Effect of liquid swine manure rate, incorporation, and timing of rainfall on phosphorus loss with surface runoff

Release of phosphorus and metal(loid)s from manured soils to floodwater during a laboratory simulation of snowmelt flooding

Phosphorus (P) and metal accumulation in manured agricultural soils and subsequent losses to waterways have been extensively studied; however, the magnitudes and the factors governing their losses during spring snowmelt flooding are less known. We examined the P and metal release from long-term manured soil to floodwater under simulated snowmelt flooding with recent manure additions. Intact soil columns collected from field plots located in Randolph, Southern Manitoba, 2 weeks after liquid swine manure treatments (surface-applied, injected, or control with no recent manure addition) were flooded and incubated for 8 weeks at 4 ± 1°C to simulate snowmelt conditions. Floodwater (syringe filtered through 0.45 µm) and soil porewater (extracted using Rhizon-Mom samplers) samples were periodically extracted and analyzed for dissolved reactive phosphorus (DRP), pH, zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), calcium (Ca), and arsenic (As). Mean floodwater DRP concentrations (mg L-1) for manure injected (2.0 ± 0.26), surface-applied (2.6 ± 0.26), and control (2.2 ± 0.26) treatments did not differ significantly. Despite manure application, DRP loss to floodwater did not significantly increase compared to the control, possibly due to the elevated residual soil P at this site from the long-term manure use. At the end of simulated flooding, the DRP concentrations increased by 1.5-fold and 5-fold in porewater and floodwater, respectively. Metal(loid) concentrations were not affected by manure treatments in general, except for Zn and Mg on certain days. Unlike DRP, where porewater and floodwater concentrations increased with time, metalloid concentration in porewater and floodwater did not show consistent trends with flooding time.

Screening fertilizers for their phosphorus runoff risk using laboratory methods

Losses of phosphorus (P) from fertilized fields may result in degradation of water quality. Various initiatives are under evaluation to minimize water contamination, including the adoption of less soluble or coated P fertilizer formulations aiming to mitigate losses of P in runoff. Field-based rainfall simulators are traditionally used to evaluate P runoff, but using these is time consuming, labor intensive, and costly given the complex apparatus and analyses involved. We hypothesized that laboratory-based methods could be useful to evaluate the risk of P runoff from fertilizers. In order to identify a rapid, inexpensive, and efficient screening process, we compared two laboratory-scale measurements, one in water (based on electrical conductivity measurements) and one in soil (based on visualization of P diffusion in soil), with runoff results from field-, glasshouse-, and laboratory-based rainfall simulators, using coated soluble phosphate fertilizers. The laboratory-based methods assessing the P release rate in water and in soil correlated closely (r ≥ .96) with the losses of P obtained in the three rainfall simulators regardless of the type of coating or solubility of the fertilizer. The faster and inexpensive electrical conductivity and diffusion visualization methodologies were useful to rank the fertilizers by P release to runoff. Hence, these tools may be useful for screening fertilizer formulations with respect to their runoff risk.

Comparing Biochar-Swine Manure Mixture to Conventional Manure Impact on Soil Nutrient Availability and Plant Uptake—A Greenhouse Study

The use of swine manure as a source of plant nutrients is one alternative to synthetic fertilizers. However, conventional manure application with >90% water and a low C:N ratio results in soil C loss to the atmosphere. Our hypothesis was to use biochar as a manure nutrient stabilizer that would slowly release nutrients to plants upon biochar-swine manure mixture application to soil. The objectives were to evaluate the impact of biochar-treated swine manure on soil total C, N, and plant-available macro- and micronutrients in greenhouse-cultivated corn (Zea mays L.) and soybean (Glycine max (L.) Merr.). Neutral pH red oak (RO), highly alkaline autothermal corn stover (HAP), and mild acidic Fe-treated autothermal corn stover (HAPE) biomass were pyrolyzed to prepare biochars. Each biochar was surface-applied to swine manure at a 1:4 (biochar wt/manure wt) ratio to generate mixtures of manure and respective biochars (MRO, MHAP, and MHAPE). Conventional manure (M) control and manure-biochar mixtures were then applied to the soil at a recommended rate. Corn and soybean were grown under these controls and treatments (S, M, MRO, MHAP, and MHAPE) to evaluate the manure-biochar impact on soil quality, plant biomass yield, and nutrient uptake. Soil organic matter significantly (<0.05) increased in all manure-biochar treatments; however, no change in soil pH or total N was observed under any treatment. No difference in soil ammonium between treatments was identified. There was a significant decrease in soil Mehlich3 (M3) P and KCl extractable soil NO3− for all manure-biochar treatments compared to the conventional M. However, the plant biomass nutrient concentrations were not significantly different from control manure. Moreover, an increasing trend of plant total N and decreasing trend of P in the plant under all biochar-manure treatments than the controls were noted. This observation suggests that the presence of biochar is capable of influencing the soil N and P in such a way as not to lose those nutrients at the early growth stages of the plant. In general, no statistical difference in corn or soybean biomass yield and plant nutrient uptake for N, P, and K was observed. Interestingly, manure-biochar application to soil significantly diluted the M3 extractable soil Cu and Zn concentrations. The results attribute that manure-biochar has the potential to be a better soil amendment than conventional manure application to the soil.

