11th International Drainage Symposium August 30-September 2, 2022 Des Moines, Iowa

1. Shallow Drainage Furrow and Tile Water Management System
Effects on Crop Yield and Water Quality in Eastern North Carolina
Mitchell Watkins, Chad A. Poole, PE, Mohamed A. Youssef

2. Drainage Water Issues in Eastern NC
● High intensity coastal rainfall events on poorly drained soils can cause
excessive surface ponding
● Flat landscape provides little to no natural method for water to move on the
soil’s surface
● In-field trafficability impacted
● Nitrate (NO3
--N) and Phosphorus pollution to surface and groundwater
from runoff and sediment loss

3. Surface Ditch Drainage
● Provides a channel that can quickly remove surface
water during high intensity or long duration rainfall
events
○ Also acts as subsurface drainage
● Extremely effective in flat land with poorly drained soil
types

4. Conventional Ditch (FD)
Design
● ~6 ft wide & ~4 ft deep
● Trapezoidal or V-shaped
○ Typically not precision grade
Benefit
● High surface water carrying capacity
Issues
● Steep banks with scouring potential
○ Increased nutrient loss
● Trafficability hazard
○ Loss of land

5. Conventional Ditch Costs
*Half-mile square, $3,000 control structure, $4,138 land value, $6 corn @ 200 bu/ac
● Initial installation cost
○ Excavator, backhoe, rotary ditcher, hydraulic plows
● Yearly cleaning cost
○ Sediment removal
○ Vegetation removal when dry
Conventional Ditch
Ditches Ditch Spacing (m) Lost Surface Area (ha)
Cost of Lost Harvest
($/yr) Control Structure Cost ($)
17 46 2.6 $7,959.61 $52,467.39
13 60 2.0 $6,102.37 $40,225.00
11 76 1.6 $4,817.66 $31,756.58
9 91 1.3 $4,023.54 $26,521.98

6. Drainage Design Potential
● System can be designed to handle surface water ponding issues from high intensity
rainfall while also minimizing the loss of productive land
● Resolve trafficability issues while operating in the field from permanent ditches
● Minimize labor requirements of managing multiple control structures
● Provide safety buffer for improper system management
● Reduce design maintenance costs while increasing the return on investment with
higher yields and lower nutrient loss

7. Shallow Furrow (SD)
Design
● Furrow depth: .15 m to .45 m
● Furrow width: .9 m
● Precision installation
○ Furrow on grade
○ Crowned between furrows
○ Control direction of surface and
subsurface flow
● Supplemental tile drainage
○ Single outlet point
● Surface furrow only for high intensity
events

8. Shallow Furrow (SD)
Potential Benefits
● Gradual vegetative banks
● Little to no subsurface drainage
● Single outlet control structure
○ Simplifies free drainage, controlled
drainage, and subsurface irrigation
transitions
Potential Issues
● Surface water carrying capacity
● Long term maintenance
● Return on investment

9. Drainage Water Management Site (Bath, NC)
Overview
● Portsmouth
sandy loam
● Slope <0.005%
● Conventional
agriculture

10. Site Description
Conventional Ditch Drainage (FD)
● Conventional ditches spaced 60 m
○ Supplemental tile 20 m spacing
■ Tile depth 105 cm average
● Three replications 1.1 ha each
● Collection Instruments (per ditch)
○ V-notch weir
○ Upstream and downstream
pressure transducers
○ Water sampler with collection
container
● Two well sites
○ Groundwater samples
○ Water table measurements
Flow Direction

11. Site Description
● 60 m furrow spacing
○ 20 m tile spacing
● Four surface furrow drains
○ Three replications 2.3 ha surface drainage only
○ Weir with measurement devices
● Outlet furrow
○ Main tile line buried parallel directly below
○ Well pump with control structure and gates
○ 11.22 h of tile drainage
Shallow Furrow Drainage & Irrigation (SD)
Tile Flow Direction

12. Research Objectives
1) Quantify the effect of shallow furrow & tile drainage water management
system on drainage water quality
● Drainage volume from FD and SD treatments
● Nutrient export
● Groundwater level
● Groundwater nutrient content
1) Quantify the drainage water management system’s impact on crop yield
● Yield differences between FD and SD treatments

13. Rainfall Weir Height Tile Depth SDI FD

14. Preliminary Drainage Volumes
20.7 cm
6.6 cm
68%

15. Preliminary Nitrate Export
6.5 kg/ha
1.3 kg/ha
80%

16. Crop Yield Effects SD vs FD
Soybeans
● Average increase: 0.30 Mg/ha (9.06%)
● Range: 0.20 Mg/ha to 0.40 Mg/ha
*Significant in all years
Corn
● Average increase: 0.39 Mg/ha (3.69%)
● Range: -0.31 Mg/ha to 1.00 Mg/ha
*Not significant in 2014 or 2016
*Grouped by crop and analyzed per year
● Data from 2014 to 2021
○ Corn and soybean rotation

19. Yield Map Comparison
2019 Soybean Yield 2020 Corn Yield

20. Potential Impacts
● Increased land in productivity
○ Increased efficiency
● Less management and maintenance
○ Single outlet structure with various
drainage management
configurations
● Preliminary water quality
○ Decreased drainage outflow
○ Reduction in nitrate loss
● Decreased field maintenance

21. Questions?