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Table 66. Rainfall and runoff on BW1 and BW3B at ICRISAT Center, 1973 through 1976.<br />
BW1<br />
BW3 B<br />
Year Treatment Rainfall Runoff Treatment Rainfall Runoff<br />
(mm)<br />
(mm)<br />
(mm)<br />
(mm)<br />
1973<br />
1974<br />
1975<br />
1976<br />
Ridged 0.6%<br />
Ridged 0.6%<br />
Ridged 0.6%<br />
Beds 0.6 %<br />
700<br />
810<br />
1040<br />
690<br />
45 Ridged 0.8 %<br />
116 Ridged 0.4%<br />
161 Ridged 1.0%<br />
73 Flat<br />
660<br />
810<br />
1050<br />
700<br />
44<br />
105<br />
193<br />
105<br />
Figure 82. Ponded water above a contour bund on<br />
rainy season fallowed land.<br />
erosion from cropped catchments on Alfisols<br />
generally exceeded that which occurred in similar<br />
deep Vertisol situations, all quantities are well<br />
within acceptable limits. 9 The presence of graded<br />
beds and furrows under rainy season fallow<br />
conditions reduced erosion considerably compared<br />
to a flat, field-bunded situation (Table 68,<br />
BW5 B vs. 4 C); the observed difference would be<br />
even greater if erosion within watersheds were<br />
considered (Fig 83). The highest intensity longduration<br />
storm (on 19 Aug) caused 80 percent of<br />
the seasonal soil loss under rainy season fallow in<br />
a flat field-bunded watershed (BW4 C). Soil<br />
erosion apparently increases much more with<br />
greater rainfall intensities under rainy season<br />
fallow than under cropped beds and furrows<br />
(Fig 84).<br />
Figure 83. Channel deposition in an uncropped<br />
Vertisol following a heavy late-season<br />
rain at ICRISAT Center.<br />
9 The runoff collection tank on BW5 A (about 6.5 ha) was<br />
cleaned from sediment deposited in 1974, 1975, and 1976;<br />
the total quantity of eroded material removed was 18<br />
metric tons, an average of less than 1 ton per hectare<br />
annually.<br />
184
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