Dissolved P Concentrations Research Articles

Stack’em Up: Field-Scale Performance of a Stacked Woodchip Bioreactor and Phosphorus Removal Structure

HighlightsBioreactor removed 5% and 2% of nitrate-nitrogen (N) and dissolved P (DP), respectively, from total drainage with 93% bypass.P removal structure (PRS) handled all flow at 7 L s-1, thereby removing 30% and 29% of DP and nitrate-N from total drainage volume, respectively, despite low DP inflow concentrations.PRS removed 74% of DP during 9-d P inflow spike test, 3x greater load removal than 2-yr natural loads.Construct PRS at P critical source areas for max efficiency; design bioreactors and PRS for treating as much peak flow as possible.Abstract. The combination of nitrate and dissolved phosphorus (P) has been identified as a cause of harmful algal blooms. Wood-chip bioreactors and P removal structures are structural edge-of-field practices that filter nitrate and dissolved P (DP) from drainage water. While both practices are cost-sharing by the Natural Resources Conservation Service, they have yet to be implemented in the same field as stacked practices. This study evaluated nitrate-nitrogen (N), DP, and total P (TP) removal from a stacked wood-chip bioreactor/P removal structure constructed on a 15 cm field tile drain outlet over a 2-yr period. A typical woodchip bioreactor was constructed at the tile outlet of an 8.9 ha field, up-pipe of a P removal structure that utilized activated Al (AA) contained in a buried tank with bottom-upward flow. All discharge was captured with automated flow measurements and sampling. Contributing soils were low in P and therefore not ideal for installation of a P removal structure, and attempts to substantially increase soil test P were not successful. Thus, an additional experiment was included in which discharge was spiked with dissolved P for nine consecutive days. Nearly 50% of the 2-yr DP load was lost within 40 days after a single fertilizer application event that only covered 10% of the field. Greater discharge rates corresponded to greater concentrations and loads of nitrate-N and P; this emphasizes the need to design structural conservation practices for handling peak flow rates. The P removal structure removed 30% of the 2-yr load (not including spike test), despite inflow DP concentrations being much less than the minimum threshold flow-weighted mean concentration (FWMC) of 0.2 mg L-1 for justification of a structure. Laboratory P removal experiments and the field P spike test demonstrated how greater inflow DP concentrations led to more efficient P removal (74% and 0.77 kg DP removal over 9d). This illustrated the importance of targeting critical source areas that optimize P load reductions. The P removal structure handled all discharge without restricting field drainage, resulting in a maximum overall event discharge rate through the structure of around 7 L s-1 while the bioreactor only treated 7% of the total discharge. As a result, the P removal structure removed nearly 10x more nitrate-N than the bioreactor; the nitrate removal mechanism is unknown, but adsorption to AA was not possible based on laboratory tests. Instead, it is possible that a redox-coupled Fe(II)–nitrate reaction was occurring on the surface of AA. Keywords: Conservation practices, Nitrate removal, Nutrient reduction, Nutrient transport, Phosphorus treatment, Stacked practices, Water quality.

Phosphorus and its solubility in aerosols from continental and marine sources in the sea areas near China: Results from a 40-day cruise mission in late spring

Accurate assessments of soluble phosphorus (P) in aerosol particles are essential to understand the atmospheric nutrients supply to the marine ecosystem. We quantified total P (TP) and dissolved P (DP) in the aerosol particles collected in the sea areas near China in a cruise mission from May 1 to June 11, 2016. The overall concentrations of TP and DP were 3.5-99.9ngm-3 and 2.5-27.0ngm-3, respectively. When the air originating from the desert areas, TP and DP were 28.7-99.9ngm-3 and 10.8-27.0ngm-3, respectively, and P solubility was 24.1-54.6%. When the air influenced mainly by anthropogenic emissions from eastern China, TP and DP were 11.7-12.3ngm-3 and 5.7-6.3ngm-3, respectively, and P solubility was 46.0-53.7%. More than half of the TP and more than 70% of the DP were from pyrogenic particles, with a considerable DP converted via aerosol acidification after the particles met humid marine air. On average, aerosol acidification promoted the fractional solubility of dissolved inorganic P (DIP) to TP from 22% to 43%. When the air originating from the marine areas, TP and DP were 3.5-22.0ngm-3 and 2.5-8.4ngm-3, respectively, and P solubility was 34.6-93.6%. About one-third of the DP was from biological emissions in organic forms (DOP), leading to higher solubility than in the particles from continental sources. These results reveal the dominance of inorganic P in TP and DP from the desert and anthropogenic mineral dust and the significant contribution of organic P from marine sources. The results also indicate the necessity to treat aerosol P carefully according to different sources of the aerosol particles and atmospheric processes the particles experience in assessing aerosol P input to seawater.