Phosphorus release from intact soil monoliths of manure-amended fields under simulated snowmelt flooding

Anaerobic conditions developed in soils with flooding can enhance the release of soil P to overlying water, but little information is available for soils with a long history of manure application. We examined the P release from manure-amended soils under simulated snowmelt flooding. Intact monoliths from manured (solid swine manure [SSM] or liquid swine manure [LSM]) and unamended (control) field plots were collected from Carman, Manitoba. Monoliths were frozen for 7 d, thawed, flooded, and incubated at 4 ± 1 °C. Redox potential, pH, and concentrations of dissolved reactive P (DRP), Ca, Mg, Fe, and Mn in pore water and floodwater were determined weekly up to 56 d after flooding (DAF) and at 84 DAF. Redox potential decreased with DAF with a greater and more rapid decrease in SSM (from ∼300 to <0 mV by 84 DAF) compared with LSM and control (∼100 mV by 84 DAF). Pore water and floodwater DRP concentrations were significantly greater in manured treatments than in the control at all DAFs and in SSM than in LSM for most DAF. Whereas floodwater DRP concentrations remained relatively stable in the control treatment, concentrations in manured treatments increased substantially from the onset of flooding to 35-42 DAF (threefold to fourfold increase) and remained relatively stable thereafter. Significantly greater P release from SSM- than from LSM-treated monoliths was due to greater input of P and the higher organic matter content in SSM-treated soils. These favored the rapid development of anaerobic conditions that further induced P release.

Impact factors and mechanisms of dissolved reactive phosphorus (DRP) losses from agricultural fields: A review and synthesis study in the Lake Erie basin

Dissolved Reactive Phosphorus (DRP) losses from agricultural fields promote algae growth in water bodies, and may increase the risk of Harmful Algal Blooms (HABs). Using existing data from the Lake Erie Basin, we applied multiple regression analysis to better understand the impacts of both site-specific conditions (e.g., soil types/properties) and management practices (e.g., Agricultural Conservation Practices [ACP]) on annual DRP losses in subsurface and surface runoff. Results showed that soil properties significantly impact DRP losses. Greater DRP losses were associated with increased soil pH and Soil Test Phosphorus (STP). By contrast, soil organic matter (SOM) was inversely correlated with DRP losses. Soil clay content was also inversely correlated with DRP subsurface losses, but had no impact on DRP surface losses. The ACPs evaluated had varied effectiveness on DRP loss reduction. Cropping systems involving soybean could reduce DRP subsurface losses, whereas winter cover crops could cause unintended DRP subsurface losses. Cropping systems involving soybean and cover crops, however, had no impact on DRP surface losses. In addition, no-till and conservation tillage also enhanced DRP losses compared to conventional tillage, particularly for soils with high SOM and/or high clay content. Precipitation amount and fertilizer application rate significantly increased DRP surface losses as expected. Fertilizer application rate, however, had no impact on DRP subsurface losses. The impact of precipitation amount on DRP subsurface losses depends on STP levels. Precipitation amount significantly increases DRP subsurface losses when STP is higher (>41 mg kg-1 in this analysis). The optimal STP level for crop growth is 30 to 50 mg kg-1. Results from this study help us to better understand DRP losses and the effectiveness of ACPs for controlling them. We suggest taking soil surveys and soil tests into consideration when designing and/or implementing ACPs to manage DRP losses. Furthermore, the method we used for this study could be applied to other agricultural regions to investigate impacts of site-specific conditions and management practices on water quality.

Effects of Applying Liquid Swine Manure on Soil Quality and Yield Production in Tropical Soybean Crops (Paraná, Brazil)

Brazil is one of the main producers of pork meat in the world. It is well-known that the agricultural sector is a key component of the economic development of this country, where super-intensive fields are only competitive in the globalized market. For the farmers, the application of swine manure to fertilize the soil can increase the yearly income, but it also may cause serious environmental problems related to soil health and soil quality. In this research, we assessed the effects of applying liquid swine manure in a tropical soybean (Glycine max) plantation to better understand when this technique stops being effective and starts causing a threat to soil health and quality. Therefore, we compared values of several soil properties and the soybean yield on treated fields at 10 random points belonging to 7 different plots that were treated with the liquid swine manure over a period ranging from 0 to 15 years. The results showed a positive linear trend in soybean production from 2.45 to 3.08 Mg ha−1 yr−1. This positive trend was also recorded for some key soil parameters such as porosity and exchangeable cations content (Ca, Mg, K, and Al). Additionally, positive effects were also found for organic matter content after 10 years of application. Our findings suggest that the use of liquid swine manure has a positive effect on soybean yield and improves soil quality, particularly on mixed farms where pigs are intensively raised nearby cultivated fields.

Managing Diffuse Phosphorus at the Source versus at the Sink

Judicious phosphorus (P) management is a global grand challenge and critical to achieving and maintaining water quality objectives while maintaining food production. The management of point sources has been successful in lowering P inputs to aquatic environments, but more difficult is reducing P discharges associated with diffuse sources, such as nonpoint runoff from agriculture and urban landscapes, as well as P accumulated in soils and sediments. Strategies for effective diffuse-P management are imperative. Many options are currently available, and the most cost-effective and practical choice depends on the local situation. This critical review describes how the metrics of P quantity in kg ha^-1 yr^-1 and P form can influence decision-making and implementation of diffuse-P management strategies. Quantifying the total available pool of P, and its form, in a system is necessary to inform effective decision-making. The review draws upon a number of " current practice" case studies that span agriculture, cities, and aquatic sectors. These diverse examples from around the world highlight different diffuse-P management approaches, delivered at the source in the catchment watershed or at the aquatic sink. They underscore workable options for achieving water quality improvement and wider P sustainability. The diffuse-P management options discussed in this critical review are transferable to other jurisdictions at the global scale. We demonstrate that P quantity is typically highest and most concentrated at the source, particularly at farm scale. The most cost-effective and practically implementable diffuse-P management options are, therefore, to reduce P use, conserve P, and mitigate P loss at the source. Sequestering and removing P from aquatic sinks involves increasing cost, but is sometimes the most effective choice. Recovery of diffuse-P, while expensive, offers opportunity for the circular economy.

