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Crop residue effects on nitrogen yield in water and sediment runoff from two tillage systems
Agriculture, Ecosystems and Environment, 39 (1992) ! 87-196
187
Elsevier Science Publishers B.V., Amsterdam
Crop residue effects on nitrogen yield in water and sediment runoff from two tillage systems S. Mostaghimi, T.M. Younos and U.S. Tim Department of Agriculturai Engineering, Virginia Polytechniclnstituw and Staw Umversity. Blacksburg. VA 24061. USA (Accepted 14 November 1991 )
ABSTRACT Mostaghimi, S., Younos, T.M. and Tim, U.S., 1992. Crop residue effects on nitrogen yield in water and sediment runoff from two tillage systems. Agric. EcosystemsEnviron., 39:187-196. Simulated rainfall was used on experimental plots to study the effects of three crop residue levels (0, 750, and 1500 kg ha- ' ) on nitrogen yield in runoff from no-till and conventional tillage systems. The study site was located near Blacksburg, Virginia. Soil type at the research plots belong to Gmseclose Series which is predominant in southwest Virginia. Approximately 100 mm of simulated rainfall with a 50 mm h- ' intensity was applied to 12 experimental field plots. Nitrogen fertilizer was applied at a rate of 147 kg ha- s prior to rainfall simulation. Water and sediment samples were collected from H-flume discharge at the base of each plot and were analyzed for nitrogen concentration. Nitrogen yield was calculated from nitrogen concentration and the corresponding flow rate at sampling time. Results indicated that at all residue levels, the no-till system was more effective in reducing nitrogen in wa~er and sediment compared to conventional tillage. For both systems, crop residue levels at 750 kg ha- s were very effective in reducing nitrogen yield in runoff. However, at 1500 kg ha- ' residue level higher nitrogen yields were observed, it was demonstrated that no-till system combined with appropriate residue management could reduce nitrogen yield in runoff and therefore can he considered an effective measure for reducing nitrogen input to surface water bodies. However, the relative effects of tillage practices on groundwater quality cannot be deduced from this study.
INTRODUCTION
Nutrient runoff from agricultural lands is a major factor in eutrophication of surface waters. Excessive growth of algae and aquatic weeds caused by eutrophication usually interfere with recreational and aesthetic uses of surface waters and adversely affect aquatic populations. Furthermore, algal growth may cause odor and taste problems in surface water, resulting in lower water quality for domestic consumption and inc[eased water treatment costs. In recent years, various approaches have been attempted to control nutrient runCorrespondence to: S. Mostaghimi, Department of Agricultural Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0167-8809/92/$05.00
188
S. MOSTAGHIM!ET AL.
off from agricultural fields. These include development of more efficient fertilizer application techniques and implementation of best management practices (BMP) such as conservation tillage. Conservation tillage is usually considered to be very effective for sediment and nutrient runoffcontrol from agricultural lands (Angle et al., 1984; Lafien et al., 1978; Johnson and Moldenhauer, 1979). However, some studies have shown that soluble nitrogen (N) concentrations in runoff from conservation tillage systems are higher than those from conventional tillage systems. For example, in one study it was observed that coulter- and chisel-plow-planting systems reduced soil loss, but runoff from these systems contained higher concentrations of soluble nitrogen (Romkens et ai., 1973). The study found that disk-planting and conventional tillage systems were less effective for erosion control, but runoff from these systems contained lower concentrations of soluble N. Another study compared the effects of two tillage systems on nutrient and sediment loss from six small watersheds (Johnson et al., 1979). The study concluded that compared to conventional tillage, conservation tilt. lage reduced runoffand soil loss but it did not affect nitrate (NO3-N) concentrations in runoff. Laflen and Tabatabai (1984) observed that N concentration and yield in runoff from no-till increased by an average of five to nine times over those of the moldtoard plow treatments. The study reported lower levels of N in runoff water co~npared to that found in sediment. Sediment to runoff N loss ratios averaged 350 for conventional tillage and 20 for no-till treatment. Baker and Laflen (1982) reported that the amount of crop residue had little impact on N concentration in runoff from conservation tillage systems. Other investigators, however, have shown that crop residue left on soil surface was a source of soluble nutrients in runoff (Timmons et al., 1973). At present, the effects ofcon~ ~rvation tillage systems on nutrient and sediment yield in runoff from crop, and are not well defined. Research data are needed to quantify the impacts of management practices on nutrient yield in general, and particularly N conc~mtrations in runoffand sediment. Therefore, the objective of this study was to investigate the effects of tillage system and crop residue level on N yield in runoffand sediment t~,om cropland. METHODS
Field plots The study site was located on the Virginia Tech's Prices Fork Agricultural Research Farm in Blacksburg, Virginia. Twelve field plots. 5.5 m wide × 18.3 m long with slopes ranging from 8.3 to 15.1% were prepared by installing metal borders to a depth of 15 cm along the designed plot boundaries. The metal borders prevented water movement from or into the plots. A gutter with a pipe outlet was constructed at the base of each plot to collect and direct
CROP RESIDUEEFFECTSON NITROGENYIELDIN RUNOFF
189
the runoff to a 15 cm H-flume. The flume discharge rates were measured by a water level recorder. Soil of the research plots is classified as Groseclose silt loam which is clayey, mixed, mesic Typic Hapludult (Soil Conservation Service (SCS), 1985 ). The soil profile was characterized as deep and well drained with slowly permeable subsoil. Particle-size distribution for the top 25 cm of the soil (Ap) horizon consisted of 23.2% clay, 58.9% silt and 17.9% sand. The soil's bulk density was 1.39 g c m 3 and the soil consisted of 3.7% organic matter. The seasonal groundwater level in the area of study is 8-9 m below ground surface. Field plots were prepared during the year before the experiments. All plots were planted with winter rye in autumn and were sprayed with paraquat in early summer of the following year to kill any growth oil the plots. Six plots were kept in no-till condition, i.e. crop residues from the preceding year were left on the ground surface. Six other plots were conventionally tilled to a depth of 10-15 cm with a rototiller and then disked. Treatments within each tillage system were randomly assigned to the field plots. The crop residue was measured by harvesting and weighting all residues within a 0.6 × 0.6 m grid. The rye was then cut to a height which left the desired amount of residue level standing on the plots. For both tillage systems, experiments were conducted at three residue levels: 0 kg ha- ~ (control), 750 kg ha-i and 1500 kg ha -I. Granular ammonium nitrate fertilizer ( 147 kg ha- ~) was surface applied to plots, 1-2 days prior to rainfall simulation. No natural rainfall occurred the week before fertilizer was applied. Antecedent soil-moisture content was 15-20%. To achieve uniform fertilizer application, TABLE I Plot characteristics and treatments Tillage treatment
Residue level (kg ha-~ )
Slope (%)
NT
0 1500 1500 0 750 750 1500 0 1500 750 750 0
9.2 9.0 9.9 14.1 15.1 14.0 9.7 8.9 9.1 9.4 8.6 8.3
CT
Average slope of NT plots - ! 1.9%; Average slope of CT plots -9.0%; NT, No-till; CT, Conventional tillage.
