Total Phosphorus Losses Research Articles

How biochar, horizontal ridge, and grass affect runoff phosphorus fractions and possible tradeoffs under consecutive rainstorms in loessial sloping land?

Agricultural interventions such as biochar, grassing, and different planting modes affect the migration and transformation of soil phosphorus (P). However, the effect of different management practices on the mechanism of runoff P fractions and possible tradeoffs associated with consecutive rainstorms is not well understood. This study aggregated management practices (biochar, grassing, and planting modes) to evaluate the surface pathways of P loss from loessial bare and grassed slopes with different slope angles (10°, 15°, and 20°) and consecutive rainstorms (60, 90, and 120 mm·h−1). Results indicated that: (i) The highest sediment yield rate and total phosphorus loss concentrations were registered during the first rainstorm event (10° slope and 60 mm·h−1). Soil erosion and P loss under different rainfall intensities could be effectively reduced by 0–3% biochar grassed slope with horizontal ridge but were aggravated under bare slope with 3–6% biochar or grassed slope with 6% biochar. (ii) Planting grass on bare slope could effectively mitigate erosion and runoff P at different rainfall intensities, and the reduction rate increased with increased rainfall intensity. The sediment reduction effect of bare slope with horizontal ridge decreased with increased rainfall intensity and was liable to fail in the 90 and 120 mm·h−1 rainfall intensities. (iii) The particulate phosphorus (PP) was the primary loss fraction of soil P from loessial sloping land (> 80%), and PP increased with increased biochar content and rainfall intensity but reduced by grass and horizontal ridge interventions. Integrating grass with horizontal ridge was considered to be the most effective way to control erosion and protect soil fertility. These outcomes provide underlying insights for employing appropriate best management practices (BMPs) to decrease runoff P on sloping soils, which can be highlighted through a reasonable allocation of biochar, ridge, growing plants, and other BMPs.

Study on phosphorus loss and influencing factors in the water source area

Maintaining drinking water security is a global issue, and phosphorus is a limiting factor affecting drinking water quality. Hence, this study took Fushi Reservoir as a test area, and set up field runoff observation plots around the reservoir catchment, which is covered by moso bamboo stands. Through field observation, the vertical variation of phosphorus loss in different stands of moso bamboo was initially studied. The results showed that: (1) For the vertical dimensions (atmospheric rainfall, stemflow, throughfall, surface runoff) from high to low, the loss of total phosphorus (TP) increased, and the proportion of dissolved phosphorus increased from 29.29% (atmospheric rainfall) to 62.76% (surface runoff). (2) Different rainfall factors had various impacts on phosphorus loss at the different vertical levels. The accumulation of rainfall had the greatest impact on surface runoff TP loss, with the correlation coefficient reaching 0.994 (P < 0.01), while surface runoff particulate phosphorus loss was mostly affected by the average rainfall intensity. (3) Modifying the forest structure in water source areas can reduce the loss of TP via stemflow and throughfall, but the effect on surface runoff TP loss is variable. Thus, it is expected that this novel study can serve as a reference for improving the environmental quality of water source areas, and help in reducing phosphorus loss and controlling non-point source pollution.

Evaluating the efficacy of targeting options for conservation practice adoption on watershed-scale phosphorus reductions

Conservation identities of farmers in the Maumee River watershed, derived from farmer surveys, were embedded into a SWAT watershed model. This was done to improve the representation of the heterogeneity among farmers in the decision-making process related to the adoption of conservation practices. Modeled farm operations, created with near field-level Hydrologic Response Units (HRUs) within the SWAT model, were assigned a modeled primary operator. Modeled primary operators held unique conservation identities driven by their spatial location within the watershed. Five pathways of targeting the adoption of subsurface placement of phosphorus and buffer strips to HRUs within the watershed were assessed. Targeting pathways included targeting by HRU-level phosphorus losses, conservation identity of model operators, a hybrid approach combining HRU-level phosphorus losses and conservation identity of the model primary operator managing the HRU, and a proxy measure for random placement throughout the watershed. Targeting the placement of subsurface phosphorus application to all agricultural HRUs resulted in the greatest reduction in total phosphorus losses (32%) versus buffer strips (23%). For both conservation practices, targeting by HRU-level total phosphorus losses resulted in the most efficient rate of phosphorus reduction as measured by the ratio of phosphorus reduction to conservation practice adoption rates. The hybrid targeting approach closely resembled targeting by phosphorus losses, indicating near optimal results can be obtained even when constraining adoption by farmer characteristics. These results indicate that by developing management strategies based on a combination of field-level information and human-operator characteristics, a more efficient use of limited resources can be used while achieving near-maximal environmental benefits as compared to managing environmental outcomes solely based on field-level information.

