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This week's Book of the Week feature is Hands-On Agronomy, by Neal Kinsey with Charles Walters.
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From Chapter 14: Plant Tissue Analysis and Fertility
Soil tests allow for application prior to planting, and a plant analysis can be a good diagnostic tool for the current season. Neither method should be considered as foolproof. Using either can help, but using both is the best combination for top results.
Consider that the soil analysis is a tool to confirm what nutrients are present as available to the plant from the soil and also shows any needed corrections that should be made to the soil itself over the next year. The soil requires that long to “process” the nutrients and have them show up as supplied, based on that soil’s nutrient “holding capacity” or TEC. Always use a soil test to determine what materials should be applied to the soil.
The results of an actual leaf analysis from good and bad plants are provided here to help show how they can be utilized. A leaf or plant analysis shows what is lacking in the plant, and should show what is there in too large an amount as well. (Hence the pluses for too much and the minuses for too little—along the right-hand side of the plant analysis pages.)
On the soil tests for the bad vs. the good plants, potassium shows to be a problem for the bad one. Although the potassium is actually higher in the bad soil, the plant is having a problem getting it because the sodium is being incorporated into the cell walls instead of the potassium (this occurs when the %Na exceeds %K in the soil). When it gets hot and humid, which can even happen in a dry climate if irrigated well, the sodium allows excess water to be taken into the cell and eventually causes the cell wall to break down killing the plants one cell at a time.
So when the plant test shows potassium as the most limiting factor that is exactly what we would expect. Notice that the sodium is actually lower in the problem plant, but this does not show where the plant has utilized it. From the soil test having a higher Na% than K%, we know that too much sodium has replaced potassium in the cell walls. This replacement is not the case in the good plants because plants will predominantly utilize whichever of the two has the highest percentage of saturation in the soil to build the cell walls. The potassium is a major limiting factor in both the good and the bad plants, but it is not as great a problem in the good leaves because the sodium percentage does not exceed the potassium percentage in the soil.
Nitrogen is the second most limiting element in the problem plants, and most needed of all nutrients in the good plants. But this is obviously not the big problem because there is less in the good leaf sample than the bad one. Zinc is next most limiting in both cases—good and bad. On the good one, it is not because the soil is lacking zinc, but because the phosphorus is too high. High phosphate blocks zinc uptake into the plant. This then causes a need for more water in the soil to correctly supply the plants because zinc aids the plant in optimizing moisture uptake.
So the resulting lack of zinc and excessive phosphate in the soil increases the need for additional moisture to accomplish the same amount of growth.
Note that the zinc level is what we would call O.K. on the problem soil, but this is only true when the phosphate is in the same category. On the Olsen phosphate test 125 lbs./acre of P2O5 is considered excellent. An excellent P2O5 with an O.K. level of zinc means not enough zinc to properly do what the plant needs done. That is why we always emphasize that building both P2O5 and Zn at the same time in the soil itself is so important. Using a 7% zinc chelate as a foliar at 12 oz./acre on both the good and the bad plants will begin to help solve this problem. Perhaps only once will do the job on the bad area, but likely more will be required to completely correct the problem on the “good” area because of the excessive P2O5 there.
Copper is the next most limiting factor on the bad area, and it is below the 2 ppm minimum on the soil test. It is much better in the good plants although only barely above the minimum of 2 ppm. Some will claim this is just happenstance, but you can see with testing and building the copper in the soil over time that it is not. Using 4 oz./acre of a 2% copper chelate as a foliar is recommended for the bad plants.
Sulfur shows to be the next most limiting factor on the good plants. (We normally concentrate only on the top four most limiting nutrients at a time.) The optimal range for sulfur is 0.15 to 0.40, and we have 0.23, which means sulfur is still being utilized basically as well on the good as on the bad area. As it stands now, once we supply the most needed nutrients for both areas, using sulfur will still keep the good ones ahead of the bad ones in terms of growth and appearance.
