C.O.R.N. Newsletter 2013-32

Dates Covered: 
September 24, 2013 - October 1, 2013
Editor: 
Adam Shepard

October Weather Update

After a heavy rainfall event last week, we will return to above normal temperatures and mainly dry weather this week. Fields will dry quickly as warm days will combine with low humidity levels. Temperatures will average 3-6 degrees above normal this week. Rainfall will generally be zero, though a few spots in the far south part of the state may see isolated showers midweek.

The next rain event will be the second half of the weekend. However, it will be a fast moving system so rainfall is forecast to be under 0.50 inches.

The start of October will also be warmer and drier than normal.

Indications are harvest should progress quickly as rainfall may go to above normal starting around mid October lasting into November.

Winter conditions are leaning toward slightly colder than normal, slightly drier than normal and near normal snowfall.

Early 2014 spring conditions appear to be leaning toward warmer and drier than normal conditions.

The lastest Climate Forecasting System rainfall outlooks by NOAA/NWS are available here:

Monthly precipitation forecast models

 

Lime Considerations

Lime Considerations

Fall is an excellent time to test soil pH and determine whether any lime needs to be applied for future crops. Proper soil pH is important for nutrient availability, herbicide activity, and crop development. For most soils, additional lime is not needed every year. Consider these points before liming your fields:

  • Do I need lime? Each year we hear stories of people adding lime to their fields without a soil test. The grower has a source of free waste-product lime that they pick up and apply to their fields. In many cases their soil pH was fine, but they did not want to pass up a "good deal". Without knowing the soil pH, a grower may inadvertently raise their soil pH to the high 7's. At this elevated pH, certain nutrients may become limited and the productivity of their crop may be reduced and require special management practices. Northwest Ohio has the greatest risk of elevating soil pH from careless applications of lime. A soil analysis is the best step to determine if a field needs lime.
  • What is the pH of my subsoil? Generally a laboratory recommends lime when the soil pH drops two to three units below the desired value. The desired value depends upon the crop and the pH of the subsoil. In parts of Ohio where the subsoil pH is less than 6.0 for mineral soils (eastern Ohio), additional lime is recommended after the soil pH drops to 6.2 for corn and soybean, and 6.5 for alfalfa. In other parts of the state (generally western Ohio), the subsoil pH for mineral soils is greater than 6.0 and lime is not needed until the soil pH drops below 6.0 for corn and soybeans, and 6.2 for alfalfa. Private laboratories may not take in account the subsoil pH and use recommendations based on a subsoil pH less than 6.0 for all parts of the state, possibly recommending lime applications several years earlier than needed for some areas.
  • What is the Effective Neutralizing Power of my lime source? An important item from a lime analysis report is the Effective Neutralizing Power (ENP) value, which is required for material sold as lime for agricultural purposes in Ohio. This value allows a producer to compare the quality among lime sources because ENP considers the purity, neutralizing power (including fineness) and moisture content. In other words, the ENP tells you how much of that ton of lime actually neutralizes soil acidity. The unit for ENP is pounds/ton (be careful not to use %ENP, which may also be on a lime analysis report). The ENP allows a producer to compare different lime sources because they can now determine price per pound or ton of actual neutralizing material.
  • Should I use “hi cal” or dolomitic lime? In most situations it does not matter, so a producer can select the least expensive of the two lime sources. Transportation is often the largest cost of a lime material, so generally the closest lime source (quarry) is often the most economical.

Several parts of the state are historically low in soil magnesium (eastern and extreme southern Ohio). Adequate soil magnesium is important to reduce the risk of such problems as grass tetany for grazing animals. Soil test magnesium levels need to be greater than 50 ppm (100 lb) for optimal corn, soybean, wheat, and alfalfa production. Often areas low in magnesium also need lime, which has made the application of dolomitic lime an economic solution for both concerns.

The ratio between calcium and magnesium is important. Soils should contain more calcium than magnesium. Extensive research has shown that crops yield the same over a wide range of calcium to magnesium ratios and will not affect crop production as long as the calcium to magnesium ratio is larger than 1. High calcium lime should be used in situations where the soil test calcium to magnesium ratio is less than 1, or in other words, the soil magnesium levels are greater than the soil calcium levels. I have not observed any Ohio soil tests where the magnesium levels are above the calcium levels. Also keep in mind that almost all dolomitic lime sources will contain more calcium than magnesium. Unfortunately, some producers have been led to believe that magnesium levels in dolomitic lime may be undesirable. The level of magnesium is unimportant as long as the calcium level is above magnesium. The focus should be selecting lime on its Effective Neutralizing Power (ENP) rather than its calcium level.

