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Tillage and Liquid Dairy Manure Effects on Overland Flow Nitrogen and Phosphorus Loss Potential in an Upper Midwest Corn Silage-Winter Triticale Cropping System

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Dairy manure is an important crop nutrient source in Wisconsin and other parts of the upper Midwest but can contribute to nitrogen (N) and phosphorus (P) losses in overland flow/surface runoff. Winter cereal grain cover crops can help reduce erosion and nutrient transport in corn systems. However, few studies have compared tillage impacts on nutrient loss in live cover crop systems. The objective of this study was to evaluate vertical (VT) and chisel tillage (CT) effects on overland flow nutrient and sediment loss potential after spring-applied liquid manure. A surface application treatment (i.e., broadcast) and a no manure control were also included for comparison. After corn (Zea mays L.) planting into a live triticale (Triticale hexaploide L.) cover crop, four artificial rainfall-overland flow events were generated (42 mm h−1 for 30 min) on replicated field-scale plots in central Wisconsin. Mean total P, total N, and suspended solids loads were consistently lower for VT at 2 days post-manure application (with 97 to 99% lower losses than broadcast, respectively). Dissolved reactive P and ammonium-N concentrations for both CT and VT were significantly lower three weeks after manure application compared to broadcast. Results suggest that VT reduced soil/residue disturbance while incorporating manure sufficiently to reduce sediment, N, and P transport potential under simulated high overland flow conditions.
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agronomy
Article
Tillage and Liquid Dairy Manure Effects on Overland Flow
Nitrogen and Phosphorus Loss Potential in an Upper Midwest
Corn Silage-Winter Triticale Cropping System
Jessica F. Sherman 1, Eric O. Young 1, * and Jason Cavadini 2


Citation: Sherman, J.F.; Young, E.O.;
Cavadini, J. Tillage and Liquid Dairy
Manure Effects on Overland Flow
Nitrogen and Phosphorus Loss
Potential in an Upper Midwest Corn
Silage-Winter Triticale Cropping
System. Agronomy 2021,11, 1775.
https://doi.org/10.3390/agronomy
11091775
Academic Editor: Ward Smith
Received: 29 July 2021
Accepted: 31 August 2021
Published: 3 September 2021
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Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1Institute for Environmentally Integrated Dairy Management, USDA-ARS, Marshfield, WI 54449, USA;
jessica.sherman@usda.gov
2Marshfield Agricultural Research Station, University of Wisconsin, Stratford, WI 54484, USA;
jason.cavadini@wisc.edu
*Correspondence: eric.young@usda.gov; Tel.: +1-715-384-9673
Abstract:
Dairy manure is an important crop nutrient source in Wisconsin and other parts of the
upper Midwest but can contribute to nitrogen (N) and phosphorus (P) losses in overland flow/surface
runoff. Winter cereal grain cover crops can help reduce erosion and nutrient transport in corn systems.
However, few studies have compared tillage impacts on nutrient loss in live cover crop systems.
The objective of this study was to evaluate vertical (VT) and chisel tillage (CT) effects on overland
flow nutrient and sediment loss potential after spring-applied liquid manure. A surface application
treatment (i.e., broadcast) and a no manure control were also included for comparison. After corn
(Zea mays L.) planting into a live triticale (Triticale hexaploide L.) cover crop, four artificial rainfall-
overland flow events were generated (42 mm h
1
for 30 min) on replicated field-scale plots in central
Wisconsin. Mean total P, total N, and suspended solids loads were consistently lower for VT at
2 days post-manure application (with 97 to 99% lower losses than broadcast, respectively). Dissolved
reactive P and ammonium-N concentrations for both CT and VT were significantly lower three
weeks after manure application compared to broadcast. Results suggest that VT reduced soil/residue
disturbance while incorporating manure sufficiently to reduce sediment, N, and P transport potential
under simulated high overland flow conditions.
Keywords:
dairy systems; cover crops; erosion; manure; nutrient loss; overland flow; planting green;
surface runoff; triticale
1. Introduction
Dairy manure is an important nutrient source for farms. However, careful manage-
ment is required to reduce nitrogen (N) and phosphorus (P) loss potential in overland
(surface runoff) and subsurface flows [
1
7
]. Applying manure to the soil surface without
incorporation (broadcast) dramatically increases the risk of dissolved N and P losses in
overland flow [
8
12
], especially when manure is applied in early spring or fall when soil
moisture and overland flow potential are high. Using some form of tillage to increase
manure–soil interaction can reduce overland flow nutrient losses compared to surface
broadcast. However, erosion and sediment-bound N and P loss potential can increase from
greater disturbance associated with tillage practices [7,10,1315].
In addition to manure management and tillage regimes, cover crops can also con-
tribute to lower erosion and nutrient loss in addition to reducing nitrate-N (NO
3
-N)
leaching by an average of 35–70% [
1
,
2
,
16
20
]. While some degree of tillage is beneficial for
incorporating manure, cover crop integrity and residue coverage can be compromised [
21
].