190
S. MOSTAOHIM!ET AL.
each plot was subdivided into four equal-sized sub-areas and each sub-area received a quarter of the total fertilizer required for the entire plot. Table 1 shows research plot and treatment characteristics.
Rainfall simulation A portable rainfall simulator (Dillaha et al., 1987) was used to apply approximately 100 mm of rainfall to each three-plot set over a 24 h period. Three simulated rainfall events were applied to each set. A 1 h duration, initial run ( R I ) was followed 24 h later by a 30 rain duration, wet run (R2), and 30 min later by a second 30 min duration, very wet run (R3). The three-run sequence of initial, wet, and very wet simulated rainfall application is a common sequence used to simulate various antecedent soil moisture conditions for erosion research (e.g. Gilley et al., 1986). The design rainfall intensity was 50 mm h - ~, a typical intensity of storms with a 2-5 year return period in Southwest Virginia (Hershfield, 1961 ). The selected rainfall intensity was expected to simulate critical conditions for N yield since fertilizer had been applied 24-48 h before rainfall application. Plots were protected from natural precipitation with plastic sheet covers whenever natural rain appeared to be imminent and were left uncovered at other times to allow evaporation and drying under natural conditions.
Sample collection and analysis Runoff samples were collected in plastic containers at 3-6 min intervals. Precise sample collection time and corresponding flow rates for each sample were marked on the stage recorder chart. Runoff rates during the rainfall simulation were frequently checked gravimetrically by runoff volume measurement versus time. All samples were refrigerated immediately after collection and were analyzed within 8 weeks in accordance with methods described in Methods for Chemical Analysis of Water and Wastes (US Environmental Protection Agency (EPA), 1979). Determination of suspended solids concentrations were made by Method 160.2; total Kjeldahl nitrogen (TKN) on both filtered and unfiltered samples by Method 351.2; ammonia-nitrogen by Method 350.1; nitrate-nitrogen by Method 353.2. Total nitrogen (NT) was calculated by summing up TKN and NO3-N concentrations or yields. Sediment and N yields were computed from sediment and N concentrations measured in each sample. This assumed that the flow volume associated with each sample was equal to the average of the flow rates at the beginning and end of each sampling interval multiplied by the duration of the sampling time interval. Field plot preparation and rainfall simulator operation require large tracts of land and labor intensive work. For the available resources, the scope of the
CROP RESIDUEEFFECTSON NITROGENYIELDIN RUNOFF
191
project was limited to only two replications for each treatment. Therefore, results presented in this article are simple arithmetic averages of the two replications and a rigorous statistical treatment to show significant differences were not possible. RESULTS AND DISCUSSION
Table 2 shows crop residue level effects on runoff and sediment losses for both tillage systems. Compared to conventional tillage, at all residue levels, the no-till system was very effective in reducing runoff and sediment. The lower runoff volume from no-till plots can be attributed to water retention by crop residue and increased infiltration opportunity. Runoff events from notill plots began 6-10 rain later than those from conventional tillage plots (Table 2) indicating higher initial infiltration rate under no-till condition. Mannering et al. (1987) suggested that the crop residue on no-till plots prevents total soil surface sealing because of reduced raindrop impact, and causes lower runoff velocities resulting in increased flow depth over the ground surface and increased infiltration volume. Table 3 shows nitrogen concentrations in the runoff. For no-tin plots, average concentrations for all N forms were highest for control plots, intermediate with 1500 kg ha- I residue level, and lowest for 750 kg ha- i residue level treatment. For conventional tillage plots, a clear trend was not observed in N concentrations in runoff. Higher NO3-N concentrations in runoff were measured as the residue level increased from 0-1500 kg ha -~. Ammonium-nitrogen and TN concentrations were highest with 1500 kg ha-~ residue level, intermediate with control plots, and lowest with 750 kg ha- ~residue level. Total sediment-bound nitrogen (TNsco) and TKN concentrations were highest for control plots, intermediate for 1500 kg ha-m residue level, and lowest for 750 kg ha- t residue level treatment. TABLE 2 Effects of residue levels and tillage systems on runoff and sediment losses Tillage system
Residue level Peak runoff rate Runoff volume Sediment yield Time runoff began ! (kgha -~ ) (mmh -t) (ram) (kgha -~ ) (min)
No-till (NT)
0 750 1500
17.0 9.0 1.0
4.5 2.6 0.2
Conventional 0 tillage 750 (CT) 1500
51.0 34.0 26.0
35.5 32.7 18.0
72.0 1 !.0 7.0 2812 1001 513
'Time lapse for recorded runoffafler simulated rainfall was started.
8 12 !7 2 5 7
192
s. MOSTAGHIMIET AL.
