June 17, 2011
Extreme soil conditions can play a role in limiting the amount and availability of nutrients to crops. Extremely high or low soil pH impacts the way nutrients bind to other minerals and impacts availability. High sand or clay content soil impacts water infiltration rate, leaching potential, and the holding strength that soil particles have on nutrients. Very high or low soil organic matter can impact the amount of nutrients present as it decomposes from organic forms. Eroded, compacted or otherwise abused soils do not hold onto nutrients and/or do not let nutrients loose. Abused soils can also have limited water holding capacity. Table 1 shows susceptible soil conditions where boron, manganese, zinc and sulfur may be prone for crop nutrition deficiency.
Table 1. Susceptible Soil Conditions Prone to Micronutrient Deficiency
|Low OM (<2%)||X||X||X|
|High pH (>6.8)||X||X|
|High OM (>6%)||X||X|
There will be times when crop plants exhibit visual discolorations, along with abnormal or unthrifty growth. Abnormal crop appearance and growth is not always a function of crop nutrition. Determining why crops are not growing properly can lead to inquiries related to insects, diseases, soil physical conditions, soil fertility, plant root health, pesticide history, current season herbicide applications, and more.
A comprehensive presentation: Soil Micronutrients From B to Z, was given at the 2010 WI Crop Management Conference. A slide presentation, including color pictures of deficiency symptoms is available at: http://www.soils.wisc.edu/extension/wcmc/2010/ppt/Sturgul.pdf .
Plant tissue analysis for nutrient content is one way to investigate abnormal crop growth if you suspect soil fertility and crop nutrition issues during the early growing season. Plant tissue analysis, combined with an associated soil sample from a suspect field area, is a reliable diagnostic tool to identify micronutrient problems.
When gathering plant tissue samples, it is important to collect specific plant parts at specified growth stages. Plant growth stage and the collected part is unique for each crop, as shown in Table 2 for Wisconsin’s three main crops.
Table 2. Crop Stage and Plant Part to Collect for Plant Tissue Analysis
|Crop||Stage of Growth||Plant Part to Sample|
|Corn||Tassel to silk||Ear leaf|
|Soybean||Prior to or at initial flower||Newest fully developed leaf|
|Alfalfa||Bud to first flower||Top 6 inches|
Plant nutrition is derived from the soil. It makes sense that when an abnormal area of crop growth is sampled for tissue nutrient content, the next question will be, “are the proper nutrients in the soil right now?” To answer that question, it is advisable to collect a soil sample from the same area as the plant tissue was taken from. Send the plant tissue and soil sample, properly packaged, to the lab at the same time.
The University of WI Soil and Plant Tissue Analysis Laboratory, located on the west side of Madison, is the lab within our university system that processes plant tissue samples. The lab web site (http://uwlab.soils.wisc.edu/madison/) contains many resources, including an article: Sampling for Plant Analysis (Kelling, Combs, and Peters). This article provides information about sample collection and handling, as well as crop and soil information to include when sending plant tissue (and soil) samples to the lab.
Some private labs also analyze plant tissue for nutrient content; check with private labs for specific services.
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