Market gardeners in the southern Great Plains continue to discover the benefits of growing in hoop houses. Some of these benefits include season extension, storm protection, yield and product quality enhancement and reduction in foliar disease.
Producing crops in hoop houses is not, however, without problems. At the Noble Research Institute, the most persistent problem we have in our hoop houses is the accumulation of salt in the raised beds. Salt's presence is indicated by the white crust that forms on the soil when it is allowed to dry. Salt tends to accumulate with regular application of fertilizer and as a result of mineralization of organic matter. Normally, rainfall would leach excess salt from the beds; however, because we do not remove the poly-film from our permanent houses, the soil becomes saltier over time.
Excess salts in the root zone hinder plants from withdrawing water from the soil. This lowers the amount of water available to plants, regardless of the amount of water in the root zone. Although the water is not held tighter to the soil, the presence of salt in the soil solution causes plants to exert more energy extracting water from the soil. More energy spent extracting less water causes stress, resulting in reduced growth and yield.
The conversion process of soil organic matter to plant available nutrients (mineral salts) is referred to as mineralization. Given adequate soil oxygen and moisture, the rate of mineralization is increased as soil temperature increases. While mineralization is normally beneficial, salts can quickly accumulate to harmful levels during solarization (the practice of using solar energy to pasteurize the soil to control soil-borne disease organisms).
To test for soluble salts, take a composite sample of several cores, 6 to 8 inches deep. Submit a minimum of one pint of the mixture to a soil testing lab. Soluble salts are measured by taking a small amount of the sample, adding enough pure water to the sample to completely saturate it and extracting water from the saturated soil. The amount of soluble salts present is measured by determining the electrical conductivity of the extract. The soluble salt content is proportional to the electrical conductivity of the solution. See Table1 for interpreting test results and tolerance ratings for selected crops.
To manage soil salinity in the hoop house, consider the following:
Managing the hoop house growing system can be challenging. Growers who fail to manage soil salinity should not expect to realize the full potential of hoop house production.