Importance of Water and Soil Analysis for High Tunnel Growers

Census data showed that in 2014 Indiana (12 acres), Illinois (11 acres) and Kentucky (13 acres) dedicated a very small portion of their food crop acreage to production under protection. According to the USDA National Agriculture Statistical Service 2014 Horticulture Specialties Census, of all the states surrounding Indiana, Ohio and Michigan have grown and sold the most food crops under protection, 24 and 25 acres, respectively.

The use of high tunnels for vegetable production seems to be a novelty in the Midwest. But it can be a very important tool for every vegetable grower as it can be used to modify the growing environment for crop earliness, to protect the growing crop against environmental stress, to reduce disease and insect pressure and to extend the growing season. Covering the soil with a high tunnel prevents natural rainfall from washing or leaching nutrients and soluble salts from the soil, can lead to very dry soil, can elevate the soil temperature and prevent the soil from freezing during the winter. The lack of rainwater to flush soluble salts can lead to an increase in soil salinity over time, which in turn has a negative impact on crop growth and production. The increased soil temperature in the high tunnel can lead to the quick breakdown of organic matter, releasing uncontrolled amounts of nitrogen and other nutrients into the soil. As a result the application of excessive levels of compost may also increase soil salinity. High soil salinity can be prevented and managed through a carefully planned soil fertility management plan.

As a first step, it is very important for an effective high tunnel soil fertility management plan to have soil and water samples analyzed. The results are crucial to design a management plan that ensures high productivity with minimal to low environmental impact. Soil sampling can be done prior to the production season. If your water source is a well then it will be appropriate to analyze the water several times during the production season. The analysis of stagnant water in the well at the beginning of the growing season can be very different from water sampled later in the growing season.

Optimum soil organic matter content for vegetables should be 3% to 6% or higher, nitrogen 20-40 ppm, available phosphorus 25-50 ppm, potassium 150-300 ppm, magnesium 60-120 ppm, calcium 1000-2500 ppm and sulfur 10-20 ppm. The pH of the soil should be 6.0 to 7.0 and the cation exchange capacity 5-35 milli-equivalent (meq) per 100 g soil. Concern should be high when the irrigation source water has an EC (electrical conductivity) of more than 1.5 dS.m-1, when the pH is below 5.0 or above 7.0 or when the total hardness (dissolved Ca and Mg) is below 50 or above 150 ppm. Optimum values can differ for different vegetable crops. Therefore, it is important that prior to planting your crop in a high tunnel you consult with your nearest laboratory to get your soil and water tested.

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