- Agronomic: clovers, cotton, millet, peas (field, cowpeas), rye, vetches, wheat
- Animals: bovine, goats, sheep
- Animal Production: grazing management, grazing - multispecies, rangeland/pasture management
- Crop Production: cover crops, nutrient management
- Production Systems: integrated crop and livestock systems
- Soil Management: organic matter, soil quality/health
Legume cover crops have potential to offset N fertilizer inputs, provide a high-value supplemental forage source for the regional livestock industry, and improve the health of agricultural soils in the Southern Rolling Plains and Permian Basin of western Texas. The fallow period between harvesting wheat and planting cotton often exceeds eight months (July–February), and the fallow period in continuous wheat systems is generally July–October. Annual precipitation in this region has a bimodal distribution, with the majority of rainfall occurring in the late spring (April, May, June) and early fall (August, September, October). The fallow periods in wheat–cotton and wheat–wheat systems are a valuable opportunity to take advantage of fall precipitation and grow a cover- or dual-use-crop.
We propose a research and extension effort expanding upon the work of SARE project OS19-131, supported by on-farm projects and farmer cooperators, to investigate management options for legume cover crops in continuous wheat, wheat-cotton, and continuous cotton systems. Successful cover crop management can contribute surface residue, soil organic matter, and organic N, reducing fertilizer input costs. In addition to potential agronomic benefits and soil health, many cultivated legumes are high-protein forage crops that may offer dual-use potential in integrated animal systems. Texas is the leading state in goat, sheep, and cattle production for the U.S. All three of these livestock species are major regional enterprises in western Texas. Many cotton and wheat farmers also manage livestock on native rangeland or improved pasture, and wheat is often managed in a dual-use system to provide winter grazing, as well as a grain crop. The proposed cover crop practices could provide a high-quality forage source to supplement livestock production during critical periods.
Warm-season cover crop species of interest include different varieties of cowpea (Vigna unguiculate (L.) Walp.), mung bean (Vigna radiata (L.) R. Wilczek), guar (Cyamopsis tetragonoloba (L.) Taubert), and sunn hemp (Crotalaria juncea L.). Cool-season cover crops (in continuous cotton) include red clover (Trifolium pratense L.), crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa), and Austrian winter pea (Pisum sativum L. ssp. sativum var. arvense). Growing these cover crop species in a biculture with common grass crops such as cereal rye (Secale cereale L.) in the winter and pearl millet (Pennisetum glaucum (L.) R. Br.) in the summer may provide greater biomass, benefit to the soil, and potential forage.
Project objectives from proposal:
This research project will be conducted on four farms in the Southern Rolling Plains and Permian Basin regions of Texas. Across the four farms, each system (continuous cotton, continuous wheat, or wheat–cotton) will be represented at a minimum of two sites as follows: sites in McCulloch County and in Runnels County will have a continuous wheat system, sites in Tom Green County and Glasscock County will have a continuous cotton system, and the Tom Green County and Runnels County sites will also have a wheat–cotton system. The growers at McCulloch and Glasscock Counties may also be candidates for the wheat–cotton system, so this arrangement may shift, or sites may be added accordingly. County Extension Agents in each county will serve as direct contacts to the farmers, and will help coordinate field operations and frequent project monitoring.
For all sites and systems, the experimental design will be a randomized complete block design with three replications. Plots will be a minimum of 1.5 m wide by 9.1 m long. Cover crop treatments following wheat (in the continuous wheat and wheat–cotton system) will be cowpea, mung bean, guar, sesbania, pigeon pea, and sunn hemp, as well as each species in a biculture with pearl millet. Cover crop treatments in the continuous cotton system will be red clover, crimson clover, hairy vetch, and Austrian winter pea. Similarly, each species will be represented as a monoculture, and in a biculture with cereal rye. All trials will have a no-cover check, and a grass species only treatment (monoculture pearl millet following wheat, and monoculture rye following cotton). This will result in a total of 14 cover crop treatments in the systems following wheat, and 12 cover crop treatments in the system following cotton. Building on the current work of project OS19-131, legume species with the greatest suitability will be entered into additional trials for the winter of 2020 and summer of 2021 to investigate impacts of other agronomic management factors such as seeding rate.
In each trial, baseline soil samples will be collected (0 to 15- and 15 to 30-cm) and cover crops will be seeded following harvest of the previous main crop. Legume seed will be inoculated with the appropriate rhizobium and planted at recommended seeding rates to ensure adequate opportunity for stand establishment. Whenever irrigation is available, it may be used to water the planted cover crop for emergence. However, some sites (McCulloch and Runnels County) will be non-irrigated. Following emergence, overhead digital imagery will be collected and processed to gauge stand establishment and percent ground cover. Cover crop biomass will be hand sampled for each species at the phenological stage associated with peak biomass production, or prior to termination for planting of the subsequent crop (whichever comes first). Samples will be weighed fresh, dried, ground, and analyzed via wet chemistry for total N content (informing crude protein), as well as acid detergent fiber (ADF), neutral detergent fiber (NDF), and 48-hour in-vitro dry matter digestibility (48-hr tiVDMD). These measurements and analyses will inform total biomass (kg ha-1), total N contribution (kg N ha-1), and forage nutritive value. If needed, cover crops will be terminated using an appropriate herbicide prior to planting the subsequent crop. If warm-season cover crops reach mature seed production, then samples will be harvested to assess potential as a double crop, or for farmers to harvest, save, and replant cover crop seed. Following the establishment of the subsequent crop, crop tissue samples will be collected from the no-cover check, the grass-cover-only treatment, and the legume cover crop treatments contributing the greatest kg N ha-1 to determine cover crop impacts on subsequent crop N uptake. If differences are observed, sampling will be implemented across all treatments to quantify intermediate differences.
All measurements will be subject to statistical analyses to quantify agronomic, economic, and environmental implications (i.e. potential fertilizer savings and associated reduction of negative environmental impacts). Economic analyses will also consider the option of livestock integration relative to cover crop forage yield and nutritive value. All findings will be integrated into extension programming, and presented at grower meetings as well as a cover crop field day.