A comparison of winter cereal species and planting dates as residue cover for cotton grown with conservation tillage

tions in plant population have been attributed to poor Winter cereals are often used as cover crops before planting cotton seed to soil contact (Grisso et al., 1984) because of the (Gossypium hirsutum L.). Black oat (Avena strigosa Schreb.) is the plant residues interfering with the planting operation. predominate cereal cover crop for cash crops in southern Brazil and Allelopathic compounds in winter cereal residues can Paraguay, but limited information is available on the suitability of also affect cotton stands. For example, Hicks et al. black oat as a cover crop in the southeastern USA. The objectives (1989) reported that compounds arising from decaying of this study were to compare black oat with adapted winter cereals wheat cover crop residues can stunt and kill young cotfor this region and to determine the effect of cereal residue species ton seedlings. When residues are left on the soil surface, and amount on cotton growth, N status, and lint yield. In a greenhouse allelopathy is less a factor in causing stand reductions study in which black oat and rye (Secale cereale L.) residues were (White and Worsham, 1989; Rickerl et al., 1989). Howmixed with soil, tap root elongation of both cotton and radish (Rapha­ nus sativa L.) was inhibited more by black oat residue than by rye ever, if residues are trapped within the seed furrow residue. In a field experiment on a Goldsboro loamy sand (fine-loamy, (especially if row cleaning attachments are not used), siliceous, thermic Aquic Kandiudult), cotton was grown in 1995 and these residues may cause damage to young cotton roots. 1996 following black oat, oat (Avena sativa L.), rye, and wheat (TritiGrowing winter cereals as winter cover crops can cum aestivum L.) that were planted at three different times (October, result in N deficiency of the succeeding cotton crop. November, and December). All four winter cereals had similar bioThe cereal cover crop scavenges N from the soil mass production at each planting date in 1995. In 1996, rye was the throughout the winter months, reducing soil-available only species not visibly damaged by a low temperature of �12.2�C N to the succeeding cotton crop. Subsequently, the high that occurred during the winter. Black oat biomass was comparable C:N ratios of winter cereal residues causes N immobili­ to wheat in all planting dates but averaged 60% less than rye over zation (Aulakh et al., 1991; Doran and Smith, 1991; all three planting dates and was 37% less than oat in the October Somda et al., 1991; Torbert and Reeves, 1991). For cotplanting date in that year. Black oat tended to have a higher N ton grown without fertilizer N, Bauer et al. (1993) found concentration than the other cereal species. Cotton plant density was lower petiole NO3-N levels in cotton following greenlowest following black oat and rye. Cotton growth, leaf blade N, and petiole NO3-N were more dependent on residue amount than on manured rye than in cotton following winter fallow. residue species. Cotton lint yield following black oat was 120 kg ha�1 Because of this, higher rates of N fertilizer has been higher than lint yield of cotton following rye. Cotton following black recommended for cotton following winter cereals oat, wheat, and oat had similar lint yield. Black oat may be a promising (Reeves et al., 1993). cover crop for the southeastern USA, but evaluations of other cultivars Cotton plant morphology may be influenced by the and/or improvement programs to improve cold hardiness are needed presence of winter cereal residues on the soil surface. to improve the utility of this species. Stevens et al. (1992) reported 11% fewer cotton floral buds (squares) on the lower fruiting nodes of cotton seeded directly into wheat stubble than of cotton grown W cereals are often used as cover crops for with conventional tillage. The light environment surcotton because they grow rapidly in the fall and rounding plants affects seedling growth (reviewed by provide ground cover throughout the winter. Several Schopfer, 1984) and residues affect the photosynthetic winter cereal species, including rye, wheat, and oat, are photon quantity and wavelength composition of light recommended as cover crops (Sustainable Agriculture reflected from the soil surface (Kasperbauer, 1994; Hunt Network, 1998) in the southeastern USA. A species that et al., 1989). Kasperbauer (1998) found a lower root: may also have potential is black oat. Black oat is the shoot ratio in 7-d-old greenhouse-grown cotton plants most widely grown cover crop species in southern Brazil that were grown over wheat straw compared with plants and Paraguay, where climatological and environmental grown over bare soil. features are similar to the southeastern USA. Limited The species and planting date of winter cereals parinformation exists on the suitability of black oat as a tially determine biomass production of a cover crop, and winter cover crop for cotton production in this region conservation tillage crop production in the southeastern of the U.S. Cotton Belt. USA can be improved with large biomass inputs to the Management of cotton following a cereal cover crop soil (Langdale et al., 1990). Since cotton crop developcan be different from that following winter fallow. Most ment and yield may be affected by the presence of winter notably, stand establishment and N management recereal residues, a characterization of these effects may quire special attention following winter cereals. Reducbe useful in designing conservation tillage management techniques. This may especially be needed for potenP.J. Bauer, USDA-ARS Coastal Plains Soil, Water, and Plant Retially new cover crops like black oat. Our objectives search Center, 2611 West Lucas Street, Florence, SC 29501; D.W. were (i) to compare black oat to adapted winter cereals Reeves, USDA-ARS National Soil Dynamics Lab., Auburn, AL. Refor growth and N accumulation when planted at differ­ ceived 25 Jan. 1999. *Corresponding author (bauer@florence.ars. ent times in the fall; and (ii) to determine how the usda.gov). species and quantity of winter cereal residue affect cotPublished in Crop Sci. 39:1824–1830 (1999). ton growth, N status, and yield.