Brownstown Agronomy Research Center Field Day – July 25

The 2013 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Thursday, July 25. Extension researchers and specialists will address issues pertinent to the current growing season. Tours will start at 8 a.m., with the second and third groups leaving the headquarters around 8:20 a.m. and 8:40 a.m. The tours will last about two and a half hours and will be followed by lunch provided by U of I Extension.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • Nitrogen Sensors & Variable-rate N Applications – Dennis Bowman
  • Wheat Disease I.D. & Management – Dr. Carl Bradley
  • Emerging Developments in Weed Management – Doug Maxwell
  • Crop Rotation:  Another Risk Management Tool – Dr. Emerson Nafziger
  • Agronomic and Environmental Assessment of Cover Crops – Dr. Angie Peltier

 The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center every year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40 / 185 junction.

For more information, contact Robert Bellm (618-427-3349); rcbellm@illinois.edu
Visit us on the web at http://web.extension.illinois.edu/barc/


Stormy weather and Goss’s wilt go hand in hand

Goss’s wilt of corn often is most severe after fields are exposed to high winds and/or hail damage, because the causal bacterium, Clavibacter michiganensis subsp. nebraskensis, readily infects corn leaves through wounds.  With the recent storm activity across the state, growers should be on the lookout for the appearance of Goss’s wilt symptoms.  Goss’s wilt lesions on the leaves generally have wavy margins with a water-soaked appearance on the edges of the lesions.  Dark spots, known as “freckles”, almost always can be found within the lesions.  The affected areas of the leaves will have a shiny appearance when observed in the sunlight, and bacterial exudates may be on the leaves that resemble drops of maple syrup.

 

Goss's wilt symptoms on a corn leaf. Note the wavy margins of the lesion, the dark spots ("freckles") inside the lesion, and the water-soaked appearance of the lesion margin.

 

Bacterial exudates (circled in red) of the Goss's wilt pathogen, which appear as drops of maple syrup.

 

Goss’s wilt incidence was at an all-time high in the 2011 season, with over 30 Illinois counties having positive detections via samples sent to the University of Illinois Plant Clinic.  This high incidence observed in 2011 means that the causal bacteria is present in the state and can cause infections again in the 2013 season if the conditions are favorable.  Fields that are at the most risk to Goss’s wilt are those that have been grown to continuous corn, have been planted to a susceptible hybrid, and have received wind or hail damage.  Because other diseases and disorders can resemble Goss’s wilt, it is important that suspicious samples be sent to the University of Illinois Plant Clinic for the most accurate diagnosis.  Be cautious of results received from test kits designed for the related bacterial canker of tomato pathogen, Clavibacter michiganensis subsp. michiganensis, because these kits have been shown to give false positives.

Unfortunately, no consistently-performing in-season control options are available for Goss’s wilt management.  Because Goss’s wilt is caused by a bacterium, foliar fungicides are not effective.  Other products may be marketed as providing control of Goss’s wilt, but field testing of these products by universities have shown these to be inconsistent and/or ineffective in providing reliable control of Goss’s wilt.  The best way to manage Goss’s wilt is to rotate to a non-host crop, such as soybean, and plant the most resistant hybrid available the next time corn is in the field.  Because the Goss’s wilt bacterium survives in corn residue, fields with severe Goss’s wilt can be tilled after harvest to help decompose the residue, which may help reduce the inoculum level in the field.


Corn Roots, Wet Soils, and Nitrogen

The June weather pattern in Illinois was variable, and the month is ending with rainfall totals ranging from a little less than normal in parts of western Illinois to nearly double the normal amounts, with some totals as high as 7 to 8 inches, in parts of southeastern and northern Illinois.

While getting rainfall in June is certainly preferable to getting little or none as happened in Illinois in 2012, standing water and wet soils can badly damage a rapidly-growing corn crop. In June of 2010, 2 to 4 inches of rain fell during the fourth week of June over most of central and northern Illinois. With the crop planted early and developing rapidly under high temperatures, standing water resulted in serious and irreparable damage to root systems. This lowered yields in low-lying fields and parts of fields, even where rains fell later in the season.

