CULTIVATING QUESTIONS
Concerning the Bio-Extensive Market Garden
by Anne and Eric Nordell of Trout Run, PA

The moveable hoophouses featured in the “2009 Cucumber Comparison” provide a nutrient management advantage over permanent high tunnels. Removing the poly cover every winter, and moving the portable season extending structures to a new location every couple of years, pretty much guarantees that mineral salts in the soil will not reach the crop damaging levels described in the following Penn State Extension bulletin.

The prevalence of salt problems in permanent hoophouses is difficult for us to determine. We know of more and more long-term tunnel growers who now must graft salt tolerant root stock on all of their hoophouse tomato plants. On the other hand, the recent series on hoophouse management in Growing For Market suggests that high soil salinity is not a widespread issue. Soil samples from 93 tunnels in use for 3-10 years indicated that salinity levels were “within the acceptable limits at nearly all the locations” even where growers observed mineral deposits on the surface of the soil.

Keep in mind that high salinity is relatively easy to deal with by leaching the easily dissolved sodium deep in the soil with irrigation or rainfall. Intensive fertilization of hoophouse crops and field vegetables may also lead to high levels of phosphorus which is not nearly as mobile in the soil. For a more comprehensive discussion of managing phosphorus, see the Summer 2001 CQ, now available on-line in the SFJ archives. – Nordells

Dealing with High Soluble Salt Levels in High Tunnels

by Elsa Sánchez, Penn State Horticulture

Some growers have expressed concern about soil test analysis revealing abnormally high soluble salt levels in the soils of their high tunnels. We have seen soluble salt levels increase in the high tunnels at Penn State’s High Tunnel Research and Education Facility, regardless of whether inorganic or organic nutrient sources have been used. In the spring of 2008 levels ranged from 0.37 to 9.38(!!) mmhos/cm.

Nutrient management can be tricky because of the unique environment within high tunnels. High tunnels exclude environmental factors (such as rain, snow and winds) that facilitate leaching and may lead to a build-up of salts that can negatively affect plant growth. In addition, most high tunnels are equipped with drip irrigation, which also limits leaching. Different crops respond differently to soluble salt levels as illustrated in the table below.

In a two-year nutrient management study at the Penn State High Tunnel Research and Education facility (Burkhart, 2002). Inorganic fertilizer was applied through drip irrigation lines to supply 75 lbs N, 150 lbs phosphate and 75 lbs of potash per acre per year. Compost was soil incorporated to a depth of 1 ft at rates of 1 or 2 inches in the fall prior to planting. Applying 1 inch of compost supplied 441 lbs of N, 1345 lbs of phosphate and 1559 lbs of potash per acre per year. Applying 2 inches of compost roughly doubled the amount of nutrients added. Recommended rates of N, phosphate and potash are 100, 100 and 100 per acre (Commercial Vegetable Production Recommendations guide) indicating that excessive nutrients were applied to the soil with compost. The baseline soil soluble salt level was 0.15 mmho/cm. Soluble salt levels remained constant after one year of applying inorganic fertilizer. After two years, they increased to 0.30 mmho/cm. Soluble salt levels tripled to 0.45 mmho/cm after one year and increased over six times to 0.81 mmho/cm after two years when 1 inch of compost was applied. Applying 2 inches of compost resulted in soil salt levels increasing about 5½ times to 0.95 mmho/cm and 13 times to 1.9 mmhos/cm each year of the study, respectively. At the soluble salt levels as a result of applying 2 inches of compost, pepper yield declined.

Eight Ideas for Preventing or Dealing with High Soluble Salt Levels

1. Monitor the soluble salt levels of the soils. Soluble salt levels of a soil sample can be analyzed by Penn State’s Agriculture Analytical Lab. It is an optional test costing $5. Request the test with your soil analysis. By monitoring the soluble salt level of your high tunnel soil, you will know when you need to act.

2. Only place high tunnels in areas with good drainage. If you already have sited your tunnel, it may be too late for this idea. However, when selecting a site for any new high tunnels, choose an area with good soil drainage. Good soil drainage will facilitate leaching of soluble salts.

3. Avoid the over application of nutrients. Soluble salt levels can be limited to some extent by applying only the amount of nutrients plants need. Use soil test reports or the Commercial Vegetable Production Recommendations guide to get current recommendations for application rates.

4. Select fertilizers with low salt indexes; limit the use of organic nutrient sources containing animal manures. When possible, select fertilizers with low salt indexes (see table below) to help limit the accumulation of soluble salts. Depending on availability and cost, this may be difficult to do. In Missouri, it is reported that many high tunnel tomato growers are using calcium nitrate and another fertilizer high in potassium to meet fertilizer needs (Watering and Fertilizing Tomatoes in a High Tunnel). If you use organic nutrient sources, try to avoid or limit those containing animal manures. Animal manures tend to be high in salts.

5. Use irrigation water with low salt levels. Irrigation water can be a source of salts. Penn State’s Agriculture Analytical offers water testing for a fee. Based on that test, 0.0 – 0.6 mmho/cm is considered normal.

6. Use a sprinkler irrigation system to establish seedlings. Seedlings are more sensitive to high soluble salt levels than mature plants. If your soluble salt levels are high, consider using a sprinkler irrigation system to establish seedlings. This will facilitate leaching of salts around the plants.

7. Rotate crops based on salinity tolerances. The table above, “Salinity Tolerance of Selected Vegetable Crops,” can be used with soil test analysis of soluble salt levels to rotate crops in high tunnels. As the soluble salt levels increase, select crops with a higher salt tolerance.