Characteristics of Runoff-related Total Nitrogen and Phosphorus Losses Under Long-term Fertilization and Cultivation on Purple Soil Sloping Croplands

To elucidate the effects of long-term fertilization and cultivation on runoff rates and runoff-related nitrogen (N) and phosphorus (P) losses, the following five treatments were established on sloping purple soil cropland:① no fertilizer with downslope tillage (CK), ② combined application of manure and fertilizer with downslope tillage (T1), ③ chemical fertilizers with downslope tillage (T2), ④ chemical fertilizer with increasing fertilization with downslope tillage (T3), and ⑤ chemical fertilizer with contour tillage (T4). The runoff rate, runoff-related total N (TN), and total P (TP) concentrations and their loss rates from 104 erosive rainfall events were determined for the period 2008-2019. Results showed that although runoff rates were not significantly different among the fertilization treatments (P>0.05), runoff was markedly lower in fertilization treatments than in the CK treatment (P<0.05). Runoff-related TN concentrations were significantly higher in the CK compared to the fertilization treatments (P<0.05), while there were no significant differences among the T2, T3, and T4 treatments, which had higher concentrations than the T1 treatment. Runoff-related TP concentrations were significantly higher from the T1, T2, and T3 treatments than the CK treatment (P<0.05), and were significantly lower in the T4 than the CK treatment (P<0.05). TN loss rates were not significantly different among the fertilization treatments (P>0.05), but were all lower than the CK treatment (P<0.05). Furthermore, TP loss rates were not significantly different among the downslope treatments (P>0.05), but were all higher than the contour treatment (P<0.05). Runoff rates showed no significant relationships with TN and TP concentrations in the CK, T1, and T2 treatments but were significantly negatively linearly correlated in T3 (P<0.05) and significantly positively linearly correlated in T4 (P<0.05). These results potentially provide scientific guidance for the prevention and control of agricultural non-point source pollution on sloping croplands in the purple soil area.

Long‐term land use/cover changes reduce soil erosion in an ionic rare‐earth mineral area of southern China

AbstractEcological restoration projects, such as the Grain‐to‐Green Program (GTGP) and the Natural Forest Conservation Program (NFCP), have been implemented to improve vegetation cover since 1998. However, rapid urbanization has caused severe land use/cover (LUC) changes in the Dong River upstream basin. Therefore, it is urgent to study the long‐term (1999–2017) spatial–temporal variation of LUC and soil erosion since the implementation of GTGP and NFCP began in this area. Soil erosion and carbon sequestration were calculated using the revised universal soil loss equation (RUSLE) and C‐fix model. During 1999–2017, forest decreased by 28,857.81 ha and built‐up area increased by 17,193.01 ha. This area experienced severe LUC change, but vegetation cover has been effectively improved. When the observation period was measured in years, vegetation cover had a greater impact on decreasing soil erosion (554.11 × 104 t yr−1) than rainfall, while in months, the impact of rainfall is greater (causing a dramatically rebound of soil erosion in 2014). Furthermore, high‐intensity human activities made soil erosion increased by 37.70% in Yuancheng District, whereas soil organic carbon, total nitrogen, and total phosphorus loss decreased by 49.96, 33.03, and 44.44%, respectively. Moreover, GTGP and NFCP also bring collateral benefits, carbon sequestered by vegetation increased from 99.11 × 106to 124.38 × 106 t CO2, during 1999–2014. And vegetation was the major factor of increased carbon sequestration, rather than temperature or solar radiation. These results elaborate on the impact of LUC changes on spatial–temporal variation of soil erosion. And it can provide a reference for the formulation of soil and water conservation measures in the future.

Effects of dung beetles on decomposition of cattle dung in spring and autumn in a Seriphi-dium-dominated desert, China.

