Water conservation practices for dryland farming

FOR REGIONS THAT HAVE SUMMER RAINFALL AND NO IRRIGATION SYSTEMS, THESE ARE FARMLANDS THAT RECEIVE 500MM OR LESS OF ANNUAL PRECIPITATION. THE MOST COMMON PRACTICE IN SEMI-ARID REGIONS OF THE U.S. IS TO LEAVE THE LAND FALLOW -- UNPLOWED AND UNPLANTED -- FOR A PERIOD LONG ENOUGH FOR IT TO STORE ENOUGH WATER-HOLDING CAPACITY. THIS PRACTICE IS CALLED "SUMMER FALLOW," BUT ACTUALLY THE LAND MAY BE LEFT FALLOW FOR 14 OR 15 MONTHS, WITH THE MOISTURE BUILDUP OCCURRING MAINLY DURING THE FALL AND WINTER MONTHS. TO PROTECT FALLOW LAND AGAINST WIND EROSION, WATER EROSION, AND WATER EVAPORATION, STUBBLE MULCHING IS PRACTICED. THE CROP RESIDUE IS UNDERCUT WITH A SUBSURFACE INSTRUMENT, AND LEFT IN THE GROUND. THIS DECREASES SURFACE WATER RUNOFF AND REDUCES THE RATE OF EVAPORATION OF MOISTURE FROM THE SUB-SURFACE OF THE SOIL. IF THE SOIL GROWS WEEDS DURING THE FALLOW PERIOD, THESE MUST BE TILLED, BECAUSE THE WEEDS WILL USE UP THE MOISTURE IN THE SUBSOIL. OTHER METHODS OF CONSERVING MOISTURE INCLUDE SHAPING THE SOIL SURFACE INTO WATER-CONSERVING STRUCTURES. THESE INCLUDE RIDGE TERRACES, LEVEL-BENCH TERRACES, PARALLEL-BENCH TERRACES, LEVEL PANS, AND THE PRACTICE OF PITTING. THOSE PRACTICES ARE DESCRIBED. STILL OTHER METHODS INVOLVE STRIP-CROPPING, WIND BREAKS, AND PARTICULAR CROP ROTATIONS. DEPENDING ON PARTICULAR TEMPERATURE AND PRECIPITATION CONDITIONS IN VARIOUS REGIONS OF THE U.S. GREAT PLAINS, VARIOUS PRACTICES ARE USED, WHEAT-FALLOW, WHEAT-SORGHUM-FALLOW, OR WHEAT-MILLET-FALLOW. FALLOW IS GENERALLY NOT USED WITH CORN OR OATS. IF LAND THAT HAS LAIN FALLOW HAS CONSERVED OR ACCUMULATED ENOUGH MOISTURE, NITROGEN FERTILIZER WILL INCREASE YIELDS OF WHEAT OR GRAIN SORGHUM. APPLICATIONS VARY, DEPENDING UPON HOW MUCH NITROGEN HAS BUILT UP IN THE SOIL DURING THE FALLOW PERIOD. APPLICATIONS IN THE GREAT PLAINS OF THE U.S. VARY FROM 34 TO 90 KG/HECTARE.