Dissolved phosphorus concentrations in runoff from ...

Dissolved phosphorus concentrations in runoff from simulated rainfall on corn and soybean tillage systems G.F. Mclsaac, J.K. Mitchell, and M.C. Hirschi

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unoff and soil erosion from rowropped land can lead to loss of soil productivity and reductions in surface water quality. Colacicco and associates (Colacicco et al.) estimated that the economic costs of water quality degradation are greater than the productivity losses on a regional scale. Sediment and nutrients in runoff from agriculture are considered leading causes of surface water quality impairment in the United States (USEPA). In Illinois, 93% of the lakes assessed for trophic status were classified as eutrophic or hypereutrophic. Numerous studies have demonstrated that soil erosion and sediment yield from cropland can be reduced by employing conservation tillage, which maintains residue cover on the soil surface (Laflen et al.). Much of the total nitrogen and phosphorus eroded from soil is bound to sediment. Thus, reducing soil erosion generally reduces transport of total nitrogen and phosphorus from a hill slope. However, much of the soil eroded from a hill slope is deposited within the field of origin and never enters a permanent water body. Although soluble nitrogen and phosphorus dissolved in runoff often represents only a small fraction of the total N and P eroded from upland soils, these dissolved chemicals are not subject to deposition and, fur~~

G.F. McIsaac, J.K. Mitchell, and M C. Hirschidre senior research specialist, professor, and associate professor respectively in the Department of Agricultural Engineering at the University of Illinois at Urbana-Champaign. J. Soil nnd Water Cons. 50(4)383-387

thermore, may be more readily available biologically than the sediment bound N and I? Sharpley and associates (Sharpley et al.) reported greater concentrations and loads of bioavailable phosphorus in runoff from no-till wheat production than from conventionally tilled wheat in Oklahoma watersheds. Other studies have demonstrated that concentrations of dissolved chemicals in runoff are greater from notill than from other tillage treatments (Baker and Laflen 1983a,b; Laflen and Tabatabai; McDowell and McGregor; Mostaghimi et al.; Romkens et al.). Concentrations of total phosphorus in excess of 0.05 mg-P/L are believed to degrade water quality of lakes and reservoirs, primarily by promoting eutrophication of surface water bodies when phosphorus is the limiting ingredient for algal growth (Alberts and Spomer; Illinois EPA). Alberts and Spomer reported concentrations of 0.8 and 0.17 mg-P/L dissolved phosphorus in runoff from watersheds under a till-plant (ridge-till) and conventional tillage systems, respectively. Thus, the effects of conservation tillage on concentrations of nutrients in runoff are not always favorable for surface water quality. The objective of this paper is to compare dissolved phosphorus in runoff from alternative tillage systems on two soils in Illinois.

Methods Rainfall simulation experiments were conducted on a Catlin silt loam soil (Fine-silty, mixed mesic, Typic Argiudolls) in east central Illinois, with slopes ranging

J U L Y - A U G U S T 1995

383

Copyright © 1995 Soil and Water Conservation Society. All rights reserved. Journal of Soil and Water Conservation 50(4):383-388 www.swcs.org

ABSTRACT: Dissolved phosphorus was measured in runofffiom simulated rainfill applied to two soih and several tillage treatments used in an annual crop rotation of corn (zea mays L.) and soybeans [Glycine max (L.)]. The average concentration and load of soluble P in the runoff were significantly greater fiom the no-till than fiom other tillage treatments. Only moldboard plowing afer ru face broadcasting of Pfertilizer reduced the soluble P concentration below 0.05 mg-P/L, a concentration of total P believed to promote eutrophication. For the Catlin soil, a variety of tillage practices (disk, field cultivation, and str$-till) appeared to result in soluble P concentrations of approximately 0.14 mg-P/L. For the Tama soil, disk-barrowfollowed by Jield cultivation and harrow afer fertilizer application appeared to reduce soluble P concentration in the runoff to approximately 0.06 mg-P/L. These results concur with other results reported in the literature which suggest that dissolved P concentrations in runofffiom reduced tillage systems (particularly no-till) may be problematicfor water quality iffertilizer P is su face applied

