Tuesday, April 8, 2014

Investigating impacts of Electrical Conductivity in Nutrient Solutions

Investigating impacts of Electrical Conductivity in Nutrient Solutions
Lettuce and Brassica winter production in NFT systems in Ohio 
By: Dr. Natalie Bumgarner


In recirculating systems producing leafy crops, one of the main factors in the control of the grower is the nutrient solution electrical conductivity (EC). In many systems, total EC, rather than single elements are controlled due to economics. In most commercial systems using electronic controllers and dosing pumps, concentrated fertilizer solution is added to the nutrient solution any time the solution goes below target EC. So, maintaining consistent EC levels is fairly straightforward, the main question becomes: What is the best EC? The answer to this question is based on two separate factors. The first relates to maintaining needed nutrients in solution. Essentially, the important question is how close to calculated nutrient levels does the solution remain over time. If there are large amounts of ions already in the source water (sodium, sulfate, or calcium for instance), this can cause the nutrient solution to become out of balance more rapidly meaning that ideal ratios of nutrients are not maintained. The second factor involves the movement of water through the plant. At lower EC, it is easier for plants to take up and transpire water. Therefore, under high light and temperature, and low humidity, lower solution EC levels makes it easier for the plant to move water. So, the EC that we use in our systems needs to address these two issues: 1) Maintain adequate levels of plant nutrients, and 2) not stress the plant too much in terms of taking up water needed for transpiration.

Plant Management

Seeding was done by hand into pre-moistened 1” x 1” x 1 ½” cubes. Seeds were germinated in 9” nursery channels that were receiving a continuous flow of nutrient solutions set at experimental levels. After 15 to 17 days, seedlings were transplanted to the production NFT channels at a spacing of 8” on centers. After transplanting, plants were grown in 4 ¾” channels until harvest. The nutrient solution was automatically and continually adjusted to maintain a target pH of 6.0. Electrical conductivity was maintained by hand additions of nutrient concentrate as 
needed based on daily measurements of EC. These trials were carried out in a system designed to pull from four different 40 gallon nutrient tanks so that differing solution could be tested in a randomized block design. At harvest, shoot fresh weight was recorded individually for each head.

Timing and Conditions

* 400W metal halide lights were used to add approximately 30-40 ┬Ámol/m2/sec of supplemental light from 4 to 11 am during the lettuce experiment, but power usage constraints prevented lights from being used during the Brassica trial.

Biomass Yield by EC Treatment

Letters signify differences between EC treatments across all three cultivars. Treatments are only significantly different if followed by different letters.

EC x Cultivar Biomass Yield

Discussion on the two trials

These two runs of a fairly straightforward nutrient concentration test reveal some interesting results and, as useful tests should, provide some additional questions for future work.

1) Under the conditions of these trials, it is quite possible that nutrition was not always the most limiting factor. Yields were statistically similar in the lettuce trial for treatments where 1.3, 1.8, and 2.3 EC was maintained. This would suggest that all three of those EC treatments provided adequate nutrition and that the generally low yields in the trial, may have been due to low light conditions. Many times growers increase EC during the winter to push growth. Certainly under some conditions, that can be a valid technique, but it is also possible that the plants may not be able to parlay those available nutrients into increased yield. It should also be stated that our nutrient targets for recirculating systems are purposefully determined in excess of minimum nutrient levels to provide buffer in our systems and prevent yield reductions.

2) For some cultivars, quality impacts can be as large a determining factor in nutrient solution adjustment as yield. For any grower who has tip-burned romaine lettuce (and that includes a high percentage of those who have grown it), it comes as no surprise that quality issues are often more prevalent than in bibb lettuce. For some of our crops, then it may be maintaining crop quality rather than growth rate that is the determining management factor. So, if tipburn increases to a costly level, we may run lower EC even if slightly higher levels would lead to increased biomass accumulation. We also need to investigate other aspects of our management (air circulation, lighting, cultivar selection, etc.) to make sure that it really is a nutrient issue causing our decreased quality. This leads into many separate areas of research, but it is important to remember that only one of the lettuce cultivars and none of the Brassicas sustained tipburn in these trials.

3) For leafy crops other than lettuce, there still is likely room for improvement in our plant nutrition and crop management. Earlier in the discussion, I mentioned the fact that the clearer separation between EC treatments in the Brassica trial may have been due to less frequent tank changes and more opportunity for nutrient limitation in the 1.3 and 0.8 EC treatments. That is possible, but it is also quite possible that kale, arugula, and pac choi may have different optimum nutrient levels than lettuce (or each other for that matter). For the past several decades, bibb lettuce has been the focus of most hydroponic research and with an increase in the number of profitable crops that can be grown in greenhouses, it is quite possible that we still have a bit to learn about these other crops.
So, what are the questions for follow up trials??

