Tolerance of Various Crops and Plants to Salinity

By Jim Bauder
MSU Extension Soil and Water Quality Specialist
 

Occasionally I get a phone call from someone wanting to know about tolerance of various crops and plants to salinity. I generally start by explaining salinity. There are two sources of salts that appear in the soil: either from the soil itself or from irrigation or drainage water. In either case, the presence of saline conditions in the soil indicates inadequate drainage, either due to slow percolation rates, high water table, not enough water to cause leaching, or upward water movement.   There are
three essential requirements for mediating a salinity problem:

1) improve the drainage to allow the removal of the excess salts;
2) remove or reduce the source of the salinity by either shutting off the water or reducing the amount of water being applied,
3) add sufficient good quality water to leach the existing salts.

So, what crops can you grow in salt-affected soil? The logical answer is salt-tolerant crops. Among crops grown in the Montana, barley has the highest degree of salt tolerance, followed closely by sugar beets.   The degree of salt tolerance is expressed by milli-mhos per centimeter (mmhos/cm), which relates to the conductivity of electricity when two electrical prongs are stuck in the soil. The following list of crops ranges from most tolerant to least tolerant, with respect to salinity.
 
 

You might consult the Western Fertilizer Handbook which contains a complete listing of salt tolerant crops. This is an excellent reference book for farmers.  Another question that comes up is something like this: "I have a saline seep which I have been trying to reclaim. What forage crops can I grow in the salt-affected area?" The answer depends on the soil conditions.

However, the list of tolerant forages is pretty well defined. It includes the following, from most tolerant to least tolerant:

Keep in mind that seedlings are generally much more sensitive to salinity than established plants.    You can assume that the yield of each of these forages and the previous crops will be reduced by 10-15 percent if the conductivity is increased 25 percent, 25-35 percent if the conductivity is increased 50 percent and 50 percent or more if the conductivity is doubled. If you suspect you have a salinity problem, collect a soil sample, send it to a lab and ask for the EC (electrical conductivity or conductance), the pH (an index of salinity), and the SAR - the sodium adsorption ratio. With that information and the list provided here, you should be able to decide what is the best cropping strategy for your situation.

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Key points to remember in controlling Kochia.

Kochia has been a real problem for small grain producers the last few years as the drought has intensified. Poor control of kochia from in-crop treatments or no in-crop treatment has resulted in increased kochia pressure during the cropping year. The end result is a tremendous problem in fallow fields the following year. Doug Ryerson, Monsanto representative at the Crop Protection and Improvement Clinic, offered these key points to remember: 1) Good weed control in the crop is essential! 2) Manage weeds post-harvest if a problem exists after combining. This is key and help reduce the seed bank in the soil. 3) Spray before weeds get large. 4) Spray during periods of least stress; early in the day or after a rain event, for example. (Some of us wonder what those rain events are really like!) 5) Good coverage is essential; slow down/raise the water volumes.

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Clearfield Wheat: New Weed Management Tool for Montana Wheat Growers 
By A.J. Bussan, Crop Weed Specialist, Montana State University

Montana wheat growers are facing greater weed populations both because of increasing weed resistance to herbicides and because some weed seeds never germinated due to drought, leaving more seeds to sprout when conditions permit. A new wheat variety may give growers fresh options. 

First the background: For years Montana wheat growers have managed downy brome, feral rye and jointed goatgrass with crop rotation and fallow. 

It has been a necessity, because no selective herbicides have been available to manage these in winter wheat.

Unfortunately, these weeds persist in crop production systems even in the most optimally managed fields. For example the drought of the past three to four years in central Montana has built up a downy brome seed reservoir. The drought prevented downy brome from germinating in fallow fields. As a result, the downy brome seed has persisted into the following winter wheat crops where it germinated and resulted in heavily infested crops. Many winter wheat fields were destroyed to manage downy brome over recent years.

Maverick and Olympus are new selective herbicides available (Olympus is not labeled yet) for managing downy brome in winter wheat. 

Neither of these will manage feral rye or jointed goatgrass and only have limited activity on spring annual grass weeds such as wild oat or Persian darnel. Maverick and Olympus are both injurious to barley and have the potential to carryover for at least 12 months (Olympus) to 24 months (Maverick).

The new tool: Clearfield wheat is a new herbicide resistant wheat developed by BASF and both university and private breeding programs in the Northern Great Plains. Clearfield wheat is resistant to imadazolinone herbicides such as Pursuit and Raptor. Beyond will be labeled for use in Clearfield wheat potentially as soon as spring of 2002. Beyond has good to excellent activity on downy brome, jointed goatgrass, feral rye, wild oat, green foxtail and Persian darnel. In addition, it is good to excellent on Russian thistle, annual mustard and other broadleaf weeds.

Availability of winter and spring wheat varieties with resistance to Beyond herbicide is limited at the moment. Montana adapted winter wheat varieties with resistance to Beyond are still 12 to 24 months from being available.

Montana adapted spring wheat varieties with resistance to Beyond will not be available for another 3 to 4 years. Current resistant spring wheat varieties have been evaluated and found not to have acceptable levels of tolerance to Beyond herbicide. MSU and private companies are working to develop spring wheat with double the current level of resistance.

