NITRATES – A CONCERN IN DROUGHT STRESSED CROPS

            Drought-stressed crops like grain sorghum and corn may result in the accumulation of nitrate at levels that are toxic to livestock.  This may be amplified when high rates of nitrogen fertilizer were applied prior to the stress period.

            Nitrate toxicity is often associated with sorghum hybrids, sudangrass, johnsongrass, sorghumsudan hybrids, corn, and carelessweed (pigweed).  If you produce or plan to use any of these crops for hay, testing for nitrates is strongly recommended when the crop is produced under conditions of moisture stress.      Many samples from the local area have already been sent to the lab and the latest lab results indicate that nitrate levels have been ranging from 0.01 to 1.08, with the average being 0.19 % nitrate.

            Research at the Texas Veterinary Medical Diagnostic Laboratory at Texas A&M University has found that it is safe to feed forage containing up to 1 percent nitrate (on a dry-matter basis) to healthy ruminants.  Forage with a higher percentage of nitrate could be fed if it is ground and mixed with low nitrate forage to reduce the overall nitrate levels to less than 1 percent (dry-matter basis).  Forage containing 0.5 to 1 percent nitrate should not be fed to weakened cattle unless your veterinarian has approved it.  The 1 percent nitrate level assumes that cattle are healthy, well-conditioned, and being fed a high-energy diet.  An online reference regarding Nitrates and Prussic Acid in Forages can be found at the web site; https://agrilifebookstore.org/ by typing E-543.

            If forages contain too much nitrate the animals cannot complete the conversion

process to protein and nitrite levels build up.  The result is the formation of methhemoglobin which can cause an animal to die from asphyxiation, or lack of oxygen.  The animal’s blood turns brown instead of the normal bright red.

            When sampling for nitrates, it is important to remember that nitrate accumulates in the lower stem, and the least is found in the leaves.  If sampling corn, grain sorghum, and sorghum-sudangrass standing forage, create a composite sample from plant parts taken from at least 10 to 15 areas with the same fertility and moisture conditions.  Do not mix plants from “good” and “bad” parts of the field. Create different composite samples for these areas.  Ship samples to the laboratory in clean paper sacks. Do not use plastic bags because the high moisture content will cause the samples to mold, which interferes with the nitrate analysis.

            To sample corn, grain sorghum and sorghum-sudangrass in bales, the bale must be split open and the lower stems of individual plants must be collected. If the bale is going to be ground before it is going to be fed, then representative core samples can be taken with a bale probe.

Samples can be submitted to the Texas AgriLife Extension Service Soil, Water,

and Forage Testing Laboratory. Submittal forms are available online at http://soiltesting.tamu.edu

Damaged Sorghum Heads - Stress Related

 The drought of 2011 has continued into 2012 in South Texas and the lack of soil moisture along with above normal temperatures has resulted in some significant stress on some grain sorghum plants.  As a result seed formation was hampered as seen in the attached photo and is likely related to stress in the sorghum plant. This symptom is  consistent with heat stress during panicle (head) formation while the developing heads are still wrapped up in the stalk surrounded by leaf sheaths.  Most fields did not have excessive damage from this "heat blasting", so if 20% of the field was impacted, with 20% of the head affected, one would expect about a 4% grain loss.  A greater grain loss will occur from simply a lack of soil moisture.

PREPARING GRAIN SORGHUM FOR HARVEST

            Dry and hot conditions have promoted early maturity of grain sorghum and as a result  sorghum hybrids have accumulated enough growing degree units to reach “black layer” or physiological maturity.  Thus harvest time is beginning here in the Coastal Bend, that is if you were fortunate enough to get some timely rain.  Some folks were not so lucky in the rainfall department and as a result, sorghum has been declared a total loss and is being cut for hay or plowed under.

            Here are some tips to prepare grain for harvest as grain sorghum growers can obtain higher prices if their sorghum meets market moisture specifications.  To help meet those specifications, growers may apply harvest aids.

            When harvest aids are applied properly, harvest is made more efficient and combining is faster, with no reductions in grain weight. Grain from the entire field will have a uniform moisture content, resulting in few “hot” loads and price discounts.  To keep the grain from losing weight, it is critical that growers apply the harvest aids at the proper time, which is once the grain reaches physiological maturity and the average grain moisture drops below 30 percent. If harvest aids are applied prematurely, both yields and grain quality will be reduced.

            Physiological maturity can be determined by sampling grain with a grain moister tester and also looking at the kernels for a black layer which indicates that the crop is mature.  Pictures of a black layer can be found in a publication L-5435 - “Harvest Aids in Sorghum,” that can be found at the following web address: http://publications.tamu.edu/CORN_SORGHUM/PUB_Harvest%20Aids%20in%20Sorghum.pdf

            There are only two products labeled for use as harvest aids: sodium chlorate (containing a fire retardant) and glyphosate. For satisfactory results, good spray coverage is needed for both products. Eight to 10 gallons per acre (GPA) of solution by ground or 3 to 5 GPA by air is recommended.

            Sodium chlorate, which can cause fires if it is not mixed with a retardant, is a chemically active salt that desiccates the plant. Growers may apply up to 6 pounds per acre. This product is sold under various trade names and concentrations of active ingredient per gallon. For good desiccation, the weather must be hot and dry.

            Glyphosate, a common herbicide, will kill the plant. Producers may make a single application of up to 2 quarts per acre.  Since formulations can vary, be sure to check the product label for correct rates per acre.  Once it is applied to sorghum, the plants move the glyphosate to the growing point over a 5- to 6- day period. Weeds that are actively growing when the product is applied will also be destroyed.  Use a sprayable grade of ammonium sulfate at a rate of 17 pounds/100 gallons of water or a prepackaged sulfate formulation to condition the water and improve effectiveness. There is a 7-day waiting interval between application and harvest. The crop is usually ready seven to 10 days after application.

            Growers should only treat those acres that can be harvested within 10 days to two weeks after application.  Weather and storms in the Gulf should also be a consideration.     To avoid any premature lodging, inspect the field before the application. Look for stalk degradation from diseases such as charcoal rot, which will cause premature lodging during natural dry down or after harvest aids are applied.  Picture may be found on web at  http://www.ksre.ksu.edu/library/plant2/L741.pdf

Conditions under which charcoal rot is favored include stressful hot soil temperatures and low soil moisture during the post-flowering period. Host plants are usually in the early-milk to late-dough stage when infection occurs. The fungus is common and widely distributed in nature. To check the plants before treatment, split the stalk lengthwise and look for a hollow stem or black rot just above the root crown. If the stalk is unhealthy, it will generally fall, whether or not it has been treated.

    As always when using farm chemicals, read and follow label directions carefully before applying the product.