Relationship between soil test phosphorus and phosphorus in runoff: effects of soil series variability

Phosphorus loss in runoff from agricultural fields has been identified as an important contributor to eutrophication. The objective of this research was to determine the relationship between phosphorus (P) in runoff from a benchmark soil (Cecil sandy loam; fine, kaolinitic, thermic Typic Kanhapludult) and Mehlich III-, deionized water-, and Fe(2)O(3)-extractable soil P, and degree of phosphorus saturation (DPS). Additionally, the value of including other soil properties in P loss prediction equations was evaluated. Simulated rainfall was applied (75 mm h(-1)) to 54 1-m(2) plots installed on six fields with different soil test phosphorus (STP) levels. Runoff was collected in its entirety for 30 min and analyzed for total P and dissolved reactive phosphorus (DRP). Soil samples were collected from 0- to 2-, 0- to 5-, and 0- to 10-cm depths. The strongest correlation for total P and DRP occurred with DPS (r(2) = 0.72). Normalizing DRP by runoff depth resulted in improved correlation with deionized water-extractable P for the 0- to 10-cm sampling depth (r(2) = 0.81). The STP levels were not different among sampling depths and analysis of the regression equations revealed that soil sampling depth had no effect on the relationship between STP and P in runoff. For all forms of P in runoff and STP measures, the relationship between STP and runoff P was much stronger when the data were split into groups based on the ratio of oxalate-extractable Fe to Al. For all forms of P in runoff and all STP methods, R(2) increased with the inclusion of oxalate-extractable Al and Fe in the regression equation. The results of this study indicate that inclusion of site-specific information about soil Al and Fe content can improve the relationship between STP and runoff P.     

Relationships between phosphorus levels in soil and in runoff from corn production systems

Phosphorus-enriched runoff from cropland can hasten eutrophication of surface waters. A soil P level exceeding crop needs due to long-term fertilizer and/or manure applications is one of several potential sources of increased P losses in runoff from agricultural systems. Field experiments were conducted at locations representative of three major soil regions in Wisconsin in corn (Zea mays L.) production systems to determine the effect of tillage, recent manure additions, soil P extraction method, and soil sampling depth (0-2, 0-5, and 0-15 cm) on the relationship between soil test P level and P concentrations in runoff. Runoff from simulated rainfall (75 mm h(-1)) was collected from 0.83-m2 areas for 1 h after rainfall initiation and analyzed for dissolved phosphorus (DP), total phosphorus (TP), and sediment. The DP fraction of the TP concentration in runoff ranged from 5 to 17% among sites with most of the variation in TP due to varying sediment concentration on the well-drained silt loam soils and to soil test P level on the poorly drained silty clay loam soil. In 213 observations across a range of soils and managements, good relationships occurred between soil test P level and DP concentration in runoff for most of the tests and sampling depths used. Recent manure additions and high levels of surface cover from corn residue sometimes masked this relationship. The slope of DP relative to soil test P level was markedly higher on the silty clay loam soil than on the silt loam soils possibly due to soil permeability-infiltration rate differences. Agronomic soil P tests were as effective as environmentally oriented soil P tests for predicting DP concentrations in runoff.     

Soil and surface runoff phosphorus relationships for five typical USA midwest soils