Quantifying groundwater phosphorus flux to rivers in a typical agricultural watershed in eastern China.

Increasing evidence indicates that groundwater can contain high dissolved phosphorus (P) concentrations, thereby contributing as a potential pollution source for surface waters. However, limited quantitative knowledge is available concerning groundwater P fluxes to rivers. Based on monthly hydrochemical monitoring data for rivers and groundwater in 2017-2020, this study combined baseflow separation methods and a load apportionment model (LAM) to quantify contributions from point sources, surface runoff, and groundwater/subsurface runoff to riverine P pollution in a typical agricultural watershed of eastern China. In the studied Shuanggang River, most total P (TP) and dissolved P (DP) concentrations exceeded targeted water quality standards (i.e., TP ≤ 0.2mg P L-1, DP ≤ 0.05mg P L-1), with DP (76 ± 20%) being the major riverine P form. Observed DP concentrations in groundwater were generally higher than those of river waters. There was a strong correlation between river and groundwater P concentrations, implying that groundwater might be a considerable P pollution source to rivers. The nonlinear reservoir algorithm estimated that baseflow/groundwater contributed 66-68% of monthly riverine water discharge on average, which was consistent with results estimated by an isotope-based sine-wave fitting method. The LAM incorporating point sources, surface runoff, and groundwater effectively predicted daily riverine TP [calibration: coefficient of determination (R2) = 0.76-0.82, Nash-Sutcliffe Efficiency (NSE) = 0.61-0.77; validation: R2 = 0.88-0.98, NSE = 0.54-0.64] and DP loads (calibration: R2 = 0.73-0.84, NSE = 0.67-0.72; validation: R2 = 0.88-0.97, NSE = 0.56-0.83). The LAM estimated point source, surface runoff, and groundwater contributions to riverine loads were 15-18%, 14-35%, and 46-70% for TP loads and 7-9%, 10-32%, and 59-82% for DP loads, respectively. Groundwater was the dominant riverine P source due to long-term accumulation of P from excess fertilizer and farmyard manure applications. The developed methodology provides an alternative method for quantifying P pollution loads from point sources, surface runoff, and groundwater to rivers. This study highlights the importance of controlling groundwater P pollution from agricultural lands to address riverine water quality objectives and further implies that decreasing fertilizer P application rates and utilizing legacy soil P for crop uptake are required to reduce groundwater P loads to rivers.

Estimating dissolved phosphorus losses from legacy sources in pastures: The limits of soil tests and small-scale rainfall simulators.

A legacy of using P fertilizers on grazed pastures has been enhanced soil fertility and an associated increased risk of P loss in runoff. Rainfall simulation has been extensively used to develop relationships between soil test P (STP) and dissolved P (DP) in runoff as part of modeling efforts scrutinizing the impact of legacy P. This review examines the applicability of rainfall simulation to draw inferences related to legacy P. Using available literature, we propose a mixing layer model with chemical transfer to describe DP mobilization from pasture soils where readily available P in the mixing layer is rapidly exhausted and contact time controls DP concentrations responsible for subsequent DP mobilization. That conceptual model was shown to be consistent with field monitoring data and then used to assess the likely effect of rainfall simulation protocols on DP mobilization, highlighting the influence of soil preparation, scale and measurement duration, and, most important, hydrology that can facilitate the physical transport of P into and out of surface flow. We conclude that rainfall simulation experimental protocols can have severe limitations for developing relationships between DP in runoff and STP that are subsequently used to estimate legacy P contributions to downstream water resources.

