Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 8, 2005
Publication Date: February 1, 2006
Citation: Merrill, S.D., Krupinsky, J.M., Tanaka, D.L., Anderson, R.L. 2006. Soil coverage by residue as affected by ten crop species under no-tillage in the northern great plains. Journal of Soil and Water Conservation, 61:7-13. Interpretive Summary: Diversification of rainfed soil-crop production systems has meant the introduction of crop species which leave considerably less residue cover on the soil than do small grain crops. Species such as sunflower, dry pea and dry bean, have much less durable and effective residues compared to wheat. Residue coverage was measured in springtime after seeding in the residues of ten crop species (barley, dry bean, canola, crambe, flax, dry pea, safflower, soybean, sunflower, and spring wheat) growing under no-tillage in a crop sequence experiment. All 100 2-year sequences of the crops could be studied. Residue coverage following small grain crops spring wheat and barley was the highest, 89% or greater. Coverage levels following sequences having spring wheat in the first year were at least 62%, whatever the crop in the 2nd year. Lowest residue coverage levels were found after sequences of sunflower - sunflower, pea - pea, and certain combinations with other crops, which all had a range of 48% to 35%. Under conditions of drought, or following tillage, such lower residue levels could lead to soil erosion hazard, especially on more fragile soils. Soil conservation potential is best enhanced in dryland conservation tillage management systems by seeding of a higher residue-producing crop (e.g., spring or winter wheat, flax) before sunflower or pulse legumes such as dry pea and bean.
Technical Abstract: Soil coverage by residue is important for protecting soil and land resources from erosion, for conserving soil water, and for maintenance of soil quality. While no-tillage with chemical weed control is the current principle means of promoting higher soil coverage, crop diversification in dryland agriculture in the northern Great Plains has featured increased use of species that produce significantly less residue coverage than small grains. Within a 10 x 10 crop sequence experiment, carried out under no-tillage in south-central North Dakota (400 mm mean precipitation), all 2-year combinations of the species (barley, dry bean, canola, crambe, flax, dry pea, safflower, soybean, sunflower, and spring wheat) were observed at two different sites one year apart. There were four replications and crop strips were 9-m wide. Residue coverage was measured by transect and photographic technique following spring wheat seeding. Soil coverage ranged from 98% to 89% following sequences of spring wheat and barley. Coverage values were intermediate for spring wheat - alternate crop sequences, 97% to 62%. Sequences with back-to-back alternative crops had the lowest value range, 86% to 35%. Coverage values after sunflower - sunflower, pea - pea, and certain combination sequences were in a lower range, 48% to 35%. Equations for erosion effects from the RWEQ model yielded the following soil loss ratio (SLR = 1.0 with no residue) values for a year 2000 sunflower-sunflower sequence with 35% coverage: SLR = 0.22 for water erosion; and SLR = 0.15 for wind erosion. Even with use of no-tillage, and especially on more fragile soils, producers need to seed a higher residue-producing crop (e.g., wheat, flax, canola) before seeding lower residue-producing crops in order to assure adequate protection of soil and land resources.