Increased awareness of different lab methods to measure extractable nutrients has been positive to help understand variations in soil test data from various regions of the country and why they may be different. Like extractable nutrients there are various lab methods for testing soil pH.
Soil pH - Water vs. Salt
There is 1:1 water which uses equal parts distilled/deionized water and soil to make a slurry for pH determination. This is the common method in most of the eastern US. In drought conditions natural salts can accumulate in the soil that interfere with the pH probes used to measure the pH of the soil and water slurry. This interference can lead to a 0.2 to 0.6 drop in soil pH readings. This drop is also common in arid regions of the Western US. The severity of the drop is based on the salt levels in the soil. To overcome this issue in the arid western regions, low concentration salt water is used to stabilize the readings at 0.5 to 0.6 pH units lower than 1:1 water pH. The target pH is different for 1:1 water vs salt pH.
Buffer pH is used to determine how much lime application rates. This is similar to soil pH in that it is a a buffer is added slurry of soil and water that strips all of the hydrogen from the CEC of the soil. The more hydrogen on the CEC the greater amount of reserve acidity in the soil leads to a greater decrease in the buffering solution. The greater the decrease of the buffer solutions after stripping the hydrogen from the soil indicates higher lime application rates. There are several buffer solutions that start at different pH’s and result in different buffer pH’s. Common Buffer solutions include:
At ALGL our standard methods are 1:1 water pH and Sikora buffer pH.
The inconsistent temperature and precipitation patterns throughout our region have raised concerns about the potential for nitrate toxicity in corn chopped for silage. Nitrates have the potential to accumulate in a corn plant under any stressful conditions that hinder plant growth. There are many guides, articles, and fact sheets available that discuss the interpretation of the lab data and sampling procedures for corn that has already been chopped, but there is little guidance for sampling the corn prior to harvest.
The most important step in collecting a sample from a standing corn field is that the sample must be representative of the portion of the plant that will be harvested. That means cutting it at the same height as the chopper. Nitrates accumulate primarily in the lower stalk section, so a few inch difference can have a significant impact on your results. Second, the plants that are collected need to be representative of the condition of the field. For example, if a quarter of the field is performing poorly as compared to the rest of the field, a quarter of the plants collected for the sample need to be from that section, three quarters from the good area of the field. A sample should consist of a minimum of 15 plants to best represent the average of the whole area being sampled. The sample also needs to be collected as close to harvest as possible, because nitrate levels can change quickly as the weather changes.
Prior to sending the sample to the lab, the plants need to be chopped and thoroughly mixed. This is best accomplished with a lawn chipper shredder. Once all the plants are chopped and mixed, collect a 1-gallon zip top bag subsample to be shipped to the lab for analysis.
Please note that a Corn Stalk Nitrate Test (CSNT) and a feed nitrate test are very different in the sample collection and will give you very different results. A CSNT involves collecting only an 8-inch section of the lower stalk around black layer. This test is used to evaluate the effectiveness of a nitrogen program and does not necessarily represent a potential for nitrate toxicity.
For more information please see our A&L Great Lakes fact sheet, Nitrate Toxicity in Feed.
Another excellent resource is from the University of Wisconsin Extension, Nitrate Poisoning in Cattle, Sheep, and Goats.
For any additional questions regarding feed nitrate testing and sampling, feel free to contact your A&L Great Lakes Laboratories agronomist or call the laboratory directly as 260-483-4759.
Collecting plant tissue samples throughout the entire growing season to monitor nutrient levels has become a common practice over the last few years. As most of the crops in our region are now well into reproductive stages, plant tissue test results need to be evaluated with a cautious eye.
As plants transition from vegetative growth stages to reproductive stages, the nutrient content of the plant leaves will change, most noticeably nitrogen and potassium. These nutrients are mobile in plants, so as the plant starts transitioning to grain-fill, they may be translocated from the leaf to the grain resulting in low tissue test ratings that may not necessarily indicate a yield-reducing nutrient deficiency.
Another common trend in plant tissue nutrient levels is an increase in micronutrient concentrations as the plants approach physiological maturity. This is a result of carbohydrates and other carbon-based molecules being translocated from the leaf tissues to the grain effectively reducing the biomass of the leaf. The micronutrients (iron, manganese, zinc, and copper) are immobile in the plant tissue, so they remain in the leaf that has a lower mass and are now present at a higher concentration. The micronutrients may be rated as high or very high, however, this not necessarily an indicator of excessive fertility or potential toxicity.