Excessively high soil P can increase P loss with surface runoff. This study used indoor rainfall simulations to characterize soil and runoff P relationships for five Midwest soils (Argiudoll, Calciaquaoll, Hapludalf, and two Hapludolls). Topsoil (15-cm depth, 241-289 g clay kg(-1) and pH 6.0-8.0) was incubated with five NH4H2PO4 rates (0-600 mg P kg(-1)) for 30 d. Total soil P (TPS) and soil-test P (STP) measured with Bray-P1 (BP), Mehlich-3 (M3P), Olsen (OP), Fe-oxide-impregnated paper (FeP), and water (WP) tests were 370 to 1360, 3 to 530, 10 to 675, 4 to 640, 7 to 507, and 2 to 568 mg P kg(-1), respectively. Degree of soil P saturation (DPS) was estimated by indices based on P sorption index (PSI) and STP (DPSSTP) and P, Fe, and Al extracted by ammonium oxalate (DPSox) or Mehlich-3 (DPSM3). Soil was packed to 1.1 g cm(-3) bulk density in triplicate boxes set at 4% slope. Surface runoff was collected during 75 min of 6.5 cm h(-1) rain. Runoff bioavailable P (BAP) and dissolved reactive P (DRP) increased linearly with increased P rate, STP, DPSox, and DPSM3 but curvilinearly with DPSSTP. Correlations between DRP or BAP and soil tests or saturation indices across soils were greatest (r > or = 0.95) for FeP, OP, and WP and poorest for BP and TPS (r = 0.83-0.88). Excluding the calcareous soil (Calciaquoll) significantly improved correlations only for BP. Differences in relationships between runoff P and the soil tests were small or nonexistent among the noncalcareous soils. Routine soil P tests can estimate relationships between runoff P concentration and P application or soil P, although estimates would be improved by separate calibrations for calcareous and noncalcareous soils.     

Soil characteristics and phosphorus level effect on phosphorus loss in runoff

The loss of phosphorus (P) in runoff from agricultural soils may accelerate eutrophication in lakes and streams as well as degrade surface water quality. Limited soil specific data exist on the relationship between runoff P and soil P. This study investigated the relationship between runoff dissolved reactive phosphorus (DRP) and soil P for three Oklahoma benchmark soils: Richfield (fine, smectitic, mesic Aridic Argiustoll), Dennis (fine, mixed, active, thermic Aquic Argiudoll), and Kirkland (fine, mixed, superactive, thermic Udertic Paleustoll) series. These soils were selected to represent the most important agricultural soils in Oklahoma across three major land resource areas. Surface soil (0-15 cm) was collected from three designated locations, treated with diammonium phosphate (18-46-0) to establish a wide range of water-soluble phosphorus (WSP) (3.15-230 mg kg(-1)) and Mehlich-3 phosphorus (M3P) (27.8-925 mg kg(-1)). Amended soils were allowed to reach a steady state 210 d before simulated rainfall (75 mm h(-1)). Runoff was collected for 30 min from bare soil boxes (1.0 x 0.42 m and 5% slope) and analyzed for DRP and total P. Soil samples collected immediately before rainfall simulation were analyzed for the following: M3P, WSP, ammonium oxalate P saturation index (PSI(ox)), water-soluble phosphorus saturation index (PSI(WSP)), and phosphorus saturation index calculated from M3P and phosphorus sorption maxima (P(sat)). The DRP in runoff was highly related (p < 0.001) to M3P for individual soil series (r2 > 0.92). Highly significant relationships (p < 0.001) were found between runoff DRP and soil WSP for the individual soil series (r2 > 0.88). Highly significant relationships (p < 0.001) existed between DRP and different P saturation indexes. Significant differences (p < 0.05) among the slopes of the regressions for the DRP-M3P, DRP-WSP, DRP-PSI(ox), DRP-PSI(WSP), and DRP-P(sat) relationships indicate that the relationships are soil specific and phosphorus management decisions should consider soil characteristics.     

Change in soluble phosphorus in soils following fertilization is dependent on initial Mehlich-3 phosphorus

