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TECHNICAL REPORT
Surface Water Quality

Effects of Tillage and Phosphorus Placement on Phosphorus Runoff Losses in a Grain Sorghum–Soybean Rotation

^a Dep. of Agronomy, 2004 Throckmorton Plant Science Center, Kansas State Univ., Manhattan, KS 66506
^b Dep. of Biological and Agricultural Engineering, Kansas State Univ., Manhattan, KS 66506

* Corresponding author (gmp{at}ksu.edu)

Received for publication April 21, 2000.

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
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.) Moench]–soybean [Glycine max (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.

Abbreviations: BMP, best management practice • ChT, chisel-till • NT, no-till • RT, ridge-till • TMDL, total maximum daily load

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
AGRICULTURE has been identified as the major source of nutrients in many rivers and lakes that have been impaired by eutrophication, and P is considered the nutrient that limits algal growth in these waters (Parry, 1998; Sharpley et al., 1994). Many factors, including runoff volume, sediment loss, concentration and forms of P found on soil exchange sites, and the depth of mixing of the soil and the runoff water, can affect the loss of P in runoff water (Sharpley et al., 1994).

Some researchers have found that conservation tillage systems reduce runoff volume compared with more intensive tillage systems using a moldboard plow (Blevins et al., 1990; Seta et al., 1993). Other researchers have found that conservation tillage systems increase runoff volume compared with conventional tillage (Lindstrom and Onstad, 1984; Gaynor and Findlay, 1995). These conflicting results may be due to differences in rainfall amounts and intensities, slope, antecedent moisture content, and infiltration rates.

Soil erosion can influence total P losses in runoff. Siemens and Oschwald (1976) reported that most of the P leaving a field is in the form of sediment-bound P. Andraski et al. (1985) reported that conventional-till had greater sediment loss than both chisel-till and no-till.

The placement of P fertilizer also affects the amount of P loss. Mueller et al. (1984) reported greater total P loss in no-till compared with chisel-till plots when manure was incorporated into the soil with a chisel.

Barisas et al. (1978) reported greater soluble P loss in reduced tillage systems and attributed it to leaching of nutrients from plant residue and decreased fertilizer incorporation. Others have reported mixed effects of tillage treatment on soluble P loss. Seta et al. (1993) found greater soluble P loss from conventional-till compared with no-till, but no significant difference in soluble P losses between chisel-till and no-till.

Regulatory pressure to reduce the amount of P lost through runoff from agricultural land is increasing. In the study reported here, concerns for eutrophication in the Hillsdale reservoir in east-central Kansas and proposed total maximum daily P loads (TMDLs) served as partial justification for this research. As TMDLs are developed, the relative contribution of P loads from point and nonpoint sources must be ascertained. For reduction of nonpoint P sources, best management practices (BMPs) can be employed, but the implementation of these practices can be costly. Therefore, careful selection of BMPs based on soil and site characteristics is essential to produce the desired outcome and to ensure effective use of resources. For the watershed in question, soils having relatively low slopes that generate considerable runoff because of restricted internal drainage are common.

The studies discussed above present contradictory evidence on the effect of conservation tillage on P loss. However, they were conducted with a single fertilizer application method and a single crop. In addition, few of the studies have evaluated ridge-till systems. Information is lacking concerning the effects of various conservation tillage and P placement methods in a two-crop rotation on the loss of P in runoff water. Further, little data are available on runoff composition from soils with restricted internal drainage. The objective of this study was to evaluate the influence of tillage and P placement and rate on soluble, bioavailable, and total P losses from a grain sorghum–soybean rotation.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
This study was conducted in 1998 and 1999 at the East Central Experiment Field near Ottawa, KS on a soil that has been in a grain sorghum–soybean rotation since 1994. Separate blocks of grain sorghum and soybean were grown each year. The soil was mapped as a Woodson silt loam with 1.0 to 1.5% slope that was uniform across the experimental area. This soil is poorly drained because of the low permeability of the B horizon and is representative of the prime production land in east-central Kansas. Considerable runoff can be generated from this soil despite the relatively low slope because of restricted internal drainage.

Three conservation tillage systems common to east-central Kansas were used, chisel-till (ChT), ridge-till (RT), and no-till (NT). Chisel-till consisted of a chisel operation in the fall or early spring and disking and field cultivating in the spring to produce a suitable seedbed. Ridge-till ridges were formed in the fall. The seeder planted on top of the ridges and moved approximately 2.5 cm of soil and residue from the tops to the furrows. No-till left all crop residue on the surface except for a small portion that was disturbed during planting. The soybeans and grain sorghum were planted in rows on 76-cm centers. The soybean variety used in 1998 was KS4694 (Kansas Agricultural Experiment Station, Manhattan, KS) and in 1999 Dyna-Gro 3388RR (UAP Seeds, Garden City, KS) was used. The sorghum hybrid both years was 8500 (Pioneer Hi-Bred Int., Johnston, IA).

