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4/28/2008 - 5/4/2008

Surface Waters: Ammonium is Not Ammonia – Part Two

By John Sawyer, Department of Agronomy

 

A previous article explained the difference between ammonium and ammonia, the relationship between the two nitrogen forms and the implication of a combined (ammonium-N plus ammonia-N) analysis related to water quality criteria for aquatic life. This article focuses on the implication of ammonia and ammonium for chlorination of drinking water.

 

Drinking water is chlorinated (often by addition of hypochlorous acid) in order to control disease causing organisms and provide protection until water is consumed. Several water properties and constituents affect the efficiency of chlorination, and therefore affect the amount of chlorine that must be added to achieve levels of chlorine compounds that have disinfecting capability (hypochlorous acid, hypochlorite and inorganic chloramine).

 

Materials that react with chlorine and reduce or eliminate the disinfecting ability include ammonia, ammonium, organics and reducing agents. Reaction products of chlorine and ammonia can have disinfectant capability, but are slow reacting and add unpleasant taste and odor at high levels.

 

In addition, the chlorine disinfecting activity and reactions are slower at lower temperature and at higher pH, as is the breakdown of chorine-ammonia reaction products. The “interfering” compounds reduce the disinfecting ability of added chlorine, and as their level increases, the amount of chlorine that must be added increases. Once the interfering materials have reacted with chlorine, additional chlorine becomes an effective disinfectant. At high levels of interfering compounds, however, it can be difficult for water treatment facilities to add enough chlorine to provide satisfactory levels of disinfecting compounds in the water and have reactions proceed at a rapid enough pace. It also adds costs for treatment.

 

In contrast to water quality criteria related to toxicity for aquatic life for which ammonia is important, for treating drinking water ammonium and other constituents are also important. Therefore, when a water system is being used for drinking purposes, the ammonia plus ammonium concentration must be considered. While ammonia and ammonium are not directly an issue for drinking water safety to humans, indirectly they are because of interference in disinfection for control of disease causing organisms. Therefore, having low concentrations of ammonia and ammonium in surface water systems is helpful for aquatic life and water treatment for human consumption.

 

John Sawyer is an associate professor of agronomy, with extension and research responsibilities in soil fertility and nutrient management.

Field Testing of N-Hibit™ Seed Treatment in Iowa*

by Greg Tylka and Chris Marett, Department of Plant Pathology

 

N-Hibit is a seed-treatment that contains harpin protein, a compound that can stimulate plant defense responses. N-Hibit is now being sold in the United States for management of the soybean cyst nematode (SCN).  Iowa State University evaluated the effects of N-Hibit seed treatment on soybean yield and SCN population densities in experiments at nine locations throughout Iowa in 2007.

 

Experiments were conducted in Albert City, Mason City and Manchester in northern Iowa, Cambridge, Farnhamville and Urbana in central Iowa, and Council Bluffs, Crawfordsville and Melrose in southern Iowa. The work was supported by the soybean checkoff through funds from the Iowa Soybean Association.

 

Map of NHibit Test Sites

Locations of experiments in 2007 where N-Hibit™ seed treatment was evaluated for effects on soybean yields and SCN population densities in Iowa.

 

At each experiment, an SCN-susceptible and an SCN-resistant variety were grown. Seeds of each of the two varieties were either untreated or treated with N-Hibit at a rate recommended by Plant Health Care Inc., the distributors of the product. Plots were four 17-foot-long rows spaced 30 inches apart and were planted at a rate of 10 seeds per foot. There were four replicate plots per variety-seed treatment combination, and 16 plots total per experiment.

 

All plots were end trimmed to 14 feet during the first three weeks of September. When plants in all plots at an experiment were mature, the center two rows of each four-row plot were harvested with a plot combine, total seed weight per plot and seed moisture were determined, and total plot seed weights subsequently were converted to bushels per acre.

 

At the beginning of the growing season, each plot was sampled for the presence of SCN. Ten 1-inch-diameter, 6- to 8-inch-deep soil cores were collected from the center 14 feet of the center two rows immediately after planting. The soil cores comprising each soil sample were mixed thoroughly, SCN cysts were extracted from a 100-cc subsample (a little less than a half cup), and SCN eggs were extracted from the cysts and counted. SCN egg population densities also were determined for each plot at the end of the growing season in an identical manner.

 

The effect of N-Hibit on soybean yields in the nine experiments varied in 2007. There was no significant difference in yield of the SCN-resistant soybean varieties treated with N-Hibit or left untreated in any of the experiments. Thus, those data are not presented in this report. Overall, yields of the SCN-resistant varieties were significantly greater than those of the susceptible varieties in eight of the nine experiments.