TABLE 3
Residue level effects on the average concentration of nitrogen in runoff (mg I- ' ) Tillage system
Residue level (kg ha- i )
No-till
0 0 0
(NT)
Run
NO3-N I
NH4-N 2
TKN 3
TNsed4
RI R2 R3
2.72 3.72 4.14 3.53 1.07 1.20 1.06 I.I I 2.00 3.41 2.38 2.60
4.89 1.59 4.09 3.52 0.64 2.00 2.87 !.84 2.15 3.24 1.88 2.43
12.16 5.74 10.06 9.32 4.05 3.60 3.85 3.84 6.58 6.26 5.21 6.02
6.07 2.78 4.41 4.42 1.49 1.20 1.23 1.31 2.62 1.49 0.88 1.66
14.88 9.46 14.20 12.84 5. ! 2 4.80 4.92 4.95 8.59 9.66 7.59 8.61
0.61 I. 16 0.62 0.80 1.23 2.62 !.52 1.79 4.51 5.28 2.57 4.12
2.34 4.60 2.54 3.16 2.94 2.24 3.22 2.80 4.75 3.41 4.02 4.06
8.98 10.20 14.56 1 !.25 12.33 5.79 7.73 8.61 I 1.64 ! !.33 6.18 9.71
6.00 4.77 10.52 7.10 7.80 2.58 3.07 4.48 6.44 6.79 1.58 4.94
9.59 ! 1.36 15.18 12.04 13.56 8.41 9.25 10.41 16.15 16.61 8.75 13.84
Average 750 750 750
R! R2 R3
Average 1500 1500 ! 500
RI R2 R3
Average Conventional tillage (CT)
0 0 0
RI R2 R3
Average 750 750 750
R! R2 R3
Average 1500 1500 1500
RI R2 R3
Average
TN s
'Nitrate-nitrogen; 'Ammonium-nitrogen; 3Total kjeldahl nitrogen; 4Sediment-bound nitrogen; STotal nitrogen.
In general, for both tillage systems, a decrease in N concentrations of all forms was observed for 750 kg ha- i residue treatment, except for NO3-N concentration from conventional tillage plots which showed an increase relative to the control plots. However, for both tillage systems, average N concentrations in runoff increased at 1500 kg ha- ~ residue level, indicating that nitrogen concentration in runoffis not proportional to residue level. Possible causes of this phenomenon are discussed later. Table 4 shows the effects of crop residue on N yields in runoff. For no-till plots, NO~-N and NH4-N yield were highest for control plots, intermediate for 1500 kg ha- ~residue level, and lowest for 750 kg h~- mresidue level treatment. For conventional tillage plots, NO3-N and NH4-N yield were highest
CROP RESIDUE EFFECTS ON NITROGEN YIELD IN RUNOFF
193
TABLE 4 Tillage system and residue effects on nitrogen yield (kg h a - ' ) Tillage systems
Residue level (kg h a - i )
NO3-N
NH4-N
TKN
TN~eo
TN
NT CT
0 0
0.210 (26) 0.285 -
0.202 (82) !.123 -
0.397 ( 9 1 ) 4.277 -
0.134 (95) 2.788 -
0.608 ( 8 7 ) 4.562 -
NT CT
750 750
0.003 (99) 0.283 -
0.006 (99) 0.502 -
0.008 ( 9 9 ) 1.382 -
0.004 (99) 0.661 -
0.009 (99) i.665 -
NT CT
1500 1500
0.106 (92) !.326 -
0.092 (93) 1.259 -
0.208 ( 9 3 ) 3.056 -
0.037 (98) 1.502 -
0.313 (93) 4.382 -
NT, No.till; CT, Conventional tillage; Numbers in parentheses show percent N reduction by no-till relative to conventional tillage.
for 1500 kg ha- ! residue level, intermediate for control treatment, and lowest for 750 kg ha- ! residue level. For all treatments no-till was more effective for nitrogen yield control (Table 4). At 750 kg ha-i residue level, 99% decrease in all nitrogen forms was observed relative to conventional tillage. At 1500 kg ha- i residue level, percent reductions by no-till ranged from 92% for NO3-N to 98% for TNsed relative to conventional tillage. Table 4 shows that crop residue enhanced the effectiveness of both tillage systems to reduce nitrogen yield. For both tillage systems total N yield at 750 kg ha- i residue level was lower in comparison with control plots. For no-till plots, in particular, the 750 kg ha-i residue treatment resulted in 98, 97, 98, 99 and 98% yield decrease in NO3-N, NH4-N, TKN, TNseo and TN, respectively. A similar trend but lower percent decrease in N yield (except for NO3-N) was observed for conventional tillage plots. For these plots, 750 kg ha- ~residue treatment resulted in 55, 68, 78 and 64% decrease in NH4-N, TKN, TNsed and TN, respectively. However, at 750 kg ha-t residue level, NO3-N concentration in runoff from conventional tillage plots was slightly higher than NO3-N concentration from control plots. Tables 3 and 4 show that N concentrations in runoffare higher for conventional tillage plots, and the nitrogen yields in runoff are much lower for notill plots. Lower nitrogen yield from no-till plots is attributed to lower runoff and sediment volume from no-till as compared to conventional tillage plots. Results of this study are consistent with other studies concerning the effectiveness of no-till practice for nutrient and sediment control in runoff (Romkens et al., 1973; McDowell and McGregor, 1980; Baker and Laflen, 1982; Lembi et al., 1985 ). Table 5 summarizes the data related to the effects of tillage system on TN yield in runoff determined in the present study. Per-
194
S. MOSTAGHIMI ET AL.
TABLE 5 Tillage system effects on nitrogen yield in runoff (kg ha- t ) ' Tillage system
NO~-N
NH4-N
TKN
TN~d
TN
Conventional tillage (CT) No-till (NT) Ratio (CT/NT)
0.632 0.107 (83) 5.9
0.960 0.103 (89) 9.3
2.905 0.205 (93) 14.2
!.650 0.059 (96) 28.0
3.537 0.310 (91) ! !.4
*Values in kg ha- *are totals for all three simulation runs across all residue levels. Numbers in parentheses show percent N reduction by no-till relative to conventional tillage.