While plant tissue testing can be a very effective tool for fine-tuning a fertility program, be careful not to make drastic decisions based on late-season plant tissue test results alone.
While we are finishing family vacations, county fairs, and getting ready to send the kids back to school, it is also time to begin preparing for the fall soil sampling season. As you begin to layout your sampling strategy and processes, please keep the lab in mind.
Planning makes the season go much better for everyone involved. If you find yourself rushed in season to get soil samples collected and then fertilizer recommendations complete, we encourage to you consider sampling a season in advance. For example. If the client spreads fertilizer in the fall, collect the soils sample in the spring so that the recommendations can be made outside of the soil sampling season.
Dry weather this year has stressed the crops enough in many areas. This additional stress has made many underlying issues visible that were normally masked with good growing conditions. Elevated populations of soybeans cyst nematode (SCN) are being found in areas of stunted and yellow soybeans. Especially in light textured soils with a history of frequent soybean crops. Other species of nematodes are impacting corn.
The best time to sample for SCN is in the fall just prior to harvest to determine max population levels in whole field sampling. Diagnostic sampling for SCN focuses samples to be collected in a smaller area where the soybeans are affected during the growing season. This earlier testing may not indicate maximum seasonal population but can identify the location and relative severity of SCN infestations. Collect a minimum of eight 0-8” deep cores near the affected soybean rows to make a composite sample. It is best to collect another sample just outside the impacted area, near the soybean rows, to determine if the injury is due to an isolated population in the field.
When collecting and shipping nematode samples to the laboratory, do so quickly and avoid exposing the samples to extreme temperatures. Overnight shipping is not required. Nematode samples sent to ALGL should request the NCYST test package that will return SCN adult and cyst numbers, along with interpretations of potential percent of yield reduction. For other crops, request the N3 package which is an adult only count of a wide variety of nematodes that impact other crops. This test will also yield an interpretation of crops that maybe impacted by the species of nematodes present.
Not All Nematodes Are the Same - Corn Nematodes
Wheat grain and fertilizer prices have been variable recently. If you are faced with the decision of whether to remove the straw or leave it in the field, take a few minutes to calculate the value of the nutrients that will be removed with the straw. Make sure you are adequately compensated for the replacement costs of these nutrients.
IPNI nutrient removal data shows wheat straw removing 12 pounds N, 3.3 pounds of P2O5, and 24 pounds of K20 per ton. An 80 bushel per acre wheat crop will produce on average 4 ton per acre of straw with a low harvest cut height.
Be sure to calculate the cost to replace those nutrients when pricing the straw product. The cost to replace the P and K removed in the straw is approximately $50 per ton. The replacement cost of the N, P, and K is about $55 per ton. These prices will vary with the fertilizer market. Several factors can affect the actual removal rates such as rainfall following harvest and prior to bailing that will leach a portion of the potassium back to the soil.
If you would like to submit a straw sample to the lab for testing, we can help you more accurately estimate the nutrients removed and your ALGL regional agronomist can help you with the calculations if needed.
Tissue samples are often submitted to the lab with the sample ID ‘s of “good” and “bad”, and sometime the tissue test data results are very similar. The dry weather this year has increased the appearance of these samples. Sometimes the “bad” sample will have higher nutrient concentrations than the “good” sample.
It is advisable in tough growing conditions to take both a “good” and “bad” sample. In some cases, the samples should be labeled “bad” and “really bad”. Even the better appearing plants may be struggling and result in low tissue test values, just not as low as the poor appearing plants.
Tissue testing lab methods are a complete acid digestion of the plant materials. The concentration is the relative amount of a given nutrient within a defined volume of plant biomass. Changing either the total amount of nutrient in the plant or changing the overall volume of plant biomass will impact the results.
The impact of nutrient uptake and plant size on tissue test results when comparing two samples.
If nutrient availability in the soil is not limiting, there is no reason to expect the tissue test data between a “good” and “bad” sample to be significantly different. If a plant is limited by physical or environmental factors leading to reduced plant growth, the biomass volume of the impacted plant will be less. Equally decreased nutrient uptake by the impacted plant will lead to a less total nutrient in the plant tissue tested. Often the decrease in plant biomass is correlated to the relative decrease in nutrient uptake. This leads to a very similar sample nutrient concentration. If the plant biomass is severely impacted while nutrient uptake continues, the impacted plant could result in elevated nutrient levels. Notes and pictures taken at the time of sampling can be very valuable in interpreting plant tissue data.
