Louisiana: Winter Cover Crops- Benefits and Planning Strategies for Cover Crop Success

Later season field of cover crops in southeastern Nebraska. Photo: Paul Jasa, UNL

Later season field of cover crops in southeastern Nebraska. Photo: Paul Jasa, UNL

Corn harvest is winding down across Louisiana, soybean harvest is in full swing and cotton harvest has begun in a few areas. As we move into the fall months, now is the time to begin planning your winter cover crop management strategy.

Cover crops are the most effective and efficient tool in improving soil fertility. Cover crops add organic materials to the soils that improve soil physical, chemical and biological properties. They can improve soil organic matter content, cation exchange capacity (CEC), water and nutrient holding capacities, water infiltration, water use efficiency, soil structure, bulk density (a measure of soil compaction), microbial biomass and nutrient cycling. Cover crops ensure year-round ground cover that reduces soil runoff and erosion potentials, decreases weed pressure and herbicide needs, scavenges nutrients left over from the previous crop and prevents leaching loss of nutrients into groundwater.

Cover crop selection will depend on the goals a producer would like to accomplish. For example, a cover crop that produces a deep tap root, such as the tillage radish, should be selected for compacted or no-till soils.

Having a clear objective will also aid in cover crop management. For example, cereal rye can be a good choice for increasing soil organic matter, minimizing soil erosion and suppressing weeds. The fibrous root system of cereal rye and other cereals helps prevent soil erosion and scavenge nutrients. In contrast, a tap-rooted cover crop — such as forage or tillage radishes, woolypod vetch and red clover — is better suited for deep nutrient scavenging and potentially aids in loosening a soil compaction layer or preventing one. Mixes of cereal and legume covers can reduce early-season N fixation issues in corn. Legume cover crops such as crimson clover and hairy vetch can be a good source of nitrogen fertilizer for the subsequent corn or cotton crop, which could reduce fertilizer need and cost. Preliminary data collected by AgCenter scientists have shown that in soybeans, legume cover crops can supply N for early growth needs until nodules develop.

Other important considerations when selecting a winter cover crop includes the cash crop to be grown and winter cover crop termination. Be sure to plant only quality seed, which will help eliminate weed seed contamination issues. When planting legumes, make sure the rhizobium inoculant strain is correct for the legume species that will be planted, and always inoculate. If planting pre-inoculated legume seed, get pure live seed per pound and adjust seeding rates accordingly; some pre-inoculated seed is larger and therefore has less pure live seed per pound. Seeding rates of cover crops will depend on seeding method, date of sowing and whether the farm is enrolled in a CSP or EQIP program. For cereals, avoid low seeding rates and/or establishment methods that could lead to spotty emergence. Spotty emergence could cause the cereal to “bunch” (a single plant with multiple tillers and a large root system), which could lead to main crop establishment issues, such as skips and variations in seed placement depth and seedling emergence. Also, avoid planting a cover crop drill into the top and middle of the seed bed. This will prevent planting the cash crop into the cover crop drill, which could lead to stand establishment issues.

Cover crops should be planted as soon as possible following the main crop harvest. When planted earlier in the fall, nutrient scavenging will be increased and growth/biomass production will be maximized prior to cold weather, which will slow the growth and development of the cover crop. Planting your cover crop soon after harvest is especially important if corn will be planted. Early cover crop termination, when planting corn, combined with late planting of a cover crop (November) will reduce overall biomass production, therefore minimizing the benefits of the cover crop. Legumes are generally slow growing if planted late (November), and biomass production will be minimal prior to the onset of cold weather. If fields are enrolled in an NRCS conservation program requiring cover crops, be sure to follow the NRCS cover crop guidelines. Below is a link (hyperlink No. 1) that contains NRCS seeding rates and planting dates for common cover crops grown in Louisiana. In cooperation with the NRCS, data provided by LSU AgCenter research resulted in a reduction in cereal rye seeding rate from 90 to 120 lb/a to the current rate of 45 to 120 lb/a.

The planting window for most winter cover crops is Oct. 1 to mid-November. Ranges for average first frost dates for Monroe, Shreveport, Alexandria and Baton Rouge are November 15, 18, 19 and 29, respectively (https://www.farmersalmanac.com/average-frost-dates). Hyperlinks No. 2 and 3 below are some useful tools that may aid in further refinement of accomplishing the intended goals for your farm. NRCS payments for cover crops change from year to year. Updated numbers are included in the decision tool (hyperlink No. 4) in estimating overall costs of cover crops implementation. If you have any questions or concerns, please feel free to contact your local AgCenter agent or one of us.

Source URL: https://www.lsuagcenter.com/profiles/lblack/articles/page1600347669454