ISSUE 6   June 19, 2008

CHECK LEGUMES FOR NODULES

Soybean, dry bean, field pea, lentil, and alfalfa are important legume crops grown in North Dakota. Specific bacteria live in symbioses with legume roots and nodules are formed where atmospheric nitrogen is transformed in plant usable nitrogen. Nodulation is a good diagnostic tool to evaluate the relative crop condition. Stressed legumes will have limited nodule numbers. Severe stress after the nodules are formed may cause nodule sloughing and decrease the active number of nodules. There are several stress factors that can occur during the growing season. Excess moisture, drought, and unbalanced plant nutrition are the most common stress factors. As the legumes depend on the nodule growth for their nitrogen supply, stressed and reduced nodulation may lead to nitrogen shortages for the growing legume plant. Drought and nutrient stress may lead to low yields and early maturing of the crop.

Nodules develop on the tender root hair tissues rather than the older tissue of the root. Nodules can be already found a few weeks after the plant emerged. Nitrogen fixation kicks in, normally at about the 2nd trifoliolate stage. Active nodules, those producing nitrogen for the crop will have a nice pink or reddish color when the nodules are cut open.

Nodulation on soybean roots
Nodulation on soybean roots

Nodulation problems

If the legume seed was inoculated with an old source of inoculum (>2 yr. old) the bacteria count could be low, and therefore nodulation is lower than with new and healthy inoculants. If the inoculant (live bacteria) was exposed to heat or long periods of direct sun the bacteria count could be reduced, it only takes an hour to kill the bacteria if left in the sun. Also, if the seed was not properly and uniformly treated nodule numbers may be low. Some of the seed treatments (fungicide, insecticide or combination) may be antagonistic with inoculants (check the label.) Manufactures of products and seed suppliers can provide product compatibility information. Other stress factors that may cause low nodulation are root rot problems, wet and saturated soils, high pH and or high salt concentrations, and cold or dry soil conditions. It is important to diagnose why nodulation is low, so preventative measures can be taken next season to avoid similar problems.

Effect of Nitrogen on early growth and nodulation

Soil Science students researched the effect of nitrogen on early growth and nodulation of soybeans. Four plants were grown per 2 kg pot of soil, amended with all nutrients except Nitrogen. The treatments were four N rates of 0, 50, 100 and 200 mg/pot by two inoculation levels; soil not inoculated and soil inoculated with a small amount of commercial inoculant. The soil was a Renshaw soil from Streeter, ND, with no history of soybeans. The data were averaged across four replicates. In Figure 1, the number of nodules was substantially higher when the seed was inoculated in soil with no history of previous soybean production. The soil was not sterilized, and a few scattered nodules were obtained per pot in the absence of inoculation.

Figure 1
Figure 1.  Effect of Nitrogen treatment on the
number of nodules per pot (four plants)

In Figure 2, the weight of the inoculated plants was higher than of the non inoculated plants. If nitrogen is available, the plant will use the nitrogen for plant growth. When plants can fix their own nitrogen in the presence of the right bacteria, NDSU does not recommend a N application for soybean.

Figure 2.
Figure 2.  Effect of Nitrogen treatment on the fresh
weight of the above-ground plant parts.

 

EFFECT OF SEED INOCULATION AND N FERTILIZATION ON SOYBEAN YIELD AND PROTEIN

Too much nitrogen can injure the Nitrogen (N) fixation and normal soybean development, leading to inadequate nitrogen being available later in the season. A study conducted by R. Jay Goos, NDSU Soil Scientist, and the Carrington Research Extension Center in 2007, demonstrated how too much available N in the soil can injure the nitrogen fixation mechanism for the entire season. A field with no history of soybeans was grown to two varieties of soybeans. Among the treatments, there was a combination of no inoculation or inoculation with or without 100 lb N/A before planting. The soil was not absolutely devoid of rhizobia bacteria, and some fixation did occur in the absence of inoculation.

Early in the growing season, the N-fertilized soybeans were much greener and more vigorous than those depending on fixation. It seemed at the time, that the N fertilizer was doing some good.

By flowering, however, that difference in color had disappeared, and all plots were dark green. The export compound of fixation (the compound going from the nodules to the tops), the ureide-N, was greatly increased by inoculation, and severely suppressed by N fixation. By harvest, the best yield, protein, and protein yield was given by the plants receiving seed inoculation only.

So, given the high price of nitrogen fertilizer, and the tendency of excess N fertilizer to induce iron chlorosis on poorly-drained soils, it is hard to recommend N fertilizer for properly inoculated soybeans.

Effect of seed inoculation and N fertilization on soybeans, Carrington, ND, 2007.

-- Flowering --

------- Harvest -------

Seed inoc.

N  fert.*

Plant growth g/plant

Ureides
in stems ppm N

Yield bu/A

Seed protein
%

Protein Yield lb/A

No

No

8.4

383

43.1

29.7

768

Yes

No

11.6

1064

47.2

34.6

980

No

Yes

9.1

128

43.3

29.0

753

Yes

Yes

10.0

363

46.8

32.7

918

* 100 lb N/A, tilled in before planting.

