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A Newsletter For New York Field Crops & Soils                   Vol.19, No.3, May-June, 2009

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Consider Resistance to Soilborne Viruses When Choosing a Winter Wheat Variety  
Gary C. Bergstrom, Department of Plant Pathology and Plant-Microbe Biology, Mark E. Sorrells, Department of Plant Breeding and Genetics, Cornell University 

Soilborne virus infection can reduce the yield of susceptible winter wheats by 30% or more under conditions favorable for disease development – and producers are seldom aware of these losses. Resistance exists among varieties adapted to New York State. Therefore, resistance to soilborne viruses should be an important criterion when selecting a winter wheat variety in New York. Two soilborne viruses occur in New York; each is transmitted by a soil-inhabiting protozoan and persists in the soil for many years between wheat crops. Wheat spindle streak mosaic virus (WSSMV) occurs in most soils in the state where wheat has once been grown. Soilborne wheat mosaic virus (SBWMV) has been confirmed in recent years in certain fields in the southern Finger Lakes region, but it is expected to spread to other areas with the movement of infested soil on farm equipment and vehicle tires. It is important to know whether SBWMV occurs on your farm or in your local area.

Contrasting the two viruses
Moist soil conditions in fall, soon after wheat emergence, favor infection of wheat plants by SBWMV and WSSMV. Plants remain infected over the winter dormant period but do not show typical leaf symptoms until spring following a number of weeks of cool weather. Soilborne wheat mosaic (SBWM) typically shows up in April with blotchy mosaic symptoms that differ by wheat variety (Fig. 1A). Some susceptible varieties can also show pronounced stunting due to SBWMV. Wheat spindle streak mosaic (WSSM) shows up typically in late April or early May and is recognized by its characteristic long, light green, spindle-shaped streaks with dark centers (Fig. 1B). Symptoms fail to develop on new leaves that emerge when average daily temperatures exceed 70 F for SBWM or 60 F for WSSM, though symptoms can reinitiate at later growth stages if persistent cool conditions occur during stem elongation and head emergence. Wheat spindle streak mosaic symptom development is extremely sensitive to warm temperatures such that we have seen very little disease in years with high temperatures in early spring. 

Resistance assessment
Resistance in a wheat variety to a soilborne virus is not an absolute trait. Even our most resistant varieties can exhibit a small percentage of plants with full-blown symptoms in a year/environment conducive for disease. We assess the percentage of plants that show typical virus symptoms (backed up by laboratory virus assay) for each variety in comparison to check cultivars that we have assessed over many years. Based on multiple year observations, we then designate a variety as resistant, moderately resistant, moderately susceptible, or susceptible to each virus in comparison with known checks. Though both viruses may infect plants in a production field, we have the advantage of long-term screening nurseries with a history of only WSSMV (in Ithaca, NY) and a history of predominant infestation by SBWMV (in Trumansburg, NY, see Fig. 2). Consensus variety ratings are presented in Table 1. We included only those varieties that we tested for multiple seasons. Information may be available from seed suppliers for varieties not included in our virus nurseries. We recommend that New York producers select wheat varieties with at least a moderate level of resistance to WSSMV (statewide) and to SBWMV (in areas with a history of this virus).   

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Field-Scale Studies Comparing the Base Genetics of Corn Hybrids with Double and Triple-Stacked Hybrids.
Bill Cox¹, Phil Atkins¹, Elson Shields², and Gary Bergstrom³, Dept. of Crop & Soil Sciences¹, Dept. of Entomology², Dept. of Plant Pathology & Plant-Microbe Biology³, Cornell University

The first genetically engineered (GE) corn hybrid, commercialized in 1996, expressed a Bt toxin that targeted European corn borer. A hybrid with resistance to Roundup was released in 1997, followed by a hybrid with resistance to the herbicide, glufosinate, in 1998. Another Bt hybrid to control corn rootworm was introduced in 2003.

Adoption rates of Roundup Ready corn were initially slow as indicated by only 7% acreage in the USA in 2001 (Table 1). Early-season weed pressure before Roundup application can significantly reduce yields so growers were probably reluctant to adopt Roundup Ready corn. European corn borer, a key pest in the Western Corn Belt and the Southeast, is an occasional pest in Eastern and Northern regions so the adoption was low in those states, resulting in only 18% adoption of Bt corn in the USA by 2001 (Table 1).

Corn rootworm, however, is a destructive and consistent pest in continuous corn fields in all regions. Consequently, Bt corn for corn rootworm control contributed greatly to increased acreage of GE corn since its 2003 introduction because growers preferred Bt corn over use of soil or seed-applied insecticides. In 2002, stacked hybrids (containing the Bt genes for corn borer and/or corn rootworm and/or the glyphosate-resistant gene) were introduced further increasing the acreage of GE corn. Increased adoption of stacked hybrids (2 percent in 2002 and 40 percent in 2008, Table 1) reflects grower preference for these traits as well as increasing lack of availability of non-stacked hybrids. By 2008, 80 percent of U.S. corn acreage was planted with some type of GE hybrid; half of these acres were stacked hybrids (Table 1).

