Phosphorus budgets and riverine phosphorus export in northwestern Ohio watersheds

Phosphorus (P) budgets for large watersheds are often used to predict trends in riverine P export. To test such predictions, we calculated annual P budgets for 1975-1995 for soils of the Maumee and Sandusky watersheds of northwestern Ohio and compared them with riverine P export from these watersheds. Phosphorus inputs to the soils include fertilizers, manure, rainfall, and sludge while outputs include crop removal and nonpoint-source export via rivers. Annual P inputs decreased due to reductions in fertilizer and manure inputs. Annual outputs increased due to increasing crop yields. Net P accumulation decreased from peak values of 13.4 and 9.5 kg P ha(-1) yr(-1) to 3.7 and 2.6 kg P ha(-1) yr(-1) for the Maumee and Sandusky watersheds, respectively. Thus, P budget analysis suggests that riverine P export should have increased throughout the study period, with smaller increases during more recent years. However, detailed water quality studies show that riverine export of total phosphorus (TP) has decreased by 25 to 40% and soluble reactive phosphorus (SRP) by 60 to 89%, both due primarily to decreases from nonpoint sources. We suggest that these decreases are associated with farmers' adoption of practices that minimize transport of recently applied P fertilizer and of sediments via surface runoff, coupled with changes in winter weather conditions. In comparison with most Midwestern watersheds, rivers draining these watersheds have high unit area yields of TP, low unit area yields of SRP, and high ratios of nonpoint source- to point source-derived P.     

EFFECT OF CATCHMENT SIZE ON PHOSPHORUS EXPORT1

ABSTRACT: We tested the common assumption, made when expressing phosphorus export on an areal basis, that this export is a linear function of catchment area and found it wanting. The data show that in agricultural catchments, TP (total phosphorus) export varies as the 0.77 power of drainage basin area, resulting in a reduction in phosphorus delivery per unit area with increasing catchment size. Following further division of catchments according to agricultural practice, we found that this spatial scale effect is restricted to row crops and pastures. We present simple statistical models to allow a comparison of TP export from catchments of different size. Such models are not needed for nonrow crops, mixed agricultural and forested catchments, where TP export is a linear function of catchment size.     

Factors controlling sediment and phosphorus export from two Belgian agricultural catchments

Sediment and total phosphorus (TP) export vary through space and time. This study was conducted to determine the factors controlling sediment and TP export in two agricultural catchments situated in the Belgian Loess Belt. At the outlet of these catchments runoff discharge was continuously measured and suspended sediment samples were taken during rainfall events. Within the catchments vegetation type and cover, soil surface parameters, erosion features, sediment pathways, and rainfall characteristics were monitored. Total P content and sediment characteristics such as clay, organic carbon, and suspended sediment concentration were correlated. Total sediment and TP export differ significantly between the monitored catchments. Much of the difference is due to the occurrence of an extreme event in one catchment and the morphology and spatial organization of land use in the catchments. In one catchment, the direct connection between erosive areas and the catchment outlet by means of a road system contributed to a high sediment delivery ratio (SDR) at the outlet. In the other catchment, the presence of a wide valley in the center of the catchment caused sediment deposition. Vegetation also had an effect on sediment production and deposition. Thus, many factors control sediment and TP export from small agricultural catchments; some of these factors are related to the physical catchment characteristics such as morphology and landscape structure and are (semi)permanent, while others, such as vegetation cover and land use, are time dependent.     

Phosphorus load to surface water from bank erosion in a Danish lowland river basin

