What Are the Advantages or Disadvantages to Injecting Nitrogen at Layby Versus Broadcast Applications in No-Till Corn?
The advantage of injecting layby nitrogen on no-till corn is that there is less chance that the urea in 30% UAN will volatilize and be lost. This is most likely to occur when the soil is dry, temperatures are above 80oF , and there is residue on the soil surface. Residue absorbs the liquid nitrogen and keeps it from be incorporated into the soil. There are also certain types of bacteria in the residue that help volatilize urea. Tests in eastern North Carolina have found that when 30% UAN is applied during a hot, dry period the loss of nitrogen results in yield reductions of 5 to 15 bushels per acre. The disadvantages to injecting nitrogen are that it requires extra equipment, increased tractor horsepower, and prevents the use of liquid nitrogen as a carrier for herbicides.
The purpose of DGPS equipment, yield monitors, grid soil sampling, and variable rate applications is to use soil or yield information to improve yield or to reduce inputs. To do this a grower must get accurate information at a reasonable cost, and then must act on this information in a way that improves profits. In the case of variable rate lime applications, these technologies are improving profit by both reducing lime applied and increasing yield. Yield monitors have also produced information that has resulted in increased yields. Currently, a grower who farms over 250 acres of corn can pay for a yield monitor in five years through increases in corn yields brought about by learning which hybrids produce best on what soils. Other practices have not been as profitable. Changing phosphorus or potassium rates based on grid soil tests or changing seeding rates have not resulted in consistent yield increases and have not increased corn profits. A grower must carefully evaluate an investment in new technologies by considering how this information can help improve the decisions he makes in managing corn production.
There is no evidence that corn borer, corn earworm, or southern cornstalk borer populations increase in no-till systems. Therefore, the decision about whether or not to plant Bt hybrids in a no-till system should be based on whether any of these pests are a significant and reoccurring problem in your area
Dr. John Van Duyn has been comparing Bt and standard corn yields for over 3 years. When corn borer, corn earworm, or southern cornstalk borer populations are high, Bt hybrids easily out-yield non-Bt hybrids. When these pests are not present, yields from Bt and non-Bt hybrids are similar. Refer to the section on Insect Management in Corn for more information.
While there has been no official study of the difference in ECB infestations, generally ECB occurs more frequently and more intensely in the tidewater and coastal plain regions of the state. In particular, the blackland (high organic) soils of eastern North Carolina usually have high numbers of ECB.
See the section on High-Oil corn in this guide for more information on High-Oil corn. Other specialty corns which are readily available for different markets include white corn, Indian corn, waxy corn, and popcorn. The management for these corn types is similar to that of conventional yellow corn. In the near future, we will see corn hybrids that have high available phosphorus (HAP), High Oleic Oil, and High Lysine. These will be available in the year 2000 and beyond.
The most effective control methods for billbugs on high organic soils is crop rotation and high doses of counter insecticide. In areas of severe billbug infestations, corn should not be grown for two years following the original corn crop. When corn is grown, Counter 20CR should be applied in a T-band at double the normal rate. This rate of Counter has been specially approved for control of billbugs in North Carolina. For more information see the section on Insect Management in Corn is this guide.
The section on narrow row corn covers the economic considerations to narrow row corn. In general, narrow row corn results in a 6-8% yield increase. However, the extra cost of changing equipment averages around $20,000. This means that to increase profits in changing to narrow rows a grower must farm over 350 acres of corn.
Crop rotation and in-furrow insecticides are the control methods for western corn rootworm. See the section on Insect Control in Corn in this guide for specific guidelines and rates.
Split nitrogen applications produce higher yields (10-15 bu/acre) than putting all the nitrogen on at planting. Current recommendations are to split apply your nitrogen, particularly on sandy soils.
Nitrogen rates should be related to soil productivity. The higher the yield potential the more nitrogen should be used. However, no-till soils present more of a problem in that the recycling of organic materials helps hold and release nitrogen to the crop. More research is needed in these systems to find optimum nitrogen rates. Currently, recommendations are to use 1 to 1.25 lbs of nitrogen for each bushel of corn harvested.
The fact that a large amount of our grain is used to feed swine and poultry means that there is a great deal of potential for marketing high value grain that has enhanced feeding qualities. Currently, the drawback to growing these hybrids is that their yield potential in North Carolina is not known. Research is underway to determine the difference in yield potential between high oil corn hybrids and conventional hybrids.
The section on Weed Management in Corn covers the current recommendations on using Accent and Exceed after Counter 20CR. The basic recommendation is that you should not use these materials following Counter 20CR on soils with less than 5% organic matter. However, depending on how you apply the Counter (T-Band or in-furrow) and the rate that it is applied (low is better than high), you may escape injury on soils with organic matter levels above 5%.