Beyond herbicide has the same mode of action as other herbicides that are already commercially available. Beyond targets the same enzyme as all sulfonylurea herbicides (Glean, Finesse, Ally, Amber, Peak, Harmony, Harmony Extra, Express, Pursuit, Raptor (same active ingredient as Beyond), Everest, Maverick, Olympus and Assert). As such herbicide resistance is a legitimate concern. Beyond will not manage Glean-resistant kochia (prevalent throughout Montana) or Assert-resistant wild oat, which occurs in isolated regions of Montana.

Continuous use of Beyond or rotation of it with other herbicides with the same site of action (Maverick or Olympus) could lead to herbicide resistance in other species. Downy brome resistant to herbicides with this site of action are a concern in grass seed production regions of Oregon. 

Studies have shown herbicide resistant hybrids of jointed goatgrass and winter wheat.

Resistance to Beyond herbicide was still present in back crosses of the hybrids to jointed goatgrass, although the backcrosses only occurred at low frequency.

The final drawback of Clearfield wheat with resistance to Beyond is the price. The price of Beyond herbicide will likely be similar to that of other post emergence wild oat herbicides ($10 to $15 per acre). This price allows for rescue management and will be an extremely valuable weed management practice on a limited basis. However, the cost of applying Beyond during every winter wheat or spring wheat year of the rotation will quickly become cost prohibitive. For the long term economic success of Montana crop production systems, growers must implement crop rotations (i.e. grow winter wheat one in four years), effectively manage weeds in fallow, delay seeding of winter crops to allow for management of early establishing downy brome and jointed goatgrass and implement other cultural management practices.

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Banvel (Dicamba) Injury to Winter Wheat 
Meghan Trainor, 994-1871 Weed Extension Associate

As field crops grow and mature, their tolerance to herbicide changes. For this reason, it is critical that postemergence herbicides be applied at the proper time to achieve maximum weed control and minimum crop injury. 

Generally, annual and biennial weeds are more susceptible to postemergence herbicides when they are in the seedling stage. As weeds mature they become more difficult to control. This places the grower in the predicament of when to apply the herbicide in order to achieve the least crop injury as well as satisfactory weed control. Different field crops have different growth stages. Therefore, field crops differ in the periods when postemergence herbicides can safely be applied. Prior to application of a specific herbicide each crop must be considered separately to determine the correct crop growth stage. 

Banvel (common name dicamba) is one among many herbicides recommended for postemergence weed control in winter wheat. Banvel, a benzoic acid, belongs to the chemical group of growth regulators. Growth regulator herbicides can act at multiple sites in a plant to disrupt hormone balance and protein synthesis, thereby causing a variety of plant growth abnormalities. Growth regulator herbicides control broadleaf weeds and can injure winter wheat. Herbicides in this group can move in both the xylem and the phloem to areas of new plant growth. As a result, many herbicides in this group are effective on perennial and annual broadleaf weeds. Herbicide uptake is primarily through the foliage but root uptake may also occur. 

The best time to apply Banvel is in the early spring (February through April) after winter wheat has begun to tiller, but before the joint stage. The plant develops additional stems during tillering, but the stems do not elongate. 

From the seedling through the tillering stages all leaves appear to originate from the base of the plant. During jointing, stems lengthen as recognized by leaves being attached at different joints (nodes) on the stem. Although some herbicide labels allow for application up to the boot stage, delaying application of Banvel beyond the joint stage will increase winter wheat injury and decrease weed control.  Winter wheat can be treated with Banvel in the spring after winter dormancy has been broken and before wheat begins to joint. If Banvel is applied to wheat in the joint stage, significant crop injury may occur. Furthermore, injury in the joint stage will affect head development. 

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Yellow Wheat, Why ?
Jack Riesselman, Plant Diseases, 

My wheat is yellow!! What is wrong with it? This has been the most common statement and question from producers and field scouts this past week. 

There is no one specific cause statewide but rather a variety of different factors that can explain this yellow condition.

Wheat streak mosaic virus has been verified from several different locations. As expected, when the temperatures increased the symptoms became more evident. Symptoms include a general yellowing, often along field margins or near areas where early volunteer developed last fall. The yellowing is accompanied by alternating silver green streaks giving the leaf a characteristic mosaic pattern. Generally the earlier seeded fields are showing more wheat streak but with the mild fall in l999, we are even observing infections is late seeded winter wheat. Some producers are confusing the symptoms of Russian wheat aphid with those of wheat streak. Be sure you correctly identify what pests are in your field prior to initiating any control!

Far more prevalent than wheat streak is a condition where the lower leaves have taken on a bright, almost mustard yellow color. This is a semi-natural senescence that is associated with physiological stress and early nitrogen unavailability. Dr. Jeff Jacobsen, MSU soil scientist suggests that with the lack of early spring moisture, in most areas, the nitrogen that is present was unavailable to the plants. He also mentioned that when soil moisture levels are low the mineralization process can be affected. The good news, the new growth in most of these fields is dark green and with moisture, the crop should continue to progress normally.  

