 |
 |
         |
Grid Soil Sampling: A Step into Precision Farming Many growers ask whether to start precision farming with yield monitoring or grid soil sampling. Either step is a solid beginning to farming on a site-specific basis. Precision farming includes many components: Global Positioning Systems (GPS), Geographic Information Systems (GIS), yield monitors, grid soil sampling, aerial imagery, and variable rate applications. Grid soil sampling plays an important role in: Determining field variability of: Nutrients pH CEC Organic matter Determining the rates of variable applications of: Fertilizer Lime Herbicide, as related to organic matter and pH Checking the impact of variable applications on yield Comparing soil type and other characteristics to yield Grid soil samples are one type of computerized records that build a database about individual fields. Like the other records, soil samples are identified by specific coordinates -- preferably assigned by GPS. What is grid soil sampling? As its name implies, grid soil sampling is taking soil samples from areas determined by
a grid pattern across a field. You use GPS to navigate to the sampling points. There are
three main methods for grid soil sampling: Systematic grid: Divide the field into equally
sized squares. Pull samples from the center of each square. Systematic diamond grid:
Divide the field into equally sized squares. In the first row of squares, pull samples
from an area to the right of the center. In the second row of squares, pull samples from
an area to the left of the center. Alternate right and left down the rows. Systematic
unaligned grid: Divide the field into equally sized squares. Take samples from areas
assigned randomly to each square. In each method, 8 to 10 soil cores are collected within
10 feet of the target area. The cores are then composited as one sample and analyzed by a
laboratory. Ask the laboratory for its recommendation on sampling depth, which varies
across the United States. Generally a depth of 6 inches is recommended. If a soil is
unconsolidated or fluffy due to recent tillage you may have to go to 8 inches. In no-till
fields, take samples from the standard depth and then from the top 2 inches to identify
nutrient stratification. The great debate in grid soil sampling is the size of the grids.
Many university experts advocate taking samples from 1-acre grids. This size obviously
increases the cost – the smaller the grid size, the more samples taken from one
field. In the Midwest, grid sizes are usually 2 ½ to 4 ½ acres. For the first year of
sampling, you may want to take samples from 1-acre grids, as this size will provide the
most accurate results. The first year of sampling lays the foundation for your database
and thus the statistics are crucial to record keeping and decision-making. In later years,
you can increase the grid size, taking extra samples from areas of concern, such as
boundaries of large nutrient and yield changes. Some agricultural professionals recommend
"smart" grid sampling. With this approach, you use different size grids, ranging
from less than an acre to several acres, based on aerial photos, soil maps, yield maps,
topography maps, and your own experience and knowledge. In other words, you research your
fields before sampling in order to predetermine the areas of concern. As a general rule
grid soil sampling (2.5 to 4.5 acre grids) is recommended every 4-6 years. Crop nutrient
removal and spot soil sampling are used in the near term to "fine tune"
fertilizer rate calculations. A farmer needs to watch areas in the field where dramatic
changes in yield or fertilizer requirements occur and sample in those areas. Whether using
systematic grids or smart grids, you can always take extra samples from hills,
depressions, wet areas, old feedlots, and other areas that may need closer attention. Traditional vs. grid sampling What’s wrong with the traditional method of soil sampling? After all, it takes
less time and money. The problem is using one composite sample from 20 or 40 acres to
gauge the needs of all that soil. It would be like a doctor diagnosing a problem by asking
one question or checking just one part of the body. Nutrient and pH levels can change
tremendously across a field. Grid soil sampling with GPS is a better way to determine that
variability. In addition, you can use grid soil samples to create a layer of information
about a field that can be compared to other layers such as yield. Value of grid soil sampling Grid soil sampling is an integral part of precision
farming. You need samples from across a field to accurately assess the types of soil and
their pH, nutrient, organic matter, and CEC levels. Use aerial imagery, yield mapping, and
your knowledge and experience to guide soil sampling. Compare the soil characteristics to
yield maps to diagnose problems and take action to improve crop performance. As with the
other areas of precision farming, the most important things to do are: Create and maintain
accurate records. |