1.4–11.8 %, with the best results obtained by minimizing runoff depth. To effectively mitigate TP runoff loss, an integrated management approach involving water, soil, and fertilizer is recommended. This study enhances quantitative understanding of cropland TP runoff loss in China, providing crucial insights for efficient cropland P management, which is key to managing nonpoint source pollution on a national level.

Evaluating the Impacts of Fertilization and Rainfall on Multi-Form Phosphorus Losses from Agricultural Fields: A Case Study on the North China Plain

Excessive fertilizer application increases the risk of eutrophication and agricultural non-point source pollution (ANPS) in rivers near farmland. However, the processes and mechanisms of runoff and phosphorus losses, particularly in the interflow, under various fertilizer treatments and rainfall scenarios are not well understood. This study used orthogonal experimental methods to investigate the combined effects of fertilization schemes and rainfall intensity on multi-form phosphorus runoff losses and to establish statistical relationships and regression models between phosphorus losses and environmental factors in surface runoff and interflow. The results indicated that (1) the optimized fertilization scheme, compared with conventional fertilization, enhanced pak choi (Brassica rapa) growth while reducing phosphorus runoff losses. By reducing phosphorus fertilization by 35.7%, total phosphorus losses decreased by 29.3%, 34.2%, and 29.8% under light, moderate, and heavy rainfall, respectively. (2) Different fertilizer applications and rainfall intensities had varying effects on phosphorus losses through different pathways. Fertilizer application was the primary factor affecting phosphorus losses in surface runoff, while rainfall intensity mainly influenced phosphorus losses through interflow. (3) Surface runoff was the dominant pathway for phosphorus losses from farmland (&gt;92.0%), with particulate phosphorus (&gt;89.4%) being the predominant form. However, under high-intensity and long-duration rainfall, interflow became a significant pathway for phosphorus losses. This study highlights the importance of optimized fertilization in reducing phosphorus losses and improving fertilizer efficiency in agricultural fields. The findings will help develop strategies to mitigate ANPS and soil nutrient losses in the North China Plain.

Characterization of runoff phosphorus loss from a combination of long-term fertilizer application and cultivation on sloping croplands

Study regionPurple soil sloping cropland, a representative landscape in the upper reaches of the Yangtze River, and is the main distributed agricultural basis of the Sichuan Basin, Southwest China. Study focusThis study investigated the responses of runoff P loss to several rainfall categories, the combined application of manure and chemical fertilizers, and contour cultivation by analyzing 120 rainfall events that transpired between 2008 and 2022 on a representative purple soil sloping cropland. There were five treatment combinations utilized in this study: no fertilizer application with downslope cultivation (CK), chemical fertilizer application with downslope cultivation (T1), manure and chemical fertilizer application with downslope cultivation (T2), 1.5-fold chemical fertilizer application with downslope cultivation (T3), and chemical fertilizer application with contour cultivation (T4). New hydrological insight of the regionThe runoff depth during large rainstorms was significantly higher (21.5–252.4 %) than that of other rainfall categories (p < 0.05). Dissolved phosphorus (DP) loss was highest during rainstorms, whereas the highest particulate phosphorus (PP) loss was observed during large rainstorms. The runoff depth and sediment yield were significantly higher in CK than those in other treatments (p < 0.05). There were significant linear relationships between runoff depth and PP loss, DP concentration (p < 0.05). The results of this study have great significance in improving our understanding of the characteristics associated with runoff P loss in sloping croplands in Southwest China.