As with most of the USA, GE corn dominates the market in NY (acreage not available). In NY, however, European corn borer is an occasional pest and western corn rootworm does not typically result in such severe damage as it does in the Midwest USA. With that in mind, we evaluated field-scale studies on four farms in NY in continuous corn and corn-soybean rotations comparing the base genetics of two hybrids (37F73 from Pioneer and DKC52-62 from Dekalb) with double-stacked (37F75 and DKC52-63) and triple-stacked (37F76 and DKC52-59) counterparts.

When averaged across four farms and two hybrids, triple-stacked hybrids (Bt endotoxin for both European corn borer and western corn rootworm and the Roundup Ready trait) compared with the base genetics yielded 6 bu/acre higher in 2007 and 3 bu/acre higher in 2008 in continuous corn (Table 2). Despite low corn rootworm pressure at all sites (data not shown), triple-stacked hybrids yielded greater on one farm in 2007 and on one farm in 2008. Nevertheless, when averaged across years and sites, triple-stacked hybrids yielded only 2.7% greater than the base genetics. Likewise, double-stacked hybrids yielded greater on one farm in 2007 and in two farms in 2008 with a 2.7% yield advantage over the base genetics. This suggests that most of the yield increase came from control of European corn borer as opposed to corn rootworm in continuous corn. This was particularly true at the Onondaga site in 2008 where significant corn borer damage and lodging occurred in the base genetics (data not shown).

When averaged across four farms and two hybrids, double-stacked hybrids did not yield higher than the base genetics in either year of the study and only on one farm in 2007 in the corn-soybean rotation (Table 3). Almost no lodging and corn borer pressure was evident on any farms in the corn-soybean rotation (or continuous corn) in 2007 (data not shown). In 2008, significant lodging was observed on two farms but lodging appeared to be more associated with anthracnose stalk rot as opposed to corn borer damage at one site, resulting in some lodging in the Bt hybrids. Consequently, the 3 bu/acre yield increase was not significant.

Grain moistures ran higher in the GE hybrids compared with the base genetics in continuous corn and the corn-soybean rotation in 2007 and 2008 (Table 4 and Table 5). Differences in grain moistures between GE hybrids and the base genetics were more pronounced in 2008 when dry-down was a slow-extended process. Growers who have challenges in dry-down of grain because of their location should consider selecting a hybrid 3-5 days earlier in maturity when selecting GE hybrids.

Conclusion
We did note improved corn rootworm ratings with triple-stacked hybrids compared to the base genetics but root damage ratings were mostly less than 0.35 on all farms, indicating almost no rootworm damage in our studies in 2007 and 2008 (data not shown). Although rootworm can result in significant damage to corn fields in NY, the overall occurrence and degree of damage on NY farms seems to be less than in the Midwest USA. Likewise, we did note less lodging with double and triple-stacked hybrids but lodging was very limited in six of the eight tests across the two years. Corn borer is an occasional pest in NY so damage shows significant location and yearly variability. On the one farm in 2008 where corn borer and lodging was significant, the Bt hybrids had less lodging, which greatly improved harvesting efficiency. We will conduct an economic analysis on the data (yield, hybrid price, and grain moisture) and will present the results in a future news article.

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Weed Management Challenges During Establishment of Warm-Season Perennial Grasses
Russell R. Hahn and Paul J. Stachowski, Dept. of Crop & Soil Sciences, and Hilary S. Mayton and Julie L. Hansen, Dept. of Plant Breeding & Genetics, Cornell University

Interest in growing switchgrass and other warm-season perennial grasses (WSPGs) for biomass has prompted a need for weed management guidelines for these grasses. Establishment of WSPGs is challenging due to their inability to compete with weeds during the seeding year. Unfortunately, there are few herbicides registered for use on these grasses during establishment. A review of herbicide labels reveals that registrations of herbicides that might be useful in this situation are limited to use on Conservation Reserve Program (CRP) acres and/or for use in Midwest and Great Plains states. None of the labels include the establishment and production of WSPGs for biomass production.

In 2007, with funding from the New York Farm Viability Institute and as part of a long-term project, several WSPG trials were established across NY State. Initial observations from the first year of this project revealed a need for weed management information and herbicide registrations for these situations. A related project, also funded by the NYFVI was initiated in 2008 to collect data on the effect of selected herbicides on the growth and development of five WSPG species. Results of this trial will hopefully provide information that will support requests for Section 24(c) Special Local Need Labels for some of the herbicides, or eventually, full EPA and DEC registrations for herbicides that prove safe on the WSPGs and that have potential to suppress weeds during WSPG establishment.

Trial Details
Five WSPG species were planted on June 3, 2008 at the Musgrave Research Farm near Aurora, NY. The species were big bluestem var. Niagara, coastal panicgrass var. Atlantic, switchgrass var. Cave-in-Rock, indiangrass var. Nebraska 54, and eastern gamagrass var. Pete. Preemergence (PRE) AAtrex 4L (atrazine) applications were made on June 10. Before the WSPGs reached a stage of development for postemergence (POST) herbicide application (generally 3- to 4-leaf stage), annual weed growth was such that the entire plot area was flail mowed on July 21 prior to POST herbicide application on August 5. Visual WSPG injury ratings (stand/vigor) were made 2 weeks after the POST applications except for gamagrass. Gamagrass emergence and establishment was too erratic for meaningful injury evaluations. Herbicides selected for the trial had an EPA registration for one or more of these grasses somewhere in the U.S., but not in NY State. Herbicide treatments and injury ratings are shown in Table 1.

