By Orvin Bontrager
One doesn’t add oil to an engine without checking the dip stick. Neither should one add fertilizer products to a field without checking the dip stick by soil sampling.
This fall, soil sample results are another clear indication of the importance of properly taking samples with sound testing results and interpretation.
Residual nitrogen is particularly high on low yielding areas and non-irrigated fields as a result of drought last summer. Normally, soybeans are excellent scavengers of nitrogen and use up all the residual from the previous corn crop. With the drought, non-irrigated fields show significant levels of residual nitrogen that was never used this year. There is as much as 40-60 pounds per acre in the top 8-10 inches alone. This can be credited to next year’s row crop along with the additional legume credit from the soybeans by leaving the soil low on residue. There will be nitrogen mineralization from the soil organic matter in the spring prior to significant crop removal.
With the low amount of rainfall this fall, the soil moisture is very low at this point. It would be best to wait to apply nitrogen fertilizer on non-irrigated fields until next spring or wait and sidedress after crop emergence. This would allow a better assessment of yield potential and adjustment of nitrogen rates.
Even the very high yield irrigated corn fields show some significant nitrogen residuals. Some areas have high levels of nitrates in the water. With extensive watering, more nitrogen was applied this year than normal through irrigation water. The high temperatures also allowed more mineralization last summer and this fall after the corn stopped nitrogen uptake. No leaching of the nitrate accrued with the drought conditions. One may be able to apply less nitrogen for 2013 than last year, even though excellent grain yields were removed.
Other nutrients, such as phosphate, may not have dropped significantly, depending on the amount of inherent fertility of the soil. One cannot make accurate fertility recommendation based on crop removal alone. Proper testing is the major tool to making cost effective recommendations.
The following is from Fred Vocasek, senior lab agronomist:
“Soil nitrate levels have been elevated this year due to the hot and dry weather conditions. We have seen some samples with extraordinarily high nitrate levels, reported in the hundreds of pounds. Why? Lab error? Maybe, but not likely, according to many sample reruns by all three labs. Weather and variability are likely culprits.
“Nitrates not taken up by the plants will move gradually with the movement of soil water. When soil sampling, we need to be aware of this variability – not just across the field or over a few feet, but an “inches” scale. We have to think of variability in the sampling positions between the row on a micro-scale.
“The photos are from the movie – ‘How water moves in soils.’ Soil was placed between sheets of glass, dots of dye tracer placed in the soil, then water was added. The upper photo illustrates the type of water movement we would expect under pivot irrigation, where water is applied uniformly across the soil surface. Assuming water moves downward and not laterally, mobile anions – like nitrate, sulfate, and chloride – will be mobilized in a downward direction. Not all at once in a slug, but gradually.
“The second photo illustrates water movement we might expect under furrow irrigation. The corresponding nitrate movement is in a radial direction, away from the furrow bottom – downward, laterally, and even ‘upward’ toward the top of the ridge. High evaporation rates will accelerate this water movement because the ridge tops are more exposed to air movement. By season’s end, mobile anions will have migrated toward the ridge top. It is common to see a faint white film of crystallized soluble salts in this area. If there are no roots developed in the soil zone immediately around the center of the ridge, nitrate uptake will be minimized.
“This becomes important when sampling. Under furrow irrigation, the ridge top will have the highest nitrate concentration and the furrow bottom will have the lowest. This summer’s extreme weather is likely to have amplified this effect, so may partially account for elevated nitrate levels in the soil sample, especially with these types of irrigation patterns.
“We may also see a variable nitrate at this scale in our strip till systems. Soil moisture will be higher at any location where the crop residue remains on the soil surface. Soil water will tend to migrate from these wetter areas under the residue to the bare soil areas where evaporation is occurring. Thus we may see differences in nitrate levels across the row depending on the exposure due to residue cover. This effect may not have been noticeable in years with more favorable weather, but is likely to be more pronounced because of the extreme conditions that occurred in summer 2012.
“Collecting more cores than usual may not be a bad idea this year. It is impossible to predict the degree of variability that has occurred in many fields, but we can be sure that soil variability may be above normal as we move into crop year 2013.”
Fred Vocasek and Steve Harrold, who both work at Servi-Tech’s Dodge City laboratory, attended the American Society of Agronomy annual meeting in Cincinnati, Ohio. The meeting is four days long with hundreds of oral and poster presentations on research in agronomy, crops, and soils.
Here are some significant items they brought home:
From Fred Vocasek:
- The established guidelines for the post-season stalk nitrate tests are not going to apply effectively this year because of the extreme conditions.
- Purple Kool-Aid is made up of two dyes, one red, one blue. The blue dye is a cation (positively charged) and the red dye is an anion (negatively charged).
- Lab studies compared maleic-itaconic copolymer (the active ingredient in Nutrisphere) to chelates and other polymer compounds with greater or lesser ionic strength. All of these were tested for their ability to affect nitrification of ammonium fertilizers or to affect ammonia volatilization loss from urea. There was virtually no effect for ANY of the compounds that were tested.
- Farmers in India and Argentina have attitudes and responses that are not much different from American farmers.
- Baxter Black was hilarious in the closing session …. at least to us former farm boys. The urban and foreign members of the audience missed the point some of Baxter’s comment because they have never had to deal with the digestive by-products of wheat pasture cattle or the fine points of preg-checking.
- Due to increases in the recent demand for plant tissue testing throughout the Midwest, there appears to be a renewed interest in improving what we know and how we can use plant tissue testing to improve nutrient management. A new look at using nutrient ratios in the plant as well as redefining the so-called sufficiency/deficiency levels were topics discussed.
- Several presenters during the meetings reminded us that the world population is projected to reach 9 billion people by 2050. Not only does this emphasize the huge challenge of producing enough food for all people, we are reminded that environmental concerns must be balanced with efficient use of our energy, fertilizer, and water resources.
- As cereal grain prices have increased in the past few years, consideration must be given to the parts of the world where people now have less to spend on nutrient-rich foods, which include the non-staple fruits, vegetables, and animal protein. Malnutrition is a real problem in parts of the world where such foods are unavailable or adequate intake of essential micronutrients, vitamins, and amino acids is unaffordable. Several speakers in a symposium entitled, Fertilizing for Crop Qualities that Improve Human Heath discussed the importance of finding ways to solve these problems.