Ca–Mg modified attapulgite for phosphate removal and its potential as phosphate-based fertilizer

The urgent concerns of controlling water body eutrophication and the alleviating phosphorus shortage have led to an urgent need for action. The removal of phosphate from polluted waters and its reuse are essential for the prevention of eutrophication and for the sustainable utilization of phosphate resources. In this study, modified attapulgite with different Ca:Mg molar ratios was synthesized to facilitate the recovery of phosphate, with subsequent use of soil fertilizer. Ca–Mg modified attapulgite with the optimal ratio (ACM-5:3) exhibited an exceptional adsorption quality, achieving a maximum adsorption capacity of 63.2 mg/g. The pseudo-second-order model and Langmuir model could well describe the adsorption kinetics and isotherms, respectively. The adsorption mechanism analyses suggested that the interaction between ACM-5:3 and phosphate depended mainly on ion exchange and electrostatic attraction. Moreover, phosphate-laden-ACM-5:3 demonstrated a significant potential as a phosphorus-releasing fertilizer. It could promote corn growth by ensuring a continuous supply of phosphorus and minimizing phosphorus runoff losses. The above results suggested that ACM-5:3 was a potential adsorbent for efficient phosphate removal and recovery.

Fifty years of environmental progress for United States dairy farms

Dairy farms in the United States have changed in many ways over the past 50 yr. Milk production efficiency has increased greatly, with ∼30% fewer cows producing about twice the amount of milk today. Other improvements include increases in crop yields, fuel efficiency of farm equipment, and efficiency in producing most resources used on farms (e.g. electricity, fuel, fertilizer). These improvements have led to changes in the environmental impact of farms. Through simulation of representative dairy farms in 1971 and 2020, changes in nutrient losses and farmgate life cycle assessments of greenhouse gas (GHG) emissions, fossil energy use, and blue (ground and surface) water use were determined for 6 regions and the United States. For all environmental metrics studied, intensities expressed per unit of fat- and protein-corrected milk produced were reduced, but the total effects over all farms or milk produced increased for 5 of the 13 environmental metrics. Reductions in the impacts of dairy farms in the eastern United States were offset by large increases in western regions because of a major increase in cow numbers in the West. The national average intensity of GHG emissions decreased by 42%, which gave just a 14% increase in the total GHG emissions of all dairy farms over the 50-yr period. The intensity of fossil energy use decreased by 54%, with the total for all farms decreasing by 9%. Water use related to milk production decreased in intensity by 28%, but due to the large increase in dairy production in the dry western regions that have a greater dependence on irrigated feed crops, total blue water use increased by 42%. Major pathways of nitrogen loss included ammonia volatilization, leaching, and denitrification, where total ammonia emissions related to US dairy farms increased by 29%, while leaching losses decreased by 39%, with little change in nitrous oxide emissions. Simulated nitrogen and phosphorus runoff losses totaled for all dairy farms decreased by 27% to 51% through more efficient fertilizer use, reduced tillage, and greater use of cover crops. Emissions of methane and reactive non-methane volatile organic compounds increased by 32% and 53%, respectively, due to greater use of long-term manure storage and silage stored in bunkers and piles. Although much progress has been made in improving production efficiency, continued improvements with new strategies and technologies are needed to meet the demand for dairy products and mitigate total environmental impacts, particularly in view of projected climate variability.

Land use planning to minimize the export of phosphorus: An optimization model for dairy production at a catchment area scale

The intensification of activities in the Santa Lucia River basin in Uruguay has resulted in an increase in the concentration of nutrients in surface waters with the consequent acceleration of the eutrophication. Dairy production, of great relevance in the area, needs to increase production to ensure the economic viability of the activity. In this context, it is necessary to find solutions that address trade-offs between productivity and polluting potential. A dairy sub-basin of the Santa Lucia River was selected as a case study to develop an optimization model with the aim of minimizing phosphorus exportation over a four-year planning horizon while meeting restrictions on the crop sequence allowed, dry matter productivity and number of crops in each sub-basin producer. An integer linear programming formulation was proposed to model the problem. It was possible to obtain a model that managed to reduce phosphorus runoff losses by planning land uses and complying the restrictions. Exists a wide field of improvement of the model, which is a useful tool for analysis of scenarios and trade-off between productivity and environmental care.