Soil nutrient variability and groundwater nitrate-N in agricultural fields

Landscape may result in uneven nutrient loads within a field. The objective of this study was to determine the influence of landscape on soil carbon and nutrient levels, and on levels of nitrate-N in groundwater. Soil samples were collected in three fields, two transects each, 30 sites in each field. The soil morphology was characterized for the profile, and soil organic carbon and nutrient levels were determined for 0-0.15 and 0.15-0.3 m depths. Each field had wells installed at three of the sites. One field showed a wide range of landscape variability, and significant effects of curvature on soil carbon and nutrient levels. Another field showed no significant effect of slope or curvature on soil carbon and nutrient levels because the nutrient levels were quite variable, including high spikes. The third field had less variable landscape trends but still showed a few significant effects on soil carbon and nutrient levels. Nitrate-N levels remained high in two of the nine wells (20 to 50 mg L^-1), suggesting that additions of nitrate-N at the concave or converging sites replaced any losses. Median nitrate-N levels at the other seven well sites were lower, ranging from 8 to 17 mg L^-1. Influence of landscape on soil carbon and nutrients was more detectable when the landscape factors were highly variable without excessive variability in soil nutrient properties.

Distribution and mass of groundwater orthophosphorus in an agricultural watershed

Orthophosphorus (OP) is the form of dissolved inorganic P that is commonly measured in groundwater studies, but the spatial distribution of groundwater OP across a watershed has rarely been assessed. In this study, we characterized spatial patterns of groundwater OP concentrations and loading rates within the 5218ha Walnut Creek watershed (Iowa) over a two-year period. Using a network of 24 shallow (<6m) monitoring wells established across watershed, OP concentrations ranged from <0.01 to 0.58mg/l in all samples (n=147) and averaged 0.084±0.107mg/l. Groundwater OP concentrations were higher in floodplains and OP mass loading rates were approximately three times higher than in uplands. We estimated that approximately 1231kg of OP is present in floodplain groundwater and 2869kg is present in upland groundwater within the shallow groundwater zone (0-5m depth). Assuming no new inputs of OP to shallow groundwater, we estimated it would take approximately eight years to flush out existing OP mass present in the system. Results suggest that conservation practices focused on reducing OP loading rates in floodplain areas may have a disproportionately large water quality benefit compared to upland areas.

Tillage and Fertilizer Management Effects on Phosphorus Runoff from Minimal Slope Fields

Phosphorus fertilization can increase P losses in surface runoff, but limited information is available for fields with <2% slopes in the US Midwest. Our objectives were to determine the effects of tillage-fertilizer placement (no-till-broadcast, strip till-broadcast; or strip till-deep placement, -15-cm subsurface band) and fertilizer rate applied in the fall (0, 52, or 90 kg PO ha yr) on runoff P concentrations and loads in fields with <2% slopes near Pesotum, IL, during fall and spring simulation runoff events, and to measure corn ( L.) and soybean [ (L.) Merr.] grain yield. Across four simulated runoff events, deep placement reduced dissolved reactive P (DRP) loads by 69 to 72% compared with the broadcast treatments. A tillage-fertilizer placement × P rate interaction showed that DRP and total P (TP) concentrations remained low when P was deep placed, regardless of P rate, whereas concentrations increased with increasing P rate for the broadcast treatments, but no differences existed for bioavailable P (BAP) (α = 0.05). At one site, rainfall simulation in the spring versus fall increased runoff volumes but sharply decreased BAP concentrations. During fall runoff simulations, deep placement reduced TP loads, and greater TP loads occurred with the 90- than the 52-kg PO ha yr rate. Similarly, when P was broadcast in the fall, DRP and TP concentrations were greater than deep-placed P, but no treatment differences occurred in the spring. Deep banding P and K did not reduce crop yield but reduced runoff losses of P from flat fields compared with broadcast P applications, particularly at high rates of P application.

Orthophosphorus Contributions to Total Phosphorus Concentrations and Loads in Iowa Agricultural Watersheds

Phosphorus (P) is delivered to streams as episodic particulate P and more continuous soluble P (orthophosphorus [OP]), and it is important to determine the proportion of each P form in river water to more effectively design remedial measures. In this study, we evaluated the annual mean ratios of OP to total P (TP) concentrations and loads in 12 Iowa rivers and found systematic variation in the ratios. The OP/TP ratios were >60% in two tile-drained watersheds of the Des Moines Lobe and in a shallow fractured bedrock watershed in northeast Iowa, whereas in southern and western Iowa, OP contributions to TP were <30%. Higher OP/TP ratios were associated with greater row crop intensity in the watershed and a greater proportion of baseflow in the river. Orthophosphorus contributions from croplands would be greater in watersheds characterized by widespread tile drainage and well-drained soils, whereas cropland TP export would be dominated by particulate P in dissected till plains with poorly drained soils. Understanding the dominant form and transport pathway of P from agricultural areas in a watershed is seen as an important first step in determining appropriate conservation practices to reduce P loads.

