|JONES O R - 6209-05-15
|SMITH S J - 6220-10-30
|SOUTHWICK L M - 6413-20-00
|SHARPLEY A N - 6220-10-30
Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/1994
Publication Date: N/A
Interpretive Summary: We measured runoff and sediment, nutrient, and herbicide concentrations in runoff for 9 years from 7 field-sized, graded-terraced watersheds. These watersheds were cropped in a dryland wheat-sorghum-fallow rotation with stubblemulch (SM) or no-tillage (NT) management. Storm runoff was greater from NT, however, the sediment load in runoff was reduced 54% with NT, thus sreducing potentially detrimental off-site effects of erosion. Nutrient concentrations and amounts in runoff were low for both NT and SM management, often less than rainfall inputs. No evidence of atrazine accumulation in the soil or leaching below the root zone was found on NT and atrazine loss in runoff amounted to a maximum of only 0.26% of total atrazine applied and was usually much less. Propazine, which was applied to sorghum grown with both NT and SM management systems, appears to have a greater potential for negatively impacting the environment than does atrazine because of high soil water contents at time of application and greater runoff potential. Losses up to 1.5% of the total propazine application were measured. Some propazine accumulation occurred in the soil, although it was not detected at depths greater than 0.6 m (2 ft) below the soil surface on either SM or NT watersheds. The environmental impacts of adopting NT management on drylands in comparison to the impacts of adopting the lower chemical input SM management appear to be minimal for the Southern High Plains.
Technical Abstract: Increased use of agricultural chemicals with no-tillage (NT) may negatively impact the environment through chemical or nutrient loss in runoff or by leaching below the root zone. We compared environmental impacts of NT and the lower chemical input stubblemulch (SM) management methods for dryland crop production in a semiarid environment. We measured runoff and sediment, nutrient, and triazine concentrations in runoff over 9 yrs from seven field-sized watersheds (3-5 ha each) cropped in a dryland winter wheat, grain sorghum, fallow sequence with SM or NT management and with no N or P fertilizer added. We analyzed soil cores to a 6-m depth for ammonium nitrate and to a 3-m depth for atrazine and propazine content. Adoption of NT management reduced sediment loss by 54% in comparison to SM, although annual runoff was 15 mm yr**-1 greater from NT. Nutrient concentrations and losses in runoff were extremely low from both tillage systems (losses < 3 kg N and < 1 kg P ha**-1 yr**-1) on these unfertilized watersheds. There was no evidence of atrazine accumulating in the soil or leaching below the root zone, and atrazine loss in runoff amounted to a maximum of 0.26% of total application. Propazine, applied to both NT and SM sorghum when runoff probability was high, appears to have a greater potential for negatively impacting the environment under semiarid conditions with up to 1.5% of propazine applications lost in runoff. Propazine accumulated in the soil profile but was not detected below 0.6 m. Perhaps the most detrimental impact of adopting NT management was increased leaching of accumulated ammonium nitrate to depths below the plant root zone as a result of higher soil water contents and improved water conservation with NT in the semiarid environment.