This tip was provided by:
Calvin Trostle, Extension Agronomy, Lubbock, 806-746-6101, ctrostle@ag.tamu.edu
Statewide
Grain Sorghum Stubble vs. Planting a Cover Crop
In past Sorghum Tips I have outlined several points regarding our management and understanding potential benefits that sorghum stubble may afford. Access some of the previous information at http://texassorghum.org/sorghum-tips (at the bottom of the page you can click on earlier pages, they are arranged in reverse chronological order). Regarding sorghum stubble three of these posts include:
- Grain Sorghum, Surface Residues, and Soil Organic Matter. July 24, 2012. Grain sorghum stubble is a ‘blanket’ to protect the soil surface and minimize erosion. Farming into stubble is increasingly a common practice across the U.S. Learn how to manage the stubble and farm it with possible modifications to your equipment. Tillage of sorghum stubble into the soil does not appreciably increase soil organic matter as some of the soil matter you already have is disturbed and lost (incorporating residues is an “exchange” of organic matter). The best route to maintaining and improving stable long-term soil organic matter content is to leave the roots undisturbed.
- Baling Sorghum Stalks: I—Loss of Nitrogen ($) from the Field. November 19, 2014. When sorghum stalks are removed from the field, a modest but significant amount of N (roughly 1% of the biomass) is nitrogen, which has a replacement cost that is often not factored into the price you receive. Grain harvest or grazing remove much less N and is not a concern.
- Baling Sorghum Stalks: II— Loss of Soil Cover Protection. December 9, 2014. Removal of sorghum stalks in baling means that you are selling an asset—and probably not getting compensated adequately for the intangible value of your “blanket.”
Cover cropping is a common topic across much of the U.S. NRCS promotes cover cropping. Several industry publications like No-Till Farmer and Dryland No-Tiller newsletter highlight producers using cover crop practices across the country. I have attended several cover crop conferences, and I have some work on the topic myself in the Texas High Plains. Much of the reporting on the successes of cover cropping come from regions of the U.S. that either have high rainfall (e.g. more than the annual crop requires) or lower evaporative demand (cooler conditions where 1” of moisture goes much further than it would in Texas).
A Cover Crop Caveat…
A caveat—and I assert a major one—is that outside of the areas noted above there is not a lot of data to date from universities, USDA Agricultural Research Service (in contrast to NRCS), etc. that clearly demonstrates value of cover cropping (and this type of data needs to be long-term to capture the potential benefits that can occur over time). The primary concern in many drier areas, which would include much of Texas, is that there is not sufficient moisture to support investing some of your water resources in a cover crop. This is a fair question though note that tillage practices are the culprit in significant potential moisture losses.
Cover crops have costs starting with the seed. Some recommendations from seed companies can easily exceed $30/acre, usually for a multi-species blend. For any area in Texas multi-species blends may be only 3 or 5 species (probably OK) vs. a shotgun approach with up to 15 species, several of which are quite possibly not well adapted and don’t grow (so why pay for them?). Also, winter blends (think colder conditions of the Texas High Plains) will include a few legumes, but Texas A&M AgriLife observations are that most legumes don’t nodulate well (may not have a crop-specific Rhizobium or Bradyrhizobium inoculant) and if soils are cold there is little nitrogen fixation occurring—thus the purported benefit of adding N to the soil ecosystem is not realized.
Grain sorghum stubble vs. separate planting of a cover crop. I believe this is an important consideration, especially in drier areas of Texas where grain sorghum is the only adapted summer annual crop you can plant that will generate much residue. Do not overlook the value of this stubble. It may preclude any need to consider costs associated with establishing a cover crop. One selling point of cover crops is “A living root in the soil at all times” which fosters microbial activity thus contributing to nutrient cycling. This is often mentioned as if to lead you and I to conclude that there is no biological activity if there is not a live root in the soil, and this is simply not true. There is massive amounts of biological activity, and though it is somewhat less, soil microorganisms are busy decomposing root matter in the months after a root dies, and these populations of organisms will increase rapidly once live root matter returns to the soil. Cover cropping may be viable for your farm, and I encourage Texas farmers to experiment. But don’t overlook existing and “free” resources—like your remaining grain sorghum stubble—in terms of achieving some of the same goals that cover crops in principle may offer.