Drip fertigation and plant hedgerows significantly reduce nitrogen and phosphorus losses and maintain high fruit yields in intensive orchards

A field experiment was carried out to evaluate the effects of drip fertigation combined with plant hedgerows on nitrogen and phosphorus runoff losses in intensive pear orchards in the Tai Lake Basin. Nitrogen and phosphorus runoff over a whole year were measured by using successional runoff water collection devices. The four experimental treatments were conventional fertilization (CK), drip fertigation (DF), conventional fertilization combined with plant hedgerows (C+H), and drip fertigation combined with plant hedgerows (D+H). The results from one year of continuous monitoring showed a significant positive correlation between precipitation and surface runoff discharge. Surface runoff discharge under the treatments without plant hedgerows totaled 15.86% of precipitation, while surface runoff discharge under the treatments with plant hedgerows totaled 12.82% of precipitation. Plant hedgerows reduced the number of runoff events and the amount of surface runoff. Precipitation is the main driving force for the loss of nitrogen and phosphorus in surface runoff, and fertilization is an important factor affecting the losses of nitrogen and phosphorus. In CK, approximately 7.36% of nitrogen and 2.63% of phosphorus from fertilization entered the surface water through runoff. Drip fertigation reduced the accumulation of nitrogen and phosphorus in the surface soil and lowered the runoff loss concentrations of total nitrogen (TN) and total phosphorus (TP). Drip fertigation combined with plant hedgerows significantly reduced the overall TN and TP losses by 45.38 and 36.81%, respectively, in comparison to the CK totals. Drip fertigation increased the vertical migration depth of nitrogen and phosphorus nutrients and reduced the accumulation of nitrogen and phosphorus in the surface soil, which increased the pear yield. The promotion of drip fertigation combined with plant hedgerows will greatly reduce the losses of nitrogen and phosphorus to runoff and maintain the high fruit yields in the intensive orchards of the Tai Lake Basin.

Effect of Thaw Depth on Nitrogen and Phosphorus Loss in Runoff of Loess Slope

Seasonal freeze-thaw erosion is a form of soil erosion caused by the topographical characteristics and climatic factors of the hilly and gully loess regions. Seasonal freeze-thaw can damage the soil pores and cause its bulk density to change. The effects of thawing depth on runoff and Nitrogen and Phosphorus loss on the rainfall erosion of an artificial slope filled with loess soil were analyzed after a rainfall test that simulated the spring thaw period in China. The results showed that: (1) The maximum runoff yield was 33.35 mm at 4 cm thawing depth, and the minimum was 12.95 mm at 6 cm thawing depth. With the increase in runoff time, the slope infiltration rate had a decreasing trend. The loss rate of available and total Phosphorus increased with the increase in runoff rate. The rate of increase was fastest when the thawing depth was 4 cm. (2) The relationships between runoff rate and Nitrogen loss and Phosphorus loss rate can be explained by linear regression equations, and the loss rate increased as the runoff rate rose for all thawing depths. Within the 0–6 cm thawing depths, the loss of total phosphorus was the largest when the thawing depth was 4 cm, and the loss of available phosphorus was the smallest when the thawing depth was 6 cm. At the shallower thawing depths, the available Nitrogen loss represented a smaller proportion of the total Nitrogen loss compared to nitrate Nitrogen loss. However, there was a gradual rise in the available Nitrogen proportion in the total amount of inorganic Nitrogen as the thawing depth increased. (3) Total Phosphorus was the available Phosphorus with a quadratic function relationship with runoff energy and runoff power. Runoff energy mainly affected the total Nitrogen and available Nitrogen loss in runoff, whereas runoff power mainly affected total Nitrogen loss in runoff. The results of this paper can improve the understanding of runoff and Nitrogen and Phosphorus loss caused by runoff during freeze-thaw conditions.

