High Tunnel: Does Soil Variability Caused By Management Affect Soil Sampling?.

High-tunnel food production presents an opportunity for urban and non-urban agricultural production. They are structures used to protect crops from excessive weather conditions. High-tunnels can provide year round sustainable food production, especially in temperate climate regions, by extending the growing season.

These structures are internally leveled areas ranging from 4.5x6.5m² to larger than 30x32m². Compared with open agricultural fields and due to their small size, high tunnels have been traditionally sampled with one soil composite sample per structure, collected at one depth.

The objective of this study was to propose a soil sampling design that represents soil growing conditions within a high-tunnel. Our hypothesis was that in high-tunnels, high spatial soil variability related to management practices, limits traditional/whole field sampling from representing the actual soil conditions.

The research was performed at West Virginia University's Organic Research Farm in a 22x8m² high-tunnel. In this structure, multiple crops (tomato, carrots, peppers) were produced in 21x1m² rows. Soil cores were taken in 1x1m² grid, to a depth of 20 cm. The cores were cut into 5cm depth increments. Soil was analyzed for pH, organic matter, and bioavailable nutrients (phosphorus, magnesium, potassium).

Our preliminary results showed high variability in bioavailable nutrients with depth and sample location. Soil Test P (STP) was 130±74ppm at 0-5cm, 63±58ppm at 5-10cm, 41±70ppm at 10-15cm and 47±97ppm at 15-20cm; 0-5cm STP in the west end of the structure was 172±59ppm and 121±55ppm in the east.

Average bioavailable nutrients estimated by traditional sampling were statistically different from “by row” sampling. Traditionally sampled 0-5cm STP was 130±74ppm, compared to row-1 STP 76±32ppm, to row-2 STP 101±48ppm.

A designed soil sampling strategy provides more informative data than traditional sampling because it accounts for bioavailable nutrients’ management related variability, and may help to guide appropriate practices to sustain production in high-tunnels.