This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, firstname.lastname@example.org
Sorghum Physiology & Management II
This is the second of a series of five Sorghum Tips AgriLife will share intermittently over fall and winter of 2017-2018. The first discussed rooting issues in grain sorghum, see http://texassorghum.org/sorghum-physiology-management-first-in-a-series.html
Physiology Driven Sorghum Management Consideration #2:
- Location of sorghum roots near the soil surface and N fertilizer application.
In Texas and other states using a knife or coulter rig to apply banded fertilizer, including nitrogen (N) after the plants are established is a convenient way to efficiently place nutrient in or near the root zone. The pluses are the specific placement, likely increased nutrient efficiency, and perhaps—due to this efficiency—reduced fertilizer cost. Disadvantages include the time it takes to fertilize a large number of acres vs. using a fertilizer spreader (which if the fertilizer remains on the soil surface is subject to volatilization losses and needs or irrigation to incorporate) or other broadcast method.
You do not want to prune roots in any significant fashion, however, as this could limit crop growth. It only takes a few minutes to determine where your roots are at. If you are knifing fertilizer in the middle of the rows, equidistant between the plants, this is not likely a significant concern though this puts the N or other fertilizer like P up to 20” away from the plant.
Using a shovel to dig a 8” deep cross-section of a plant’s root profile perpendicular to the planted row of sorghum. This will indicate where the roots are present near the soil surface. Farmers should ensure that no more than a minimal amount of the grain sorghum root system is severed. If this may occur, then sidedress N applications need to be made further from the row. Checking to see the location of the root system is also helpful as the same hybrid planted in the same soil type but in a different year may have a somewhat different rooting pattern, particularly in wet vs. dry years.
I will discuss in the next Sorghum Tip a major growth and development stage (growing point differentiation). Due to the importance of that stage of growth it is preferable that side-dress N applications or any other fertilizer applications need to be applied by a certain stage of growth, which may be earlier than some farmers realize. For this reason, waiting to apply sidedress N when sorghum is taller (say 18-24”) can have reduced benefit. The later applications also are more likely to be the maximum distance from the plant (middle of row). An earlier application closer to the row will position the sorghum plant to “grow into the fertilizer band.” That is good for efficient nutrient uptake.