Pathways and mechanisms by which biochar application reduces nitrogen and phosphorus runoff losses from a rice agroecosystem

Biochar application has the potential to reduce nitrogen (N) and phosphorus (P) losses in agricultural runoff, but little is known about how and to what extent biochar is effective in rice agroecosystems. In this study, in a typical double-rice cropping system, N and P runoff losses and soil carbon (C), N, and P contents (soil CNP contents) were observed under three different biochar application rates (0, 24, and 48 t ha−1, which were defined as CK, LB, and HB, respectively) from 2017 to 2019. The results showed that the two-year averages of soil total organic C (TOC), total N (TSN), total P (TSP), available P (Olsen P), microbial biomass N (MBN), and microbial biomass P (MBP) contents were generally higher in the biochar treatments than in CK (P < 0.05). Specifically, the TSP, TOC, and MBN contents increased with the increasing biochar application rate, thus demonstrating the significant effects of biochar application on the paddy soil CNP contents and composition. The HB and LB treatments reduced the seasonal mean runoff flow-weighted total N (TN_wc) and total P (TP_wc) concentrations by 32.4% and 42.1%, respectively, compared to CK. Structural equation modeling (SEM) further revealed that the paths and mechanisms by which biochar reduced the TN_wc and TP_wc were different, depending on the different application rates. HB reduced the TN_wc mainly through the direct absorption of N, followed by the indirect inhibition of N mineralization, whereas LB decreased the TP_wc mainly through the strong P sorption capacity of the biochar. The direct effect of HB on the TN_wc was 1.58 times as strong as the indirect effect (path coefficients: −0.68 vs. 0.43, respectively), and the direct effect of LB on the TP_wc was 1.78 times as strong as the indirect effect (path coefficients: −0.89 vs. 0.50, respectively). Given the distinct pathways and mechanisms by which biochar reduced NP runoff losses, in practice, the biochar application rate should be optimized according to a targeted priority of reducing either N or P runoff losses in rice agroecosystems.

Responses of maize yield, nitrogen and phosphorus runoff losses and soil properties to biochar and organic fertilizer application in a light-loamy fluvo-aquic soil

Nitrogen (N) and phosphorus (P) are the primary nutrients to the promoting of crop yield, however, the losses of N and P by runoff dominated the non-point pollution. In the context of maintaining high farmland productivity and mitigating negative impacts on the environment, it is important to understand how biochar and organic fertilizer application influence maize yield, N and P use efficiency and losses by runoff, as well as soil quality. To address this, the current study was conducted based on a three-year field experiment that includes five fertilized treatments: No fertilizer (CK), chemical fertilizer (CF), CF + biochar (CFB), 20% chemical N was replaced by organic fertilizer (OF) and OF + biochar (OFB). The amendments of biochar and organic fertilizer significantly increased maize yield, N and P use efficiency, and meanwhile, decreased the N and P losses by runoff. From 2017 to 2019, the yield of OFB treatment was 4.4–161.9% higher than that of other treatments, The N and P use efficiencies of OFB treatment was 3.0–83.7% and 9.9–195.1% higher than that of other treatments respectively. N losses by runoff were decreased by 35.1–59.7% in OFB than CF, and −0.6–42.0% in OFB than other fertilized treatments. P losses by runoff were decreased by 39.9–48.8% in OFB than CF, and 5.6–32.0% in OFB than other fertilized treatments in 2018 and 2019. Moreover, biochar amendment significantly improved soil aggregate stability, and increased extracellular urease and acid phosphatase activities. Soil alkaline hydrolysable nitrogen and available potassium contents were significantly increased by the biochar amendment, but no significant impact on soil available P. These findings indicate that the integrated use of chemical fertilizer, organic fertilizer and biochar has the potential to maintain high grain yield with mitigating environmental impact.

