Rye (Secale cereale L.) is a cool-season annual grass with an upright growth habit, known as cereal, winter, or grain rye, adapted to uplands (mountains, piedmont) and lowlands(coastal plain, tidewater) in North Carolina. Rye can tolerate up to minimum temperatures of -30 to -40 degrees F, making it highly winter hardy, with a good ability to survive the heat. Rye can withstand flooded conditions and effectively function in drought. It can be grown in shady conditions with an excellent ability to thrive in less fertile soils. Rye can also adapt to acid soils with suitable pH ranging from 5 to 7. It can be grown as a fall or late summer cover crop.

Benefits:

Produces the highest biomass among small grain cover crops, in the range of 3,000 to 8000 lbs./acre, leaving behind a residue that can retain on the field for longer, boosting organic matter, and facilitating soil erosion resistance in sandy textured coastal plain soils. Compared to other small grain crops like oats and wheat, rye is more tolerant of acidic soils and most suited to sandy soils. Rye can scavenge nitrogen up to 25 to 50 lbs./acre in its aboveground biomass and help reduce nitrate leaching, a significant concern in coastal plain soils with low residual nitrogen. Persistent residue and allelopathy (chemicals released by cover crops while growing or decomposing, that can prevent germination or growth of weeds) can contribute to effective weed suppression of weeds like palmer amaranth. Cereal rye biomass of 5,500 lbs./acre has been shown to reduce palmer amaranth weeds by 50% in cotton production. More than 8000 lbs./acre rye biomass can help in weed control and yield management in soybean fields. As soybean can fix nitrogen, initial unavailability of nitrogen tied up by rye is not an issue. The ability to withstand flooded conditions, heat, and acidic pH range help rye adapt to Tidewater region muck soils (organic soils). Tidewater organic soils have less bulk density, making them lightweight, floaty when dry, and susceptible to wind erosion, which can be controlled with rye cover. 

Including cereal rye with conservation tillage can be beneficial while cultivating a less residue cash crop, owing to its high biomass and heavy, persistent residues. Rye can facilitate topsoil loosening, helping control surface compaction, but not effective in alleviating subsurface compaction. Mature rye has a high carbon: nitrogen ratio of 40, with complex organic compounds that take time to break, thus leading to residues staying longer on the field and making nitrogen less available to succeeding crops. Crop rotation of rye with low-residue crops like cotton has been beneficial in terms of soil, water conservation, and pest and disease control.

Planting and Management:

Rye can be planted late as it can grow at lower temperatures (by 5 degrees) in the fall than other small grains and mature early in spring. Rye can either be seed drilled with a seeding rate of 60 to 120 lbs./acre or broadcasted at 90 to 160 lbs./acre, with disking. The optimum seeding depth is ¾ to 2 inches, and care should be taken to avoid it going more than 2 inches. Aerial seeding is also practiced in North Carolina; however, the efficacy is variable and dependent on soil moisture. Late fall planting will require higher seeding rates of 300 to 350 lbs./acre to ensure a well-established stand. A low to medium seeding rate is preferred when planted in cover crop mixtures with other grasses. When planted with legumes, the lowest available seeding rate can be adopted. Rye can also be seeded as a companion crop to the main cash crop in spring for weed control. As rye does not vernalize in spring due to the lack of an extended cold climate, chances of seeding are nil, making sure that it dies on its own within a few months into the main crop growth. Rye growth must be kept in check either with tillage or herbicides to avoid over usage of soil resources like soil moisture, which should be available for the main crop.

Termination:

Depending on the crop maturity, the effects of rye termination on soil quality can be varied. If terminated when the rye is succulent, the nitrogen taken up would be made available faster, and soil moisture can be conserved. However, if followed by spring rains, that can lead to nitrate leaching problems. On the other hand, if rye is left to mature too long, nitrogen gets immobilized, becoming unavailable to succeeding crops, more residue is produced that is hard to manage with tillage and soil moisture can be depleted. The addition of nitrogen fertilizer at the planting of the main crop can help tackle the initial unavailability of nitrogen. Milk to soft dough stage termination is recommended if weed suppression is the goal. If nitrogen immobilization should be less, then terminating rye before flowering is ideal. 

Rye can be killed either with tillage, mowing, rolling and crimping, and herbicides or a combination of these practices. Rolling can pose challenges for creating a good cash crop stand in cotton, soybean, and corn due to poor seed-soil contact caused by the rye residue cover on the surface. The rye residue should be dry enough and not on crop rows to avoid this. Strip tillage, a conservation practice that tills in strips only along the crop rows, can help remove rye residue from crop rows. Incorporating rye when it is at least 12 inches high or mowing after flowering but before grain filling can prevent rye from becoming a weed.

A minimum period of two weeks should be given for the rye residue to dry up before the main cash crop is planted to avoid possible cutworm damage. This also facilitates easy cutting of the dried residues with the tillage equipment. The rye residue can also have allelopathic effects for about 30 days after termination. Therefore, a three to four weeks gap is better if they are followed with small grain crops like carrots and onions. If left upright than flat, the rye residue can help keep the seed zone warmer, facilitating quicker growth and good germination of the subsequent main crop. 

Cover crop mixtures:

Legume rye mixture can help balance N scavenging by rye and N fixation by legumes, allowing for late termination. This mixture also produces more dry matter than cultivating rye alone. As rye has an erect posture, legumes like hairy vetch and winter peas with vining habits can provide complementary growth. If weed suppression is the goal, early planting can help legumes to establish well and suppress winter annual weeds like horseweed, primrose, Carolina geranium, field pansy, etc. If the cover crop mixture is cultivated for grazing purposes, then a mixture of small grains alone-rye, wheat and barley is more nutritious and can be grazed for longer. 

References:

Managing Cover Crops Profitably

Southern Cover crops council Cover crop Information sheet

Virginia NRCS Cover Crop Planning Manual

USDA Cereal Rye Plant Guide

Managing Cereal Rye for Benefits in Cotton and Soybeans

Gearing Up for Cover Crops: Consider Weed Management Benefits

Chapter 11: Rolled Cover Crop Mulches for Organic Corn and Soybean Production

Planting Soybeans Into a Cereal Rye Cover Crop