Phosphorus loss from bank erosion was studied in the catchment of River Odense, a lowland Danish river basin, with the aim of testing the hypothesis of whether stream banks act as major diffuse phosphorus (P) sources at catchment scale. Furthermore, the study aimed at analyzing the impact of different factors influencing bank erosion and P loss such as stream order, anthropogenic disturbances, width of uncultivated buffer strips, and the vegetation of buffer strips. A random stratified procedure in geographical information system (GIS) was used to select two replicate stream reaches covering different stream orders, channelized vs. naturally meandering channels, width of uncultivated buffer strips (≤ 2 m and ≥ 10 m), and buffer strips with different vegetation types. Thirty-six 100-m stream reaches with 180 bank plots and a total of 3000 erosion pins were established in autumn 2006, and readings were conducted during a 3-yr period (2006-2009). The results show that neither stream size nor stream disturbance measured as channelization of channel or the width of uncultivated buffer strip had any significant ( < 0.05) influence on bank erosion and P losses during each of the 3 yr studied. In buffer strips with natural trees bank erosion was significantly ( < 0.05) lower than in buffer strips dominated by grass and herbs. Gross and net P input from bank erosion amounted to 13.8 to 16.5 and 2.4 to 6.3 t P, respectively, in the River Odense catchment during the three study years. The net P input from bank erosion equaled 17 to 29% of the annual total P export and 21 to 62% of the annual export of P from diffuse sources from the River Odense catchment. Most of the exported total P was found to be bioavailable (71.7%) based on a P speciation of monthly suspended sediment samples collected at the outlet of the river basin. The results found in this study have a great importance for managers working with P mitigation and modeling at catchment scale.     

Reducing Fertilizer‐Nitrogen Losses from Rowcrop Landscapes: Insights and Implications from a Spatially Explicit Watershed Model

We present conceptual and quantitative models that predict changes in fertilizer‐derived nitrogen delivery from rowcrop landscapes caused by agricultural conservation efforts implemented to reduce nutrient inputs and transport and increase nutrient retention in the landscape. To evaluate the relative importance of changes in the sources, transport, and sinks of fertilizer‐derived nitrogen across a region, we use the spatially explicit SPAtially Referenced Regression On Watershed attributes watershed model to map the distribution, at the small watershed scale within the Upper Mississippi‐Ohio River Basin (UMORB), of: (1) fertilizer inputs; (2) nutrient attenuation during delivery of those inputs to the UMORB outlet; and (3) nitrogen export from the UMORB outlet. Comparing these spatial distributions suggests that the amount of fertilizer input and degree of nutrient attenuation are both important in determining the extent of nitrogen export. From a management perspective, this means that agricultural conservation efforts to reduce nitrogen export would benefit by: (1) expanding their focus to include activities that restore and enhance nutrient processing in these highly altered landscapes; and (2) targeting specific types of best management practices to watersheds where they will be most valuable. Doing so successfully may result in a shift in current approaches to conservation planning, outreach, and funding.     

Mathematical modeling of phosphorus losses from land application of hog and cattle manure

Mathematical models may provide a means to estimate phosphorus (P) losses from land application of manure. Phosphorus losses typically occur during brief episodes of runoff and erosion. Models must be able to simulate P losses during these episodes by representing the basic chemical, physical, and biological processes by which these losses occur. The mathematical model ecosys combines dynamic distributed flow of solutes and nonsolutes through runoff and erosion with convective-dispersive transport of solutes, and both biologically and thermodynamically driven transformations between solutes and nonsolutes. This model was tested against P lost in runoff, erosion, and leachate measured during 90 min of controlled rainfall at 65 mm h(-1) on soils from six sites at which different rates of manure had been applied over the previous 3 to 6 yr. Transport and transformation kinetics in the model enabled it to simulate changes of dissolved inorganic phosphorus (DIP) in runoff from >1.0 to <0.05 mg L(-1) and changes of total phosphorus (TP) in sediment from 15 to 3 mg L(-1) measured during controlled rainfall on soils with diverse P contents. Results from 60-yr model runs using these kinetics with different application rates of cattle manure indicated that (i) a positive interaction exists between annual rainfall and application rate on P losses and (ii) rates greater than 30 Mg ha(-1) yr(-1) would cause TP concentrations in water leaving the site to rise above acceptable limits. The interaction between rainfall and rate suggests that P losses from manure application at any site should be assessed under the upper range of likely rainfall intensities.     