from 1.5 to 4%, and a Tama silt loam soil (Fine-silty, mixed mesic, Typic Argiudolls) in northwestern Illinois, with slopes ranging from 6 to 13%. Both soils consisted of approximately 7 0 % silt, while the Tama soil tended t o have more clay (23%) than the Catlin (18%). Tillage systems evaluated in this study included no-till, ridge-till, strip-till, fall moldboard, chisel, and sweep plow treatments and are described in detail in Table 1 and other publications (McIsaac et al. 1987, 1991a, b; McIsaac and Mitchell). Rainfall simulations were conducted 0 to 10 days afier planting and 30 to 40 days after planting corn or soybeans in a cornsoybean rotation. The sequence of rainfall simulation experiments are summarized in Table 2. The rainfall simulation studies were initiated in 1982 on the Catlin soil, when corn was planted and continued in 1983 with soybeans planted. In those two years, the conventional, subsoil ridge, and no-till treatments were evaluated on the contour and up-and-down slope, and the disk and sweep plow treatment were evaluated on the contour only. ( T h e conventional tillage system involved moldboard plowing after corn and chisel plowing after soybeans.) In 1984 and 1985, rainfall simulations were conducted on the Tama soil to evaluate the moldboard, chisel, strip-till, and no-till oriented up-anddown slope and on the contour. In 1986 and 1987, rainfall simulations were again conducted on the Catlin soil to evaluate the conventional, ridge-till, strip-till, and the strip-till with ridge treatments with four replicate plots of each treatment oriented on the contour and up-and-down slope. Additionally, in 1986, the disk and no-till treatments were evaluated on the contour and the sub-soil ridge treatment was evaluated up-and-down slope. For the Catlin soil, 33 kg-P/ha (29 lb/ac) was applied in granular form to the soil surface in the fall afier fall tillage, except in the final year of the experiments (1987), when fertilizer was applied before moldboard plowing. For the Tama soil, 50 kg-P/ha (45 Ib/ac) was applied in granular form in the spring of 1984, three weeks prior to tillage and planting soybeans. P-fertilizer was not applied in 1985 on the Tama soil when corn was planted. For both soils, approximately 210 kgN/ha (188 Ib/ac) was injected into the soil as anhydrous ammonia in the spring prior to planting corn. Simulated rainfall was applied at a rate of 64 mm/hr (2.5 in/hr) using a rotating boom rainfall simulator as described by Swanson. For each tillage treatment, row

Results The effects of contouring on dissolved P concentrations were not great and rarely 384

Table 1. Tillage systems evaluated in the rainfall simulation experiments Tillage treatments evaluated on both the Catlin and Tama soils: No-tiI I :

Corn and soybeans were planted without pre-plant tillage and the only other soil disturbance was that caused by injecting anhydrous ammonia in the spring prior to planting corn.

Strip-till:

The Bushog Ro-till' unit, which uses fluted coulters, an 18 cm (7 in) deep chisel, and a rolling basket was pulled ahead of the planter, to place the seed into the chisel mark.

Tillage treatments evaluated on the Catlin soil only Conventional:

After soybean harvest, the land was chisel plowed approximately 24.5 cm (9.6 in) deep in the fall. In the spring, the soil surface was leveled by disking 10 to 12 cm (4-4.7 in) deep, and then the seedbed was prepared and herbicides incorporated by disking and field cultivating before planting corn. One month after planting, the crop was row cultivated with a sweep type cultivator. After harvesting corn, the soil was moldboard plowed and secondary tillage operations were the same as after soybeans except soybeans were planted.

Sweep plow:

Land was tilled with a sweep plow in the fall after crop harvest. The sweep plow had subsoiler shanks on a V-frame unit with 70 cm (27 in) sweeps attached to the bottom of the shank and was operated about 25 cm (10 in) deep. Secondary tillage in the spring was identical to the Conventional treatment.

Subsoil-ridge:

Corn stalks were shredded after corn harvest, and the land was subsoiled 30 cm (12 in) deep and ridged in the fall with a John Deere Subsoiler-Bedder.' In the spring, a rolling cultivator was used to reshape the ridges and to incorporate herbicides prior to planting.

Disk:

The land was disked 10 to 12 cm (4-4.7 in) deep in the fall after corn harvest. Secondary tillage operations were identical to the Conventional, except that the first spring disking operation was omitted.

Ridge-till:

Corn or soybeans were planted into ridges formed the previous year by row cultivating and reforming the ridges with a rolling cultivator one month after planting.

Strip-till with ridges

Strip-till treatment described above with ridges formed with a rolling cultivator one month after planting.

