SOIL WATER STRUCTURE AND PROPERTIES OF WATER - POLAR MOLECULE: NEGATIVE CHARGE ON ONE END, POSITIVE ON THE OTHER - COHESION AND ADHESION - ATTRACTION TO CLAY SURFACES - HYDRATION OF IONS - SURFACE TENSION IMPORTANCE OF WATER IN SOIL - SUPPLY WATER TO PLANTS - SOLVENT FOR SOIL SOLUTION - MODIFIES TEMPERATURE AND AERATION - CAPILLARITY => ADDITIVE EFFECTS OF ADHESION AND COHESION SOIL WATER MOVEMENT - MOVEMENT AFFECTED GRAVITY IN SATURATED SOIL - MOVEMENT AFFECTED BY TENSION GRADIENT IN UNSATURATED SOIL - MOVEMENT OF WATER GOES FROM HIGH TO LOW FREE ENERGY - SATURATED SOIL=HIGH FREE ENERGY - DRY SOIL=LOW FREE ENERGY - MOVEMENT ALWAYS FROM WETTER SOIL TO DRYER SOIL TEXTURE EFFECTS - SATURATED FLOW GREATER IN SANDY SOILS - UNSATURATED FLOW GREATER IN MEDIUM AND FINE TEXTURED SOILS - RELATED TO POROSITY/PORE SIZE - INFILTRATION PATTERN AFFECTED BY TEXTURE - MOVEMENT AFFECTED BY LAYERS WHICH GENERALLY IMPEDE FLOW AVAILABLE WATER THE PORTION OF THE SOIL WATER THAT IS USABLE BY PLANTS. DIFFERENCE BETWEEN FIELD CAPACITY AND WILTING POINT.
- FIELD CAPACITY=SOIL MOISTURE CONTENT WHEN GRAVITATIONAL DRAINAGE CEASES IN A SOIL THAT WAS SATURATED - WILTING POINT=SOIL MOISTURE CONTENT AT WHICH THE PLANT CAN NO LONGER ABSORB WATER - AVAILABLE WATER=FIELD CAPACITY - WILTING POINT - AVAILABLE WATER RELATED TO TEXTURE - SILT LOAM HAS THE HIGHEST AVAILABLE WATER - SOIL CHARACTERISTICS, NOT ROOT CHARACTERISTICS CONTROL WATER UPTAKE BY PLANTS SOIL TEXTURE AND WATER CONTENT (IN/FT) TEXTURE FC WP AW SAND 1.4 0.4 1.1 SANDY LOAM 1.9 0.6 1.4 LOAM 3.1 1.2 1.9 SILT LOAM 3.4 1.4 2.0 CLAY LOAM 3.7 1.8 1.9 CLAY 3.9 2.5 1.4 MEASURING SOIL WATER - GRAVIMETRIC METHOD GRAVIMETRIC WATER CONTENT % MOISTURE = (WET WT. DRY WT.) / DRY WT. X 100 EXAMPLE: (100g 80g) / 80g x 100 = 25% VOLUMETRIC WATER CONTENT GRAVIMETRIC WATER CONTENT x BULK DENSITY EXAMPLE: SILT LOAM -- 25 % x 1.3 = 32.5 % SAND 25 % x 1.5 = 37.5 %
ESTIMATE WATER AVAILABLE FOR IRRIGATION VOLUMETRIC WATER CONTENT x 12 in. EXAMPLE: 0.325 x 12 in. = 3.9 in./ft. THIS EXAMPLE CALCULATES THE TOTAL WATER, NEED TO KNOW AVAILABLE WATER (AW) FIELD CAPACITY WILTING POINT = AW 32.5 % - 15.0 % = 17.5 % 0.175 x 12 in. = 2.1 in. AVAILABLE WATER/ft. WHEN SCHEDULING IRRIGATION MAINTAIN >45 % AVAILABLE WATER 0.45 x 2.1 = 0.95 in. USE CHECKBOOK METHOD TO ADJUST FOR EVAPOTRANSPIRATION LOSS WATER MANAGEMENT AND CONSERVATION HYDROLOGIC CYCLE - 97 % OF EARTH S WATER IN OCEANS - CYCLE FUELED BY ENERGY OF SUN - FATE OF PRECIPITATION o RUNOFF o PERCOLATES THROUGH SOIL o EVAPORATES FROM SURFACE o ABSORBED BY PLANTS - IN WISCONSIN o ANNUAL PRECIPITATION ~ 31 in/yr o 21 in. EVAPOTRANSPIRATION o 4 in. RUNOFF o 6 in. PEROCOLATION CONSERVING WATER IN AGRICULTURE - REDUCE RUNOFF o TERRACES, DIVERSIONS, ETC. o CONTOUR TILLAGE o STRIP CROPPING
o CONSERVATION TILLAGE o CROP ROTATION - REDUCE CONSUMPTIVE USE o REDUCE EVAPORATION WITH MULCHES, CROP RESIDUE o REDUCE TRANSPIRATION WITH WIND BREAKS, WEED CONTROL o IRRIGATION SCHEDULING - MANAGE PLANT USE EFFICIENCY o PROPER FERTILIZATION INCREASES WATER USE EFFICIENCY o LIMIT COMPACTION TRANSPIRATION RATIO=WATER USE/DRY MATTER CROP TRAN. RATIO ALFALFA 858 OAT 635 POTATO 575 CORN 372 SORGHUM 271 LAMBQUARTER 658 PIGWEED 300 PURSLANE 281 lb WATER USED/lb DRY MATTER PRODUCED DRAINAGE PROBLEMS WITH POOR DRAINAGE - REDUCE AERATION TO ROOTS - DENITRIFICATION - NUTRIENT UPTAKE REDUCED - DELAYS TILLAGE AND OTHER OPERATIONS - COOLER SOIL DELAYS GROWTH WETLANDS vs WET SOILS - WILDLIFE AREAS (1/3 ENDANGERED SPECIES) - NATURE S SPONGE AND FILTER - CRANBERRIES ARTIFICIAL DRAINAGE - SURFACE
o LAND LEVELING ON SLOWLY PERMEABLE SOILS OF NC WISCONSIN o DIVERSIONS ABOVE FIELDS, BARNYARDS - SUBSURFACE o BURIED DRAIN TILE o REQUIRES AN OUTLET o WATER ONLY ENTERS IF SOIL IS SATURATED o SPACING DEPENDS ON SOIL TYPE, PLACEMENT DEPTH IRRIGATION - SUBSURFACE o UTILIZES CAPILLARY RISE o PERMANENT o INEFFICIENT IN SANDY SOILS - SURFACE - FURROW o WESTERN US o RELATIVELY INEFFICIENT - TRICKLE o MOST EFFICIENT o USUALLY PERMANENTLY SET o HORTICULTURE - SPRINKLER o HAND MOVED=LABOR INTENSIVE o SOLID SET=GOLF COURSES, BERRIES o TRAVELING GUN o CENTER PIVOT o LINEAR IMPROVING IRRIGATION EFFICIENCY - MAINTAIN EQUIPMENT - BASE RATE ON CROP NEED (SCHEDULING) - RATE SHOULD NOT EXCEED INFILTRATION