Phosphorus treatments were applied in the spring and applied only prior to planting of the grain sorghum crop: (i) 24 kg P ha^-1 knifed into the soil approximately 10 cm deep on 38-cm centers, (ii) 24 kg P ha^-1 surface-broadcast, and (iii) no P applied (check). Phosphorus was applied as a liquid product containing 70 g N kg^-1, 95 g P kg^-1, and 58 g K kg^-1. Nitrogen was balanced at 112 kg ha^-1 across all treatments using liquid ammonium nitrate solution containing 280 g N kg^-1. Phosphorus was knifed into the soil in all tillage treatment combinations where subsurface application of P was required (ChT-knife, RT-knife, and NT-knife). Surface broadcast P under chisel tillage was incorporated prior to planting. The tillage and P treatments have been in place since 1994.

Runoff from grain sorghum was collected from 4.65-m² areas demarcated with metal frames inserted approximately 8 cm deep into the ground. Runoff from soybean plots was collected from 58-m² areas demarcated with soil berms. In the soybean plots, sheet metal was placed on the downhill end of the plot to direct water to the collection point. Runoff water from both areas was directed to sump pumps by 10-cm-diameter PVC pipe. Runoff was then pumped through flow splitters set in the field. The splitters collected a portion of the runoff water and stored it in polyurethane containers until the rainfall event ended. Then water was collected from the containers and stored at 5°C in glass jars until analysis. Splitters were calibrated before they were removed from the field to determine the percentage of water collected from each event.

Runoff was collected from at least one runoff event prior to fertilizer application and planting in the grain sorghum plots. Collection equipment was placed in the sorghum plots on 18 May 1998 and 26 May 1999, and the splitters were calibrated. Prior to planting the grain sorghum, the equipment was removed, and the treatments were applied. After planting, the splitters and frames were replaced in the field (6 July 1998 and 21 July 1999) and the splitters were calibrated again at the end of the season.

Because fertilizer was not applied on the soybean plots, the splitters were placed in the field only after planting. Placement dates were 26 June 1998 and 9 July 1999 (Blocks 1 and 2) and 13 July 1999 (Block 3). For these plots, only one calibration of the splitters was required and was performed at the end of the growing season prior to harvest. For both the sorghum and soybean plots, runoff was collected from three to five events after planting.

The greatest amount of rainfall and the most intense storms occur during the spring and summer months in eastern Kansas; therefore, most runoff occurs during the period of collection used in this study. The dates of rainfall and runoff collection are summarized in Table 1. Runoff water was analyzed for concentrations of sediment, bioavailable P, total P, and dissolved inorganic P (soluble P).

Bioavailable P was determined by a modification of the iron oxide, filter paper extraction method (Sharpley, 1993). Whatman (Maidstone, UK) No. 50, 5.5-cm-diameter filter papers were coated with iron oxide. Each then was placed in a SpectraMesh screen (Fisher Co., St. Louis, MO), which was placed in a 118-mL glass bottle along with 50 mL of unfiltered runoff water sample and 30 mL of deionized water (Myers et al., 1997). The bottle was shaken for 16 h on a reciprocating shaker at 125 excursions min^-1. The filter paper then was removed from the glass bottle, and the iron oxide coating was dissolved using 0.2 M H₂SO₄.

Total P concentration was determined by modification of the nitric–perchloric acid digestion method (Kuo, 1996). Five milliliters of unfiltered runoff water were digested with 2 mL of concentrated nitric acid for 30 min at 120°C. Three milliliters of concentrated percholoric acid was then added and the samples were heated at 200°C. Heating continued for 1 h after the appearance of white fumes.

Soluble P was determined by filtering runoff water through a 0.45-µm pore size filter and measuring the concentration of the P in the filtrate.

After all required digestion or extraction techniques, P concentrations were determined by the Murphy and Riley (1962) procedure on a Beckman DU 64 spectrophotometer (Beckman Instruments, Fullerton, CA).

The study design was a randomized complete block with split plots. Tillage was the main plot factor, and fertilizer application method was the subplot factor. Each combination of tillage and fertilizer application method was replicated three times. Runoff volume and sediment, total P, soluble P, and bioavailable P losses were summed over the collection period for each year.

Data were analyzed by using the PROC MIX procedure in Statistical Analysis System (SAS Institute, 1997). The PROC MIX procedure ensures the correct error terms are used with each comparison for the split-plot design. Tillage and P placement main effects are discussed when the tillage by P placement interaction was not significant and individual treatment means are discussed when the interaction is significant. Significant differences were determined at P 0.1 using LSMEANS.

