Cost Analysis of Using Soil Electrical Conductivity Information for Precision Management in Cotton Production

1
Cost Analysis of Using Soil Electrical
Conductivity Information for Precision Management
in Cotton Production
J.A. Larson R.K. Roberts B.C. English C. Hicks
2
Introduction

• One of the most popular precision farming
  technologies used by cotton farmers is grid soil
  sampling.
• With grid soil sampling, GPS technology is used
  to create small sub-field areas for soil
  samplingtypically 2.5 acre (1 hectare)
  grids.
• 205 of 1,021 (20) farmers in a 2005 survey of
  cotton farmers used grid soil sampling.

Source Veris Technology
3
Introduction

• Grid sampling relies on labor-intensive manual
  sampling and laboratory analysis.
• There is nearly as much variability within the
  2.5 acre grid cells as among them.
• The variability in grids raises questions about
  the usefulness of the grids in capturing actual
  field variability.
• On-the-go soil electrical conductivity (EC) and
  pH sensing have been suggested as a way to more
  accurately measure soil variability.

Source Veris Technology
4
Introduction

• Soil electrical conductivity (EC) is the ability
  of soil to conduct electrical current.
• The most common method of EC data collection uses
  electrodes shaped like coulters that make contact
  with the soil to measure EC.
• One set of coulters applies electrical current
  into the soil, while the other set of coulters
  measures the drop in voltage.
• EC is influenced by a number of factors including
  clay content, soluble salts, bulk density,
  organic matter, soil moisture, and soil
  temperature.

Source Veris Technology
5
Introduction

• Potential uses of EC information include
• Estimating soil propertiestexture (sand, silt,
  clay), soil moisture, organic matter, topsoil
  depth, and soil salinity
• Measuring nutrient levels in the soil (e.g.,
  nitrogen, potassium, etc)
• Predicting pest distributions in fields
  Interpretation of yield maps and
• Guidance for placement and interpretation of
  on-farm tests.
• Potential management applications include
• Directed soil sampling within more accurate soil
  boundaries,
• Drainage remediation,
• Soil salinity remediation,
• Delineation of management zones for input
  applications,
• Variable rate pesticide application, and
• Variable rate nutrient application.

6
Introduction

• Currently, very little research has been done on
  the costs of collecting on-the-go EC and pH
  information versus the potential benefits to
  cotton farmers.
• Whether it is economically feasible for farmers
  to use on-the-go EC and pH data will depend on
  what VRT decisions are made using the EC
  information.
• Like any precision agriculture technology, if
  farmers can decrease their input costs or
  increase their yields using EC and pH
  information, they may be able to improve crop
  profitability.
• Information on costs of on-the-go EC and pH data
  collection would be useful to farmers considering
  purchasing equipment and to consultants, input
  suppliers, and others interested in providing
  custom on-the-go services.

7
Objectives

• Evaluate an equipment compliment designed to
  collect on-the-go EC and pH data in farm fields
• Ownership and operating costs as a function of
  farm size.
• Breakeven values to cover the cost of the system
  
• Lint yield gains and
• Reduced input costs.

8
Assumed Components of an EC and pH Information
System

• Veris Mobile Sensor Platform (MSP) with the EC/pH
  instrument package, dual array EC surveyor kit,
  and a Veris soil pH manager.
• AgLeader GPS 3100 unit.
• The GPS unit provides a way to geo-reference the
  EC and pH data to specific locations in the
  field.
• AgLeader Advanced Lightbar unit.
• The lightbar technology provides a way to provide
  precision guidance of the unit as it makes
  measurements throughout the field.
• 65-HP tractor to pull the MSP unit through the
  field.

9
Calculating Ownership and Operating Costs for
On-The-Go EC and pH data

• Veris MSP Unit
• Depreciation and interest
• Repairs
• Electrodes and
• Taxes, insurance, and housing.
• GPS and Guidance
• Depreciation and interest
• Repairs
• Taxes, insurance, and housing and
• GPS signal subscription.
• Tractor
• Depreciation and interest
• Repairs
• Taxes, insurance, and housing
• Fuel and lube and
• Labor time.