Assessment of manure phosphorus export through turfgrass sod production in Erath County, Texas

A best management practice (BMP) for exporting manure phosphorus (P) in turfgrass sod from the North Bosque River (NBR) watershed in central Texas was assessed using a geographic information system (GIS). The NBR watershed has a mandate to reduce the total annual P load to the NBR by 50% as a result of total maximum daily load regulation. Since dairy waste applications to fields are identified as the major nonpoint source of P to the river, innovative BMPs, such as export of manure P in turfgrass, will be needed to achieve the 50% reduction. However, methods are needed to evaluate the feasibility of these innovative management practices prior to their implementation. A geospatial database of suitable turfgrass production sites was developed for Erath County using GIS. Erath County largely encompasses the upper portion of the NBR watershed. Information from field experiments, production practices, and ground-truthing was used to search, analyze, and verify a geospatial database developed from national and regional sources. The integration and analyses of large databases supports the search by turf producers for sites suitable for turfgrass sod production in Erath County. In addition, GIS enables researchers and regulators to estimate manure P exports and reduced P loading due to implementation of the manure export BMP on a county scale. Under optimal conditions 198,000 kg manure P yr(-1) could be used and 114,840 kg manure P yr(-1) exported from the NBR watershed through implementation of a system using dairy manure to produce turfgrass sod. This is the equivalent of the manure P applied from 10,032 dairy cows yr(-1) and exported from 5808 dairy cows yr(-1). Application of GIS to large-scale planning and decision-making transcends traditional field-scale applications in precision agriculture.     

Phosphorus runoff from incorporated and surface-applied liquid swine manure and phosphorus fertilizer

Excessive fertilization with organic and/or inorganic P amendments to cropland increases the potential risk of P loss to surface waters. The objective of this study was to evaluate the effects of soil test P level, source, and application method of P amendments on P in runoff following soybean [Glycine max (L.) Merr.]. The treatments consisted of two rates of swine (Sus scrofa domestica) liquid manure surface-applied and injected, 54 kg P ha(-1) triple superphosphate (TSP) surface-applied and incorporated, and a control with and without chisel-plowing. Rainfall simulations were conducted one month (1MO) and six months (6MO) after P amendment application for 2 yr. Soil injection of swine manure compared with surface application resulted in runoff P concentration decreases of 93, 82, and 94%, and P load decreases of 99, 94, and 99% for dissolved reactive phosphorus (DRP), total phosphorus (TP), and algal-available phosphorus (AAP), respectively. Incorporation of TSP also reduced P concentration in runoff significantly. Runoff P concentration and load from incorporated amendments did not differ from the control. Factors most strongly related to P in runoff from the incorporated treatments included Bray P1 soil extraction value for DRP concentration, and Bray P1 and sediment content in runoff for AAP and TP concentration and load. Injecting manure and chisel-plowing inorganic fertilizer reduced runoff P losses, decreased runoff volumes, and increased the time to runoff, thus minimizing the potential risk of surface water contamination. After incorporating the P amendments, controlling erosion is the main target to minimize TP losses from agricultural soils.     

Spatial variability of soil phosphorus in relation to the topographic index and critical source areas: sampling for assessing risk to water quality

A measure of soil P status in agricultural soils is generally required for assisting with prediction of potential P loss from agricultural catchments and assessing risk for water quality. The objectives of this paper are twofold: (i) investigating the soil P status, distribution, and variability, both spatially and with soil depth, of two different first-order catchments; and (ii) determining variation in soil P concentration in relation to catchment topography (quantified as the "topographic index") and critical source areas (CSAs). The soil P measurements showed large spatial variability, not only between fields and land uses, but also within individual fields and in part was thought to be strongly influenced by areas where cattle tended to congregate and areas where manure was most commonly spread. Topographic index alone was not related to the distribution of soil P, and does not seem to provide an adequate indicator for CSAs in the study catchments. However, CSAs may be used in conjunction with soil P data for help in determining a more "effective" catchment soil P status. The difficulties in defining CSAs a priori, particularly for modeling and prediction purposes, however, suggest that other more "integrated" measures of catchment soil P status, such as baseflow P concentrations or streambed sediment P concentrations, might be more useful. Since observed soil P distribution is variable and is also difficult to relate to nationally available soil P data, any assessment of soil P status for determining risk of P loss is uncertain and problematic, given other catchment physicochemical characteristics and the sampling strategy employed.     