Sources, Transport, and Management of Phosphorus Loss during the Cranberry Harvest

Wet (flood) harvesting is essential to commercial cranberry (Vaccinium macrocarpon Ait.) production in Massachusetts, where one‐fifth of the US cranberry crop is produced. However, periodic flooding may lead to impaired water quality in lakes that receive harvest flood discharges. In this study, harvest flood inputs and outputs of P were measured to determine the net flux of P (Mnet) from a 19.2‐ha cranberry bog and its five bog units. Results showed that the cranberry bog was a source of dissolved P (DP) (Mnet = 0.32 kg P ha−1) and a minor sink of particulate P (PP) (Mnet = −0.03 kg P ha−1). For the five bog units, values of Mnet were highly variable, ranging from −0.49 to 1.48 kg P ha−1 with a coefficient of variation of 223% for DP. Variation in Mnet was not strongly related to P fertilizer rate, soil test P, or flood holding time, but was inversely related to the water flux from the cranberry bog to the underlying aquifer. Groundwater concentrations of DP were not statistically different before, during, or after the harvest flood, suggesting minimal subsurface leaching of P to shallow groundwater. Collectively, these findings point to soil P retention in some cranberry bogs, as might be expected in natural wetlands. Although there is potential for subsurface P leaching, the use of select cranberry bogs as filter beds of high‐P floodwater may help to curtail surface water export of P from cranberry agriculture.Core Ideas Wet (flood) harvested cranberry bogs may contribute to water quality problems. Harvest flood P losses varied from 0.49 to 1.48 kg P ha−1 for five cranberry beds. Harvest flood P losses were not related to P fertilizer, soil P, or flood length. Rather, the best indicator of harvest flood P loss was groundwater recharge. Groundwater recharge may facilitate P sorption and reduce harvest flood P losses.

Effects of Manure and Tillage on Edge-of-Field Phosphorus Loss in Seasonally Frozen Landscapes.

Environmental conditions and management practices affect nutrient losses in surface runoff, but their relative impacts on phosphorus (P) loss during frozen and nonfrozen ground periods have not been well quantified. More specifically, the relative importance of manure application, tillage, and soil-test P (STP) has not been assessed at the field scale. In this study, we compiled a dataset composed of 125 site-years of data from 26 fields that were continually monitored for edge-of-field P loss during snowmelt and storm events. Regression tree analyses were performed to rank the level of influence each environmental and management factor had on nutrient loads. Dissolved P (DP) was the majority of the total P (TP) during frozen conditions, but a small portion of TP during nonfrozen conditions. Manure application had a greater influence on the flow-weighted mean concentrations (FWMCs) of TP and DP during frozen conditions than during nonfrozen conditions. No-till resulted in greater TP and DP FWMCs during frozen conditions than conventional tillage, whereas the opposite effect for TP FWMC was seen during nonfrozen conditions. However, regression tree analysis revealed that STP (0- to 5-cm depth) was the most important factor in predicting DP and TP FWMCs during frozen conditions and DP FWMC during nonfrozen conditions. Extremely high STP values were associated with late-frozen manure applications and grazed pastures. Reducing surface P loss in seasonally frozen landscapes will require prioritizing management strategies that avoid manure application through early- and late-frozen conditions and lead to a drawdown of STP, particularly in the top 5 cm.

Phosphorus dynamics during storm events in a subtropical rural catchment in southern Brazil

Abstract The intensification of agricultural activities increases the transfer of phosphorus (P) to surface water bodies causing a wide range of environmental, social and economic problems, such as eutrophication. This paper describes the dynamics of P loss during rainfall events (intra-event) and between events (inter-event) in a rural catchment with intensive soil use in southern Brazil, emphasizing the relationships of the solutes with the hydrosedimentological variables. The information on the magnitude and the pattern of P transport was obtained during eighth significant rainfall events, in addition to the sampling performed during the baseflow period (between events). During the events, we evaluated the transfer dynamics of the total P (TP), dissolved P (DP), particulate P (PP) and suspended sediment concentration (SSC). Phosphorus (dissolved and particulate) is predominantly lost during events. The concentrations of DP and PP were low in samples collected in the period between events, when groundwater flow predominates. There is predominance of subsurface flow for the total volume of DP drained into the catchment. The hysteresis of TP forms a loop in the counterclockwise direction at the moment the soil is exposed by plowing, due to P transfer from the cropland to the water course. The transfer of P occurred predominantly in the particulate form (88%) due to the high affinity of P with mineral colloids. There was predominance of clockwise hysteresis for TP and SSC during the fallow period and at the beginning of soil mobilization, indicating the presence of P and sediment sources closer to the catchment outlet. However, during the development period of the crop, when the soil was more exposed due to plowing, counterclockwise hysteresis was observed for TP, which indicates a predominance of sources farther from the outlet, such as the cropland. Thus, we believe that efforts towards adopting practices that reduce erosion can contribute to a reduction of P transfer to water sources. Consequently controlling the process of eutrophication.