When soils remain saturated for more than a day or two, the lack of oxygen causes nutrient uptake to slow quickly, and root tips start to die off. It helps that temperatures have not been above normal; cooler water carries more dissolved oxygen, and also slows growth and nutrient uptake. Also, plants during vegetative growth have much better ability to grow back damaged root systems once soils drain than do plants during or after pollination.

These factors, along with the very good crop color (which indicates good root activity and adequate supplies of soil N) before the rains in late June, point to good chances for recovery of crop yield potential  in fields and parts of fields where the water is no longer standing. In the short run, plants may lose some of their green color before roots are fully functional again, but this will likely be a temporary condition. While many worry that any stress during mid-vegetative growth will lower yield potential, there’s not much evidence that a few days with reduced photosynthetic rates has much effect on yields, at least if this occurs more than a week before tasseling.

Regardless of how quickly the crop returns to normal after an event like temporary flooding, questions will remain about how standing water might affect the amount of nitrogen left in the soil to meet the needs of the crop. Warm, saturated soils lose nitrogen (as gas back into the air) through the process of denitrification. We do not think that such losses have been very large in most fields, given the temperatures and the fact that most flooding was temporary. In better-drained fields, denitrification would be less, but percolating water has probably moved some of the nitrate-nitrogen deeper, perhaps below the root system or into tiles lines.

In central Illinois we have accumulated about 1,100 growing degree days (GDDs) since May 1, and about 930 GDDs since May 15. By the time corn accumulates 1,000 GDD, reaching about stage V13, it has accumulated about 20 percent of its dry weight and about 40 percent its season-long nitrogen accumulation (Abendroth et al., 2011) During this period the crop takes up 3 to 3.5 lb of N per acre per day, and by the time of pollination, it will have taken up about 60 percent of its nitrogen and produced about 40 percent of its dry weight.

At the time the crop reaches stage V13 (about head-high), it still has to take up 110 to 120 lb of N, and in years when June is wet, a common question is whether or not the crop might run out of nitrogen, leaving the crop short. While the need for 20 or more lb of N per week would seem to raise the possibility of a shortage, the production of plant-available N from soil organic matter through the process of mineralization is also at its maximum rate in mid-season.

For a crop with a good root system growing in a soil with 3 percent organic matter, mineralization at mid-season likely provides at least half the N needed by the crop on a daily basis. This means that normal amounts of fertilizer N, even if there has been some loss, should be adequate to supply the crop.

Though we could measure soil N present or apply urea by air on the wetter field or parts of fields where the crop shows deficiency, it would seem prudent to wait to see if the crop recovers its green color before going to this expense. The loss of crop color in wet soils is due mostly to loss of root function, and roots will need to recover before the canopy does. Even without adding more N, odds are good that the crop will recover and thrive in the coming weeks, providing the weather remains favorable.

Reference:

Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marley. 2011. Corn growth and development. PMR 1009, Iowa State University Extension, Ames, Iowa.


Purple and Yellow Corn Plants

The corn crop that was planted in May is up and growing in most fields, but there have been numerous reports of fields with uneven plant sizes and colors, including purple and yellow plants. Many are wondering if this will decrease potential yields.

Based on past experience many people expect to see purple corn when soils are cool and dry during early plant growth stages, or in that rare field with low soil test phosphorus levels. The purple color is from a pigment that forms when there is more sugar in the leaves than the plant can utilize. Low phosphorus inhibits sugar movement out of leaves, and cool, dry soils reduce root growth and sugar movement to the roots. Both of these increase sugars in the plant and can make the tissue turn purple.

Soils are not cool and dry in Illinois now, but surface soils are drying out in many fields, and it’s likely that roots growth up to now has been restricted some by having soils too wet and in some cases also compacted by tillage and planting operations. In fields where the plants have taken up enough nitrogen and water to grow well but roots remain constricted, purpling might be common now, especially in those hybrids that have a tendency to form the purple pigment.

We expect the problem of purple corn to correct itself as root growth continues. It will help if wet soils continue to dry out, but in fields with dry surface soils, root growth might benefit from some rainfall. The high sugar content that leads to purpling means that the plant is producing sugars through photosynthesis, which is a good sign. There is no evidence that temporary purpling affects yield of the crop, though factors such as soil compaction that can lead to purpling might also reduce yields if the weather is dry later in the season.