Research progress on nitrogen and phosphorus runoff loss models for rice paddy

水稻是全球最重要的粮食作物，但种植过程中不合理的水肥管理引起了稻田氮磷径流流失，对邻近水体造成污染风险.稻田氮磷径流流失模型是理解区域水体污染排放时空特征和评估水污染风险的有效手段.论文阐述了稻田氮磷径流流失的发生机制和关键过程，梳理了统计经验模型、物理机理模型、水文过程模型和生态系统模型的研发历程.结果表明，当前模型缺乏水-土-气界面过程的有效参数化，基于高分辨率、多年多站点、全通量的模型参数的合理化，以及区域尺度农艺管理（种植制度、施肥制度、灌排制度）和田-沟-塘联合调控措施（分布、规模、运行规则）的模块化，造成了稻田氮磷径流流失的不确定性.同时，提出了面向稻田氮磷循环的高分辨率全通量观测网络建设、农艺管理与调控措施的区域数据集研发、模型开发与先进技术手段的集成与融合、稻田氮-磷-水耦合的多模型集合等，为稻田氮磷径流流失模型的改进、农艺管理措施的优化以及气候智能型稻田的建设提供科学依据.;Rice is the most significant food crop in the world, but nitrogen and phosphorus runoff loss, a risk of pollution to adjacent water bodies, would occur during cultivation by unreasonable water and fertilizer management. Nitrogen and phosphorus runoff loss model for rice paddies is an effective way, in addition to assessing the risk of water pollution, to understand the spatial and temporal characteristics of regional water pollution discharge. Here, the authors expound the occurrence mechanism and key processes of nitrogen and phosphorus runoff loss in rice paddies, and then systematically reviews the research and development history of statistical empirical model, physical mechanism model, hydrological process model and ecosystem model. The authors point out that current models are limited by the uncertainty of nitrogen and phosphorus runoff losses in paddy fields, due to deficiency in the effective parameterization of the water-soil-air interface process, rationalization of model parameters based on high resolution, multi-year, multi-site and full flux, as well as regional-scale agricultural management (planting, fertilization, irrigation and drainage system) and the modularization of the joint control measures (distribution, scale, operation rules) of paddy-ditch-pond. Finally, the authors propose outlook on the establishment of high-resolution and full flux observation network for rice paddies' nitrogen and phosphorus cycles, regional data set research and development of agricultural management and control measures, integration and fusion of model development and advanced technological means, and multi-model integration of nitrogen-phosphorus-water coupling in rice paddies. Achieving these prospects will provide scientific support for the improvement of nitrogen and phosphorus runoff models for a rice paddy, the optimization of agricultural management measures, and the construction of climate-smart rice paddies.

Grazing Systems to Retain and Redistribute Soil Phosphorus and to Reduce Phosphorus Losses in Runoff

A study of phosphorus accumulation and mobility was conducted in eight pastures in the Georgia piedmont, USA. We compared two potential grazing treatments: strategic-grazing (STR) and continuous-grazing-with-hay-distribution (CHD) from 2015 (Baseline) to 2018 (Post-Treatment) for (1) distribution of Mehlich-1 Phosphorus (M1P) in soil and (2) dissolved reactive phosphorus (DRP) and total Kjeldahl phosphorus (TKP) in runoff water. STR included rotational grazing, excluding erosion vulnerable areas, and cattle-lure management using movable equipment (hay-rings, shades, and waterers). After three years of treatment, M1P had significantly accrued 6- and 5-fold in the 0–5 cm soil layer and by 2- and 1.6-fold in the 5–10 cm layer for CHD and STR, respectively, compared to Baseline M1P. In STR exclusions, M1P also increased to 10 cm depth post-treatment compared to Baseline. During Post-Treatment, TKP runoff concentrations were 21% and 29% lower, for CHD and STR, respectively, in 2018 compared to 2015. Hot Spot Analysis, a spatial clustering tool that utilizes Getis-Ord Gi* statistic, revealed no change in Post-Treatment CHD pastures, while hotspots in STR pastures had moved from low-lying to high-lying areas. Exclusion vegetation retained P and reduced bulk density facilitating vertical transportation of P deeper into the soil, ergo, soil P was less vulnerable to export in runoff, retained in the soil for forage utilization and reduced export of P to aquatic systems

Nitrogen and phosphorus runoff losses were influenced by chemical fertilization but not by pesticide application in a double rice-cropping system in the subtropical hilly region of China.

