Agriculture is intrinsically linked to the weather and climate. A thorough knowledge of weather patterns is critical in managing crops and livestock, and an understanding of past patterns can also be very useful.
Automated weather stations continually and automatically record and store weather data. This can be used to assist in many decision-making processes around the farm.
Automated weather stations have been installed at Myrtleford, Rosewhite, Porepunkah, Coral Bank, Whorouly, Beechworth, Dinner Plain and the King Valley.
The following weather and climate parameters are recorded:
Temperature is important in the transpiration and growth processes of crops and the performance and behaviour of livestock.
Our weather stations calculate degree-days and chill-days using a sensor housed in a protective enclosure which shields it from rain and solar radiation, but allows free airflow.
Degree-days are a measure of the cumulative heat input to a crop, and is a moving sum of the product of time and temperatures above 10°C.
The degree-days calculation is useful in estimating how long it will take for a crop to move from one phonological stage to another.
Chill-days is a very similar calculation, being the product of temperatures below 10°C and time elapsed.
It is used particularly in orchards to determine whether sufficient cold days have occurred for fruit to set.
Dew Point is the temperature at which moisture from the air condenses to form dew. It has a correlation to temperature and humidity. The dew point will be closer to the air temperature during higher humidity.
The dew point calculation is pressure corrected using the mean standard pressure at the station's altitude.
Relative humidity is the degree of saturation of water vapour in the air, at a given temperature. It tells us how much moisture the atmosphere is holding relative to the worst case scenario (a tropical rainforest)at that temperature and is expressed as a percentage.
The higher the temperature, the more moisture the air can hold. Hence, for a given amount of moisture, relative humidity is higher during the cool of the morning and lower during the heat of the day.
Relative humidity is important (along with air temperature, rainfall, leaf wetness and hours of darkness) in models that predict disease outbreaks such as mildew in onions and botrytis in grapes. Fungal spores nearly always require relative humidity above 95% to reproduce.
Delta-T is the agricultural term for wet bulb depression. It is generally used as an indicator for evaporation and droplet lifetime for spraying applications. Our weather stations do not measure wet bulb temperature directly, but it can be approximated from the measured air temperature and relative humidity.
Delta T is becoming one of the standard indicators for acceptable spray conditions. It is indicative of evaporation rate and droplet lifetime. When applying pesticides, Delta T should ideally be between 2 and 8.
Wind direction or bearing is measured every 5 seconds and displayed as a 16-point compass bearing. Average wind speed is calculated over a 15-minute interval.
Both are measured 2m above the ground to facilitate the calculation of evapotranspiration, whereas BoM stations make these calculations at 10m.
Solar radiation is another term for sunshine, whether it be direct or back-scattered from the atmosphere (diffuse solar radiation).
This weather station measures global solar radiation which is the sum of the above.
Solar radiation levels have a major impact on the calculation of evapotranspiration.
Rainfall is obviously a critical factor for all farmers.
Our stations use a tipping bucket rain gauge to measure local rainfall.
These systems have been used for many years and adopt a self-emptying device which registers 0.2mm of rainfall per tip via a magnet and reed switch sensor that is registered in the data logger.
The leaf wetness is an indication of rain or dew formation.
This sensor is used mostly for fungal disease prediction and is mounted in the crop canopy to detect the presence of droplets of rain on surrounding leaf surfaces.
Soil temperature is measured 100mm beneath the soil surface and can be used as an indicator for determining sowing dates etc.
It should be noted that soil temperatures can vary markedly between sites depending on soil type, cultivation history and mulch content.
The weather station will calculate potential evaporation using a complex equation (the Penman-Monleith equation) which uses solar radiation, wind speed, air temperature and relative humidity data.
The Evapotranspiration figures quoted are daily Reference Crop Evapotranspiration (mm) and are intended as a guide only as actual crop ETo may depend on other factors relating to crop characteristics such as canopy management in grape vines.
To generate estimates of crop water requirements in millimetres, simply multiply the daily ETo figure by an appropriate Crop Coefficient (Kc value).
The recommended Kc can vary depending upon the age of the crop and stage of growth.
Evapotranspiration (ETo) is different from evaporation which is normally measured from a
Evaporation data is often used in conjunction with a Crop Factor to estimate crop water requirements. Crop Factors are not the same as Crop Coefficients and should not be used with ETo data to calculate irrigation needs.