There is a lack of information on how fertilization and initial Mehlich-3 phosphorus (M3P) interact to affect water soluble P (WSP) in soils. Our objectives were to (i) quantify the relationship between WSP and M3P for four textural diverse benchmark soils of North Carolina (NC) and (ii) quantify the change in WSP concentrations following P additions to soils over a wide range of initial M3P. Soils known to represent a wide range in M3P were collected from an Autryville loamy sand (loamy, siliceous, subactive, thermic Arenic Paleudults), Wasda muck (fine-loamy, mixed, semiactive, acid, thermic Histic Humaquepts), Georgeville silt loam (fine, kaolinitic, thermic Typic Kanhapludults), and Pacolet sandy clay loam (fine, kaolinitic, thermic Typic Kanhapludults) and analyzed for M3P, Fe, Al, and WSP. An incubation study was also conducted where four samples representing a range in M3P from each series were fertilized at rates of 150 and 300 kg P ha(-1), and WSP was measured at 1, 7, and 21 d after fertilization. The Wasda muck exhibited a change point at 115 mg P kg(-1) across a broad range of M3P concentrations (60-238 mg kg(-1)) while Autryville, Georgeville, and Pacolet series (with ranges in M3P of 32-328, 119-524, 0-1034 mg P kg(-1), respectively) maintained linear relationships between WSP and M3P. For the fertilized soils, significant increases in WSP occurred regardless of P rate. Yet, WSP concentrations were greater in soils with greater initial M3P. Thus, these data suggest that shifting animal waste applications to fields of relatively lower M3P concentrations would have an immediate impact on reducing risk for P losses, if all other factors are equal.     

Effects of tillage and phosphorus placement on phosphorus runoff losses in a grain sorghum-soybean rotation

Phosphorus enhances eutrophication of fresh water bodies. This study was conducted to determine the influence of tillage and P placement on P losses in runoff water from a somewhat poorly drained soil (Woodson silt loam [fine, smectitic, thermic Abruptic Argiaquoll], 1.0-1.5% slope) in a grain sorghum [Sorghum bicolor (L.) Moenchl-soybean [Glycine mar (L.) Merr] rotation. Chisel-disk-field cultivate (ChT), ridge-till (RT), and no-till (NT) in combination with 0 kg P ha(-1) or 24 kg P ha(-1) broadcast or knifed (applied prior to planting grain sorghum) were studied. Runoff volume and losses of sediment and P were summed over the growing season. Significant interactions between tillage and P placement for soluble P losses were found. For example, soluble P loss in 1999 for NT-broadcast in grain sorghum was 358 g ha(-1); significantly greater than 31 g ha(-1) for NT-knife or 23 g ha(-1) for NT-check. Similar results were found for RT but no such differences were found for ChT. Bioavailable P losses were generally highest with broadcast P placement and for NT and RT. Total P losses were significantly higher at 959 g ha(-1) with broadcast P on grain sorghum in 1998, compared with 521 g ha(-1) for the check and 659 g ha(-1) for the knifed P applications. Total P losses in 1999 for soybeans were only 18 g ha(-1) for NT, which was significantly lower than 75 g ha(-1) for ChT and 66 g ha(-1) for RT. The results indicate that broadcast P applications on RT and NT will increase P losses, but the influence of tillage was not consistent.     

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 history and long-term tillage effects on soil properties and phosphorus losses in runoff

Manure additions to cropland can reduce total P losses in runoff on well-drained soils due to increased infiltration and reduced soil erosion. Surface residue management in subsequent years may influence the long-term risk of P losses as the manure-supplied organic matter decomposes. The effects of manure history and long-term (8-yr) tillage [chisel plow (CP) and no-till (NT)] on P levels in runoff in continuous corn (Zea mays L.) were investigated on well-drained silt loam soils of southern and southwestern Wisconsin. Soil P levels (0-15 cm) increased with the frequency of manure applications and P stratification was greater near the surface (0-5 cm) in NT than CP. In CP, soil test P level was linearly related to dissolved P (24-105 g ha(-1)) and bioavailable P (64-272 g ha(-1)) loads in runoff, but not total P (653-1893 g ha(-1)). In NT, P loads were reduced by an average of 57% for dissolved P, 70% for bioavailable P, and 91% for total P compared with CP. This reduction was due to lower sediment concentrations and/or lower runoff volumes in NT. There was no relationship between soil test P levels and runoff P concentrations or loads in NT. Long-term manure P applications in excess of P removal by corn in CP systems ultimately increased the potential for greater dissolved and bioavailable P losses in runoff by increasing soil P levels. Maintaining high surface residue cover such as those found in long-term NT corn production systems can mitigate this risk in addition to reducing sediment and particulate P losses.     