Injury Evaluations
The PRE applications of AAtrex 4L caused 30% or less injury to each of the four WSPGs evaluated and there were no differences in WSPG response between the 1 and 2 qt/A rates (Table 1). While injury to big bluestem and indiangrass ranged from 25 to 30%, the two Panicum species, switchgrass and coastal panicgrass showed no significant injury from these treatments. On the other hand, POST application of 1.5 qt/A of AAtrex 4L with 1.25% (V/V) of crop oil concentrate caused stand and/or growth reduction of all four species, though none greater than 33% injury.

Several of the other POST applications produced what was interpreted as acceptable levels of injury on all four species. These included three sulfonylurea herbicides, Permit (halosulfuron), Cimarron (metsulfuron), and Outrider (sulfosulfuron). The one exception to this observation was the 45% injury rating from Outrider on indiangrass (Table 1). Of the two imidazolinone herbicides, Pursuit DG (imazethapyr) and Plateau (imazapic), Pursuit DG was especially injurious (65%) to switchgrass and Plateau was quite injurious to both switchgrass and coastal panicgrass (~80%). Finally, Paramount (quinclorac), which has activity against broadleaf and grass weeds, resulted in 26% or less injury to each of these grasses. These WSPG plots will be harvested in the fall of 2009 to determine which of these herbicides had an effect on yield in the first harvest year. In addition, these forages will be analyzed for bioenergy quality.

Registration Effort
Efforts have been initiated to obtain a Section 24(c) Special Local Needs Label for PRE and POST applications of AAtrex for use during establishment of switchgrass in NY State. Since PRE AAtrex applications have activity against a broad spectrum of annual weeds, except for triazine-resistant biotypes of several weeds, and appear to be very safe on switchgrass, this registration would provide a valuable weed management tool during the slow emergence and establishment of this WSPG. In the meantime, clipping annual weed growth during this challenging establishment phase can be a useful practice.

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An Early Warning System for Soybean Rust

Gary C. Bergstrom and Mary E. McKellar, Department of Plant Pathology and Plant-Microbe Biology, Cornell University

Since 2005, New York has participated in the national surveillance initiative (now called Soybean Rust ipmPIPE) to detect soybean rust and provide an early warning to farmers in time to apply protective fungicides if warranted. Fortunately, soybean rust has not yet progressed into New York State by the end of a soybean growing season. But it has come close – southwestern Ontario in fall 2007 and southeastern Maryland in fall 2008 (Figure 1). The soybean rust fungus Phakopsora pachyrhyzi can overwinter on living legume hosts (including kudzu vines) in frost-free areas of Florida, south Texas, Mexico, Caribbean islands, and, in some years, along coastal areas of Alabama, Mississippi, and Louisiana, or even further north. Spore inoculum is increased thousands-fold on infected soybean in southern states and spore clouds can potentially be transported long distances in the atmosphere, especially in storm systems, and the spores may then be deposited on soybean leaves in northern states. Drought in the southeastern U.S. has limited the early development of rust on soybean over the past four years. That pattern may be changing as several southern states have reported normal to excessive rainfall this spring. Rust was detected in sentinel soybean plots in Alabama and Louisiana in early June 2009 – more than three weeks earlier than the previous first annual detection in these states. While it is much too soon to make any reliable predictions, there are early indications that soybean rust could spread earlier and further and be more severe in 2009. Thus New York soybean producers have a stake in the continuing early detection and warning system for soybean rust.

Sentinel Detection Network in 2009
The intensity of rust scouting activity in 2009 is apportioned according to three tiers of states (Figure 2). Tier 1 states along the Gulf Coast and in the Southeast represent only 4% of the U.S. soybean crop, but they are most critical to the early warning system. Major scouting efforts in Tier 1 states begin during the winter and continue through the early spring focusing on the detection of soybean rust on kudzu which provides spores for the ensuing annual epidemic on soybean. Soybean sentinel plots will also be scouted throughout the extended growing season in the southern states. Tier 2 states represent 69% of the U.S. soybean crop. Cooperators in these states will establish at least 10 sentinel soybean observation sites per state and they will also conduct some mobile scouting when spore transport has been predicted. The Tier 3 northern states (including New York) represent 27% of the U.S. soybean crop and rust may or may not occur in these states in any particular growing season. Cooperators in the Tier 3 states are prepared to perform mobile scouting as warranted in late summer and some also will monitor a small number of sentinel soybean plots. In New York State, we will take a two-pronged approach to rust scouting in 2009. Sentinel fields of soybean in Cayuga, Columbia, Jefferson, Livingston, Seneca, and Wayne Counties will be scouted regularly by cooperators in Cornell Cooperative Extension from the onset of flowering through pod-filling (Figure 3). Leaf samples will be sent to the Cornell Plant Disease Diagnostic Clinic for visual identification and molecular confirmation of soybean rust. Also, depending on national spore movement advisories, we are prepared to conduct roaming regional surveys of production soybean fields in late summer and fall. Beyond these planned scouting activities, we encourage all people involved with soybean production in New York to be on the lookout for soybean rust this summer and to contact the Diagnostic Clinic (phone: 607-255-7850) if you see symptoms or signs on soybean that you suspect are rust.  

