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Experts urge scouting, sampling to diagnose nutrient deficiencies

AFP Correspondent

STATE COLLEGE, Pa. (May 16, 2017) — “Know what to look for,” Penn State Professor Douglas Beegle counseled students at their recent Agronomy Scout School.
Beegle illustrated his presentation with descriptions of several nutrient deficiencies.
On corn leaves, nitrogen deficiency exhibits a yellow ‘V’ pattern which starts at the leaf tip and goes toward the middle of the leaf.
The lower leaves are affected first.
Phosphorus deficiency is marked by purple coloration.
It also begins at the tip of the leaf and progresses along the edges of the lower leaves. Young plants are typically more affected.
A yellow-brown color — again starting at the leaf tips, then edging along the lower leaves — indicates a potassium deficiency.
Signs of a magnesium deficiency includes white striping between the leaf veins.
It begins on the lower leaves.
The lack of chlorophyll manifested in a sulfur deficiency exhibits stunted and pale green leaves.
Beegle cautioned that the visual symptoms can be similar to nitrogen deficiency, but since sulfur is not easily translocated from old to new growth, the symptoms appear first in younger leaves.
Zinc deficiencies show white stripes or bands between the midrib and the edge of the leaf, usually on younger leaves.
When diagnosing, Beegle advised, “Look at the whole plant.”
The exact symptoms such as the edge or middle of the leaf, the full length or partial leaf length, interveinal or broad stripes, and the coloration are all important.
The position on the plant is significant, and in addition, patterns in the field must be examined.
Beegle also suggested assessment of field patterns.
The soil properties, topography, plus management operations such as tilling, spraying and fertilizing, should be considered.
The timing of the symptoms will help in diagnosing and managing corrective strategies for any deficiencies.
Turning to plant sampling, Beegle first stressed that the guidelines must be strictly followed.
Routine plant sampling can monitor plant nutrition.
The sufficiency levels for corn, alfalfa, small grain and soybean crops specify that at least ten subsamples should be taken for a complete sample to submit to the lab.
The report lists the sufficiency ranges for twelve elements at a specific growth stage.
Corn, for example, is at the ear leaf silking.
The soybean stage is for the uppermost full leaves prior to or early flowering.
In the plant analysis for corn for instance, the report gives the data for four growth stages.
Beegle provided guidance for diagnosing deficiencies from plant sampling.
He advised taking both good and poor samples.
In general, he instructed sampling the newest fully developed leaves. While the actual time and part is not as critical, he emphasized sampling the same plant part at the same time for both plant and soil.
In comparing the results of plants and soils, he noted that if the problem is nutritional, the nutrient difference between good and poor samples of both the plants and soils should be obvious.
If the plant samples show differences, but the soil samples are similar, Beegle advised looking for factors that might reduce uptake.
These include compaction, low pH, insect feeding, moisture stress and pesticide injury.
“Lots of problems relate to pH,” Beegle said. In low pH, for instance, poor root growth can result in a mixture of deficiency symptoms.
Further, Beegle cautioned, “A soil test is no better than the soil sample submitted for analysis.”
He noted that sampling error is the most common source of error in soil test results.
Obtaining a representative sample should be the goal of soil sampling.
To emphasize its importance, he reported that 2.5 grams of soil in the lab must represent 20 million lbs. of soil in a 20 acre field.
Using GPS to lay out a virtual grid can be performed, but Beegle noted that small fields are difficult to grid sample.
Because soil test results vary dramatically with depth, Beegle said, sampling must be performed at a consistent depth.
Also, Penn State recommendations are based on ‘plow depth’ even with no-till.
At least 15–20 cores should be taken at uniform areas.
Atypical areas should either be avoided or sampled separately.
Beegle pointed out that farmers must understand the terms and recommendations in order to fully interpret the results of the tests.
Penn State’s Agricultural Analytical Services Laboratory provides a range of testing for plants and soils plus other agricultural materials.
Its website,, contains links to the services and other information.