Less pronounce yellowing has also be observed in several fields of wheat. The slightly off green-yellow color can be caused by lack of, or the unavailability of sulfur. This nutrient is generally not considered to be lacking in Montana soils but in some years when dry and mild conditions exist sulfur deficiency symptoms in wheat, and other crops, can occur.

In the few regions of the state that have received showers we are seeing some foliar leaf disease developing. Most common has been tan spot which can also result in some leaf yellowing. Thus far, the severity has been
light. 

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How to Decide Whether It's Economical to Treat Cutworms and Aphids

After producers scout their field for cutworms or Russian wheat aphids, there are several numbers that can help them determine whether it is more profitable to treat field with insecticide or to continue monitoring the infestation.

For cutworms, determining whether treatment is economical involves simply getting a good sample from your field. The threshold based on entire-season adult sampling in moth traps is either 800 army cutworm moths, or 200 pale Western cutworm moths. In spring, finding 4-5 army cutworm larvae per square foot or 2 pale western cutworm larvae per square foot means it is time to control the larvae..

For Russian wheat aphid treatment levels, the number is derived by a formula. Scout the field in question, determining the percent of wheat tillers that have Russian wheat aphids on them. The formula to determine whether or not it is economical to treat Russian wheat aphids is then: Cost of insecticide application X 200 Expected yield per acre X the bushel per acre selling price

If you have a higher percent infestation than the number derived above, you will make more money treating the aphids than not treating them. The benefit of this calculation is that it takes price of the wheat and cost of insecticide application into account, said Greg Johnson, head of Montana State University's Entomology Department.

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MWBC Annual Report from the Research Centers Now Available on the Web

2000 Annual Report to the Montana Wheat and Barley Committee for all studies funded under a joint project involving the Research Centers at Conrad, Havre, Huntley, Kalispell, Moccasin and Sidney is now available on the web at: http://wbc.agr.state.mt.us/ or direct at: http://www.sarc.montana.edu/mwbc/2000/

This 318-page report includes 29 separate project headings involving numerous individual field experiments conducted across Montana, mostly at off-station locations on cooperating producer’s farms.  Included are all off-station variety trials conducted by the Research Centers statewide in 2000.  Multi-year summaries for individual locations are further available in many cases.

In addition, summaries of 2000 data for uniform statewide dryland and irrigated Winter Wheat, Spring Wheat, Barley and Oat variety trials conducted on-station at each of these six Research Centers plus Post Farm at Bozeman (and WRC-Williston for winter wheat) are included courtesy of plant breeders Phil Bruckner, Luther Talbert, Tom Blake and their research associates Jim Berg, Susan Lanning, and Pat Hensleigh.  (Note: Moccasin on-station winter wheat, spring wheat and barley trials were lost to hail in 2000).

You can use the Table of Contents to directly access desired individual reports by title or you can use the “search” feature provided to “zero in” on any and all reports involving a desired location, researcher, crop, variety, whatever.  Complete help documentation for using this feature is available under “Search Tips.”

Most documents listed in this overall report were created using Adobe Acrobat Version 4 and require the latest Acrobat Reader for proper viewing.  Older versions of the reader, including 3.x versions may not display all text and features.  A link to Adobe is provided to download the latest version of the “reader only”, free of charge.  You will find it under “Store Products” under “Adobe Store” at the Adobe web site.  Or, you may also accomplish the same thing by clicking on the Adobe icon under “Downloads” at MWBC’s web site. 

The reports can be readily viewed on-screen, printed, or e-mailed to your clientele.  The recipient of an e-mailed report must of course also have installed an appropriate version of the reader to view the file.

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An array of outstanding new oats and barleys for the West is coming from an Agricultural Research Service plant-breeding program based at Aberdeen, Idaho. The new varieties are intended for planting primarily in Idaho, Montana, Washington, Oregon, Wyoming or Colorado. The program, regarded as one of the best of its kind in the nation, is directed by scientists at the ARS Small Grains and Potato Germplasm Research Unit at Aberdeen. 

One new oat variety, Powell, produced greater yields than some leading commercial varieties when tested in Idaho and Wyoming. ARS scientists collaborated with Lyle R. Bjornestad of the University of Wyoming and with other colleagues in that state and in Idaho to develop Powell.

Other new oats are the hull-less varieties Lamont and Provena. There's interest in hull-less oats as high- quality feed for horses and dairy cattle. However, in the past, few if any hull-less oats have been well- adapted to the West. Now, Lamont and Provena could help change that.

Provena boasts good yields and impressive resistance to lodging. Lamont also resists lodging and is adaptable to a wide range of growing conditions.

Outstanding new barleys from the Aberdeen breeders include Garnet, for springtime planting. Garnet is proving ideal for malting and brewing. It is also suitable as feed for beef and dairy cattle. The Aberdeen breeders worked with ARS colleagues in Madison, Wis., and university co-researchers, to develop Garnet.

Spring barleys like Garnet need moisture from rain or irrigation throughout the growing season. For nonirrigated farms in the West that don't get enough rain to consistently produce high-value malting barley, the Aberdeen team is working on new, winter malting barleys. One or two winter barleys may be ready for release to breeders and seed producers by 2002 or 2003.