Cover crop impacts on overland flow water quality from cropland varies by species,
planting density, planting/termination dates, root density, soil type, and overall cropping
system [
22
]. While terminating cover crops closer to the time of annual crop planting is
Agronomy 2021,11, 1775. https://doi.org/10.3390/agronomy11091775 https://www.mdpi.com/journal/agronomy
Agronomy 2021,11, 1775 2 of 12
usually assumed to be detrimental to corn yield potential [
23
25
], it may contribute to soil
quality (lower bulk density, organic carbon additions, decrease erosion potential) without
necessarily diminishing corn yield [
26
28
]. Tillage can sometimes help offset potential
corn yield reductions associated with cover crops. Raimbault et al. reported that moving
residue from the row in no-till plots reduced negative effects on growth, while Ewing et al.
reported that subsoiling improved water availability and increased grain yield where cover
crops were present [
23
,
25
]. In contrast, Duiker and Curran found no yield benefit of in-row
tillage compared to no-till on corn yield or weed control with winter rye terminated in the
late boot stage [27].
Planting an annual crop into a living cover crop or ‘planting green’ is a relatively new
approach, with only a few studies on corn yield and nutrient loss potential in overland
flow. In general, when planting green, cover crop termination is delayed for 1 to 2 weeks
after annual crop planting to maintain a soil cover which reduces raindrop impact and
erosion [
20
,
26
,
29
32
]. For example, Gyssels et al. found an exponential reduction in soil
erosion rates with increasing cover crop biomass [
17
,
33
]. In dairy systems where manure is
routinely applied, some degree of tillage combined with planting green into a cover crop
may provide the dual benefits of offsetting corn yield depression from delayed emergence
and competition from the cover crop while reducing nutrient loss potential in overland
flow and maintaining higher soil quality.
Given dairy producer interest in improving nutrient use efficiencies and the need
for additional tools for mitigating nutrient transport to protect water quality, site-specific
manure application and cover crop management systems will be important for reducing
overland flow and subsurface hydrologic nutrient loss risk [
34
]. Winter grains such as
triticale and rye have excellent forage yield potential with timely fall seeding and can be
left in place prior to planting annual crops or harvested as a high-quality hay crop forage in
the spring [
35
,
36
]. Winter grains can thus function as effective cover crops while offering a
potential double cropping opportunity for farmers and greater economic incentive to plant
cover crops. The objective of our study was to evaluate the impact of spring application of
liquid dairy manure to a live winter triticale cover crop on overland flow, sediment, and
dissolved/particulate N concentrations and loads (runoff volume ×concentration) using
artificial rainfall-overland flow simulations. Specifically, we compared spring broadcast
manure application/no-till with: (i) broadcast manure application followed by one-pass
chisel plow tillage (CT), (ii) broadcast manure application followed by one-pass vertical
tillage (VT), and (iii) a no manure control. We hypothesized that VT would increase
infiltration, reducing overland flow, while the presence of cover crop biomass would also
help to decrease erosion and nutrient losses.
2. Materials and Methods
2.1. Field Site and Experimental Design
This field experiment was conducted on a moderately well-drained Loyal silt loam soil
(fine-loamy, mixed, superactive, frigid Oxyaquic Glossudalfs; 1 to 6% slope; USDA-NRCS
Web Soil Survey; https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm) located
on the University of Wisconsin Marshfield Agricultural Research Station at Stratford, WI
(44.758238,
90.100229). The field used was planted with triticale (Triticale hexaploide L.)
on 12 September 2017 with a grain drill (Landoll Farm Equipment, Brillion, WI, USA) at
224 kg ha
1
. Sixteen rectangular plots (4.6
×
15.2 m) were established within a forage crop
production field in a randomized complete-block design (4 blocks/4 treatments). Blocks
were set up along two transects oriented along the main field slope with borders around
each block to accommodate the size and turning radius of field equipment (border 3 m
in width between blocks one and two and between blocks three and four and a border
17 m in width between blocks one and three, and two and four). Plots were positioned
with the long side perpendicular to the slope in the same direction of field operations
and manure applications. Triticale was hand-cut/sampled (10 cm height) on 29 May 2018
Agronomy 2021,11, 1775 3 of 12
from individual plots, after which the whole field was cut for triticale silage (Case IH,
8830 haybine, Racine, WI, USA).
2.2. Manure Application and Tillage Treatments
Liquid dairy manure was applied to all plots (VT, CT, broadcast) except the no manure
controls on 4 June 2018 at approximately 66,200 L ha
1
using a toolbar with 30 cm drop
tubes (Yetter Avenger, Yetter Manufacturing, Colchester, IL, USA) applied at 38 cm above
the soil surface. In addition to the surface manure application treatment (broadcast) and no
manure control, tillage treatments consisted of either chisel plow tillage (CT; Landoll Farm
Equipment, Brillion, WI, USA) (15 cm deep) or one-pass with a vertical tillage implement
(VT; McFarlane Incite 5000, Manufacturing, Sauk City, WI, USA); VT is designed to reduce
compression and shear forces caused by chisel shanks while conserving more residue and
was operated at a shallow depth (3.5 cm) and disk angle (3
). Since the heavy silt loam
soils were too uneven to plant after chisel tilling, CT plots also had one pass with the VT
implement to prepare an acceptable seedbed. Tillage occurred in all CT and VT plots within
the first 10 min of manure application.