 

With the SCN-susceptible varieties, plots treated with N-Hibit yielded 3 bushels per acre greater than untreated plots at the Urbana experiment, in central Iowa, and 2.1 bushels per acre greater than untreated plots at the experiment in Melrose, in southern Iowa (see table 1). There was no significant difference in yield of untreated and N-Hibit-treated, SCN-susceptible soybean varieties in the other seven experiments in 2007.

 

Table 1. Locations, soybean yields and SCN egg population densities of a SCN-susceptible soybean variety with and without N-Hibit seed treatment in nine experiments in Iowa in 2007.

NHibit Table Iowa Test Results

 

Numbers presented for yield and final SCN egg population density are means of four replicate plots. Numbers followed by different letters within a row (within an experimental location) for yield and final SCN egg population density are significantly different.

 

There was no significant difference in final SCN egg population densities in plots with untreated seed versus seed treated with N-Hibit with SCN-resistant soybean varieties at any of the nine experimental locations in 2007. Similarly, there was no significant difference in final SCN egg population densities between plots established with untreated seed versus seed treated with N-Hibit with SCN-susceptible varieties at eight of the nine locations in 2007. But at Farnhamville, the average end-of-season SCN egg population density was significantly greater in plots treated with N-Hibit than in untreated plots planted with an SCN-susceptible soybean variety.

 

The yield data from individual experimental locations also were combined by district (north: Albert City, Manchester and Mason City experiments, central: Cambridge, Farnhamville and Urbana experiments, and south: Council Bluffs, Crawfordsville and Melrose experiments) for analysis. No significant effects were detected for the SCN-susceptible or the SCN-resistant varieties in the combined data.

 

Table 2. Soybean yields and SCN egg population densities of a SCN-susceptible soybean variety with and without N-Hibit seed treatment from three combined experiments in each of three Iowa districts in 2007.

 District  

Initial SCN Egg Density (eggs/100c)

  Untreated

N-Hibit Treated

North

2,917

52.2

51.8

Central

4,386

52.7

53.3

South

2,017

59.2

60.4

Numbers presented are means of 12 replicate plots.

 

It is not known why yields were significantly greater in plots with N-Hibit than in untreated plots at the experiments in Urbana and Melrose, Iowa, but not at the other seven experimental locations in 2007. Also, it is interesting that there were no statistical differences in final SCN egg population densities at eight of the nine experiments, including the two in which significant differences in yield of SCN-susceptible varieties were detected in 2007. Additional experiments are planned to obtain more information about the effects of N-Hibit on soybean yields and SCN egg population densities in Iowa in 2008.

 

Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes. Chris Marett is an assistant scientist with responsibilities for research on the biology and management of the soybean cyst nematode.

 

* Editor's Note: This article first appeared in the Dec. 10, 2007 issue of the ISU Integrated Crop Management Newsletter. At the time of original publication, much of the SCN data were not yet available, but the article was published to provide growers and agronomists with a preliminary report of the results that were obtained. The above article contains a complete discussion of all facets of the research, including all of the SCN data.

Don’t Use More Pressure than Needed on Wet Soils

Mark Hanna, Department of Agricultural and Biosystems Engineering

 

Many Iowa planter operators are faced with wet soil conditions this spring. Operators will want to wait for suitable conditions to avoid “mudding in” a crop with significant investments in seed, fertilizer, machinery and time.

 

Once in the field, attention should be paid to the amount of weight being transferred from the planter frame through parallel links to the individual row units. Use only enough down pressure on depth-gauge wheels to ensure that they stay in contact with the soil surface. In wet soil conditions, excess load transferred to the depth-gauge wheels beyond the point where they firmly touch the soil simply adds more potential compaction to the seed zone.  Compacted soil in the seed zone can be more difficult for seedling roots to penetrate, particularly if subsequent weather allows soil to become dry and hard. 

 

 

Photo Cutline Depth-gauge wheels adjacent to the seed opener

Depth-gauge wheels adjacent to the seed opener

 

 

Also adjust spring pressure on closing wheels to a relatively light setting, using only enough down pressure on the soil to establish seed-to-soil contact. Too much spring pressure adds excessive down force, compacting soil and building excessive soil strength around the seed. Letting the closing wheels “float” on the soil surface without any spring pressure may be adequate to establish soil contact with the seed.

 

Check behind the planter by digging up a few seeds to evaluate conditions. Using a finger-type or spader wheel might be considered in place of a conventional closing wheel for one or both wheels if they are easily available for use.These types of closing wheels, used by some operators in wetter soil planting conditions, tend to leave soil looser over the seed.  