To understand the decomposition of cattle dung in Seriphidium-dominated desert, the changes of dung physical and chemical properties were determined by setting different stacking times (0, 7, 29, 48, 58 h) in May (spring) and September (autumn), respectively. Mesh cage with different openings (no mesh cage, opening up and down, opening up, totally enclosed) were set up to explore the effects of different ecological functional groups of dung beetles on decomposition. The results showed that species richness of dung beetles in spring was significantly higher than that in autumn, and that the abundance of dung beetles in autumn was significantly higher than that in spring. The losses of moisture, total carbon, total nitrogen and total phosphorus in dung were mainly concentrated during 0-29 h in spring, being decreased by 39.4%, 13.9%, 32.1% and 26.7% at 29 h, respectively. Neutral detergent fiber and acid detergent fiber of the dung stacked for 58 h decreased significantly by 8.0% and 16.0% respectively. In autumn, moisture, neutral detergent fiber and acid detergent fiber decreased most rapidly during 0-7 h, being decreased by 85.6%, 10.2% and 20.2% at 7 h, respectively. The concentrations of neutral detergent fiber and acid detergent fiber increased during 7-58 h by 20.0% and 13.7%, respectively. The decomposition of total carbon, total nitrogen and total phosphorus mainly concentrated during 0-29 h, being reduced by17.5%, 55.0% and 64.8%, respectively. The mesh cage with different openings effectively prevented the entering of dung beetles from the corresponding ecological functional groups. With the increases of functional groups of dung beetles, the decomposition rate accelerated, with cattle dung of no mesh cage being significantly higher than other treatments. The species richness and abundance of dung beetles and the stacking time of dung significantly affected the decomposition of cattle dung.

Long-term performance of three mesophilic anaerobic digesters to convert animal and agro-industrial wastes into organic fertilizer

Few studies have investigated the performance of anaerobic digestion (AD) to convert animal and agro-industrial wastes to organic fertilizers over a long-term field conditions. This paper studied three large-scale mesophilic digesters (D1–D3) over two years for their effects on feedstocks, which were dairy manure for D1 and D2 and co-digestion mixed manure and agro-industrial wastes for D3. Hydraulic retention times (HRT) were 9 d for D1, 12 d for D2, and 34 d for D3. Digester influent and effluent samples were taken every two months from the digesters and analyzed for pH, and concentrations of total solids (TS), ammonium nitrogen (NH4-N), total Kjeldahl nitrogen (TKN), total phosphorus (TP), and eight metals. The study revealed high variability in converting feedstock in the three digesters. Compared with their respective influent, the mean digester effluent pH decreased from 7.9 by 0.6 in D1 (p < 0.01) and by 0.3 in D2 (p < 0.01), but it increased from 6.1 by 1.8 in D3 (p < 0.01). The mean digester effluent TS increased from 3.4% by 0.1% (p > 0.05) in D1, but it decreased from 4.9% by 1.3% in D2 (p < 0.05) and from 12.3% by 4.8% in D3 (p < 0.01). All three digesters significantly increased NH4-N concentrations by 21.4–81.8% (p < 0.05), but insignificantly changed TKN and TP concentrations (p > 0.05). Effects of AD on all metal concentrations were mixed and were insignificant (p > 0.05) because of large concentration variations. However, study of a ratio quotient (qMg) using magnesium (Mg) as the reference discovered accumulation of NH4-N, copper, potassium, and sodium, but loss of TKN, TP, iron, manganese, zinc, and calcium during AD for D2 and D3. The impact of AD conversion was closely related with types of feedstock (on pH) and HRT (on TS and NH4-N). The results of this study can assist in developing strategies for cleaner production using AD in an environmentally sustainable manner.

Effects of rainfall intensity on runoff and nutrient loss of gently sloping farmland in a karst area of SW China.

Nutrient losses from sloping farmland in karst areas lead to the decline in land productivity and nonpoint source pollution. A specially tailored steel channel with an adjustable slope and underground hole fissures was used to simulate the microenvironment of the "dual structure" of the surface and underground of sloping farmland in a karst area. The artificial rainfall simulation method was used to explore the surface and underground runoff characteristics and nutrient losses from sloping farmland under different rainfall intensities. The effect of rainfall intensity on the nutrient loss of farmland on karst sloping land was clarified. The results showed that the surface was the main route of runoff and nutrient loss during the rainy season on sloping farmland in karst areas. The influence of rainfall intensity on the nutrients in surface runoff was more substantial than that on underground runoff nutrients. Nutrient loss was more likely to occur underground than on the surface. The losses of total nitrogen, total phosphorus, and total potassium in surface and underground runoff initially increased and then gradually stabilized with the extension of rainfall duration and increased with increasing rainfall intensity and the amount of nutrient runoff. The output of nutrients through surface runoff accounted for a high proportion of the total, and underground runoff was responsible for a low proportion. Although the amount of nutrients output by underground runoff was small, it could directly cause groundwater pollution. The research results provide a theoretical reference for controlling land source pollution from sloping farming in karst areas.

