In my previous tip I noted the value of existing subsoil (below 6”) nitrate that is readily available to grain sorghum and other crops, which should be fully credited to grain sorghum N requirements nor soil nitrate between 6” and 24” deep. Now for irrigated crop producers, let’s consider the amount of nitrate-N (also expressed as nitrate-nitrogen or NO3-N) that potentially exists in irrigation water. This N—like soil N—should be fully credited to crop production with only a minor exception or two.
For reference read the three-page Extension publication “Nitrates in Irrigation Water: An Asset for Crop Production” (Texas A&M AgriLife Extension Service, E-619, type ‘nitrate’ in the search box at http://agrilifebookstore.org). This recent 2012 document explains the justification for valuing nitrate in irrigation water, which by reducing fertilizer N requirements, can save producers input costs. Most Texas irrigation waters contain 3 to 10 parts per million (ppm) nitrate-N, but some waters are over 20 ppm.
In general, for each 1 ppm of nitrate-N in your irrigation water you are adding 0.23 lbs. of N per acre. A producer who irrigates 12” and has 6 ppm nitrate-N in the water is applying about 14 lbs. of N per acre. For a 6,000 lbs./A yield goal, this level of long-term N concentration is about 12% of your total crop requirement. The cost of N fertilizer, were you to buy it, would currently be about $9/acre for this example, and that does not include application costs.
Across Texas crop consultants, producers, AgriLife staff, etc. are becoming more aware of the potential for accumulating nitrate-nitrogen (NO3-N) in the soil. This nitrogen has value for your sorghum and other crops. “Profile N” is nitrogen accumulating below standard soil sampling depths, most often 6”. This accumulation is due to over fertilization (or underutilization in years when production is sub-par) with N, and the majority of the time producers are not aware of the presence of this N in the soil. Historically this N is not accounted for in supplying crop nutrient requirements, but it should be.
The level of N accumulation can vary greatly due to fertilization practices, downward percolating moisture from rains which carries the soluble and mobile nitrate, soil type, etc. Sometimes substantial N is found even below 3’ in the soil, but only deep rooted crops can tap that N. Texas A&M AgriLife’s Soil, Water, and Forage Testing Lab offers a “Profile Soil Sample Information Form” (SP12) that pairs your standard 0-6” soil sample (analyzed for multiple nutrients including N, P, etc.; routine analysis, $10) with a second soil sample from 6” to as deep as 24”. This paired soil sample is analyzed for nitrate-N only, $4. The submitter marks the depth to a proper calculation of nutrient requirements can be made by the soil test lab.
Is profile nitrate-nitrogen down to 24” deep 100% available to grain sorghum?
Yes. Even slightly deeper N is largely available. The Profile Soil Sample form for N credits any 6-24” N to your crop requirement thus reducing fertilizer costs. Extension recommends that producers include at least some profile soil N sampling to establish whether there might be deeper N present.
The current Profile Soil Sample form is found at http://soiltesting.tamu.edu/files/profilesoil.pdf
Texas A&M AgriLife’s Crop Testing Program (http://varietytesting.tamu.edu) annually conducts fee-based hybrid performance tests across Texas. These replicated tests also report multi-year data for up to three years at most locations. With increased interest in grain sorghum for 2013, visit the above website and click on ‘Grain Sorghum’ to learn about trials in your region. Results for 2012 to date—all including a 3-year summary—are posted for Monte Alto, Gregory, Thrall, College Station, and Farmersville. Results are forthcoming from Uvalde, Danevang, and High Plains irrigated and dryland locations.
Producers in the Texas Coastal Bend may contact extension agronomist Dr. Dan Fromme, Corpus Christi, (361) 265-9203, firstname.lastname@example.org, for a copy of results of additional hybrid trials he coordinates with county Extension agents in his area.
What about seed company hybrid trials?—Numerous companies have in-house tests which focus primarily on their own hybrids but often include a few competitor’s hybrids. Though these trials are not considered ‘independent’ in the sense that a farmer or researcher would desire, these trials have an important role in identifying performance leaders within an individual company’s hybrid selections, especially as new hybrids are released that must be compared to the company’s old favorites.
The Freeze & Frost of October 8, 2012
An unexpected heavy frost/freeze occurred in the lower High Plains region on October 8th. Due to later plantings, often after failed cotton, many acres were subject to extended hours of frost and freeze. Lubbock recorded the second earliest freeze on record (average first freeze is Oct. 31). Texas Tech Univ. “Mesonet” weather stations (http://www.mesonet.ttu.edu) recorded lows of 28°F at Muleshoe, Floydada, Hart, and as far south as Tahoka.
