Soil Moisture Monitoring for Ginseng

By Rebecca Shortt, Water Quantity Engineer, OMAFRA and Sean Westerveld, Ginseng and Medicinal Herbs Specialist, OMAFRA

With variable rains across the ginseng growing region it can be difficult to know when it is necessary to irrigate. Even if soil moisture is slightly lower than optimum for a week, yield can be impacted. Furthermore, seed yield and quality will be significantly affected by low soil moisture, especially if combined with a period of high temperatures, low humidity and/or windy conditions. There are many tools that can be used to improve water management decisions and avoid both wasting water and unnecessary yield losses.

Importance of Monitoring Water Use with a Meter

Knowing how much water you use is the first step to increasing farm water use efficiency.  Installing a water meter- is a beneficial step for any farm practice which uses water.

A water meter provides an instantaneous reading of the flow of water for the application (e.g. irrigation system) and helps to diagnose if the system is operating as designed.

  • Higher than usual flow? Check the system for leaks, worn nozzles and malfunctioning valves.
  • Lower than usual flow? Check the system for plugging, malfunctioning valves and pump station performance.

Monitoring the water flow from an application over a period of time, and tracking the total flow reading will help to assess the on-going water use from each application and will help you to evaluate new practices or equipment.

  • Assesses the impact of new management practices on the basis of their water usage.
  • Allows for an optimization of water use by comparing the water use and associated costs of different practices.

Under scenarios of climate change and where water supplies are stressed, a water monitoring program is the first tool needed to identify water-efficient opportunities.

In addition to the meter itself, wireless transmission of the meter readings, loggers and software to graph the output are all useful tools to assist you in making good use of the data collected in a timely manner.

The Water Adaptation Management and Quality Initiative (WAMQI) is conducting a pilot program which will partially subsidize water meters for use in select agricultural operations. Through this pilot program agricultural irrigators and vegetable wash water users can receive a subsidy of 50% of the cost of a water meter and associated installation, up to a maximum of $750 per farm. Refer to the program website for more information:

Importance of Monitoring Soil Moisture with an Instrument

Monitoring soil moisture is the key to getting the right amount of water to crops at the right time.  The use of soil moisture monitoring equipment will benefit decision-making on all irrigated farms.

Monitoring soil moisture and taking action to use the information provided in irrigation decisions will help growers manage soil moisture.  Choosing the right times and the right amounts to irrigate can lead to:

  • Higher yields
  • Better product quality
  • Improved plant vigour
  • Reduction in disease
  • More effective use of water (water efficiency)
  • Reduced irrigation costs

Soil moisture instrument demonstrations have occurred in southern Ontario and cooperating farms reported the following outcomes:

  • “My understanding of soil moisture monitoring has improved. I now know the field capacity, wilting point and my optimum irrigation trigger points.”
  • “Soil moisture monitoring helps me determine when irrigation is beneficial.”
  • “Now I know what is going on in the soil profile; before I was guessing”
  • “The soil moisture instruments taught me the best timing and quantities to apply; you can see the trends in the graphs to see if you’ve applied enough or too much.”
  • “From the soil moisture instruments I learned that I was not applying enough water.”

In addition to the soil moisture instruments themselves, wireless transmission of the moisture readings, loggers and software to graph the output are all useful tools to assist you in making good decisions based on the data collected.

There are several methods and tools for monitoring soil moisture in a ginseng field. For an outline of these methods, refer to the OMAFRA FactSheet “Monitoring Soil Moisture to Improve Irrigation Decisions” at These tools are eligible for Growing Forward 2 Implementation Funding assistance.

Monitoring Soil Moisture Based on Rainfall and Evapotranspiration Rates

Soil moisture monitoring equipment is the most accurate means to determine the need for irrigation, but at the very least growers should have a rain gauge in each field and compare the amount of rain and irrigation to evapotranspiration rates. Rain gauges should be placed outside of the garden in an open location away from overhanging branches and from objects that might cause rain to splash into the rain gauge. Rain does not easily splash out of a rain gauge, so any water splashing into the rain gauge will result in an over-estimate of the amount of rainfall. Rain gauges should never be placed under the shade because of the variability caused by the drip lines. Rain splashing off the shade will also interfere with accurate measurements if the rain gauge is within a few metres of the shade structure.

Evapotranspiration rates are provided for Simcoe and other locations in southern Ontario at (click on “Maps/Tools” and then “ET”). The ET rates need to be adjusted by a crop factor to account for the thickness of the canopy. A seedling garden will not dry out nearly as fast as a 3 or 4-yr garden. Although these have not been tested for ginseng, growers should multiply ET by an approximate conversion factor of 0.3 for a seedling garden, 0.7 for a 2-yr garden and 0.8 for mature gardens. These rates can be adjusted over time based on observations of the crop.

Sandy soil can only retain about 25 mm of water in the rooting zone. Heavier rains will drain out of the field and will not be available to the crop. This needs to be factored into calculations of available water in the field. For example, if the water availability in the soil is 15 mm and you get a 20 mm rainfall, only 25 mm will be available to the crop once the excess water drains out of the root zone.

For more information on irrigation and soil moisture, refer to the main OMAFRA irrigation page:

About Sean Westerveld

Ginseng and Medicinal Herbs Specialist, OMAFRA
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