As one of the important nitrogen (N) and phosphorus (P) pollution sources of waters, the paddy water N and P runoff losses are still poorly understood in the double rice cropping system under the interaction of chemical fertilizer and pesticide. In the subtropical hilly region of China, we conducted a 1.5-year continuous and high-frequency monitoring of paddy water N and P concentrations, runoff N and P losses, and grain yield in a double rice-cropping system with different chemical fertilizer and pesticide application rates. The results showed that the high-risk periods for N loss were in the first 5days after the base fertilizer (BF) application and the first 10days after the topdressing fertilizer application in both early and late rice seasons, while the high-risk periods for P loss were in the first 5days after BF application in the early rice season and the first 15days after BF application in the late rice season. The N and P runoff losses in the early rice season were greater than those in the late rice season, due to that the N and P fertilizers use efficiencies were lower, and thus paddy water N and P concentrations were higher in the early rice season. The paddy N and P concentrations and N and P runoff losses increased significantly with increased fertilizer application rates, while the pesticide application rate did not significantly affect N and P losses. Therefore, special effects (e.g., avoiding high irrigation, fertilizer deep application) should be taken during the high-risk periods of N and P losses to reduce the N and P runoff losses in the double rice cropping system, especially in the early rice season. There are also potentials to reduce fertilizer and pesticide input without reducing rice grain yield for the double rice cropping system in the subtropical hilly region of China.

Carbon-nutrient stoichiometry drives phosphorus immobilization in phototrophic biofilms at the soil-water interface in paddy fields

Phototrophic biofilms are distributed widely at the sediment/soil-water interfaces (SWI) in paddy fields, where they immobilize phosphorus, thereby reducing its runoff loss. However, how soil carbon, nutrient availability and nutrient ratios drive the phototrophic biofilm community and its contribution to phosphorus cycling is largely unknown. A large scale field investigation in Chinese paddy fields reported here shows that soil organic carbon (SOC) and soil total nitrogen (STN) contents rather than soil total phosphorus (STP) triggered phosphorus immobilization of paddy biofilms, as they changed algal diversity and EPS production. High C: P and N: P ratios favored phosphorus immobilization in biofilm biomass via increasing the abundance of green algae. The C: N ratio on the other hand had only a weak effect on phosphorus immobilization, being counteracted by SOC or STN. Results from this study reveal how the in-situ interception of phosphorus in paddy fields is driven by soil carbon, nutrient availability and nutrient ratios and provide practical information on how to reduce runoff losses of phosphorus by regulating SOC and STN contents.

Direct seeding for rice production increased soil erosion and phosphorus runoff losses in subtropical China

Estimating soil erosion and nutrient losses from surface runoff in paddy fields is essential for the assessment of sustainable rice (Oryza sativa L.) production and water quality protection. Different rice establishment methods have been used in the last three decades in Asia; however, it is still unclear how these methods influence sustainable agriculture and environmental protection in humid areas. The aim of this study was to evaluate the impacts of rice establishment method on soil erosion and phosphorus (P) losses from surface runoff in Hydragric Anthrosols under a subtropical monsoon climate. Total suspended solids (TSS), total P (TP), dissolved P (DP), and particulate P (PP) runoff losses were measured under four rice establishment treatments in 2013 and 2014, including traditional manual transplanting (TT), mechanical transplanting (MT), dry direct seeding (DD), and wet direct seeding (WD). The results showed that the seasonal TSS in the runoff varied from 59.9 to 829.8 kg ha−1 in the two years. Compared with TT, the DD significantly increased the TSS by 481% in 2013 and by 349% in 2014, while the WD significantly increased TSS by 783% in 2013 and by 571% in 2014. In the 2013 and 2014 rice seasons, the field-observed TP runoff losses were from 0.18 to 1.51 kg ha−1. Compared with TT, the DD significantly increased the TP lost by 222% in 2013 and by 197% in 2014, whereas the WD significantly increased the TP lost by 483% in 2013 and by 387% in 2014. However, the TSS and P losses from the MT and TT were similar in both years. The PP runoff losses accounted for 58–77% of the seasonal TP lost. These findings demonstrate that the conversion of traditional manual transplanting to direct seeding increased soil erosion and P runoff losses in subtropical China.