Phosphorus loading in the Frome catchment, UK: seasonal refinement of the coefficient modeling approach

This paper describes the results of an export coefficient modeling approach to predict total phosphorus (TP) loading in the Frome catchment, Dorset, UK from point and diffuse sources on a seasonal (monthly) basis in 1998 and on an annual basis for 1990-1998. The model predicted an annual TP load of 25 605 kg yr(-1), compared with an observed (measured) value of 23400 kg yr(-1). Monthly loads calculated using the export coefficient model agreed well with monthly observed values except in months of variable discharge, when observed values were low, probably due to infrequent, and therefore unrepresentative, sampling. Comparison between filterable reactive phosphorus (FRP) and TP concentrations observed in the period 1990-1997 showed that trends in FRP could be estimated from trends in TP. A sensitivity analysis (varying individual export coefficients by +/-10%) showed that sewage treatment works (STWs) (3.5%), tilled land (2.7%), meadow-verge-seminatural (1.0%), and mown and grazed turf (0.6%) had the most significant effect (percent difference from base contribution) on model prediction. The model was also used to estimate the effect of phosphorus stripping at STWs in order to comply with a pending change in the European Union wastewater directive. Theoretical reduction of TP from the largest STW in the catchment gave a predicted reduction in TP loading of 2174 kg yr(-1). This illustrates the value of this seasonal export coefficient model as a practical management tool.     

Regional scale variability in sediment and nutrient delivery from small agricultural watersheds

Although many studies have pointed out the various controlling factors of sediment and nutrient delivery on a plot or watershed scale, little is known on the spatial variability of sediment and nutrient delivery on a regional scale. This study was conducted to reveal regional variations in sediment-associated nutrient delivery in central Belgium. Sediment deposited in 13 small retention ponds was sampled and analyzed for total phosphorus (TP), K, Mg, and Ca content. The TP content of the sediment deposits varied from 510 to 2001 mg P per kg sediment. Nutrients are predominantly fixed on the very fine sediment fraction (<16 microm), which is the reason why the nutrient trap efficiency of the ponds is only a fraction of the sediment trap efficiency. Average nutrient trap efficiency of the studied ponds varies between 4 and 31%, whereas sediment trap efficiency varies between 10 and 72%. For watersheds ranging from 7 to 4873 ha, sediment yield ranged between 1.2 and 20.6 Mg ha(-1) yr(-1), whereas TP export varied from 1.8 to 39.7 kg ha(-1) yr(-1). The observed spatial variability in nutrient losses is primarily attributed to regional variations in erosion and sediment yield values and to a far lesser degree to the spatial variations in fertilizer application. Redistribution of manure in the framework of an agricultural policy may increase the rate of nutrient delivery by ways of erosion and sediment transport.     

Evaluating agricultural best management practices in tile-drained subwatersheds of the Mackinaw River, Illinois

Best management practices (BMPs) are widely promoted in agricultural watersheds as a means of improving water quality and ameliorating altered hydrology. We used a paired watershed approach to evaluate whether focused outreach could increase BMP implementation rates and whether BMPs could induce watershed-scale (4000 ha) changes in nutrients, suspended sediment concentrations, or hydrology in an agricultural watershed in central Illinois. Land use was >90% row crop agriculture with extensive subsurface tile drainage. Outreach successfully increased BMP implementation rates for grassed waterways, stream buffers, and strip-tillage within the treatment watershed, which are designed to reduce surface runoff and soil erosion. No significant changes in nitrate-nitrogen (NO-N), total phosphorus (TP), dissolved reactive phosphorus, total suspended sediment (TSS), or hydrology were observed after implementation of these BMPs over 7 yr of monitoring. Annual NO-N export (39-299 Mg) in the two watersheds was equally exported during baseflow and stormflow. Mean annual TP export was similar between the watersheds (3.8 Mg) and was greater for TSS in the treatment (1626 ± 497 Mg) than in the reference (940 ± 327 Mg) watershed. Export of TP and TSS was primarily due to stormflow (>85%). Results suggest that the BMPs established during this study were not adequate to override nutrient export from subsurface drainage tiles. Conservation planning in tile-drained agricultural watersheds will require a combination of surface-water BMPs and conservation practices that intercept and retain subsurface agricultural runoff. Our study emphasizes the need to measure conservation outcomes and not just implementation rates of conservation practices.     

