Farmers often question the economic value GPS based technology.
Does precision agriculture pay? In most precision agriculture circles, this is the most often asked question, and at times a most difficult question to answer.
Today’s technology allows farmers to vary the application rates of crop inputs throughout a field. These practices are creating vast and sweeping changes on many farms. This technology allows such inputs as herbicide, insecticide, fertilizer, manure, etc. to be altered at any particular point within a field. GIS software allows various field data such as soil test results, crop scouting data and yield data to be analyzed and incorporated into the decision making process.
Theoretically, combing field based data with the ability to vary input usage at specific points within a field should increase input efficiency. Increased efficiency should improve profit margin and result in the adoption of more environmentally sound practices. – But does it pay?
To answer this question data was analyzed from a 45 acre Central Ohio farm. Seven years of accurate and calibrated yield data was available for this field utilizing a GPS based yield monitor. This field was in a strict corn-bean rotation. Fertilizer recommendations were developed utilizing the four following scenarios.
Scenario 1: Fertilizer recommendations were made according to the farmers normal production practices. Variable rate technology was not utilized in this scenario.
Scenario 2 : The field was divided into 2.5 acre grids. Soil samples were collected and sent to a lab for analysis. The fertilizer application data was developed for this field utilizing variable rate technology based upon the results from the soil test data.
Scenario 3 : The field was divided into management zones based upon soil type. Soil samples were then collected from each soil type. Each sample size was approximately 2.5 acres or less. The fertilizer application data was developed for this field utilizing variable rate technology based upon the results from the soil test data.
Scenario 4: GIS software was used to divide the field into management zones. These zones were based upon actual, historic crop removal data from this field. Fertilizer recommendations were based upon the actual crop removal in each of these management zones. Fertilizer applications were made utilizing variable rate technology.
Table 1 contains the data from this analysis. Fertilizer recommendations were made for each of the four scenarios using the Tri-State Fertilizer Recommendations as a guide. Overall fertilizer use was the highest using the farmers normal production practices (scenario 1). Utilizing grid soil sampling and variable rate applications (scenario 2) fertilizer use was reduced by 3,420 pounds. Soil sampling using management zones based upon soil type and utilizing variable rate fertilizer applications (scenario 3) reduced overall fertilizer use by more than 3.5 tons. Scenario 4 which utilized G.I.S. software to divide the field into management zones based upon crop removal and utilizing variable rate fertilizer applications produced the most efficient fertilizer use. This scenario, which is based on the actual field production, shows phosphorus recommendations were reduced by almost 1.5 tons and the potash recommendations were cut in half – But does it pay?
Fertilizer prices of $250/ton for Potash and $315/ton for D.A.P. were used for this analysis. Soil testing charges and variable rate fertilizer application charges were included where appropriate. Scenario 4, fertilizer recommendatins based upon crop removal produced the greatest savings. This scenario which had the lowest fertilizer use and no soil testing charges resulted in a savings of $17.67 per acre when compared to the farmers normal production plans. Soil sampling by soil type (scenario 3) and 2.5 acre grid sampling (scenario 2) resulted in savings of $16.26 per acre and $4.85 per acre respectively, when compared to the normal production practices for this farm.
But does it pay? In this analysis Yes! Each scenario involving variable rate fertilizer applications resulted in lower fertilizer use and a greater net return. With today’s soaring fertilizer prices, savings of almost $5 to more than $17 per acre can have a significant impact on most Central Ohio farms.
| Normal | 2.5 Acre Grid | Soil Type | Crop Removal | |
| P Recommendation (LBS./Field) | 8325 | 7380 | 6030 | 5445 |
| P Cost ($/A) | $27.94 | $24.76 | $20.23 | $18.27 |
| K Recommendation (LBS./Field) | 9000 | 6525 | 4050 | 4500 |
| K Cost ($/A) | $25.00 | $18.13 | $11.25 | $12.50 |
| Total Fertilizer Use (Lbs./Field) | 17,325 | 13,905 | 10,080 | 9,945 |
| Fertilizer Cost ($/A) | $52.94 | $42.89 | $31.48 | $30.77 |
| Soil Test Cost($/A/Year) | $0.00 | $0.70 | $0.70 | 0.00 |
| Fertilizer Cost + Soil Test ($/A) | $52.94 | $43.59 | $32.18 | $30.77 |
| Variable Rate Fert. Application | $0.00 | $4.50 | $4.50 | 4.50 |
| Total Cost ($/A) | $52.94 | $48.09 | $36.68 | $35.27 |
| Saving vs. Normal Plan ($/A) | $0.00 | $4.85 | $16.26 | 17.67 |