Dryland Crop Sequence and Tillage Influences On Soil Water Storage: First 15 Years.

Management practices and cropping systems have greatly changed over the past half century.  In the northern Great Plains, soil water storage during the non-crop period of annual cropping systems helps to stabilize crop yields.  Our objectives were to determine the influences of six crop sequences and two tillage practices on soil water storage after the harvest of spring wheat.  The six crop sequences were:  1) continuous spring wheat, residue left in place (CSW+); 2) continuous spring wheat, residue removed (CSW-); 3) spring wheat-millet; 4) spring wheat-safflower-fallow; 5) spring wheat-safflower-rye partial cover crop; and 6) spring wheat-fallow.  Tillage treatments were minimum-till (30 to 60% soil surface covered by residue) and no-till (>60% soil surface covered by residue).  Soil water content was determined by using a neutron moisture meter to a depth of 2.1 m in 0.30 m increments.  Soil water storage after spring wheat harvest and before seeding another crop was divided into after harvest (harvest of spring wheat to late October), over-winter (late October to the first part of May), and total soil water storage from harvest to the time of seeding another spring wheat crop.  Averaged over all years, conservation tillage treatments were not significantly different in soil water storage or percent of precipitation stored for after harvest, over-winter, or total for the non-crop period.  As crop diversity in the crop sequences increased, the percent of precipitation stored as soil water for the total storage period increased from 27.6% for CSW+ and CSW- to 34.5% for spring wheat-safflower-rye.