THE PORTION OF THE SOIL WATER THAT IS USABLE BY PLANTS. DIFFERENCE BETWEEN FIELD CAPACITY AND WILTING POINT.

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1 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.

2 - 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 SANDY LOAM LOAM SILT LOAM CLAY LOAM CLAY 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 % x 1.3 = 32.5 % SAND 25 % x 1.5 = 37.5 %

3 ESTIMATE WATER AVAILABLE FOR IRRIGATION VOLUMETRIC WATER CONTENT x 12 in. EXAMPLE: 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 % % = 17.5 % 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

4 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

5 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