Manure was sampled twice during the application process, and subsequently analyzed
(University of Wisconsin Soil and Forage Laboratory, Marshfield, WI) for total nitrogen
(TN), total phosphorus (TP), ammonium-N (NH
4+
-N), water-extractable P (WEP) and
solids content [
37
,
38
]. Manure application supplied an average of 15 and 106 kg ha
1
of
TP and TN, respectively. Of the total manure N and P applied, an estimated 84 kg ha
1
NH4+-N and 5 kg ha1water-extractable P (mainly orthophosphate) were applied.
Plots were planted to silage corn (Zea mays L.) (Prairie Estates C-2908 hybrid, Middle-
ton, WI, USA) (FAO CPC 01121) immediately after manure application and incorporation
(where utilized) on 4 June 2018 with a six-row corn planter (1750 MaxEmerge, John Deere,
Moline, IL, USA) at a rate of 69,000 seeds ha
1
along with banded application of a liquid
fertilizer formulation of 7-9-13-2(S) applied 50 mm to the side and 50 mm beneath seed
rows at a rate of 93.5 L ha
1
. Triticale stubble was sprayed on 25 June 2018 with Roundup
®
(Monsanto, St. Louis, MO, USA) and Status
®
(BASF, Florham Park, NJ, USA) to terminate
the cover crop and reduce competition with corn.
2.3. Rainfall-Overland Flow Simulations
Four rainfall-overland flow simulations were performed in 2018 with individual
events performed over two consecutive days (2 blocks simulated/day) following the
general procedures of Humphrey [
39
]. Dates for individual events were: (i) 2 days after
manure application on 6–7 June (Event 1), (ii) 27–28 June (Event 2), (iii) 17–18 July (Event 3),
(iv) 30–31 July (Event 4). Runoff was collected from a 2
×
2 m area bordered on three sides
by steel panels (15 cm wide) driven 7.5 cm into the soil. A PVC gutter at the lower end of
the plot collected runoff, which was pumped from a small collection pail into a 132 L plastic
drum placed on a platform scale. The average plot slope was 4.4% and frame locations were
identical for all events. Water was pumped through the rainfall simulator (average flow
rate = 125 mL s
1
) and applied to plots at an average rate 42 mm h
1
for 30 min. Simulated
rainfall was applied through TeeJet
®
#30 nozzles (Spraying Systems Co., Wheaton, IL, USA)
positioned 305 cm above the soil surface (Joerns, Inc., West Lafayette, IN, USA). Time to
initiation of overland flow was recorded and 1 L subsamples were collected, weighed and
mixed thoroughly after 30 min. Samples were analyzed for total dissolved solids (TDS)
(Method 2540C) [
40
], suspended solids (SS) (Method 3977-97B) [
41
], volatile solids (VS)
(Method 2540E) [
39
], TN and TP (acid persulfate/autoclave method) [
42
]. A second sample
(60 mL) was passed through a 0.45
µ
m pore size filter followed by analysis of dissolved
reactive P (DRP) [
43
], NO
3
-N [
44
] and NH
4+
-N [
45
] by automated flow injection analysis.
Solids and nutrient loads were estimated by multiplying event overland flow volumes by
their corresponding concentrations.
Agronomy 2021,11, 1775 4 of 12
2.4. Plant and Soil Measures
Before each rain simulation, photographs were taken (2 per plot, 2.25 m
2
) for subse-
quent digital imagery analysis (SamplePoint Software) to estimate the plot area covered
with soil, residue (desiccated corn or triticale biomass), live corn/triticale stubble, and
manure coverage [
46
]. Just outside the runoff area, ten 2 cm diameter soil cores were
collected to a 10 cm depth for nutrient analysis. Samples were dried, ground (2 mm) and
analyzed for plant-available P, and potassium (K) using the Bray soil test solution [
38
]. Soil
TN and total carbon (TC) were determined by high temperature combustion (Elementar
VarioMax CN analyzer, Elementar Americas Inc., Mt. Laurel, NJ, USA). Soil NO
3
-N, and
NH
4+
-N were analyzed by flow injection analysis after extraction in a 5:1 (solution:soil)
2 M potassium chloride (KCl) solution [
47
,
48
]. Soil organic matter (OM) was estimated
by loss on ignition [
49
] and converted to OM equivalents by regression [
50
]. Initial soil
moisture was determined by averaging 6 samples taken immediately outside the runoff
area by a capacitance sensor (ML2 ThetaProbe, Delta-T Devices, Cambridge UK) prior
to rain simulations and periodically throughout the growing season. Weather conditions
were monitored throughout the season with a portable unit at the edge of field (Spectrum
Technologies, Aurora, IL, USA).
