Ed Twidwell & Steve Harrison
LSU School of Plant Environmental & Soil Sciences
Data from the LSU AgCenter wheat and oat performance trials have been posted at: http://www.agronomy.lsu.edu/LSUWheat/LSUWHEAT.html. This information should be used by growers to help choose varieties for planting this fall. In August the Wheat Research Summary publication will be placed on the LSU AgCenter website at the following address:
The LSU AgCenter trials for 2012 were plagued by weather-related problems. No yield data were collected from south Louisiana due to poor stands, severe lodging, failure to vernalize and other issues. The data at Bossier City and Alexandria were of marginal quality and was not published.
Wheat prices have surged recently, resulting in increased demand and a potentially short supply of wheat seed for planting this fall. Growers should consider booking wheat seed quickly in order to have access to the better varieties this fall.
To spread out their risks, growers should look at the two-year data tables and select several different wheat varieties to plant this fall. It is not a good idea to plant all of their acreage to one single variety. Yield is the most obvious consideration in choosing varieties, but other factors also influence profitability:
- Disease susceptibility – a single $20 fungicide application is equal to about four bushels in yield. Stripe rust and leaf rust susceptible varieties frequently require fungicides inLouisiana.
- Insect resistance – Hessian Fly was not an issue in Louisiana in 2011 or 2012 so there may not be data available for the newest varieties.
- Test weight – a low test weight can result in dockage at the elevator. Test weight is influenced by weather conditions following grain dry down and prompt harvest is important. Test weight is strongly influenced by genetics such that varieties with low average test weights in the data tables are likely to have low test weight in most environments.
4. Lodging resistance – lodging increases harvest costs and decreases yield and test weight.
Recommended planting dates for wheat range from October 15 to November15 innorthLouisianaand from November 1 to November30 incentral and southLouisiana. Planting wheat earlier than the recommended planting dates will subject the plants to greater insect and disease pressure and also makes the plants more prone to winter injury due to excessive fall growth. Wheat can be planted later (two weeks past the recommended window) but this increases the probability of stand loss and reduces tillering due to wet weather and shortened growing season. Seeding rates should be increased when planting late and into cold wet soil.
Planting wheat with a grain drill is the preferred method because it allows uniform depth of planting and results in a more uniform stand. A seeding rate of 60 to75 poundsper acre of high quality seed planted into a good seedbed with adequate moisture is satisfactory for drilling. Adjust the seeding rate up from 75 to120 poundsper acre for broadcast planting, late planting, or planting into a poorly prepared seedbed.
Fall fertilization and liming should be carried out to supply any needs indicated by soil testing. Phosphorus and potassium, where recommended, should be incorporated into the seedbed before planting. If lime is recommended, apply before seedbed preparation if possible. Fall application of nitrogen is usually not needed where wheat follows soybeans. Where wheat follows corn, sorghum or rice, application of 15 to20 poundsof nitrogen per acre may be beneficial.
By Dr. Josh Lofton, Agronomist – Macon Ridge Research Station
Throughout the month of May and the first week of June the majority of the state experienced hot and dry conditions. Coupled with the rapid growth rates experienced by corn, soybeans and cotton, this situation has required some producers to irrigate for almost two months. While this is a mild concern for some, this intensive irrigation season is a major concern for producers with irrigation water containing elevated levels of salt. Many may not be aware of their potentially low quality irrigation water or may be experiencing this threat for the first time this year, and if current trends continue, irrigation water with high salt concentrations will become an increasing threat to crop production in coming years.
What is the best way to identify crops suffering from salt injury? Plants will usually resemble drought injury, such as wilting and a reduction in leaf area, even though adequate moisture is present within the soil system. Other visual symptoms include pale green and yellow leaves followed by necrosis. These symptoms usually begin exhibiting themselves around the leaf margins (Figure 1). Continuous salinity problems will cause these symptoms to spread throughout the plant and if severe issues are present the plants will eventually die. Because these symptoms first appear in the lower leaves, early identification may be difficult to spot until serious conditions exist. An example of this occurred in soybean trials at the Macon Ridge Station, where there appeared to be no signs of damage across the canopy (Figure 2); however, there was clear evidence of salt injury in the under-canopy (Figure 3). Therefore, in-field scouting may be needed to help identify this problem.
If salt damage has been identified, how detrimental is this to your current crop? The answer can be difficult to determine for every situation not only because crops are affected by salt levels differently but also soil texture and location within the field can influence salt injury. Areas that receive higher rates of low quality irrigation, such as within the first third of a field under furrow irrigation, usually show higher incidence and intensity of salt injury than areas further through the field. Lower portions of the field, where irrigation water can accumulate, will show worse salinity problems than higher, well drained areas. Further, sandier soils have greater leaching of salts during rainfall events than soils with higher clay content. However, it takes approximately 5 to 6 inches of rainfall to decrease the salt level of the topsoil by 50%. The crop itself can be highly influential on the severity of the salt injury that occurs. Some crops such as rice, soybeans, and corn, can show a rapid decline in yield compared to cotton and to a lesser degree wheat and grain sorghum (Table 1). In addition, soybean varieties can show higher salt tolerance, termed salt excluders, than others, termed includers. Damage ratings are currently available for soybean varieties through the 2011 soybean OVTs at the Macon Ridge location.
If a problem field is identified, what is the next step? Since salt injury can vary in severity and symptoms can be similar to other deficiencies or toxicities, proper samples need to be collected from the soils and irrigation wells. Samples can be sent to the LSU AgCenter Soil Testing and Plant Analysis Laboratory (STPAL) located on the LSU campus in Baton Rouge. A soluble salts test, at $5 per sample, can be used to determine the amount of salts in your soil that could potentially be affecting your crops. Additionally, irrigation samples can be submitted to the STPAL with a “quick water analysis” for $6 per sample, determining not only total salts in the irrigation water but also electrical conductivity (E.C., estimate of soluble salts), sodium, and chloride concentration.
If your soils are found to be at toxic levels for salts/, what steps can be taken within this growing season to minimize the detrimental effects? Unfortunately, based on the current data available unless another fresh source of water can be obtained, little can be done in-season. However, at this point one of the greatest concerns is high salt accumulation in the soil. If this salty irrigation water continues to be applied to the soil, irreparable damage can be done within a very short time and will be detrimental to crops and soils for many years. The best management practice for the long term sustainability of the production system would be to limit irrigation events or even completely stop irrigating if water is found to be severely low quality.
What steps can be taken during future growth seasons to minimize the impact to production and soil systems? As mentioned previously there are varieties within sensitive crops that are more tolerant to salinity than others. However, if salt levels in the irrigation water are high, switching production systems to a crop that has a lowered irrigation demand, such as grain sorghum or cotton, may be the best alternative. In these instances this would change how both producers and landlords determine the crop rotations and land allocations; however, long term productivity of our valuable resources and being a good steward needs to be a consideration in these situations.
As we continue to see this problem become a greater issue across many areas of Louisiana, everyone within the agricultural community must become more knowledgeable about salinity issues and the damage to our production systems that this issue can cause.