Can the watershed non-point phosphorus pollution be interpreted by critical soil properties? A new insight of different soil P states

The physicochemical properties of surface soil play a key role in the fate of watershed non-point source pollution. Special emphasis is needed to identify soil properties that are sensitive to both particulate P (PP) pollution and dissolved P (DP) pollution, which is essential for watershed environmental management. The Chaohu Lake basin, a typical eutrophic lake in China, was selected as the study site. The spatial features of the Non-point Source (NPS) PP loads and DP loads were calculated simultaneously based on the integration of sediment delivery distributed model (SEDD) and pollution loads (PLOAD) model. Then several critical physicochemical soil properties, especially various soil P compositions, were innovatively introduced to determine the response of the critical soil properties to NPS P pollution. The findings can be summarized: i) the mean PP load value of the different sub-basins was 5.87 kg, and PP pollution is regarded to be the primary NPS P pollution state, while the DP loads increased rapidly under the rapid urbanization process. ii) iron-bound phosphorus (Fe-P) and aluminum-bound phosphorus (Al-P) are the main components of available P and showed the most sensitive responses to NPS PP pollution, and the correlation coefficients were approximately 0.9. Otherwise, the residual phosphorus (Res-P) was selected as a sensitive soil P state that was significantly negatively correlated with the DP loads. iii) The DP and PP concentrations were represented differently when they were correlated with various soil properties, and the clay proportion was strongly negatively related to the PP loads. Meanwhile, there is a non-linear relationship between the DP loads and the critical soil properties, such as Fe and Total Nitrogen (TN) concentrations. Specifically, a strong inhibitory effect of TN concentration on the DP load was apparent in the Nanfei river (NF) and Paihe (PH) river basins where the R2 reached 0.67, which contrasts with the relatively poor relationship within the other five basins. In addition, the degree of correlation between the Fe and DP loads severely degraded in the basins that were mostly covered by construction land or those that underwent a rapid urbanization process. The findings indicate that land use/cover change (LUCC), especially the distribution of agricultural land and construction land, as well as the soil background information (TN, Fe and Soil organic matters, etc.) can be considered as factors that influence NPS P pollution.

Influence of Flue Gas Desulfurization Gypsum on Reducing Soluble Phosphorus in Successive Runoff Events from a Coastal Plain Bermudagrass Pasture.

Controlling the threat that pastures intensively managed with poultry litter (PL) pose to accelerating eutrophication is a major issue in the southeastern United States. Gypsum (CaSO) has been identified as a promising management tool for ameliorating litter P losses to runoff. Thus, research was conducted to elucidate gypsum's residual effects on P losses from a bermudagrass ( L.) pasture. Runoff events (60 min) were created using rainfall simulations. Treatments consisted of applying four flue gas desulfurization (FGD) gypsum rates (0, 2.2, 4.4, and 8.9 Mg ha) to bermudagrass fertilized with 13.4 Mg ha PL plus a nonfertilized check (no litter or gypsum) and 8.9 Mg ha FGD gypsum only as controls. Rainfall simulations (∼ 85 mm h) were conducted immediately, 5 wk, and 6 mo (i.e., at the end of growing season) after PL application to determine gypsum's effectiveness at controlling P loss over successive runoff events. The greatest dissolved P (DP) in runoff occurred immediately after PL application. Gypsum effectively reduced cumulative DP concentration losses (54%) compared with PL alone in initial runoff events. Gypsum reduced DP concentrations in succeeding runoff events also regardless of timing, suggesting that its effect is persistent and will not diminish over a growing season. Generally, maximum DP reductions were achieved with 8.9 Mg ha. However, it was surmised from this study that optimal P reduction in a bermudagrass pasture can be achieved with 4.4 Mg ha. Information ascertained from this study may be useful in aiding land managers making prescriptions for management practices that reduce DP losses from agricultural fields.

