LINCOLN — Yellow streaks in a field aren’t a welcome sight. But by the time you can see light green leaves, the crop has already been affected by low nutrient levels and you’ve already lost yield potential. Stay ahead of the curve by taking plant tissue samples during the growing season to monitor your crop’s nutrient status.
“The difference in the shade of green between nitrogen levels that are adequate and levels that are growth-limiting is difficult to see. A plant tissue test is the best tool to identify that,” states Dr. Jim Friedericks, AgSource Laboratories’ Outreach and Education Advisor.
Plant tissue testing for row crops has traditionally focused on collecting a leaf sample early in the season and adjusting the crop’s nutrient supply based on critical levels for that growth stage. Samples could be collected once or twice, while there is still time to apply nutrients for the current year. Sampling much later in the season can be used to evaluate the current crop and make nutrient adjustments for the next year.
Recently the idea of intensively monitoring crops with plant tissue testing throughout the season has been catching on, especially among producers who are pushing for maximum yields. Eliminating stresses on the crop are the key to reaching higher yields. Watching the rate of nutrient uptake will help you anticipate any shortfall in nutrient supply.
Kevin Klink, Great Plains Division Manager for AgSource Laboratories indicates that “within the last three years the number of acres under continuous plant tissue monitoring has increased dramatically. Samples sent to the lab from growers in the central Great Plains doubled last year from the year before and the acreage under this testing program has already doubled again with early sign-up for the current year.” These acres are under both corn and soybean production as well.
Changes in sampling strategies are not new. “In the past we would take a composite soil sample of representative areas in a field and fertilize accordingly. Now we grid sample and customize fertilizer application based on a map of fertility,” notes Friedericks. “Monitoring plant nutritional status can be thought of in the same way. If it’s possible to apply nutrients to the crop over a longer part of the growth cycle, then weekly or biweekly tissue samples will give you the specific information you need to make the right time and right rate applications.”
Spoon feeding crops allows the application of a nutrient when it is required by the plant. For elements that can be lost to the environment it is less efficient to apply all the crop’s requirement before planting, as in the case of nitrogen loss through nitrate leaching. But applying the right amount at the right time, can save money and boost yield. (The 4R principles to nutrient management are applying the Right fertilizer source at the Right rate and at the Right time, in the Right place).
Under this tissue sample monitoring program leaf samples are collected every week, starting at V4 or V5 and continuing through maturity, R6 for corn. Pre-arranged mailing and reporting protocols with the laboratory will ensure quick turn-around time so that timely fertility adjustments can be made.
When evaluating the data from plant tissue samples collected for a monitoring program pay attention to nutrients trends. Concentrations of N, P, K, and S will decline over the season as the biomass of the plant increases. This is not necessarily an indication that these elements are limiting unless their concentrations in the plant go below the amount required for maximum growth. Other elements, such as Ca and Mg, will increase in concentration as plants accumulate these nutrients.
With micro-nutrients this ‘dilution effect’ of plant growth is not expected and concentrations might actually increase as root growth allows plants to extract nutrients from larger soil volumes.
Figure 1 – Nutrient levels change throughout the season. This graph includes 13 sample dates from May to August. The red lines indicate expected lower limits of the sufficient nutrient amounts for the crop. Green line is the nutrient content of the plant.
Below is an example of several observed trends in nitrogen levels for corn. Interpretations of an individual field can be made by comparison to expected ranges (indicated as High and Low), or to the relative trends of other fields.
Figure 2 – Season-long Nitrogen in Corn Tissue Sample: Values for the High (green line) and Low (red line) were created referencing the Purdue University’s Cooperative Extension Service National Corn Handbook (1991). https://www.extension.purdue.edu/extmedia/nch/nch-46.html
Plant tissue testing can be done on row and forage crops such as corn, alfalfa and soybeans, small grains and cotton, and on high value crops like grapes, tobacco, potatoes, cranberries and fruit trees.
Plant tissue analysis should be a routine part of every crop producer’s nutrient management program as a way to accurately measure a crop’s health and optimize production. Complete sampling instructions, along with a pictorial sampling guide, can be found on the AgSource Laboratories website in the agronomy section at www.agsource.com/PlantTissue.
AgSource is a leader in agricultural, turf and environmental laboratory analysis and information management services, with facilities in Iowa, Nebraska, Oregon and Wisconsin. A division of Cooperative Resources International, AgSource Laboratories provides testing services to clients in the United States and across the globe. Learn more at www.AgSource.com.
— AgSource