Saturday, 15 July 2006

Effect of Tillage and Chemically-Weeded Fallowing on Measured Wind Erosion on Sunflower Stubble Land in the Northern Great Plains, USA.

Stephen D. Merrill1, Ted M. Zobeck2, Donald L. Tanaka1, Lawrence J. Hagen3, Joseph M. Krupinsky1, John E. Stout2, and Brenton Sharratt1. (1) USDA-ARS, Northern Great Plains Research Lab, P.O. Box 459, Mandan, ND 58554, (2) USDA-ARS, Cropping Systems Research Lab, 3810 4th St., Lubbock, TX 79415, (3) USDA-ARS, GMPRC, Wind Erosion Research Unit, 1515 College Ave., Manhattan, KS 66502

Diversification of cropping systems in the northern Great Plains of the USA includes crop species with residues that are less durable than small cereal grains, creating potential wind erosion hazards under drought and tillage disturbance. No-tillage with chemical weed control is currently considered to be one of the best soil conservation practices available because it conserves crop residues. But even under long-term no-tillage management, soil residue coverage in the spring after seeding wheat can be less than 50% following prior crops of sunflower (Helianthus anuus L.) or legumes such as dry pea (Pisum sativum L.). Information is needed to better understand the interaction of different tillage and fallowing practices with lower residue-producing crops under dryland conditions. A wind erosion experiment was established in central North Dakota (mean precipitation 410 mm yr-1) on silt loam soil (Pachic Haplustolls). Management practices applied in the year following a no-till sunflower crop (50-60 cm high sunflower stubble) consisted of tillage in mid-April followed by season-long chemical fallowing with glyphosate. Tillage treatments were: (a) no-tillage (NoT); (b) single pass disking (MedT); (c) two passes with a heavier disk and rotary harrowing (MaxT). Soil losses were measured after tillage until winter wheat seeding in mid-September. Sediment samplers of the BSNE-type were placed at the middle of boundaries of square 1.3 ha replicated plots (6 total), and piezoelectric moving particle sensors were placed in the middle of each plot. Non-erodible strips of land that were roughened by seeder passage and covered with wheat partially or fully surrounded the plots. Vertical profiles of transported sediment were measured in MaxT plots with stacked sediment samplers (at 5, 10, 20, 50, and 100 cm).Wind erosion losses prior to July were considerably lower than losses later in the season due to greater soil roughness in tilled treatments and greater density of standing sunflower stalks in the NoT treatment. Attenuation of roughness by precipitation and loss of standing sunflower stalks during the season increased wind erodibility over time. During the June through mid-September period in 2003, estimated losses for MaxT, MedT, and NoT totalled 38, 12, and 6 Mg ha-1. Low soil residue cover combined with poor soil surface structure to accelerate erosion in the MaxT treatment to levels that were potentially damaging to soil health. Estimated soil losses under MaxT during the top 5 wind erosion periods during the summer of 2003 summed to 36 Mg ha-1, reflecting relatively dry conditions and superior weed control. More frequent precipitation during the summer of 2004 and greater weed growth escaping control resulted in estimated MaxT soil losses for the top 5 wind erosion periods of no more than 3 Mg ha-1. During two 8 to 13 day periods in May 2003, estimated soil losses for a dry period were 0.70 and 0.02 Mg ha-1 for MaxT and NoT treatments (ratio = 35), and estimated losses for a heavily rain-affected period were 0.74 and 0.36 Mg ha-1 for MaxT and NoT (ratio = 2.1). During two 2 to 6 day periods in Aug.-Sept. 2004, estimated losses for MaxT and NoT in the dry period were 1.29 and 0.17 Mg ha-1 (ratio = 7.6), and losses in the period with rain were 0.77 and 0.49 Mg ha-1, respectively (ratio = 1.6). These results are believed to result from part of the soil movement during rain-affected periods consisting of “wind-driven rain-splash” erosion. The relative increases of apparent soil movement in the NoT treatment during rain-affected periods probably reflects lesser sensitivity of wind-driven rain-splash transport to standing and prostrate sunflower residues compared to the effect of residues on sediment movement by dry wind erosion with its different transport physics. Data from stacked sediment samplers in the MaxT treatment indicated that the midpoint heights (half of mass above) of sediment mass transport profiles were more than double in value compared to midpoint heights of profiles published for soils in the southern Great Plains that had coarser texture than the silt loam of this study.

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