Effect of tillage on macropore flow and phosphorus transport to tile drains

AbstractElevated phosphorus (P) concentrations in subsurface drainage water are thought to be the result of P bypassing the soil matrix via macropore flow. The objectives of this study were to quantify event water delivery to tile drains via macropore flow paths during storm events and to determine the effect of tillage practices on event water and P delivery to tiles. Tile discharge, total dissolved P (DP) and total P (TP) concentrations, and stable oxygen and deuterium isotopic signatures were measured from two adjacent tile‐drained fields in Ohio, USA during seven spring storms. Fertilizer was surface‐applied to both fields and disk tillage was used to incorporate the fertilizer on one field while the other remained in no‐till. Median DP concentration in tile discharge prior to fertilizer application was 0.08 mg L−1 in both fields. Following fertilizer application, median DP concentration was significantly greater in the no‐tilled field (1.19 mg L−1) compared to the tilled field (0.66 mg L−1), with concentrations remaining significantly greater in the no‐till field for the remainder of the monitored storms. Both DP and TP concentrations in the no‐till field were significantly related to event water contributions to tile discharge, while only TP concentration was significantly related to event water in the tilled field. Event water accounted for between 26 and 69% of total tile discharge from both fields, but tillage substantially reduced maximum contributions of event water. Collectively, these results suggest that incorporating surface‐applied fertilizers has the potential to substantially reduce the risk of P transport from tile‐drained fields.

Spatial Scale and Field Management Affect Patterns of Phosphorus Loss in Cranberry Floodwaters.

Although cranberries ( Ait.) are indigenous to the northeastern United States, phosphorus (P) fertilizer additions and periodic flooding make commercial cranberry a potential source of P to the region's lakes and streams. In this study, we report values of P export in cranberry floodwaters that range from <0.8 to 4.7 kg P ha, generally reflecting differences in the hydrological, edaphic, and management factors underlying soil P transfer to floodwater. The relatively high P loading rate (4.7 P kg P ha) was associated with harvest flooding of organic-rich soils. Periods of winter flooding and the discharge of harvest floodwater from mineral soils resulted in relatively low P loss (<0.8 kg P ha). Increases in concentrations of total dissolved P (DP) and total particulate P (PP) in floodwater as stage decreased below the surface of the cranberry bed were consistent with the transport of dissolved P in soil porewater and mobilization of particulate P in ditches. Variations in floodwater DP, as well as conservative and reactive tracer concentrations, suggested that the processes by which soil P is released to porewater included desorption of near-surface soil P and anaerobic dissolution of iron-P compounds deeper in the soil profile. At the farm scale, concentrations of DP and PP steadily increased over time, presumably because drainage waters from beds farther upgradient had longer contact times with P-rich sources, such as soil porewater and ditch sediments. Overall, the study illustrates the role that scale-dependent processes impart on patterns of P loss in agricultural production systems.

Phosphorus losses from an irrigated watershed in the northwestern United States: case study of the upper snake rock watershed.

Watersheds using surface water for irrigation often return a portion of the water to a water body. This irrigation return flow often includes sediment and nutrients that reduce the quality of the receiving water body. Research in the 82,000-ha Upper Snake Rock (USR) watershed from 2005 to 2008 showed that, on average, water diverted from the Snake River annually supplied 547 kg ha of total suspended solids (TSS), 1.1 kg ha of total P (TP), and 0.50 kg ha of dissolved P (DP) to the irrigation tract. Irrigation return flow from the USR watershed contributed 414 kg ha of TSS, 0.71 kg ha of TP, and 0.32 kg ha of DP back to the Snake River. Significantly more TP flowed into the watershed than returned to the Snake River, whereas there was no significant difference between inflow and return flow loads for TSS and DP. Average TSS and TP concentrations in return flow were 71 and 0.12 mg L, respectively, which exceeded the TMDL limits of 52 mg L TSS and 0.075 mg L TP set for this section of the Snake River. Monitoring inflow and outflow for five water quality ponds constructed to reduce sediment and P losses from the watershed showed that TSS concentrations were reduced 36 to 75%, but DP concentrations were reduced only 7 to 16%. This research showed that continued implementation of conservation practices should result in irrigation return flow from the USR watershed meeting the total maximum daily load limits for the Snake River.