Other fields are showing the yellow color that characterized nitrogen deficiency. In some cases this diagnosis is strengthened by our being able to see patterns such as N applicator knife tracks where the plants are greener. As is the case with purpling, we tend to see more yellow plants in the lower areas of the field. This is both where soils were wetter at planting time, so are more compacted, and where we would expect more N loss and poor root growth due to wet soils.

Some have already responded to yellow corn by applying a higher rate of sidedress N than had been planned, or by, or applying sidedress N on top of a full rate of N already there. Some may even have applied foliar N or broadcast urea by air to try to get N into plants quickly. If soils are still wet in such fields, plants are continuing to struggle with poor root growth and poor root function, so adding N might not have much immediate effect.

It is likely that the problem of yellow corn is, like that of purple corn, more related to poor root growth than to low level of soil nutrients. Student interns working at the Orr Center in Perry sampled soils the first week of June in a study where different N rates were applied as UAN in the first week of April. That site received some 17 inches of rain in April and May, and we expected that some of the N would have been moved to below the top two feet.

In fact, we found as much or more total N (nitrate plus ammonium) in the top two feet the first week of June than we applied as UAN the first week of April. We recovered about 90 lb. of N where we had applied 60 lb., and just over 240 lb. of N where we had applied 240 lb. So it’s likely that some of the N there now was produced by mineralization, and that some fertilizer N was moved down below two feet deep, but the net amount available to the crop after high-loss conditions certainly has not been drastically reduced.

As soils dry out in most areas of Illinois and temperatures stay warm, it’s likely that many fields with yellow corn plants will improve, in some cases rapidly. Late planting and warm temperatures do tend to favor top growth over root growth, but we expect that as leaves grow and start improve in color and as soil oxygen levels increase as soils dry, sugars will become more available to the roots as well as the tops, and this will further improve root uptake of nutrients.

If crop color remains poor even after a week of drying soils and good growing conditions, then it is possible that N movement to below the rooting depth is affecting the ability of the crop to grow out of this problem. Our soil measurements suggest that in most cases N is likely still present, but a small “booster” shot of N might help the crop revive and reach the N more quickly. The crop has roots extending to the middle of the rows by the time it have 4 or 5 leaves, so injecting N between the rows should work to get it into the plant.  Broadcast urea will need some rainfall to reach the roots.


How Late Can We Plant Corn and Soybeans?

The latest report from NASS indicates that 96 percent of the corn and 62 percent of the soybean crop in Illinois had been planted as of June 9. Some of the corn is struggling, however, with 13 percent of the crop rated as poor or very poor. Much of this is due to heavy rainfall, which has caused problems with stands, including areas in fields where the crop has drowned out from standing water. In other cases, the crop has emerged poorly in fields or areas in fields due to crusting and some low temperatures.

It’s very late to plant or to replant corn, and for many with unplanted fields or with poor stands that may need to be replanted, the choice is whether it makes sense to plant corn this late, and if not, whether the best option is prevented-planting insurance or replacement with soybeans, as crop insurance provisions allow.

Table 2.3 in Chapter 2 of the Illinois Agronomy Handbook http://extension.cropsci.illinois.edu/handbook/  indicates that we can expect a corn crop to yield about two-thirds of its expected (early-planted) maximum yield if the crop is planted on June 8 and has a full stand. That is a projection, since most of our corn planting date studies include planting only through the end of May. Based on this, however, we have projected that corn reaches the point where we can expect 50 percent of maximum yield if it is planted sometime between June 15 and June 20.

I reanalyzed our more recent planting date data, and if – this is a big “if” – we can accept projections of yield that go well past the last planting date, we would move the planting date from which we’d expect half a crop a little later, closer to the end of June. But we know that corn planted during or after the middle of June will produce fair to good yields in some years and very little yield in other years, depending on unpredictable weather that follows. Hence it makes sense to consider June 15 to 20 to be that last “practical” date on which to plant corn if we want to produce grain.

If we do plant corn in mid- to late June, planting a very early hybrid, having the option of harvesting the crop as silage if grain production looks unlikely, and getting good rainfall throughout the rest of the season will all improve the chances of ending up with a profitable crop. The chances of having enough frost-free days to grow a crop are higher in central and southern Illinois than farther north, but higher water loss rates and lower water-holding capacity of soils can cancel this advantage. It may also be difficult to get seed of very early hybrids, and because early hybrids are not developed for the central and southern Corn Belt, there is no guarantee that they will do well under late planting.