Effect of manure application timing, crop, and soil type on phosphorus leaching

Phosphorus (P) leaching losses from manure applications may be of concern when artificial drainage systems allow for hydrologic short-cuts to surface waters. This study quantified P leaching losses from liquid manure applications on two soil textural extremes, a clay loam and loamy sand soil, as affected by cropping system and timing of application. For each soil type, manure was applied at an annual rate of 93 800 L ha(-1) on replicated drained plots under maize (Zea mays L.) in early fall, late fall, early spring, and as a split application in early and late spring. Manure was applied on orchardgrass (Dactylis glomerata L.) in split applications in early fall and late spring, and early and late spring. Drain water was sampled at least weekly when lines were flowing, and outflow rate and total P content were determined. High P leaching losses were measured in the clay loam as soon as drain lines initiated flow after manure application. Flow-weighted mean P leaching losses on clay loam plots averaged 39 times higher (0.504 mg L(-1)) than those on loamy sand plots (0.013 mg L(-1)), and were above the USEPA level of concern of 0.1 mg L(-1). Phosphorus losses varied among application seasons on the clay loam soil, with highest losses generally measured for early fall applications. Phosphorus leaching patterns in clay loam showed short-term spikes and high losses were associated with high drain outflow rates, suggesting preferential flow as the main transport mechanism. Phosphorus leaching from manure applications on loamy sand soils does not pose environmental concerns as long as soil P levels remain below the saturation level.     

Approximating phosphorus release from soils to surface runoff and subsurface drainage

Phosphorus application in excess of crop needs has increased the concentration of P in surface soil and runoff and led many states to develop P-based nutrient management strategies. However, insufficient data are available relating P in surface soil, surface runoff, and subsurface drainage to develop sound guidelines. Thus, we investigated P release from the surface (0-5 cm depth) of a Denbigh silt loam from Devon, U.K. (30-160 mg kg-1 Olsen P) and Alvin, Berks, Calvin, and Watson soils from Pennsylvania (10-763 mg kg-1 Mehlich-3 P) in relation to the concentration of P in surface runoff and subsurface drainage. A change point, where the slopes of two linear relationships between water- or CaCl2-extractable soil P and soil test phosphorus (STP) (Olsen or Mehlich-3) meet, was evident for the Denbigh at 33 to 36 mg kg-1 Olsen P, and the Alvin and Berks soils at 185 to 190 mg Mehlich-3 P kg-1. Similar change points were also observed when STP was related to the P concentration of surface runoff (185 mg kg-1) and subsurface drainage (193 mg kg-1). The use of water and CaCl2 extraction of surface soil is suggested to estimate surface runoff P (r2 of 0.92 for UK and 0.86 for PA soils) and subsurface drainage P (r2 of 0.82 for UK and 0.88 for PA soils), and to determine a change point in STP, which may be used in support of agricultural and environmental P management.     

Estimating dissolved reactive phosphorus concentration in surface runoff water from major Ontario soils

Phosphorus (P) loss from agricultural land in surface runoff can contribute to eutrophication of surface water. This study was conducted to evaluate a range of environmental and agronomic soil P tests as indicators of potential soil surface runoff dissolved reactive P (DRP) losses from Ontario soils. The soil samples (0- to 20-cm depth) were collected from six soil series in Ontario, with 10 sites each to provide a wide range of soil test P (STP) values. Rainfall simulation studies were conducted following the USEPA National P Research Project protocol. The average DRP concentration (DRP30) in runoff water collected over 30 min after the start of runoff increased (p < 0.001) in either a linear or curvilinear manner with increases in levels of various STPs and estimates of degree of soil P saturation (DPS). Among the 16 measurements of STPs and DPSs assessed, DPS(M3) 2 (Mehlich-3 P/[Mehlich-3 Al + Fe]) (r2 = 0.90), DPS(M3)-3 (Mehlich-3 P/Mehlich-3 Al) (r2 = 0.89), and water-extractable P (WEP) (r2 = 0.89) had the strongest overall relationship with runoff DRP30 across all six soil series. The DPS(M3)-2 and DPS(M3)-3 were equally accurate in predicting runoff DRP30 loss. However, DPS(M3)-3 was preferred as its prediction of DRP30 was soil pH insensitive and simpler in analytical procedure, ifa DPS approach is adopted.     

