The pH of Water & the Growth of Bean Plants

Water pH and Plants

• Water pH levels slowly alter the soil's pH, altering its mineral components and affecting the ability of bean plants to absorb certain nutrients. Most plants thrive best in soil with a somewhat neutral pH range, although beans prefer a bit of acidity. As it changes soil chemistry, the pH of water affects the availability of vital nutrients that the plant can absorb, as well as the activity of organisms in the soil. Optimum pH varies slightly between plant types but is generally close to 7. Before planting a garden, use a pH tester to determine if irrigation water should be amended to ensured optimum soil pH.

Low pH

• Water with an extremely low pH (acidic) may limit bean growth and development. In a 1981
  Oregon State University study scientists simulated acid rain by irrigating plants with water at a pH of 3.1. They found that the acidic water decreased pod and seed number in pinto bean plants. Scientists observed that soybean seed and total weight increase when receiving water with a pH of 3.1, but soybean total weight decreased at a pH of 2.5. In a separate study published by "Plant Physiology" in 1991, a pH below 4.0 stopped the root growth of broad beans, suggesting that very acidic pH levels are detrimental to bean plant development.

High pH

• Water that has a high pH (alkaline) may cause mineral deficiencies that harm bean plants. Alkaline water slowly raises soil pH and makes it difficult for beans to absorb certain essential nutrients. Beans are especially susceptible to zinc deficiencies, which result when pH rises above 7.5. Zinc deficiency often is seen in the navy bean and creates yellowing and dying leaf tissue between veins. It may lead to stunted leaves and growth. Alkaline water also can make it difficult for beans to absorb iron, manganese, and boron, which are essential to growth. Iron deficiency, for example, causes stunted plants with yellowing foliage. Another problem with alkaline water is that it often contains excess bicarbonates and carbonates, which can reduce calcium content and make it difficult for beans to grow.

Testing and Adjusting pH Levels

• To determine the pH of irrigation water, use a pH tester kit by placing the test strip in a clean glass of water. Tap water tends to be somewhat alkaline, but usually not at harmful levels. Adjust water pH levels by adding sulfuric acid (to decrease pH) or lime (to increase pH). Beans grow best in water that is slightly acidic or neutral.

  You can counter pH levels in water by adding amendments directly to the soil. Increase the pH of soils below 5.5 with lime, dolomite or phosphate. Acidify alkaline soils with iron sulfate or acidic sphagnum moss. Some nitrogen fertilizers that slowly acidify soil include ammonium sulfate or urea.