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Site Specific Soil Analysis with Variable Rate Technology – Details You Ought to Know 

When looking at effective soil analysis and better crop production, there are certain factors that must be known before establishing a site-specific or precision management program. Many of these factors are economic, some are agronomic, and others are technology related. A very crucial technology-related question is “what are the available methods of variable rate application (VRA) of fertilizer, chemicals, and seeds?”.

There are two fundamental methods to implement site-specific management (SSM) for variable rate application of fertilizers, chemicals, and seeds. They are:

  • Sensor Based
  • Map Based

Both methods have their unique benefits and limitations.

Map-Based Site-Specific Soil Analysis & Management :

The first site-specific soil analysis and management method is based on maps representing crop yields, soil properties, variable rate application plans, and pest infestations. The map-based method is implemented using a wide array of strategies based on the soil type, texture, color, crop yield, topography, field scouting data, remotely sensed images, etc. For developing a variable rate fertilizer application plan in a specific field, the map-based soil analysis includes the following steps:

  • Performing a systematic soil sampling and lab analysis of the field.
  • Generating site-specific maps of the soil nutrient properties of interest
  • Developing a site-specific fertilizer application map
  • Using the map to control the variable-rate fertilizer application

A positioning system is used throughout the soil analysis and application process to continuously track and record the vehicle location in the field. Differently corrected Global Positioning System (DGPS) receivers are the most commonly used positioning devices.

Sensor-Based Soil Analysis & Management:

Sensor-based soil analysis and management offers the capability to vary the application rate of the crop production inputs without any mapping. The sensor-based method uses sensors to measure the desired soil properties on the go. Measurements made by such a system are processed and immediately used to control a variable rate applicator. It doesn’t use a DGPS system. Nor does it require a huge amount of data analysis before making variable rate applications.

Why Map-Based Soil Analysis and Management is More Popular?

Currently, most available technologies and applications in site-specific farming use map-based methods for soil analysis and variable-rate application. This is a more popular method because of the scarcity of sensors to rapidly monitor the soil and crop conditions. Also, laboratory analysis is the most reliable method for determining soil and plant properties.

Once the field data is collected, mapping can be done with a computer program, specifically known as the Geographic Information System (GIS) program. Such programs use mathematical techniques to interpolate the data between sampling points. However, there are some site-specific practitioners who choose a constant value for the measured property over every sampling area or grid cell. Regardless of how data is represented, mapping facilitates the long-term planning and soil analysis. It offers the opportunity to decide about selecting and purchasing crop production inputs well in advance.

Maps are great for collecting and interpreting data for soil properties that don’t fluctuate every year. Organic matter content and soil texture tend to change quite slowly. On the other hand, soil fertility changes frequently. Specific nutrients like potassium and phosphorous might change yearly, but you can benefit from sampling every two/three years. The levels of other nutrients might also vary during even a single season.

For instance, the concentrations and forms of nitrogen in the soil are highly affected by temperature and moisture conditions. Therefore, it can fluctuate rapidly. Nitrogen is an example of a crucial soil fertility factor that is not confined to a site-specific soil management program based on soil sampling data because of the delays between sampling and fertilizer applications. Nitrogen management approaches have been developed depending on more stable information like crop yield.

The Importance of Variable Rate Controllers in Soil Analysis

The variable rate controllers synchronize the applicate rate with the position in the field by “looking ahead” on the map. This includes the vehicle’s ground speed and the time needed to change the product rate that comes out of the applicator. The fertilizer spreader truck might operate at field speeds of more than 15 miles per hour. Without the “look ahead” feature, if the applicator took only a second to respond to a rate change command from the controller, an area of 22 feet long and as wide as the spread pattern will be treated at the wrong rate. With the “look ahead” feature of the map-based applications systems, it is not necessary to reduce the travel speeds for accomplishing accurate variable-rate applications.

A crucial aspect of map-based method is the knowledge of the necessary amounts of the chemicals or inputs for the operations before entering a field. This knowledge helps in managing field operations. The multiple data sources needed to facilitate map-based applications is also used in other decision-making process of a farming operation. The farm manager uses GIS software to examine all the yield, pest, soil properties, and as-applied data.

Sensor Based Technologies

When it comes to sampling density, sensor-based systems play a crucial role. A sensor-based system collects dozens of samples from each store. This increase in sampling density produces more accurate depiction of within-field variability. The challenge with sensor-based technologies is it is tough to find sensors that will work accordingly in the field conditions at realistic working speeds.

Sensor-based application systems should be capable of sensing, processing data, and ensuring application rate adjustment steps in one machine pass. Speed is crucial for true sensor-based systems in the case of sensing and processing. There is a lag between sensing a soil or crop property and converting the sensor signal to usable information to change the application rate. The developers of sensor-based systems should synchronize the sensor measurement site along with the preferred application rate for the same site.

In Conclusion

Both map-based and sensor-based variable rate applications are available to the site-specific management. There are also VRA strategies that implement both sensing and mapping aspects. Each VRA method includes advantages and disadvantages. If you want precise soil analysis and testing services, contact SoilOptix® today! Visit for details.