Putting Variable-Rate Seeding to Work on Your Farm
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Crop Insights written by Mark Jeschke, Ph.D., Pioneer Agronomy Manager
Key Points
- Extensive field research has documented the value of planting higher corn seeding rates in more productive field areas and decreasing rates where productivity is lower.
- To maximize VRS value, appropriate crop management zones, or Decision Zones, must be defined. When available, Decision Zones can include soil types, topography, irrigation, and long-term yield history. In some cases, other information like soil EC can also be used.
- Corteva Agriscience researchers conduct thousands of population trials at hundreds of locations across North America. Data from these trials provide the basis for seeding rate recommendations for each Decision Zone.
- Appropriate differences between seeding rates are field-specific and depend on the capabilities of the planting equipment, yield targets, field variability, soil productivity and understanding of hybrid specific interaction of genotype by environment. Agronomically, seeding rates should differ by at least 4,000 seeds/acre.
- Granular Variable Rate Seeding tool helps farmers increase yields and maximize their seed input investment on every acre. Recommendations are provided through Pioneer sales professionals.
Granular Variable Rate Seeding Tool
The Granular Variable Rate Seeding tool helps farmers increase yields and maximize their seed input investment on every acre. Recommendations can be provided through Granular certified services agents and Pioneer sales professionals.
Introduction
Each year, an increasing number of farmers are utilizing planters with variable-rate seeding (VRS) capability, and more farmers report putting this feature to work to vary corn and soybean seeding rates. Those using the technology expect it to help increase yields as well as maximize the value of their seed investment.
The growing number of VRS-enabled planters and wide-spread on-farm use of GPS technology make it easier than ever to deploy a VRS strategy. However, growers still need to understand the variability within their fields and implement the appropriate hybrid-specific seeding rates. This Crop Insights will discuss guidelines for developing a VRS strategy, designating management zones, selecting seeding rates, and implementing a field prescription.
A growing number of VRS-enabled corn planters allows for more widespread implementation of variable-rate seeding strategies. (Image courtesy of CNH.)
Developing a Variable-Rate Strategy
Creating Decision Zones
Creating Decision Zones within a field is based on the following (Figure 1):
- Grower knowledge of yield history, cropping history, and general productivity of field areas
- Environmental Response Units (ERUs) based on soil type, topography, landscape, slope, and drainage
- Yield history based on multiple years of harvest data
- Crop productivity ratings based on soil type, if yield history is not available
- Irrigated and dryland areas of fields, if appropriate
Decision Zones can also sometimes include:
- Soil electrical conductivity and/or soil color
- Remote imagery to determine NDVI, bare soil, crop-vigor
The grower is best qualified to identify management zones that will be predictive from year to year, based on trends that are historically consistent. For example, low-lying field areas may perform best in dry years and poorly in wet years, and the grower is most familiar with how to best manage such nuances.
Figure 1. Decision Zones incorporate a field’s historical yield data and management layers to segment and improve the precision of the soil productivity zones.
Selecting a Hybrid and Seeding Rates
Selecting a Hybrid
The next step is selecting the proper corn hybrid for the field, taking into account the range of possible growing conditions and resulting yield potential of field areas. Your local Pioneer sales professional is a valuable resource to help identify the right product for your growing environment.
Selecting Seeding Rates
Corteva Agriscience researchers conduct thousands of field research trials at hundreds of locations annually across North America to help understand grain yield response to planting rate for Pioneer® brand hybrids. In addition, many growers have their own data on variable planting rates gathered from as-planted and yield data. Decades of Corteva Agriscience research have shown that corn yield response to seeding rate within a commercially relevant range can usually be well-described by a quadratic function. Grain yield will increase with seeding rate up to an optimum point and then decline as seeding rate is increased above the optimum due to a higher rate of barrenness and extended anthesis-silking intervals (Jeschke et al., 2009). The optimum seeding rate can vary based on hybrid genetics. Figure 2 shows an example of quadratic response functions for two hybrid families with the same CRM that have been shown to differ in their response to plant population in Corteva Agriscience research trials.
Figure 2. Economic optimum planting rates of two Pioneer brand hybrid families with similar comparative relative maturity at a 250 bu/acre yield level.