Phosphorus Retention in a Newly Constructed Wetland Receiving Agricultural Tile Drainage Water

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. This study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010-2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Inflow TP and DP concentrations varied greatly (0.02-1.09 mg L) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water flow in line with air temperature variations. Outflow P concentrations were generally lower than inflow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specific retention of 69 kg TP, 17 kg DP, and 30 t TSS ha yr, corresponding to a reduction in losses of 0.22 kg TP ha yr from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography.

Hot moments and hot spots of nutrient losses from a mixed land use watershed

Summary Non-point nitrogen (N) and phosphorus (P) pollution from agriculture has increasingly received more public attention. In this study, NO 3 –N, dissolved P (DP) and particulate P (PP) concentrations and loads were investigated for four sub-basins (labeled 1–4 going up the watershed) within a mixed land use watershed (39.5 ha) in the Appalachian Valley and Ridge Physiographic Province. The hot moments of NO 3 –N concentration and load occurred in base flow and during the non-growing season. Great and temporally variable DP and PP concentrations were observed in storm flow. The hot moments of DP concentration and load were in storm flow from May to December and from September to Nov, respectively, while the hot moments of PP concentration and load were in storm flow from January to June. The NO 3 –N, DP, and PP loads were compared for all four sub-basins on a loss per length of stream reach basis to determine the hot spots and their corresponding losses. The hot spots and hot moments of NO 3 –N loads were in Sub-basins 1 and 4 during the non-growing season base flow period and Sub-basin 2 during the post-growing season base flow period (>110 g m −1 mo −1 ). The hot spots of DP loads were also in Sub-basins 1 and 4, but during the growing and post-growing season storm flow period (>1.4 g m −1 mo −1 ). In contrast, the hot spots and hot moments of PP load were in Sub-basin 3 during the pre-growing and growing season storm flow, as much as 13.4 and 14.1 g m −1 mo −1 , respectively. Controlling factors of nutrient export were discussed in this study, including season, hydrology (base flow, storm flow, surface and subsurface runoff), and land use. Although different hot moments and hot spots within the watershed were identified for NO 3 –N, DP, and PP losses, the implementation of a couple of management practices (cover crops and no-till) might be sufficient to effectively reduce nutrient losses from this and similar Valley and Ridge watersheds.

Phosphorus in runoff from two highly weathered soils of the tropics

Ramirez-Avila, J. R., Sotomayor-Ramirez, D., Martinez-Rodriguez, G. A. and Perez-Alegria, L. R. 2011. Phosphorus in runoff from two highly weathered soils of the tropics. Can. J. Soil Sci. 91: 267-277. Agricultural fields with high soil phosphorus (P) content are important contributors to surface water degradation. Two consecutive simulated rainfall events were conducted on two Ultisols previously amended with inorganic P fertilizer or broiler litter. Soil test P (Bray 1 and Olsen) levels evaluated ranged from 1 to 350 mg kg-1. Surface runoff concentrations of total P (TP) and dissolved P (DP) generated by a 30-min runoff event were quantified. Runoff DP concentrations ranged from 0.08 to 3.98 mg L-1 in fertilizer P-amended soils and from 0.08 to 4.93 mg L-1 in broiler litter-amended soils. A single exponential model adequately described the relationships between soil test P and DP concentrations in runoff. For each soil, the soil test P-DP concentration relationships were positively influenced by soil or...