2.5. Statistical Analysis
Plots were arranged in a randomized complete-block design with tillage method
as the main treatment effect. Analysis of variance via the mixed modeling procedure
in SAS (proc mixed) was used to test the fixed effect of manure application/tillage (CT
or VT); block and simulation event (time) were treated as random effects. Least square
means were separated using the “PDIFF” option. Dependent variables included overland
flow volume, solids and nutrient concentrations/loads, and percent residue and live crop
coverage. Data were tested for normality (proc univariate) and transformed as needed
(log10 or square root) to achieve normality and homogeneity of variance. However, all
data are presented as back-transformed means for ease of interpretation. Overland flow
data had significant treatment
×
rainfall event interactions, therefore events were analyzed
individually. Because of the high inherent variability associated with soil hydrology and
nutrient dynamics, significance was declared at p
0.10 [
4
,
5
,
9
,
14
,
15
,
35
]. Linear associations
were assessed with Pearson correlation coefficients (proc corr) and linear regressions (proc
reg) were also performed for pairs of select variables.
3. Results and Discussion
3.1. Weather
Average temperatures in June through August were within 5% of the 40 year average
(20
C, Jason Cavadini, personal communication, 2017). Rainfall varied from long-term
averages and was 139%, 67% and 150% of the 40 year average for June, July, and August,
respectively, and the total over the three months was 389 mm. Most of the rain for 2018
fell in a few large events in June and the end of August, with a few smaller events the rest
of the season (Figure 1). This growing season rainfall amount was 1.2-fold greater than
the average of the last 10 years but similar (within 3% on average) to four of the last ten
years, suggesting that 2018 was similar to recent weather patterns. During the growing
season, soil temperature averaged 20.5
C, with fluctuations reflecting air temperature
changes, and volumetric moisture content averaged 22.4%, with marked increases after
rain events. There were few significant differences in soil temperature or moisture content
among treatments. However, CT tended to be warmer and drier than other treatments
(data not shown).
Agronomy 2021,11, 1775 5 of 12
Agronomy 2021, 11, x FOR PEER REVIEW 5 of 12
Figure 1. Daily precipitation totals (mm), air temperature (°C), and volumetric soil moisture content
(%) near the study site located at the Marshfield Agricultural Research Station, Stratford, Wisconsin,
USA.
3.2. Manure and Tillage Effects on Soil Nutrient Concentrations and Total Carbon
Compared to the control, labile K and P concentrations in addition to soil TC, TN,
and OM contents were greater where manure remained on or closer to the surface (Table
1). Mean soil OM, TC, and TN were all significantly lower for CT, presumably because of
deeper incorporation of manure and triticale stubble/residue (to 15 cm). The fact that OM,
TC, and TN for CT were lower than control plots (which have only minor N-P-K inputs
from fertilizer) suggests that CT more effectively mixed surface soil layers with manure
and mixed C and N deeper into the soil than the sampled layer. Average soil NH
4+
-N and
NO
3
-N concentrations were numerically higher for manure treatments but did not differ
from control (data not shown). In general, results indicate the importance of manure as a
labile source of C, N, K, and P in addition to the tendency for greater dilution effects on
soil nutrients and OM from CT compared to surface broadcast and VT.
Table 1. Treatment averages for select soil nutrient characteristics.
Treatment OM † Total N Total C Bray-1-P Bray-1-K
% g kg
1
mg kg
1
Control 4.7 b‡ 2.4 a 24.5 b 32.3 bc 235 b
Broadcast 4.9 a 2.5 a 25.4 a 36.6 ab 302 a
Vertical 4.8 ab 2.5 a 25.4 a 36.8 a 285 a
Chisel 4.4 c 2.2 b 22.5 c 28.8 c 227 b
CV †† 6 6 5 6 3
p-value ‡‡ <0.001 <0.001 <0.001 0.008 <0.001
† OM = soil organic maer, Bray-1 soil extract; used by University of Wisconsin Extension for as-
sessing plant availability and making crop nutrient recommendations.
‡ values with the same
letter are not significantly different at p 0.10. †† Coecient of variation. ‡‡ p-value for
main effect of incorporation method.
3.3. Manure and Tillage Effects on Overland Flows
Overland flows did not differ among treatments for any simulation event (Table 2).
A lack of overland flow differences among treatments was not unexpected, since the field
as a whole was in one crop rotation with similar management prior to the present study.
Other studies have also similarly reported little impact on overland flow after applying
differing liquid manure application methods, including low-disturbance application in
Figure 1.
Daily precipitation totals (mm), air temperature (
C), and volumetric soil moisture content (%) near the study site
located at the Marshfield Agricultural Research Station, Stratford, Wisconsin, USA.
3.2. Manure and Tillage Effects on Soil Nutrient Concentrations and Total Carbon
Compared to the control, labile K and P concentrations in addition to soil TC, TN, and
OM contents were greater where manure remained on or closer to the surface
(Table 1).
Mean soil OM, TC, and TN were all significantly lower for CT, presumably because of
deeper incorporation of manure and triticale stubble/residue (to 15 cm). The fact that OM,
TC, and TN for CT were lower than control plots (which have only minor N-P-K inputs
from fertilizer) suggests that CT more effectively mixed surface soil layers with manure
and mixed C and N deeper into the soil than the sampled layer. Average soil NH
4+
-N and
NO
3
-N concentrations were numerically higher for manure treatments but did not differ
from control (data not shown). In general, results indicate the importance of manure as a
labile source of C, N, K, and P in addition to the tendency for greater dilution effects on
soil nutrients and OM from CT compared to surface broadcast and VT.
