Introduction

      With corn prices at enticing levels, many are considering converting CRP ground or other grassland into cropland. This conversion can be wildly successful or a complete failure, depending on the approach taken.

Stand Renovation

      The process of killing or renovating the perennial grass depends on the species. Warm-season grasses, like big bluestem, Indiangrass, little bluestem, and switchgrass are killed differently than cool-season grasses like bromegrass, tall fescue, orchardgrass, and wheatgrasses. One caution: do not try to kill a sod with tillage alone, especially a warm-season grass sod. Effect control will take multiple tillage trips, resulting in a light fluffy seedbed in which seed-to-soil contact is very difficult to obtain. The result is a loss of much of the organic matter built up over the lifetime of the grass. It would be much better to kill the sod with herbicides and use a no-till program to retain the desirable soil structure the grasses have built up.              

The procedure for killing a warm-season grass is to spray the stand 60 days prior to average first frost in fall. Use a 2 quart rate of glyphosate (4#/gal formulation), complete with all necessary adjuvants and ammonium sulfate. This coincides with the time warm-season grasses begin translocating carbohydrates to the roots for winter storage.

      Applications made earlier than mid-July are usually not effective. An additional application may be made 30 days later if regrowth occurs. Applications made after frost have little effect.

      The level of control can be greatly increased by haying or grazing the stand heavily until mid-July, then allowing 6” of regrowth before spraying. Burning the stand to remove old dead material before greenup also greatly increases success.

      Another good move is to fertilize a stand of warm season grasses at greenup, after burning, with 80-120 lb/A of nitrogen and any other nutrients called for by soil test. This will not only greatly increase the amount of hay or grazing possible, but also narrow the carbon: nitrogen ratio of the residue after killing.

      Warm-season grasses are notoriously low in nitrogen content, but especially so on low organic matter soils like the eroded areas often put to CRP.  This means that the residue will be very slow to decay after killing, and will result in the immobilization of a great deal of nitrogen during this long slow decay process, unless additional nitrogen is added. This stand will be ready to plant next spring.

      Soybeans are often more successful than corn on renovated warm-season grass sods, unless additional nitrogen is added.  It is often tempting to plant wheat in fall on a freshly killed sod. Resist this temptation. Native grasses harbor take-all fungus, which can completely killed wheat planted into freshly killed sods. The same holds true for cool-season grass sods, as well.

      One other caution: warm-season grasses are usually bunchgrasses and the stands are often very rough due to the grass clumps. Often, the temptation is to use tillage to level these clumps. If you try this, you are committing yourself to a very long process. One trip usually pulls those clumps out of the soil and several subsequent trips are needed to chop them up. It is probably better to drive very slowly when planting so that the planter or drill stays in contact with the ground, rather than bouncing.

      The conversion process for cool-season grasses is much quicker and easier than for warm-season grasses. The best time to renovate a cool-season sod is in fall, about 2 weeks after average first freeze, when cool-season grasses begin translocating carbohydrates to the roots for winter storage.

      Cool-season grasses can be killed in the spring much easier than a warm-season grass.  If a spring kill is desired, apply 2 quarts of glyphosate to grass after about 4 inches of new growth appears. Nitrogen applied prior to greenup will make this occur earlier in the spring than if nitrogen is not applied.

      If going to corn, any regrowth can be sprayed with atrazine and crop oil concentrate prior to planting.  Atrazine will injure or kill cool-season grasses, but not warm-season grasses. Roundup Ready^® corn allows yet another rescue option if regrowth occurs.

Planter and Drill Adjustments

     In spring killed sod, there will not be enough time for decay. As a result, there will be difficulty closing the seed furrow behind the planter, because the fine roots act like springs and hold it open. Ensuring that your planter or drill is adjusted and operating correctly will help overcome this problem.

      Planter attachments such as row cleaners/trash whippers and no-till coulters can be helpful in fields with residue. Sharpening your coulters so that they cut the residue ahead of the planter row opener is critical to avoid “hair-pinning” residue in the seed trench. 

      When setting the attachments, set the residue managers/trash whippers to clear loose residue in front of the planter row opener. Setting the residue manager/trash whippers too low will create a furrow effect and adverse results from subsequent wind or water erosion. 

      If you’re using coulters, set the depth low enough to cut residue ahead of the row opener. However, don’t set the coulters lower than the row opener or seed trench. Doing so may create an uneven seeding depth and/or air pockets that limit seed to soil contact. Plant at an appropriate speed to allow good planter performance and minimize planter bouncing. Closing wheels and seed firmers may need to be added or upgraded to obtain good germination.

Pest Management

      Weed and plant species composition and density in CRP fields may help determine the follow crop. If these plants are not effectively controlled during renovation, they can be a significant problem in the follow crop.

      Grasses are effectively controlled by glyphosate and other grass herbicides in soybeans. Perennial broadleaves such as alfalfa, clover, thistles and brush are a problem in soybeans since glyphosate and other soybean herbicides may not provide effective control.

      Roundup Ready corn is a good option for fields following CRP since you can effectively control the grasses with glyphosate and tough broadleaves with existing herbicides.   

      Fields following CRP often have an influx of cutworm species and secondary soil insects. In all cases when planting into a killed sod, use insecticide treated seed for sod webworms, wireworms, and other seed attacking insects, as these seem to be much more prevalent in sods than cropland. Careful scouting for insects through the entire season is necessary. 

