Agricultural Weather Services

The information supplied in this article is supplied by Bob Robinson from the Agricultural Section.

Why weather service specifically for agriculture? Here is a quote from the Commission on Agricultural Meteorology of the World Meteorological Organization, from the publication Weather and Food: “Much can be done by the application of existing knowledge, much more could be done if we knew a little more”….”As the value of meteorological help becomes realized and its capabilities improve, the present trickle can become a flood which could carry away to oblivion centuries of hunger and want.”

Like fire-weather and marine-weather programs, services to agriculture are designed to help the user solve a variety of weather-induced problems. The user for an agricultural weather forecast program can be anyone in the chain from farm site selection - to field preparation - to planting - to crop & water management - to harvest - to removal and transport of a crop from the field. Aside from the goal of providing weather forecast information, an important goal is the understanding of the responses of living organisms to the physical environment.

While a number of weather parameters are important to agriculture, the main benefit to farmers comes from communication of the criticality of weather at a time when management techniques can provide mitigation to crops. The spectrum of applications can be broken into several categories: Scheduling of cultivation, planting, and harvesting, crop protection (general), insect control, disease control, irrigation, and appropriate selection of crops - or sites for crops.

During the growing season the vulnerability of crops to different weather events can change. Consequently, it is of primary importance to understand the relationship between the stage of development of a crop (plant or animal) and weather as the growing season progresses. The source for much of this knowledge has been, and continues today to be collaboration between farmers, agricultural research, such as U.S.D.A or university Cooperative Extension, and agricultural meteorologists.

Temperature –

For many crops, a proxy, such as the Growing Degree Day (GDD) can be used to measure crop growth since many plants respond strongly to thermal conditions when all other factors needed by the plant are in adequate supply. The GDD is similar to the Heating Degree Day but different thresholds are used depending upon the crop. Both farmers and agricultural meteorologists can keep track of the accumulation of GDDs, and they can also be forecast to provide an indication of an upcoming critical stage. Since GDD are related to crop growth, they can indicate the appropriate time to make crop management decisions that are based on stage of growth, such as spraying of pesticides or harvesting.

GDD are also an indicator of insect pest development since many growing season-emergent insect pests have their development driven by temperature. Forecasting GDD for insect pests can alert farmers of the necessity to take appropriate action such as pest scouting, pest control, or other pest treatment. As with GDD for crops, there are a variety of baselines and thresholds for insect development GDD. An accurate GDD forecast can help farmers decide whether or not there may be significant (economic) damage based on the relationship of temperature to insect activity, and thereby minimize any environmental impact that any control may bring.

Other important temperature-based forecast information includes Livestock Heat Stress, Poultry Heat Stress, and soil temperatures. The latter are important for crop planting advice.

Moisture –

Rain and dew are important to agriculture, not only as a necessary source of plant moisture but also as a harbinger of disease. Forecasting rain or dew, intensity and duration, can provide useful information to growers who need to protect crops from diseases that each element may encourage. Typical diseases are Corn Leaf Spot, Potato or Tomato Blight, Peanut Leaf Spot. Typically, the onset of the disease can be estimated by the duration or intensity of moisture, or both. Protection may follow in the form of a fungicide spray.

Also important are forecasts of soil moisture in terms of field-drying time. This information allows farmers to plan when they can return to fields that have been flooded.

Frost or Freeze –

While frosts and freezes are typically temperature forecasts, here again agricultural meteorologists must be aware of the stage of development and the location of a crop. Is the crop ground-based such as cranberries or is it tree fruit (apples, peaches)? For tree fruit in the spring, the buds lose hardiness (become more sensitive to cold) as the spring progresses and buds progress toward the flower and fruit stage. As a result, no damage may occur early when hardiness may be down near 18 deg. F., but near flowering, the damage threshold may be closer to 30 to 32 deg. F. Consequently, protection against ‘frost’ is taken at differing temperatures across the season. Since many growers protect against frost by using wind machines to bring down warmer air from inversions, the meteorologist must be able to forecast the character of the inversion during the night.

Wind –

Forecasting wind direction and speed and the time of day it occurs is important in the aerial application of pesticides and herbicides. Unwanted spray drift can become a serious problem where adjacent fields contain crops that are not registered for the same chemicals or where environmental damage may occur.

Irrigation –

In a large part of the country artificial irrigation is necessary for agriculture. For these areas useful forecasts of water needs provide farmers with information for managing their irrigation scheduling. Forecast schemes based on temperatures, wind, and evaporation have been successful in providing irrigators with the ability to anticipate their water needs.

Instrumentation –

The routine set of weather station instrumentation is often not sufficient to make measurements that are required for the observation and forecasting of agriculturally important weather elements. Numerous networks, including state, university and privately owned, have outfitted their weather stations with special sensors. Among these are soil temperature, solar radiation, and leaf wetness.

Precision Agriculture –

The future of agricultural production, especially for high-value-per-acre crops such as tree fruit, grapes, tomatoes, and others, may lie in precision agriculture. Precision farming is a data intensive practice which almost continuously monitors and analyses both the physical and environmental factors affecting crop production. It is accomplished at such a scale that no data pertaining to a significant piece of farmland would be overlooked. The results of this monitoring and analysis are used as management tools to produce the highest quality crop possible on every piece of ground. The scale of monitoring and management define how “precise” the farming will be. This will likely also require that forecast resolution match the observations. A network for a small grower in the western U.S. (<100 acres), may require a finer-than-mesoscale forecast. Obviously, precision farming will bring many challenges and opportunities to those involved in agricultural weather prediction..

This information is supplied by Bob Robinson

from the Agriculture Section.