Tillage treatments evaluated on the Tama soil only Moldboard:

The soil was moldboard plowed in the fall, disked and field cultivated in the spring prior to planting. When the previous crop was soybeans, the spring disking was omitted and a second field cultivation was performed.

ChiseI:

Identicalto moldboard treatment except chisel plowing was substituted for moldboard plowing.

~~~

~~~

_ ~ _

~~

__

~~~~~~~~

' Use of trade names is for the purpose of identification only and does not imply endorsement of this product.

statistically significant for any tillage treatment, and for the sake of brevity, the average concentrations of the two row orientations will be presented. Furthermore, the effect of runoff sampling time (i.e., whether the sample was taken a few minutes after runoff was initiated or after steady runoff rate was observed) was not statistically significant a n d thus flow weighted mean concentrations were used to represent the concentrations of dissolved P in runoff from the tillage systems. T h e flow weighted mean concentrations of dissolved phosphorus in the runoff from the no-till treatment were statistically greater than all other treatments at the 0.05 level of significance for both

JOURNAL O F SOIL A N D WATER CONSERVATION

soils, when averaged across all growing seasons and crop stages and variations across year and crop stage were accounted for by other terms in the analysis of variance model (Table 3). For the Catlin soil, the mean dissolved P concentration in r u n o f f f r o m m o s t tillage t r e a t m e n t s ranged from 0.1 to 0.2 mg-P/L and were significantly less than from the no-till but greater than from the conventional treatment (0.01 mg-P/L) when fertilizer was applied prior to moldboard plowing. For the Tama soil, soluble P concentration from the strip-till system was 0.23 mgP/L, which was significantly greater than from the moldboard a n d chisel plow treatments, but less than the no-till. For


orientation, crop and crop stage, and rainfall simulation experiments were conducted on at least two replicate plots 3 m wide by 11 m long (10 ft by 36 ft). For most tillage treatments, there were four or more replicate plots for each rainfall simulation event. The initial simulated rain storm, event 1, was conducted for 1 hour. A natural rainfall of this intensity and duration is expected to recur once every 20 to 25 years on average in central Illinois. At the end of the plot, a triangular sheet metal form was installed to concentrate the runoff into a 15 cm (6 in) wide opening, where the runoff rate was measured with a calibrated bucket and a stop watch. Furthermore, runoff samples were collected at this outflow point with 0.5 liter (0.13 gal) wide mouthed bottles. These samples were analyzed to determine phosphorus and sediment concentrations in the runoff. For most plots, a 0.5 liter runoff sample for phosphorus analysis was taken a few minutes after the initiation of runoff, and a second sample bottle was taken after the runoff rate appeared to be steady. In some cases more samples were taken, and in a few cases only one sample was available for analysis. Runoff samples were stored at 3 ° C (37.4"F) for several weeks until chemical analyses could be conducted. At that time, each sample bottle was mixed in order to obtain a representative sub-sample. T h e sub-samples were then centrifuged to separate the sediment from the solution. The solution was analyzed for dissolved P using a Technicon Auto Analyzer (Greenberg et al.). Analysis of variance was used to determine whether tillage treatment, row orientation, year, crop stage, or runoff sampling time were statistically significant main effects on dissolved phosphorus concentration. Loads and flow weighted mean concentrations of dissolved phosphorus in the runoff generated from 60 minutes of rainfall were statistically compared across tillage treatments using the method of Least Significant Difference (SAS Institute). O n the Catlin soil in 1986, 0 to 10 days after planting, water quality samples were also collected from a second simulated rain event, event 2, which was initiated 60 minutes after the conclusion of run 1, and was maintained for a 30 minute duration. In addition to comparing concentrations across tillage treatments, these concentrations were also compared across rainfall simulation runs.

Tama Soil Dissolved P in Runoff, ppm P sovbeans, 1984 0.80

a

50 kg-P/ha applied

0.60

i

ab

0.40

corn, 1985 0 kg-P/ha applied

0.20

0.00

0-10 no-till

30-40 0-10 days after planting strip-till

IBzzl

=

moldboard

30-40 chisel plow

Figure 1. Flow weighted mean dissolved P concentrations in runoff from simulated rainfall on tillage systems on the Tama soil in two growing seasons (For a given crop and crop stage, bars with any identical letters are not statistically different at the 0.05 level of significance according to the method of Least Significant Difference.)

of clarity, only three key treatments are presented in Figure 2. The maximum observed dissolved P concentration in runoff from the no-till in the Catlin soil was 0.57 mg-P/L, which was somewhat less than the maximum observed for the Tama soil. T h e least concentration (0.01 mgP/L) was observed from the conventional tillage treatment in 1987, when P fertilizer had been applied just prior to moldboard plowing in the previous fall. In the second year of corn production o n the Catlin soil (1 986), there was little difference in P concentration in the runoff from the tillage systems. Furthermore, in the second year that soybeans were grown, the mean dissolved P concentration from the ridge till treatment was 0.25 mg-P/L (0.40 mg-P/L for the up-and-down slope treatment, 30-40 days after planting soybeans). T h e cause of these variations is unknown and may be related to environmental conditions that influence the rate of P mineralization. Flow weighted mean concentrations of dissolved P in runoff from a second simulated rainfall event conducted one hour