Effects of dynamic factors of erosion on soil nitrogen and phosphorus loss under freeze-thaw conditions

Soil erosion directly leads to the decline of soil fertility, and under hydraulic erosion, the soil nitrogen and phosphorus released by hydrolysis enter the adjacent water body along with surface runoff and soil erosion. This causes potential hazards such as eutrophication and river siltation in the watershed, seriously affecting the safety of the ecological environment. The mechanism of action of the dynamic factors of erosion on nitrogen (N) and phosphorus (P) loss remains unclear. In this study, a series of laboratory experiments were carried out to characterize the N and P loss and its influencing factors under freeze–thaw conditions. Two treatments (i.e., LC: loess control and FT: freeze–thaw treatment) and five soil water contents on a gravimetric basis (SWCs) (i.e., 10%, 15%, 20%, 25% and 30%) were considered. The results showed that the total runoff was higher under 30% SWC and lower under 20% SWC for the LC and FT treatments. The freeze–thaw action caused higher sediment loss under low water content (10% and 15%). The runoff-associated total nitrogen (RTN), runoff-associated total phosphorus (RTP), and sediment-associated total phosphorus (STP) loss rate showed a larger fluctuation for FT than for LC. Freeze-thaw action not only caused the instability of the N and P loss behavior but also caused increased diversity among individual samples. The soil erodibility, runoff energy and runoff power were important dynamic factors associated with erosion, and the freeze–thaw action had a very large impact on these factors. Under freeze–thaw action, the effect of dynamic factors on phosphorus and nitrogen loss was significantly enhanced. For the LC treatments, the SWC could explain 60% of the variation in RTN loss and 63% of the variation in RTP loss; the runoff explained 90% of the variation in STN loss and the runoff time explained 97% of the variation in STP loss. For the FT treatments, the runoff time explained 63% of the variation in STN loss and 53% of the variation in STP loss. The results enable us to understand further the relationship between dynamic factors of rainfall erosion and nitrogen and phosphorus loss under freeze–thaw conditions.

Effect of organic fertilizers on nitrogen and phosphorus runoff in purple soil farmland

Fertilizer nutrient loss by surface water contribute to eutrophication becoming one of the international problems. In order to study the effect of application of organic fertilizer on N/P loss in purple soil, an indoor simulating artificial rainfall experiment and in-situ natural rainfall experiment experiment was conducted in Chongqing, southwestern China. The result shows that TN(total nitrogen) loss in the simulation rainfall experiment was in the order of cow dung>compound fertilizer>chemical fertilizer>biogas slurry>oil cake>blank, whereas, TP(total phosphorus) loss was in the order of cow dung>chemical fertilizer>compound fertilizer>oil cake>biogas slurry>blank. TN content form organic fertilizer treated soil in the in-situ runoff test were lower than in chemical fertilizer treated soil at first, whereas the proportion of TN content form organic manure was increase and even higher than that form chemical fertilizer overtime. Grain nitrogen was the dominant nitric species in runoff under 15°, whereas Ammonium nitrogen was the dominant nitric species in runoff under 5°. The slope significant affect grain nitrogen content in runoff, while it has little effect on soluble nitrogen. Soluble phosphorus content in chemical fertilizer treatment was higher than that in organic fertilizers treatments, while particulate phosphorus concentration in chemical fertilizer treatment was lower than that in organic fertilizers treatments. Particulate phosphorus is the main form in runoff simulation, accounting for 50%∼90% of total phosphorus; while soluble phosphorus was the dominant phosphoric species with the slope, rainfall intensity and fertilizer dosage reduced. Rainfall intensity could increase P concentration in runoff. There was a significant positive correlation between the TN and TP concentration in runoff and rain intensity, fertilizer addition level, slope.

Soil Tillage and Crop Growth Effects on Surface and Subsurface Runoff, Loss of Soil, Phosphorus and Nitrogen in a Cold Climate

Most studies on the effects of tillage operations documented the effects of tillage on losses through surface runoff. On flat areas, the subsurface runoff is the dominating pathway for water, soil and nutrients. This study presents results from a five-year plot study on a flat area measuring surface and subsurface runoff losses. The treatments compared were (A) autumn ploughing with oats, (B) autumn ploughing with winter wheat and (C) spring ploughing with spring barley (n = 3). The results showed that subsurface runoff was the main source for soil (67%), total phosphorus (76%), dissolved reactive phosphorus (75%) and total nitrogen (89%) losses. Through the subsurface pathway, the lowest soil losses occurred from the spring ploughed plots. Losses of total phosphorus through subsurface runoff were also lower from spring ploughing compared to autumn ploughing. Total nitrogen losses were higher from autumn ploughing compared to other treatments. Losses of total nitrogen were more influenced by autumn ploughing than by a nitrogen surplus in production. Single extreme weather events, like the summer drought in 2018 and high precipitation in October 2014 were crucial to the annual soil and nutrient losses. Considering extreme weather events in agricultural management is a necessary prerequisite for successful mitigation of soil and nutrient losses in the future.

