Tillage induced soil movement (63 Mg [ha.sup.-1] [yr.sup.-1]) by conventional contour moldboard plowing of an Oxisol was reduced by 53% using a combination of ridge tillage and contour natural grass barrier strips. Corn production was greater for the latter system (Thapa et al.
In addition, for treatments GCMP and GCRT, soil samples were taken in grass barrier strips GS 2 and GS 4, and at distances of 0.15 m downslope and 0.15 m upslope from the lower and upper edges of these grass barrier strips (Figure 1).
The corn crop for the GCMP and GCRT systems was grown in terraces between adjacent contour grass barrier strips (Figure 1).
Figures 2-7 show the observed chemical species concentrations in the surface soil (0-20cm depth) versus compartment, that is, across the landscape of the "open field" plots (CMP and CRT) and individual terrace of management with grass barrier strips (GCMP and GCRT).
To our knowledge, the observed soil acidity increase in the upper portion of an individual terrace has not been considered as a possible factor for yield decline near the contour barrier strips. The soil acidity increase in the surface soil may have secondary effects on nutrient availability and chemical toxicity.