Dennis W. Hancock

Emerging land use practices rapidly increase soil organic matter

The loss of organic matter from agricultural lands constrains our ability to sustainably feed a growing population and mitigate the impacts of climate change. Addressing these challenges requires land use activities that accumulate soil carbon (C) while contributing to food production. In a region of extensive soil degradation in the southeastern United States, we evaluated soil C accumulation for 3 years across a 7-year chronosequence of three farms converted to management-intensive grazing. Here we show that these farms accumulated C at 8.0 Mg ha(-1) yr(-1), increasing cation exchange and water holding capacity by 95% and 34%, respectively. Thus, within a decade of management-intensive grazing practices soil C levels returned to those of native forest soils, and likely decreased fertilizer and irrigation demands. Emerging land uses, such as management-intensive grazing, may offer a rare win-win strategy combining profitable food production with rapid improvement of soil quality and short-term climate mitigation through soil C-accumulation.

Animal performance and environmental efficiency of cool- and warm-season annual grazing systems

Annual forage crops can provide short-term grazing between crop rotations or can be interseeded into perennial pastures to increase forage quality and productivity. They also provide an opportunity to increase the economic and environmental sustainability of grazing systems. Cool-season annual forage crops provide high-quality, abundant forage biomass when forage availability from perennial forage species is lacking, reducing the need for stored feeds during the winter months. For example, ADG of 1.5 kg have been reported using small grains alone and in mixtures with annual ryegrass (Lolium multiflorum Lam.) while maintaining an average stocking rate of 3.5 animals/ha. No-till (NT) establishment has been shown to be as effective as conventional tillage for establishing small grain pastures. Stocker performance during the fall was not affected by tillage treatment, but during the spring grazeout, BW gain per hectare was 8% greater in NT pastures. An in vitro study showed that daily production of CH4 was 84% lower, respectively, in turnip (Brassica rapa L.) and rapeseed (B. napus L.) diets compared with annual ryegrass. Warm-season annuals are frequently used during the summer forage slump when perennial pasture growth and quality are reduced. Research has shown that brown mid-rib sorghum × sudangrass (BMR SSG; Sorghum bicolor L. × S. arundinaceous Desv.) and pearl millet (PM; Pennisteum glaucum L.R. Br.) with crabgrass (Digitaria sanguinalis (L.) Scop.) tended to have greater ADG (0.98 kg) than sorghum × sudangrass or peal millet alone (0.85 kg). However, non-BMR and BMR SSG tended to have greater gains per hectare than PM or PM + crabgrass (246, 226, 181, and 188 kg/ha, respectively). Feeding of brown mid-rib sorghum × sudangrass reduced daily production of CH4 and CH4 per gram of NDF fed by 66% and 50%, respectively, compared with a perennial cool-season forage in continuous culture. Cool- and warm-season annual pastures not only provide increased animal gains, but also increase soil cover and in vitro data suggest that annual forages (i.e., brassicas and warm-season annual grasses) decrease enteric CH4 emissions. Establishment method, grazing management, and weather conditions all play important roles in the productivity and environmental impact of these systems. A more complete life cycle analysis is needed to better characterize how management and climatic conditions impact the long-term economic and environmental sustainability of grazing annuals.

The Effect of Drought on Lignin Content and Digestibility of Tifton-85 and Coastal Bermudagrass ( Cynodon dactylon L.) Hays Produced in Georgia

Digestibility of “Tifton 85” Bermudagrass has been noted to be higher than most other Bermudagrass cultivars. However, the superior digestibility of Tifton-85 has not been verified based on samples from producers, nor is it known how water availability might affect this comparison. Recent past weather conditions in Georgia allowed this comparison. Much of Georgia was in severe drought in 2007 and 2008. In contrast, there was less/no drought in 2006 and 2009. In each of these years, producers submitted a substantial number of Tifton-85 and Coastal forage samples to our laboratory for lignin and “Digestible Neutral Detergent Fiber (dNDF48)” analyses. Over all years, Tifton-85 had lower lignin content than coastal. However, Tifton-85 had significantly lower lignin content only in drought free 2006 and 2009, whereas the lignin content of Coastal was unaffected by drought in 2007 and 2008. The lignin of Tifton-85 increased during these two drought years. Despite this, the dNDF48 for Tifton-85 was significantly higher than coastal in all four years, suggesting that drought had hardly any effect on the digestibility of Tifton-85. Apparently, the type of lignin in Tifton-85 is different from that in coastal. Higher dNDF48 for Tifton-85 has been attributed to its lower concentrations of ether-linked ferulic acid than in Coastal. Decreased ether bonding in lignin results in higher digestion.