Comparison of Nutrient and Metal Loadings with the Application of Swine Manure Slurries and Their Liquid Separates to Soils

The accumulation of phosphorus (P) and metals is a serious concern with the continuous application of manure to agricultural soils. Solid-liquid separation of swine slurry is a promising approach to reduce P and metal loadings through application of separated liquid (SL) as a nutrient source. However, little information is available on nutrient and metal loadings with the application of SL compared with unseparated raw manure (RM). We analyzed element concentrations and calculated nutrient and metal loadings for RM and their respective SL applications, considering an application rate of 100 kg total nitrogen (N) ha. Samples of SL were obtained through three separation techniques: (i) centrifugation without a flocculant, (ii) centrifugation with a flocculant, and (iii) rotary press with a flocculant. Irrespective of separation technique, calculated P loadings with the application of SL were only 50 to 70% of that of RM at equivalent rates of total N yet exceeded crop removal rate. In contrast, calculated K and Na loadings with SL application were significantly greater than with RM, indicating a possible build-up of K and Na in soil. Calculated Ca and Mg loadings were significantly greater with RM than with SL. Loadings of Al, As, Ba, Cd, Cr, Fe, Mn, Ni, Pb, Sn, Se, Ti, and V were low, whereas Cu and Zn loadings were above crop removal rates for RM and SL. For solid-liquid separation to provide a lasting solution to the problem of P and metal accumulation, the SL must be supplemented with commercial N fertilizer to meet crop N demand.

Estimating spatio-temporal dynamics of stream total phosphate concentration by soft computing techniques

This study attempts to model the spatio-temporal dynamics of total phosphate (TP) concentrations along a river for effective hydro-environmental management. We propose a systematical modeling scheme (SMS), which is an ingenious modeling process equipped with a dynamic neural network and three refined statistical methods, for reliably predicting the TP concentrations along a river simultaneously. Two different types of artificial neural network (BPNN-static neural network; NARX network-dynamic neural network) are constructed in modeling the dynamic system. The Dahan River in Taiwan is used as a study case, where ten-year seasonal water quality data collected at seven monitoring stations along the river are used for model training and validation. Results demonstrate that the NARX network can suitably capture the important dynamic features and remarkably outperforms the BPNN model, and the SMS can effectively identify key input factors, suitably overcome data scarcity, significantly increase model reliability, satisfactorily estimate site-specific TP concentration at seven monitoring stations simultaneously, and adequately reconstruct seasonal TP data into a monthly scale. The proposed SMS can reliably model the dynamic spatio-temporal water pollution variation in a river system for missing, hazardous or costly data of interest.

Comparison of Surface Water Quality and Yields from Organically and Conventionally Produced Sweet Corn Plots with Conservation and Conventional Tillage

Organic agricultural systems are often assumed to be more sustainable than conventional farming, yet there has been little work comparing surface water quality from organic and conventional production, especially under the same cropping sequence. Our objective was to compare nutrient and sediment losses, as well as sweet corn ( L. var. ) yield, from organic and conventional production with conventional and conservation tillage. The experiment was located in the Appalachian Mountains of North Carolina. Four treatments, replicated four times, had been in place for over 18 yr and consisted of conventional tillage (chisel plow and disk) with conventional production (CT/Conven), conservation no-till with conventional production (NT/Conven), conventional tillage with organic production (CT/Org), and conservation no-till with organic production (NT/Org). Water quality (surface flow volume; nitrogen, phosphorus, and sediment concentrations) and sweet corn yield data were collected in 2011 and 2012. Sediment and sediment-attached nutrient losses were influenced by tillage and cropping system in 2011, due to higher rainfall, and tillage in 2012. Soluble nutrients were affected by the nutrient source and rate, which are a function of the cropping system. Sweet corn marketable yields were greater in conventional systems due to high weed competition and reduced total nitrogen availability in organic treatments. When comparing treatment efficiency (yield kg ha /nutrient loss kg ha ), the NT/Conven treatment had the greatest sweet corn yield per unit of nutrient and sediment loss. Other treatment ratios were similar to each other; thus, it appears the most sustainably productive treatment was NT/Conven.

Subsurface Band Application of Poultry Litter and Its Influence on Phosphorus Concentration and Retention after Runoff from Permanent Pastures

Excessive phosphorus (P) loss from agricultural fields is a major cause of eutrophication to rivers, lakes, and streams. To mitigate P loss after poultry litter (PL) applications, technology is being developed to apply litter below the soil surface. Thus, research was conducted to evaluate the effects of subsurface PL banding on soil P under pasture management. Treatments consisted of surface-broadcasted or subsurface-banded PL (38 cm apart) at 9 Mg ha, surface-broadcasted commercial fertilizer (CF; urea and triple superphosphate blend) at N (330 kg N ha) and P (315 kg N ha) application rates equivalent to PL, and a nonfertilized control. Runoff events lasting 40 min were simulated in bermudagrass ( L.) pastures on common soil types of the Coastal Plain and Piedmont regions. One day later, Mehlich-1 and water-soluble P concentrations in soil were measured at depths of 0 to 5 cm and 5 to 10 cm to determine P distribution and movement. The greatest P concentrations were observed at the shallow depth for all treatments. Phosphorus measurements at the point of application for PL bands were greater than for the surface-applied treatments (PL and CF) and control. Measurements between subsurface PL bands were slightly higher than the control but were statistically similar, suggesting that this application method can abate short-term P movement. Results obtained from this study show that subsurface band applying PL could increase P retention and reduce movement by precluding contact between surface water and litter nutrients.

