Soil Sampling - November 21, 2023 - Amy Timmerman, Extension Educator
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- [0:00] This is Amy Timmerman with Nebraska Extension and this weeks’ Ag Update.
- [0:05] Soil sampling and testing are essential to determine
- [0:08] soil properties and fertility levels to make good management
- [0:12] decisions about fertilizer, manure, and lime application rates.
- [0:16] Appropriate nutrient and amendment applications can increase crop yield,
- [0:21] reduce input cost, and minimize environmental impact.
- [0:25] Soil testing becomes inexpensive when compared to the total
- [0:28] investment in crops and fertilizers.
- [0:31] Soils are typically sampled in the fall or spring.
- [0:34] Either time works to determine potassium, phosphorous,
- [0:38] sulfur, micronutrient and lime requirements.
- [0:42] However, if trends in nutrient concentrations are being
- [0:45] compared over time, it is important to sample at
- [0:48] similar times of the year.
- [0:50] For nitrogen recommendations, it’s recommended that both
- [0:54] soil organic matter and residual soil nitrate-N be measured.
- [0:58] The timing of soil sampling for making Nitrogen recommendations
- [1:02] could be important as snowmelt and precipitation during early spring
- [1:07] may affect Nitrogen losses (especially for coarse-textured soils),
- [1:11] resulting in under application of pre-plant or in-season Nitrogen.
- [1:16] Collecting pre-plant soil nitrate-N soil samples to
- [1:20] a two- or three-foot depth is a good practice for determining
- [1:24] residual soil nitrate-Nitrogen to be credited in Nitrogen rate decisions.
- [1:30] A critical step for successful soil sampling is to collect
- [1:34] representative samples from the field.
- [1:36] The University of Nebraska provides detailed information
- [1:39] about different approaches for soil sampling for
- [1:42] uniform and variable-rate fertilizer application.
- [1:46] More information can be found by googling
- [1:48] Nebraska’s Guidelines for Soil Sampling, NebGuide 1740.
- [1:53] The sampling pattern should be selected based on the nutrient
- [1:57] management decision needing to be made and to best represent the field.
- [2:02] For uniform fertilizer applications, samples can be collected randomly
- [2:07] within representative areas of the field.
- [2:09] However, accounting for known sources of variability in soil fertility such as
- [2:14] soil types, cropping history and erosion, is still helpful in adjusting
- [2:20] recommendations even if the fertilizer is uniformly applied.
- [2:24] Consider grid sampling of one to 2.5 acres
- [2:27] if soil type or previous managment such as differences in
- [2:31] in livestock containment, manure application, irrigation amounts
- [2:36] or cropping history causes variation in nutrient availabilities.
- [2:40] Consider zone or directed sampling if yield maps,
- [2:45] remotely sensed images or other sources of spatial information
- [2:48] are available and show consistency from one layer to another layer.
- [2:53] Both grid and directed soil sampling are valid options for precision soil sampling.
- [2:58] Grid sampling for nitrate-N is not recommended because
- [3:02] annual fluctuations in nitrate levels would require
- [3:06] annual grid sampling, which is not cost-effective.
- [3:09] Instead, residual nitrate sampling (to a depth of three feet)
- [3:13] should be done on a directed sampling basis.
- [3:16] Sampling depth is another key factor for good sampling.
- [3:20] It is important to represent the root zone where the
- [3:23] plant will uptake nutrients, but it must be consistent
- [3:26] with the sampling depth used in developing the
- [3:28] calibration data set to be used for interpreting the soil tests.
- [3:33] In dry years, when it is difficult to push the probe into the ground,
- [3:36] there is a danger of not getting the proper depth.
- [3:39] Sampling too shallow will often lead to unusually high soil test results
- [3:44] because of the tendency for nutrients to become concentrated near the surface.
- [3:48] Shallow sampling will thus overestimate the actual soil nutrient status
- [3:53] and lead to underestimating fertilizer rates needed.
- [3:57] Soil samples for determining soil pH, soil organic matter, and availability
- [4:03] of any nutrient other than N should be taken from the 0-8 inch soil depth.
- [4:08] A single sample should be comprised of thoroughly
- [4:12] mixed soil from 12 or more places in the sampling zone.
- [4:16] Sampling zones should be 40 acres or less.
- [4:19] Guidelines for interpreting soil test results for nutrient
- [4:23] application decisions are available in crop-specific
- [4:26] UNL Extension publications and in the Extension book,
- [4:29] Nutrient Management for Agronomic Crops of Nebraska.
- [4:33] Or reach out to your local extension office for assistance.
- [4:36] This has been Amy Timmerman with Nebraska Extension.