Plant Analysis Do’s and Don’ts

Dave Franzen, PhDExtension Soil Specialist

North Dakota State University, Fargo

The goal is high yield with lowestexpenses possible.

That starts with healthy crops provided with adequate nutrients

Sometimes we start out with crops that look something like this?

Plant analysis, combined with a soil test, can be very helpful indiagnosing nutrient deficienciesduring the season.

Early sampling can lead to yieldimprovements.

Later sampling in non-irrigated landis a kind of post-mortem.

NutrientMelsted et al.1969 Jones 1967

Neubert et al. 1969

UW soil lab

N% 3.0 2.76-3.50 2.60-4.00 2.76-3.75P, % 0.25 0.25-0.40 0.25-0.50 0.25-0.50K% 1.90 1.71-2.50 1.70-3.00 1.75-2.75Ca% 0.40 0.21-1.00 0.21-1.00 0.30-0.60Mg% 0.25 0.21-0.60 0.31-0.50 0.16-0.40Zn, ppm 15 20-70 50-150 19-75B,ppm 10 4-25 15-90 5-40Mn, ppm 15 20-150 34-200 19-75Fe, ppm 25 21-250 21-250 50-250Cu, ppm 5 6-20 8-20 3-15

Critical level ranges, corn ear leaf silking to tassel

Nutrient Deficient Low Sufficient HighN% <1.75 1.76-2.76 2.76-3.75 >3.75P% <0.16 0.16-0.24 0.25-0.50 >0.50K% <1.25 1.25-1.74 1.75-2.75 >2.75Ca% <0.10 0.10-0.29 0.30-0.60 0.61-0.90Mg% <0.10 0.10-0.15 0.16-0.40 >0.40S% <0.10 0.10-0.15 0.16-0.40 >0.50Zn, ppm <12 12-18 19-75 76-150B, ppm <2.0 2-5 5.1-40 41-55Mn, ppm <12 12-18 19-75 >75Fe, ppm <10 10-49 50-250 251-350Cu, ppm ------- <3 3-15 16-30

Interpretive ranges for corn ear leaf from silking to tassel(University of Wisconsin, 1991, Schulte and Kelling)

Nutrient

Whole plant, 24-45 days

3rd leaf 45-80 days

Earleaf,Green silks

Earleaf brown silks

Earleafmature

N% 4-5 3.5-4.5 3-4 2.8-3.5 2.5-3.5P% 0.4-0.6 0.35-0.50 0.3-0.45 0.25-0.40 0.2-0.3K% 3-5 2-3.5 2-3 1.8-2.5 1.6-2.5Ca% 0.51-1.6 0.2-0.8 0.2-1.0 0.2-1.2 0.2-1.5Mg% 0.3-0.60 0.2-0.6 0.2-0.8 0.2-0.8 0.2-0.8S% 0.18-0.40 0.18-0.40 0.18-0.40 0.18-0.35 0.16-0.35B, ppm 6-25 6-25 5-25 5-25 5-25Cu, ppm 6-20 6-20 5-20 5-20 4-20Fe, ppm 40-500 25-250 30-250 30-250 30-250Mn, ppm 40-160 20-150 20-150 20-150 20-150Zn, ppm 25-60 20-60 20-70 20-70 16-50

Nutrient sufficiency ranges for corn at severalgrowth stages, From Schulte and Kelling, 1991

Nutrient Small GrainsTillering Boot Heading

N 3.8-5.5 3.8-5 2.5-3.5P 0.3-0.5 0.3-0.5 0.21-0.5K 2.5-3.5 2-3.5 1.6-3S 0.2-0.5 0.2-0.5 0.2-0.5Ca 0.2-0.5 0.2-0.5 0.2-0.5Mg 0.13-0.4 0.15-0.4 0.13-4Zn 20-70 20-70 20-70Fe 50-250 50-250 25-250Mn 25-100 25-100 5-25Cu 5-25 5-25 3-40B 3-40 3-40 3-40Cl 0.3-0.6 0.21-0.5 0.21-0.5

NPK, maybe S are probably decent ranges, the rest are guesses taken from a variety of non-local sources. Using alone will result in unnecessary costs.

Table froman independentND lab

Example- actual lab results from a commercialcompany, recommendations and my comments-

Wheat, tillering stage, whole plants.

N 2.88%, Recommendation- wheat is N deficient.Apply 1-2 gallons per acre of a slow-release N productfoliar.

Comments- this N concentration is likely deficient. Thesample was taken in the Valley, where severe denitrificationaffected the available N of all crops.However, the recommendation of a low rate ofa slow-release N product is a very poor one.Slow-release products do not have foliar efficienciesgreater than 28-0-0. The recommendation should havebeen apply 20 gal/acre of 28-0-0 as soon as possiblewith stream-bars.

Example, continued-

P 0.41% - Recommendations- adequate. Comments, agree

K 4.01%- Recommendation- excessive. Comments,Excessive implies the K content is hurting yield. Thisdescription is not accurate. Most plants ‘luxury’ consumeK if in excess of what is required; however, theaccumulation of K is not harmful to the plant.

Ca 0.21%- Recommendation- low. Apply 2-4 qt/acre ofa calcium supplement. Comments- totally wrong! Mostguess charts indicate adequacy of Ca down to 0.2%Recommending Ca without local data to support itis not a correct recommendation.

