Irrigation is one of the most important parts of any farmer’s care of their crops, whether they’re growing onions, sunflowers, tree seedlings or grapes. Too much or too little water can cause plants to feel distress – and that affects everything, from the soil to the plant to the farmer to consumer. The study described below offers up a way for more data-driven nursery growers to measure container water loss and gain in their businesses.
“Monitoring Container Water Loss and Gain with a Data-Logging Scale” by Jeff Million and Tom Yeager, Dept. of Environmental Horticulture, University of Florida, IFAS
What Million and Yeager were focused on with this study was divining a simple weighing system that container nursery producers could use for measuring and monitoring plant water loss and irrigation water gain. The information gleaned from the system would provide an evaluation of irrigation effectiveness – and allow growers to adjust irrigation practices to maintain proper moisture levels.
The researchers used an off-the-shelf scale and data logger for their experiments to record container weights, with relatively short data-logging intervals (every five minutes). They used a 15 kg bench scale to weigh one-gallon and three-gallon containers and a 60 kg bench scale to weigh seven- and 15-gallon containers. They utilized a USB-logger which could record weights as often as every second up to every hour. At nurseries, at least one scale was placed in the irrigation zone to monitor water weights.
One area focused on in this study was container evapotranspiration (ET) – how much water a container loses over the course of a day. The researchers used as an example a pre-dawn sprinkler-irrigated Burfordii Chinese holly crop, with its stable wet weight established before sunrise. The dry weight measurement was taken once ET water loss ended (usually around sunset, at the earliest). The dry weight was subtracted from the wet weight to show an average loss of about 0.7 kg – about 0.54 inches of water per 10 inch-diameter container. A nursery owner could compare that loss to the irrigation rate of inches per hour to reevaluate their watering practices.
Another important item looked at was the possibility of over-irrigation, especially in sprinkler-irrigated crops. This example used Parsonii juniper plants in trade three-gallon, 10-inch containers, watered at 7:30 a.m., with weight data recorded every five minutes. “The steep drop in weights immediately following the peak weight of irrigation…is evidence for excessive irrigation,” the study states. “Although not definitive, approximately 0.2 kg of excess water was applied. If the total applied was 0.7 kg, this indicates a leaching fraction of approximately 30%.”
Additionally, the research team discovered that weight measurements following a significant rain could provide solid baseline values for the container capacity of a given crop. A post-rain baseline weight is also a better indicator of container capacity for determining if water deficits are approaching the lower limit of available water for plants.