Varying Influence of Dairy Manure Injection on Phosphorus Loss in Runoff over Four Years.

Surface application of manure on no-till farms can exacerbate P losses in runoff, contributing to the eutrophication of surface waters. We monitored 12 400-m field plots over 4 yr to compare P losses in surface runoff and lateral subsurface flow with shallow disk injection and broadcast application of dairy manure. Given the substantial variability in annual P losses, as well as a gradual, annual buildup of residual soil test P, significant differences in runoff P losses were detected in only 1 of 4 yr: in 2014, total P losses in runoff were 68% greater from broadcast manure plots than injected manure plots. Dissolved and particulate P were roughly even in their contribution to runoff. Even so, there were significant relationships between annual dissolved P losses and P in the soil surface, which pointed to soils as a regular source of P in runoff. Overall, results confirm the potential for injection to reduce P loss in runoff relative to broadcast application, but because in a few sampling dates injection resulted in greater losses, this study also highlights the importance of assessing mitigation benefits of manure application practices over longer timeframes.

Impact of conservation tillage on nitrogen and phosphorus runoff losses in a potato crop system in Fuquene watershed, Colombia

Intensive tillage (IT) in potato crops is considered as one of the main non-point sources (NPS) of local water eutrophication in the Fuquene Lake of Colombia. Therefore, the local government has invested in several programs aiming at the adoption of principles of conservation tillage (CT) which would allow for developing and applying the agricultural best management practices (BMPs). The complexity of hydrological and geological heterogeneity makes the degree of benefit that CT has in different locations uncertain. In this study, the Soil and Water Assessment Tool (SWAT) was used to assess the impacts of changing IT for CT on nitrogen (N) and phosphorus (P) losses in surface water runoff from the potato crop in the Fuquene watershed. This is done at field and watershed levels. A two-year study quantified the changes in surface water runoff pollutants for three potato crop cycles under the traditional IT practice and CT practice - which included reducing tillage, green manure, and permanent soil cover - at twelve runoff plots installed in the Fuquene watershed (Quintero and Comerford, 2013). This information was used to build, calibrate and validate the SWAT model. The results suggest that CT for the Fuquene watershed can be reduced up to 26% of the sediment yield and 11% of the surface runoff compared with IT, which means an overall reduction of load. The main CT effect on nutrient losses in runoff is an increase in the total N and P (2% to 18% respectively) compared to IT. However, the results at watershed level showed different patterns from those obtained at field level. Despite the model uncertainties, the results show a possibility of using hydrological models to assess the effectiveness of various field management practices in agriculture.

Limited Dissolved Phosphorus Runoff Losses from Layered Double Hydroxide and Struvite Fertilizers in a Rainfall Simulation Study.

The enrichment of P in surface waters has been linked to P runoff from agricultural fields amended with fertilizers. Novel slow-release mineral fertilizers, such as struvite and P-exchanged layered double hydroxides (LDHs), have received increasing attention for P recycling from waste streams, and these fertilizers may potentially reduce the risk of runoff losses. Here, a rainfall simulation experiment was performed to evaluate P runoff associated with the application of recycled slow-release fertilizers relative to that of a soluble fertilizer. Monoammonium phosphate (MAP), struvite, and LDH granular fertilizers were broadcasted at equal total P doses on soil packed in trays (5% slope) and covered with perennial ryegrass ( L.). Four rainfall simulation events of 30 min were performed at 1, 5, 15, and 30 d after the fertilizer application. Runoff water from the trays was collected, filtered, and analyzed for dissolved P. For the MAP treatment, P runoff losses were high in the first two rain events and leveled off in later rain events. In total, 42% of the applied P in the MAP treatment was lost due to runoff. In the slow-release fertilizer treatments, P runoff losses were limited to 1.9 (struvite) and 2.4% (LDH) of the applied doses and were more similar over the different rain events. The use of these novel P fertilizer forms could be beneficial in areas with a high risk of surface water eutrophication and a history of intensive fertilization.