Information for New York Producers
The New York Soybean Rust Information Center (http://www.ppath.cornell.edu/soybeanrustny/default.htm) is a one-stop shop for up-to-date information on soybean rust for New Yorkers (Figure 4). Please bookmark this site for frequent checking during the growing season. The site features regular updates on the status of soybean rust in the U.S., visual aids for identification of soybean rust and diseases that can be confused with it, guidelines for control of rust with fungicides registered in New York, and links to other soybean rust sites.

The Future of Surveillance and Rust Management
Over the past five years, many millions of dollars have been saved by soybean producers who decided not to apply fungicides in response to information from the ipmPIPE that projected low risk of soybean rust. In some southern locations, growers prevented crop loss by spraying recommended fungicides where there was a projected risk of soybean rust. Despite the incredible success of the national monitoring network, it is very expensive to maintain in terms of federal government support, state and regional commodity funding, and contributed person hours by many local cooperators. Researchers are investigating ways to reduce the intensity of scouting, and to employ atmospheric spore sampling and other monitoring and predictive tools that might reduce the costs in future years, while not reducing the accuracy and usefulness of the risk forecasts. Our 2009 scouting program in New York is already reduced from the 20 sentinel plots we scouted in 2007 and the 13 in 2008. We welcome suggestions from New York soybean producers as to the value of the scouting program and what information they'd like to have about soybean rust in future years. One very encouraging development is that the first commercial soybean varieties with resistance to soybean rust are anticipated to become available in 2012, with many more to follow in subsequent years.

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Evaluation of ISNT-Based Nitrogen Management for Multi-Year Corn Sites

Quirine M. Ketterings, Joe Lawrence, Greg Godwin, Nancy Glazier, Pete Barney, and Karl J. Czymmek

Introduction
With high fertilizer and low milk prices and greater awareness of the environmental impact of over-application of nitrogen (N) to corn, many producers are interested in tools that help identify sites that don't need extra fertilizer N. Several extension educators and farmers worked together with campus staff in the Nutrient Management Spear and PRO-DAIRY Programs over the past 6 years (67 NY field trials to date) to compare the effectiveness of four soil and two plant tests in identifying fields that do not need extra N. The most promising tests were the Illinois Soil Nitrogen Test (ISNT) and the late-season stalk nitrate test.

In this What's Cropping Up? article we report on evaluation of the Illinois Soil Nitrogen Test (ISNT) for N management of multi-year (3-4 year) studies on two New York farms. Specific questions were "How often does an ISNT sample need to be taken?" and "How big can the fertilizer savings be?".

Earlier Studies
It is well documented that soil N tends to be a main source of N for corn. It is therefore important to get a better idea of the inherent soil N supply in order to fine-tune N management and reduce the risk of over-application of fertilizer. The ISNT estimates a labile organic N fraction, potentially mineralizable during the growing season(s) following sampling (Khan et al. 2001).

The ISNT-N result alone could not be calibrated for the range of New York state growing conditions and soils. However, when combined with organic matter estimates derived from loss-on-ignition (LOI; 2 hrs at 500^oC and corrected for initial moisture), the ISNTxLOI combination was effective in separating fields that needed extra N from those that had sufficient soil organic N supply to meet crop needs (Klapwyk and Ketterings, 2006). To ensure this interpretation could be used for corn in rotation, we conducted an additional 34 N-rate studies, most on commercial farms. This dataset confirmed that 1^st year corn after sod rotation does not need to be fertilized beyond 20-30 lbs N/acre starter (Lawrence et al., 2008), while the ISNTxLOI calibration was 83% accurate in separating responsive from non-responsive sites for 2^nd or higher year corn (Lawrence et al., 2009). This percentage is similar to the accuracy of the pre-sidedress nitrate test (PSNT) in ideal sampling conditions but greatly exceeded the accuracy of the PSNT in more challenging (wet) spring seasons (the PSNT was less than 50% accurate in our most recent study years). In other words, the overall performance of the ISNTxLOI matches the best performance of the PSNT. In addition, the ISNT is more user-friendly than the PSNT as it can be performed on standard soil samples rather than requiring 12 inch cores. Since the test estimates soil N supply potential, current year manure credits and sod N credits need to be taken into account in addition to the ISNT-N values to determine if extra N is needed. And, because the ISNT procedure measures ammonium-N in addition to the labile organic-N fraction, samples should be taken outside the window of elevated ammonium-N levels created by recent manure application or sod kill (i.e. not within five weeks after manure application of sod kill). Samples can be taken any other time of the year. Also, "potential soil N supply" means that if mineralization conditions are not good (e.g. during drought) the full potential to mineralize this soil organic N (as well as other organic N sources) is not realized.