Example, continued-

Mg 0.19 % - Recommendations- low. Comments, totallywrong. Local labs rate Mg OK down to 0.13%. Withoutlocal data to support a lower critical value this is nota correct recommendation.

S 0.21%- Recommendation- low. Comments, totally wrong.Local labs rate S OK down to 0.2%. Again, local datais needed to support a lower critical value for S. This isnot a correct recommendation.

Fe 125 ppm, Recommendation- adequate. Comments-A foliar Fe test is hard to come by without messingwith the rest of the nutrients. The leaves need to be gently rinsed of soil or they are contaminated. Soil releases high amounts of Fe under plant analysis preparation. I have only seen an Fe deficiency in wheatunder extreme iron chlorosis conditions in soggy, wethigh carbonate and salty soils.

Example, continued-

Mn 30 ppm - Recommendations- deficient. Comments, totally wrong. Local labs rate Mn OK down 25 ppm. Mn content is adequate.

B 9 ppm Recommendation- adequate. Comments, agreed,but company critical level is 8 ppm, while local labsindicate that down to 3 ppm is adequate. Be on guard.

Cu 6 ppm, Recommendation- deficient, apply 1 pt/acreof a copper foliar product. Comments- Totally wrong.Local labs indicate adequate copper down to 5 ppm.The recommendation is not correct.

Zn 17 ppm, Recommendation- deficient (company recs havea critical level of 30 ppm- way too high), apply 1 qt/acreof a zinc foliar product. Comments- The Zn content isclose to the local lab critical level (20 ppm). Given this number isa guess not supported by research, I would notthink Zn is the issue here.

Bottom line-

When receiving the results from a plant analysis,insist on seeing plant critical levels and sufficiencyranges from some entity not selling fertilizers.

Fertilizer people are continuously pressured by theircorporate marketing arm to sell products that may or may not be needed.

An unbiased source of information, an independent lab,your county Extension agents, are the best sourceof information regarding the interpretation of plantanalysis results.

During periods of flowering and grain-fill,large amounts of nutrients are being mobilized andsent to the grain forming structures.

Pinning down deficiencies is very hard without a reference of a good sample from an enriched area.

Nitrogen could vary up to 1% due to the timing of thesample- without a reference point in the field, in thesame variety, no one can know if the value isadequate or not.

The latest plant analysis interpretative guide waspublished by Univ. of Wisconsin in 2001.

Most of the information within it and the others thatwere developed before used data from the 1960’s through early 1970’s.

The Wisconsin guide and many others caution against using plant analysis as a stand alone.An accompanying soil sample may indicate thataddition of a deficient nutrient is not required, butthat the level may be caused by something environmental.

A classic case is purple corn in a cold spring. Plant analysis might reveal low plant P, but a soil test mayshow that plenty is available. It’s the cold weather that isthe problem.

“No simple and reliable tissue test exists to identify the conditions that increase the chance of corn or soybean response to P and K fertilization. In spite of many field trialsin Iowa, we have not been able to identify a useful critical or optimal P or K concentration in plant tissue. “Antonio Mallarino, Iowa State, 2010.

Non-relationship of corn yield to small plant orearleaf P or K in Iowa, Mallarino, 2010.

Non-relationship of soybean yield to small plant andfully extended leaf P and K. Mallarino, 2010.

In a recent meeting of the North Central States Extension Soil Specialists, includingMissouri, Illinois, Wisconsin, Indiana, Ohio,Nebraska, South Dakota, North Dakota, Minnesota,Iowa and Michigan,not a single researcher or lab manager would be willing to make fertilizer recommendations solely ona plant analysis concentration, particularly micronutrients.

Although there are critical levels and sufficienciesestablished for micronutrients, they are ball parkfigures related to levels seen by researchers intotal analysis of plant tissue and are often notassociated with deficiencies.

In order to relate plant tissue analysis to crop response,there has to be a response.

The only micronutrient problems in North Dakotaare zinc on corn, iron in soybeans/flax, and sometimescopper in wheat.

Correctly using plant analysis-

It should not be a diagnosis by itself. Taking a soilsample at the same time is recommended.

It should be used to compare poorly growing areasof a field to a good-growing area.

Take a soil sample from the correct depth from thepoor and good area and keep them separate.

Good areasample

‘Bad’ areasample

Soil sample + plant sample

Soil sample + plant sample

Corn Plant analysis report-

Good areaZinc lowPhosphate highNitrogen highSulfur OK

Bad areaZinc lowPhosphate HighNitrogen HighSulfur low

Corn Soil analysis report-

Good areaZinc mediumPhosphate highNitrogen highSulfur high

Bad areaZinc mediumPhosphate HighNitrogen HighSulfur low

Look for the commonproblem

Situation-Spring wheat, very good growth, green, healthy,soil water good, salts low, cool weather.Flag leaf stage-

Plant analysis- Soil testCopper low 0.5 ppm (medium)zinc low 0.5 ppm (medium)manganese low 4 ppm (high)sulfur OK not usefulnitrogen OK not useful right now

Recommendation- no micros needed.

In a high-yielding environment, micronutrient levels willbe at the lower end of the scale naturally. No supplements are needed in these nutrients based onrecent research in the region.