Hans Kandel
NDSU Extension Agronomist
hans.kandel@ndsu.edu  

R. Jay Goos
NDSU Soil Scientist
RJ.Goos@ndsu.edu

 

TOO MUCH WATER AGAIN

After a very dry start this season, rainfall has been so abundant these past two weeks in parts of the state that we are now dealing with problems of excessive moisture. Water logging in eastern ND was also a problem last year, though temperatures tended to be much warmer in 2007. The small grain crops that have not been affected by water logging, are developing nicely. On the other hand, the warm season crops are yellow and struggling to developed due to the double whammy of low temperatures and saturated soils. Perhaps the warmer weather predicted for this week will give a big boost to these crops and hasten soil drying that is so urgently needed. Water logging (ponding, saturated soils) affects a number of biological process in plants and soils, and is damaging to crop growth. Many factors, however, influence the extent of yield loss caused by excessive moisture. The following notes on water logging are drawn from an article I wrote last year on the same topic, that appear to relevant again this year.

Effect of water-logging on the developing plant

Crop injury from water-logging is primarily caused by the lack of oxygen. All plants need oxygen for cell division, growth and the uptake and transport of nutrients. When soils become saturated, the amount of oxygen available to plant tissues below the surface of the soil (or water level if ponding occurs) decreases rapidly as plants and microorganisms use up what is available. The movement of oxygen from the air into water/saturated soil is much slower than in a well aerated soil and much less than needed by the various organisms in the soil. The rate of depletion of oxygen in a saturated soil is dependant on a number of factors, but temperature is the most important and predictable factor; the higher the temperature the faster the rate of oxygen depletion. In that regard, the cooler temperatures this year have slowed damaged caused by water logging. Generally, the oxygen level in a saturated soil reaches the point that is harmful to plant growth after about 48-96 hours.

In cereals, the growing point is below or near the soilís surface during early vegetative growth (5-6 leaf stage in corn and small grains). While the growing point is below the soilís surface, cereals are quite sensitive to waterlogged conditions. In fields with timely planting, corn is now in the 3-4-leaf stage, spring wheat is starting to joint and winter wheat is beginning to flower, so much of the spring sown cereals are quite sensitive to water logging at this time. Young plants can be killed if soils are saturated beyond 48 hours, particularly when soil temperatures are high (i.e. above 65 F) Water-logged conditions also reduce root growth and can predispose the plant to root rots later in the season, so the ultimate effect of excess moisture may not be known until late in the season. It is common to observe plants that have experienced waterlogging to be especially sensitive to hot temperatures and to display nitrogen and phosphorus deficiencies later in the season due to restricted root development. Leaf yellowing is the most common symptom of waterlogging in plants not killed by excessive soil moisture. Yield losses can occur, however, even if these visible symptoms are not observed.

Effect of water logging on the soil

Water-logging can also indirectly impact cereal growth by affecting the availability of nitrogen in the soil. Excessive water can cause leaching of nitrate nitrogen beyond the rooting zone of the developing plant, particularly in lighter textured soils. Furthermore, when oxygen levels become depleted, soil microbes extract oxygen from the nitrate molecule, causing nitrogen to be converted to a gaseous form that is lost to the air (denitrification). The amount of N loss through denitrification depends on the amount of nitrate in the soil (the ammonium form of nitrogen is not lost through denitrification), soil temperature, and the length of time that the soil is saturated. Research conducted in other states has found losses between 1 and 5% of the nitrate N lost for each day that the soil remains saturated.

Can anything be done to improve crop recovery after water logging?

Plants subjected to saturated soils most urgently need oxygen. Oxygen will move into the soil as water drains from or is extracted from the rooting zone. In a corn crop, tillage may seem to be a way to introduce oxygen into the soil, but is not recommended due to the potential for compaction, the high cost of diesel fuel and limited impact of this practice. With the promise of warmer and dry weather, soils will dry out about as quickly on their own.

Adding additional nitrogen to fields that have had significant N losses, once they have dried, can remedy these losses, particularly for corn, which can effectively utilize N applied much later in the season than small grains. In small grains, in order to impact yield, additional N should be applied prior to the 6-leaf stage. Additional N, after this stage, however, does have the potential to increase protein levels. Before adding extra nitrogen to fields that experienced water logging, you should first consider the likely yield potential of the crop that has probably already been damaged. Nitrogen losses are not likely to be uniform throughout the field and additional N may only be needed in low spots where losses were the highest. If you do decide to apply some additional N, you should consider varying the rate to target those areas in the field where N is likely to be the most limiting.

Is replanting a viable option for corn given the late date? We have limited data on the effect of planting corn in late June. Nevertheless, even with the earliest available hybrids, it is suffice to say that planting this late would be a high risk proposition unless the corn crop is intended for silage. With a fourth of the growing season behind us, there is not likely to be enough growing degree days to make a crop even in southeastern ND.

Joel Ransom
Extension Agronomist - Cereal Crops
Joel.Ransom@ndsu.edu

 

STUBBLE HEIGHT AFFECTS HAY DRYING WHEN SOIL IS WET?