Sample Once in Two Years or Three?
One question that arose from these studies was: "How quickly do ISNT-N values change over time?" Or in other words, "How often should I sample for ISNT?" The project included ten fields for which ISNT-N was measured two years in a row. A comparison of the data in years 1 and 2 showed that ISNT values were stable over two years (no manure was added to these plots during the study). What about sampling every 3 years as currently required for standard soil testing for regulated farms?

Two non-manured farm fields were studied for 3 or more years, one in Northern NY (3 years) and one in Western NY (4 years). The ISNT-N values of the Northern NY site remained constant during the 3 years (363, 360, and 363 ppm in 2005, 2006 and 2007, respectively), suggesting that sampling once in 3 years might be sufficient. For the Western NY location, ISNT-N was constant in years 1 and 2 but lower in years 3 and 4 (Figure 1). All four years were correctly predicted (no yield response to extra N in years 1-3 and a yield response in year 4), but the decline in ISNT-N after two years at the Western NY location suggests samples should be taken once in 2 years rather than once in 3 years (at least for fields where no manure was added). Earlier research showed that manure application does result in an increase in ISNT-N over time, consistent with current organic N credits from manure.

How Big Are the Savings?
The Northern and Western New York sites showed something of great economic interest: no need for extra N for two to three years after sod turnover. For the Western New York site, yields in the first three years in the control plots (starter N only) were 22.3, 29.0 and 19.0 tons of silage per acre (35% DM). The Cornell soils database lists a yield potential of 23 tons of silage/acre which in years 2 and 3 after sod turnover would have resulted in an N recommendation of 110 lbs N/acre and 125 lbs N/acre, respectively. For the Northern New York site yields of the control plots (starter N only) were 26.0, 22.2 and 22.5 tons/acre for years 1, 2 and 3, respectively. Cornell yield potential for this site is 21.3 tons/acre (35% DM) and the recommendations for this site would have been 100 lbs N/acre (year 2) and 125 lbs N/acre (year 3). So, implementation of ISNT-based management would have, with current fertilizer prices, resulted in about $150 to $160 per acre saving in fertilizer N costs (years 2 and 3 combined) for both of these farms. Add to this the actual application costs and it becomes clear that with current N fertilizer prices, the N savings for these two non-responsive fields could have been substantial, a great return for the investment of the soil sampling and analysis.

Remaining Questions
In our research trials, we had a number of sites whose ISNT value was within 10% of the critical value. Although our field trials show results to be accurate even if the plot ISNT is within 5% of the critical value, reality is that in our field plots, we sample at greater density than is usually done for the average production field. Work is currently ongoing to estimate the number of samples needed to obtain values within 10% of the field mean. We will report on the results of this study in a future What's Cropping Up? article. Keep in mind: no extra N is needed for first year corn fields after a good sod, and don't sample within 5 weeks of manure application for most accurate predictions of soil N supply potential. Also, ISNT-based guidance should not be confused with the official Cornell fertilizer guidelines for corn at this time but given the current economic situation, it might be worth doing an ISNT test to determine priority fields for fertilizer N applications.

References
1. Khan, S.A., R.L. Mulvaney and R.G. Hoeft (2001). A simple soil test for detecting sites that are responsive to nitrogen fertilizer. Soil Sci. Soc. Am. J. 65:1751-1760.
2. Klapwyk, J.H. and Q.M. Ketterings (2006). Soil tests for predicting corn response to nitrogen fertilizer in New York. Agron. J. 98:675-681.
3. Lawrence, J.R., Q.M. Ketterings and J.H. Cherney (2008). Effect of nitrogen application on yield and quality of first year corn. Agron. J. 100(1): 73-79.
4. Lawrence, J.R., Q.M. Ketterings, M.G. Goler, J.H. Cherney, W.J. Cox and K.J. Czymmek (2009). Accuracy of the Illinois Soil Nitrogen Test (ISNT) in predicting N responsiveness of corn in rotation. Soil Sci. Soc. Am. J. 73(1): 303-311.

For More Information
For more information on the project and other work, see our project website: http://nmsp.css.cornell.edu/projects/Nitrogenforcorn.asp. You will also find a downloadable spreadsheet on this site that graphically shows the results of the ISNT test.

_{Nutrient Management Spear Program http://nmsp.css.cornell.edu/}  

_{A collaboration among the Department of Animal Science, Pro-Dairy, and Cornell Cooperative Extension.}

 

 

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Impact of Clover Incorporation and Ammonium Nitrate Sidedressing on Ammonium, Nitrate and Illinois Soil Nitrogen Test Dynamics over Time

Greg Godwin, Quirine M. Ketterings, Charles L. Mohler, Brian Caldwell, Karl Czymmek