after the conclusion of the first event were statistically greater than from the first at the 0.01 level of significance for all treatments except for the no-till (Table 4). For the no-till, t h e concentrations in the runoff from the second rainfall event were greater at the 0.15 level of significance. These results suggest that antecedent rainfall and/or moisture conditions may have a large effect on soluble P concentrations in runoff over short periods of time. Interestingly, P concentration in the runoff from the no-till treatment was significantly greater than the strip-till with ridge treatment in run 1, but in run 2, the concentration from the strip-till with ridge treatment was significantly greater than from the no-till and the ridge till treatments. A similar phenomenon of increasing soluble phosphorus from a second rainfall event on wet soil has been observed in some settings at lesser concentrations of P (Baker and Laflen 1983a; Brasias et al.) and has not been observed in some other settings (Brasias et al.; Flanagan and Foster). Baker and Laflen suggested that the JULY-AUGUST 1395

385


the moldboard and chisel treatments, the use of the disk-harrow followed by field cultivation with harrow after fertilizer application appeared to effectively incorporate the fertilizer P into the soil and thereby reduce soluble P concentration to approximately 0.06 mg-P/L. The greater concentrations of dissolved P led to statistically greater loads of dissolved P in the runoff from the up-anddown slope no-till treatments than all other treatments except the subsoil-ridge on the Catlin soil (Table 3). Concentrations of dissolved P in the runoff from the subsoil-ridge treatment also tended to be greater than other tillage treatments tested up-and-down slope and hence loads were somewhat greater than other treatments. For the strip-till on the Tama soil, runoff was considerably less than other treatments and therefore dissolved P loads were not significantly greater than other treatments in spite of the greater concentration o f dissolved P in t h e runoff. Runoff and dissolved P loads from the first 60 minutes of rainfall were generally significantly reduced by contouring by increasing detention storage. Once runoff had overtopped the contour tillage marks, contouring had little impact o n runoff. Generalizing results obtained from exact contours on small plots is difficult since in larger fields contours are rarely exact. Thus, these results are not presented here. There was considerable variation in dissolved P concentrations over time (Figures 1 and 2). For the Tama soil, the maximum observed concentration, 0.78 mgP/L, was from the no-till treatment in the first rainfall simulation experiment, which was conducted three weeks after P fertilizer had been applied to the soils (Figure 1). Phosphorus fertilizer was not applied in the following year (1985) and, consequently, phosphorus concentrations in the runoff from the no-till treatment decreased dramatically over the course of the two growing seasons. Furthermore, there was little difference in P concentration among tillage treatments in 1985. Phosphorus concentration from the strip-till treatment was initially less than from the no-till treatment but greater than the moldboard and chisel plow treatments, probably because the strip-till incorporated a portion of the fertilizer into the soil. However, after the initial rainfall simulation event, the concentrations from the no-till and the strip-till were not statistically different. There was also considerable temporal variation in P concentrations in runoff from the Catlin soil, where P fertilizer was applied each fall (Figure 2). For the sake

Catlin Soil

of other events or long term average runoff water quality (McIsaac a n d Mitchell). Thus, continuous and longterm monitoring and/or modeling of water quality in runoff is necessary to assess the consequences of various land use practices.

Dissolved P in Runoff, ppm P 0.80

sovbeans, 1983

0.60

Discussion

a

The mean concentrations of dissolved

P in the runoff from the no-till for the

a 0.40

corn, 1982 soybeans, 1987

0.20

0-10

30-40 0-10

30-40 0-10

30-40

0-10 30-40

days after planting no-till

conventional

ridge-till

m

Figure 2. Flow weighted mean dissolved P concentrations in runoff from simulated rainfall on tillage systems on the Catlin soil in four growing seasons (For a given crop and crop stage, bars with any identical letters are not statistically different at the 0.05 level of significance according to the method of Least Significant Difference.)

phenomenon may be due to P mineralization. Romkens and Nelson observed increasing concentrations of P during a 1hour simulated rainstorm which they attributed to dissolution of recently app 1i e d fe r ti 1i z e r. Add i t i o n ally, w h e n Romkens and Nelson repeated the simulated rainfall experiment several months after the fertilizer had been applied, dissolved P concentrations again increased over the course of the I-hour storm, but to a lesser degree than was observed immediately after fertilizer application. Considering the rapidity with which algal blooms can occur and their long term consequences, such temporal variations in dissolved P concentration may be of great importance to surface water quality in agricultural watersheds. This temporal variability indicates a need for understanding the dynamics of phosphorus release from soils if agricultural land is to be managed for water quality considerations. Furthermore, it is important to recognize that runoff from a single rainfall event may not be representative 386

Table 2. Sequence of rainfall simulation experiments conducted 0-10 and 30 to 40 days after planting

Year

Soil

Crop Planted

Tillage Treatments

Row Orientation -