Use of Zeolite with Alum and Polyaluminum Chloride Amendments to Mitigate Runoff Losses of Phosphorus, Nitrogen, and Suspended Solids from Agricultural Wastes Applied to Grassed Soils

Diffuse pollutant losses containing phosphorus (P), nitrogen (N), and suspended solids (SS) can occur when agricultural wastes are applied to soil. This study aimed to mitigate P, N, and SS losses in runoff from grassed soils, onto which three types of agricultural wastes (dairy slurry, pig slurry, and dairy-soiled water [DSW]), were applied by combining amendments of either zeolite and polyaluminum chloride (PAC) with dairy and pig slurries or zeolite and alum with DSW. Four treatments were investigated in rainfall simulation studies: (i) control soil, (ii) agricultural wastes, (iii) dairy and pig slurries amended with PAC and DSW amended with alum, and (iv) dairy and pig slurries amended with zeolite and PAC and DSW amended with zeolite and alum. Our data showed that combined amendments of zeolite and PAC applied to dairy and pig slurries reduced total P (TP) in runoff by 87 and 81%, respectively, compared with unamended slurries. A combined amendment of zeolite and alum applied to DSW reduced TP in runoff by 50% compared with unamended DSW. The corresponding reductions in total N (TN) were 56% for dairy slurry and 45% for both pig slurry and DSW. Use of combined amendments reduced SS in runoff by 73 and 44% for dairy and pig slurries and 25% for DSW compared with unamended controls, but these results were not significantly different from those using chemical amendments only. The findings of this study are that combined amendments of zeolite and either PAC or alum reduce TP and TN losses in runoff to a greater extent than the use of single PAC or alum amendments and are most effective when used with dairy slurry and pig slurry but less effective when used with DSW.

Forms of phosphorus transfer in runoff under no-tillage in a soil treated with successive swine effluents applications

Successive swine effluent applications can substantially increase the transfer of phosphorus (P) forms in runoff. The aim of this study was to evaluate P accumulation in the soil and transfer of P forms in surface runoff from a Hapludalf soil under no-tillage subjected to successive swine effluent applications. This research was carried out in the Agricultural Engineering Department of the Federal University of Santa Maria, Brazil, from 2004 to 2007, on a Typic Hapludalf soil. Swine effluent rates of 0, 20, 40, and 80 m3 ha(-1) were broadcast over the soil surface prior to sowing of different species in a crop rotation. Soil samples were collected in stratified layers, and the levels of available P were determined. Samples of water runoff from the soil surface were collected throughout the period, and the available, soluble, particulate, and total P were measured. Successive swine effluent applications led to increases in P availability, especially in the soil surface, and P migration through the soil profile. Transfer of P forms was closely associated with runoff, which is directly related to rainfall volume. Swine effluent applications also reduced surface runoff. These results show that in areas with successive swine effluent applications, practices that promote higher water infiltration into the soil are required, e.g., crop rotation and no-tillage system.

Injection of Dicyandiamide-Treated Pig Slurry Reduced Ammonia Volatilization without Enhancing Soil Nitrous Oxide Emissions from No-Till Corn in Southern Brazil

There is a lack of information on how placement in soil and nitrification inhibitors affects nitrous oxide (NO) and ammonia (NH) emissions from pig slurry (PS) applied under no-till (NT) conditions. Our objective was to determine the impact of injecting PS and treating it with the nitrification inhibitor dicyandiamide (DCD) on NH and NO emissions from soils under NT in subtropical southern Brazil. The emissions of these gases were compared for shallow (∼ 10 cm) injection and surface broadcasting of PS with and without DCD (8.1-10.0 kg ha; 6.5-8.4% of applied NH-N). Measurements were made at two sites during two summer growing seasons under NT corn crops. Injection reduced NH volatilization by 70% but increased NO emissions 2.4-fold (from 2628 to 6198 g NO N ha) compared with surface broadcast application. Adding DCD to PS inhibited nitrification and reduced NO emissions by an average of 28% (730 g NO-N ha) for surface broadcast and 66% (4105 g NO-N ha) for injection but did not increase NH volatilization. Consequently, NO emission factors were much higher for injection (3.6%) than for surface broadcast (1.3%) application and were reduced (0.9%) when DCD was added to injected PS. In conclusion, the injection of DCD-treated slurry is a recommendable practice for reducing NH and NO emissions when applying PS on NT corn in southern Brazil.

Mitigation options to reduce phosphorus losses from the agricultural sector and improve surface water quality: a review

The EU Water Framework Directive (WFD) obliges Member States to improve the quality of surface water and groundwater. The measures implemented to date have reduced the contribution of point sources of pollution, and hence diffuse pollution from agriculture has become more important. In many catchments the water quality remains poor. COST Action 869 was an EU initiative to improve surface water quality that ran from 2006 to 2011, in which 30 countries participated. Its main aim was a scientific evaluation of the suitability and cost-effectiveness of options for reducing nutrient loss from rural areas to surface waters at catchment scale, including the feasibility of the options under different climatic and geographical conditions. This paper gives an overview of various categories of mitigation options in relation to phosphorus (P). The individual measures are described in terms of their mode of action, applicability, effectiveness, time frame, environmental side-effects (N cycling) and cost. In total, 83 measures were evaluated in COST Action 869.