When a nutrient deficiency is occurring, it normally only impacts one or possibly two nutrients. When all or several of the nutrients are shifted, then external forces like lack of water limiting mass flow uptake of nutrient or soil compaction reducing root mass may be the cause. This is why taking a soil test close to the sampling location of the tissue test is very helpful. If the tissue test is low and the soil test is low, there is a lack of supply. If the tissue test is low and the soil test is good, then there is a lack of access.
Getting a tissue test report back from the lab showing that both the “good” sample and “bad” sample have adequate nutrient concentrations to support plant growth does not mean the tissue test did not tell you anything. It means the issue affecting the growth of the “bad” sample is most likely not directly related to specific nutrient deficiency. Contact your ALG agronomy representative for support using plant tissue data in diagnosis situations.
While much of the Great Lake’s region was fortunate to get some rain in the last couple of weeks, we still remain well below average for the growing season. These dry conditions are having an impact on the results of some soil and plant tissue tests.
One of the most noticeable trends is very low potassium levels in corn tissue samples. When testing the most recently mature leaves of corn in the V5 to V7 growth stages, the normal potassium level ranges from 2.0% to 2.5%. This summer most corn samples are below this range with a surprising number of samples showing severely low levels below 1.0% potassium. While potassium soil test levels have been steadily declining for several years, that is not the likely cause of these low tissue tests. The plants simply cannot take up the potassium that is there. Plants take up potassium through two main mechanisms, mass flow and diffusion. Both require adequate soil moisture to occur. This means that adding more potassium to these fields is not likely to correct these deficiencies until we get some more rain.
Another common trend is high testing soil nitrate levels. This is the result of there being just enough moisture for the soil microbes to mineralize and nitrify the nitrogen from soil organic matter and manure, but not enough moisture for efficient plant uptake or to leach the nitrate through the soil profile. This has made it very difficult to decide how much additional nitrogen should be used in a sidedress application. Traditional PSNT interpretations will say that no additional nitrogen is needed when soil test levels are greater than about 25 ppm. In a season with adequate moisture, soil nitrate levels are often 20-40 ppm. This season nitrate levels have commonly been between 50-100 ppm. Some will take a conservative approach and not apply any more nitrogen with the expectation yields are likely to be reduced with the dry season. Some will still apply some additional nitrogen while there is an opportunity to make the application in hopes we will get more moisture as the season progresses. Either approach is justified. Unfortunately, we might not know if we made the right decision until the combine goes through the field this fall.
Routine soil tests so far this season do not seem to be impacted by the dry conditions. However, should the droughty conditions continue, this could potentially change as samples are collected following wheat harvest and into regular fall sampling season. The two most common measurements impacted by drought conditions are potassium and pH. The potassium levels will be lower due to collapsing of clay particles trapping potassium inside. The pH can possibly come back lower than it should be due to excess salts in the sample that interfere with pH electrode readings. Fortunately, it takes a severe drought to have extreme impacts on routine soil tests. We have not seen this level of drought since 2012, and hopefully won’t anytime soon.
Plant tissue testing continues to grow in popularity as growers and crop advisors work to fine-tune their fertility programs. With the ever-increasing costs of inputs, it is important to identify which ones are necessary and which ones work. Plant tissue analysis can help in several ways. It can potentially identify a nutrient deficiency prior to the development of visual symptoms. It can be used as a general monitoring of an overall fertility program. It can be used as a comparison between areas of a field that are obviously performing differently. Whatever the reason for collecting a plant tissue sample may be, it is critical to get a good quality sample to the laboratory. Here are some tips to help ensure that you receive reliable data back from the laboratory.
If you have any questions or concerns about plant sample collection or shipping process, please do not hesitate to contact us. The customer service and agronomy staff will be more than happy to assist.
There have been quite a few questions about the label position on the new soil bags. Below is a picture of the new soil bag on the left and the previous soil bag on the right.
The area for those clients using pre-printed bag labels was moved to the top of the bag from the bottom while leaving the area for handwritten bag labeling in about the same place. There was good reason for the change.
When the bags are in the inbound process we call “layout”, the bags are lined up in submittal form order on tables. This process allows lab staff to verify that all samples listed on the submittal form are present and accounted for. Before the samples are placed into drying containers, the order of the samples is verified. The information at the bottom of the soil bag is very hard to see. Most inbound samples use pre-printed labels on them and are difficult to check when placed at the bottom of the bag. Below is the view of a staff member verifying sample order when the labels are at the bottom of the bag.
If you find the label position at the top of the bag problematic for your sample collection procedures, please place the label as high up on the bag as possible.