Hay harvest in the eastern part of North Dakota and western Minnesota has been delayed by the cool wet spring. Producers are just now starting to harvest their hay because the soils have been too wet to carry the harvesters and many have yet to begin. Those that have started are laying the hay on very wet soils, which will delay the drying of the hay. The soil water keeps the humidity high within the hay decreasing the drying rate.

Leaving 3 to 5 inches of stubble standing in the field when cutting alfalfa tends to keep the hay off the ground allowing breezes to circulate around the windrow speeding the drying rate. Many producers typically cut at 3- to 4-inch stubble heights because it is difficult to get their harvesting equipment to harvest at lower stubble heights and some producers believe regrowth will be faster if harvested at a higher stubble height. If this is the case, do not increase the stubble height, 3 to 4 inches of stubble is adequate to decrease the drying rate.

Stubble height has a major impact on forage yield of alfalfa. We harvested alfalfa at 1, 3, and 5 inches in height at Fargo (dryland) and Carrington (irrigated), ND, in 1999 to 2001. Forage yield for a 3-cut system average 6.3, 5.1, and 4.3 tons/acre each year over the 3-year period, respectively. Thatís 2 tons/acre difference between the 1 and 5-inch stubble heights left standing in the field over the season! Granted, the quality of the lower stem is relatively poor, but to give up the yield with the current high hay prices is really questionable. Many alfalfa fields in eastern ND and western Minnesota have lodged from the pounding rainfall and high winds. In this case, it will be impossible to get even a 3-inch cutting height with a swather and yield loss will be inevitable.

Forage quality can be improved by leaving some stubble in the field. For example, relative feed value increased with each increase in stubble height for all three years due to decreasing acid and neutral detergent fibers while crude protein increased with increasing stubble height. If forage quality pays, i.e., cash hay or dairy producers, some of the lost yield potential with increasing stubble height is off set with the value of increased quality.

Leaving additional stubble height in the first harvest had absolutely no effect on the regrowth rate since all the regrowth occurred from the crown in these experiments. Regrowth for the third or fourth harvests occurred much more from remaining stubble; however, canopy height was not affected by stubble height. As a result, forage yield still decreased with increasing stubble height in the third and fourth harvests.

Drying rate in the field probably can be increased more by windrow width than stubble height. Many experiments have shown that wide windrows or unwindrowed hay dries faster than relatively narrow windrows (2 to 3 feet wide) due to the depth of the windrow. The faster drying reduces plant respiration maintaining a higher level of soluble carbohydrates within the forage. Yes, raking is recommended to improve drying rate, but be sure to rake when the moisture content of the hay is about 50%, so leaf loss is minimal. Raking hay that has been placed on wet soil greatly aids drying because frequently the soil dries between the windrows before raking. Therefore, the window can be place on relatively dry soil and the windrow inverted to expose the wettest hay. Conditioning the hay when cutting improves drying rate also, especially in the first harvest. Conditioning may not help in latter harvests since the stem size generally is much smaller with less lignification and cutinization than what occurs in the first harvest.

The best recommendation then is lay the alfalfa in wide windows, rake at 50% moisture, invert the windrow, place on soil that has dried, and keep the stubble height as low as possible. If youíre a beef cow producer, maybe consider a small increasein stubble height (no more than 3 to 4 inches) to increase quality for a cash hay or dairy producer.

 

ALFALFA HAY PRICES INCREASING RAPIDLY

Alfalfa hay prices have increased $40/ton since February (see enclosed figure). Average hay price in the United States reached $177/ton. This includes all alfalfa hay marketed in the United States, which means high-quality hay is much higher.

Alfalfa hay sold this past month at Stearn DHIA at Sauk Centre, MN, quality-tested auction averaged $254/ton for 151 to 174 relative feed value (RFV) with two small lots at $300/ton. Lower-quality hay (101 to 125 RFV hay) sold for $150 to $190/ton.

I believe that you can expect the hay price for quality alfalfa to continue to rise in the next few months. One factor driving the price is that some of the first harvest in Nebraska, Iowa, Illinois, Wisconsin, etc. has yet to be harvested due to the heavy and frequent rainfall. Hay that has been harvested is lower in quality than usual due to delayed harvest. As a result, quality hay will be very scarce. Another factor affecting the price is that the hay price must increase to compete for acreage with $7 corn and $15 soybean price.

North Dakota hay price averaged only $72/ton last month. North Dakota has always been under the national hay price due in part to a beef-cow-based market versus a dairy-based market. However, I have heard of central North Dakota producers getting $180 to $200/ton in the quality-tested marked. It costed them $65 to $75/ton for transportation, but the price differential resulted in a much better deal for the producer.

Producers that get good quality alfalfa in the pile from the first harvest might want to consider marketing it into the high-priced dairy market. Prices will continue to climb in the short term due to poor quality, and it may increase due to aligning with other crops.

Alfalfa hay graph

Dwain W. Meyer
Extension Forage Specialist
dwain.meyer@ndsu.edu


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