The advantage to this system would be to control soil movement under windy conditions and to trap more moisture. While there has been little research into this system, these advantages could improve corn yields on very sandy soils or on high organic soils where wind erosion is a problem.
What Is the Difference in Drought Tolerance Between Conventional and Genetically Engineered Corn Hybrids?
Indications are that genetically engineered corn hybrids (Bt corns or herbicide tolerant corn hybrids) are as good as conventional hybrids in withstanding drought.
The primary advantage of aeration tools for no-till systems should come in the spring when the greater porosity should help increase moisture penetration into the soil and provide quicker drying and warming of the soil surface. Remember, the key problem with no-till systems is getting the corn planted into soil that is warm enough to allow for quick germination and emergence. As for the loss of mulch, one would expect less ground cover with these tools, but not so much as to reduce the impact of mulch on soil erosion or moisture holding capacity. Once could also expect that in these warmer soils weed emergence would be greater early in the spring.
Is There a Seed Vigor Test to Determine the Germination Potential of Different Corn Hybrids in Cool Soils?
Currently, there is not a seed vigor test for determining germination potential in cool soils. While several researchers have proposed using a cold germination test, the industry has not embraced this concept. The best a grower can do is to keep in mind that germination percentage under cool, wet conditions will be lower than that reported on the hybrid seed label.
In this guide you will find recommendations for matching corn planting populations to several different soil types based on yield expectations. Since it is impossible to develop guidelines for all soils and all conditions in the state, compare your soil type and growing conditions to those listed to determine which plant population to use.
Is There a Difference in Yield Loss Between Corn Field Dried to 15% Vs. Corn That Is Harvested Wet and Heat Dried to 15%?
Reports in the popular press suggest that when corn is left to dry down in the field there is an Ainvisible yield loss@ that occurs due to kernel respiration. Field studies in North Carolina showed that reductions in kernel weight as a result of respiration that occurred during field dry-down were very small (less than 1% weight loss), and that this only occurred on certain corn hybrids. Therefore, we currently don=t feel that there is a significant yield loss due solely to kernel weight loss in the field. However, there is a significant yield loss occurring from ear drop and kernel loss in fields where corn is allowed to stand over several weeks.
Unfortunately, farmers don't have much control on grain prices. However, a good marketing plan can protect you from taking a loss and give you some control over the price you receive. See the section in this guide on Corn Marketing.
Breeding efforts are underway to improve the drought tolerance of corn by improving rooting mass and stay green. The problem is that transpiration is necessary for photosynthesis and respiration which is linked to the plants ability to produce high yields. Therefore, any drought tolerance in the plant comes at the expense of yield. The best bet for improving drought tolerance of your corn crop is to improve the water-holding capacity of the soil. No-till, mulch-till, deep ripping, or other strategies that improve root penetration and/or water-holding should improve drought tolerance.
There are yield differences based on the source of nitrogen fertilizer used at layby in no-till systems. Ammoniated nitrogen sources such as ammonium nitrate, ammonium sulfate, and anhydrous ammonia increase yields from 5 to 15 bu/acre over 30% solution or urea. The implications are that nitrogen is being lost to the atmosphere when urea based nitrogen sources are used. Possible solutions to using 30% nitrogen solution are to use a nitrogen stabilizer such as Agrotain or to inject the liquid nitrogen into the ground.
At present there is no independent data that compares hybrids for tolerance to Gray Leaf Spot. Until that data is collected, the best way to determine hybrid tolerance is to examine the ratings provided by hybrid seed companies. Ask your sales representative for these ratings.
The North Carolina Official Variety Tests list comparisons between corn hybrids in silage yield and maturity. Ask your cooperative extension office for a copy of the measured crop performance booklet for corn and corn silage. Currently, there are no tests that compare nutritional value among corn hybrids. Since the timing of harvest has as much or more impact on nutritional value than the hybrid selected, it is difficult to get good comparisons among hybrids with differing maturity ratings.
The following table shows the latest comparison of soil applied insecticides for controlling western corn rootworm.
Table 10-1. Comparison of soil applied insecticides for controlling western corn rootworm.
|Insecticide||Placement||Oz product Per 1000'||Percent Consistency1||Root Rating|
|1 Numbers followed by the same letter are not significantly different
2 The lower the root rating, the less damage caused by rootworm.
There have been studies that have examined the potential for gene transfer from crop plants to weeds and the impact that could have on the environment. All of these studies have concluded that the potential for transferring genes naturally between crops and weeds is almost non-existent. However, the environmental impacts of such an occurrence could be significant depending on what gene was transferred to what weed. For instance, the transfer of the Roundup Ready gene into a weed plant could have impacts ranging from slight to major depending on whether there were other herbicides capable of controlling that weed species.
Publication date: Jan. 1, 2003
Other Publications in Corn Production Guide
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