1)How do seasonal conditions impact tests such as these?

As discussed earlier, both of these trials were carried out in low light, winter conditions. It is quite likely that when light is less limiting that more nutrition impacts will be present. Likewise, quality impacts (tipburn) may be more of a factor in summer trials.

2)What about the impact of the frequency of tank changes?

In most of our recirculating systems, our goal is to manage solutions to prevent nutrients from becoming limiting. Tank changes at specific intervals are often how we accomplish this goal (without purchasing specific ion probes). Only through nutrient testing and trials will we know for sure what the optimum EC and intervals between solution changes will be. While it stands to reason that tank changes may need to be less frequent at higher EC levels and/or higher light conditions, we need data to back up our practices and theories.

Tuesday, February 4, 2014

Summer to Fall Mixed Leafy Trial

Summer to Fall Mixed Leafy Trial
Kale, endive, and cress in NFT production in Ohio
By: Dr. Natalie Bumgarner


While lettuce fills a large majority of the spaces in most greenhouse nutrient film technique (NFT) systems in the US, there are many other crops that can be profitable for growers in these systems. In addition to herbs, other leafy crops, such as kale, cress and endive are currently being investigated by growers to address specialty markets. In recent years, more growers are experimenting with these varied leafy crops. However, less is known about crop productivity and timing in relation to both cultivar and seasonal impacts. It is also important to note that unlike bibb and some other lettuce types, most kale, endive and cress are not specifically bred and developed for controlled environment production. So, there is a potential for greater seasonal variability in production than is seen in some of the common bibb lettuce crops. This trial was designed to evaluate a selection of kale and other leafy crops through a range of summer to fall conditions to evaluate their potential for greenhouse growers in the Midwest and Northeast. This trial obviously only used a portion of the cultivars available, but was intended to provide information for future more extensive trials.  

Methods and Management

Seeding was done by hand into pre-moistened 1” x 1” x 1 ½” cubes. Seeds were germinated in clear water in seeding trays, and were transferred to the nursery and nutrient solution 3 to 5 days after seeding. Seedlings were produced in flowing nutrient solution in the nursery for an additional week to two weeks before transplanting (No supplemental lighting was provided during the seedling phase). After transplanting, plants were grown out in the channel until harvest. The nutrient solution was continually cycled through the Fertroller where automatic pH and EC adjustments met programmed solution set points. The pH was maintained at 5.8 by the addition of dilute sulfuric acid. EC was maintained at 1.6 to 1.9 (lower light levels = higher EC) by the addition of concentrated fertilizer solution and source water.

* It is important to note that these trials were carried out across a range of seasonal conditions, so transplanting and harvesting were completed at slightly different plant ages in different runs as detailed in the next slides. Additionally, this trial measured single harvest yields to produce the most accurate and comparable yield totals. However, some growers will take multiple harvests from a single kale or cress plant, which would likely increase the total yield per plant but require additional time in the channel.

Timing and Conditions

Biomass Yield

* Watercress was seeded with multiple seeds per cube as is typical in production, but this increased the yield variability. Additionally the multiple plants grew together and created difficulty in accurately assessing yield per cube, so those comprised data are not presented, and a more upright cultivar was chosen for the next two runs of the trial.

Daily Biomass Accumulation

Some thoughts on the trial

After reviewing these data, there are a few items that are important to consider and understand about this trial.

• An important trend to note in these data is that the leafy crop cultivars in the trial did not always respond similarly to changes in seasonal conditions. Red Russian kale, which had the largest leaves and plant stature, tended to be the highest yielding kale cultivar and the yields across the first three runs were consistent. Under lower light conditions in run 4, the yield dropped to near half even with the longer production cycle. That same trend was also true for the smaller leaved Toscano cultivar. Starbor kale yields were more variable across the three first runs. In run 4, Starbor seeds could not be obtained, so Winterbor kale replaced Starbor. In future trials, it would be a good comparison to trial both Starbor and Winterbor across changing seasons.

• Seedling production was a key factor in this trial. One important note about using seeds and species not specifically bred and adapted for greenhouse conditions is that germination and early growth may be more variable than growers may be accustomed to with bibb seeds. For example, the variation between endive yield in run 2 and 3 was more likely due to germination and seedling size than to environmental conditions. The photo on the left is a close up of some of the endive seedlings in that run, and it is apparent that germination was uneven. This difference in early growth and size at transplant has a direct influence on yield in a short cycle leafy crop. The more even seedlings from another run are shown in the image on the right.