Characteristics of Soil Nitrogen and Phosphorus Losses Under Different Land-use Schemes in the Shipanqiu Watershed

In order to understand the characteristics of soil nitrogen and phosphorus loss under different land use patterns in the small watershed of the Three Gorges Reservoir area and provide a scientific basis for the prevention and control of agricultural non-point source pollution, a field test method was used to study the paddy fields and drought in the small Shipanqiu Watershed in the Three Gorges Reservoir area. The characteristics of different runoff concentrations and the fluxes of nitrogen and phosphorus in surface runoff under the five land use schemes of paddy filed, slope land, woodlands, citrus orchards, and vegetable land. The results show that the annual total nitrogen loss followed the order of paddy field[17.73 kg·(hm2·a)-1] > citrus orchards[4.86 kg·(hm2·a)-1] > dry slope land[4.33 kg·(hm2·a)-1] > vegetable field[4.00 kg·(hm2·a)-1] > woodland[2.41 kg·(hm2·a)-1]. The annual total phosphorous loss followed the order of vegetable fields[4.97 kg·(hm2·a)-1] > Citrus orchards[1.87 kg·(hm2·a)-1] > paddy fields[0.93 kg·(hm2·a)-1] > woodlands[0.27 kg·(hm2·a)-1] > dry slope land[0.19 kg·(hm2·a)-1]. The nitrogen and phosphorus losses under the five land use methods were mainly concentrated from April to May with frequent rainfall events, accounting for 53.80%-96.52% and 56.03%-87.78% of the total annual nitrogen and phosphorus losses. Nitrogen loss was mainly in the form of nitrate nitrogen (16.16%-52.70%), and the total nitrogen loss flux and runoff showed a significant positive correlation (R2=0.9826). Particulate phosphorus was the main form of phosphorus loss in vegetable fields (83.30%), but in other land use schemes it is not significant. There were significant differences in the loss of different forms of nitrogen and phosphorus under the different land use schemes. Among them, measures should be taken in vegetable fields to deal with the problem of particulate phosphorus loss under conditions of heavy rainfall. Fertilization should be avoided in paddy fields during periods of concentrated rainfall. Scientific fertilization and reasonable land use configurations are important ways to control agricultural non-point source pollution in small watersheds.

Temporal Trends in Phosphorus Concentrations and Losses from Agricultural Monitoring Sites in Latvia

Abstract The Baltic Sea is the youngest sea on our planet, the environment of the sea is considered to be unique and fragile. It is affected by various human activities resulting in the impairment of water quality. Riverine nutrient (nitrogen and phosphorus) loads are among the major causes of eutrophication of the Baltic Sea. This study examines temporal trends in water discharge, total phosphorus (TP) and orthophosphate-phosphorus (PO4-P) concentrations and losses from three agricultural runoff monitoring sites in Latvia including Berze, Mellupite, and Vienziemite. The annual datasets of TP and PO4-P concentrations and losses were tested for statistical trends using a nonparametric test - the Mann-Kendall trend test. The timeframe of this study was from 1995 until 2018. The results show a large variety of annual mean concentrations and losses of TP and PO4-P in the study period. No statistically significant trend was detected for TP losses. Meanwhile, statistically significant downward trends were observed for TP concentrations in four out of six study sites and in two study sites for PO4-P concentrations.

