Yohn, C.W., Extension Agent, West Virginia University
Basden, T.J., Extension Specialist - Nutrient Management, West Virginia University
Fullen, J. T., Certified Crop Advisor, Allegheny Fertilizer
Pena-Yewtukhiw, E. M., Assistant Professor of Soil Science, West Virginia University
Rayburn, E. B., Extension Specialist - Forage Management, West Virginia University

ABSTRACT

In 2005, West Virginia University Extension provided seed money to demonstrate precision soil sampling and precision nutrient management. West Virginia University Extension Service partnered with a crop consultant and "custom applicator" (Allegheny Ag) to perform this task. In 2006 11 land owners consigned 670 acres to an expanded demonstration. These farms were soil sampled using conventional (1.38 acres per sample) and precision (1.87 acres per sample) method. WVU Extension paid for the conventionally taken samples. The individual soil data points were used to determine the number of acres represented by the sample, the soil type and yield potential for alfalfa, mixed grass and corn from soil survey. Results showed that precision sampling and application required more lime than recommended by conventional sampling. Precision management required more phosphorous and less potash on fewer acres than recommended by conventional management. Extension education through presentations, a field day and farmer to farmer talks resulted in 1545 additional acres being sampled. Over 1600 acres received precision application of lime, phosphorous and potash. This occurred on five of the twelve cooperators and eight new land owners. Producers have used this information to change management practices including using mineral feeders and hay placement to guide cattle to specific field areas, delineate areas for variable nutrient application using conventional equipment. Acquisition of precision tools has increased in the area. Private consultants are partnering to help farmers interpret collected data.

INTRODUCTION

Precision agriculture has its roots in the mid to late 1990’s with adoption by farmers and custom applicators being slow. This slow adoption has brought into question the economic benefit of site-specific management of cropland. A review of 108 refereed journals, non-refereed monograghs and popular press found that 63% indicated positive net returns for a given precision agriculture technology, while 11% indicated negative returns . Mixed results were indicated in 26% of the studies (Lambert and Lowenberg-DeBoer, 2000).

A case study conducted by West Virginia University Extension Agent Brian Wickline and Tim Fullen of Allegheny Ag showed an economic advantage to zone sampling techniques and the precision application of lime, phosphorous and potash over conventional recommendations and application using a composite sample and whole field application of nutrients on one farm. This case study stimulated a small WVU grant to duplicate the trial in several other areas of the state.

One of those was a beef and hay farm in Jefferson County, located in the karst limestone geology of the Shenandoah Valley approximately 50 miles west of Washington, DC. This demonstration duplicated the same procedures followed in the Wickline\Fullen trial and demonstrated an economic advantage when soil type and crop response was taken into account. The small trial conducted on 35 acres with fields that were less than twenty acres in size in 2006 lead to an expansion in the spring of 2007.

MATERIAL AND METHODS

The goal of this project was to recruit at least 40 acres per farm for a total of 400 acres sampled and at least 30% of those acres treated using precision management. Allegheny Ag and West Virginia University Extension Service took both precision and conventional samples in the same fields at the same time using the same equipment. A variety of farming enterprises were identified. These farms provided differences in how nutrients had been applied, how often soil tests had been taken and how nutrients may change with the influence of animal manures. The farms were located throughout the county increasing soil type diversity. Producers were past cooperators with the Extension Service and had shown to be early adopters of proven technologies.

All samples were taken in the spring of 2007 between by Allegheny Ag using a 4x4 ATV mounted Simple Simon sampler. Precision samples were taken in field zones. Each geo-positioned sample was represented with five 1.25 inch diameter cores, four inches deep, one in the center and four on the circumference of an approximately 40 foot radius circle. Position data was collected using a Raven GPS connected to an IPaq which was installed with Farm Works Farm Site Mate. Conventional samples were pulled in a random pattern. Fields larger than 40 acres were subdivided into smaller management units based on topography and field characteristics.