• My final comments are based on both data and observations and discussions with growers. When growing alternative leafy crops, like kale, endive, and cress, it is essential to know your market and select cultivars based on the needs of your buyers and your productivity. The cress is an example of that fact in that the highest biomass producing cultivars may have been less marketable due to their difficult to manage size. In the kale, there were large differences in cultivar biomass production and appearance. It may well be that the most desirable cultivars for buyers may not be the most productive. So, growers need to be aware of the production capacity so that prices can be properly established. This knowledge and preparation will enable growers to best capitalize on the demand for these less common leafy crops.

Plant Images

Red Russian Kale- 20 days after seeding

Red Russian Kale- At harvest (38 days after seeding)

Starbor Kale- 20 days after seeding

Starbor Kale- 38 days after seeding

Toscano- 20 days after seeding
Toscano- 38 days after seeding

Cress 38 days after seeding

Cress- 20 days after seeding

Endive- 38 days after seeding
Endive- 20 days after seeding

Monday, January 6, 2014

Beefsteak Cultivar Trials- Part 2 (The Numbers)

Beefsteak Cultivar Trials- Part 2 (The Numbers)
Dr. Natalie Bumgarner


•This evaluation was carried out both to increase our knowledge
of several available beefsteaks and to provide information for
growers who may be considering these tomato cultivars. 
Cultivars were obtained from a variety of seed suppliers to
represent a broad selection.
•Ten cultivars were trialed in small 4-plant blocks with two
•The whole evaluation was completed in one row of a 22’ x 64’ x
10’ greenhouse
•Seeded 12/18  (All seedlings)
•Transplanted 1/14 (~ 4 ft2 per plant)
•First harvest 4/8
•Growing point removal 11/11
•Last harvest occurred on 12/16
•Data analyzed with Proc GLM and means difference letters calculated by LSD (different letters represent
statistically different cultivar averages)

Data Considerations
In this post, I would like to give a perspective on comparative yield and fruit size throughout the season for
one of the trials in our greenhouse. However, before presenting this data, some important facts need to be

• Always keep in mind that this is small plot research. Due to size constraints in our trial greenhouse and the
time involved in data collection, these trials cannot be carried out on a full production scale.
• It is critical to keep in mind that production numbers reported here are not necessarily repeatable in your
greenhouse due to the influence of light, humidity and other environmental factors.
• This whole trial was completed in an outside row of the greenhouse so light conditions were more optimum
and interior rows may not produce comparable yields. 
• The percentage of difference between cultivars in full row trials do not always directly follow small plot
• This work was carried out in OH, so our environmental conditions will not necessarily match other

Environmental Overview

*40% white shade cloth was installed July 16th and removed August 20th, so these solar radiation averages
reflect the loss of light in the greenhouse due to shading. Additionally, in the warmest and most humid
portions of the summer, some condensation on the plastic also reduced incoming radiation.  

 Cluster Counts/Fruit Set

         These numbers were derived from periodic counts of harvestable fruit from each cluster. The numbers were not statistically analyzed in the same way as the yield data that follows, but standard deviations  (sd) are reported. These sd illustrate that there was variability in fruit set across clusters due to nutrition and environmental conditions. Additionally, they suggest that some cultivars were more sensitive in terms of loss of flowers or fruit. One other note about these cluster counts is that in May we installed a reverse osmosis system in response to higher than optimum sodium levels in our source water which impacted fruit set on some clusters. Counts were not taken on Pink Brandymaster due to the uneveness of clusters as a result of cultivar tendencies. 

Fruit Number

These numbers were derived from fruit counts taken at 
harvest. So, these data correspond closely to the data 
presented inthe previous table. Keep in mind that the 
cluster count averages represent clusters 1 through 25, 
but fruit was harvested from 28 to 32 clusters per plants 
in many cultivars. Not surprisingly, the cultivars
that maintained the highest average fruit per cluster 
finished with the highest numbers of fruit.

Fruit Size

         It is important to keep in mind that these fruit sizes are averaged across the whole harvest season. To give a perspective on fruit sizes across the season, the previous blog post gave fruit weight averages from an early and a late season harvest for each cultivar. With all cultivars combined, the average of all April harvests was 0.61 lbs per fruit. Across all June harvests, the average fruit weight was 0.56 lbs and in November harvests, the average fruit weight was 0.49 lbs.

        Relationship of Fruit Size and Number

        One interesting thing to consider about these data is the 
        relationship between fruit number per plant and average 
        fruit size. Fruit size and fruit number in this trial were 
        significantly negatively related meaning that when fruit 
        size went up fruit number often went down 
(r=-0.60, P=0.0049). Cultivars like Guyana will many smaller fruit
and Pink Brandymaster with fewer larger fruit illustrate this trend.
However, this was not true for all cultivars. For instance, Foronti had the second highest average fruit weight
while averaging the 3rd highest fruit number per plant.  