Distribution of copper, zinc, and phosphorus in coastal plain soils receiving repeated liquid biosolids applications

Continuous N-based application of biosolids contributes to a gradual increase of trace elements and P in soils. The objectives of this study were to assess the accumulation and vertical transport of Cu, Zn, C, N, and P within the profile of two coastal plain soils. Liquid (6-8% total solids) biosolids were applied to an Acredale silt loam (fine silty, mixed, thermic typic Ochraqualfs) and Bojac loamy sand (coarse loamy, mixed, thermic typic Hapludult) annually from 1984 to 1998. The repeated applications supplied 70, 204, and 3823 kg ha(-1) of Cu, Zn, and P, respectively, to the Acredale and 81, 225, and 4265 kg ha(-1) of Cu, Zn, and P, respectively, to the Bojac. The total C and N contents were not different than background levels in the Bojac soil and were slightly higher in the Acredale soil 7 years after cessation of biosolids application. Phosphorus, Cu and Zn are still concentrated in the top 0.25 m of the Acredale soil. Enrichment of P, Cu, and Zn were detected to the deepest soil increment in the coarse-textured Bojac soil. Approximately 20 to 40% of the Cu and Zn applied in the biosolids could not be accounted, which was likely due to a combination of leaching and incomplete extraction. Excessive Mehlich 1-P concentrations and a high degree of P saturation were found in amended soil, raising the potential for P release to runoff or leaching water.     

Relating soil phosphorus to dissolved phosphorus in runoff: a single extraction coefficient for water quality modeling

Phosphorus transport from agricultural soils contributes to eutrophication of fresh waters. Computer modeling can help identify agricultural areas with high potential P transport. Most models use a constant extraction coefficient (i.e., the slope of the linear regression between filterable reactive phosphorus [FRP] in runoff and soil P) to predict dissolved P release from soil to runoff, yet it is unclear how variations in soil properties, management practices, or hydrology affect extraction coefficients. We investigated published data from 17 studies that determined extraction coefficients using Mehlich-3 or Bray-1 soil P (mg kg(-1)), water-extractable soil P (mg kg(-1)), or soil P sorption saturation (%) as determined by ammonium oxalate extraction. Studies represented 31 soils with a variety of management conditions. Extraction coefficients from Mehlich-3 or Bray-1 soil P were not significantly different for 26 of 31 soils, with values ranging from 1.2 to 3.0. Extraction coefficients from water-extractable soil P were not significantly different for 17 of 20 soils, with values ranging from 6.0 to 18.3. The relationship between soil P sorption saturation and runoff FRP (microg L(-1)) was the same for all 10 soils investigated, exhibiting a split-line relationship where runoff FRP rapidly increased at P sorption saturation values greater than 12.5%. Overall, a single extraction coefficient (2.0 for Mehlich-3 P data, 11.2 for water-extractable P data, and a split-line relationship for P sorption saturation data) could be used in water quality models to approximate dissolved P release from soil to runoff for the majority of soil, hydrologic, or management conditions. A test for soil P sorption saturation may provide the most universal approximation, but only for noncalcareous soils.     

Ground cover impacts on sediment and phosphorus export from manured riparian pasture

