It could be salty out there !

Ajay Nair

Assistant Professor, Department of Horticulture
Iowa State University

High tunnels are simple, plastic-covered, greenhouse-like structures that are passively ventilated and heated and the crops are grown directly in the soil. Over the last 4-5 years, an increasing number of fruit, vegetable, and flower growers have added high tunnels or are considering adding them to their farming operation to extend the season in the spring and fall. High tunnels have become an important tool for Iowa’s specialty crop producers to extend the growing season, increase production of quality crops, and increase profitability.

The environment without rainfall, limited space, and potential climate control in a high tunnel calls for unique set of crop management skills and serious attention towards management of soils. Both chemical and biological properties of soil, associated with continuous crop production inside high tunnels, can substantially change over short course of time. An important issue most growers are reporting is the buildup of excessive salts inside high tunnels. This is due to continuous application of synthetic fertilizers, animal manures, or manure-based compost in high tunnels. Intensive use of water soluble fertilizers of N, P, and K which are salts of respective nutrients significantly contributes to the salinity issue. Composts and manures high in salts can substantially increase soil salinity especially when they are applied in large amounts. The salt is often visible as a white crust on top of the soil (Figure 1). The issue salt buildup is compounded by the lack of precipitation inside high tunnels which prevents leaching of salts.  A build-up of salts over time leads to poor seed germination, causes salt injury including burnt leaf margins, stunted plants, reduced plant vigor, and reduces crop yield. Nutrient uptake and other metabolic processes can also be disturbed by soil salinity.

Fig. 1 Salt crust on soil aggregates inside high tunnels

One way for growers to keep track of salt levels is to regularly test their soils. Soil testing at least once a year will provide data on soil nutrient levels for proper nutrient management and help monitor soil attributes such as pH and salinity. Salt concentration in soil is estimated by testing the electrolytic conductivity (EC) of the soil. Soils with higher salt concentration have increased EC as compared to pure water which does not conduct electricity that well. There is lot of information available on ranges of soil EC that are detrimental to plant growth and cause plant injury; however, information on the method applied to measure EC is equally important to know. Depending upon method used, EC values change and so do the interpretation of those values. Three methods are generally used to measure soil EC.  The saturation paste extract method (SPE) is the most commonly used laboratory procedure for determining conductivity. In this method the soil sample is saturated with distilled water and mixed to a paste consistency. After letting the paste stand for one hour, the electrical conductivity of water extracted from the paste is measured using electrodes. A variant of this method involves measuring conductivity from a 1:1 or 1:2 soil-water mixture. In this case EC is measured after 15-20 minutes of shaking. The latter methods take less time but often are not as well related to the soil solution as is the SPE method. Electrolytic values from the 1:1 extracts are typically lower than those of SPE extracts due to increased dilution. Despite the differences in results between the two methods, many soil salinity samples are analyzed using a 1:1 extract because of reduced monetary and time investments. A conversion factor is used to convert EC values between two methods; however, value of the conversion factor is influenced by soil texture and organic matter content of the soil. A general rule of thumb to convert EC value obtained from 1:1 method to SPE method is to multiply by 2. So, an EC value of 1.5 dS/m from 1:1 method is equal to 3.0 dS/m in the SP method. Most plant responses to salinity levels reported in literature are based on values obtained from the SPE method. Table 1 shows various levels of EC at which plants show salt stress symptoms.

Table 1. Electrolytic Conductivity values from Saturated Paste Extraction method and respective plant responses

Electrolytic conductivity (dS/m)	Plant Response
0 - 2	Optimum plant growth
3 – 4	Plants show initial stress symptoms; smaller leaves
5 – 7	Growth affected; smaller and distorted leaves; reduced yields
>8	Detrimental to plant growth; plant death; only salt tolerant plants can survive

Different plant species have various levels of salt tolerance levels (Figure 2). Plants with higher drought tolerance typically handle increased soil salt concentrations better than more drought susceptible plants. Table 2 below provides information on threshold values beyond which crops would show reduction in yields.

Fig. 2 Salt stress symptoms on pepper crop

Crop	EC (dS/m)
Beans	1.0
Broccoli	2.7
Cantaloupe	2.2
Carrot	1.0
Sweet corn	1.7
Cucumber	2.5
Lettuce	1.3
Onion	1.2
Pepper (bell)	1.3
Potato	1.7
Tomato	2.5
Watermelon	2.0

High tunnel growers should periodically check their soils for salinity issues and take steps to prevent high salt build up. Under high tunnels, investment per square foot is high and any crop damage or injury would significantly reduce profitability of the production enterprise. Below are some steps growers could take to prevent salt build up in their high tunnels

1.      Flush out salts periodically. This can be done by removing the cover, leaving the tunnel open, or flooding the tunnel with water to leach out salts. Flooding could be an expensive option, but leaving the tunnel sides open during the winter months is less expensive and doable. This would allow the snow to get in (certainly in a windy area for which Iowa is a strong contender). Alternatively when changing tunnel cover every 3-4 year, it could be left open for a period of time for the natural precipitation to get in

2.      Provide adequate drainage inside the high tunnels.

3.      Use of cover crops to improve soil organic matter and soil structure, reduce compaction, and improve drainage (installation of drainage tile pipes)

4.   Judicious use of water soluble fertilizers and compost.

R.I.D.S to get RID of dirt !