Plant Production

Data was collected to as accurately as possible describe the yield potential of the plant under conditions 
tested. Marketable fruit included in these totals included first quality and slightly blemished fruit of all sizes
that were saleable. All fruit with damage due to blossom end rot, botrytis, etc. were not included in
production totals.

A few closing thoughts
This overview has thrown quite a bit of data at you the reader, but hopefully some of it has been useful. I
would like to close with a few comments and certainly feel free to email me with any further questions.

Due to management and environmental factors, these yield numbers are not appropriate for basing
production estimates in your operation.  
This trial was undertaken to introduce our team at CropKing to several of the beefsteak cultivars currently
available. We used this project to chose cultivars to trial further and to suggest to growers for their own
evaluation. So, these numbers are only from one crop and are not the end- rather, they
are the beginning. Look for data in upcoming years from some of these cultivars.  

Friday, November 22, 2013

Beefsteak Cultivar Trials- Part 1 (The Pictures)

Beefsteak Cultivar Trials- Part 1 (The Pictures)
By Dr. Natalie Bumgarner


Greenhouse tomato production in the United States now encompasses a wide spectrum of fruit types and cultivars. Producers desire both attractive and distinctive crop cultivars to meet consumer demand, but consistency in both productivity and quality is still a key. Even with the increasing desire for specialty cultivars, many small to mid-scale growers still often establish and maintain their a large portion of their sales with beefsteak tomatoes. For many US consumers, high visual and taste quality in beefsteak tomatoes is the basis for greenhouse tomato price premiums. Because many greenhouse vegetable producers rely on a few specific cultivars, the production and reliability of those cultivars is essential.  Additionally, over time their customers become accustomed to the taste and appearance of a certain cultivar and change must be carefully weighed. However, cultivars are sometimes discontinued or unavailable due to seed shortages, so being familiar with other options is quite important for growers. We generally encourage tomato growers to trial small sections of different cultivars on a consistent basis to remain up to date on new offerings and to be prepared if they are forced to switch cultivars.  It is obviously important for us at CropKing to be familiar with cultivar options for growers. So, this evaluation was carried out both to increase our knowledge of several available beefsteaks and to provide information for growers who may be considering these tomatoes as options for their current crops.  Cultivars were obtained from a variety of seed suppliers to represent a broad selection of cultivars available to greenhouse tomato producers. 

Crop Overview

• Ten cultivars were trialed in a small block, two replicate evaluation
• Seeded 12/18
• Transplanted 1/14
• First harvest 4/8
• Growing point removal 11/11
• Last harvest likely will occur between 12/15 and 12/25

Plant Management

•All ungrafted seedlings transplanted from 1.5” rockwool cubes into perlite filled Bato buckets
•Plant density was 4 ft2 per plant or 2.7 plants/m2
•Began feeding seedlings  at 1.5 mS/cm EC and increased feed to 2.2-2.4 mS/cm as mature plants
•Target leach ECs were 0.3-0.6 above feed ECs (2.5 to 2.8 mS/cm)

Data Collection and Calculations

Cluster number and harvestable fruit count at each cluster
Plot weight and fruit counts at each harvest
Cumulative fruit yield as well as a breakdown across the season
Average fruit weight across the season

The images and fruit weights presented here represent an April harvest with fruit from the 1st and 2n
clusters. The November pictures were taken near the end of the crop and were generally fruit
produced on the 25th through 28th clusters.  

In an upcoming blog after harvest is complete for the year, there will be a post that describes
comparative yield and fruit size throughout the season. This blog is designed to introduce the cultivars
and provide some initial visuals and fruit weights at an early and late harvest to provide a general
overview of the cultivars with more analysis and summary data planned for a later blog. 

The Cultivars

Average fruit wt. these two harvest dates

BigDena-April 0.581 lb
BigDena-November 0.502 lb

Foronti-November 0.601 lb
Foronti-April 0.837 

Guyana-November 0.438 lb
Guyana-April 0.525 lb

Heritage-November 0.516 lb
Heritage-April 0.566 lb

Ladoga-November 0.562 lb
Ladoga-April 0.601 lb

Lola-November 0.484 lb
Lola-April  0.513 lb

Rapsodie-November 0.417 lb
Rapsodie-April 0.653 lb

BeOrange-November 0.511 lb
BeOrange-April 0.598 lb 

Brandymaster-November 0.903 lb
Brandymaster-April 0.910 lb

Montenegro-November 0.431 lb
Montenegro-April 0.535 lb