The effects of soil carbon on phosphorus and sediment loss from soil trays by overland flow

Soil chemical constituents influence soil structure and erosion potential. We investigated manure and inorganic fertilizer applications on soil chemistry (carbon [C] quality and exchangeable cations), aggregation, and phosphorus (P) loss in overland flow. Surface samples (0-5 cm) of a Hagerstown (fine, mixed, semiactive, mesic Typic Hapludalf) soil, to which either dairy or poultry manure or triple superphosphate had been applied (0-200 kg P ha(-1) yr(-1) for 5 yr), were packed in boxes (1 m long, 0.15 m wide, and 0.10 m deep) to field bulk density (1.2 g cm(-3)). Rainfall was applied (65 mm h(-1)), overland flow collected, and sediment and P loss determined. All amendments increased Mehlich 3-extractable P (19-177 mg kg(-1)) and exchangeable Ca (4.2-11.5 cmol kg(-1)) compared with untreated soil. For all treatments, sediment transport was inversely related to the degree of soil aggregation (determined as ratio of dispersed and undispersed clay; r = 0.51), exchangeable Ca (r = 0.59), and hydrolyzable carbohydrate (r = 0.62). The loss of particulate P and total P in overland flow from soil treated with up to 50 kg P ha(-1) dairy manure (9.9 mg particulate phosphorus [PPI, 15.1 mg total phosphorus [TP]) was lower than untreated soil (13.3 mg PP, 18.1 mg TP), due to increased aggregation and decreased surface soil slaking attributed to added C in manure. Manure application at low rates (<50 kg P ha(-1)) imparts physical benefits to surface soil, which decrease P loss potential. However, at greater application rates, P transport is appreciably greater (26.9 mg PP, 29.5 mg TP) than from untreated soil (13.3 mg PP, 18.1 mg TP).     

Phosphorus loss from an agricultural watershed as a function of storm size

Phosphorus (P) loss from agricultural watersheds is generally greater in storm rather than base flow. Although fundamental to P-based risk assessment tools, few studies have quantified the effect of storm size on P loss. Thus, the loss of P as a function of flow type (base and storm flow) and size was quantified for a mixed-land use watershed (FD-36; 39.5 ha) from 1997 to 2006. Storm size was ranked by return period (<1, 1-3, 3-5, 5-10, and >10 yr), where increasing return period represents storms with greater peak and total flow. From 1997 to 2006, storm flow accounted for 32% of watershed discharge yet contributed 65% of dissolved reactive P (DP) (107 g ha(-1) yr(-1)) and 80% of total P (TP) exported (515 g ha(-1) yr(-1)). Of 248 storm flows during this period, 93% had a return period of <1 yr, contributing most of the 10-yr flow (6507 m(3) ha(-1); 63%) and export of DP (574 g ha(-1); 54%) and TP (2423 g ha(-1); 47%). Two 10-yr storms contributed 23% of P exported between 1997 and 2006. A significant increase in storm flow DP concentration with storm size (0.09-0.16 mg L(-1)) suggests that P release from soil and/or area of the watershed producing runoff increase with storm size. Thus, implementation of P-based Best Management Practice needs to consider what level of risk management is acceptable.     