cent reductions in NO3-N,NH4-N, TKN, TNsedand TN were 83, 89, 93, 96 and 91%, respectively for no-till plots in comparison with conventional tillage plots. With conventional tillage the soil disturbance and the greater interaction between soil and fertilizer may have resulted in nitrogen ion attachment to soil particles and therefore higher NH4-N and TNsed concentrations in the runoff. It should be noted that the N accumulation and movement through the soil profile is affected by soil characteristics, i.e. pore size distribution, particle size, and antecedent soil-moisture content (Baker, 1987). However, the impact of soil properties on N movement could not be deduced from the plot research studies reported here. Results from this study indicate that, in general, a 750 kg ha- ~residue level was more effective in N loss control than a higher 1500 kg ha- ' residue level. This result cannot be explained from the available data. Some investigators have reported that crop residue left on the soil surface could contribute to soluble nutrient levels in runoff (Timmons et al., 1973). However, the complex relationships among amounts of residue, nitrogen release and moisture retention relationship within the residue, and fertilizer interception by the residue could influence N concentrations and yields in runoff. Additional research is needed to determine critical residue levels for effective N control from no-till and conventional tillage systems. Furthermore, lower runoff volumes compared to applied rainfall volume, indicate higher infiltration rate in the soil profile and the probability of higher N concentration in subsurface flow in no-till system with residue treatment. Additional research is needed to determine the impact of crop residues on N concentration in subsurface water. CONCLUSIONS
This study demonstrated that, in general, no-till practice is very effective for total sediment and nutrien~control in runoff. For both tillage methods, the N yield was decreased when the residue level was maintained at 750 kg ha-~. When the residue level was doubled, average nitrogen yield was in-
CROP RESIDUE EFFECTS ON NITROGEN YIELD IN RUNOFF
195
creased for both tillage systems indicating a complex interaction between fertilizer, residue amount, and hydrologic processes. Additional research is recommended to determine critical residue levels for effective nitrogen management. Total N losses from agricultural land usually constitute a small fraction of total nitrogen fertilizer applied to crops and may not be a major economic concern to the farmer. However, normally observed levels of N concentrations in runoff are considered a major cause of nutrient enrichment and eutrophication of surface waters. This study demonstrated that no-till practice, with appropriate residue management, could be a very effective method for reducing nitrogen yield in runoff and thereby minimizing the impact of agricultural fertilizer use on nonpoint source pollution of surface waters. Therefore, it is anticipated that in future, no-till system will become a major component of the low (chemical) input and sustainable agricultural systems. ACKNOWLEDGMENTS
The work upon which this paper is based was supported by the Virginia Agricultural Experiment Station through funds provided by the Virginia Water Resources Research Center. REFERENCES Angle, J.S., McClung, G., Mclntosh, M.S., Thomas, P.M. and Wolf, D.X., 1984. Nutrient losses in runofffrom conventional and no-till corn watersheds. J. Environ. Quai., ! 3:431-435. Baker, J.L. and Laden, J.M., 1982. Effects of corn residue and fertilizer management on soluble nutrient losses. Trans., ASAE, 25 (2): 344-348. Baker, J.L., 1987, Hydrologic effects of conservation tillage and their importance relative to water quality. In: T.J. Logan, J.M. Davidson, J.L. Baker and M.R. Overcash (Editors), Effects of Conservation Tillage on Groundwater Quality - Nitrates and Pesticides. Lewis, Chelsea, MI, pp. 113-124. Dillaha, T.A., Reneau, R.B., Mostaghimi, S. and Magette, W.L., 1987. Evaluating nutrient and sediment losses from agricultural lands: vegetative flter strip. Chesapeake Bay Program, CBP/TRS4/87, US Environmental Protection Agency, Annapolis, MD, 92 pp. Gilley, J.E., Finkner, S.C., Spomer, R.G. and Mielke, L.N., 1986. Runoff and erosion as affected by corn residue: Part I. Total losses. Trans., ASAE, 29 ( 1 ): 157-160. Hershfield, D.N., 1961. Rainfall frequency atlas of the United States. US Weather Bureau Tech. Paper 40. Washington, DC, 115 pp. Johnson, C.B. and Moldenhauer, W.C., 1979. Effect of chisel versus moldboard plowing on soil erosion by water. Soil Sci. Soc. Am. J., 43:177-179. Johnson, H.P., Baker, J.L., Shrader, W.D. and Laden, J.M., 1979. Tillage system effects on sediment and nutrient in runoff from small watersheds. Trans., ASAE, 22 (5): 1 i 10-1114. Lafien, J.M., Baker, J.L., Hartwig, R.O., Buchele, W.F. and Johnson, H.P., ! 978. Soil and water loss from conservation tillage systems. Trans., A.$AE, 21:881-885. Laden, J.M. and Tabatabai, M.A., 1984. Nitrogen and phosphorus losses from corn-soybeans rotations as affected by tillage practices. Trans., ASAE, 27( I ): 58-63.
! 96
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Lembi, C.A., Bdtton, M.D. and Ross, M.A., 1985. Evaluation of nitrogen application technique and tillage system on nitrogen runoff from erodible soil. Tech. Report 174. Purdue Univ., W. Lafayette, IN, 41 pp. Mannering, J.V., Schenz, D.L. and Julian, B.A., 1987. Overview of conservation tillage. In: T.J. Logan, J.M. Davidson, J.L. Baker and M.R. Overcash (Editors), Effects of Conservation Tillage on Groundwater Quality - Nitrates and Pesticides. Lewis, Chelsea, MI, pp. 3-18. McDoweil, L.L. and McGregor, L.C., i 980. Nitrogen and phosphorus losses in runoff from notill soybeans. Trans., ASAE, 23 (3): 643-647. Romkens, J.J.M., Nelson, D.W. and Mannering, J.V., 1973. Nitrogen and phosphorus composition of surface runoff as affected by tillage method. J. Environ. Quai., 2 (2): 292-298. Soil Conservation Service, 1985. Soil Survey Montgomery County, Virginia. US Department of Agriculture, SCS, Richmond, VA, 158 pp. Timmons, D,R., Burweil, R.E. and Holt, R.F., 1973. Nitrogen and phosphorus losses in surface runoff from agricultural land as influenced by placement of broadcast fertilizer. Water Resour. Res., 9: 658-667. US Environmental Protection Agency, 1979. Methods for the Chemical Analysis of Water and Waste. US EPA, Report No. 600/4-79-020. Washington, DC.