Application of the single-stage anaerobic membrane bioreactor (1S-AnMBR) for the co-digestion of organic kitchen waste and sewage

In the scenario of sustainable technology application, the minimization of waste and resource consumption are more fundamental compared to effluent quality. In recent years, many kinds of researches related to green technology in wastewater treatment have been conducted, such as constructed wetland, membrane bioreactor, etc. With the same perception, the co-digestion of kitchen waste and sewage study was carried out. The principle of this environmentally friendly technology is to create a low-cost pretreatment for domestic wastewater, by taking advantage of the organic carbon available in the leftovers to remove contaminants in the wastewater, improve water quality, reduce excess sludge and save money. The study is aimed to evaluate the carbon and nutrient recovery of a laboratory single-stage anaerobic membrane bioreactor (1S-AnMBR), which included an Up-flow Anaerobic Sludge Blanket (UASB) continuous with an UF membrane bioreactor. The result shown that the obtained COD removals were above 80% at all organic loading rates (OLRs). The effluent COD concentrations were 160±21, 227±45, 340±78, 563±104 and 886±96 mg.L-1 at OLRs of 0.9 to 1.5; 2.0; 3.5; 5.0 and 7.0 kg COD.m-3.day-1, respectively. The biogas yields collected were 1119±76, 1550±68, 2155±80, 3610±86 and 5989±88 mL.day-1 at OLRs of 0.9; 1.5; 2.0; 3.5; 5.0 and 7.0 kg COD.m-3.day-1. High performance of ammonia conversion from organic nitrogen was obtained in the AnMBR. Total nitrogen and phosphorus losses were 12% and 15%, respectively. Transmembrane pressure (TMP) increased to the pressure limit of 45kPa after 11 days of operation at OLR of 5 kg COD.m-3.d-1. Thus membrane fouling is a big challenge for AnMBR. Besides these promising research outcomes, the technology is expected to bring convincing results into practice in the co-digestion of solid wastes and sewage that may be suitable for rural or remote areas, in which solid waste and sewage collection systems are not available.

Reallocating crop rotation patterns improves water quality and maintains crop yield

Meeting the growing food production needs of a society, while simultaneously maintaining or improving water quality, is a challenge facing many watersheds around the world. Across many nations, the agricultural norm is for farmers to dictate what, when and where to plant based on market demand and the most economically efficient use of land resources for the individual farm enterprise. As an alternative, the European Union (EU) has explored the potential of a soil-based, land use framework to achieve economic and environmental targets in agriculturally dominated watersheds; however, this framework has not been explored in the United States (US). We investigated the potential for an EU style soil-based, land use framework to improve water quality, while maintaining crop yields, in a sub-watershed of the Chesapeake Bay. The Soil and Water Assessment Tool (SWAT) was utilized to model crop growth, and losses of total nitrogen (TN), total phosphorus (TP) and sediment for an 8-year period (2010 - 2017). Based on SWAT model results, an algorithm was developed to spatially reallocate crop rotations within existing agricultural land to reduce TN, TP, and sediment losses based on soil properties while maintaining a similar production area of each rotation. Hay was reallocated onto landscapes most vulnerable to erosion and nutrient loss, whereas corn-soybean rotations were reallocated onto less vulnerable areas. In the reallocated scenario, 28% of agricultural lands retained the same crop rotation as the baseline scenario while 72% were reassigned. In a SWAT simulation of the reallocated scenario, TN, TP and sediment losses were reduced by 15%, 14% and 39%, respectively at an average annual scale. These results suggest that simply redistributing crop rotations within an impaired watershed can make significant water quality improvements even without additional structural best management practices. Although watershed-scale benefits were evaluated here, future research is needed to understand how this approach affects farm-level factors, as implementation may require some farmers to change the type of crops they grow.

Sugarcane planting patterns control ephemeral gully erosion and associated nutrient losses: Evidence from hillslope observation

Globally, the hillslope currently supporting sugarcane production is accelerating soil erosion and nutrient losses that degrade agroecosystem services and increase water pollution. However, sugarcane planting patterns (SPP), involving the arrangement of perennial (P) and newly planted (NP) sugarcane along hillslopes, may influence hillslope erosion and nutrient losses due to changes in root density and litter cover. Yet, no study to date has investigated the contribution of SPP to rill/and ephemeral gully (EG) erosion and associated nutrient losses. Thus, we investigated changes in EG erosion and losses of total nitrogen (TN), phosphorus (TP) and soil organic carbon (SOC) in response to SPP and the underlying mechanisms on hillslopes. Five hillslopes with different SPPs (P–P–P, NP–P–P, P–NP–P, NP–NP–P and P–NP) were identified in a sugarcane growing watershed. Annual EG erosion rates ranged from 56.6–96.1 Mg ha−1 yr−1 in the order of P–P–P < P–NP–P < P–NP < NP–P–P < NP–NP–P. The average EG erosion and associated TN, TP and SOC losses from the newly planted sugarcane fields were 2–3-fold of the perennial fields. The average annual yield of newly planted sugarcane was 10 % higher than the perennial sugarcane, but the increased yield benefit was dwarfed by significant increase in EG erosion and nutrient losses. Simple regression analyses indicated that EG erosion was inversely correlated with sugarcane litter cover and fine root density (root diam. < 1 and 1–2 mm), but positively correlated with slope-length factor. The principal component regression (PCR) showed that fine root density, litter cover, and slope-length were the main predictors for EG erosion. The results of this study revealed that appropriate SPP that replaces perennial sugarcane, at ≤30 % on different slope positions, with newly planted sugarcane, could minimize rill and EG erosion and nutrient losses as well as maintaining the annual yield.