Table 1. Treatment averages for select soil nutrient characteristics.
Treatment OM Total N Total C Bray-1-P Bray-1-K
%g kg1mg kg1
Control 4.7 b‡ 2.4 a 24.5 b 32.3 bc 235 b
Broadcast 4.9 a 2.5 a 25.4 a 36.6 ab 302 a
Vertical 4.8 ab 2.5 a 25.4 a 36.8 a 285 a
Chisel 4.4 c 2.2 b 22.5 c 28.8 c 227 b
CV †† 6 6 5 6 3
p-value ‡‡ <0.001 <0.001 <0.001 0.008 <0.001
OM = soil organic matter, Bray-1 soil extract; used by University of Wisconsin Extension for assessing plant
availability and making crop nutrient recommendations.
values with the same letter are not significantly
different at p0.10. †† Coefficient of variation. p-value for main effect of incorporation method.
3.3. Manure and Tillage Effects on Overland Flows
Overland flows did not differ among treatments for any simulation event (Table 2). A
lack of overland flow differences among treatments was not unexpected, since the field as a
whole was in one crop rotation with similar management prior to the present study. Other
studies have also similarly reported little impact on overland flow after applying differing
liquid manure application methods, including low-disturbance application in hay and corn
fields [
9
11
]. Notwithstanding, the broadcast treatment had 4- to 30-fold greater overland
flow than other treatments. Yague et al. also reported larger overland flow from broadcast
Agronomy 2021,11, 1775 6 of 12
liquid manure treatments possibly due to the manure creating a sealing effect on surface
soil pores, thus limiting infiltration of manure and water during rainfall simulations [
15
].
Other studies have reported that fall CT increased surface roughness, resulting in lower
overland flows in corn systems [
11
]. However, overland flow for subsequent simulations in
our trial tended to increase for CT (8 to 14-fold greater than other treatments), suggesting
that a lack of cover/residues and disruption of surface soil structure may have contributed
to lower infiltration and correspondingly greater overland flow potential for CT in the
later events.
Table 2. Overland flow and nutrient loads for each simulation.
Treatment Runoff TP TN DRP NO3-N NH4+-N SS TDS VS
mm g ha1kg ha1
Simulation 1
Control 0.05 0.19 bc ‡ 3.19 b 0.07 b 1.38 0.42 0.08 bc 0.32 b 0.17 b
Broadcast 0.31 7.25 a 36.3 a 3.72 a 12.2 9.95 1.95 a 2.62 a 1.39 a
Vertical 0.01 0.06 c 0.84 c 0.03 b 0.37 0.20 0.05 c 0.08 c 0.06 c
Chisel 0.08 0.32 b 4.60 b 0.13 ab 2.86 0.72 0.16 b 0.34 b 0.20 b
CV 43 65 103 51 5216 159 40 65 44
p-value NS 0.05 0.06 0.10 NS NS 0.05 0.07 0.07
Simulation 2
Control 0.07 0.51 3.96 0.31 2.70 0.14 0.15 0.35 b 0.29
Broadcast 0.08 1.99 14.4 0.54 3.70 0.39 0.40 1.37 b 1.19
Vertical 0.52 2.59 26.3 0.83 20.1 0.03 1.28 2.43 ab 2.00
Chisel 0.98 7.69 55.5 1.17 36.6 0.01 6.97 6.19 a 4.65
CV 96 168 92 112 147 41 258 2692 554
p-value NS NS NS NS NS NS NS 0.03 NS
Simulation 3
Control 0.17 1.26 27.2 0.54 16.9 1.01 0.42 1.33 0.82
Broadcast 0.36 3.11 35.7 0.64 21.7 0.96 2.92 3.12 2.17
Vertical 0.27 2.46 34.1 0.56 20.7 0.69 1.58 1.83 1.26
Chisel 1.37 11.8 120 1.44 67.6 2.26 25.8 11.4 8.04
CV 112 112 126 146 170 233 1258 1251 818
p-value NS NS NS NS NS NS NS NS NS
Simulation 4
Control 0.42 2.54 32.4 0.76 25.8 0.18 1.45 2.78 1.15
Broadcast 0.75 7.20 68.3 1.10 48.6 0.40 9.81 3.87 2.22
Vertical 0.30 1.79 22.5 0.22 17.0 0.02 1.36 1.95 0.91
Chisel 4.26 31.5 271 2.67 164 0.46 63.8 26.1 13.7
CV 167 253 54 204 62 67 437 175 324
p-value NS NS NS NS NS NS NS NS NS
TP = total P, TN = total N, DRP = dissolved reactive P, NO
3
-N = nitrate-N, NH
4+
-N = ammonium-N, SS = suspended solids, TDS = total
dissolved solids, VS = volatile solids; ‡ values with the same letter are not significantly different at p0.10, NS = not significant.