187
Elsevier Science Publishers B.V., Amsterdam
Crop residue effects on nitrogen yield in water and sediment runoff from two tillage systems S. Mostaghimi, T.M. Younos and U.S. Tim Department of Agriculturai Engineering, Virginia Polytechniclnstituw and Staw Umversity. Blacksburg. VA 24061. USA (Accepted 14 November 1991 )
ABSTRACT Mostaghimi, S., Younos, T.M. and Tim, U.S., 1992. Crop residue effects on nitrogen yield in water and sediment runoff from two tillage systems. Agric. EcosystemsEnviron., 39:187-196. Simulated rainfall was used on experimental plots to study the effects of three crop residue levels (0, 750, and 1500 kg ha- ' ) on nitrogen yield in runoff from no-till and conventional tillage systems. The study site was located near Blacksburg, Virginia. Soil type at the research plots belong to Gmseclose Series which is predominant in southwest Virginia. Approximately 100 mm of simulated rainfall with a 50 mm h- ' intensity was applied to 12 experimental field plots. Nitrogen fertilizer was applied at a rate of 147 kg ha- s prior to rainfall simulation. Water and sediment samples were collected from H-flume discharge at the base of each plot and were analyzed for nitrogen concentration. Nitrogen yield was calculated from nitrogen concentration and the corresponding flow rate at sampling time. Results indicated that at all residue levels, the no-till system was more effective in reducing nitrogen in wa~er and sediment compared to conventional tillage. For both systems, crop residue levels at 750 kg ha- s were very effective in reducing nitrogen yield in runoff. However, at 1500 kg ha- ' residue level higher nitrogen yields were observed, it was demonstrated that no-till system combined with appropriate residue management could reduce nitrogen yield in runoff and therefore can he considered an effective measure for reducing nitrogen input to surface water bodies. However, the relative effects of tillage practices on groundwater quality cannot be deduced from this study.
INTRODUCTION
Nutrient runoff from agricultural lands is a major factor in eutrophication of surface waters. Excessive growth of algae and aquatic weeds caused by eutrophication usually interfere with recreational and aesthetic uses of surface waters and adversely affect aquatic populations. Furthermore, algal growth may cause odor and taste problems in surface water, resulting in lower water quality for domestic consumption and inc[eased water treatment costs. In recent years, various approaches have been attempted to control nutrient runCorrespondence to: S. Mostaghimi, Department of Agricultural Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
© 1992 Elsevier Science Publishers B.V. All rights reserved 0167-8809/92/$05.00
188
S. MOSTAGHIM!ET AL.
off from agricultural fields. These include development of more efficient fertilizer application techniques and implementation of best management practices (BMP) such as conservation tillage. Conservation tillage is usually considered to be very effective for sediment and nutrient runoffcontrol from agricultural lands (Angle et al., 1984; Lafien et al., 1978; Johnson and Moldenhauer, 1979). However, some studies have shown that soluble nitrogen (N) concentrations in runoff from conservation tillage systems are higher than those from conventional tillage systems. For example, in one study it was observed that coulter- and chisel-plow-planting systems reduced soil loss, but runoff from these systems contained higher concentrations of soluble nitrogen (Romkens et ai., 1973). The study found that disk-planting and conventional tillage systems were less effective for erosion control, but runoff from these systems contained lower concentrations of soluble N. Another study compared the effects of two tillage systems on nutrient and sediment loss from six small watersheds (Johnson et al., 1979). The study concluded that compared to conventional tillage, conservation tilt. lage reduced runoffand soil loss but it did not affect nitrate (NO3-N) concentrations in runoff. Laflen and Tabatabai (1984) observed that N concentration and yield in runoff from no-till increased by an average of five to nine times over those of the moldtoard plow treatments. The study reported lower levels of N in runoff water co~npared to that found in sediment. Sediment to runoff N loss ratios averaged 350 for conventional tillage and 20 for no-till treatment. Baker and Laflen (1982) reported that the amount of crop residue had little impact on N concentration in runoff from conservation tillage systems. Other investigators, however, have shown that crop residue left on soil surface was a source of soluble nutrients in runoff (Timmons et al., 1973). At present, the effects ofcon~ ~rvation tillage systems on nutrient and sediment yield in runoff from crop, and are not well defined. Research data are needed to quantify the impacts of management practices on nutrient yield in general, and particularly N conc~mtrations in runoffand sediment. Therefore, the objective of this study was to investigate the effects of tillage system and crop residue level on N yield in runoffand sediment t~,om cropland. METHODS
Field plots The study site was located on the Virginia Tech's Prices Fork Agricultural Research Farm in Blacksburg, Virginia. Twelve field plots. 5.5 m wide × 18.3 m long with slopes ranging from 8.3 to 15.1% were prepared by installing metal borders to a depth of 15 cm along the designed plot boundaries. The metal borders prevented water movement from or into the plots. A gutter with a pipe outlet was constructed at the base of each plot to collect and direct
CROP RESIDUEEFFECTSON NITROGENYIELDIN RUNOFF
189
the runoff to a 15 cm H-flume. The flume discharge rates were measured by a water level recorder. Soil of the research plots is classified as Groseclose silt loam which is clayey, mixed, mesic Typic Hapludult (Soil Conservation Service (SCS), 1985 ). The soil profile was characterized as deep and well drained with slowly permeable subsoil. Particle-size distribution for the top 25 cm of the soil (Ap) horizon consisted of 23.2% clay, 58.9% silt and 17.9% sand. The soil's bulk density was 1.39 g c m 3 and the soil consisted of 3.7% organic matter. The seasonal groundwater level in the area of study is 8-9 m below ground surface. Field plots were prepared during the year before the experiments. All plots were planted with winter rye in autumn and were sprayed with paraquat in early summer of the following year to kill any growth oil the plots. Six plots were kept in no-till condition, i.e. crop residues from the preceding year were left on the ground surface. Six other plots were conventionally tilled to a depth of 10-15 cm with a rototiller and then disked. Treatments within each tillage system were randomly assigned to the field plots. The crop residue was measured by harvesting and weighting all residues within a 0.6 × 0.6 m grid. The rye was then cut to a height which left the desired amount of residue level standing on the plots. For both tillage systems, experiments were conducted at three residue levels: 0 kg ha- ~ (control), 750 kg ha-i and 1500 kg ha -I. Granular ammonium nitrate fertilizer ( 147 kg ha- ~) was surface applied to plots, 1-2 days prior to rainfall simulation. No natural rainfall occurred the week before fertilizer was applied. Antecedent soil-moisture content was 15-20%. To achieve uniform fertilizer application, TABLE I Plot characteristics and treatments Tillage treatment
Residue level (kg ha-~ )
Slope (%)
NT
0 1500 1500 0 750 750 1500 0 1500 750 750 0
9.2 9.0 9.9 14.1 15.1 14.0 9.7 8.9 9.1 9.4 8.6 8.3
CT
Average slope of NT plots - ! 1.9%; Average slope of CT plots -9.0%; NT, No-till; CT, Conventional tillage.