Effects of particulate fractions on critical slope and critical rainfall intensity for runoff phosphorus from bare loessial soil

Slope and rainfall intensity are important factors affecting runoff phosphorus (P), but the dynamic mechanism of their coupled influence on P fractions in loessial bare sloping lands is not completely understood. The critical slope and critical rainfall intensity are thresholds associated with significant changes in runoff, erosion, and/or nutrient loss. In this study, 30 rainfall events (45, 60, 75, 90, 105 and 120 mm/h; 5°, 10°, 15°, 20° and 25°) were simulated to estimate the contribution of particulate P (PP) and soluble P (SP) fractions to P loss from bare loessial soils and identify the critical slope and critical rainfall intensity for different P forms and TP fluxes. The results indicate that: (i) total phosphorus (TP) and PP loss concentrations are significantly correlated to sediment yield and slope gradient, although there were close relationships between the average TP loss concentration and rainfall intensity at slopes of 20° and 25°; (ii) P in runoff from bare loessial soil consists almost entirely of the reactive PP form (96.6%), regardless of rainfall intensity and slope. The average PP fraction for different rainfall intensities increases with increasing slope, from 94.6% at a 5° slope to 98.0% at a 25° slope; and (iii) PP and TP have the same critical slope and critical rainfall intensity for bare loessial soil because of the dominance of PP in runoff P. The critical slope for the sharp increases in PP and TP was found to be in the range of 15–20° because the average losses at 20–25° increased about 1.67 times compared to 5–15°, and the critical rainfall intensity for significant increases in PP and TP was found to be in the range of 90–105 mm/h. The hydrological pathways transporting the various P fractions under storms may help to provide new insights needed to guide sloping farmland management in rainfed land agroecosystems of loess hilly regions.

Effect of organic amendment on properties and nutrient loss of soils of selected parent material

Soils of Southeastern Nigeria like those of other humid tropical countries are prone to leaching due to high rainfall resulting in low fertility, nutrient status, and crop yield. Evaluating the effects of selected organic amendments on retention of nutrients in soils is of major concern and formed the purpose of the study. Soil samples were collected from Asu River Group, (ARG), Bende Ameki Group (BAG), Coastal Plain Sand (CPS) and Falsebedded Sand Stone (FBS) which were the four respective parent materials studied. Three replicates of 10 kg of prepared samples from each parent material were bagged and thereafter applied with 10 tons ha-1 each of poultry (PD) and goat droppings (PD, GD). The thoroughly mixed combinations laid in a completely randomized design (CRD) were allowed to blend for three months after which, samples were collected from each bag and analyzed. The remaining amended soils were subjected to a rainfall simulation which enabled the collection of sediment yield which was also analyzed to determine the nutrients in them. Generated soil data were analyzed with analyses of variance (ANOVA). Means were separated using the least significant difference (LSD) at 5% probability level. The result showed that soil organic carbon increased from 15.80 – 17.70, 6.90 - 14.20, 7.10 – 13.90 and 11.39 - 17.50 gkg-1 in ARG, BAG, CPS and FBS respectively before and after amendment and later decreased to 10.8, 11.30, 6.70, and 8.30 g kg-1 in the sediment yield following simulation. Similarly, there were significant losses of about 23.52, 60.85; 60.00 and 47.20 % of total nitrogen to detached soils in the respective lithologies. Total nitrogen and available phosphorus losses in the soils followed the order: CPS > FBS > BAG > ARG and FBS > CPS > BAG > ARG respectively.