      Fields following CRP often have rodents, cutworm species, and secondary soil insects.  Soybeans can be affected by these pests, but may not experience damage from these pests as often as corn. They also have the ability to compensate for lost plants.

      CROPLAN GENETICS corn hybrids with a Roundup Ready-Herculex^® I stack provide protection against early season cutworm flushes as well as having the Roundup Ready trait. All CROPLAN GENETICS hybrids are treated with a Cruiser^® seed treatment which provides seed and seedling protection against early season secondary soil insects.

      If you expect a high level of rodents, a rodenticide, such as zinc phosphide pellets, may be warranted.

Fertility

      Fertility will be a key variable to manage when taking a field out of CRP. One misconception many people have is that these fields, when taken out of CRP or grassland, will be similar in nature to native sod. While the organic matter levels in most cases will have risen, it took 10,000 years to accumulate the organic matter levels found in native prairie.

      Also, unless fertilizer was applied during the CRP contract, soil fertility levels will be no better than, and often worse than, the same soil prior to enrolling in CRP. It is best to start with a soil test to determine what nutrients will be needed well ahead of any conversion process. Additional nitrogen may be needed for corn to compensate for the immobilization of nitrogen that takes place when the sod decays. Research done at Tribune, KS, by Kansas State indicated that as much as 150-200 lb/A of nitrogen may be immobilized by a decaying native grass sod.

      All corn backgrounds (genetic families) will need careful nitrogen management. However, Southern and Eastern genetic origins will be extremely sensitive to nitrogen mismanagement. Both backgrounds tend to build large plants or factories, utilizing lots of nitrogen. If you have capability to provide a late season nitrogen boost, Southern or Eastern origins are likely to benefit.

Inoculation

      Inoculation is critical if you plant soybeans after CRP. Using inoculants like Optimize^®, Cell-Tech^®, or Apex Pro^STF allows soybeans to grow in a nitrogen deficient environment.

Crop and Seed Selection

      Understanding the problems or potential problems fields have is very important in seed selection. Some examples include: soil texture, drainage, pH; insect pressure, and disease pressure. Many CRP field had production problems before they were placed in CRP. They may be your toughest fields to produce crops in after they are taken out of CRP.

      After the initial year of cropping, former CRP fields are no more difficult to farm than any other field. In fact, the improved soil structure in no-tilled fields usually makes them much more productive than the same field prior to being planted to grass. Amazingly good corn and soybean yields have been produced off fields considered very poor prior to being planted to grass.

      Today’s seed technology provides greater flexibility in crop selection for fields coming out of CRP than a decade ago.  Roundup Ready technology in corn or soybeans makes either crop a suitable candidate as the first crop.

      CROPLAN GENETICS is the industry leader in providing diverse genetics and technology options to help you in tough agronomic situations such as converting a field from CRP to field crops. Using the background information on corn and soybeans will help you take some of the guesswork out of your seed decision. 

Variety Selection- Soybean

The key to selecting the correct soybean variety depends on the microenvironments that you expect in the field. Fields that are poorly drained and/or in areas where disease pressure is likely should be planted to a variety with more defensive characteristics.  In addition, a seed applied fungicide, such as Warden^® RTA^® provides protection against early season seedling diseases.

      Understanding your soil test and the potential for iron chlorosis due to high pH is  critical in variety selection. If you have a field with high pH, select a variety that tolerates high pH.

      Soybean cyst nematodes (SCN) are not as likely to be a problem following long term CRP  than in fields where soybeans have been part of a regular rotation. Exceptions to this may be fields that are alongside watersheds downstream from SCN problem areas and have had a history of flooding in recent seasons. 

      If you are fortunate to be in an area with low stress on soybean growth and development, choose a variety with more offensive characteristics. If you expect several microenvironments to develop across your field, you may need both offensive and defensive characteristics. If this is the case, choose a Precision Blend from CROPLAN GENETICS. A Precision Blend contains soybeans with different offensive and defensive strengths and helps take some of the “guesswork” out of separating a field into offensive and defensive environments.

Variety Selection- Corn

      For fields with heavy clays and slower drainage, CROPLAN GENETICS hybrids with an Eastern or Northern background may provide you with the best fit. On fields with heavy clays and slow internal drainage, you should avoid place a hybrid with strong Southern or Western origins.

      If you have a field that is sandier soil texture, has good internal drainage, and is under irrigation or in a good rain fed area, choosing a Southern hybrid is the logical choice. Well drained medium textured soils in areas where drought is likely and/or late season disease pressure is likely are a good fit for Western origin hybrids. If diseases are not likely to be a problem, the soil is medium textured, and there is high likelihood of adequate moisture, Southern origin hybrids will perform well.

      The tillage system and genetic origin interact. Northern origins exhibit the best emergence under cool conditions. Eastern and Western origins have the best early vigor. Southern origins exhibit the most difficulty emerging under cool conditions and also have poor early season vigor.  

      If you think a hybrid with Southern origin has more strengths than weaknesses for your situation and you are no-tilling, use planter attachments that clear residue over the seed row to help warm the soil sooner. This may help the Southern origin establish better. 

      Strip-till systems also help warm the soil in the seed row alleviating some of the problem of establishing a good stand in the spring.

©2007 Agriliance LLC