Phosphorus in runoff from two highly weathered soils of the tropics

Ramírez-Ávila, J. R., Sotomayor-Ramírez, D., Martínez-Rodríguez, G. A. and Pérez-Alegría, L. R. 2011. Phosphorus in runoff from two highly weathered soils of the tropics. Can. J. Soil Sci. 91: 267–277. Agricultural fields with high soil phosphorus (P) content are important contributors to surface water degradation. Two consecutive simulated rainfall events were conducted on two Ultisols previously amended with inorganic P fertilizer or broiler litter. Soil test P (Bray 1 and Olsen) levels evaluated ranged from 1 to 350 mg kg−1. Surface runoff concentrations of total P (TP) and dissolved P (DP) generated by a 30-min runoff event were quantified. Runoff DP concentrations ranged from 0.08 to 3.98 mg L−1in fertilizer P-amended soils and from 0.08 to 4.93 mg L−1in broiler litter-amended soils. A single exponential model adequately described the relationships between soil test P and DP concentrations in runoff. For each soil, the soil test P-DP concentration relationships were positively influenced by soil organic matter and negatively influenced by antecedent soil moisture (P&lt;0.05). For both soils, the soil test P-DP concentration relationships were positively influenced by groundcover percentage and negatively influenced by slope. Environmental soil test P critical levels corresponding to a runoff threshold of 1 mg L−1DP, ranged between 176 and 296 mg kg−1(Olsen) and 143 to 276 mg kg−1(Bray 1) in soils amended with fertilizer-P. In broiler litter-amended soils, threshold values were 88 and 111 mg kg−1using Olsen and Bray 1, respectively. Differences in surface runoff-P concentrations due to amendment sources, antecedent soil moisture content, soil organic matter, groundcover and slope suggest that these factors need to be considered in P management decisions at the farm level.

Evaluación de mejores prácticas de manejo para reducir las pérdidas de nutrientes contaminantes en escorrentía desde suelos enmendados con carnada de pollos parrilleros. I. Adiciones de alum.

El efecto de alum [AI2(S04)3-14H20] en la reducción de las concentraciones de fósforo (P) en las aguas de escorrentía desde los suelos enmendados con residuos de carnadas de pollos parrilleros se evaluó en varios eventos de lluvia simulada. Adiciones de alum a razón de 20% (peso/peso) causaron una reducción significativa en la fracción de P "soluble" (CaCI2-extraíble) presente en la matriz de la carnada de pollos parrilleros. Como resultado, el P soluble añadido al suelo se redujo en un 43% y un 75% para los tratamientos de 6 t/ha y 20 t/ha de residuos de carnada de pollos parrilleros con alum en comparación con sus contrapartes sin alum. Las concentraciones de P total en la escorrentía de los tratamientos 6 t/ha y 20 t/ha de residuos de carnada de pollos parrilleros sin alum resultaron altamente enriquecidas, promediando 2.59 y 6.10 mg/L, respectivamente. En la dosis más alta de residuos de carnada de pollos parrilleros (20 t/ha), el tratamiento de 20% de alum logró una reducción de 52% en la concentración de P total en la escorrentía relativo al tratamiento sin alum. Sin embargo, el efecto más notable de alum fue en la reducción de las pérdidas de P disuelto. Las pérdidas en las concentraciones de P disuelto promedio en el tratamiento de 20 t/ha de residuos de carnada de pollos parrilleros (sin alum) fue de 3.55 mg/L, un valor significativamente mayor que el umbral de 1.0 mg/L que ha sido sugerido como el límite potencial para el control de pérdidas de P por escorrentía de predios agrícolas. En dicha dosis de aplicación los tratamientos de 10% y 20% de alum alcanzaron reducciones de 58% y 70% en las concentraciones de P disuelto en la escorrentía, espectivamente. Las pérdidas en las concentraciones de P disuelto observadas para los tratamientos con 20% de alum cumplieron con el valor umbral de 1.0 mg/L en prácticamente todos los casos, irrespectivamente de la dosis de residuos de carnada de pollos parrilleros evaluada. Las pérdidas de P total en la escorrentía fue correlacionada positivamente tanto con la fracción de P soluble (extraíble con CaCI2) aplicado a los suelos, como con los niveles de P (Olsen) en el suelo durante las diferentes etapas de los eventos de simulación de lluvia. El contenido nutricional (N, P, y K) para muestras de hierba Bermuda reflejó el efecto de las diferentes dosis de residuos de carnada de pollos parrilleros. Se observó un mayor contenido nutricional en los tratamientos de 20 t/ha comparado con los de 6 t/ha. No obstante, los efectos solo fueron estadísticamente significativos para nitrógeno. El alum no parece ejercer un impacto significativo en el contenido nutricional de la yerba Bermuda, aunque se observaron disminuciones leves (no significativas) para N y P en el tratamiento de 20 t/ha de carnada de pollos parrilleros con 20% de alum.