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Runoff Volume and Sediment Losses
There was a significant main effect for tillage for runoff volume for the grain sorghum in 1998 and for soybean in 1999 (Table 2). There were no significant effects for P placement or for the tillage by P placement interaction. For grain sorghum in 1998, RT produced significantly higher runoff volume compared with ChT with runoff volume from RT and ChT not significantly different than NT (Table 4). Runoff volumes were significantly higher for RT and ChT compared with NT for soybeans in 1999.

There were no interaction effects between tillage and P placement on sediment loss or a P placement main effect on sediment loss in either the soybean or grain sorghum plots (Table 2). There was never a significant tillage main effect on sediment loss in grain sorghum and the only instance in which there was a tillage effect on sediment loss was for soybean in 1999. No-till soybean had significantly less sediment loss compared with either ChT or RT (Table 4).

McIsaac et al. (1987) and Blevins et al. (1990) also reported no significant differences in sediment loss between the tillage methods ChT and NT. Gaynor and Findlay (1995) found no differences in sediment loss between RT and NT. However, Shelton et al. (1983) and Seta et al. (1993) reported greater sediment loss in ChT compared with NT. The relatively low slope of the site used for this study probably reduced the chances of having consistent significant effects of tillage on sediment loss. The beneficial effects of residue on the soil surface would be minimized with a shallow slope and reduced kinetic energy of runoff water compared to soils with a steeper slope.

Soluble Phosphorus Losses
There were significant interaction effects between tillage and P rate and placement on soluble P loss in grain sorghum during 1998 and 1999 and in soybean in 1999 (Table 3). Individual treatment means and mean separations for comparisons across P placement method within a tillage method or for comparisons across tillage methods within a P placement method are illustrated in Fig. 1 to 3. Table 6 reports the F statistics to determine significant differences in soluble P loss between any treatment combinations.

View larger version (22K): [in this window] [in a new window]   Fig. 1. Seasonal soluble P loss in 1998 grain sorghum. Tillage designations are ChT for chisel-till, NT for no-till, and RT for ridge-till. Means with the same lowercase letter within a tillage method are not significantly different at P < 0.1. Means with the same uppercase letter within a P application method are not significantly different at P < 0.1.

View larger version (28K): [in this window] [in a new window]   Fig. 3. Seasonal soluble P loss in 1999 soybean. Tillage designations are ChT for chisel-till, NT for no-till, and RT for ridge-till. Means with the same lowercase letter within a tillage method are not significantly different at P < 0.1. Means with the same uppercase letter within a P application method are not significantly different at P < 0.1.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Seasonal soluble P loss in 1999 grain sorghum. Tillage designations are ChT for chisel-till, NT for no-till, and RT for ridge-till. Means with the same lowercase letter within a tillage method are not significantly different at P < 0.1. Means with the same uppercase letter within a P application method are not significantly different at P < 0.1.

These results indicate that broadcasting P onto NT or RT plots results in the greatest amount of soluble P loss. Mueller et al. (1984) and Barisas et al. (1978) reported similar results. Mueller et al. (1984) reported greater annual soluble P losses in no-till with manure surface-applied compared with chisel-tilled plots. Barisas et al. (1978) found greater soluble P loss with ridge-till compared with chisel-till with surface-applied fertilizer. Conversely, Seta et al. (1993) and Blevins et al. (1990) observed no difference in soluble P loss between chisel-till and no-till when P was surface-applied.

For soybean in 1999, soluble P losses are generally lower than those in 1998 (Table 3). The reason for this is not known but may be related to fewer runoff events in 1999 compared with 1998 and the fact that these events were late in the growing season (Table 1). Soluble P losses for RT-broadcast were greater than RT-knife or RT-check and losses for RT-knife were greater than RT-check in 1999 (Fig. 3). The NT-knife treatment had less soluble P loss compared with ChT-knife or RT-knife, and RT-broadcast had significantly more loss than ChT-broadcast or NT-broadcast. No significant differences in soluble P losses were found between tillage systems for the check treatments. The RT-broadcast treatment also had significantly higher soluble P loss compared with ChT-check, ChT-knifed, NT-check, and NT-knifed (Table 6).

There was no significant interaction between tillage and P placement on soluble P loss in 1998 soybean, but there were significant tillage and P placement main effects (Table 2). Ridge-till had significantly greater soluble P loss compared with ChT (Table 4), but there was no difference in soluble P loss between RT and NT or NT and ChT. Broadcast P had significantly higher soluble P losses compared with the check or knifed treatments (Table 5). The soybean data demonstrate that P fertilizer management can influence runoff composition more than one year after P applications.