Phosphorus fractions in solid and liquid separates of Swine slurry separated using different technologies

Solid-liquid separation is a manure management option whereby P-rich solid is separated from N-rich liquid, allowing the separated liquid to be used as a fertilizer without oversupplying P. Little information is available on how the different P fractions in manures are partitioned to solid and liquid during separation. We examined the distribution of various P fractions in liquid and solid separates of swine manure, separated using different techniques, to gain information useful for making choices regarding the optimum use of manure separates. Samples of raw manure (RM) and their separated solid (SS) and liquid (SL) were obtained using three different separation techniques: (i) centrifugation without flocculant (CNF), (ii) centrifugation with a flocculant (CFL), and (iii) rotary press with a flocculant (RFL). These were subsequently analyzed for P using a modified Hedley fractionation scheme. Only a small proportion of RM, ranging from 5 to 12%, was recovered in SS, an advantage if SS is to be transported off-site. Concentrations of molybdate-reactive P and total P in all P fractions were less in SL than in the corresponding RM on a fresh-weight basis. The separation index (percentage partitioned to SS) for total labile P (water-extractable + NaHCO-extractable P) was 63, 81, and 75% for CNF, CFL, and RFL, respectively. The proportion of total P in labile form was significantly lower in SL than in RM. Therefore, using SL as a fertilizer instead of RM may help to avoid excessive buildup of soil test P with manure applications.

Forage and tree seedling growth in a soil with an encased swine sludge layer

The closure of swine farms requires decommissioning of lagoons that contain large amounts of swine solids (sludge). Sludge is typically transported and land applied to soils. However, in some cases this process could be economically prohibitive and/or unpractical. An alternative idea is to encase sludge with lagoon soil berms after removing overlying effluent, followed by establishment of forages or short-rotation woody crops on the encased sludge. The objective of this study was to investigate growth potential for several forages and tree species into a pure layer of swine sludge. Alfalfa (Meticago sativa), bermudagrass (Cynodon dactylon), switchgrass (Panicum virgatum), green ash (Fraxinus pennsylvanica), black locust (Robinia pseudoacacia), and sycamore (Platanus occidentalis) were established in 40 cm deep pots consisting of a lagoon berm soil overlaying a sludge layer for 12 w followed by analysis of aboveground and belowground biomass production. "New" and "old" sludge was collected from an active 10 year old lagoon and decommissioned 50 year old lagoon, respectively. A control (soil only) was used. Encased sludge treatments increased forage biomass production. Sycamore and green ash were sensitive to new sludge but not old sludge as these species had less biomass production in new sludge than control and showed tissue trace nutrient deficiencies. While both sludge materials contained adequate nutrients, the new sludge had a salt concentration 1.8 times higher than old sludge as indicated by electrical conductivity (12.4 mS). Thus, the forage crops and black locust were able to thrive in new sludge due to their salt tolerance.

Chemical amendment of pig slurry: control of runoff related risks due to episodic rainfall events up to 48 h after application

Losses of phosphorus (P) from soil and slurry during episodic rainfall events can contribute to eutrophication of surface water. However, chemical amendments have the potential to decrease P and suspended solids (SS) losses from land application of slurry. Current legislation attempts to avoid losses to a water body by prohibiting slurry spreading when heavy rainfall is forecast within 48 h. Therefore, in some climatic regions, slurry spreading opportunities may be limited. The current study examined the impact of three time intervals (TIs; 12, 24 and 48 h) between pig slurry application and simulated rainfall with an intensity of 11.0 ± 0.59 mm h(-1). Intact grassed soil samples, 1 m long, 0.225 m wide and 0.05 m deep, were placed in runoff boxes and pig slurry or amended pig slurry was applied to the soil surface. The amendments examined were: (1) commercial-grade liquid alum (8 % Al2O3) applied at a rate of 0.88:1 [Al/ total phosphorus (TP)], (2) commercial-grade liquid ferric chloride (38 % FeCl3) applied at a rate of 0.89:1 [Fe/TP] and (3) commercial-grade liquid poly-aluminium chloride (10 % Al2O3) applied at a rate of 0.72:1 [Al/TP]. Results showed that an increased TI between slurry application and rainfall led to decreased P and SS losses in runoff, confirming that the prohibition of land-spreading slurry if heavy rain is forecast in the next 48 h is justified. Averaged over the three TIs, the addition of amendment reduced all types of P losses to concentrations significantly different (p < 0.05) to those from unamended slurry, with no significant difference between treatments. Losses from amended slurry with a TI of 12 h were less than from unamended slurry with a TI of 48 h, indicating that chemical amendment of slurry may be more effective at ameliorating P loss in runoff than current TI-based legislation. Due to the high cost of amendments, their incorporation into existing management practices can only be justified on a targeted basis where inherent soil characteristics deem their usage suitable to receive amended slurry.

Phosphorus losses from low-emission slurry spreading techniques

Low emission slurry spreading techniques are known to improve nitrogen use efficiency, but their impact on phosphorus (P) losses in surface runoff has received little attention. The current study was designed to examine the effect of slurry spreading technique on P losses in runoff. Twelve treatments were examined on 0.5- m by 1.0-m plots in a nominal 2 × 6 factorial design experiment. Treatments comprised grass swards at two different stages of growth, a stubble and a 4-wk regrowth, and six different slurry application treatments: control (no slurry), and slurry applied to simulate splash-plate, injection (across and down slope), and trailing shoe (across and down slope) spreading. Slurry was applied by hand (40 m ha). Rainfall simulations (40 mm h) were conducted at 2, 9, and 28 d post-slurry application. When slurry was applied to the stubble, dissolved reactive P (DRP) concentrations in runoff at Day 2 were 47 and 37% lower ( < 0.05) from the injection and trailing shoe treatments compared with the splash-plate treatment. Similarly, at Day 2, TP concentrations in runoff from the injection treatments were 27% lower ( < 0.05) than the splash-plate treatment. In contrast, application technique had no effect ( 0.05) on P concentrations in runoff following slurry application to the regrowth treatment. Phosphorus concentrations in runoff were unaffected by direction of slurry spreading (across or down) at both applications. Our results indicate that trailing shoe and injection techniques offer the potential to reduce DRP concentrations in runoff during the period immediately after slurry application.