Greenhouse gas emissions and soil indicators four years after manure and compost applications

Understanding how carbon, nitrogen, and key soil attributes affect gas emissions from soil is crucial for alleviating their undesirable residual effects that can linger for years after termination of manure and compost applications. This study was conducted to evaluate the emission of soil CO2, N2O, and CH4 and soil C and N indicators four years after manure and compost application had stopped. Experimental plots were treated with annual synthetic N fertilizer (FRT), annual and biennial manure (MN1 and MN2, respectively), and compost (CP1 and CP2, respectively) from 1992 to 1995 based on removal of 151 kg N ha(-1) yr(-1) by continuous corn (Zea mays L.). The control (CTL) plots received no input. After 1995, only the FRT plots received N fertilizer in the spring of 1999. In 1999, the emissions of CO2 were similar between control and other treatments. The average annual carbon input in the CTL and FRT plots were similar to soil CO2-C emission (4.4 and 5.1 Mg C ha(-1) yr(-1), respectively). Manure and compost resulted in positive C and N balances in the soil four years after application. Fluxes of CH4-C and N2O-N were nearly zero, which indicated that the residual effects of manure and compost four years after application had no negative influence on soil C and N storage and global warming. Residual effects of compost and manure resulted in 20 to 40% higher soil microbial biomass C, 42 to 74% higher potentially mineralizable N, and 0.5 unit higher pH compared with the FRT treatment. Residual effects of manure and compost on CO2, N20, and CH4 emissions were minimal and their benefits on soil C and N indicators were more favorable than that of N fertilizer.     

Increase in phosphorus losses from grassland in response to Olsen-P accumulation

The Olsen-P status of grazed grassland (Lolium perenne L.) swards in Northern Ireland was increased over a 5-yr period (March 2000 to February 2005) by applying different rates of P fertilizer (0, 10, 20, 40, or 80 kg P ha(-1) yr(-1)) to assess the relationship between soil P status and P losses in land drainage water and overland flow. Plots (0.2 ha) were hydrologically isolated and artificially drained to v-notch weirs, with flow proportional monitoring of drainage water and overland flow. Annually, the collectors for overland flow intercepted between 11 and 35% of the surplus rainfall. Single flow events accounted for up to 52% of the annual dissolved reactive phosphorus (DRP) load. The Olsen-P status of the soil influenced DRP and total phosphorus (TP) concentrations in land drainage water and overland flow. Annual TP loss was highly variable and ranged from 0.19 to 1.55 kg P ha(-1) yr(-1) for the plot receiving no P fertilizer and from 0.35 to 2.94 kg P ha(-1) yr(-1) for the plot receiving 80 kg P ha(-1) yr(-1). Despite the Olsen-P status in the soils ranging from 22 to 99 mg P kg(-1), after 5 yr of fertilizer P applications it was difficult to identify a clear Olsen-P concentration at which P losses increased. Any relationship was confounded by annual variability of hydrologic events and flows and by hydrologic differences between plots. Withholding P fertilizer for over 5 yr was not long enough to lower P losses or to have an adverse effect on herbage P concentrations.     

Nitrate and sediment fluxes from a California rangeland watershed

Long-term water quality records for assessing natural variability, impact of management, and that guide regulatory processes to safeguard water resources are rare for California oak woodland rangelands. This study presents a 20-yr record (1981-2000) of nitrate-nitrogen (NO(3)-N) and suspended sediment export from a typical, grazed oak woodland watershed (103 ha) in the northern Sierra Nevada foothills of California. Mean annual precipitation over the 20-yr period was 734 mm yr(-1) (range 366-1205 mm yr(-1)). Mean annual stream flow was 353 mm y(-1) (range 87-848 mm yr(-1)). Average annual stream flow was 48.1 +/- 16% of precipitation. Mean annual NO(3)-N export was 1.6 kg ha(-1) yr(-1) (range 0.18-3.6 kg ha(-1) yr(-1)). Annual NO(3)-N export significantly (P < 0.05) increased with increasing annual stream flow and precipitation. Mean daily NO(3)-N export was 0.004 kg ha(-1) d(-1) (range 10(-5) to 0.55 kg ha(-1) d(-1)). Mean annual suspended sediment export was 198 kg ha(-1) yr(-1) (range 23-479 kg ha(-1) yr(-1)). There was a positive relationship (P < 0.05) between annual suspended sediment export, annual stream flow and precipitation. Mean daily suspended sediment export was 0.54 kg ha(-1) d(-1) (range 10(-4) to 155 kg ha(-1) d(-1)). Virtually no sediment was exported during the dry season. The large variation in daily and annual fluxes highlights the necessity of using long-term records to establish quantitative water quality targets for rangelands and demonstrates the difficulty of designing a water quality monitoring program for these ecosystems.     