If it’s too late to plant corn and we don’t expect enough yield to make a profit (or at least to make more than crop insurance would pay to plant nothing), does it make sense to plant soybeans instead? We have run our soybean planting date studies into the first or second week of June, but we still have to project expected yields past the last date we actually planted.

Going through the same exercise as we did for corn, we would expect soybeans planted at the end of June or early in July to yield half what they would if planted early. This is about two weeks later than the normal doublecrop planting date in southern Illinois. Doublecrop soybeans have averaged 72 percent of full-season soybean yields over the past 10 years at Brownstown, so using early July as the 50-percent-of-maximum-yield planting date seems reasonable.

We know that doublecrop (or very late-planted) soybean yields can range from zero to good, and there’s no way to predict when they are planted which end of this range they’ll be on. As many found out in 2012, planting into bone-dry soils is not usually conducive to high doublecrop soybean yields. And in northern and central Illinois, doublecrop soybeans or soybean planted (or replanted) in late June or early July have had a considerably lower rate of success than doublecrop soybeans in southern Illinois.

There is one important difference between doublecrop soybeans and soybeans that are planted late but that don’t follow wheat harvest. Wheat removes a substantial amount of water from the soil as it matures, and in years with average June rainfall, the soybean crop that follows wheat has much less soil water available to it than does the crop that follows only the crop from the previous year. As is always the case, good rainfall through the rest of the season can cancel out this advantage, but it won’t eliminate it averaged over years.

Soybean planted in mid- to late June needn’t be managed much differently than early-planted soybeans. Our recent research indicates that narrow rows tend to yield more regardless of planting date, and raising seeding rates seldom produces an advantage when planting late. Unless a late-maturing variety (for example, a Group 4 variety in central Illinois) was the first choice, there is no advantage to changing to an earlier variety for late planting.


Dates and Locations for the 2014 University of Illinois Corn & Soybean Classics

The dates and locations for the 2014 University of Illinois Corn & Soybean Classics are set for next January.  Our next series of meetings marks the 17th year of the Classics and will continue the program’s tradition of providing our clientele with the most current and timely information related to crop production, marketing and pest management.

The dates and meeting locations for the 2014 Corn & Soybean Classics are:

▸ January 6 (Monday): Champaign I Hotel and Conference Center

▸ January 7 (Tuesday): Mt. Vernon Holiday Inn

▸ January 10 (Friday): Springfield Crowne Plaza

▸ January 13 (Monday): Peoria Par-A-Dice Hotel

▸ January 14 (Tuesday): Moline i wireless Center

▸ January 15 (Wednesday): Malta Kishwaukee College

Please mark your calendar and plan to join us at one of these locations.  We will provide additional information related to the program in a future Bulletin article.

 


Wheat scab rearing its ugly “head”

Head scab of wheat (a.k.a. Fusarium head blight) is showing up in Illinois wheat fields.  Incidence is ranging from low (less than 10% of the heads affected) to moderately high (over 25% of the heads affected).  Affected wheat heads will appear “bleached” in color.  Heads often are partially affected, with both healthy green and affected bleached areas being present in the same head.  Although I have not been in all wheat production areas in the state, my general observations are that fields in southern Illinois (south of Interstate 70) range from low to moderate incidence of scab, while fields in central Illinois seem to have moderate to high incidence of scab (it may be a little too early to see scab in northern Illinois fields currently).  These differences in scab incidence from field to field likely are due to differences in susceptibility of the varieties planted, application or no application of fungicides, and local weather.

Wheat field affected by head scab (Fusarium head blight). Note the "bleached" heads. (Photo by Carl Bradley)

Wheat head affected by scab (Fusarium head blight). (Photo by Carl Bradley)

Wheat growers may want to evaluate the level of scab in their fields.  It is easiest to observe this disease before heads completely mature.  Growers with moderate to high levels of scab should consider making adjustments to their combine that would allow low test-weight, scabby kernels to be blown out the back of the combine.  Recent research conducted at the Ohio State University indicated that adjusting the combine’s fan speed between 1,375 and 1,475 rpm and shutter opening to 90 mm resulted in the lowest discounts that would have been received at the elevator due to low test weight, % damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain (Salgado et al., 2011).