An article in the August issue of the ARS monthly journal, Agricultural Research, tells more. View it on the World Wide Web at: http://www.ars.usda.gov/is/AR/archive/aug01/oats0801.htm 

ARS is the U.S. Department of Agriculture's chief scientific research agency. The ARS Small Grains and Potato Germplasm Research Unit is on the web at: http://www.ars-grin.gov/ars/PacWest/Aberdeen

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When is Organic Matter Built Up or Used Up?
By Jim Bauder
MSU Extension Soil and Water Quality Specialist

This article continues information on organic matter begun in my last column. The last column talked about the benefits of soil organic matter. In this one I will give information about the development of soil organic matter.

Plant and animal residues, sewage sludge, wastes and manures in various stages of decomposition are the sources of organic matter in soil. The degree of decomposition depends partially on micro and macro organisms, burrowing animals and insects, earthworms, centipedes and ants. These are important in decomposition and translocation of plant residues in soil.

The amount of organic matter in soil and the rate of its accumulation or decomposition is a result of the balance of organic matter production, climate, environment and land use practices.

The threshold soil temperature for organic matter accumulation is 77 degrees Fahrenheit (25 degrees Centigrade). Below this temperature, organic matter accumulates, and above it organic matter decomposes. Organic matter and nitrogen in soils increase about two-to-three times for each 10-degree C decrease in mean annual temperature.

Wet soils tend to accumulate organic matter more than comparable dry soils; organic matter generally accumulates under cold, anaerobic conditions (oxygen devoid), such as wetlands, bogs, swamps and frequently wet soils.

Dry/desert soils generally have low organic matter content, because decomposition is faster than accumulation. Organic matter content of two percent or less is common (based on dry soil mass). Volcanic soils usually have high organic matter content, as much as 10-12 percent. Organic matter levels tend to be higher under grassland or prairie than under forests, because grassland roots contribute more to organic matter than leaves and stems of woody species.

Surface soil organic content is almost always greater than that of associated subsoils. The bulk density of surface soils with 1-2 percent organic matter are usually 1.3-1.5 g/cc.

The following list shows examples of the affect of organic matter on bulk density (from "Soils in Our Environment," Miller and Donahue, 1995)
        decomposed peat (low particle density)  0.66 g/cc
        clay soil 3 years in pasture                      1.13
        clay soil 3 years in barley crop                1.3
        sandy loam under bush 15-20 years        1.15
        sandy loam 5 years conventional corn     1.51

Soils with more than 30 percent organic material are considered 'organic' soils and are generally referred to as peat or muck. These soils have bulk densities as low as 0.4 to 0.6 g/cc.

Generally, as one moves from a warmer to a cooler area, whether by a change in latitude, elevation, slope or direction of the slope, the organic matter and associated nitrogen content of comparable soils tend to increase.

The greater the organic matter in a soil and the coarser it is, the faster water will enter. Organic surface mulches are especially helpful in keeping infiltration high, because they protect soil aggregates from breakdown by reducing the impact of raindrops and by continuing to supply cementing agents for aggregates as the mulch decomposes.

One percent soil organic matter is considered "low." Soil organic carbon content in mineral soils usually ranges from 0 to 4 percent by weight and may be as high as 20-30 percent.

Organic matter usually is lowest in locations with high temperatures and low rainfall. Organic carbon increases with precipitation and clay content, and decreases with temperature. Carbon losses due to cultivation increase with precipitation.

Generally, finer-textured soils have higher organic matter content than sandy soils, because of greater nutrient and water-holding capacities and plant production and slower decomposition. Relative organic carbon losses are lowest in clay soils.

Generally, cropped soil has much less nitrogen and organic matter than comparable virgin areas, and a tenth to two-thirds of the above ground part of a crop is incorporated into the soil.

If you are a cereal grain producer, you've probably been told that you need to 'add a little extra nitrogen' when you have a lot of straw being worked into the soil during tillage. And, if you are a gardener, you may have even noticed that there are times when composting seems to be counter-productive.

In both cases, there is a reason, and, yes, it is a good idea to add a little extra nitrogen when you have a lot of straw and stubble to incorporate. The reason relates to the carbon/nitrogen ratio of the plant material you incorporate.

Forty-five to 58 percent of stable soil organic matter is carbon, while nitrogen makes up 5-6 percent. A mineral soil with 4 percent organic matter contains as much as 80,000 pounds per acre of organic matter in the 0-6-inch depth; 31,800 - 41,000 pounds of carbon, and 4,200 pounds of nitrogen per acre. Needless to say, carbon is a significant component of organic matter.

Organic matter has a cation exchange capacity 2-30 times that of clay minerals and can account for 20-90 percent of the soil cation exchange capacity.

About 75 percent of plant material is water. Ninety percent of the remaining dry material is made up of carbon, oxygen, hydrogen and nitrogen. Sulfur, phosphorus, potassium and calcium are the other important components.

The breakdown that organic matter undergoes leaves a dark-colored organic residue that resists decomposition and is responsible for much of the property of organic matter called 'humus.' In fact, some of the very stable materials in the organic matter complex can remain in the soil for hundreds or thousands of years.

The carbon/nitrogen ratio of organic matter is important in soil quality. The ratio of organic matter in  cultivated surface soil ranges from 8/1 to 15/1, with the median about 12/1 (58 percent/5 percent). The carbon/nitrogen ratio is relatively uniform among different soils within a climatic region.