Phosphorus accumulation in cultivated soils from long-term annual applications of cattle feedlot manure

Historically, manure has been recognized as an excellent soil amendment that can improve soil quality and provide nutrients for crop production. In areas of high animal density, however, the potential for water pollution resulting from improper storage or disposal of manure may be significant. The objective of this study was to determine the P balance of cultivated soils under barley (Hordeum vulgare L.) production that have received long-term annual manure amendments. Nonirrigated soils at the study site in Lethbridge, AB, Canada, have received 0, 30, 60, or 90 Mg manure ha(-1) (wet wt. basis) while irrigated plots received 0, 60, 120, and 180 Mg ha(-1) annually for 16 yr. The amount of P removed in barley grain and straw during the 16-yr period was between 5 and 18% of the cumulative manure P applied. There was a balance between P applied in manure and P recovered in crops and soils (to the 150-cm depth) of nonirrigated plots during the 16-yr study. In irrigated plots, as much as 1.4 Mg P ha(-1) added (180 Mg ha(-1) yr(-1) treatment) was not recovered over 16 yr, and was probably lost through leaching. The risk of ground water contamination with P from manure was greater in irrigated than nonirrigated plots that have received long-term annual manure amendments. Manure application rates should be reduced in nonirrigated and irrigated plots to more closely match manure P inputs to crop P requirements.     

Nitrogen input from residential lawn care practices in suburban watersheds in Baltimore county,MD

A residential lawn care survey was conducted as part of the Baltimore Ecosystem Study, a Long-term Ecological Research project funded by the National Science Foundation and collaborating agencies, to estimate the nitrogen input to urban watersheds from lawn care practices. The variability in the fertilizer N application rates and the factors affecting the application rates were examined. Results indicated that the annual input of nitrogen from fertilizer is a major component of the urban watershed nitrogen budget and it is both spatially and temporally variable. There is a wide range in the application rate of fertilizer N to residential lawns applied by homeowners and by professional lawn care companies. Survey data estimated a mean fertilizer application rate of 97.6 kg N/ha/yr with a standard deviation of 88.3 kg N/ha/yr. Analyses suggested that the fertilizer application rate is affected by social economic factors and soil characteristics to include the market value of the house, age of development, soil bulk density and soil nitrogen content.     

The MANAGE database: nutrient load and site characteristic updates and runoff concentration data

The "Measured Annual Nutrient loads from AGricultural Environments" (MANAGE) database was developed to be a readily accessible, easily queried database of site characteristic and field-scale nutrient export data. The original version of MANAGE, which drew heavily from an early 1980s compilation of nutrient export data, created an electronic database with nutrient load data and corresponding site characteristics from 40 studies on agricultural (cultivated and pasture/range) land uses. In the current update, N and P load data from 15 additional studies of agricultural runoff were included along with N and P concentration data for all 55 studies. The database now contains 1677 watershed years of data for various agricultural land uses (703 for pasture/rangeland; 333 for corn; 291 for various crop rotations; 177 for wheat/oats; and 4-33 yr for barley, citrus, vegetables, sorghum, soybeans, cotton, fallow, and peanuts). Across all land uses, annual runoff loads averaged 14.2 kg ha(-1) for total N and 2.2 kg ha(-1) for total P. On average, these losses represented 10 to 25% of applied fertilizer N and 4 to 9% of applied fertilizer P. Although such statistics produce interesting generalities across a wide range of land use, management, and climatic conditions, regional crop-specific analyses should be conducted to guide regulatory and programmatic decisions. With this update, MANAGE contains data from a vast majority of published peer-reviewed N and P export studies on homogeneous agricultural land uses in the USA under natural rainfall-runoff conditions and thus provides necessary data for modeling and decision-making related to agricultural runoff. The current version can be downloaded at http://www.ars.usda.gov/spa/manage-nutrient.