Reference:

Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Disease 95:1448-1457.


New Mobile Corn Replant Decision Aid

Deciding on whether or not to replant can be a difficult decision. Cutworm, compaction and seedling blight are some of the problems that can lead to reduced plant populations. The sight of an uneven reduced stand is often more than many farmers can take, but the desire to “fix-it” may not make sense agronomically or economically.

For fields where the stand has been relatively evenly thinned out the following advice is most relevant. Where flooding or ponding has completely wiped out a stand in large areas the decision to replant is easier but may be difficult to execute until these areas have fully dried out.

To make a more objective decision, start with an accurate assessment of the current plant population. In the past we recommended that you use Table 2.3 on page 24 of the Illinois Agronomy Handbook (corn chapter). This chart provides the percent of maximum yield for various planting dates and populations. The Agronomy Handbook is available on-line at http://extension.cropsci.illinois.edu/handbook/.  This table will assist you in comparing yield potential of an early planted crop with reduced population and a late planted stand with optimum population.

To make this a little simpler we have created a mobile calculator that looks up the information for you. All you have to do is put in:

  • Realistic optimum yield for the field
  • Original planting date
  • Current plant population
  • Replant planting date
  • Corn price

The calculator utilizes the formulas that were the basis of the original Agronomy Handbook table and compares the replant yield potential with that of the existing stand. It quickly provides you with a dollar per acre amount you can use to determine if there is a economic incentive to replant and if the difference will be enough to cover replanting expenses.

The replant calculator is available as:
Android app: http://ow.ly/lMtxV
IPhone/IPad mobile spreadsheet: http://ow.ly/lMtCQ
PC: http://ow.ly/lMtGS


Nitrogen and the 2013 Corn Crop

The NASS report indicated that corn planting in Illinois was 89% complete by May 26. This leaves more left to plant than we’d like, and it’s still wet in some areas, so we expect a long “tail” to corn planting this year, unless some of the acres intended to corn get switched to soybeans.

The rainfall that delayed planting across Illinois this year is also affecting nitrogen fertilizer management. For many, the rush to get the crop planted meant abandoning or modifying plans to apply N before or after planting or before tillage. Some ammonia was applied last fall or in early April, and some producers were able to broadcast UAN before or after planting. But in many cases planting took precedence, and where it remains wet it’s likely that a lot of acres still have not had N applied.

Later-applied N has little time in which to be lost before plant uptake begins. This means lower overall loss potential and so less need to apply “insurance” amounts of N. As an example, a plan to split-apply N – right after planting and again at sidedress – might, if the first application couldn’t be made before the crop emerged, now be modified to apply less total N but in a single application.

It is important to get N applied before the crop becomes deficient. But the chance of having N deficiency early in corn planted into warm soils is fairly small. One reason for this is that small plants take up little N – by the time the corn crop reaches V5 (5 leaves fully emerged) it has taken up only about 10 lb of N or so per acre. The other reason is that mineralization – the production of plant-available N from soil organic matter – is getting underway as soils warm up. Hence we tend to see little sign of N deficiency when temperatures are warm early in the season, even where little or no N fertilizer has yet been applied.

I wrote in early April about spring sampling for N to see how much we might have left after last year’s drought and the higher than normal amounts of soil N found last fall. Volunteers this spring sent in about 60 samples taken in the same place and to the same depth as samples last fall. As we can see in Figure 1, nitrate-N levels dropped from the fall to the spring, especially in the top foot. Ammonium-N levels tended to be close to what we might consider a “baseline” of about 5 ppm in both fall and spring.

Figure 1. Soil N in 60 Illinois fields sampled in both fall 2012 and early spring 2013.

If we calculate plant-available N as the totals (ppm x 4 for each foot of depth) of nitrate-N and ammonium-N in the top 2 ft, we find that N dropped from about 180, 150, and 180 lb N/acre in northern, central, and southern Illinois last fall, to about 140, 105, and 112 lb N/acre this spring, respectively. This represents disappearance of about 23, 30, and 38 % in northern, central, and southern Illinois, respectively, or about 42, 46, and 68 lb N/acre.

