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Salts affecting your high tunnel crops?

Posted: December 2, 2010

Do you have high tunnels? Have you tested your soil salt levels lately? High salt levels in your soil may be affecting your plants and decreasing your yield.
Salt stunted strawberries. Photo courtesy Kathy Demchak.

Salt stunted strawberries. Photo courtesy Kathy Demchak.

When we grow in a high tunnel with drip irrigation, we are creating a mini Arizona or California – hot and dry. Drip irrigation is great. It releases water efficiently right where the crop needs it. But there is a drawback. Drip does not flush the soil washing excess nutrients out of the root zone where they can result in high salt levels.

Let me give you an example. At the Penn State High Tunnel Facility we conducted a test using compost. One year we applied 1” or 2” of compost to provide crop nutrients to bell peppers. With 1” of compost we added 441 lbs of nitrogen versus the 75 lbs the bell pepper crop needed. With 2” it was a whopping 883 lbs of nitrogen. The story was similar with phosphorus. 1345 lbs of P with 1” or 2683 lbs of P with 2”, far more than the 150 lb needed. This affected our yields. When we added 2” of compost the yields actually went down. Worse, the soil was effected too. The soil salt levels skyrocketed to 0.45 mmhos/ cm (1” compost) and 0.81 mmhos/ cm (2” compost) compared to 0.14 mmhos/cm in the control treatment. In just one year we had reached the threshold (0.40 mmhos/cm) where salts  affect bell pepper yield.

Remember nutrients are also salts. In excess they will affect plant growth by making it difficult for plants to take up water. In addition to affecting yields, salt injury can cause burning of leaf margins, stunt plants, wilt and even kill your plants.

So what can you do?

1.Monitor the soluble salt levels in your soil. Penn State’s soil lab will measure salts for $5 per sample.

2.Only place high tunnels in areas with good drainage.

3.Avoid over application of nutrients.

4.Use irrigation water with low salt levels.

5.Leach out the salts with irrigation.

For more information on how soluble salts affect plant growth, how to measure them and alleviate the problem download: Fact Sheets