SOIL SAMPLING SOILution
A properly implemented soil sampling program is typically considered the cornerstone to any properly designed fertility program. Being what we know about soil fertility it is amazing to know that as of writing this article less that 30% of producers are soil sampling their fields consistently. I am not at all saying that soil sampling is the only thing available, but it is typically considered the baseline to understanding your soil chemically (nutrients, pH, EC), physically (structure, texture, SOM) and more recently biologically (soil respiration, soil organic carbon). With the rapid developments in Ag technology there has been both adoption and development of new practices that either compliment or in some instances replace a typical soil sampling program. The goal of most advances in the fertility industry, whether technological, chemical or biological, are focused on improving one or more of the 4-R’s of Nutrient Stewardship. Those being:
- Right Rate,
- Right Source,
- Right Place, and
- Right Time
a bit of a mouthful I know. Soil sampling typically focuses on improving application of the Right Rate of fertilizer for a given crop by supplying what the crop needs. In this article I will go over some of the basics of soil sampling, emerging technologies and practices relating to soil and crop fertility and why it is important for producers to consider implementing or improving their current soil sampling program. I will also try to tie back into how each of these things affects the 4-R Nutrient Management system and in turn provides economic, social, and environmental benefits including improved soil health, increased crop yields and improved water quality. Sounds great right? Well, the first step to getting started is determining what style of soil sampling program you want to utilize on your operation. Let’s get started.
There are 3 main types of soil sampling programs that are being implemented on farms that we will discuss:
- Zone, and
COMPOSITE SOIL SAMPLING
Composite sampling is typically what producer will begin with and will help producers to understand the variability in their soil across their farm, and if your one of the 30%, more than likely have already implemented. This sampling technique involves collecting numerous cores from across a field and combining them into one “composite” sample. This will allow the producer to custom tailor fertilizer rates (or blends) on a field-by-field basis. This is an improvement over crop-based fertilizer rates as over time different management practices, soil types and climates lead to variability in soil productivity and background fertility levels. Composite soil samples are considered the entry level and most cost-effective to begin a soil sampling program. Although composite soil samples provide a look at the variability between fields on your farm, the one major disadvantage to composite samples is they fail to capture the variability in productivity within a field. The result of this is overapplication of fertilizer in lower productivity areas (hill tops, sandy areas) and under application in higher productivity areas (low areas, higher clay or soil organic matter content). Rising input prices and increased regulatory pressure has led to the development of Variable Rate Technology allowing producers to apply different rates of fertilizer across a single field using GPS driven equipment and predetermined productivity regions or management zones.
ZONE SOIL SAMPLING
Zone based sampling is becoming a widely popular choice when it comes to implementing Variable Rate Technology, especially in lower productivity regions where grid sampling may be cost prohibitive. Zone sampling is based on the premise that areas of similar productivity within a field, referred to as “management zones”, can be identified and sampled independently of each other. This allows for more precise fertilizer management as producers can put less fertilizer down in low producing areas and more down in areas of higher production eliminating the main drawback of composite sampling. There are many sources of data that can be utilized to identify productivity zones within a field including yield data, satellite imagery, elevation data, soil survey data and various soil mapping tools (EM-38 / VERIS / SWAT). Do to the widely debated and evolving topic of Management Zone Creation I will not be covering these in detail here but rather in a separate article specifically on Variable Rate Technology which can be found here. There I will go over in more detail what these different data sources are and the advantages and drawbacks to using each so you can choose which method best fits your operation. Typical variable rate programs on the Hi-Line implement a zone sampling strategy due to its relative simplicity and cost effectiveness over large acre farms. Producers in other areas with smaller field sizes and higher productivity have been moving towards a more intensive grid style soil sampling program to further increase savings and fertilizer use efficiency.
GRID SOIL SAMPLING
Grid soil sampling is considered the costliest form of soil sampling but ultimately provides the most accurate representation of soil variation within a field. As previously mentioned, grid sampling is often reserved for high value and high yielding crops where even properly managed fertility programs are becoming cost prohibitive to farmers. Grid sampling involves sectioning off the field into grids, typically 1 to 10 acres in size, and sampling each grid independently. Although this allows for the most in-depth look at nutrient variability within a field, the labour and analytic costs can quickly diminish the financial benefits of implementing this type of program. To combat these higher costs, some companies have developed in field tools utilizing Infrared and Hyperspectral imagery to determine soil fertility levels. These tools aim to drastically reduce soil sampling costs and enable farmers in lower productivity regions to implement and more intensive soil sampling strategy. Aside from typically being cost-prohibitive, fertility levels are not always indicative of yield potential, and I believe this strategy fails to address the question of varying yield potential due to moisture availability, Montana’s most limiting factor. This is not something I typically recommend in Montana because of these reasons.
If you are looking to improve both your farms profitability and soil health while minimizing environmental impacts implementing a soil sampling program is a great place to start. Whether you want to get started with a composite sampling program or are ready to implement a Variable Rate program, Agrological Solutions team of experienced professionals is here to help. Since 2017 we have been designing and implementing soil sampling programs including management zone creation, soil sampling design, soil sample collection, soil sample analysis and Variable Rate Prescriptions (VRT Rx). We have experience working with composite, zone and grid sample collection and work with producers to identify and implement a strategy that meets their goals and budget.