Heavily leached soils are likely to have much higher C/N ratios, i.e., 30/1 or more. Organic matter with a high carbon to nitrogen ratio, i.e., C/N ratio 15, frequently have unstable soil organic matter and intense competition among micro organisms for available soil nitrogen.

Residues which contain the lowest amount of carbon in relation to nitrogen, (C/N ratio <12), come from green manure/cover crops like legumes and mustards. These decompose rapidly and provide nutrients in excess of microbial needs. Residue from grain, grass and cotton are low in nitrogen but high in carbon and thus take longer to decompose.

        Typical Carbon and Nitrogen Contents and C/N Ratios
Material                              % C     % N     C/N
Spruce sawdust                     50      0.05    600/1
Wheat straw                          38      0.5        80/1
Corn stover                           40      0.7        57/1
Rye cover crop, anthesis        40      1.1        37/1
Bluegrass - lawn                    40      1.3        31/1
Rye cover crop, vegetative     40      1.5        26/1
Mature alfalfa hay                  40      1.8        25/1
Rotted barnyard manure        41      2.1        20/1
Young alfalfa hay                   40      3.0        13/1
Hairy vetch cover crop          40      3.5        11/1
Digested sludge                     31      4.5          7/1

Soil organic matter
        Grassland                     56       4.9      11/1
        Forest                          52       2.3       23/1
        Subsoil                         46       5.1        9/1
        Forest soils                  3.6     0.18      20/1
        Prairie/grass                 2.8     0.22      13/1
 

Most soil microbes obtain the energy necessary to grow from carbon in the soil organic matter. Most organic matter undergoes essentially a "burning" or oxidation process. Since nitrogen is an essential for cellular components, micro organisms must obtain nitrogen from organic matter, other microbes or from the air. When organic materials with high carbon concentrations relative to nitrogen concentrations are added to the soil, soil microbes use most of the available nitrogen in the soil, thus creating deficiency conditions for higher plants. Organic residues with C/N ratios greater than 25/1 often will result in nitrogen deficiencies. This is called nitrate depression, sometimes referred to as the 'priming effect,' which will persist until activity of the soil micro organisms decreases due to a lack of carbon.

Generally, nitrogen will not be released from the soil organic matter complex through mineralization until the C/N ratio has dropped below 20/1. Hence, it is often necessary to add supplemental nitrogen fertilizer when carbon-rich organic materials are added to the soil.
 

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Organic Matter: The Rest of the Story
By Jim Bauder
MSU Extension Soil and Water Quality Specialist

On your land, have you noticed pockets of erosion, drainage problems or soils that crust easily or are highly compacted? Or perhaps you've noticed droughty areas, slow water absorption in the soil, or recurrent deficiencies of micro nutrients, nitrogen or sulfur.  These are signs pointing to a possible lack of organic matter.

In balanced soil systems, the level of organic matter remains relatively stable over time, being controlled by climate and affected by vegetation, disturbance and vegetation patterns. But this balance can be upset by such disturbances as tillage, burning, residue additions, flooding, erosion, drainage or deforestation.

So, why should you be concerned about your soil's organic matter? Well, a key reason is to build soil humus levels to improve soil conditions. Organic matter can reduce the effects of clay and poor soil structure. Organic materials such as crop residue or other waste can also provide a protective mulch on the soil surface.

Organic matter levels can be affected by the type and frequency of tillage practices, the crops grown, rotations, and the use of fertilizers, animal manures and soil amendments.

Rotations: Research shows that a rotation of corn, oats and clovers resulted in a higher soil organic matter level than continuous corn. The addition of animal manure and phosphorus increased organic matter levels. A rotation of continuous cereal grains resulted in a decrease in soil organic matter levels. Soils kept highly productive by supplemental applications of fertilizers, lime and manure and by high-yielding crop varieties are likely to have more organic matter than comparable, less productive soils.

The following information illustrates the amount of fresh organic residue left following certain crops. Each harvested crop leaves different amounts of residues.
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Estimated addition of organic matter to soils by crops grown and residues left on the field.

Crop            Root portion    Plant Tops      Total           Yield
corn,                 2200            4100           6300            grain harvested (100 bu/a)
soybeans          1000            2200            3200            grain harvested (32 bu/a)
wheat               1700            3100            4800            grain harvested (45 bu/a)
field beans          500            1400            1900            seed harvested (1500 lb/a)
 alfalfa              3400              800            4200            hay removed (3 t/a)
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The carbon/nitrogen ratio can have a significant effect on the rate of decomposition; organic residue with a low C/N ratio tends to decompose more rapidly than material with a high C/N ratio. In one study approximately 90 percent of a hairy vetch residue with a C/N ratio of 10/1 decomposed over a 4 month period, while only 60 percent of a cereal rye residue with a C/N ratio of 38/1 decomposed during the same period.