Effect of slope farmland soil and water and soil nitrogen and phosphorus loss based on different crop and straw applications and ridge patterns in the basin of the main stream of the Songhua River

For soil and water erosion control in slope farmland, field experiments consisting of corn + no straw application + longitudinal ridge (CNL-CK), corn + stubble standing + cross ridge (CSSC), corn + straw application + cross ridge (CSC), soybean + straw application + cross ridge (SSC) and alfalfa + straw application + cross ridge (ASC) were conducted. Compared with the traditional CNL cropping pattern, soil loss in CSSC, CSC, SSC, and ASC was decreased 43.6%, 48.6%,58.2% and 62.1%, respectively, soil nitrogen loss load was decreased 53.8%, 50.8%, 62.1% and 66.2%, respectively, and soil phosphorus loss load was decreased 50.7%, 50.7%, 60.0%, and 66.7%, respectively. Runoff volume was decreased 42.4%, 52.3%, 54.6% and 61.0%, runoff nitrogen loss load was decreased 52.8%, 56.8%, 46.1% and 50.2%, respectively, and runoff phosphorus loss load was decreased 46.9%, 78.2%, 67.2%, and 62.7%, respectively. Soil and water erosion control of soybean and alfalfa were better than that of corn. Soil loss was decreased 19.2% and 26.7%, soil nitrogen loss load was decreased 22.9% and 31.3% respectively, soil phosphorus loss load was decreased 18.9% and 32.4% respectively, runoff volume was decreased 4.8% and 18.4% respectively, runoff nitrogen loss load was decreased −24.9% and −15.3% respectively, and runoff phosphorus loss load was decreased −50.4% and −71.2% respectively. Though runoff volume of SSC and ASC were lower than CSC, the concentration of nitrogen and phosphorus in SSC and ASC runoff liquid were higher than CSC, so the runoff nitrogen and phosphorus of SSC and ASC were increased. The runoff nitrogen and phosphorus loss load could be negligible because the soil nitrogen and phosphorus loss load were large. The concentration of nitrogen and phosphorus of all treatment runoff liquid was less than the environmental quality standards for class III surface water, so the runoff from slope farmland did not influence the water quality of the Songhua River.

The Promise, Practice, and State of Planning Tools to Assess Site Vulnerability to Runoff Phosphorus Loss.

Over the past 20 yr, there has been a proliferation of phosphorus (P) site assessment tools for nutrient management planning, particularly in the United States. The 19 papers that make up this special section on P site assessment include decision support tools ranging from the P Index to fate-and-transport models to weather-forecast-based risk calculators. All require objective evaluation to ensure that they are effective in achieving intended benefits to protecting water quality. In the United States, efforts have been underway to compare, evaluate, and advance an array of P site assessment tools. Efforts to corroborate their performance using water quality monitoring data confirms previously documented discrepancies between different P site assessment tools but also highlights a surprisingly strong performance of many versions of the P Index as a predictor of water quality. At the same time, fate-and-transport models, often considered to be superior in their prediction of hydrology and water quality due to their complexity, reveal limitations when applied to site assessment. Indeed, one consistent theme from recent experience is the need to calibrate highly parameterized models. As P site assessment evolves, so too do routines representing important aspects of P cycling and transport. New classes of P site assessment tools are an opportunity to move P site assessment from general, strategic goals to web-based tools supporting daily, operational decisions.