Samples were partially air dried and sent to Waters Agricultural Laboratory. A Melich 1 analysis was conducted for water and buffered pH, phosphorous, potassium, calcium, magnesium, and sulfur. Virginia Tech nutrient recommendations were used. Mapping interpolation was accomplished by Allegheny Ag using AGIS developed by Delta Data Systems. Each producer received soil sample results, printed maps showing nutrient levels, pH and application maps for lime, diammonium phosphate and muriate of potash. Each producer was given a copy of ViewPoint a software product from Delta Data Systems that allowed the producer to view maps and evaluate acres that require treatment. Results were shared with producers and explained by Allegheny Ag and the author. Precision application was accomplished with a Trimble Ag 132, a Rockwell Vision System and a Dickey John Land Manager 2.

Results were shared through an October, 2007 field day with seventeen farmers, certified crop advisors and nutrient management consultants in attendance and a 2008 field day with 50 farmers, custom applicators and others in attendance. Two presentations were made to grower groups in Virginia by the author with over 100 producers in attendance. The results were shared in a December newsletter with a circulation of 1300 area producers in a three county area and two fact sheets were developed.

RESULTS AND DISCUSSION

Approximately 670 acres on twelve farms were sampled both precision and conventionally (35 fields). Most of the farms were located in the eastern portion of the county.

Large fields were subdivided into smaller management units to more accurately determine nutrient needs. Figure 1 below demonstrates how a 65 acre field was divided into three units that were each conventionally sampled. The entire field was also precision sampled.

Figure 1. Large fielddivided for conventional sampling purposes

The maximum unit size was 35 acres; the minimum was 5.03 acres with an average of 19.35 acres. In all, three fields and one farm were further divided because of size or management units. Two fields were 65 acres and were each divided into three management units. Another 87 acre field was divided into three units and a small 43 acre farm was divided into 5 fields because of fencing that would limit equipment movement.

In these same fields, 344 precision samples were taken. Each sample represented an average of 1.87 acres with a maximum acreage of 3.75 acres and a minimum of 0.87 acres. To determine the economic variables of precision and conventional fertility management costs were gathered for nutrients and the services (Table 1).

Table 1 – Summary of costs used in economic analysis

Item	Conventional	Precision
Soil sampling and analysis	$3.00 per acre	$8.00 per acre
through commercial lab
Lime spreading	$22.00 per ton	$10.00 per acre
Fertilizer spreading	$7.50 per acre	$10.00 per acre
Diammonium phosphate	$778.00 per ton	$778.00 per ton
(DAP)
Muriate of potash	$490.00 per ton	$490.00 per ton
Lime	Included in lime cost	$10.00 per ton

Figure 2. Application map generated byAGISdemonstrating that only 18 acres of the 127acres required an application of muriate of potash.

Precision sampling costs also included mapping and software provided to the producer to view the maps. Printed copies of the maps, analysis and recommendations were also provided. All spreading cost is based only on the acres requiring application (Figure 2).

The differences in costs for lime spreading are explained by pricing procedures in this region. Most conventional applicators charge by the ton applied rather than a flat fee for spreading on a per acre basis and a separate charge for lime. Summarizing by nutrient applied, the following can be said.

Lime

An additional 86.8 tons would have been applied to an additional 56 acres with precision recommendations versus conventional recommendations. On nine (75%) of the twelve farms more lime would have been applied. Six (50%) of those farms would have had more acres treated while the remaining six farms would have been split evenly between treating less or the same acres as was recommended with the conventional sampling.

Diammonium phosphate (DAP)

An additional 13.3 tons would have been applied to 103 fewer acres with precision recommendations nearly doubling the rate per acre treated over conventional sampling. Ten of the farms (83%) required more material. Nine (75%) of the farms would have had the material applied to less acres while three (25%) required it on the same acres as was recommended with conventional sampling.

Muriate of Potash

Cooperators would have applied 4.8 tons less material to 200 less acres using the precision recommendations over the recommendations from conventional sampling. Eight (67%) of the farms required less material and on ten of the farms (83%) the material would have been applied to less acres. The other two (17%) required material on more acres.