8. Leach out salts. As a general guideline for leaching out soluble salts from the top foot of soil, apply 6 inches of water to leach about 50% of the salts, apply 12 inches to leach about 80% of the salts and 24% to leach about 90% of the salts (Western Fertilizer Handbook, 8th Ed.). Out at the high tunnel facility I’ve been managing 4 high tunnels since 2003. In the fall of 2007 the soluble salt level was on average 0.40 mmho/cm. This was starting to get into the range where plant yields of salt sensitive crops could decline. That November the tops of the tunnels ripped off due to high speed winds and because the plastic was getting old. We decided to leave the tops off until the spring to see what would happen to the soluble salt levels. In April of 2008 we put new tops on and had the soluble salt level of the soils analyzed. On average, the soluble salt level decreased to 0.09 mmho/cm or about 77%. Between November of 2007 and April of 2008 we got about 11.5 inches of rain.

If the tops of the tunnels cannot be removed, leaching soluble salts with irrigation is also an option. This can be accomplished with any irrigation system. However, since most high tunnels are outfitted with drip/trickle irrigation systems the table below is included. It shows the hours required to apply 1 inch of water through a trickle irrigation system depending on the width of the mulched bed.

To use the table select the trickle tube flow rate (columns) in gallons per hour per 100 ft of tape (gph/100ft) or in gallons per minute per 100 feet of tape (gpm/100ft). Then select the width of the mulched row (columns). The value you get will be the number of hours the irrigation systems should run in hours to apply 1 inch of water. If you want to apply 12 inches of water, multiply this value by 12.

In the high tunnels at Penn State’s Center for Plasticulture we use a trickle tape with a 0.40 gpm/100 ft flow rate and mulched beds that are 2.5 ft wide. So, we need to run the irrigation system for 6.5 hours to apply 1 inch of water and 78 hours to apply 12 inches of water.

Soil texture (i.e., sand, loamy sand, sandy loam, clay loam, silt loam) is another factor affecting the length of time that an irrigation system needs to be on to apply 1 inch of water. Table C-5 on page C3 of the 2009 Commercial Vegetable Production Recommendations guide lists the maximum number of hours for trickle irrigation systems to apply 1 to 1.5 inches of water based on soil texture.

References

Brady, N.C. 1990. The Nature and Properties of Soils, 10th Ed. Macmillan Pub Co, NY.

Burkhart, E.P. 2002. Utilization of Compost in High Tunnel Cropping Systems: Opportunities and Challenges. M.S. Thesis. The Penn State University.

CA Fertilizer Association. 1995. Western Fertilizer Handbook, 8th Ed. Interstate Pubs, Inc., IL.

Foth, H.D. and B.G. Ellis. 1996. Soil Fertility, 2nd Ed. Lewis Publishers, NY.

Jett, L. 2006. Watering & Fertilizing Tomatoes in a High Tunnel. UMO Ext Pub G 6462.

Orzolek, M.D., E. Sánchez, W.J. Lamont, Jr., T. Elkner, K. Demchak, G. Lin, J.M. Halbrendt, B.K. Gugino, S.J. Fleischer, L. LaBorde, K. Hoffman, G.J. San Julian. 2009. Commercial Vegetable Production Recommendations – Pennsylvania. PSU Cooperative Extension Publication AGRS-28.

2009 Cucumber Comparison

1b. Caterpillar in 2009 with 46 Olympian cucumber plants (5/13) and third planting of protected lettuce (5/1). Soil management: 10 gallons of henpecked compost 6 per 100 square feet of planting area forked into the soil surface with winter-killed oat stubble.

2b. Quad of bumblebees placed in caterpillar on June 16 to pollinate cucumber blossoms and Brandywine tomatoes (5/5) at the other end of the tunnel. The tomatoes significantly increased bumblebee activity and the return on the purchased pollinators.

3b. Due to the consistently cool weather, cucumbers were slow to come into production. As of this July 12 photo, we had only harvested 117 marketable fruit from the caterpillar, 121 from the portahoopy and 7 from the field planting with row cover. Total harvest from the caterpillar, 6/30-8/7: 667 marketable fruit and 138 culls (20%).

4b. Portahoopy with 46 Olympian cucumbers (5/ 13) and second planting of protected lettuce (4/22) and spinach (4/10). The wider portahoopy dimensions allowed for two more rows of early greens. Soil management in the portahoopy was the same as the caterpillar.

5b. After completing the lettuce and spinach harvest, we attached the anti-insect barrier with zipper door to the portahoopy’s end frames. Although a few determined cucumber beetles managed to find their way into both the portahoopy and caterpillar, no damage was evident on the fruit or vines.

6b. From 6/30-8/7, we harvested 596 marketable fruit and 101 culls (17%) from the portahoopy plus a good bit of summer basil. The lower yield than the caterpillar was probably due to cold air stunting the plants closest to the portahoopy doors.

7b. Early, blemish-free cucumbers in the portahoopy and caterpillar increased the income and diversity of our stand at The Williamsport Outdoor Growers Market. So did the fall salad mix and cilantro (8/30) that followed the early cucumbers in the high tunnels.

8b. Removing the floating row cover for pollination of the field planting of 46 Olympian cucumbers (5/13) on June 16. Soil management: shallow plow hairy vetch and 15 yards/acre of hog composted horse manure.

9b. Cucumber beetle damage very evident on the vines and the fruits of the field cucumbers. From 7/9- 8/2, we harvested just 374 marketable fruit and 106 culls (28%). Peak production was much later, and harvesting noticeably slower, than in the caterpillar or portahoopy.