10
Assumptions for Calculating Costs

• All costs are charged to the cotton enterprise.
• Average one trip per year for EC measurement is
  made over each cotton field.
• Average one trip every four years for pH
  measurement is made over each cotton field.
• Cotton enterprise sizes ranged from 500 acres up
  to 3,000 acres.
• Recommended 9.3 pH samples/acre (4 mph travel
  speed, 80 ft between passes in the field) was
  used to calculate tractor time and electrode use
  
• 3 samples/acre (10 mph, 100 ft)
• 5 samples/acre (5 mph, 100 ft)
• 14.9 samples/acre (10 mph, 20 ft), and
• 37.1 samples/acre (4 mph, 20 ft).

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Breakeven Yield Gains and Input Cost Savings

• VRT decisions made using EC and pH information
• Whole field N, P, K, and lime costs of
  91.93/acre.
• Input cost savings scenarios of 0, 10, 20, and
  30 were evaluated.
• Analysis and VRT map making costs (3/acre).
• Difference in application cost for VRT over URT
  (4.93/acre).
• Cotton lint price used to calculate yield gains
  was 0.55/lb.

12
Annual Ownership and Operating Costs for
Different Farm Sizes
Cotton Acres Cotton Acres Cotton Acres
Item 1,000 2,000 3,000
--------------------/Year-------------------- --------------------/Year-------------------- --------------------/Year--------------------
Depreciation Interest 4,956.69 4,956.69 4,956.69
Taxes, Insurance, Housing 615.50 615.50 615.50
Repair Maintenance 2,495.00 2,495.00 2,495.00
Total Annual Ownership Cost 8,067.19 8,067.19 8,067.19
Annual Subscription for GPS 200.00 200.00 200.00
pH Electrodes 93.00 186.00 279.00
Total EC/pH Unit Cost 8,360.19 8,453.19 8,546.19
Power Unit/Labor Cost 804.75 1,609.50 2,414.25
Total Cost 9,164.94 10,062.69 10,960.44
13
Annual EC pH Data Costs for Different Farm
Sizes and Sampling Regimes
Cotton pH Samples/Acre pH Samples/Acre pH Samples/Acre pH Samples/Acre pH Samples/Acre
Acres 3.0 5.0 9.3 14.9 37.1
--------------------------/Acre-------------------------- --------------------------/Acre-------------------------- --------------------------/Acre-------------------------- --------------------------/Acre-------------------------- --------------------------/Acre--------------------------
500 17 17 18 18 21
750 11 12 12 13 16
1,000 9 9 9 10 13
1,250 7 7 8 9 11
1,500 6 6 7 7 10
1,750 5 5 6 7 9
2,000 5 5 5 6 9
2,250 4 4 5 6 8
2,500 4 4 4 5 8
2,750 3 4 4 5 8
3,000 3 3 4 5 7
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Annual EC pH Data Costs for Different Farm
Sizes and Sampling Regimes
Cost/Acre ()
15
Breakeven Yield Gains and Input Cost Savings
Input Savings Input Savings Input Savings Input Savings
Acres 0 10 20 30
-------------Lint yield Gain (Lb/Acre)------------ -------------Lint yield Gain (Lb/Acre)------------ -------------Lint yield Gain (Lb/Acre)------------ -------------Lint yield Gain (Lb/Acre)------------
500 47 30 13 -4
750 37 20 3 -14
1,000 32 15 -2 -19
1,250 29 12 -5 -22
1,500 27 10 -7 -24
1,750 25 8 -8 -25
2,000 24 7 -9 -26
2,250 23 7 -10 -27
2,500 23 6 -11 -28
2,750 22 5 -11 -28
3,000 22 5 -12 -29
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Conclusions

• More economically feasible for larger cotton
  farms to purchase EC and pH information gathering
  equipment because costs can be spread over more
  cotton acreage.
• Farmers with a more cotton acreage may find it
  cheaper to own rather than custom hire depending
  on available labor resources.

17
Conclusions

• If overall input usage remains the same, the
  required yield gains to payback the investment in
  EC and pH information range from
• 47 lb/acre for a 500 acre cotton enterprise, to
• 22 lb/acre for a 3,000 acre cotton enterprise.
• Yield gains to payback the investment are smaller
  if overall input usage is reduced from using
  on-the-go EC and pH information to make input
  decisions.