View larger version (26K): [in this window] [in a new window]   Fig. 4. Seasonal bioavailable P loss in 1999 soybean. Tillage designations are ChT for chisel-till, NT for no-till, and RT for ridge-till. Means with the same lowercase letter within a tillage method are not significantly different at P < 0.1. Means with the same uppercase letter within a P application method are not significantly different at P < 0.1.

There are less data in the literature on bioavailable P losses and concentrations in surface runoff as compared with soluble or total P. Bioavailable P can also be estimated by a number of procedures. Grain sorghum 1999 results are similar to these reported by Mueller et al. (1984), who reported that NT had higher algae-available P losses compared with ChT when manure had been surface-applied.

Total Phosphorus Losses
There were no interaction effects between tillage and P rate and placement on total P loss in either soybean or grain sorghum throughout the study (Table 3). There was a significant P placement main effect in grain sorghum in 1998 and a tillage main effect in 1999 soybean.

For grain sorghum in 1998, broadcast P had a greater total P loss compared with the knifed or check P application methods (Table 5). There was not a significant difference in total P loss between the check or knife P. There were no tillage effects on total P loss in our study when fertilizer was applied but Andraski et al. (1985) reported greater total P loss in ChT compared with NT when P was subsurface-banded.

In the 1999 soybeans, ChT and RT had significantly greater total P loss compared with NT (Table 4). In contrast to our study, Mueller et al. (1984) reported greater total P loss in NT compared with ChT when no P was applied.

	SUMMARY AND CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
The primary objective of this study was to evaluate the influence of tillage and P placement and rate on soluble, bioavailable, and total P losses from a grain sorghum–soybean rotation on a poorly drained soil with restricted internal drainage. One possible application of the results would be to develop BMPs for the Hillsdale reservoir watershed.

The most pronounced effects of tillage were the interactions with P placement for soluble P and, to a lesser extent, with bioavailable P. The interaction was evident as higher soluble or bioavailable P with broadcast P placement on RT or NT compared with the remaining two P placement methods, with no such differences with ChT. Tillage had somewhat variable effects on runoff volume. For grain sorghum in 1998, runoff volume was highest for RT compared with ChT, and for soybeans in 1999 runoff volume for RT and ChT were similar and both significantly higher than NT.

It was somewhat unexpected that tillage did not have a larger effect on sediment loss and, by association, total P loss. The only significant effects were found with soybean in 1999 when there were only a few runoff events late in the growing season. This is probably due to the characteristics of the soil and site. With restricted internal drainage the soil generates considerable runoff despite a relatively low slope. However, the low slope also reduces the soil erosion potential and minimizes the influence of tillage practices on sediment losses. Since P TMDLs are based on total P loads, it would be difficult based on this study to recommend widespread adoption of reduced tillage practices on this soil, for the purpose of meeting a P TMDL.

In addition to the interaction with tillage noted above, there were significant P placement main effects. In each case, soluble, bioavailable, or total P losses were highest with broadcast P compared with either the knifed or check treatments. The knife placement puts the P in a small volume of soil compared with broadcast P placement, and places the P below the zone of interaction between the soil and surface runoff. The data do support the use of subsurface P placement as a BMP if P is used in crop production.

Overall, P losses were generally lower with soybean compared with grain sorghum because of more recent P fertilizer applications to grain sorghum. Some treatment effects were still evident, however, demonstrating that P fertilizer management can influence runoff composition for multiple years.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Contribution no. 00-358-J from the Kansas Agric. Exp. Stn.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 

• Andraski, B.J., D.H. Mueller, and T.C. Daniel. 1985. Phosphorus losses in runoff as affected by tillage. Soil Sci. Soc. Am. J. 49: 1523–1527.[Abstract/Free Full Text]
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• Gaynor, J.D., and W.I. Findlay. 1995. Soil and phosphorus loss from conservation and conventional tillage in corn production. J. Environ. Qual. 24:734–741.[Abstract/Free Full Text]
• Kuo, S. 1996. Phosphorus. p. 869–919. In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical methods. SSSA Book Ser. 5. SSSA, Madison, WI.
• Lindstrom, M.J., and C.A. Onstad. 1984. Influences of tillage systems on soil physical parameters and infiltration after planting. J. Soil Water Conserv. 39:149–152.
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• Myers, R.G., G.M. Pierzynski, and S.J. Thien. 1997. Iron oxide sink method for extracting soil phosphorus: Paper preparation and use. Soil Sci. Soc. Am. J. 61:1400–1407.[Abstract/Free Full Text]
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Kimmell, R.J. Articles by Barnes, P.L. Search for Related Content PubMed PubMed Citation Articles by Kimmell, R.J. Articles by Barnes, P.L. Agricola Articles by Kimmell, R.J. Articles by Barnes, P.L. Related Collections Water Quality Surface Water Quality Nutrient Management Water Pollution