~~~~

_

_

~ _ ~_

1

conventional subsoil-ridge no-till disk sweep plow

Contour and UD* Contour and UD Contour and UD Contour Contour

1

moldboard plow chisel plow strip-till no-till

Contour and UD Contour and UD Contour and UD Contour and UD

1982 1983

Catlin Catlin

1984 1985

Tama Tama

soybeans corn

1986

Catlin

corn

conventional no-till disk subsoil-ridge ridge-till strip-till strip-till whidges

Contour and UD Contour Contour UD Contour and UD Contour and UD Contour and UD

1987

Catlin

soybeans

conventional ridge-till strip-till strip-till whidges

Contour and UD Contour and UD Contour and UD Contour and UD

~~

* UD = Up-and-down slope.

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corn soybeans


0.00

Catlin and the Tama soils, 0.33 and 0.34 mg P/L, respectively, were similar to results reported by McDowell and McGregor for annual average concentrations in runoff from no-till under natural rainfall. Furthermore, the results reported in this paper also concur with other studies (Alberts and Spomer; Baker and Laflen 1983a,b; Brasias et al.; Mostaghimi et al.; Romkens e t al.; Sharpley et al.) which indicate that dissolved P concentrations in runoff from no-till and ridgetill systems may be problematic for surface water quality. Studies by Baker and Laflen and Mostaghimi et al. indicate that soluble P concentrations and losses from row-cropped land under no-till or ridge-till management may be reduced by subsurface placement of fertilizer. However, these studies simulated subsurface placement of fertilizer by the injection of a solution using means other than standard commercial fertilizer applicat i o n methods. A l t h o u g h subsurface placement of fertilizer may be more costly than surface broadcasting (Mengel et

Table 3. Mean flow weighted concentration and load of dissolved phosphorus in runoff from 64 mm (2.5 in) of simulated rainfall for several different tillage treatments on silt loam soils in Illinois. Concentrations are mean values from plots oriented on the contour and up-and-down slope, while loads were calculated from the up-and-down slope plots only. Variations across year and crop stage were accounted for by other terms in the analysis of variance model

Dissolved P concentration

Tillage treatment __

~~~

Up-and-downslope dissolved P load n

n

~

~

(mg-P/L)

-

~~~

(g/ha)