Economic Evaluation

Variations in application levels and acres covered affect the costs of precision sampling and application. In more than one case no lime was recommended from the conventional samples taken, but lime application was recommended from the precision sampling. Costs for each farm are more a reflection of nutrients needed and the variation in the fields than the additional cost of the precision technology. Table 2 below demonstrates the difference in acres treated between the two methods.

Table 2. Comparison of Treated Acres by Sampling Method

	Conventional	Precision
Acres Sampled	669.28	669.28
Percent Treated with Lime	67.27%	77.20%
Percent Treated with
Phosphorous	93.88%	80.75%
Percent Treated with Potash	59.86%	34.71%

The cost per acre by farm was variable as well. Only one farm would have realized a savings by using precision over conventional sampling and application. A 36 acre field would have saved $17.61 per acre by using precision soil testing and application. The other eleven farms had an added expense by using this precision technology. The cost per acre ranged from $5.06 per acre to $65.89 per acre. The average cost among all twelve farms was $21.61 per acre. The high cost of diammonium phosphate (DAP) greatly influenced costs. Many more pounds (26,570) were recommended through precision sampling.

Management practices changed\technology adopted

The largest impact of precision sampling has been field variation and how this has affected land owners. The mapping showing this variability has lead to producers sampling more fields and talking to neighbors about the technology. Of the original twelve producers, five have had more acres sampled and had at least lime applied at a variable rate. An additional nine producers requested and used this technology through the fall of 2007 and spring of 2008. Four of those new producers were influenced by Extension publications and presentations. The remaining five were encouraged by producers who have previously participated in the program. Three of the producers have drawn on the expertise provided by Allegheny Ag to purchase and learn how to use a light bar, a yield monitor and worked with a custom planter and harvester to coordinate and overlay yields and variable rate planting with fertility.

Several farmers used the maps in nontraditional ways to distribute nutrients. The original pilot farm used the maps to direct cattle to areas requiring nutrients through the strategic placement of mineral feeders and moving hay feeding to nutrient deficient areas. This same producer directed the custom application of poultry litter to nutrient deficit areas in a hayfield. Another producer used the results to divide a 65 acre field into the three smaller management units. While this was not a normal precision application, the division into three management units was an improvement over managing the field as one unit. A third producer physically flagged 16 acres to direct the local custom applicator to treat these deficit areas more than once to improve fertility in those areas.

CONCLUSIONS

Twelve farms participated in a trial to evaluate the precision soil sampling and application of nutrients versus conventional sampling and nutrient application. Nearly 670 acres were represented and included acres in crops pasture and hay land. Precision sampling recommendations required the application of more lime on more acres, more phosphorous on fewer acres and less potash on fewer acres than recommended through conventional sampling. Only one farm would have realized a savings by using precision sampling and application over conventional sampling and application. That farm would have realized a $17.61 per acre savings. The other eleven farms had an expense by using this precision technology. The cost per acre ranged from $5.06 per acre to $65.89 per acre. The average cost among all twelve farms was $21.61 per acre. This was mostly due to the additional lime and diammonium phosphate (DAP) applied based on precision recommendations. Through Extension publications and presentations, farmer to farmer encouragement and expansion of acres on five of the twelve original farms, over 2000 acres (a 298% increase from the original acres) have been sampled on a total of twenty-one farms. Ten of the twenty-one farms precision applied lime and two farms precision applied phosphorous and one precision applied both phosphorous and potash for a total of 1600 acres (80%).

Producers have utilized the information generated to distribute nutrients in nontraditional ways, have expanded the use of other precision agriculture tools on the farm and utilized the expertise offered by Allegheny Ag to expand precision agriculture technology beyond soil fertility. More acres will be sampled precision followed by precision application of nutrients as this technology is being embraced by more producers.

Future challenges include evaluating the yield response that uniform fertility across the field may bring which will improve adoption of this technology and improved stewardship of the land.

REFERENCES

AGIS. Delta Data systems, Inc. http://www.deltadatasystems.com/agis/index.html Lambert, D and Lowenberg-DeBoer, J. 2000. Precision agriculture

Profitability Review. Site-specific Management Center School of Agriculture Purdue University http://www.agriculture.purdue.edu/ssmc/Frames/newsoilsX.pdf

 

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