Seeding Rate Response to Productivity
Yield response to seeding rate by productivity level is the critical factor for creating variable-rate seeding prescriptions. The population required to maximize yield increases as yield level increases. When grouped by yield level, results from Corteva Agriscience plant population trials showed that the economic optimum seeding rate increased from approximately 31,000 seeds/acre at the 150 bu/acre yield level to over 39,000 seeds/acre at the 240 bu/acre yield level (Figure 3). An Iowa State University study comparing corn yield response to plant population across soils with different corn suitability ratings found similar results. The most productive soils tended to have a higher optimum population for maximum yield (Woli et al., 2014).
Figure 3. Corn grain yield response to seeding rate at nine yield levels, average of all hybrids tested over a six-year period. Dots indicate the economic optimum seeding rate within each yield level.
The increase in optimum seeding rate by yield level has been shown to be roughly linear within the range represented by research data (Figure 3).
Economic and Agronomic Optimum Rates
It is important to note that suggested seeding rates produced via the Pioneer Planting Rate Estimator and Granular Variable Rate Seeding Tools are based on economic optimum rates that consider both the revenue from yield and the cost of additional seed. This provides the most useful information for optimizing return on seed investment. When comparing recommendations from different companies, farmers need to understand the economic and genetic assumptions that affect each recommendation.
Building a VRS Prescription
- Working with a Pioneer sales professional, assign Decision Zone yield targets for each field. Decision Zones are typically defined by soil properties, topography, yield history, and irrigation management.
- Select each Pioneer® brand corn product and review the suggested seeding rates. Select any additional hybrids or varieties and seeding rates. Granular Variable Rate Seeding prescriptions will be ready to review and edit (Figure 4).
- Review each prescription in Granular and make any Decision Zone specific edits to seeding rates. Granular conveniently generates prescriptions for every product, for every field to maximize flexibility when conditions or product changes occur during the planting season.
- Prescriptions can be received via email and copied to a storage device or uploaded wirelessly to capable monitors.
- Review planter monitor settings for user preferences and default settings (out of bounds rate, loss of signal rate, offset distance, etc.). Make sure the controller is set to record as-planted information. Upload the as-planted data to Granular Insights for further analysis.
Evaluating Prescription Effectiveness
Setting up Checks
The recommended best practice for evaluating the effectiveness of VRS prescriptions is planting check strips at rates higher and rates lower than the prescribed rates for the rest of the Decision Zone. These checks can help farmers understand those areas where they might be able to increase yields through higher seeding rates or decrease seeding rates where lower productivity doesn’t typically support higher yields.
Strips are typically field-length strips of a single planting rate that pass through several management zones. A strip should be placed so that it crosses management zones of most or all other rates. There should be at least one strip for each designated seeding rate. Strips are typically one planter pass wide. Check strips can be created as part of the prescription or from the planter monitor in the field.
Blocks are an alternate approach where generally square blocks of higher and lower planting rates are located within different management zones. Their utility is decreasing as growers strive to differentially manage smaller and smaller areas of fields.
Figure 4. Example of a Granular Variable Rate Seeding prescription. View a larger version here or click on the above image.
In-Season Monitoring
After stand establishment, take stand counts in the different planting rate zones and check areas (e.g. strips). It is important to verify that target populations were actually attained to assure the validity of the test. Pay special attention to high stress areas such as poorly drained spots or high crop residue areas.
Interpreting the Results
- Work with your Pioneer sales professional to analyze your yield results.
- Did higher seeding rates produce greater yields in higher productivity Decision Zones? What impact did weather play? What do you want to do differently next season?
- Evaluate profitability by comparing yields and accounting for seed costs for any two rates in question.
References
- Doerge, T., M. Jeschke, and P Carter. 2015. Planting Outcome Effects on Corn Yield. Crop Insights. Vol 25, No. 1. Pioneer.
- Jeschke, M. 2019. Corn Seeding Rate Considerations. Crop Insights.
- Jeschke, M., S. Paszkiewicz, and J. Mathesius. 2009. Corn Performance at Very High Plant Populations. Field Facts. Vol. 9, No. 15. Pioneer.
- Woli, K.P., C.L. Burras, L.J. Abendroth, and R.W. Elmore. 2014. Optimizing corn seeding rates using a field’s corn suitability rating. Agron. J. 106:1523-1532.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.
Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.