Tillage: Some cropping systems tend to cause greater soil organic matter changes than others. Tillage affects organic matter concentrations. The greater the amount of tillage, the less the amount of humus that accumulates. Uncultivated soils are higher in soil organic matter than they are after cultivation. Tillage reduces organic matter levels by accelerating the oxidation process. This happens when the organic matter is broken into finer pieces and mixed with air in moist soil. Some studies have reported
decomposition rates of as much as 50 percent per week for fresh plant material; the typical rate for humus is approximately 3 percent per year.

Cultivation of grassland soils leads to depletion of soil organic matter. Soil organic carbon losses of as much as 50 percent have been documented in the U.S. Central Plains grasslands. The amount of the losses depended on the management regime and regional location.

Management practices that decrease tillage and residue incorporation can reduce soil organic matter losses and increase soil organic carbon to a limited extent.

Organic matter content of the soil is usually estimated from other measurements. The usual procedure is to measure organic carbon content of the soil and then adjust this figure by multiplying by 1.72 to give an approximate amount of organic matter present. The organic nitrogen can then be estimated by dividing the organic carbon content by 12, assuming the typical carbon/nitrogen ratio of 12/1.

More information on soil organic matter is included in the Certified Crop Advisors Competency Training Manual in Soil and Water Management.

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Adding Manure: What are the benefits?

Organic matter can play a valuable role in your farm management program. The recent series of Agronomy Notes dealing with organic matter pointed out some of the benefits of a good organic matter management program. One issue that doesn't get enough attention is the nutrient value or potential of organic matter. Occasionally a producer will ask me about the amount of nitrogen in a ton of composted or stockpiled cattle manure.

The following information came from the Western Fertilizer Handbook.

_____________________________________________________________________________
Composition of Manures and Waste Materials

* Adapted from L. S. Murphy in Fertilizer Solutions magazine, March-April
1972. See Table B-16 in Appendix B for a more extensive list.
 

In some parts of Montana, particularly east of the Continental Divide, phosphorus deficiency in soils seems to be a recurring topic of discussion. Many research projects, including my own, have documented the consistent response of crops to phosphorus, even when soil test show that phosphorus levels are relatively high. Well, organic matter can help. Humus adsorbs phosphate ions. This is good. Consequently, the effect of soil organic matter on providing available phosphorus is significant. When the carbon:phosphorus ratio is wide, available phosphorus is immobilized. When the ratio is narrow, available inorganic phosphorus is increased. Phosphorus adsorbed to organic matter is more available to growing plants than phosphorus precipitated as insoluble compounds such as apatite. Thus, soils high in humus usually contain greater quantities of available phosphorus than soils low in humus.

Stubble residues from grain, grasses or forages are generally low in nitrogen but high in carbon and thus take longer to decompose than do green manures. Adding nitrogen fertilizer - or livestock manures - to these residues speeds up decomposition and helps satisfy the microbial demand for the nutrients.

It takes a fairly good "dose" of animal waste to supply the nitrogen needs of a grain crop which is going to be harvested. We are talking tons per acre. However, for a grass or forage crop that does not fix its own nitrogen or enhance the performance of a soil, the addition of animal wastes has much to offer.

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Calculating the Amount of Seed to Plant

By Jim Bauder
MSU Extension Soil and Water Quality Specialist
 

For some answers,  turned to a web site developed by the Alberta, Canada office of Agriculture, Food and Rural Development. (http://www.agric.gov.ab.ca/crops/seed01.html)

Seeding rates and plant populations should be customized to each farm, field and location, according to the site's authors. In addition, crops should be seeded with the expected plant population in mind, which means the 1,000-kernel weight must be known.

The 1,000-kernel weight is the weight in grams of 1,000 seeds of a grain sample. It varies from one variety to another and from one crop to another. In fact, the 1,000-kernel rate of a single variety will vary from year to year and from field to field. Using the 1,000-kernel weight allows a producer to account for these variations when determining seeding rate and calibrating seed drills. It might even save you money, especially with large-seeded crops.

Seed quality is important when using the 1,000-kernel weight. Plump, large seed produces the most vigorous plants. Poor seed produces weak plants. You should use seed that has had foreign material and shrunken or misshapen kernels removed. To calculate seeding rates and calibrate seed drills, germination tests should be done on all seed lots. A seeding mortality
estimate is also needed. A common value for seedling mortality -- seeds that germinate but don't develop -- is 3 percent.

Seeding the same amount of seed each year won't mean you always get the same plant population. Barley seed, for instance, can vary 25 percent in size and weight, which can dramatically affect the final plant population. Differently shaped seeds flow at different rates in the drill. Because of this, you should use the 1,000-kernel weight of your own seed when calculating seed rates and calibrating seed drills.

Seeding rate:

Seeding rate is an important factor when considering all the decisions that need to be made at planting time. A high seeding rate, for instance, can result in: higher crop yields, better weed competition, earlier maturity, fewer tillers, smaller seed size and shorter plant height.

To calculate the seeding rate in pounds per acre, you need the following information:
        · Desired plant density in plants per square foot
        · Germination rate (%)
        · Emergence mortality (%)
        · Row spacing in inches
        · 1000-kernel weight in grams

It's a good idea to have a value for the 1000-kernel weight. Otherwise, you'll need to count out 1,000 seeds and weigh them. The Postal Service has good scales. Remember that 1 ounce equals 28.3 grams. So, if you weigh 1,000 kernels in ounces, multiply by 28.3 to get grams of seed per 1000 kernels.