Should there be any adjustment of this year’s N rate based on the amount of N in the soil this spring? In the earlier Bulletin article I suggested making adjustments only if there were more than 10 ppm nitrate-N in the top foot in spring samples. Most of the spring samples had less than 10 ppm, and it’s likely that even some of that N was moved out of the top foot by rainfall after sampling. Thus we doubt that any adjustments should be made based on amounts of soil N present this spring.

On the large scale, increases in nitrate-N concentrations in river-fed reservoirs now being reported are largely the result of loss of nitrate-N from soils through tile lines. With the large amounts of nitrate in the soil found last fall and with rainfall at or above average over the past three months in Illinois, it’s no surprise that some of the leftover soil N from last year entered tile lines and moved out of fields. While fall-applied N might have contributed in a small way to this, the large amount of soil nitrate present at harvest last fall is certainly the major source of nitrate in drainage water. It’s also certain that N in drainage water is truly “lost” to this year’s crop.

Sampling results from Dan Schaefer of the Council on Best Management Practices provide some hints about availability of N from fall fertilizer applications. One Champaign County field that was in drought-affected corn in 2012 had 16 ppm of nitrate-N and 3 ppm of ammonium-N in the top foot of soil last fall, and 15 and 4 ppm, respectively, in the second foot, for a total of 152 lb. N. The producer applied 100 lb. N as NH3 in November using N-Serve; adding these amounts gives a total of 252 lb. N/acre in the soil last fall. Samples taken in early May this spring had 10 and 13 ppm nitrate-N and ammonium-N in the top foot, and 14 and 4 ppm in the second foot, respectively, for a total of 164 lb. N/acre. Most of the 88 lb N/acre that disappeared from the top two ft of soil probably came from the 124 lb. of nitrate-N present last fall. The 10 ppm difference in ammonium-N would suggest that about 40 percent of that applied in the fall is still in this form.

In a second field, 170 lb N was applied as NH3 with N-Serve on soybean stubble last November. In early May, it had 16 ppm nitrate-N and 10 ppm ammonium-N in the top foot and 16 and 5 ppm, respectively, in the second foot. Based on finding about 5 ppm of both nitrate and ammonium from outside the application band, we called that a baseline amount and subtracted it to calculate that about 108 lb. of N (64 percent) remained in the top two ft from last fall’s application, and that about 80 percent of it was in the nitrate form.

So some of the N that was present last fall moved deeper in the soil, and some moved out of fields in drainage water. Still, a considerable amount of N is present this spring, and it is not clear that the amounts “lost” are greater than normal. Applications were made in a way that minimized nitrification last fall, and soil temperatures were normal this winter. So while any nitrate-N present last fall would have been able to move with rainfall starting in late winter, it’s not likely that fertilizer N would have been mobilized (in nitrate form) earlier than normal. It is possible that some of last fall’s N was also taken up as crop residue started to decompose; this would look like a “loss” but such N might become available this season as residue breakdown continues.

A major concern, especially in those parts of Illinois that have been the wettest over the past three months, is whether or not N applied last fall or early this spring will still be available for the crop this spring. Because so much depends on what happens during the season, there’s not a clear answer to this question, but we can consider some of the factors that will affect N availability to the crop.

With soil temperatures now in the mid- to upper 60s in central and southern Illinois, the biological processes that convert ammonium to nitrate are gearing up, though they are still only at about half-speed compared to what they will be when soil temperatures reach the upper 70s or lower 80s over the next month. Conversion to nitrate only means increased potential for loss; loss still requires enough water to move the N out of the rooting zone.

In the more saturated parts of the state, denitrification – the conversion of nitrate to gaseous forms of N – may be causing some loss of N at this point, though we wouldn’t expect losses from this to be as large as they would be with warmer soils. The length of time water stands on the soil will directly affect how much N is lost.

Even with the movement of some N to more than two feet deep and some N loss from the field altogether, it is difficult to predict that we’ll see N deficiency if normal N fertilization practices are used. As mentioned above, N produced from soil organic matter is an important source of N for the crop. We normally expect about 2 percent of the N contained in soil organic matter to be mineralized over the course of the season. Soil organic matter is about 5 percent N, so a soil with 3 percent organic matter in the top foot (about 4 million lb. of soil) contains about 6,000 lb of organic N. At 2 percent, about 120 lb of N would mineralize in a season.