3.4. Manure and Tillage Effects on Overland Flow Nitrogen Loss
Many of the differences noted among treatments occurred in the first simulation
event, with consistently higher TN loads for broadcast relative to CT, VT, and control
(Tables 2and 3).
Though not significant given the high variability in the data, greater
overland flows from broadcast treatment invariably contributed to the higher N losses than
VT and CT. Manure application increased TN concentrations, with greater concentrations
for unincorporated treatments (broadcast and VT) where manure was closer to the surface
and could interact with overland flow (Table 3). In contrast, TN concentrations for CT
were reduced 12% from broadcast and similar to the control. Loads of TN also differed
among treatments with CT similar to control. Average TN loads for VT and CT were 87 and
98% lower than broadcast, respectively (Table 2), demonstrating the critical importance of
incorporating manures to increase N retention while mitigating overland flow loss potential.
While differences in dissolved inorganic N (NO
3
-N and NH
4+
-N) concentrations were
Agronomy 2021,11, 1775 7 of 12
similar and loads did not differ significantly, NO
3
-N loads were reduced by 77% and 97%
for CT and VT, respectively; NH4+-N loads were reduced by 93% and 98%, respectively.
Table 3. Concentrations in runoff for each simulation.
Treatment TP TN DRP NO3-N NH4+-N SS TDS VS
mg/L
Simulation 1
Control 0.30 5.36 b ‡ 0.20 3.04 1.00 126 514 274 c
Broadcast 1.12 7.41 a 0.51 3.30 1.69 375 518 281 bc
Vertical 0.57 7.57 a 0.25 3.53 1.92 335 703 485 a
Chisel 0.65 6.49 ab 0.29 3.16 1.12 372 559 384 ab
CV 72 16 53 14 50 10 21 21
p-value NS 0.10 NS NS NS NS NS 0.03
Simulation 2
Control 0.97 5.91 0.66 b 3.95 0.23 b 274 531 495
Broadcast 1.45 6.14 1.23 a 9.11 0.38 a 172 584 510
Vertical 0.66 5.42 0.25 b 3.91 0.04 c 357 526 513
Chisel 0.93 5.63 0.18 b 3.95 0.02 c 522 490 653
CV 54 19 102 28 31 69 9 7
p-value NS NS 0.03 NS 0.0003 NS NS NS
Simulation 3
Control 0.53 11.4 0.19 6.24 1.37 433 b 1011 596
Broadcast 0.73 8.27 0.18 4.83 0.23 509 b 592 393
Vertical 0.87 12.6 0.23 7.76 0.25 582 b 801 671
Chisel 0.75 9.09 0.12 5.55 0.24 1158 a 608 423
CV 27 32 23 40 73 28 25 5
p-value NS NS NS NS NS 0.06 NS NS
Simulation 4
Control 0.54 7.38 0.17 5.69 0.07 296 644 224
Broadcast 0.81 7.48 0.13 5.01 0.07 854 618 304
Vertical 0.51 6.73 0.08 5.00 0.02 375 666 293
Chisel 0.70 6.48 0.06 4.21 0.01 1236 591 309
CV 44 24 48 31 105 14 8 22
p-value NS NS NS NS NS NS NS NS
TP = total P, TN = total N, DRP = dissolved reactive P, NO
3
-N = nitrate-N, NH
4+
-N = ammonium-N, SS = suspended solids, TDS = total
dissolved solids, VS = volatile solids, ‡ values with the same letter are not significantly different at p0.10, and NS = not significant.
The large overall yet variable decrease in overland flow N loss potential with tillage
indicates the important role different types and degrees of tillage have on N loss. Our
findings support others showing variable overland flow N loss depending on manure
application management system and other site-specific factors, with some showing no
tillage effects on TN, NO
3
-N, or NH
4+
-N [
9
,
10
,
14
,
51
]. While not significant, TN and NO
3
-
N loads for CT increased with subsequent rainfall simulation events and likely associated
with higher runoff quantities. We hypothesize that the presence of live triticale biomass may
have contributed to maintenance of soil structure immediately after manure incorporation,
thus helping to retain water infiltration and N more effectively than situations where cover
crops are terminated earlier or subject to winter kill.
3.5. Manure and Tillage Effects on Overland Flow Phosphorus and Sediment Loss
Similar to N results, incorporating manure reduced mean P loads to levels similar
to the control. Compared to broadcast treatment, VT and CT reduced TP and DRP loads
by >96% on average (Tables 2and 3). Greater P losses from surface manure application
compared to manure application with tillage incorporation is similar to results reported
elsewhere, although TP and DRP concentrations and loads in our study were generally
lower than those reported elsewhere [
4
,
5
,
9
,
52
]. Both CT and VT substantially reduced
DRP losses in overland flow compared to broadcast only which is supported by other
studies [
3
,
9
,
13
,
52
]. Some studies report larger TP losses in overland flow with tillage
Agronomy 2021,11, 1775 8 of 12
presumably due to greater erosion and particulate-P transport [
13
,
14
,
52
]. However, this
did not appear to be the case with the first event after manure application. Among other
possible confounding factors, low runoff volumes for the first event could have limited
overland flow TP transport in our study. Additionally, lower erosion potential in the live
triticale (compared to bare soil more typical of annual systems) may have also contributed
to more limited particulate-P mobilization to overland flow. Similar to TN trends, we
speculate that larger TP loads for CT with later events could be related to altered surface
soil structure from greater compaction/disturbance potential of CT shanks compared to
broadcast or VT in these fine-textured silt loam soils.
