VARIATION OF SURFACE SOIL QUALITY BY INTENSIVE DONKEY-DRAWN TILLAGE ON A STEEP SLOPE

Authors: LI, YONG - 5060-00-00; Lindstrom, Michael; BORK, H - 5060-00-00

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/14/2003
Publication Date: N/A
Citation: N/A

Interpretive Summary: Tillage operations result in a progressive and relatively rapid redistribution of soil from upland positions to field depressions or lower field boundaries. This redistribution of soil can change soil properties and effect the productive capacity of the soil. Few direct measurements have been made for this effect. To study this problem, we moldboard plowed a representative field in the Chinese Loess Plateau 50 times in a short time period. Objectives of this study were to determine topographic changes over a steep dissected hillslope and measure the net effects on surface soil quality across the hillslope. Results showed a dramatic lowering of the upper field boundary (1.25 m) with subsequent deposition at the lower field boundary resulting in an elevation increase of 1.33 m. A rapid decrease in soil organic matter, nitrogen and phosphorus was observed in the upper and middle portions of the slope. An overall decline in soil quality was observed over the hillslope, although a short-term increase in organic matter and soil nutrients was found in the lower slope position during the tillage operations. Conservation planners who develop management strategies will use these data to maintain soil quality in intensively tilled crop production systems.

Technical Abstract: The progressive but relatively rapid redistribution of soil from uplands to field depressions or lower field boundaries by tillage has the potential to modify soil properties. However, few direct measurements have been made for this effect. We conducted 50 plowing operations using a donkey-drawn moldboard-plow tillage system on a representative steep backslope area in the Chinese Loess Plateau. The objectives were to determine topographic changes in a steep dissected hillslope and quantify the net effects of intensive tillage on surface soil quality at different slope positions. Changes in soil surface levels (SSL) were measured by using survey-grade Differential Global Positioning System (DGPS). Soil quality parameters, i.e., soil organic matter (OM), available P, N and surface bulk density (Db) were measured by direct sampling surface soil materials in a downslope transect immediately after a series of tillage operations. Fifty tillage operations resulted in maximum SSL decrease of 1.25 m in the upper slope position and maximum SSL increase of 1.33 m at the bottom of the slope. A reduction in slope gradients from 37 deg to 14 deg at the upper slope position and from 18 deg to near zero at the lower slope position was observed, whereas no changes occurred in the middle portion of the slope. Average soil OM content in the upper and middle portions of the slope decreased from 8.3 to 3.6 g kg**-1, N from 43.4 to 17.4 mg kg**-1 and P from 4.5 to 1.0 mg kg**-1 after 50 tillage operations. Intensive tillage resulted in the overall decline in soil quality for the whole slope, although a short-term increase in OM and available nutrients were found in the lower portion during tillage operations. Initial soil profile properties controlled the changing magnitude of surface soil quality in the upper portion while the dispersion of nutrients associated with soil redistribution by tillage from the upper parts of the slope controlled the magnitude of the variation in surface soil quality of the lower portion. On-site impacts (Y) of soil redistribution by tillage on OM, N and P in the lower portion were estimated using the variations (X) in the upper portion based on a simple logarithmic upper-lower portion regression function, Y = aLn(X) + b. The average relative errors for prediction of OM, N and P contents by using this function were less than 8%.