Mineralization occurs whenever there are favorable temperatures and moisture conditions. So it is a source of N for the crop throughout the season, but the mineralization rate doesn’t keep up with the N needs of the crop once rapid uptake begins. In fields that were in corn the previous year we also expect some of the soil N, including mineralized N, to be tied up as microbes continue to break down old stalk and root tissue for some weeks after soil temperatures warm up.

We would expect the N uptake rate to exceed the rate of mineralization at some point in vegetative growth, perhaps at about stage V6 or V7. With late planting into warmer soils this year, mineralization might have gotten a little bit of a “running start” so might provide enough N to carry the crop a little longer. Warm temperatures also tend to bring the crop to each vegetative stage with a little less dry weight, so N demands may be lowered slightly during plant development. On the other hand, rainfall can move some mineralized N deeper and out of reach of the roots.

Another important factor in determining how much N will be available to the crop is how well the crop will be supplied with water. With the rush to plant this year, some fields were planted before the soils were as dry as would have been ideal. This means that there was some soil compaction, and possibly some sidewall smearing. The fact that it has not dried out much since planting means that nodal root penetration is not likely to be a problem this year like it was in 2012, however.

Wet soils will help roots proliferate well enough, but they will tend to stay shallow due to higher oxygen levels at the surface. Nitrogen moves to roots with water and is taken up as water enters the plant. Under wet conditions, water uptake comes from shallow roots, and N deeper in the soil can remain unavailable. Once the surface starts to dry out, however, roots will grow deeper and water will move towards the roots, carrying N from deeper in the soil.

Movement of N from deeper in the soil under drying conditions could considerably improve the N supply in cases where the N has moved deeper but is still in the soil. How much of this might happen this year depends on the weather in the coming weeks. If we get a stretch of dry weather for a week or so, we can expect rapid root growth with increased soil oxygen. But with soils holding maximum amounts of water now, it could take several weeks of relatively dry weather before water and N start to move up from deeper in the soil. If it stays wet, this might never happen, or at least not in time to stave off N deficiency.

So have we “lost” enough N to justify reapplying some amount, or applying more than we had planned to apply? In parts of western Illinois where May rainfall has been well above normal, losses through tile lines might be considerable, and it may make sense to increase the sidedress rate to replace some of any N previously applied. The replacement rate should be tied to how much of the previously-applied N is likely to be, or to have been, in the nitrate form before rainfall events. The earlier the application and the more N applied as nitrate, the greater the potential for loss up to now. For ammonia applications made in early April, there’s little reason to expect that a lot of N has been lost from the field.

Nitrogen loss is likely to be low or moderate in areas with normal rainfall in May. In these areas, it might be prudent to wait to see what the weather does over the next few weeks before applying additional N to those fields where N went on early. If it dries out and warms up, crop growth should take off and N supply should improve. If it returns to wet weather, especially warm and wet, then some supplemental N might be considered.

In cases where most of the N still needs to be applied, application should be made as soon as possible, with whatever form works best, using normal rates, or even a little less than previously planned. Do not apply solution UAN over the top of the emerged crop, and inject UAN or use urease inhibitor with urea or UAN applied on the surface, especially if the weather is warm and dry at the time of application. Then hope that rainfall returns to normal so the applied N can be taken up and used well by the crop.


Mark Your Calendars for the 2013 AGMasters Conference

The 2013 AGMasters Conference will be held at the i Hotel and Conference Center in Champaign, IL on December 2 and 3. The conference will begin with a morning general program followed with 1 1/2 days of specialized sessions. Participants will be able to pick and choose the sessions of most interest to them. These sessions are designed to encourage interaction between instructors and students and cover a broad range of topics including crop production challenges, soil fertility, water resource management, entomology, plant pathology, weed science, and introductory statistics. Each session is taught twice and is limited to 40 students (per session). Registration for the most popular topics is very competitive. The overall conference is limited to the first 160 registrants. The conference will be pieced together over the summer and registration information will become available by early fall. For now, please add these dates to your calendar and look for more conference information to follow in this Bulletin. Conference co-chairs include Dennis Bowman, Carl Bradley, Aaron Hager, Sandy Osterbur and me, all members of the Crop Sciences Department. As the growing season unfolds, please contact any of us with your suggestions for the 2013 program. We welcome your input.

Mike Gray