Soil Sampling and Testing

Amy Timmerman, Extension Educator Author

11/20/2023 Added

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Soil sampling and testing are essential to determine soil properties and fertility levels to make good management decisions about fertilizer, manure, and lime application rates.

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[00:00:00.599]This is Amy Timmerman with Nebraska Extension and this weeks’ Ag Update.
[00:00:05.655]Soil sampling and testing are essential to determine
[00:00:08.735]soil properties and fertility levels to make good management
[00:00:12.205]decisions about fertilizer, manure, and lime application rates.
[00:00:16.563]Appropriate nutrient and amendment applications can increase crop yield,
[00:00:21.152]reduce input cost, and minimize environmental impact.
[00:00:25.040]Soil testing becomes inexpensive when compared to the total
[00:00:28.800]investment in crops and fertilizers.
[00:00:31.530]Soils are typically sampled in the fall or spring.
[00:00:34.702]Either time works to determine potassium, phosphorous,
[00:00:38.702]sulfur, micronutrient and lime requirements.
[00:00:42.400]However, if trends in nutrient concentrations are being
[00:00:45.410]compared over time, it is important to sample at
[00:00:48.700]similar times of the year.
[00:00:50.510]For nitrogen recommendations, it’s recommended that both
[00:00:54.058]soil organic matter and residual soil nitrate-N be measured.
[00:00:58.936]The timing of soil sampling for making Nitrogen recommendations
[00:01:02.689]could be important as snowmelt and precipitation during early spring
[00:01:07.389]may affect Nitrogen losses (especially for coarse-textured soils),
[00:01:11.768]resulting in under application of pre-plant or in-season Nitrogen.
[00:01:16.387]Collecting pre-plant soil nitrate-N soil samples to
[00:01:20.167]a two- or three-foot depth is a good practice for determining
[00:01:24.755]residual soil nitrate-Nitrogen to be credited in Nitrogen rate decisions.
[00:01:30.048]A critical step for successful soil sampling is to collect
[00:01:34.048]representative samples from the field.
[00:01:36.530]The University of Nebraska provides detailed information
[00:01:39.552]about different approaches for soil sampling for
[00:01:42.252]uniform and variable-rate fertilizer application.
[00:01:46.082]More information can be found by googling
[00:01:48.632]Nebraska’s Guidelines for Soil Sampling, NebGuide 1740.
[00:01:53.871]The sampling pattern should be selected based on the nutrient
[00:01:57.251]management decision needing to be made and to best represent the field.
[00:02:02.385]For uniform fertilizer applications, samples can be collected randomly
[00:02:07.295]within representative areas of the field.
[00:02:09.775]However, accounting for known sources of variability in soil fertility such as
[00:02:14.841]soil types, cropping history and erosion, is still helpful in adjusting
[00:02:20.211]recommendations even if the fertilizer is uniformly applied.
[00:02:24.211]Consider grid sampling of one to 2.5 acres
[00:02:27.401]if soil type or previous managment such as differences in
[00:02:31.401]in livestock containment, manure application, irrigation amounts
[00:02:36.048]or cropping history causes variation in nutrient availabilities.
[00:02:40.817]Consider zone or directed sampling if yield maps,
[00:02:45.487]remotely sensed images or other sources of spatial information
[00:02:48.827]are available and show consistency from one layer to another layer.
[00:02:53.677]Both grid and directed soil sampling are valid options for precision soil sampling.
[00:02:58.815]Grid sampling for nitrate-N is not recommended because
[00:03:02.455]annual fluctuations in nitrate levels would require
[00:03:06.185]annual grid sampling, which is not cost-effective.
[00:03:09.176]Instead, residual nitrate sampling (to a depth of three feet)
[00:03:13.226]should be done on a directed sampling basis.
[00:03:16.896]Sampling depth is another key factor for good sampling.
[00:03:20.460]It is important to represent the root zone where the
[00:03:23.300]plant will uptake nutrients, but it must be consistent
[00:03:26.230]with the sampling depth used in developing the
[00:03:28.556]calibration data set to be used for interpreting the soil tests.
[00:03:33.046]In dry years, when it is difficult to push the probe into the ground,
[00:03:36.366]there is a danger of not getting the proper depth.
[00:03:39.456]Sampling too shallow will often lead to unusually high soil test results
[00:03:44.179]because of the tendency for nutrients to become concentrated near the surface.
[00:03:48.586]Shallow sampling will thus overestimate the actual soil nutrient status
[00:03:53.269]and lead to underestimating fertilizer rates needed.
[00:03:57.269]Soil samples for determining soil pH, soil organic matter, and availability
[00:04:03.109]of any nutrient other than N should be taken from the 0-8 inch soil depth.
[00:04:08.957]A single sample should be comprised of thoroughly
[00:04:12.520]mixed soil from 12 or more places in the sampling zone.
[00:04:16.520]Sampling zones should be 40 acres or less.
[00:04:19.362]Guidelines for interpreting soil test results for nutrient
[00:04:23.302]application decisions are available in crop-specific
[00:04:26.362]UNL Extension publications and in the Extension book,
[00:04:29.452]Nutrient Management for Agronomic Crops of Nebraska.
[00:04:33.502]Or reach out to your local extension office for assistance.
[00:04:36.715]This has been Amy Timmerman with Nebraska Extension.

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