Introduction
The Illinois Soil Nitrogen Test (ISNT) is a new soil organic N test developed by Kahn et al. (2001) that has been evaluated for use in New York corn systems over the past 6 years. The ISNT, conducted in enclosed incubation units in the laboratory (Klapwyk et al., 2005), was shown to be an accurate predictor of corn N responsiveness for 34 on-farm trials conducted in New York State if the test results were used in conjunction with loss-on-ignition (LOI) organic matter (Klapwyk and Ketterings, 2006). The test reflects past manure N credits but samples should not be taken within 5 weeks after manure application (Klapwyk et al., 2006) to isolate past manure additions and background soil N supply from ammonium N credits associated with just-applied manure. In 2005-2008, an additional 34 N-rate studies were conducted throughout New York State (mostly on-farm trials) to determine the effectiveness of the ISNT and LOI combination in identifying sites that did not need extra N beyond a small (less than 30 lbs N/acre) banded starter. These studies indicated (1) 83% success rate for the test for corn two or more years after alfalfa (Lawrence et al., 2009), and (2) potential for substantial savings in N fertilizer costs for farms with organic N sources. Corn following alfalfa/grass plowdown did not respond to extra N (Lawrence et al., 2008) and ISNT samples taken at sidedress time did not reflect the nitrate-N pool released from sod decomposition (Lawrence et al., 2009). These results suggest that for ISNT results to accurately reflect soil N supply, samples should not be taken within 5 weeks of sod turnover or manure application.

In this study we addressed the question: How do clover plowdown and sidedressing of ammonium nitrate influence ISNT-N results?

Methods
We monitored ISNT-N, ammonium-N and nitrate-N levels on a weekly basis under two contrasting management systems within the "Organic Grain Cropping Systems Experiment" initiated at the Aurora Research Farm in 2005. As part of this experiment, five fertility treatments were implemented in 2005 with two entry points for a soybean-spelt/red clover-corn rotation (http://www.organic.cornell.edu/ocs/grain/index.html). The corn years in the following two systems were sampled in 2007 and 2008:

• System 2: Organic - organically-managed corn planted after one year old (cover crop) clover plowdown.
• System 5: Conventional - conventionally managed corn (starter plus sidedress N); no clover plowdown.

Actual fertility amendments and their date of application are shown in Table 1. The conventional treatment was separated from the randomized block design for the other treatments. Plots were randomly split into two rotation entry points, so that one half of each plot was a year behind in the crop rotation sequence. The plots that were sampled for N dynamics were part of Entry Point A in 2007 and Entry Point B in 2008.

Prior to plowing, we collected samples of above-ground clover biomass in system 2 plots (21 May, 2007 and 21 May 2008). The initial soil sampling round (0-8 inch depth; 12 cores per 120' x 40' plot) occurred prior to plowdown of the clover cover crop on 18 May 2007 and 21 May 2008. The next sampling round occurred at plowdown (22 May 2007 and 22 May 2008) and was followed by 8 additional sampling rounds at weekly intervals thereafter. Corn was planted 23-24 May 2007 and 29 May 2008. The conventional plots were sidedressed 22 June 2007 and 2 July 2008 with 265 lbs/acre of ammonium nitrate (34-0-0). The plots in system 2 received 380 lbs of a dry organic starter fertilizer (2-4-2). The corn in the conventional system was planted with 240 lbs/acre of 10-20-20 starter.

Soil samples were analyzed for ISNT-N in the Cornell Nutrient Management Spear Program (NMSP) laboratory using the enclosed griddle modification of Klapwyk and Ketterings (2005). Soil samples were also analyzed for 2 N KCl extraction of exchangeable nitrate+nitrite and ammonium as described in Mulvaney (1996).

Results and Discussion
In 2007, the clover above-ground dry biomass was 1.6 ton/acre. In 2008, it was 2.4 tons/acre. The year 2007 was a drought year with low corn grain yields (87 bu/acre) while 2008 was a wet year with much higher corn grain yields (165 bu/acre).

In the organically managed system, ISNT-N levels remained stable over time with coefficients of variation of 4.3 and 2.2% for 2007 and 2008, respectively. Such stability would suggest lack of variability in ammonium-N over time, which was confirmed by the ammonium-N data for these two years as well (Figure 1). The difference in total clover biomass between the years was consistent with the height of the nitrate-N peak (just over 60 mg/kg in 2007 versus almost 90 mg/kg in 2008). Clover incorporation increased soil nitrate-N levels over time with the greatest increase occurring after week 3. Peaks in nitrate-N were measured in week 5 showing that the timing of nitrate-N release from clover was very well aligned with the period of highest corn N needs. With weekly sampling, we were unable to detect an accumulation of ammonium-N. These results suggest that for the clover-based system, timing of ISNT sampling is not restricted (i.e. sampling can occur before or after cover crop termination).

In the conventional systems, sidedressing of ammonium nitrate greatly increased soil nitrate-N levels (large increase in nitrate-N between weeks 4 and 5 in 2007 and weeks 5 and 6 in 2008; Figure 1). The ammonium nitrate addition increased ammonium-N levels for 2-3 weeks and this increase was reflected in ISNT-N values after sidedressing, especially in 2008. For the conventional system, across all sampling points, the ammonium-N and ISNT-N content were positively correlated (P=0.0031) whereas in the organic system, ammonium-N was not correlated to ISNT-N (P=0.2084). This indicates that ISNT-N is not an accurate predictor of soil N supply from mineralization of soil organic matter if samples are taken within 2-3 weeks after addition of an ammonium-containing fertilizer, as at that time, the ISNT-N value reflects both ammonium-N from the fertilizer and soil N supply from mineralization of soil organic matter (Figure 2).