Frost damage and termination of grain sorghum is well known in the High Plains but rarely catches much sorghum that is not yet mature. Early assessment suggests significant foliage damage is present. How some sorghum fields respond may depend on stalk (culm) survival from the head down into the foliage. If the culm survives the freeze then the plant can continue to deliver nutrients and carbohydrates to the developing grain. But at a minimum, I expect reduced test weights on many acres of grain and in some cases little to no further grain development as the grain will now simply dry down without further starch accumulation. This is particularly a concern as numerous fields appear to be in the range of seed development at 20% hard dough/60% soft dough/20% milk stage, with 5% of the total grain at black layer (physiological maturity). Fields that show evidence of major injury which were likely >50% milk stage should be considered for hay or grazing.
For additional information on handling grain sorghum damaged by a freeze, consult “Harvesting Grain from Freeze-damaged Sorghum (~2001)” from Kansas State Univ., http://www.agronomy.ksu.edu/extension/p.aspx?tabid=86. This includes decisions for low test weight grain sorghum, which is price discounted, and may be rejected outright if test weight is <50 lbs./bushel. If faced with low test weight, compare discounts among local and regional grain buyers. Allow time to take a preliminary test cutting to assess your test weight. If low, you may reset the combine to blow out more of the lighter immature kernels.
Freeze damaged grain sorghum on a pound-per-pound basis has similar feed value to mature grain, however, the small kernel size makes grinding more difficult in order to crack the seed and capture the grain’s full nutritional value.
Texas AgriLife will post additional information on the regional grain sorghum freeze discussion at http://lubbock.tamu.edu in mid-afternoon on October 10th.
Applications in Sorghum Forages
When nitrates and prussic acid accumulate in forage, the feed may not be safe for livestock consumption. This Extension document—available for view, print, or download at https://agrilifebookstore.org/ (then use the search box) —highlights the symptoms of nitrate and prussic acid poisoning.
Prussic acid (cyanide) occurs primarily when a strong frost hits sorghum family forages or grain sorghum. It can also occur in fresh growth on drought-stressed forages. Cattle normally need to be off the forage at least 1 week after a frost or freeze, and properly cured hay should be OK. Testing for prussic acid is tricky because handling the forage can lead to decomposition of the prussic acid. If you need a prussic acid test decide first which lab you are going to use and call them ahead of collection for their instructions.
Nitrate accumulation in sorghum and sorghum hays is most likely in rainfed conditions when either significant N applications have been made or the crop is drought stressed but still accumulating N. Nitrate is likely accumulated in the base of the stalk, so simple measures to use this forage include raising the cutting height 3-4”. Drought stressed grain sorghum in the High Plains that may be used for hay should consider testing the forage for nitrate accumulation in 2012.
Numerous producers in all regions of Texas are already considering increasing their grain sorghum acreage in 2013. Cotton price prospects for 2013 do not appear strong and grains do. Aflatoxin concerns have backed some growers off of corn in Central and South Texas. Producers are already checking seed supplies of favorite sorghum hybrids for next year.
A pitfall to avoid, however, for grain sorghum production is going too far into the too-common low-input mentality for grain sorghum production. For too many producers, this in fact approaches a no-input mentality. Or at least minimal inputs. This applies foremost to nitrogen (N) fertilizer, but can affect P fertilizer, the willingness to spray for insects like headworms or stink bug when economic thresholds suggest you should, etc. Yes, grain sorghum production at the yields we expect on an acre is less than for corn. But we know that if inputs are cut significantly below crop requirements then you receive mediocre and even poor results. And then the tendency is to blame the crop for underperformance.
I attended the recent national grain sorghum conference at Kansas State University. Colleagues with KSU as well as Oklahoma State Univ. spoke highly of grain sorghum’s role in Great Plains farming, that sorghum has a fit in many production systems that is more appropriate than corn. But they noted producers must ensure inputs are managed appropriately to maintain good profitable yields else reduced inputs restrict yield potential and lead to disappointment.
When can I stop irrigating grain sorghum?
Irrigation cut-out will most likely occur prior to hard dough stage. The sorghum seed will proceed through grain development from watery ripe to milky ripe to mealy ripe (the seed when squeezed no longer squirts, but oozes a gel-like or mealy material) then begins to firm at soft dough on to hard dough. As a rule of thumb, if good soil moisture is still available to the plant (at least 2 inches) then terminate irrigation as sorghum moves past soft dough. It is not reliable to base irrigation termination on grain color as different hybrids do not change color in the same fashion. A final irrigation may be applied during hard dough only if soil moisture storage is completely depleted or drought conditions are severe enough to hinder stalk quality at harvest.
When examining the head for seed maturation be sure to check many heads and check the whole head. Some difference in maturity will be observed on each head as seeds at the tip could be up to 7 days older (and more mature) than seeds at the bottom of the head, and primary tillers may also be several days later than the main head.
