HAY MOISTURE & WEATHER: IMPLICATIONS FOR HAY HARVEST Paul Brown Extension Specialist, Biometeorlogy University of Arizona
Harvest Losses vs. Moisture From Collins & Owens, 1995
Losses During Haymaking
From Collins & Owens, 1995 Heating, Heat Damage, Fire
Evaporation Energy Required Liquid (Water) Gas (Water Vapor)
EVAPORATION Liquid Gas (Humidity) Evaporation Tightly Packed Molecules Held By Polar Attraction Isolated, Free Molecules Moving in Air
EVAPORATION FROM VEGETATION/HAY Weather Regulates/Supplies Energy SOLAR RADIATION TURBULENT TRANSFER ADVECTION WIND WIND Dry Air Dry Air Heat Moist Air Moist Air Heat VEGETATION VEGETATION Hot, Dry Surface Vegetation Solar Radiation, Wind, Temperature, Humidity
From Collins & Owens, 1995 HAY DRYING
Seasonal Drying Trends & Weather Drying related to available energy & vapor transport along with yield (amount of water) Month Solar Radiation W/m*m Vapor Gradient kpa Wind Speed m/s February 160 0.68 1.8 April 264 1.44 2.5 June 347 3.55 2.4 August 302 3.14 2.3 October 231 2.48 1.8 December 139 0.70 1.4 Compare June to any other month. The challenges of winter drying are obvious!
Moisture, % EQUILIBRIUM MOISTURE CONTENT The moisture content of a material that is stabilized at a given temperature and humidity. 40 35 30 25 20 15 10 5 0 Shelled Corn 50 F 0 20 40 60 80 100 Relative Humidity, %
Moisture, % Equilibrium Moisture Content Alfalfa Hay 30 25 95 F 77 F 20 15 10 5 0 0 20 40 60 80 100 Relative Humidity, % Can we predict hay moisture from humidity data?
Does This Work in Arizona? Can we better use relative humidity in harvest management?? RH = 43.2% RH = 57.6% RH = 75.3% K 2 CO 3 NaBr NaCl Allow alfalfa moisture equilibrate to various humidity levels developed using saturated salt solutions.
Moisture, % Equilibrium Moisture Content Alfalfa Hay 30 25 95 F 77 F 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity, % From: Collins & Moore, 1995
Moisture, % HAY MANAGEMENT 30 25 95 F 77 F 20 15 Small Square Large Round Large Square 10 5 70-80% 0 0 20 40 60 80 100 Relative Humidity, %
HAY MOISTURE vs. HUMIDITY Challenging Period: April-July Optimum Relative Humidity for Haymaking: ~70% Maximum Relative Humidity Commonly Stays Below 70% From April-June
HAY METEOROLOGY: NIGHT Relative humidity (RH) at surface increases due to moisture movement from soil to air and surface cooling (due to radiation loss) which increases the saturation level (RH) of the air. Warmer Temperatures, Lower Relative Humidity Surface Cools Due Radiative Loss Inversion Winds Transport Limited Moisture From Surface Increasing Hay Moisture Good Baling: 70% RH Cool Temperatures Higher Relative Humidity Windrow Slow Moisture Movement Slow Moisture Movement
Infrared Radiation WHERE DOES DEW COME FROM? Dew Warm, Moist Soil Dew forms when water vapor from warm moist soils moves upward into the vegetation which is chilled below the dew point.
HAY METEOROLOGY: NIGHT Relative humidity (RH) at surface increases due to moisture movement from soil to air and surface cooling (due to radiation loss) which increases the saturation level (RH) of the air. Warmer Temperatures, Lower Relative Humidity Surface Cools Due Radiative Loss Inversion Winds Transport Limited Moisture From Surface Increasing Hay Moisture Good Baling: 70% RH Cool Temperatures Higher Relative Humidity Windrow Slow Moisture Movement Slow Moisture Movement
Cool, Moist Wind: The Great Evil! Wind mixes warmer and drier air aloft down to the surface replacing the cooler, moist air. This leads to high surface temperatures and lower surface relative humidity and much drier hay. Wind Surface Cools Due Radiative Loss Winds Transport Limited Moisture From Surface Warm, Dry Low Hay Moisture Poor Baling Windrow Slow Moisture Movement Slow Moisture Movement
WINDROW HUMIDITY Wind Sunset
WIND EFFECT: LAST NIGHT
Moisture vs Overnight Weather Measure Temperature & Humidity - 50 cm - 100 cm - 150 cm - 200 cm - Surface temperature (IRT) Hay Placed at Different Levels - Measure increase in moisture
Calm Night Peak Humidity: 76% Moisture increased 9.4%
Windier Night Note Lower Humidity! Peak Humidity: 60% Moisture increased 5% Peak Humidity: 82% Moisture increased 11%
Windrow Structure Short & wide during dry season Tall & skinny during the wetter season Warm, Dry Cool, Moist Windrow Windrow Moisture Movement Moisture Movement
LINK REAL TIME WEATHER TO HAYMAKING CONDITIONS When weather station humidity approaches 50% and winds are light, humidity at surface should approach levels supporting good baling conditions (70%).
WATCHDOG HAY CELLULAR ALERT Spectrum Technologies Humidity Sensor Small Datalogger Cell Phone GSM CDMA At Selected Humidity Calls/Texts Four Numbers Cost $1125-$1375 Phone Charges Need to Determine Proper Humidity Setting 50%??
Infrared Radiation WHERE DOES DEW COME FROM? Dew Warm, Moist Soil Dew forms when water vapor from warm moist soils moves upward into the vegetation which is chilled below the dew point.
Water Vapor in Soil Water Vapor in Air Water Management Even Lower We Vapor need transfer to encourage is higher diminished levels when of soil soils are moisture dry and much during of the dry vapor season is reabsorbed to enhance in the vapor dry transfer surface soil. to the surface. Less/No Dew Dew Lower Lower Irrigation management may be a tool. Subsurface drip irrigation may offer significant benefits. Reduce Irrigation & dry soil Higher
QUESTIONS? Email:pbrown@ag.Arizona.edu Phone: 520-419-2991
Moisture, % Equilibrium Moisture Content Alfalfa Hay 40 35 30 95 F 77 F 25 20 15 Small Square Large Round Large Square 10 5 63-77% 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity, % From: Collins & Moore, 1995