7/2/2013 - By Dr. Travis Shaddox

Whether one is growing flowering perennials or large shade trees, the common denominator of all nursery operations is water. You know the liquid form of two hydrogen ions latching on to the mother ship ion, oxygen. But water itself is not the biggest issue compared to what else is in it. So this month's topic is some fundamentals of water quality. Books are written on this, as they should be, but here are some basics. Water quality is most affected by which solids are dissolved in it. These are often ions swimming freely in solution and they will affect soil chemistry and plant physiology. The sum of all of these solids is called a TDS or total dissolved solids. In Florida, calcium and carbonates or bicarbonates are often found as our aquifer that the water flows through is largely made of limestone. In South Florida these components will raise water pH levels often above 8.0. Using this water regularly will eventually cause soil pH to rise and possibly influence nutrient availability. This is a common problem for all plants, but especially smaller containerized crops like bedding plants. Some nurseries have opted to inject an acid source to alleviate this, which is a costly but sometimes necessary option. Calcium can also cause a residue issue on leaf surfaces. Water quality can not have any greater area of concern than with sodium and chloride better known as, salt. Salt water intrusion to water sources such as wells or canals is a huge concern all over the world.

• Iron levels: 2 ppm or below is best
• Boron levels: 0.5 ppm or below is best
• Chloride levels: 50 ppm or below is best
• Copper levels: 0.08 – 0.15 ppm is best

As sodium (and chloride) is much more readily absorbed through leaf tissue than root systems, many nurseries have adapted to drip systems that mainline the water to roots versus overhead irrigation. Even light levels of sodium can affect plants through accumulation in the leaves. Some plants like Hibiscus are great sodium accumulators. Things can be done to slow the uptake, such as keeping up potassium fertility or adding gypsum to the soil. Potassium and calcium basically compete for binding sites with sodium. Sodium will bind in the soil, while chlorides will leach out. Both ions are toxic once they reach certain thresholds in leaf tissue as well as interfere with water uptake in plants due to their salt gradient influencing osmosis. Then there are dissolved solids such as iron or boron that also affect plant growth. Iron primarily is a residue issue staining plants and potentially hindering photosynthesis but primarily a cosmetic issue affecting plant sales. Some nurseries are using reclaim water, which not only often have salt or brine, but also boron. Boron being a byproduct of human waste. This too in time can accumulate and become toxic in plant tissue. Lose any sleep yet? Well obviously it is a great idea to run water analysis through a lab such as QAL Labs or A&L Labs. An irrigation suitability test will measure all the dissolved solids in the water as well as give your pH and conductivity. Conductivity is directly proportionate to TDS. Pure water is a poor conductor of electricity. The higher the ion content or TDS, the more electricity will pass through it hence the conductivity reading. All these things greatly influence what type of fertilizer to use or soil to use or what plants to grow or not grow. Well you get the picture.

Glossary of Terms