What is in this article?:
- Minimizing groundwater nitrates with proper fertigation
- Distribution vital
- Know the water
- Even distribution of water and fertilizer are key to reducing nitrates and saving water.
Bill Green, an educational specialist at Fresno State, shows equipment that can be used to apply nutrients efficiently and safely through irrigation systems.
He said distribution uniformity of water – and with it fertilizer -- is a key and results in saving water, fertilizer and energy.
“If you’re doing a poor job distributing water, you’re also doing a poor job distributing fertilizer” when fertigating, Green said.
Uneven distribution can result from poor design of a system, differences in elevation and poor maintenance that results in leaks, plugged emitters, pressure valves not calibrated properly or poor filter maintenance or design, he said.
Inefficient systems may result in delivering too much water and fertilizer to some parts of the field, pushing nitrates past the root zone and into groundwater, while skimping on nutrients and water in the root zones of other plants.
Green recommends auditing the system to determine distribution uniformity levels.
Simply using check valves that cost as low as $3 can be important for a watering system, he said, adding that a good injection system should include backflow prevention and automated system shutdown in the event of a pressure or flow loss.
An injection line check valve will keep reverse flow from the pressurized irrigation system from overflowing the fertilizer supply tank, Green said.
Presenters at the seminar armed participants with web sites that can serve as resources as they fine tune their fertigation systems so as to deliver nutrients to their crops through their irrigation lines without sending those nutrients past the root zones.
For example, Sajeemas “Mint” Pasakdee, soil scientist at the university, cited a web site that can be used to help determine how much “plant available nitrogen” may already be in the soil, thereby cutting down the amount of nitrogen needed to feed the crop.
She said helpful web sites for those wanting to learn the soil nutrient capacity include http://vric.ucdavis.edu/ (search for “nitrogen quick test); http://vric.ucdavis.edu/ and http://www.nal.usda.gov/understand-soil-testing-results.
Soil tests can cost from $20 to $25, she said, adding that part of knowing the soil involves collecting samples, understanding its texture by feel and recognizing that soils vary on the ability to hold water.
Pasakdee’s pointers were aimed at development of nutrient management plans that are important to monitoring and quantifying fertilizer inputs and outputs and maximizing fertilizer use efficiency, thereby protecting groundwater and soil efficiency. She said maintaining soil health is important to sustainability and the livelihood of future generations of farmers.
She also recommended knowing the soil’s pH level because nutrients are taken up differently in soils depending on pH levels. A chart showing nutrient availability depending on pH range is available at http://www.extension.org/pages/13064/soil-ph-modification.
In addition to knowing the soil, the grower should also “know the crop,” for example how much of crop nutrients are removed by it and the periods when it is most in need of those nutrients.
She said a worksheet developed by the U.S. Department of Agriculture can be used to calculate nutrient management and nitrogen in storage by following a link to http://plants.usda.gov/npk/main.