Results indicate that both CT and VT helped to limit P transport in overland flow
in the presence of live triticale after spring liquid dairy manure application. Based on
previous trials and our results here, a low-intensity form of tillage incorporation while
maintaining maximum residue/cover is an important factor affecting overland flow P loss
potential. Overland flow SS concentrations did not differ significantly among treatments
for the first event. However, loads were higher for broadcast and probably again related to
higher average overland flow volumes (Table 3). Additionally, overland flow from soils
receiving broadcast manure applications can sometimes contribute substantially to total SS
loads via organic matter “flocs” and total particulate OM transport [
53
,
54
]. Compared to
surface broadcast, SS loads for CT and VT were reduced by 92% and 97%, respectively and
similar to the control.
The large reduction in apparent erosion and sediment-bound P transport potential
with tillage could also be related to greater short-term infiltration and a concomitant
decrease in overland flow. It is of note that the SS concentrations and loads in our study
were lower than numerous others examining the effects of different tillage practices on
overland flow water quality and could be related to multiple factors including live triticale,
small plot runoff volumes, and inherent limitations of rainfall-runoff simulations [
9
,
10
,
13
,
15
].
Events after the first simulation also showed some evidence of sediment, N, and P
transport as CT had consistently greater TN and TP (5-fold greater) and TDS and SS loads
(6- and 10-fold greater, respectively) compared to other treatments. VT evidently caused
less soil structure disruption than CT from the combined effects of greater downforce and
shear stress imposed by CT shanks. Moreover, VT left more surface stubble/residues
than CT. While there were only minor concentration differences for the first event, DRP
and NH
4+
-N were greater for broadcast compared to CT or VT three weeks later (6- and
13-fold greater, p= 0.03 and p= 0.0003, respectively). While loads did not differ, the greater
bioavailable N and P concentrations indicate that manure was an important contributor to
overland flow nutrient loss and suggest that some level of incorporation may be needed to
adequately reduce overland flow N and P loss risk where transport to surface waters is a
concern. Results further suggest that the presence of a live cover crop was insufficient to
adequately mitigate overland flow DRP concentrations and thus some incorporation may
be necessary for fields with overland flow potential and close to surface waters.
3.6. Plot Surface Coverage and Overland Flow Water Quality
Digital plot imagery showed that mean percent triticale stubble coverage was reduced
by approximately 50% of the control for VT and 75% for CT (p< 0.0001) (Figure 2). Manure
coverage was also reduced with VT and CT to 16% and 10%, respectively, of broadcast
levels, (p< 0.0001). In addition, manure was positively correlated with concentrations of
TP (r= 0.25, p= 0.09) and NH
4+
-N (r= 0.34, p= 0.01) and loads of TP (r= 0.25, p= 0.09),
DRP (r= 0.59, p< 0.0001), and NH
4+
-N (r= 0.77, p< 0.0001) in overland flow. Previous
studies have similarly reported significant correlations among measures of plant/residue
and manure coverage and SS, N, and P in overland flow [
4
,
9
,
13
,
55
]. While several studies
also indicate correlations between labile soil P measures (i.e., soil test and water-extractable
P) and overland flow DRP concentrations [
56
58
], there was no correlation in our study
(p= 0.47) which could be related to the relatively high SS losses for CT (which had the
Agronomy 2021,11, 1775 9 of 12
lowest Bray-P concentration) in addition to a relatively small overall range in Bray-P
concentrations.
Agronomy 2021, 11, x FOR PEER REVIEW 9 of 12
3.6. Plot Surface Coverage and Overland Flow Water Quality
Digital plot imagery showed that mean percent triticale stubble coverage was re-
duced by approximately 50% of the control for VT and 75% for CT (p < 0.0001) (Figure 2).
Manure coverage was also reduced with VT and CT to 16% and 10%, respectively, of
broadcast levels, (p < 0.0001). In addition, manure was positively correlated with concen-
trations of TP (r = 0.25, p = 0.09) and NH
4+
-N (r = 0.34, p = 0.01) and loads of TP (r = 0.25, p
= 0.09), DRP (r = 0.59, p < 0.0001), and NH
4+
-N (r = 0.77, p < 0.0001) in overland flow. Pre-
vious studies have similarly reported significant correlations among measures of
plant/residue and manure coverage and SS, N, and P in overland flow [4,9,13,55]. While
several studies also indicate correlations between labile soil P measures (i.e., soil test and
water-extractable P) and overland flow DRP concentrations [56–58], there was no correla-
tion in our study (p = 0.47) which could be related to the relatively high SS losses for CT
(which had the lowest Bray-P concentration) in addition to a relatively small overall range
in Bray-P concentrations.
Figure 2. Average plot surface coverage (%) by treatment for soil, manure, residue, corn, and tritcale stubble. † values with
the same letter are not significantly different at p 0.1. †† leers to the right of the bar represent % residue differences and
letters to the left represent % manure differences.