Also, note how much higher the molybdenum is in the good plants, which was not requested to be run as part of the soil test. Using 71/2 oz. per acre of sodium molybdate on the problem area just one time should be extremely helpful if none has been used in the last 3 years.
Test the soil and plants again before using more of the required materials. After this initial application wait until testing shows a definite need to use any foliar at all on the good area.
With these points in mind, there is one other aspect of leaf, plant or tissue analysis that is a critical consideration. The analysis and recommendations can only be correct if the sample is taken correctly.
First, be sure to select clean specimens to send for analysis. If that is not possible, lightly rinse off the plants or leaves using distilled water. Water from the well or tap can contain nutrients that will affect the analysis. It does not require much soil residue to throw off the analysis. Soil splashed on plants from rainfall or overhead irrigation, or extremely dusty conditions that cause it to settle on the leaves are some good examples. If you fail to send clean plants, it is usually easy to recognize on the test because the iron, aluminum and manganese will be extremely elevated, making it appear that all are at seriously high or toxic levels.
Next use clean bags to place the leaves or plant tissue inside. Paper bags are best. And if plastic must be used, then punch holes in the side to help avoid moisture accumulation and a possible moldy sample that arrives to be analyzed.
The plant parts to sample and send in for analysis will depend on the circumstances.
When plants are small, the entire above-ground portion can be sampled and sent. In some cases a particular plant or leaf sampling method may have been used for years and changing may mean a loss of correlation with data from the past. If no guidelines are provided, then taking enough of the youngest completely mature leaves for doing the analysis works well. For cotton, take the leaf opposite the bole. On fruit trees, take the leaf from a fruiting branch and avoid the leaves from non-fruiting branches. If in doubt, call our office first to see if there are any special instructions for the particular crop. Petioles can be analyzed if requested, but it is strongly recommended that if one or the other is to be used, the plant or leaf analysis would be considered the better of the two. Drying the leaves first is no problem, so long as contamination can be avoided in doing so.
Due to regulations in place, any tissue or plant samples sent from other countries must be dried and cut into small pieces before they will be cleared for testing in the U.S. by the Customs authorities. This virtually eliminates any quick solution to growing problems of plants outside the U.S. Be sure to check for any further special instructions before sending plants or plant tissue to be tested.
Overall, plant or plant tissue analysis can be a helpful tool and help solve immediate nutrition problems and needs for growing plants. Such tests are also very helpful at evaluating whether insufficient or excessive amounts of a particular nutrient are present at any given time in the crop. If you have a good testing program that works well for you, stay with it. But if your program does not include crop monitoring through use of timely leaf analysis, it may be useful to consider leaf analysis in addition to the use of soil testing.
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About the Authors:
Neal Kinsey grew up in southeast Missouri and worked on the farm for his father until he graduated from high school. To pay his way through college, he worked part-time and summers as a crop reporter for the USDA’s ASCS in Missouri and Illinois. He obtained his B.S. degree, and in the fall of 1966, Neal enrolled in a master’s degree program at University of Missouri, Columbia.
In 1968, Neal and his wife, Linda, moved to Texas, where he eventually became a certified consultant for Brookside Farms Laboratory of New Knoxville, Ohio. In 1977, Neal established Kinsey Agricultural Services, and now works with growers in all 50 of the United States.
Charles Walters founded Acres U.S.A. and completed more than a dozen books as he edited the Acres U.S.A. magazine, while co-authoring several more. A tireless traveler, Walters journeyed around the world to research sustainable agriculture, and his trip to China in 1976 inspired others. By the time of his death in 2009, Charles Walters could honestly say he changed the world for the better.
More By Neal Kinsey:
Browse the Neal Kinsey Audio Lecture Collection and learn more about agronomy!
More By Charles Walters:
Browse the Charles Walters Collection for all of his titles and works.
Similar Books of Interest:
Soils & Agronomy DVD Seminar, by Arden Andersen
Organic No-Till Farming, by Jeff Moyer
Advancing Biological Farming, by Gary Zimmer and Leilani Zimmer-Durand