0.33 a* 0.18 b 0.11 c 0.10 c 0.18 b 0.19 b 0.20 b 0.15 bc 0.01 d

40 32 32 32 22 14 32 40 16

61 ab 59 b 3c

18 18 8

-Tama silt loam soil-No-till Strip-till Chisel plow Moldboard plow

0.34 a 0.23 b 0.05 c 0.07 c

64 63 64 64

86 a 9b 16b 15b

32 31 32 32

94 a 47 b 41 c 38 bc

10 16 16 16

t t

t t

__

~~~

* For a given soil type, values within a column followed by any identical letters are not statistically different at the 5% level of significance according to the method of Least Significant

Difference. The moldboard plow treatment for the Catlin soil refers to the one year (1987) of the conventional-tillagetreatment as described in Table 1 where fertilizer P was applied prior to moldboard plowing. t Due to space limitations, there were no up-and-down slope plots for these treatments, and thus no data collected. n = number of observations +

Table 4. Dissolved phosphorus concentrations from the first and second simulated rainfall events on the Catlin silt loam soil 0 to 10 days after corn was planted in 1986 following a year of soybean production

Elage treatment +atlin silt loam soilNo-till Ridge-till Strip-till Strip-till w/ridge Disk Subsoil ridge Conventional ~~

~-

Dissolved P concentration event 2 event 1 __ (mg-P/L)--

PA t

n

0.18 a* 0.12 ab 0.17 ab 0.08 b 0.08 ab 0.11 ab 0.12 ab

0.15 0.0003 0.009 0.0001 0.01 0.001 0.006

8 8 8 8 4 8 8

0.26 c 0.46 b 0.38 bc 0.61 a 0.50 ab 0.52 ab 0.40 bc

~~

* For a given rainfall simulator event, values within a column followed by any identical letters

are not statistically different at the 5% level of significance according to the method of Least Significant Difference. + Probabilitythat differences in concentrations between the two rainfall simulator runs are the result of random sampling variation. n = number of observations

al.), it may be a cost-effective means of controlling dissolved P concentrations in runoff from conservation tillage systems. Chinchester and Morrison evaluated several techniques for subsurface placement of fertilizer for sorghum. The fate of the dissolved P in runoff from agricultural fields is likely to depend upon the hydrologic context of each particular field in question. Dissolved P may be absorbed by vegetation or soils in buffer strips, wetlands, riparian zones, or

in stream banks. Whether elevated levels of dissolved P in runoff represent a problem in a watershed depends upon these processes, Furthermore, dissolved P losses also need to be considered in the context of the water quality consequences of sediment and adsorbed chemicals. Runoff, soil erosion, and adsorbed N and P losses for the experimental conditions presented in this paper have been reported by McIsaac et al. 1987, 1991a,b; McIsaac and Mitchell).

Simulated rainfall was applied to two soils and several tillage treatments in a corn soybean rotation. Dissolved phosphorus concentration and loads in the runoff were measured. The average concentration of dissolved P in the runoff was significantly greater for the no-till than for other tillage treatments tested and the average load of dissolved P in runoff from no-till was significantly greater than all treatments except the subsoil-ridge treatment. Only moldboard plowing after surface broadcasting of P fertilizer reduced the soluble P concentration below 0.05 mg-PIL, a concentration of total P believed to promote eutrophication. For the Catlin soil, a variety of tillage practices (disk, field cultivation, and strip-till) appeared to result in soluble P concentrations of approximately 0.14 mg-P/L. For the Tama soil, disk-harrow followed by field cultivation and harrow after fertilizer application appeared to reduce soluble P concentration in the runoff to approximately 0.06 mg-P/L. In one growing season, for all tillage treatments, soluble P concentrations were greater in runoff from a second rainfall simulation event initiated 1 hour after the conclusion of the first event. This result suggests an effect of antecedent rainfall and/or soil moisture that may cause a high degree of temporal variability in the dissolved P concentrations in runoff. Temporal variability in P concentrations in runoff may have important water quality consequences that should be considered when monitoring, modeling, and assessing the water quality consequences of land management practices. Additional research is recommended to identie the factors that cause the temporal variability in phosphorus release from soils as well as in understanding and quantifjring the fate and consequences of dissolved P on the watershed scale. REFERENCES CITED Alberts, E.E., and R.G. Spomer. 