The pre-sidedress nitrate test (PSNT) data for both systems confirm the increase in available N upon incorporation of a clover cover crop; averaged across plots, the PSNT were 20 and 29 ppm where clover had been plowed down in 2007 and 2008, respectively, consistent with the biomass difference between the two years. Both years, the average PSNT for the conventionally managed plots was 11 ppm. Because of the separation in space of the conventionally managed plots, we can not conclude if PSNT values are statistically different between the two treatments but the weekly sampling and the PSNT results of the clover systems do suggest that the clover supplied a considerable amount of N. Comparison of the organic plots in this study with other organic plots in the same experiment that received 1900 lb/acre of 4.0-5.2-2.4 poultry manure compost in addition to the plowed down clover showed no yield increase with compost addition. This suggests that the nitrate-N released from clover decomposition was sufficient to meet the needs of the corn in both years.

Preliminary Observations
Clover incorporation greatly increased the amount of available N for the following crop. Decomposition of the clover resulted in nitrate peaks 5-6 weeks after incorporation, well-aligned with N needs of the corn and showing that clover plowdown is an excellent choice for providing N to corn in organic and conventional production systems. Clover decomposition did not result in ammonium-N accumulation. In contrast, the ammonium-containing fertilizer did increase ammonium-N levels for 2-3 weeks. This increase was measured by the ISNT procedure indicating that ISNT-N results of samples taken within 2-3 weeks after addition of an ammonium containing fertilizer will not reflect soil N supply from soil organic matter only. This study needs to be duplicated at other locations but our preliminary observations are that in cropping systems where N fertility is derived from a clover cover crop, ISNT sampling is not restricted in time, whereas sampling within 2-3 weeks after addition of an ammonium containing fertilizer should be avoided for accurate interpretations of soil N supply with the ISNT.

References
1. Khan, S.A., R.L. Mulvaney and R.G. Hoeft (2001). A simple soil test for detecting sites that are responsive to nitrogen fertilizer. Soil Sci. Soc. Am. J. 65:1751-1760.
2. Klapwyk, J.H., and Q.M. Ketterings (2005). Reducing laboratory variability of the Illinois soil N test with enclosed griddles. Soil Sci. Soc. Am. J. 69: 1129-1134.
3. Klapwyk, J.H. and Q.M. Ketterings (2006). Soil tests for predicting corn response to nitrogen fertilizer in New York. Agron. J. 98:675-681.
4. Klapwyk, J.H., Q.M. Ketterings, G.S. Godwin, and D. Wang (2006). Response of the Illinois soil nitrogen test to liquid and composted dairy manure applications in a corn agroecosystem. Can. J. Soil Sci. 86:655-663.
5. Lawrence, J.R., Q.M. Ketterings and J.H. Cherney (2008). Effect of nitrogen application on yield and quality of first year corn. Agron. J. 100(1): 73-79.
6. Lawrence, J.R., Q.M. Ketterings, M.G. Goler, J.H. Cherney, W.J. Cox and K.J. Czymmek (2009). Accuracy of the Illinois Soil Nitrogen Test (ISNT) in predicting N responsiveness of corn in rotation. Soil Sci. Soc. Am. J. 73(1): 303-311.
7. Mulvaney, R.L. (1996). Nitrogen-Inorganic Forms. In Methods of soil analysis. Part-3- Chemical Methods. SSSA, Inc., ASA, Inc. Madison, WI. P. 1123-1184.

For More Information
For more information on the New York State Nitrogen for Corn project and other work, see our project website: http://nmsp.css.cornell.edu/projects/Nitrogenforcorn.asp. You will also find a downloadable spreadsheet on this site that graphically shows the results of the ISNT test. This spreadsheet was recently revised upon suggestions by extension educators, and now includes a multiple field entry form and graph.

 

_{Nutrient Management Spear Program http://nmsp.css.cornell.edu/}  

_{A collaboration among the Department of Animal Science, Pro-Dairy, and Cornell Cooperative Extension.}

 

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Winter Wheat: Reds or Whites? That is the Question!

Margaret Smith, Mark Sorrells, and David Benscher, Dept. of Plant Breeding and Genetics, Cornell University

New York is one of relatively few production areas for soft white winter wheat. The soft whites have both some benefits and some risks associated with their production, so deciding whether to grow a soft white or soft red winter wheat can be a challenge for New York growers. Here, we aim to outline the pros and cons of both the reds and the whites, along with providing the most recent variety testing data for both types.

Both soft red and soft white winter wheat are low to medium in protein content and generally are used for cake and pastry flour. In addition to this use, however, soft white wheat is the market class of choice to produce bran for cereals, due to the light color and preferred flavor of white wheat bran. Consequently, mills pay a premium price for good quality soft white wheat. White wheat straw is also preferred for some uses over straw from red wheat. On the down side, most soft white wheat varieties are more susceptible to pre-harvest sprouting than soft red wheat varieties, and growers can be hit hard by having to sell a sprouted wheat crop for feed rather than food use.