A Review of the Use of Organic Amendments and the Risk to Human Health

Historically, organic amendments—organic wastes—have been the main source of plant nutrients, especially N. Their use allows better management of often-finite resources to counter changes in soils that result from essential practices for crop production. Organic amendments provide macro- and micronutrients, including carbon for the restoration of soil physical and chemical properties. Challenges from the use of organic amendments arise from the presence of heavy metals and the inability to control the transformations required to convert the organic forms of N and P into the minerals available to crops, and particularly to minimize the losses of these nutrients in forms that may present a threat to human health. Animal manure and sewage biosolids, the organic amendments in greatest abundance, contain components that can be hazardous to human health, other animals and plants. Pathogens pose an immediate threat. Antibiotics, other pharmaceuticals and naturally produced hormones may pose a threat if they increase the number of zoonotic disease organisms that are resistant to multiple antimicrobial drugs or interfere with reproductive processes. Some approaches aimed at limiting N losses (e.g. covered liquid or slurry storage, rapid incorporation into the soil, timing applications to minimize delay before plant uptake) also tend to favor survival of pathogens. Risks to human health, through the food chain and drinking water, from the pathogens, antibiotics and hormonal substances that may be present in organic amendments can be reduced by treatment before land application, such as in the case of sewage biosolids. Other sources, such as livestock and poultry manures, are largely managed by ensuring that they are applied at the rate, time and place most appropriate to the crops and soils. A more holistic approach to management is required as intensification of agriculture increases.

Incidental phosphorus and nitrogen loss from grassland plots receiving chemically amended dairy cattle slurry

Chemical amendment of dairy cattle slurry has been shown to effectively reduce incidental phosphorus (P) losses in runoff; however, the effects of amendments on incidental nitrogen (N) losses are not as well documented. This study examined P and N losses in runoff during three simulated rainfall events 2, 10 and 28 days after a single application of unamended/chemically amended dairy cattle slurry. Twenty-five hydraulically isolated plots, each measuring 0.9 m by 0.4 m and instrumented with runoff collection channels, were randomly assigned the following treatments: (i) grass-only, (ii) slurry-only (the study-control), (iii) slurry amended with industrial grade liquid alum comprising 8% Al₂O₃, (iv) slurry amended with industrial grade liquid poly-aluminum chloride (PAC) comprising 10% Al₂O₃, and (v) slurry amended with lime. During the first rainfall event, lime was ineffective but alum and PAC effectively reduced dissolved reactive P (DRP) (by 95 and 98%, respectively) and total P (TP) flow-weighted-mean-concentrations (by 82 and 93%, respectively) in runoff compared to the study-control. However, flow-weighted-mean-concentrations of ammonium-N (NH₄--N) in runoff were increased with alum- (81%) and lime-treated (11%) slurry compared to the study-control whereas PAC reduced the NH₄--N by 82%. Amendments were not observed to have a significant effect on NO₃--N losses during this study. Slurry amendments reduced P losses for the duration of the study, whereas the effect of amendments on N losses was not significant following the first event. Antecedent volumetric water content of the soil or slope of the plots did not appear to affect runoff volume. However, runoff volumes (and consequently loads of P and N) were observed to increase for the chemically amended plots compared to the control and soil-only plots. This work highlights the importance of considering both P and N losses when implementing a specific nutrient mitigation measure.

Impact of manure phosphorus fractions on phosphorus loss from manured soils after incubation

The risk of P loss from manured soils is more related to P fractions than total P concentration in manure. This study examined the impact of manure P fractions on P losses from liquid swine manure- (LSM), solid cattle manure- (SCM), and monoammonium phosphate- (MAP) treated soils. Manure or fertilizer was applied at 50 mg P kg soil, mixed, and incubated at 20°C for 6 wk to simulate the interaction between applied P and soil when P is applied well in advance of a high risk period for runoff. Phosphorus fractions in manure were determined using the modified Hedley fractionation scheme. We used simulated rainfall (75 mm h⁻¹ for 1 h) to quantify P losses in runoff from two soils (sand and clay loam). The proportion of total labile P (total P in water+NaHCO fractions) in manure was significantly greater in LSM (70%) than SCM (44%). Mean dissolved reactive P (DRP) load in runoff over 60 min was greatest from MAP-treated soil (18.1 mg tray⁻¹), followed by LSM- (14.0 mg tray⁻¹) and SCM- (11.0 mg tray⁻¹) treated soils, all of which were greater than mean DRP load from the check (5.2 mg tray⁻¹). Total labile P (water+NaHCO) in manure was a more accurate predictor of runoff DRP loads than water extractable P, alone, for these two soils. Therefore, NaHCO extraction of manure P may be a useful tool for managing the risk of manure P runoff losses when manure is applied outside a high risk period for runoff loss.