190
S. MOSTAOHIM!ET AL.
each plot was subdivided into four equal-sized sub-areas and each sub-area received a quarter of the total fertilizer required for the entire plot. Table 1 shows research plot and treatment characteristics.
Rainfall simulation A portable rainfall simulator (Dillaha et al., 1987) was used to apply approximately 100 mm of rainfall to each three-plot set over a 24 h period. Three simulated rainfall events were applied to each set. A 1 h duration, initial run ( R I ) was followed 24 h later by a 30 rain duration, wet run (R2), and 30 min later by a second 30 min duration, very wet run (R3). The three-run sequence of initial, wet, and very wet simulated rainfall application is a common sequence used to simulate various antecedent soil moisture conditions for erosion research (e.g. Gilley et al., 1986). The design rainfall intensity was 50 mm h - ~, a typical intensity of storms with a 2-5 year return period in Southwest Virginia (Hershfield, 1961 ). The selected rainfall intensity was expected to simulate critical conditions for N yield since fertilizer had been applied 24-48 h before rainfall application. Plots were protected from natural precipitation with plastic sheet covers whenever natural rain appeared to be imminent and were left uncovered at other times to allow evaporation and drying under natural conditions.
Sample collection and analysis Runoff samples were collected in plastic containers at 3-6 min intervals. Precise sample collection time and corresponding flow rates for each sample were marked on the stage recorder chart. Runoff rates during the rainfall simulation were frequently checked gravimetrically by runoff volume measurement versus time. All samples were refrigerated immediately after collection and were analyzed within 8 weeks in accordance with methods described in Methods for Chemical Analysis of Water and Wastes (US Environmental Protection Agency (EPA), 1979). Determination of suspended solids concentrations were made by Method 160.2; total Kjeldahl nitrogen (TKN) on both filtered and unfiltered samples by Method 351.2; ammonia-nitrogen by Method 350.1; nitrate-nitrogen by Method 353.2. Total nitrogen (NT) was calculated by summing up TKN and NO3-N concentrations or yields. Sediment and N yields were computed from sediment and N concentrations measured in each sample. This assumed that the flow volume associated with each sample was equal to the average of the flow rates at the beginning and end of each sampling interval multiplied by the duration of the sampling time interval. Field plot preparation and rainfall simulator operation require large tracts of land and labor intensive work. For the available resources, the scope of the
CROP RESIDUEEFFECTSON NITROGENYIELDIN RUNOFF
191
project was limited to only two replications for each treatment. Therefore, results presented in this article are simple arithmetic averages of the two replications and a rigorous statistical treatment to show significant differences were not possible. RESULTS AND DISCUSSION
Table 2 shows crop residue level effects on runoff and sediment losses for both tillage systems. Compared to conventional tillage, at all residue levels, the no-till system was very effective in reducing runoff and sediment. The lower runoff volume from no-till plots can be attributed to water retention by crop residue and increased infiltration opportunity. Runoff events from notill plots began 6-10 rain later than those from conventional tillage plots (Table 2) indicating higher initial infiltration rate under no-till condition. Mannering et al. (1987) suggested that the crop residue on no-till plots prevents total soil surface sealing because of reduced raindrop impact, and causes lower runoff velocities resulting in increased flow depth over the ground surface and increased infiltration volume. Table 3 shows nitrogen concentrations in the runoff. For no-tin plots, average concentrations for all N forms were highest for control plots, intermediate with 1500 kg ha- I residue level, and lowest for 750 kg ha- i residue level treatment. For conventional tillage plots, a clear trend was not observed in N concentrations in runoff. Higher NO3-N concentrations in runoff were measured as the residue level increased from 0-1500 kg ha -~. Ammonium-nitrogen and TN concentrations were highest with 1500 kg ha-~ residue level, intermediate with control plots, and lowest with 750 kg ha- ~residue level. Total sediment-bound nitrogen (TNsco) and TKN concentrations were highest for control plots, intermediate for 1500 kg ha-m residue level, and lowest for 750 kg ha- t residue level treatment. TABLE 2 Effects of residue levels and tillage systems on runoff and sediment losses Tillage system
Residue level Peak runoff rate Runoff volume Sediment yield Time runoff began ! (kgha -~ ) (mmh -t) (ram) (kgha -~ ) (min)
No-till (NT)
0 750 1500
17.0 9.0 1.0
4.5 2.6 0.2
Conventional 0 tillage 750 (CT) 1500
51.0 34.0 26.0
35.5 32.7 18.0
72.0 1 !.0 7.0 2812 1001 513
'Time lapse for recorded runoffafler simulated rainfall was started.
8 12 !7 2 5 7
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s. MOSTAGHIMIET AL.