Maintaining pasture ground cover is important in preventing environmental degradation of grasslands and associated riparian areas. The objective of this work was to determine the effect of ground cover on sediment and P export from pastured riparian areas under simulated rainfall events. Plots were established on two sites in the North Carolina Piedmont: a 10% slope with Appling sandy loam soils (fine, kaolinitic, thermic Typic Kanhapludults) and a 20% slope with Wedowee sandy loam soils (fine, kaolinitic, thermic Typic Kanhapludults), both with mixed tall fescue (Festuca arundinacea Schreb.)-dallisgrass (Paspalum dilatatum Poir.) vegetation. Existing forage stands were modified to represent a range of ground cover levels: 0, 45, 70, and 95% (bare ground, low, medium, and high cover, respectively), and amended with beef steer (Bos taurus) feces and urine (about 10 kg P ha(-1)). Mean runoff volume from bare ground was generally twice that observed from low, medium, and high levels of cover, which were similar. For all rainfall events combined, export of dissolved reactive P was greatest (P < 0.1) at bare ground and was reduced 31% at low cover, which did not differ from medium or high cover. Mean total Kjeldahl P export was greater (P < 0.001) from bare ground than from other cover levels. Results indicate that riparian bare areas can contribute substantial sediment (>215 kg ha(-1)) and P (0.7 kg P ha(-1)) to surface waters during heavy rainfall, whereas export may be reduced equally well by low cover (45%) as by high cover.     

Evaluation of phosphorus transport in surface runoff from packed soil boxes

Evaluation of phosphorus (P) management strategies to protect water quality has largely relied on research using simulated rainfall to generate runoff from either field plots or shallow boxes packed with soil. Runoff from unmanured, grassed field plots (1 m wide x 2 m long, 3-8% slope) and bare soil boxes (0.2 m wide and 1 m long, 3% slope) was compared using rainfall simulation (75 mm h(-1)) standardized by 30-min runoff duration (rainfall averaged 55 mm for field plots and 41 mm for packed boxes). Packed boxes had lower infiltration (1.2 cm) and greater runoff (2.9 cm) and erosion (542 kg ha(-1)) than field plots (3.7 cm infiltration; 1.8 cm runoff; 149 kg ha(-1) erosion), yielding greater total phosphorus (TP) losses in runoff. Despite these differences, regressions of dissolved reactive phosphorus (DRP) in runoff and Mehlich-3 soil P were consistent between field plots and packed boxes reflecting similar buffering by soils and sediments. A second experiment compared manured boxes of 5- and 25-cm depths to determine if variable hydrology based on box depth influenced P transport. Runoff properties did not differ significantly between box depths before or after broadcasting dairy, poultry, or swine manure (100 kg TP ha(-1)). Water-extractable phosphorus (WEP) from manures dominated runoff P, and translocation of manure P into soil was consistent between box types. This study reveals the practical, but limited, comparability of field plot and soil box data, highlighting soil and sediment buffering in unamended soils and manure WEP in amended soils as dominant controls of DRP transport.     

Response of turf and quality of water runoff to manure and fertilizer

Manure applications can benefit turfgrass production and unused nutrients in manure residues can be exported through sod harvests. Yet, nutrients near the soil surface could be transported in surface runoff. Our research objective was to evaluate responses of bermudagrass [Cynodon dactylon (L.) Pers. var. Guymon] turf and volumes and P and N concentrations of surface runoff after fertilizer or composted manure applications. Three replications of five treatments were established on a Boonville fine sandy loam (fine, smectitic, thermic Vertic Albaqualf) that was excavated to create an 8.5% slope. Manure rates of 50 and 100 kg P ha(-1) at the start of two monitoring periods were compared with P fertilizer rates of 25 and 50 kg ha(-1) and an unfertilized control. Compared with initial soil tests, nitrate concentrations decreased and P concentrations increased after two manure or fertilizer applications and eight rain events over the two monitoring periods. The fertilizer sources of P and N produced 19% more dry weight and 21% larger N concentrations in grass clippings than manure sources. Yet, runoff volumes were similar between manure and fertilizer sources of P. Dissolved P concentration (30 mg L(-1)) in runoff during a rain event 3 d after application of 50 kg P ha(-1) was five times greater for fertilizer than for manure P. Observations during both monitoring periods indicated that total P and N losses in runoff were no greater for composted manure than for fertilizer sources of P at relatively large P rates on a steep slope of turfgrass.     

