High Tunnel Crop Production Project
A high tunnel is a low-cost version of a standard greenhouse that most people are familiar with. The definition of a high tunnel is a freestanding or gutter-connected covered structure, without heating or electrical power, using passive ventilation for air exchange and cooling, and an irrigation system for crop production. “Hoophouse” is another name that is used interchangeably with “high tunnel” and means the same thing.
Sometimes it is hard to distinguish between a high tunnel and a greenhouse. High tunnels could be as simple as only pipes or other framework covered by a single layer of greenhouse-grade 4- to 6-mil plastic, or as complicated as greenhouses.
There is often no electricity in the high tunnel, and hence no automated cooling or heating systems, which often requires electricity to run. Cooling is realized by passive ventilation from the roll-up sides and opening door at both ends. Heating is by naturally trapping heat during the day time and retaining heat within covered plastic during night. Although there is normally no permanent heating system, a portable heater or other methods of heating is sometimes employed by growers to protect crops against low temperature extremes. The only external connection is often the irrigation line.
There are many forms of high tunnels, just as there are many forms of greenhouses. The simple high tunnel is a single (one-bay) free standing ground-to-ground structure (Quonset-shaped). Multi-bay high tunnels with two or more bays have each bay sharing the side wall with the next bay. And there are also high tunnels leaning to walls or similar structures.
Use high tunnel for season extension
High tunnels provide a protected environment compared to open field production. High tunnels are used extensively for season extension around the world, especially in Europe and East Asia. High tunnels are mainly used in temperate regions to increase temperature in early spring, fall and sometimes winter or to moderate the fluctuation of temperatures for crop production.
Vegetables are the main crops growing in high tunnels around the world. The primary vegetable crops for high tunnel production, in order of importance, are tomato, sweet pepper, cucumber, muskmelon, lettuce, summer squash, and eggplant. The other major horticultural crops produced in high tunnels include small fruits, tree fruits and cut flowers.
Mississippi and the central Gulf Coast states have minimum annual temperatures in the teens and single digits in most years. In winter, average daily high temperatures range from the upper 40s F in the northern part of Mississippi to the upper 50s in southern Mississippi. Lows are mostly in the 30s and upper 20s. Temperatures can be quite variable, however, with highs in the 60s and low 70s on many days. Combined with monthly rainfall of 3.5 to over 5.0 inches in most places in December, January, and February, this makes the outdoor environment very inhospitable for most winter vegetable crops. Some English peas, collards are grown, along with annual strawberries, faba beans, and some other minor crops.
The average maximum and minimum daily temperature from Dec. 1, 2007 to April 21, 2008 was 62 °F and 40 °F, respectively in Starkville, MS (Fig. 1). However, during the 143 days, there were 46 days when the minimum temperatures were below the freeze point and the latest was on April 15, 2008. Unlike northern states where prolonged periods of cold temperatures limit growing crops in the winter, in the mid-south the average maximum and minimum daily temperature are suitable to grow many crops in the winter. Farmers face the obstacle of a limited growing season only because short spells of subfreezing temperatures during the mild winter and early spring put crops in danger. Low cost technologies to temper the environment and reduce the environmental and economic risks of year-round production are of great interest to small farmers and marketers in Mississippi.
Other benefits of high tunnel production
High tunnel production is a hybrid of open field and greenhouse production. It does not require as much capital investment as greenhouse production while provide certain level of protection that field production could not offer.
Premium price for off season produce---
Growers could start planting in high tunnel earlier than the field in spring, and thus have an early harvest, and crops could keep producing under high tunnel when the temperature is too cold for field production.
Better quality and improved yield---
In addition to the season extension aspect of high tunnel production, another major advantage of high tunnel is the exclusion of rain water, thus less moisture on the foliage and reducing the amount of disease pressure. In tropical regions, high tunnel works more like a rain shelter to crop production during the rainy or monsoon seasons. High tunnels also are used as wind breaks or storm protection to reduce wind damage on crops. It has been reported on various crops that high tunnel yields better than field production in terms quality and quantity, which is translated into better profit.
Less weed pressure---
In most high tunnels, crops are grown on plastic mulch and drip irrigation is employed to provide water to where it is needed. Weed seed germination is reduced tremendously due to no natural rain water and less soil moisture where crops are not grown. Less bird, insect or other similar damages ---Crops are protected by the plastic from birds or deer damage. Insect screen could be installed to prevent entry of insects and thus reduce damage on crops.
Figure 1. The temperatures in Starkville, MS in Winter and illustration of eason extension technology in China: a. The average maximum and minimum daily temperature from Dec. 1, 2007 to April 21, 2008 in Starkville, MS; b. Illustration of season extension structure from Chinese text book showing multiple layers for insulation and heat retention, along with drainage trench opposite heat wall.
This project is partially funded by USDA NRI,
USDA ISE, USDA SCBGP, and MAFES SRI