TABLE 3
Residue level effects on the average concentration of nitrogen in runoff (mg I- ' ) Tillage system
Residue level (kg ha- i )
No-till
0 0 0
(NT)
Run
NO3-N I
NH4-N 2
TKN 3
TNsed4
RI R2 R3
2.72 3.72 4.14 3.53 1.07 1.20 1.06 I.I I 2.00 3.41 2.38 2.60
4.89 1.59 4.09 3.52 0.64 2.00 2.87 !.84 2.15 3.24 1.88 2.43
12.16 5.74 10.06 9.32 4.05 3.60 3.85 3.84 6.58 6.26 5.21 6.02
6.07 2.78 4.41 4.42 1.49 1.20 1.23 1.31 2.62 1.49 0.88 1.66
14.88 9.46 14.20 12.84 5. ! 2 4.80 4.92 4.95 8.59 9.66 7.59 8.61
0.61 I. 16 0.62 0.80 1.23 2.62 !.52 1.79 4.51 5.28 2.57 4.12
2.34 4.60 2.54 3.16 2.94 2.24 3.22 2.80 4.75 3.41 4.02 4.06
8.98 10.20 14.56 1 !.25 12.33 5.79 7.73 8.61 I 1.64 ! !.33 6.18 9.71
6.00 4.77 10.52 7.10 7.80 2.58 3.07 4.48 6.44 6.79 1.58 4.94
9.59 ! 1.36 15.18 12.04 13.56 8.41 9.25 10.41 16.15 16.61 8.75 13.84
Average 750 750 750
R! R2 R3
Average 1500 1500 ! 500
RI R2 R3
Average Conventional tillage (CT)
0 0 0
RI R2 R3
Average 750 750 750
R! R2 R3
Average 1500 1500 1500
RI R2 R3
Average
TN s
'Nitrate-nitrogen; 'Ammonium-nitrogen; 3Total kjeldahl nitrogen; 4Sediment-bound nitrogen; STotal nitrogen.
In general, for both tillage systems, a decrease in N concentrations of all forms was observed for 750 kg ha- i residue treatment, except for NO3-N concentration from conventional tillage plots which showed an increase relative to the control plots. However, for both tillage systems, average N concentrations in runoff increased at 1500 kg ha- ~ residue level, indicating that nitrogen concentration in runoffis not proportional to residue level. Possible causes of this phenomenon are discussed later. Table 4 shows the effects of crop residue on N yields in runoff. For no-till plots, NO~-N and NH4-N yield were highest for control plots, intermediate for 1500 kg ha- ~residue level, and lowest for 750 kg h~- mresidue level treatment. For conventional tillage plots, NO3-N and NH4-N yield were highest
CROP RESIDUE EFFECTS ON NITROGEN YIELD IN RUNOFF
193
TABLE 4 Tillage system and residue effects on nitrogen yield (kg h a - ' ) Tillage systems
Residue level (kg h a - i )
NO3-N
NH4-N
TKN
TN~eo
TN
NT CT
0 0
0.210 (26) 0.285 -
0.202 (82) !.123 -
0.397 ( 9 1 ) 4.277 -
0.134 (95) 2.788 -
0.608 ( 8 7 ) 4.562 -
NT CT
750 750
0.003 (99) 0.283 -
0.006 (99) 0.502 -
0.008 ( 9 9 ) 1.382 -
0.004 (99) 0.661 -
0.009 (99) i.665 -
NT CT
1500 1500
0.106 (92) !.326 -
0.092 (93) 1.259 -
0.208 ( 9 3 ) 3.056 -
0.037 (98) 1.502 -
0.313 (93) 4.382 -
NT, No.till; CT, Conventional tillage; Numbers in parentheses show percent N reduction by no-till relative to conventional tillage.
for 1500 kg ha- ! residue level, intermediate for control treatment, and lowest for 750 kg ha- ! residue level. For all treatments no-till was more effective for nitrogen yield control (Table 4). At 750 kg ha-i residue level, 99% decrease in all nitrogen forms was observed relative to conventional tillage. At 1500 kg ha- i residue level, percent reductions by no-till ranged from 92% for NO3-N to 98% for TNsed relative to conventional tillage. Table 4 shows that crop residue enhanced the effectiveness of both tillage systems to reduce nitrogen yield. For both tillage systems total N yield at 750 kg ha- i residue level was lower in comparison with control plots. For no-till plots, in particular, the 750 kg ha-i residue treatment resulted in 98, 97, 98, 99 and 98% yield decrease in NO3-N, NH4-N, TKN, TNseo and TN, respectively. A similar trend but lower percent decrease in N yield (except for NO3-N) was observed for conventional tillage plots. For these plots, 750 kg ha- ~residue treatment resulted in 55, 68, 78 and 64% decrease in NH4-N, TKN, TNsed and TN, respectively. However, at 750 kg ha-t residue level, NO3-N concentration in runoff from conventional tillage plots was slightly higher than NO3-N concentration from control plots. Tables 3 and 4 show that N concentrations in runoffare higher for conventional tillage plots, and the nitrogen yields in runoff are much lower for notill plots. Lower nitrogen yield from no-till plots is attributed to lower runoff and sediment volume from no-till as compared to conventional tillage plots. Results of this study are consistent with other studies concerning the effectiveness of no-till practice for nutrient and sediment control in runoff (Romkens et al., 1973; McDowell and McGregor, 1980; Baker and Laflen, 1982; Lembi et al., 1985 ). Table 5 summarizes the data related to the effects of tillage system on TN yield in runoff determined in the present study. Per-
194
S. MOSTAGHIMI ET AL.
TABLE 5 Tillage system effects on nitrogen yield in runoff (kg ha- t ) ' Tillage system
NO~-N
NH4-N
TKN
TN~d
TN
Conventional tillage (CT) No-till (NT) Ratio (CT/NT)
0.632 0.107 (83) 5.9
0.960 0.103 (89) 9.3
2.905 0.205 (93) 14.2
!.650 0.059 (96) 28.0
3.537 0.310 (91) ! !.4
*Values in kg ha- *are totals for all three simulation runs across all residue levels. Numbers in parentheses show percent N reduction by no-till relative to conventional tillage.