Nutrient loss from slope cropland to water in the riparian zone of the Three Gorges Reservoir: Process, pathway, and flux

Eutrophication of the surface water in the Three Gorges Reservoir (TGR) area in response to anthropogenically derived nutrients is a serious concern. Widespread cultivation in the riparian zone could lead to a large amount of nitrogen and phosphorus being transported via runoff during the cropland cultivation period or being released during the submerging period into the water of the TGR. However, little is known about the nutrient release fluxes from slope cropland into water during the submerging period. It is also not clear which process is critical. The experimental site in this study is representative of arable land on slopes in the riparian zone in the TGR area. Free-drainage lysimeters were constructed on a block of intact sandstone at a water level of 165 m in the riparian zone in the TGR area. The treatments were as follows: (1) no fertilizer (NF), (2) reduced nitrogen fertilizer treatment (RFT), and (3) conventional fertilizer treatment (CFT). The experimental plots were cropped conventionally with summer maize (Zea mays L.) from March to early September, and the experimental plots were submerged in water from October to March of the next year. Runoff water samples were collected during the 3-year experimental period (March 2016-October 2018). The results from this study indicate that nitrogen losses via interflow and phosphorus losses via overland flow are the dominant processes in the slope cropland in the riparian zone in the TGR area during the cropland cultivation period. In the CFT treatment, the average annual total nitrogen (TN) loss fluxes were 4.28 ± 0.10 kg hm−2 via overland flow and 26.17 ± 3.68 kg hm−2 via interflow. Additionally, the average annual total phosphorus (TP) loss fluxes in the conventional fertilizer treatment were 0.83 ± 0.43 kg hm−2 via overland flow and 0.15 ± 0.02 kg hm−2 via interflow. Before submerging, there were significant seasonal changes in the nutrient loss flux in every treatment. During the submerging period, the NO3--N, NH4+-N, and available phosphorus release fluxes from soil to water in the CFT treatment were 5.40 ± 0.75 kg hm−2, 4.38 ± 3.30 kg hm−2, and 12.09 ± 11.08 kg hm−2, respectively. The NO3--N release fluxes during the submerging period were higher than the NO3--N loss fluxes via overland flow, but they were lower than the NO3--N loss fluxes via interflow. Different from the pattern of NO3--N, the NH4+-N and available phosphorus release fluxes in the three treatments were much higher than the sum of the NH4+-N and available phosphorus loss fluxes via overland flow and interflow. Based on these findings, our results suggest that efforts to avoid further eutrophication of the reservoir water should take into account nutrient release from the soil of arable croplands in the riparian zone during the submerging period.

Responses of soil total phosphorus to freeze and thaw cycles in a Mollisol watershed

Freeze-thaw cycles (FTCs) change soil physiochemical properties and biogeochemical processes and inevitably influence the spatial distribution of soil phosphorus (P). In this study, a field investigation was conducted on the Mollisol soil of the Guangrong watershed from 2016 to 2018 to clarify the effect of FTCs on the spatial distribution of total phosphorus (TP) at soil depths of 0–5, 5–10 and 10–20 cm. A laboratory incubation experiment was conducted to reveal the effect of FTCs on TP in soil profiles (0–30 cm) in Mollisols. The results showed that (1) the spatial autocorrelation (nugget to sill ratio) of TP decreased by 5.92% after the FTCs while the spatial variance (coefficient of variation) increased by 17.19%. The TP in 85% of the watershed area decreased after the FTCs, and the mean content of TP decreased by 9.53%. These changes were mainly influenced by land use types, topographical factors, soil properties and human activities. (2) TP increased in the intersection between farmland and forestland (0.01 g kg−1) after the FTCs, while TP decreased both in the areas near the hydrological channel (0.06 g kg−1) and at the outlet of the watershed (0.13 g kg−1). Compared with down-slope tillage, maize planting, south-facing slopes and low vegetation coverage areas, the cross-slope tillage, soybean planting, north-facing slopes and high vegetation coverage areas reduced TP losses by 56.1%, 19.5%, 115.8% and 141.9%, respectively, in the 0–20 cm soil layer. (3) The effects of FTCs on TP in soil profile were mainly influenced by the soil moisture content, FTC frequency and soil bulk density in the laboratory incubation experiment. TP variability showed a V-shaped trend as the number of FTCs increased, and decreased as the initial moisture content increased at 1.1 g cm−3 of soil bulk density. (4) An equation based on the TP and mean value of normalized difference snow index, normalized difference vegetation index, ferrous minerals index and normalized difference soil moisture index from the freezing period to the thawing period was built to roughly predict the TP after FTCs (R2 = 0.72). Generally, the TP tended to decrease during both the freezing stage and the thawing stage in the field. Areas with down-slope tillage, existing maize fields, south-facing positions, low vegetation coverage and high snow coverage should be focused on to reduce P losses during FTCs.