1985. Dissolved nitrogen and phosphorus in runoff from watersheds in conservation and conventional tillage. J o u r n a l of Soil a n d W a t e r Conservation 40(1):153-157. Baker, J.L., and J. M. Laflen. 1983. Runoff losses of nutrients and soil from ground fall-fertilized after soybean harvest. Transactions of the ASAE 1122-1 127. Baker, J.L., and J. M. Laflen. 1983. Water quality consequences of conservation tillage. Journal of Soil and Water Conservation 38(3):186-193. Brasias, S.G., J.L. Baker, H.P. Johnson, and J.M. Laflen. 1978. Effect of tillage system on runoff losses of nutrients, a rainfall simulation study. Transactions of the ASAE 21:893-897. Colacicco, D., T. Osborn, and K. Alt. 1989. Economic damages from soil erosion. Journal of Soil and Water Conservation 44( 1):35-39. JULY-AUGUST 1995

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Catlin silt loam soilNo-till Ridge-till Strip-till Strip-till w/ridge Sweep plow Disk Subsoil ridge Conventional Moldboard plow

Summary and conclusions

388

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Chinchester, F.W., and J.E. Morrison. 1992. Agronomic evaluation of fertilizer placement methods for no-tillage sorghum in vertisol clays. Journal of Production Agriculture 5(3):378-382. Flanagan, D.C., and G.R. Foster. 1989. Storm pattern effect on nitrogen and phosphorus losses in surface runoff. Transactions of the ASAE 32(2):535-544. Greenberg, A.E., R.R. Trussell, and L.S. Clesceri. 1985. Standard Methods for the Examination of Water and Wastewater 16th Edition. American Public Health Association, Washington, D.C. Illinois Environmental Protection Agency. 1992. Illinois Water Quality Report. Bureau of Water, 2200 Churchill Road, Springfield, Illinois. Laflen, J.M., W.C. Moldenhauer, and T.S. Colvin. 198 1. Conservation tillage and soil erosion on continuously row cropped land. In: Crop Production with Conservation in the 80s. ASAE Pub1 7-8 1. St. Joesph, Michigan. Laflen, J.M., and M. Tabatabai. 1984. Nitrogen and phosphorus losses from corn-soybean rotations as affected by tillage practices. Transactions of the ASAE 27( 1):58-63. McDowell, L.L., and K.C. McGregor. 1984. Plant nutrient losses from conservation tilled corn. Soil and Tillage Research 479-9 1. McIsaac, G.F., M.C. Hirschi, and J.K. Mitchell. 1991. Nitrogen and phosphorus in eroded sediment from corn and soybean tillage systems. Journal of Environmental Quality 20(3):663-670. McIsaac, G.F., and J.K. Mitchell. 1992. Temporal Variation in Runoff and Soil Loss from Simulated Rainfall on Corn and Soybeans. Transactions of the American Society of Agricultural Engineers 3 5(2):465-472. McIsaac, G.F., J.K. Mitchell, M.C. Hirschi, and L.K. Ewing. 1991. Contour and Conservation Tillage Systems for Corn and Soybeans in the Tama Silt Loam Soil: T h e Hydrologic Response. Soil and Tillage Research 19(1):29-46. McIsaac, G.F., J.K. Mitchell, J.C. Siemens, and J.W. Hummel. 1987. Row Cultivation Effects on Runoff, Soil Loss and Corn Grain Yield. Transactions of the American Society of Agricultural Engineers 30 ( 1): 12 5- 12 8,136. Mengel, D.B., J.F. Moncrief, E.E. Schulte. 1992. Fertilizer Management. In: Conservation Tillage Systems and Management. Midwest Plan Service, Ames, Iowa. pp 83-87. Mostaghimi, S., J.M. Flagg, T. Dillaha, and V.O. Shanholz. 1988. Phosphorus losses from cropland as affected by tillage system and fertilizer application method. Water Resources Bulletin 24(4):735-742. Romkens, M.J.M., and D.W. Nelson. 1974. Phosphorus relationships in runoff from fertilized soils. Journal of Environmental Quality 3( 1):10- 13. Romkens, M.J.M., D.W. Nelson, and J.V. Mannering. 1973. Nitrogen and phosphorus composition of surface runoff as affected by tillage method. Journal of Environmental Quality 2 (2):292-29 5 , SAS Institute, Inc. 1985. SAS@ User’s Guide: Statistics, Version 5 Edition. Cary, North Carolina. Sharpley, A.N., S.J. Smith, O.R. Jones, W.A. Berg, and G.A. Coleman. 1992. T h e transport of bioavailable phosphorus in agricultural runoff. Journal of Environmental Quality 2 130-35. Swanson, N. 1965. Rotating-boom rainfall simulator. Transactions of the American Society of Agricultural Engineers 8(1): 71-72. U.S. Environmental Protection Agency. 1992. National Water Quality Inventory 1990 Report to Congress. USEPA, Washington, D.C. 214 p.