 

A key point is to recognize existing soil conditions and be willing to make planter adjustments to improve the chances of good early plant growth. In wet soils, inserting the double-disc seed-opener into the ground and establishing seed-to-soil contact typically do not require as much down pressure on depth-gauge wheels and closing wheels, respectively, as is required in drier soils.

 

Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery.

 

Adapting to Alfalfa Winterkill and Winter Injury

Stephen K. Barnhart, professor, Department of Agronomy

 

Significant areas of alfalfa winterkill are now evident in Iowa.  The worst areas are along the Highway 20 corridor in eastern and northeast Iowa, with notable losses to the Minnesota border in Iowa and also in random fields in other parts of the state. Frozen alfalfa crown and upper taproot tissue is not able to recover. Evidence of the injury was delayed because some plants began to green-up and then died. Plants that still exhibit good taproot and crown tissue are likely unaffected.

 

The decision producers must make is whether to keep a less productive field, whether to try to boost the production of forage from that field by supplemental seeding, or to plan on planting a new alfalfa field as well as planting an "emergency" short-term forage crop for immediate future forage needs.  Some of the most common questions arising include:


What fields are still worth keeping? 

The answer to this varies greatly. Research would say that a ‘keeper’ field with no appreciable yield loss would be a first production year field with 12 or more healthy plants per square foot; second and third production year fields, six or more crowns per square foot;  and older fields, four or more healthy plants per square foot. Or, stands of any age with 55 or more harvestable stems per square foot and healthy taproots. Any fields with less than that stand level will likely produce proportionally less yield per acre. Associated forage grasses may compensate some toward higher seasonal yields as alfalfa stands decline. Producers often choose to retain less productive fields out of necessity or convenience.

 

Can I interseed to thicken the stand – with more alfalfa?
Interseeding alfalfa to thicken a uniformly thin alfalfa stand will generally not work. If the stand is one year or less old, plants will generally come up and then be outcompeted by the survivors from last year. Large dead spots should be disked first and then seeded. If the stand is two or more years old, interseeded alfalfa will be adversely affected by autotoxicity.

 

For two or more year old alfalfa stands, autotoxic compounds will likely reduce the stand and/or future yield of the alfalfa and you should wait one year before reseeding.

 

You can interseed grasses (annual ryegrass for one year or orchardgrass or tall fescue for two or more years) or clovers to thicken a stand.

 

What are some options for an ‘emergency forage crop’?
This decision depends on when you need the forage, and what kind of storage is to be used.

 

  1) When tonnage is needed quickly to replace lost first cutting

a) A small grain is the best option to replace the loss of first cutting alfalfa. The crop will be able to be harvested at the middle to end of June. Oats is likely the best choice, spring triticale a second choice and barley a third choice (due to lower yield). Harvest can be as silage or hay.


b)
Planting small grain with peas (60 lbs/acre of 50/50 mix) will increase crude protein and palatability of the mix but not yield. Harvest is most often made as silage.


c)
Spring planting winter wheat, winter rye or winter triticale is not a good idea due to low yield.

  2) When high season-long yield is needed

a) For silage, corn is the best high-tonnage option.

b) For forage silage the  best choices are seeding sorghum x sudangrass hybrids, sudangrass, Japanese millet, hybrid pearl millet;  alfalfa seeded alone (12 to 15 lbs/acre) into a field where alfalfa autotoxicity is not a concern (see above), or plant Italian or annual ryegrass at 2 to 4 lbs/acre with alfalfa (12 lbs/acre)


c) For hay,
best choices are small grains such as oats, spring triticale a second choice and barley a third choice (due to lower yield).  Alfalfa seeded alone (12 to 15 lbs/acre) into a field where alfalfa autotoxicity is not a concern (see above), or plant Italian or annual ryegrass at 2 to 4 lbs/acre with alfalfa (12 lbs/acre). Sudangrass will produce the most tonnage for a multi-cut annual for those who want grass hay ( two to three cuttings harvested at 36 to 40 inches in height). Japanese millet is also a multi-cut summer annual option. Some producers have difficulty drying sudangrass and Japanese millet thoroughly enough for safe dry hay storage. Foxtail millet is an annual one-cut emergency crop for dry hay. Teff, a relatively new annual grass to the U.S.,  is a new possible alternative. However, teff grass has not been widely tested in the Midwest and seed supplies are virtually non-existent.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

When is it Too Late Plant Forages?

Stephen K. Barnhart, Department of Agronomy

 

Spring hay and pasture seedings are normally done from late February through late April in Iowa. The extended period of wet weather in 2008 has many producers still waiting to get their forages planted.

 

Can they still successfully plant forage crops? 

