DIMENSION AND VOLUME OF CRACKS IN A VERTISOL UNDER DIFFERENT CROP COVERS

Depth, width, and length, per unit area of cracks were measured in a Udic Haplustert from India during the summer season after the harvest of different crops (chickpea, wheat, sorghum, sunflower, and safflower) and compared with that of a fallow plot. The width, depth and length of cracks exhibited a wide size range. Crack width was significantly less (1.3 cm) in the fallow plot compared with those plots planted to crops. Crack depth in a majority of the plots was not significantly different from fallow except for plots planted to safflower and sorghum. Crack length was the highest in the fallow plot compared with cropped plots and, as a result, the surface cracking pattern was more intricate in the fallow plot. No single crack dimension adequately characterized the cracking intensity. Hence, crack volume per unit area was considered to be a better index of cracking intensity because it includes all three crack dimensions. Crack volume computed by measuring length, depth, and width, and that measured directly by infilling with sand, approximated each other. The crack volume was highest in plots planted with safflower (445 m3 ha-3) because of its deep rooting and efficient moisture extraction and least in the fallow plot (234 m3 ha-3). In other cropped plots the values were intermediate. The crack space assumes significance in that it can accommodate 23-44 mm of rainfall facilitating moisture recharge in these otherwise slowly permeable soils.