Thursday, August 4, 2011

The drought continues

    It hasn't been this dry since the summer of 1980. I was out in the grove the other day checking out the pecan crop and inspecting the dry weather cracks that have formed in the soil. In a field of 20-year-old pecan trees, the cracks were enormous (photo at right). That's  a grafting knife (6.5 inches long) in the photo spanning a soil crack that was over 30 inches deep. What was interesting to me about these soil cracks was their location among the trees. The widest cracks were found exactly half way between adjacent trees (trees planted 30 ft. x 30 ft.). In fact, each tree has a soil crack ring around the tree that runs about 15 feet from the trunk. The formation of these rings tell us that each tree has its own, separate area for soil water extraction
    The situation in our native groves is very different. Large soil cracks have not developed. The roots of our native trees are so intertwined that each trees does not have an individual root zone and water is being extracted from the soil evenly across the grove.
   The soil at the research station is an Osage silty clay. The shrink/swell capacity of this soil is extremely high. We see soil cracking almost every summer but 6 inch wide cracks represent the extreme end of the soil cracking phenomenon. It will take 10 to 15 inches of rain to close up these cracks before harvest.