So how do you decide whether to try soft whites and aim for the premium price or choose soft reds instead? As with many choices in the world of agriculture, the risks and benefits are affected by unpredictable circumstances like weather and commodity prices, so it's not straightforward! Understanding more about the nature of the risks and benefits, however, can help in making the best possible choice for your situation.

First, it's important to understand pre-harvest sprouting itself. Pre-harvest sprouting is when seeds germinate while still on the plant, due to exposure to prolonged cool, wet weather at harvest time. When seeds germinate, they use some of the energy reserves stored in the endosperm of the seed to supply the energy needed for early growth of the seedling. Thus, sprouting involves degradation of the starchy endosperm in the wheat kernel, and consequently reduces quality and test weight of the crop. If these reductions are significant, the crop may be marketable only as animal feed, and severe economic losses result. Long-term weather data indicate that in any given year, there is a 75% chance of pre-harvest sprout-inducing rain in New York.

The potential for pre-harvest sprouting is related to wheat kernel color, since the biochemical pathway that leads to compounds causing red kernel color also produces compounds that slow sprouting (i.e., increase dormancy). Growers should realize, though, that both soft white and soft red wheat will sprout if they are exposed to enough wet conditions at harvest time. So simply growing red wheat will not avoid the potential for losses associated with pre-harvest sprouting. Recent soft white wheat breeding efforts have strongly emphasized resistance to pre-harvest sprouting, by selecting for mechanisms of resistance that are unrelated to the kernel color trait. These efforts have resulted in white wheat varieties with dramatically improved pre-harvest sprouting resistance.

Cornell's small grains breeding program screens thousands of wheat heads every year for pre-harvest sprouting resistance, using a misting system in the greenhouse. This system is illustrated in Figure 1. Wheat heads subjected to this treatment experience much more constant and prolonged moisture than they would be likely to ever encounter in the field. After mist exposure, the heads are rated on a scale from 1 (no sprouting) to 9 (long sprouts on the whole head), as illustrated in Figure 2. This scale indicates which heads can hold out the longest in wet conditions without sprouting – in other words, which are most resistant to pre-harvest sprouting.

Figure 3 shows pre-harvest sprouting scores for a few red and white wheat varieties. As noted above, the red wheats as a group tend to be more resistant to sprouting. But even red wheats do sprout if they stay wet long enough. Cayuga white wheat is just as resistant to pre-harvest sprouting as the red wheat varieties, showing that it is possible to build pre-harvest sprouting resistance into a soft white wheat. The down side to Cayuga is that it is notably lower yielding than the best yielding soft white wheat varieties.

To take into account the whole package, then, growers must consider variety characteristics like pre-harvest sprouting, but of course also yield, test weight, lodging and disease resistance, and milling and baking quality. Cornell's recent field testing data for soft white winter wheat varieties is shown in Table 1 and for soft red winter wheat in Table 2. The soft red winter wheat testing data includes a couple soft white wheat varieties (noted with an asterisk) for comparison purposes. Looking at these two tables, it is clear that the soft white wheat varieties generally yield as well as the soft red wheat varieties, and are comparable in test weight, lodging, heading date, and plant height. All the soft white wheat varieties shown have resistance to spindle streak mosaic virus and a number also are resistant to soil borne mosaic virus. Among the red wheat varieties there are fewer choices with either moderate or good resistance to these viruses. All varieties in both of these tables have acceptable milling and baking quality.

Jensen, a recently released soft white wheat, and the experimental variety NY03180FHB-10, which will be available in the future, both have greatly improved resistance to pre-harvest sprouting. They are not quite as resistant as most of the soft red wheat varieties, but will sprout less readily in the field than other soft white wheat varieties. As an added bonus, both of these varieties have improved Fusarium head blight (or scab) resistance.

So what's the bottom line? Good quality soft white wheat will gain a premium price in the market (recent premium is $0.25/bushel) and white wheat straw also is preferred for some uses. To help in getting good quality grain from a soft white wheat crop, growers should choose varieties with the best available resistance to pre-harvest sprouting and Fusarium head blight. The crop should be watched carefully as it matures so growers can harvest in the most timely manner possible. As always, it's worth spreading your risk. Growing some white wheat and some red would allow both a focus on harvesting the white wheat first and quickly if weather conditions are undesirable at harvest, and would dedicate some acres to a red wheat that will be able to hold out a bit longer in the field without sprouting. Care would need to be taken to avoid mixture of the red in the white wheat, however.

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What's Cropping Up? is a bimonthly newsletter distributed by the Crop and Soil Sciences Department at Cornell University.  The purpose of the newsletter is to provide timely information on field crop production and environmental issues as it relates to New York agriculture.  Articles are regularly contributed by the following departments at Cornell University: Crop and Soil Sciences, Plant Breeding, Animal Science, Plant Pathology, and Entomology. To receive a hard copy, send your name and address to Larissa Smith, 237 Emerson Hall, Cornell University, Ithaca, NY 14853 or lls14@cornell.edu.