The germination rate is specified on the seed tag when you purchase your seed. You will need to correct for emergence mortality, which should not be more than a few percent.

With the above values, you can use the seeding rate calculator on the web site to get the desired seeding rate. I used the calculator to determine these rates for winter wheat:

 For now, if you are looking for some suggested seeding rates, here is a summary of the information contained in this web page:

Calibrating seeding equipment:

The following procedure involves pre-weighing the amount of seed needed per 100 feet of row. You will need a clear plastic measuring cup or tube (any narrow container will do - even an empty pop bottle with the top cut off). Calculate the weight of seed needed per 100 feet of row. Weigh the required amount of seed and pour it into your calibration tube. Mark the tube for
future reference in the field.

Hang a bag or collection container on one run of the seed drill and drive 100 feet. Pour the seed from the collection bag into the calibration tube to see if the correct amount is coming through. Adjust the drill setting and repeat the procedure if necessary. Catching the seed from more than one drill run will increase overall accuracy.

And, one more simple conversion: Collect the seed that would be planted in 100 feet of row by placing a bag over one of the openers.

Weigh the seed.

The seeding rate can then be calculated as follows:
        Seeding rate = grams of seed/100 feet of row x 12/row spacing

For example, if the grams of seed per 100 feet of row are 39 and the row spacing is 7 inches, then the seeding rate is equal to:
        39 grams x 12/7 = 66.8 lbs/acre
 

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 Preplant Weed Control - The First Key to Successful Management
By Alvin J. Bussan
MSU Extension Cropland Weed Specialist

Grass in yards, along roadsides or in pastures may or may not be greening up with the warm temperatures South Central Montana has received over the last few weeks. However, one thing is for sure: weed seed buried in the soil will soon germinate and emerge and winter annuals will break dormancy. In fact, weeds like wild oat, mustards and kochia begin germinating at soil temperatures less than 40 degrees Fahrenheit.

As field work begins, think about how to ensure these early emerging weeds are managed before planting.

Early emerging weeds cause the greatest yield loss and produce the most seed if they are not managed before planting. For example, research at Montana State University suggests wild oat infesting a barley field at 10 plants/ft2 would cause 5-10 percent more yield loss if they emerged prior to the crop than if the wild oat emerged at the same time as the crop.

Likewise, the early emerging weeds produce much more seed than weeds emerging with the crop. In addition, early emerging weeds will be large when post-emergence herbicides are applied making them harder to control.

Therefore, the key to successful weed management and profitable crop production is to control early emerging weeds as they are the most detrimental to yield and produce the most seed.

Managing weeds before planting can be achieved by tillage or with a "burndown" herbicide treatment. To be effective, weeds should be tilled when less than 2 inches tall, or they may re-root and continue to grow (this is especially true for dense patches). In addition, crops should be planted within a day or two of the final tillage. Increasing the time between the final tillage and planting increases the head start weeds can get over the crop.

Burndown herbicides such as Roundup at 12 oz/A or Gramoxone Extra at 2 pt/A can be applied before planting to control emerged weeds. Crops should be planted three to five days after burndown herbicides are applied for best results. Roundup and Gramoxone Extra applications also can be made after planting, but before the crop emerges to manage existing weeds.
However, if rain occurs shortly after planting but before the herbicide is applied, the window for post-plant treatment may be narrow for preventing crop injury.

Many growers use a combination of tillage and applying burndown herbicides to control early emerging weeds. Tillage after applying a burndown herbicide, a common practice, can cause deeply buried or dormant seed to germinate. This can lead to increased weed pressure and decrease the effectiveness of the burndown herbicide. However, tilling fields in the fall or early spring can stimulate a large flush of weeds. This technique followed by a burndown herbicide treatment can be very effective at
reducing the weed pressure in problematic fields.

Managing early emerging weeds is extremely important to preventing crop yield loss and weed seed production. However, effective tools exist to help prepare a seedbed free of weeds. Growers should pay special attention to use these tools properly within their own system.

New Model Saves Farmers Costs of Fertilizer, Soil Tests

A new computer model from the Agricultural Research Service could save farmers worldwide millions of dollars in increased crop yields, fewer soil tests and less use of nitrogen fertilizer.

The Nitrogen Fertilizer Decision Aid is available on the World Wide Web. It eliminates uncertainties that lead many farmers to over apply nitrogen as so-called "insurance fertilizer."

ARS soil scientist Alan E. Olness in Morris, Minn., developed the new model. It uses soil and weather information to predict how much nitrogen will be produced by soil microbes after spring planting. Often, that amount can be 50 to 100 pounds per acre.

Results from a soil test just before planting tell the model how much nitrogen the soil has at that time. In addition, the model requires farmers to know the soil's clay and organic matter content and pH and to provide data from a field weather station.

The model predicts nitrate-nitrogen content for up to 90 days after planting, well before the critical nitrogen uptake period for corn.

If the rate of natural nitrogen production doesn't meet their crop needs, farmers will add nitrogen fertilizer to make up the difference. If production of nitrogen is predicted to be too rapid, farmers can slow it down by planting without tillage.