Ajay Nair
Department of Horticulture
Iowa State University

To have an effective research program you need sharp, curious, and committed graduate students. I should say my lab has one. Brandon Carpenter has been working in the Sustainable Vegetable Production Lab for a year now. He is working on the biochar project assessing its implication on carrot and pepper production. In his free time Brandon has constructed a number of cool gadgets for the lab (mechanical seed transplanter, sweet potato and tomato grader, compost bin, and now RIDS (Repurposed Inexpensive Drum-washer Sanitizer). There are many aspects of vegetable production that need to be addressed by growers who are looking to keep their customers safe. Brandon and his team of students at Iowa State University’s Horticulture Research Station in Gilbert Iowa sought to answer this question by building a drum washer to clean and sanitize produce grown at the station. The foundation of the drum washer is a platform for a composting drum. The platform consisted of a frame, two axles with pneumatic tires, and an electric motor. The frame is not the only part of this project that is finding new purpose. The drum is piece of corrugated pipe that originally served as a spool for a large role of drainage tile.

There were a few minor adjustments that needed to be made to the drum after it was made, but none of the changes were major. One of the first changes made was to add baffles in the form of PVC pipes that run the length of the drum. This was done to get the produce to role and the drum turns. Before this modification was made the produce would climb the side of the drum, as it turned, then the produce would slide back down to the middle of the drum without rolling over. Some of the heavier soils were not being removed, so strips of indoor-outdoor carpet were also added to the inside of the drum. It is thought that this is due to the weakness of the spray nozzles being used. The spray nozzles, from TeeJet, are basic cone shaped nozzles that would be used on herbicide sprayers. These nozzles were chosen because they are inexpensive and readily available.

The drum washer is now operational, although it does not yet have the ability to sanitize produce. The intention for the future of this washer is to improve the spray boom to better rinse the produce, and to have one of the two spray booms attached to a chlorine injector, so produce will be sanitized as the soil is being removed. The second spray boom will then rinse the chlorine off.

Radish production in soil benches

Ajay Nair
Department of Horticulture
Iowa State University

Students from the HORT 471 class (Vegetable Production and Management) conducted experiments to assess the feasibility of growing vegetables in soil benches. They chose radish as one of their crops and learned about growing a radish from seed to completion. They made decisions on crop spacing, nutrient and irrigation management, harvest timing, and assessed the final quality of the produce. The video below illustrates the project.

In Iowa to boost local food supply during winter months, leafy and some root vegetables could be grown in soil benches provided adequate amount of heat is available. Growing crops that are adapted to cool conditions and do not require much heat, could increase the supply of locally grown produce during fall and winter months.

2012 Fruit and Vegetable Field Day

Ajay Nair
Department of Horticulture, Iowa State University

The Department of Horticulture in partnership with Iowa Fruit and Vegetable Growers Association and the Leopold Center for Sustainable Agriculture organized a Fruit and Vegetable Field Day at the Horticulture Research Station, Ames IA on 23 July, 2012. The event was coordinated by Dr. Ajay Nair, Assistant Professor in the Department of Horticulture. Other researchers who participated include Drs. Jeff Iles (Dept. Chair), Kathleen Delate, Paul Domoto, Gail Nonnecke, Mark Gleason, and Mr. Malcolm Robertson. 

This education and outreach event was designed specifically for fruit and vegetable growers and featured research-based information on a variety of topics including biochar application in vegetable production, row covers, plasticulture, cultivar trials, organic production practices, high tunnel fruit & vegetable production, apple root stocks and training systems, and cover crops. The event gave growers an opportunity for a real time assessment of new, innovative, and sustainable research initiatives in the area of fruit and vegetable production. Although geared towards commercial production the event was attended by small scale growers, master gardeners, and home owners interested in enhancing their production skills and diversifying their gardens and acreages. The event showcased the HORT 465 course which is a student-run vegetable enterprise geared towards developing student entrepreneurial and business skills. Graduate students from the Department of Horticulture (Brandon Carpenter, Leah Riesselman, and Dylan Rolfes) actively participated in the event by engaging growers in their research projects and answering their questions.