Apatite Control of Phosphorus Release to Runoff from Soils of Phosphate Mine Reclamation Areas

Phosphorus (P) in runoff can pose a water quality risk in phosphate mine reclamation areas. High dissolved P (DP) concentrations (about 0.4–3.0 mg L−1) in runoff from these areas and high equilibrium P concentrations for the soils led us to hypothesize that P release is controlled by dissolution of apatite rather than by desorption mechanisms. Objectives were to (a) verify via chemical- and solid-state assessments that P in the reclamation soils is mainly in the form of apatite and (b) examine evidence that DP concentrations in runoff water from these soils is controlled by apatite dissolution. Soil analyses included total P (TP), P sorption isotherms, P fractionation, mineralogy, and P distribution by particle size classes. Runoff samples were chemically characterized and modeled for speciation. Results showed high TP concentrations and the presence of apatite. The Ca- and Mg-bound P accounted for about 95% of TP. Runoff samples were undersaturated with respect to apatite. A strong relationship between calculated apatite specific surface area and measured DP concentration in water extracts is supportive of other evidence that apatite dissolution is a major factor controlling P release from these soils. Data indicate that these soils will be a long-term P source rather than sink. Results are applicable to other phosphate mine reclamation sites and illustrate the need to account for compositional differences between reconstructed soils on reclaimed mining sites and their indigenous soil analogues.

Artificial Neural Network estimation of soil erosion and nutrient concentrations in runoff from land application areas

The transport of sediment and nutrients from land application areas is an environmental concern. New methods are needed for estimating soil and nutrient concentrations of runoff from cropland areas on which manure is applied. Artificial Neural Networks (ANNs) trained with a backpropagation (BP) algorithm were used to estimate soil erosion, dissolved P (DP) and NH4-N concentrations of runoff from a land application site near Lincoln, Nebraska, USA. Simulation results from ANN-derived models showed that the amount of soil eroded is positively correlated with rainfall and runoff. In addition, concentrations of DP and NH4-N in overland flow were related to measurements of runoff, EC and pH. Coefficient of determination values (R^2) relating predicted versus measured estimates of soil erosion, DP, and NH4-N were 0.62, 0.72 and 0.92, respectively. The ANN models derived from measurements of runoff, electrical conductivity (EC) and pH provided reliable estimates of DP and NH4-N concentrations in runoff.

Evaluation of quick tests for phosphorus determination in dairy manures

Nutrients in animal manure are valuable inputs in agronomic crop production. Rapid and timely information about manure nutrient content are needed to minimize the risks of phosphorus (P) over-application and losses of dissolved P (DP) in runoff from fields treated with manure. We evaluated the suitability of a commercial hand-held reflectometer, a hydrometer, and an electrical conductivity (EC) meter for determining DP and total P (TP) in dairy manures. Bulk samples (n = 107) collected from farms across CT, MD, NY, PA, and VA were highly variable in total solids (TS) concentration, ranging from 11 to 213gL(-1), in suspensions' pH (6.3-9.2), and EC (6.2-53.3 dS m(-1)). Manure DP concentrations measured using the RQFlex reflectometer (RQFlex-DP(s)) were related to molybdate-reactive P (MRP(s)) concentrations as follows: RQFlex-DP(s) = 0.471 x MRP(s) + 1102 (r2 = 0.29). Inclusion of pH and squared-pH terms improved the prediction of manure DP from RQFlex results (r2 = 0.66). Excluding five outlier samples that had pH < or = 6.9 the coefficient of determination (r2) for the MRP(s) and RQFlex-DP(s) relationship was 0.83 for 95% of the samples. Manure TS were related to hydrometer specific gravity readings (r2 = 0.53) that were in turn related to TP (r2 = 0.34), but not to either RQFlex-DP or MRP. Relationships between suspensions' EC and DP or TP were non-significant. Therefore, the RQFlex method is the only viable option for on-site quick estimates of DP that can be made more robust when complemented with TS and pH measurements. The DP quick test can provide near real-time information on soluble manure nutrient content across a wide range of handling and storage conditions on dairy farms and quick estimates of potential soluble P losses in runoff following land applications of manure.