Runoff losses of sediment and phosphorus from no-till and cultivated soils receiving dairy manure

Managing manure in no-till systems is a water quality concern because surface application of manure can enrich runoff with dissolved phosphorus (P), and incorporation by tillage increases particulate P loss. This study compared runoff from well-drained and somewhat poorly drained soils under corn (Zea mays, L.) production that had been in no-till for more than 10 yr. Dairy cattle (Bos taurus L.) manure was broadcast into a fall planted cover crop before no-till corn planting or incorporated by chisel/disk tillage in the absence of a cover crop. Rainfall simulations (60 mm h(-1)) were performed after planting, mid-season, and post-harvest in 2007 and 2008. In both years and on both soils, no-till yielded significantly less sediment than did chisel/disking. Relative effects of tillage on runoff and P loss differed with soil. On the well-drained soil, runoff depths from no-till were much lower than with chisel/disking, producing significantly lower total P loads (22-50% less). On the somewhat poorly drained soil, there was little to no reduction in runoff depth with no-till, and total P loads were significantly greater than with chisel/disking (40-47% greater). Particulate P losses outweighed dissolved P losses as the major concern on the well-drained soil, whereas dissolved P from surface applied manure was more important on the somewhat poorly drained soil. This study confirms the benefit of no-till to erosion and total P runoff control on well-drained soils but highlights trade-offs in no-till management on somewhat poorly drained soils where the absence of manure incorporation can exacerbate total P losses.     

Effects of a waste paper product on soil phosphorus, carbon, and bulk density

Applications of manures to agricultural fields have increased soil test values for P to high levels in parts of the USA and thus increased the likelihood that P will be transported to surface water and degrade its quality. Waste paper applications to soils with high STP (soil test P) may decrease the risk of P transport to surface water by decreasing DRP (dissolved reactive P) by the formation of insoluble Al-P complexes and providing organic matter to improve infiltration. A field experiment was conducted near Booneville, AR (USA) to assess the effects of different rates of a waste paper product addition on STP, soil bulk density, and total soil C with a soil with approximately 45 mg Bray1-P kg-1 soil (dry weight). A Leadvale silt loam soil (fine-silty, siliceous, thermic Typic Fragiudult) was amended with 0, 22, 44, or 88 Mg waste paper product ha-1 to supply approximately 90, 170, or 350 kg Al ha-1, respectively. One year after additions, there was a strong negative correlation between waste paper product application rates and soil bulk density, and a strong positive correlation between rates and total soil C content. Soil bulk density and total C 2 yr after additions, and soil DRP and Bray1-P were not affected by waste paper additions. These results support the hypothesis that decreases in DRP in runoff from soils receiving waste paper additions were probably due to changes in soil organic matter and bulk density, rather than changes in the chemical forms of soil P.     

Distribution of phosphorus in manure slurry and its infiltration after application to soils

Computer models help identify agricultural areas where P transport potential is high, but commonly used models do not simulate surface application of manures and P transport from manures to runoff. As part of an effort to model such P transport, we conducted manure slurry separation and soil infiltration experiments to determine how much slurry P infiltrates into soil after application but before rain, thus becoming less available to runoff. We applied dairy and swine slurry to soil columns and after both 24 and 96 h analyzed solids remaining on the soil surface for dry matter, total phosphorus (TP), and water-extractable inorganic (WEIP) and organic (WEOP) phosphorus. We analyzed underlying soils for Mehlich-3 and water-extractable P. We also conducted slurry separation experiments by sieving, centrifuging, and suction-filtering to determine which method could easily estimate slurry P infiltration into soils. About 20% of slurry solids and 40 to 65% of slurry TP and WEIP infiltrated into soil after application, rendering this P less available to transport in runoff. Slurry separation by suction-filtering through a screen with 0.75-mm-diameter openings was the best method to estimate this slurry P infiltration. Measured quantities of manure WEOP changed too much during experiments to estimate WEOP infiltration into soil or what separation method can approximate infiltration. Applying slurries to soils always increased soil P in the top 0 to 1 cm of soil, frequently in the 1- to 2-cm depth of soil, but rarely below 2 cm. Future research should use soils with coarser texture or large macropores, and slurry with low dry matter content (1-2%).