As a general rule of thumb, if you have doubts about whether to irrigate one more time prior to hard dough then do so, especially when grain prices are high.
Plant population in grain sorghum is a key to fitting your production potential to field conditions. But seeding rate does not equal plants per acre, and just because you set an air-vacuum planter to a target seed drop doesn’t ensure you are close to that number of seeds let alone plants.
Whether you have an existing crop in West Texas or have already harvested in South Texas (but your stubble is still standing), estimate actual plants per acre. Record this number in your field notes. Use the equation below and repeat it at least 3 times in a typical field area. Calculate a separate average for a thin area of the field, but watch it at harvest time to see if your yield is actually different (you may expect lower yield, but that is not always the case). Use all measurements in feet (including how wide the row is).
(43,560 sq. ft./acre) X (Plants in count area) = Plants per acre
(Length of count area) X (Row width) X (# of rows)
For example, if you measure two 30-inch rows 25 feet long and count 110 plants, then:
(43,560 sq. ft. per acre) X (110 plants) = 38,332 plants per acre
(25) X (2.5) X (2)
Round to the nearest 1,000, i.e., 38,000, then average this with at least 3 other points. You may have difficulty distinguishing tillers from the main stem, but count only individual plants (ignore small plants that will not contribute to grain yield). This method is easiest if counted 30 to 45 days after planting.
Some producers are familiar with counting plants in a fixed distance per single row, then multiplying by 1,000 to determine plants per acre. For a specific row spacing, use the length provided below (e.g., 1/1000th of an acre) then multiply by 1,000 to estimate plants per acre.
Row Spacing Length of row for plant count
20” 26’ 2”
30” 17’ 5”
36” 14’ 6”
38” 13’ 9”
40” 13’ 1”
We all know that crop rotation has its place in cropping of any type, but factors like commodity prices, crop insurance, the equipment you have, and even your landlord will influence cropping and rotations. Sorghum, like corn, no—more than corn—affords a residue producing crop on your land with a fibrous root system that is well distributed in at least the top 2 feet of your soil. When sorghum is a part of your rotation, you generate residues, which depending in Texas you farm, these residues are a key component to reducing erosion from water and wind, catching and keeping more of the rainfall you receive, etc. Texas AgriLife encourages producers to consider means to retain significant residues on the soil surface. Give your precious soil resource a blanket! This is a challenge for many producers, and I encourage you to learn about different types of coulters, trash whippers, and residue managers that fit on your planter so you can preserve the surface stubble as long as possible. Ask neighbors who farm a lot of sorghum how they approach this and watch for fields that retain a lot of stubble and learn the pros and cons to see if doing so fits your farming.
Likewise, turning grain sorghum under with any form of tillage does not increase soil organic matter from the surface residues. Instead you are more likely to disturb and destabilize existing soil organic matter. Soil organic matter increases from grain sorghum will come from the root system, and the longer you can leave it alone, the less tillage you use, the more likely grain sorghum can increase soil organic matter. It is not easy and sometimes not even practical to try to deliberately increase soil organic matter (a long, slow process), but leaving the roots in place is the most effective means of doing so.
So consider your 2012 grain sorghum—whether you have already harvested in South Texas or your crop is only 3 weeks old in the High Plains—and think about how to use this resource to enhance your soil quality and potential productivity for 2013 and beyond.
Sodium chlorate and glyphosate are labeled for pre-harvest use in grain sorghum. The former is a burn down chemical that acts as a defoliant, whereas glyphosate (technically labeled for weed control) kills the plant which aids in drydown. For seed milo growers, diquat dibromide is also labeled. Although limited Texas AgriLife research has not demonstrated yield differences among treated and untreated grain sorghum, the ability to manage and potentially accelerate harvest can have significant advantages in Texas, especially when humid conditions slow drydown. Furthermore, combine operators have often noted that the uniform condition of the crop at harvest makes use of these harvest aids a plus. The primary physiological criteria for application include seed moisture below 30% AND physiological maturity, which is best determined by identifying black layer in the seed (Figure 1).
For a summary of grain sorghum harvest aid uses in grain sorghum, whether this may be an appropriate management tool in your farming, as well as links to Texas AgriLife guidelines, consult Nueces Co. ag. agent Jeff Stapper’s blog at http://cbagbriefs.blogspot.com/2012/06/preparing-grain-sorghum-for-harvest.html.
Figure 1 (below). Sorghum kernels in various stages of maturity harvested from the same head from the most mature (1) to the least mature (5). The black layer is first readily visible in (3) and becomes more distinguishable as the seed loses moisture. Do not confuse black layer, which develops where the seed is attached to the plant (bottom end when in the head), with the black dot on the opposite end of the seed.