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Post-harvest is an ideal time to sample fields for both soil fertility and soybean cyst nematode (SCN). Yield loss is a primary symptom of SCN and can occur with or without visual symptoms. Quality of sampling greatly influences the accuracy of soil test results and provides the opportunity to make more precise management decisions.
Collecting Samples. Soil tests are recommended every 3 to 4 years. If there is concern about fertility or SCN populations, take additional soil tests to aid with management decisions. Key items to consider when soil sampling are timing, depth, and tillage systems. To increase consistency, sample fields at the same time each year (similar soil environment in terms of moisture content relative to the time of the growing season), ideally after harvest and before the ground freezes. SCN sampling is most effective after corn harvest and prior to soybean planting. It is best to collect samples from the same location each time testing is done; this can be made easier with the use of GPS equipment.
The recommended number of samples is a balance between what is acceptable by the grower from both a cost and precision standpoint. However, the number of samples collected should be sufficient enough to capture variability within the field. Take soil cores to plow depth or at least the top 6 to 7 inches. To help with year-to-year comparisons, samples from the same field should always be taken at the same depth.1 In no-till or reduced-tillage systems, more cores will be needed due to less mixing and more spatial variation. Other soil tests may have different soil sampling requirements; the nitrate test for certain western Minnesota counties requires soil cores to be taken at a depth of 24 inches.2 Check with your soil testing laboratory for specific instructions on collecting soil cores and preparing samples. If dry soil conditions prohibit taking soil cores to the appropriate depth, wait to sample when soil conditions improve. Fertilizer recommendations become more accurate as the number of samples and cores per sample increases.
Sample Handling. Sample cores should be collected in clean plastic containers, mixed, and placed into containers designed for soil samples. Label each sample so it can be identified by the field it originated from. Fertility samples can either be sent immediately to a testing facility or left to dry in a dust-free location. SCN samples should always be kept cool and out of direct sunlight. If the samples are mailed directly to the testing facility, the sample should be sent early in the week to avoid hot storage conditions over the weekend.3
Fertility Test Results. Fertilizer applications should be based on the values received from the soil fertility test and crop removal rates (Table 1). Levels that are adequate for the crop to be grown may only require a maintenance level of fertilizer. Lower levels will require “build up�? amounts of fertilizer along with the maintenance amount. Always consider residual fertility from previous crops and and manure applications when determining application amounts.
SCN Sample Results. SCN egg population densities help to determine best management practices. Depending on SCN population (Table 2), selecting SCN resistant soybean products and rotating with non-host crops can be effective ways to manage populations for increased yield potential.3
Nitrogen. During wet years, the loss of nitrogen (N) from the soil via leaching and denitrification can be elevated. If nitrogen remains in nitrate form in the soil prior to the next planting, continued precipitation will further subject the soil to loss via leaching and denitrification. The remaining N can be assessed next spring by measuring N-Nitrate in soil samples taken a week or two before sidedressing from depths of 0-1 and 1-2 feet.
Cation Exchange Capacity (CEC). Soil CEC is the ability of soil particles, which are negatively-charged (anions), to attract, hold, and release positively-charged nutrient particles (cations). The three cations used the most during crop establishment and growth are calcium, potassium, and magnesium. Actively growing plants adsorb these cations from the soil solution. The soil solution refers to the thin layer of water surrounding roots, root hairs, and soil particles.4 Higher amounts of clay and organic matter produce higher CEC, which results in a greater capacity to hold nutrients.
In May, Monsanto announced that the U.S. EPA approval of a novel nematicide branded NemaStrike™ Technology. Expected to be available in most states beginning in 2018, NemaStrike Technology will provide broad-spectrum control of plant parasitic nematodes and consistent yield protection performance in corn, soybeans and cotton. NemaStrike Technology has a novel mode of action that provides broad spectrum control of plant parasitic nematodes that include, but are not limited to, soybean cyst, root knot, and reniform nematodes in soybeans and lesion, lance, needle, sting, and stubby root nematodes in corn.
In three years of field testing in all soil types and levels of nematode pressure, products with NemaStrike Technology showed a yield benefit in soybeans and corn. In corn, NemaStrike Technology provided an average yield protection advantage of 7 bu/acre versus the competitive standard with a 73 percent win rate. In soybeans, NemaStrike Technology provided an average yield protection advantage of 3 bu/acre versus the competitive standard with a 68 percent win rate.
Acceleron® Seed Applied Solutions with NemaStrike Technology provide a novel mode of action that stays in the root zone, where nematodes attack, for up to 75 days. NemaStrike Technology is designed to provide broad-spectrum control of plant parasitic nematodes and consistent yield protection performance in corn, and soybeans.
Table 1. Average nutrient removal rates for crops.Source: Average nutrient removal rates for crops in the Northcentral region. 2008. International Plant Nutrition Institute. http://nanc.ipni.net/ (verified 9/05/2017).13;10;
Table 2. Effect of SCN egg population on potential yield.Source: University of Wisconsin-Extension. 2014. Wisconsin soybean cyst nematode management guide for Wisconsin. (verified 9/10/2014).