The event also hosted local growers (Berry Patch Farms and Rinehart Farms) who set up booths to sell farm fresh produce. Field day participants also had a chance to visit with representatives from USDA sponsored Sustainable Agriculture Research & Education program and the Leopold Center for Sustainable Education.

The morning session of the field day was followed a post-lunch panel discussion where growers, researchers, agriculture professionals, and extension personnel interacted with researchers from the Department of Horticulture and Field Extension Specialists to discuss current and future needs of fruit and vegetable industry in Iowa. Afternoon keynote speech was delivered by Dr. John Lawrence, Associate Dean, ISU Extenstion and Outreach. He stressed on developing strong grower-researcher relationship to address ongoing issues and challenges, and develop new ideas for fruit and vegetable research in Iowa. 

What is happening to the blossom end?

Ajay Nair
Department of Horticulture, Iowa State University


Lately a number of growers are finding small black spots, often with black concentric rings, on their tomato and pepper fruits. This is a typical symptom of a physiological disorder called blossom end rot. It is caused by lack of calcium uptake from the soil and transfer to the fruits during dry weather. The first symptom of rot is a slight water-soaked area near the blossom end of the fruit. This lesion soon darkens and enlarges in a constantly widening circle until the fruit begins to ripen. The affected area begins to turn black from colonization by saprophytic Alternaria fungal species.  Such fruits become non-marketable and could lead to significant losses. 

Calcium ions mostly move with water in the transpiration stream, up the xylem vessel, toward the upper plant parts. With current drought conditions and moisture stress, plants are not getting enough water and this directly affects calcium uptake. Calcium uptake by fruit can also be affected due to excessive nitrogen fertilization which leads to rapid shoot growth. Rapid shoot growth, occurring simultaneous with fruit growth, causes calcium to preferentially move into growing leaves as opposed to fruits, primarily because of higher transpirational pull from leaves. Transpiration pull from fruit is lower as they are covered with waxy coating. Below are some measures which growers/gardeners could take to mitigate blossom end rot:

1. Supply adequate water especially during high stress period (heat and drought). Uniform watering is critical for a steady flow of water in to the plants

2. Eliminate any other stress (insects, diseases, etc.) by addressing those issues promptly 

3. Avoid excessive use of nitrogenous fertilizers

4. Provide calcium to the plant (calcium fertilizers like calcium nitrate, calcium chloride, or various chelated calcium fertilizer materials). Foliarly-applied Ca fertilizers are not likely to correct or prevent blossom end rot

Hornworm season

Ajay Nair

Department of Horticulture, Iowa State University

Past few weeks growers have been experiencing foliar damage in solanaceous crops, especially tomatoes and pepper. When observed closely one can spot large green colored caterpillars defoliating the plant. These caterpillars are commonly called hornworms and are fairly common this time of the season. It is extremely important to manage this pest immediately as these are voracious feeders and can defoliate the whole plant in a matter of few days (usually when more than 2 caterpillars present on one plant). The caterpillars blend in with the foliage and are not easy to detect and are often not observed until they cause considerable damage.

Hornworm camouflaged in the pepper plant

There are two kinds of hornworms, tomato and tobacco hornworm, although they are very similar in appearance and biology. The most striking feature of the hornworm is the presence of a "horn" located at the terminal end of their abdomen. This horn is usually "red" in color for the tobacco and "black" for the tomato hornworm. This is an easy way to identify them. There are on an average 2 generations of this pest in Iowa. The adult is a grayish white moth. Most of the damage is caused by the caterpillar and so it has to be controlled at that stage.

Tomato hornworm (notice the black horn) 

Adult tomato hornworm moth (picture courtesy Univ. of Florida) 

A number of synthetic and organic insecticide are available to manage this pest. Some of the common synthetic insecticides are  Asana XL, Sevin, Mustang, and Pounce. Within the synthetic group there are insecticides that have reduced impact on the environment, are less toxic to non-target organisms and humans, and have low pest resistance potential. Some of these reduced risk products include Intrepid, Entrust, Avaunt, and Coragen. Biopesticides have also shown excellent results in managing hornworms. A biological control organism that is highly effective and sold commonly is Bacillus thuringiensis (Bt). Some commercial Bt formulations include Dipel, Biobet, Javelin, and Thuricide. Please follow pesticide instructions accurately while handling the product. 

April 10 Frost damage

Ajay Nair, Lynn Schroeder, and Paul Domoto

Department of Horticulture, Iowa State University

Much across Iowa we saw freezing temperatures which gave sleepless nights to a majority of our growers. Unfortunately the temperatures dipped to lower 20's which set the stage for damage on apple blossoms which were 3-4 weeks ahead in bloom. Below are pictures which show some damage to fruit and petal. 

Frost damage on petals

Frost damage to ovary (dead black tissue in the center)