Manure application technology in reduced tillage and forage systems: a review

Managing manure in reduced tillage and forage systems presents challenges, as incorporation by tillage is not compatible. Surface-applied manure that is not quickly incorporated into soil provides inefficient delivery of manure nutrients to crops due to environmental losses through ammonia (NH3) volatilization and nutrient losses in runoff, and serves as a major source of nuisance odors. An array of technologies now exist to facilitate the incorporation of liquid manures into soil with restricted or minor soil disturbance, some of which are new: shallow disk injection; chisel injection; aeration infiltration; pressure injection. Surface banding of manure inforages decreases NH3 emissions relative to surface broadcasting, as the canopy can decrease wind speed over the manure, but greater reductions can be achieved with manure injection. Soilaeration is intended to hasten manure infiltration, but its benefits are not consistent and may be related to factors such as soildrainage characteristics. Work remains to be done on refining its method of use and timing relative to manure application, which may improve its effectiveness. Placing manure under the soil surface efficiency by injection offers much promise to improve N use efficiency through less NH3 volatilization, reduced odors and decreased nutrient losses in runoff, relative to surface application. We identified significant gaps in our knowledge as manyof these technologies are relatively new, and this should help target future research efforts including environmental, agronomic, and economic assessments.

Swine manure injection with low-disturbance applicator and cover crops reduce phosphorus losses

Injection of liquid swine manure disturbs surface soil so that runoff from treated lands can transport sediment and nutrients to surface waters. We determined the effect of two manure application methods on P fate in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] production system, with and without a winter rye (Secale cereale L.)-oat (Avena sativa L.) cover crop. Treatments included: (i) no manure; (ii) knife injection; and (iii) low-disturbance injection, each with and without the cover crop. Simulated rainfall runoff was analyzed for dissolved reactive P (DRP) and total P (TP). Rainfall was applied 8 d after manure application (early November) and again in May after emergence of the corn crop. Manure application increased soil bioavailable P in the 20- to 30-cm layer following knife injection and in the 5- to 20-cm layer following low-disturbance injection. The low-disturbance system caused less damage to the cover crop, so that P uptake was more than threefold greater. Losses of DRP were greater in both fall and spring following low-disturbance injection; however, application method had no effect on TP loads in runoff in either season. The cover crop reduced fall TP losses from plots with manure applied by either method. In spring, DRP losses were significantly higher from plots with the recently killed cover crop, but TP losses were not affected. Low-disturbance injection of swine manure into a standing cover crop can minimize plant damage and P losses in surface runoff while providing optimum P availability to a subsequent agronomic crop.

Runoff phosphorus loss immediately after poultry manure application as influenced by the application rate and tillage

Excessive or N-based application of poultry manure for crops may result in significant risk of P loss with surface runoff. This study assessed P loss immediately after poultry manure application to soybean [Glycine max (L.) Merr.] residue with and without tillage at eight Iowa fields. Manure from chickens (Gallus gallus domesticus) or turkeys (Melleagris gollopavo) was applied at intended rates of 0, 84, or 168 kg total N ha(-1) (total P was 0, 21-63, 50-123 kg P ha(-1), respectively) with three replications. Simulated rainfall (76 mm h(-1)) was applied to 3-m2 sections of larger field plots with 2 to 7% slope, usually within 2 d of application, to collect runoff during 30 min. Runoff was analyzed for concentrations of sediment, dissolved reactive P (DRPC), bioavailable P (BAPC), and total P (TPRC). Non-incorporated manure consistently increased (P < or = 0.10) concentrations of all runoff P fractions in five sites, but there were increasing trends at all sites, and on average manure increased DRPC, BAPC, and TPRC 32, 23, and 12 times, respectively, over the control. Tillage to incorporate manure reduced DRPC, BAPC, and TPRC by 88, 89, and 77% on average, respectively, although in non-manured plots tillage seldom affected DRPC or BAPC and often increased TPRC. Tillage increased sediment concentration in runoff but not enough to offset the benefits of manure P incorporation. Runoff P loads generally followed trends of runoff P concentrations but were more variable, and significant treatment effects were less frequent. Overall, incorporation of manure by tillage was very effective at reducing P loss during runoff events shortly after poultry manure application under the conditions of this study.

Managing biosolids runoff phosphorus using buffer strips enhanced with drinking water treatment residuals

Vegetated buffers strips typically have limited ability to reduce delivery of dissolved phosphorus (DP) from agricultural fields to surface waters. A field study was conducted to evaluate the ability of buffer strips enhanced with drinking water treatment residuals (WTRs) to control runoff P losses from surface-applied biosolids characterized by high water-extractable P (4 g kg(-)(1)). Simulated rainfall (62.4 mm h(-1)) was applied to grassed plots (3 m x 10.7 m including a 2.67 m downslope buffer) surface-amended with biosolids at 102 kg P ha(-1) until 30 min of runoff was collected. With buffer strips top-dressed with WTR (20 Mg ha(-1)), runoff total P (TP = 2.5 mg L(-1)) and total DP (TDP = 1.9 mg L(-1)) were not statistically lower (alpha = 0.05) compared to plots with unamended grass buffers (TP = 2.7 mg L(-1); TDP = 2.6 mg L(-1)). Although the applied WTR had excess capacity (Langmuir P maxima of 25 g P kg(-1)) to sorb all runoff P, kinetic experiments suggest that sheet flow travel time across the buffers ( approximately 30 s) was insufficient for significant P reduction. Effective interception of dissolved P in runoff water by WTR-enhanced buffer strips requires rapid P sorption kinetics and hydrologic flow behavior ensuring sufficient runoff residence time and WTR contact in the buffer. Substantial phosphate-adsorbent contact opportunity may be more easily achieved by incorporating WTRs into P-enriched soils or blending WTRs with applied P sources.