The short answer is – yes, into the first 10 days to 2 weeks into May. The ‘end of the spring forage planting season’ is limited by seedling development and growth into the summer months. Most forage seedlings  are emerging and growing root systems into the top 1 to 3 inches of the seedbed during the 3 to 4 weeks following germination. 

 

The increasingly dry and hot soil surfaces in late May and June increase the risk that the small forage seedlings do not establish. So, the risk depends on rainfall and soil temperatures from here on. If conditions turn normal or hotter and dryer than normal, the risk of late planted forage seeding failures increases.  If late May and early June conditions remain cooler and wetter than normal, then later-than-desired spring  forage seedings may survive very well.

 

If you do plant later than desired, be aware that you are still as vulnerable or more vulnerable to erosion and weed competition.  Keep cereal companion crop planting rates to half of a full seeding rate or less, and mow or clip new seedings several times during the early seedling development months to allow light to reach small developing legume and grass seedlings. Also scout for and manage potato leafhoppers in new alfalfa seedings.

 

What about skipping spring planting and planting the new hay and pasture fields in late-summer?

The success of ‘late summer plated forages’ is set by both the ‘planting window’ that provides for a 6 to 8 week establishment time requirement for seedlings before the first killing freeze of the fall, and the necessity of adequate existing soil moisture and likelihood of average or better fall rainfall. 

 

For alfalfa and other forage legumes, the seed should be planted by Aug. 10 for the northern third of Iowa, by Aug 20 for the middle third of the state and by late August or the first week of September for the southern third of the state. Cool-season forage grasses can be planted a few weeks later in each of these zones.

 

The risk of stand failure is high if seed is planted in dry soil, and rainfall patterns for the remainder of the fall season are erratic.

 

Can purchased seed be carried over until fall or next spring ?

Seed is perishable.Germination declines over storage time, and declines faster if seed storage conditions are warm and in high humidity. Certainly try to store carry-over seed in a cool, dry place. Even better, try to arrange for storage in a more desirable seed storage facility. If you do have concerns about the viability of carry-over forage seed, have a germination test done before planting, and adjust sowing rates to compensate for any germination percentage losses.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Managing 2,4-D for No-Till Burndown Treatments

By Bob Hartzler, Department of Agronomy

2,4-D is commonly added to glyphosate for burndown of existing vegetation in no-till fields. The advantages of including 2,4-D include:

  • better activity on dandelion, horseweed and many winter annual broadleaves than glyphosate alone,
  • more consistent than glyphosate during cool conditions, and
  • reduces selection pressure for glyphosate resistant horseweed. 

However, as weather delays compress the time available to complete planting and associated field operations, the wisdom of including 2,4-D in burndown treatments may be questioned.

The risk associated with 2,4-D use is injury to emerging corn or soybean plants. For soybeans, a 7-day interval between application of 0.5 lb 2,4-D/A (2/3 pt of a 6 lb LVE formulation) and planting is required. For corn, most labels recommend applying up to 1 lb ae 2,4-D/A (1.3 pt LVE 6) 7 to 14 days prior to planting or 3 to 5 days after planting. Following these label restrictions minimizes, but does not eliminate, the threat of crop injury.The risk of injury to both crops is determined by how much herbicide reaches the depth of the germinating seed and developing seedling. This is determined by several factors, including

  • depth of planting, 
  • 2,4-D rate and formulation,
  • soil type, and
  • rainfall.

Planting the seed at the proper depth reduces the risk of injury by providing a more favorable environment for germination and minimizing the amount of herbicide reaching the seed.

Shallow planting or failing to close the seed furrow increases the risk of injury. Ester formulations are recommended for burndown applications because they are less mobile in the soil than amines, thus they are less likely to reach the seed. Adsorption of 2,4-D to soil colloids minimizes movement through the profile, thus injury is most likely to occur on coarse textured soils or soils with little organic matter.

Finally, rainfall is required to move the herbicide through the profile to the depth of the emerging seedlings. Since 2,4-D breaks down relatively quickly in the soil (approx. 10 day half-life), it is the rainfall that occurs within the first two weeks after application that determines the threat of injury. After this period the 2,4-D should have degraded to levels unlikely to injure the crop. Corn is most sensitive to 2,4-D when the herbicide is present in the water that is initially imbibed by the seed, this is why 2,4-D can be applied shortly after planting.

2,4-D is a valuable tool in no-till systems, but it must be used properly to manage the risk of crop injury. In situations where the planting interval restrictions cannot be followed, alternative products are available. Alternatives may not be as broad-spectrum as 2,4-D, thus their selection must be based on the specific weeds present in individual fields.

Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities.



This article was published originally on 5/5/2008 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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