The model can be downloaded from:

http://www.infolink.morris.mn.us/~lwink/products/products.htm

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Top Dressing Nitrogen for Winter Wheat Yield
By Jim Bauder
MSU Extension Soil and Water Quality Specialist

In spring, many farmers consider top-dressing their winter wheat with nitrogen. Whether your yield would increase if you top-dress nitrogen depends on the weather, the soil, the growth stage of the wheat and the nitrogen source.

The most important factor is available water. Without enough water stored in the soil and from rainfall during the growing season, top-dressed nitrogen will not be used by the crop. So the rate at which nitrogen is top-dressed on winter wheat and the time when it is applied should be closely matched to the potential yield established by the available water.

If the amount of water you expect can support only a 40 bushel per acre winter wheat yield, there is nothing to be gained by top-dressing more nitrogen than a 40 bushel yield can use. So, the actual amount of nitrogen top-dressed will depend on how much nitrogen was applied last fall and what level of yield the field is capable of producing.

Another factor influencing effectiveness of spring top-dressed nitrogen on winter wheat is the inherent fertility and potential of the soil. Winter wheat grown on high organic matter soils will respond less to spring top-dressed nitrogen than less fertile soils. Organic matter mineralization makes more nitrogen available to the crop in the spring.

In general, it takes two to three pounds of nitrogen to produce a bushel of winter wheat. The total amount of nitrogen that should be applied, preplant plus top-dressed, should be matched to a realistic yield goal for the field. If a realistic yield goal is 40 bushels per acre, based on available water, then the total nitrogen requirement by the crop will be about 80 to 120 pounds of nitrogen per acre from all the available nitrogen sources.

Fine textured soils in areas of low winter precipitation have the ability to hold most of the nitrogen that may have been applied at planting. That means there is little potential for loss due to leaching. In such cases, there may be no advantage to top dressing nitrogen, especially if adequate nitrogen was applied preplant. Urea, which converts to ammonium shortly after being applied to the soil, and anhydrous ammonia are tightly held by fine soil particles and organic matter. If nitrogen was applied as nitrate at planting time, then there is a possibility that a positive response can be seen from top-dressing nitrogen in the spring.

If the soil is sandy and over winter and spring precipitation are heavy there is also good possibility that winter wheat will respond to spring top dressing nitrogen.

Late winter and early spring top-dress has the advantage that fertilizer rates can be adjusted to soil moisture and general conditions of the wheat at the time of top-dressing. If winter precipitation was much greater this  year than average, and the soil is holding more moisture now than it usually does in the spring, then top-dressing may add bushels.

Another key to successful top-dressing in the spring is early application. Most crop needs for nitrogen are met early in the growing period. The earlier nitrogen is top-dressed, the greater the likelihood of a beneficial yield response. The following guidelines may be of some help in making the decision about whether to top-dress winter wheat with nitrogen this spring:

Winter wheat requires about two to three pounds of nitrogen per bushel of grain.

Grain protein may be increased slightly by applying 20 to 30 pounds of nitrogen per acre above the level of nitrogen required for the anticipated yield potential.

Nitrogen top-dressed on winter wheat after jointing will generally have no effect on yield or will reduce yields. If you decide to top-dress winter wheat, the earlier the better.

One final note: Replicated studies have shown no advantage from top-dressing versus nitrogen applied at planting when sufficient nitrogen is applied preplant to achieve yield potential and preplant nitrogen has not been leached out of the soil.

Top-dressing nitrogen is likely to produce more response on sandy soils, where over-winter precipitation has been high, than on fine textured soils in low rainfall areas.

For additional information or to receive a regular email distribution of agronomy notes such as the one above, Jim Bauder can be contacted by email at "jbauder@montana.edu" or by calling 406-994-5685 at Montana State University.
 
 

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Narrow Row Spacing Leads to Higher Grain Yields

In cereal crops that receive adequate moisture, narrow row spacing generally results in higher grain yields than wider row spacing.  Narrow-row spacing should consistently increase wheat yields, because tiller numbers are increased without depressing the other yield components, according to researchers.

Generally, the higher yields from narrow row spacing occur under irrigation or when adequate water is available throughout the growing season. Narrow row spacing also results in a more rapidly maturing crop.

Also, test weight usually increases as row width is reduced, as long as the crop has adequate moisture.

Effect of row width on oat yield and percentage of maximum yield.
 

Row width (inches)	Grain yield (bu/acre)	% of maximum (%)	Test weight (lb/bu)
8	86.6	100	29.8
16	69.7	80	28.9
24	57.2	66	28.3
32	46.6	54	28.4

Studies on a variety of cereal crops have shown similar benefits from narrow row spacing.

Studies comparing yields of wheat, triticale and rye planted in 5- and 10-inch row spacings found that yields were greater when rows were spaced 5 inches apart. Similar studies with soft red winter wheat, comparing yields from 4- and 8-inch row spacings, showed that the narrow row spacing produced the highest grain yield. The average grain yield from 4-inch row spacings
was approximately 12 percent higher than from an 8-inch row spacing.

In oat studies, reducing row spacing from 32 to 8 inches increased yields nearly 50 percent. Similarly, test weights increased as row width decreased.