cent reductions in NO3-N,NH4-N, TKN, TNsedand TN were 83, 89, 93, 96 and 91%, respectively for no-till plots in comparison with conventional tillage plots. With conventional tillage the soil disturbance and the greater interaction between soil and fertilizer may have resulted in nitrogen ion attachment to soil particles and therefore higher NH4-N and TNsed concentrations in the runoff. It should be noted that the N accumulation and movement through the soil profile is affected by soil characteristics, i.e. pore size distribution, particle size, and antecedent soil-moisture content (Baker, 1987). However, the impact of soil properties on N movement could not be deduced from the plot research studies reported here. Results from this study indicate that, in general, a 750 kg ha- ~residue level was more effective in N loss control than a higher 1500 kg ha- ' residue level. This result cannot be explained from the available data. Some investigators have reported that crop residue left on the soil surface could contribute to soluble nutrient levels in runoff (Timmons et al., 1973). However, the complex relationships among amounts of residue, nitrogen release and moisture retention relationship within the residue, and fertilizer interception by the residue could influence N concentrations and yields in runoff. Additional research is needed to determine critical residue levels for effective N control from no-till and conventional tillage systems. Furthermore, lower runoff volumes compared to applied rainfall volume, indicate higher infiltration rate in the soil profile and the probability of higher N concentration in subsurface flow in no-till system with residue treatment. Additional research is needed to determine the impact of crop residues on N concentration in subsurface water. CONCLUSIONS
This study demonstrated that, in general, no-till practice is very effective for total sediment and nutrien~control in runoff. For both tillage methods, the N yield was decreased when the residue level was maintained at 750 kg ha-~. When the residue level was doubled, average nitrogen yield was in-
CROP RESIDUE EFFECTS ON NITROGEN YIELD IN RUNOFF
195
creased for both tillage systems indicating a complex interaction between fertilizer, residue amount, and hydrologic processes. Additional research is recommended to determine critical residue levels for effective nitrogen management. Total N losses from agricultural land usually constitute a small fraction of total nitrogen fertilizer applied to crops and may not be a major economic concern to the farmer. However, normally observed levels of N concentrations in runoff are considered a major cause of nutrient enrichment and eutrophication of surface waters. This study demonstrated that no-till practice, with appropriate residue management, could be a very effective method for reducing nitrogen yield in runoff and thereby minimizing the impact of agricultural fertilizer use on nonpoint source pollution of surface waters. Therefore, it is anticipated that in future, no-till system will become a major component of the low (chemical) input and sustainable agricultural systems. ACKNOWLEDGMENTS
The work upon which this paper is based was supported by the Virginia Agricultural Experiment Station through funds provided by the Virginia Water Resources Research Center. REFERENCES Angle, J.S., McClung, G., Mclntosh, M.S., Thomas, P.M. and Wolf, D.X., 1984. Nutrient losses in runofffrom conventional and no-till corn watersheds. J. Environ. Quai., ! 3:431-435. Baker, J.L. and Laden, J.M., 1982. Effects of corn residue and fertilizer management on soluble nutrient losses. Trans., ASAE, 25 (2): 344-348. Baker, J.L., 1987, Hydrologic effects of conservation tillage and their importance relative to water quality. In: T.J. Logan, J.M. Davidson, J.L. Baker and M.R. Overcash (Editors), Effects of Conservation Tillage on Groundwater Quality - Nitrates and Pesticides. Lewis, Chelsea, MI, pp. 113-124. Dillaha, T.A., Reneau, R.B., Mostaghimi, S. and Magette, W.L., 1987. Evaluating nutrient and sediment losses from agricultural lands: vegetative flter strip. Chesapeake Bay Program, CBP/TRS4/87, US Environmental Protection Agency, Annapolis, MD, 92 pp. Gilley, J.E., Finkner, S.C., Spomer, R.G. and Mielke, L.N., 1986. Runoff and erosion as affected by corn residue: Part I. Total losses. Trans., ASAE, 29 ( 1 ): 157-160. Hershfield, D.N., 1961. Rainfall frequency atlas of the United States. US Weather Bureau Tech. Paper 40. Washington, DC, 115 pp. Johnson, C.B. and Moldenhauer, W.C., 1979. Effect of chisel versus moldboard plowing on soil erosion by water. Soil Sci. Soc. Am. J., 43:177-179. Johnson, H.P., Baker, J.L., Shrader, W.D. and Laden, J.M., 1979. Tillage system effects on sediment and nutrient in runoff from small watersheds. Trans., ASAE, 22 (5): 1 i 10-1114. Lafien, J.M., Baker, J.L., Hartwig, R.O., Buchele, W.F. and Johnson, H.P., ! 978. Soil and water loss from conservation tillage systems. Trans., A.$AE, 21:881-885. Laden, J.M. and Tabatabai, M.A., 1984. Nitrogen and phosphorus losses from corn-soybeans rotations as affected by tillage practices. Trans., ASAE, 27( I ): 58-63.
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Lembi, C.A., Bdtton, M.D. and Ross, M.A., 1985. Evaluation of nitrogen application technique and tillage system on nitrogen runoff from erodible soil. Tech. Report 174. Purdue Univ., W. Lafayette, IN, 41 pp. Mannering, J.V., Schenz, D.L. and Julian, B.A., 1987. Overview of conservation tillage. In: T.J. Logan, J.M. Davidson, J.L. Baker and M.R. Overcash (Editors), Effects of Conservation Tillage on Groundwater Quality - Nitrates and Pesticides. Lewis, Chelsea, MI, pp. 3-18. McDoweil, L.L. and McGregor, L.C., i 980. Nitrogen and phosphorus losses in runoff from notill soybeans. Trans., ASAE, 23 (3): 643-647. Romkens, J.J.M., Nelson, D.W. and Mannering, J.V., 1973. Nitrogen and phosphorus composition of surface runoff as affected by tillage method. J. Environ. Quai., 2 (2): 292-298. Soil Conservation Service, 1985. Soil Survey Montgomery County, Virginia. US Department of Agriculture, SCS, Richmond, VA, 158 pp. Timmons, D,R., Burweil, R.E. and Holt, R.F., 1973. Nitrogen and phosphorus losses in surface runoff from agricultural land as influenced by placement of broadcast fertilizer. Water Resour. Res., 9: 658-667. US Environmental Protection Agency, 1979. Methods for the Chemical Analysis of Water and Waste. US EPA, Report No. 600/4-79-020. Washington, DC.