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).
Mean downslope soil tracer displacement over a two year period beginning July 1994 was 3.3 m for CMP, 1.8 m for CRT, 2.2 m for GCMP, and 1.5 m for GCRT. During this period, the last four corn crops out of eight were grown.
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).
The total C concentration distributions across the entire plot in 1996 for treatments CMP and CRT, and for individual compartments in terraces 1 (footslope) and 4 (shoulderslope) for treatments GCMP and GCRT, are shown in Figure 2.
Comparison of the regression slopes in Figure 2E and 2F with that in Figure 2B leads to a similar conclusion for GCRT for terrace 1, but not for terrace 4.
In 1992, the P concentration was nearly constant across each plot (CMP and CRT) or terrace (GCMP and GCRT), being [less than or equal to] 2 [micro]g [g.sup.-1] soil.
The P concentration in the terraces of treatment GCRT was higher and more variable because the soil was not mixed each year by moldboard plowing.
In 1996, the negative regression slopes for GCMP were 6-9 times steeper than for CMP (compare Figure 4A, C, D) whereas the negative regression slopes for GCRT in 1996 were about 3-4 times steeper than CRT (Figure 4B, 4E, 4F).
The general trend for both Cu (Figure 6) and Zn (Figure 7) was for concentration to increase with increase in elevation in the terraces (GCMP and GCRT) and open fields of CMP and CRT.
The pH versus compartment relationship is periodic for GCMP and GCRT (Figure 8C).