In summary, make sure you take a soil test to determine if lime is needed, determine if magnesium is needed, know the historic pH of your subsoil, and then use the ENP to select the most cost effective lime material. A soil test every three to four years will determine the lime requirements for your fields. Additional information on ENP and lime sources may be found at the following location:

Ohio State Factsheet on effective neutralizing power and lime sources

Be on the lookout for unexpected lodging during harvest

Be on the lookout for unexpected lodging during harvest

For the past few years, we have been warning about the presence of Bt-resistant western corn rootworms.  The western corn belt has been experiencing greater than expected damage on Bt-corn expressing the single trait Cry3Bb1.  Most often these observations are found in continuous corn, although a report a couple of weeks ago in the Bulletin (from the University of Illinois) reported damage in first-year corn (see http://bulletin.ipm.illinois.edu/?p=1629).  We have not yet detected the presence of resistant rootworms in Ohio, but detecting damage is often difficult.  As corn producers begin their harvest, keep a sharp eye out for any areas of significant lodging that may be indicative of western corn rootworm damage in corn expressing Bt, specifically Cry3Bb1 and in continuous corn.  Keep in mind that many factors can cause lodging including wind damage and poor root growth, so a careful examination of the roots is necessary.  If you suspect damage, please contact entomology state specialists (michel.70@osu.edu; hammond.5@osu.edu) or your local OSU extension educator. 

Preplan for quality soil test results

Preplan for quality soil test results

Soil testing is a very profitable practice to manage fertility input cost and promote environmental stewardship. The primary goal is to measure the soil’s ability to provide the soluble nutrient needed for crop production for two of our three macro nutrients (phosphorus and potassium) plus measure soil acidity which governs availability of micro nutrients and other soil functions. A secondary goal is to compare soil test results over time with crop response and fertilizer additions to identify trends in the fertility program as it is executed or what is becoming known as “adaptive management”. The key to accomplishing both these goals is to take a quality soil sample that represents the field area being sampled.

A soil sample sent in for analysis is around one pound. A 6.7 inch slice of soil with a surface area of one acre is approximately 2 million pounds known as an “acre furrow slice”.  As we include more acres in the sample you can see how small a volume is collected compared to the volume we want to represent. Some preplanning and establishing standard sampling criteria should be considered as good first steps to taking a quality soil test.

Preplanning involves determining the field area that will be collected for inclusion in the sample. There are a number of different methods on dividing up a landscape that can be effective. The overall goal is to have sample areas in the field that have similar crop yields, crop rotation histories, fertilizer application methods and sources of applied nutrient. Fields or field areas with a history of manure, banded fertilizer application or other unique characteristics require a different sampling strategy. Field areas represented by a single sample should be less than 25 acres.

The second focus area for a quality soil test is the sample collection.

First, a single soil sample is not a single core but a composite of numerous cores collected over the field area represented by the sample. Where broadcast applications have occurred a composite sample of 10-15 cores is suggested. Where a history of banded application exist in a field or manure application, then increase the number of cores to 20-25. The samples are bulked and then a subsample submitted to the lab.

The next critical collection item to define is the sample depth of the cores. Nutrients in the soil are naturally stratified with higher nutrient generally found on the surface due to residue breakdown and fertilizer placement then decreasing deeper in the soil profile due to plant removal. Each core taken should be taken to the same depth in the soil profile. Generally a 6 or 8 inch sample should be taken.

Finally, some other factors in sample collection should be included. Scrape the soil surface before taking a core so the sample core does not contain residue or live plant material.  If manure has been applied wait at least 6 months before sampling or if fertilizer is applied wait 2 months.  To compare sample trends, the soil samples should be done at approximately the same time of the year.

Controlling the sampling process is critical to think about implementing adaptive management principles. Adaptive management is a continuous loop of considering site factors, making a management decision, measuring outcome and then modifying the decisions to reach production goals. Adaptive management  from a soil fertility stand point involves  taking soil test, making fertilizer decisions, then measuring yield response followed by a follow-up soil test to provide a basis  to judge if the fertility program is providing nutrient in sufficient quantity to meet yield potential and maintaining soil test at the critical soil test level. An additional consideration in soil sampling to meet adaptive management is to use geo-referenced sampling to try and limit site sample variability from year to year.

The whole goal of soil sampling is to make a fertilizer recommendation for crop production. To provide the recommendation calibration studies are done with the soil test to measure crop response. For Ohio, the Tri-state fertilizer recommendations provide the calibration study history for recommendation development. For more information on the Tri-state Fertilizer recommendations or developing a soil sampling strategy several references are provided at https://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins.

 

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About the C.O.R.N. Newsletter

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.