When the first event was analyzed alone, there was no significant correlation be-
tween Bray-P and overland flow DRP or TP concentrations, suggesting that labile P from
manure was likely a more important P source to overland flow than soil P. Bray-P con-
centrations would likely be more important for DRP release to overland flow for later
events after manure P has been more fully integrated into the soil P pool. Interestingly,
total live plus dead plant material was negatively correlated with cumulative overland
flow (r = 0.48, p = 0.0002), suggesting that residue coverage was important for reducing
overland flow. Total plant material was also negatively correlated with DRP (r = 0.29, p
= 0.03) and SS (r = 0.52, p = 0.0001) concentrations in addition to loads of TP (r = 0.47, p =
0.0005), TN (r = 0.49, p = 0.0002), DRP (r = 0.26, p = 0.05), NO
3
-N (r = 0.51, p < 0.0001),
SS (r = 0.46, p = 0.0009), TDS (r = 0.47, p = 0.0007), and VS (r = 0.497, p = 0.0003). Collec-
tively, these relationships support the idea that residue coverage is an important factor
affecting SS and overland flow P mobilization, even after cover crop termination.
4. Conclusions
Both vertical (VT) and chisel tillage (CT) operations conducted after liquid dairy ma-
nure application to the soil surface of corn-triticale plots substantially mitigated overland
flow nutrient concentrations compared to broadcast application alone. Compared to VT,
CT resulted in numerically larger overland flow in subsequent rainfall-overland flow sim-
ulations and slightly larger TN and SS loads. A live triticale cover crop was not sufficient
Figure 2.
Average plot surface coverage (%) by treatment for soil, manure, residue, corn, and tritcale stubble.
values with
the same letter are not significantly different at p
0.1.
††
letters to the right of the bar represent % residue differences and
letters to the left represent % manure differences.
When the first event was analyzed alone, there was no significant correlation between
Bray-P and overland flow DRP or TP concentrations, suggesting that labile P from manure
was likely a more important P source to overland flow than soil P. Bray-P concentrations
would likely be more important for DRP release to overland flow for later events after
manure P has been more fully integrated into the soil P pool. Interestingly, total live plus
dead plant material was negatively correlated with cumulative overland flow (r=
0.48,
p= 0.0002), suggesting that residue coverage was important for reducing overland flow.
Total plant material was also negatively correlated with DRP (r=
0.29, p= 0.03) and SS
(r=
0.52, p= 0.0001) concentrations in addition to loads of TP (r=
0.47, p= 0.0005),
TN (r=
0.49, p= 0.0002), DRP (r=
0.26, p= 0.05), NO
3
-N (r=
0.51, p< 0.0001),
SS (r=
0.46, p= 0.0009), TDS (r=
0.47, p= 0.0007), and VS (r=
0.497, p= 0.0003).
Collectively, these relationships support the idea that residue coverage is an important
factor affecting SS and overland flow P mobilization, even after cover crop termination.
4. Conclusions
Both vertical (VT) and chisel tillage (CT) operations conducted after liquid dairy
manure application to the soil surface of corn-triticale plots substantially mitigated overland
flow nutrient concentrations compared to broadcast application alone. Compared to VT,
CT resulted in numerically larger overland flow in subsequent rainfall-overland flow
simulations and slightly larger TN and SS loads. A live triticale cover crop was not
sufficient to adequately mitigate nutrients and SS in overland flow immediately after
manure application. Results showed that VT significantly reduced TP, TN, and SS losses
to 99, 98, and 97% of broadcast levels, respectively. Additionally, VT maintained greater
triticale stubble/residue coverage that may have aided infiltration of overland flow after
manure application. Overall, our results suggest that some tillage after liquid dairy manure
application to the soil surface may be required when planting green into a live cover crop
to reduce overland flow sediment and nutrient loss risk in addition to helping to prepare a
more favorable seed bed in some conditions. However, additional research is needed to
determine combinations of cover crops and tillage that are most suitable across a range of
growing environments in order to maximize the potential benefits of this practice.
Agronomy 2021,11, 1775 10 of 12
Author Contributions:
Conceptualization, J.F.S.; methodology, J.F.S.; validation, J.F.S. and E.O.Y.;
formal analysis, J.F.S. and E.O.Y.; investigation, J.F.S.; resources, J.C. and J.F.S.; data curation, J.F.S.;
writing—original draft preparation, J.F.S.; writing—review and editing, E.O.Y.; visualization, J.F.S
and J.C. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author.
Acknowledgments:
The authors thank Robin Ogden and Antoinette Kaiser for excellent technical
support in field work, Matt Akins for providing student help, as well as the UW-MARS staff for
equipment operation.
Conflicts of Interest: The authors declare no conflict of interest.
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... Triticale is an important food crop that combines the genomes of wheat and rye. Due to its high ecological plasticity and adaptability, triticale is successfully grown in poor soils and is resistant to a wide range of fungal diseases [1][2][3][4][5][6][7][8]. Triticale is grown as a forage crop for grain and green mass. ...
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