Wheatgrass Production Trial: A Comparison of STG Pads to 3 Other Media

Wheatgrass Production: A Comparison of STG Pads to 3 Other Media

 

Short Title: Bucket Culture with Sure to Grow® Loose Fill Media

Source/Author/Date: Dr Lynette Morgan PhD, Suntec International Hydroponic Consultants, New Zealand, November 2008

Long Title: A Comparison of Sure to Grow® Pads to 3 Other Growing Media for Production of Wheatgrass in a Standard NFT Tray Greenhouse System, Including Relative Growth rate Analysis and Postharvest Assessment, Arugula, Red Cabbage and Broccoli

The primary objective of this study was to compare the growth of wheatgrass sown into 4 different pad/media products used in US commercial production, these being Cornell Peat-Lite Mix, horticultural grade perlite and vermiculite and the Sure to Grow® Pads.

RESULTS AND CONCLUSIONS

 

The main findings of this trial were: Perlite consistently performed the poorest of all 4 media evaluated in terms of plant growth rate and yield. Perlite plants were shorter and due to the particles on the bed surface, needed to be cut higher up on the plant at harvest, which may have reduced fresh yields. As with relative growth rates, yield differences are affected by planting date as well as by growing media treatment and by the interaction of these variables. Chi square analysis of the yield data showed differences observed in yield were greater than would be expected, so are therefore caused by treatment.

Harvested product quality was inconsistent in perlite – in planting one the wheatgrass was shorter, but darker green than the other treatments and resisted post harvest yellowing. However in planting two, perlite leaf blade yellowing and some tip burn developed in the production system which reduced harvest quality. STG produced the most consistent shelf life results with minimal yellowing and absence of any post harvest rots, although the perlite treatment from planting one had the highest quality at the end of shelf life assessment due to a darker green color.

The vermiculite was the only treatment to experience any root rot disease towards the end of the trial, this may have been due to the high water holding capacity of this media which may have pre disposed the plants to pathogen attack.

Foliar mineral levels did not show any major deficiencies or toxicities between treatments. The Peat-Lite treatment had higher foliage levels of some elements, which is most likely the result of additional fertilisers in the Peat-Lite mix which added to the nutrients applied via the nutrient solution. STG and perlite had low foliar potassium levels in both planting dates, while vermiculite, an inert media, and Peat-Lite which had additions of potassium nitrate in the mix, ran higher than expected levels. These differences are difficult to explain, given the nutrient solution was not recirculated and had sufficient potassium in the formulation for growth and development.

STG had a clear advantage in the efficiency and management of NFT wheatgrass production systems including greatly reduced set up time, ease of irrigation management, and effective control of root zone moisture levels.

 

INTERNATIONAL HYDROPONIC CONSULTANTS

 

 

 

Private and Confidential

 

Report Prepared for: Sure to Grow®, 6062 Holdings, LLC, Beachwood, Ohio

USA

 

 

 

 

Dr. Lynette Morgan PhD

Suntec International Hydroponic Consultants

New Zealand

November 2008

A COMPARISON OF SURE TO GROW® PADS

TO 3 OTHER MEDIA FOR THE PRODUCTION OF WHEATGRASS

IN A STANDARD NFT TRAY, GREENHOUSE SYSTEM, INCLUDING RELATIVE

GROWTH RATE ANALYSIS and POSTHARVEST ASSESSMENT

 

EXECUTIVE SUMMARY

 

The objectives of this study were to:

 

  1. Compare the relative growth rates of wheatgrass, sown into 4 different pad/media products used in US commercial production, these being Cornell Peat-Lite mix, horticultural grade perlite and vermiculite and the Sure to Grow® (STG) Pads.

 

  1. To compare harvested fresh weight and quality of wheatgrass grown in 4 different pad/media products including post harvest shelf life assessment.

 

  1. To assess various aspects of wheatgrass production in each of 4 media/pad products including occurrence of disease, changes in nutrient solution EC and pH, ease of use, salt build up, time required for set up and crop removal and disposal of spent media.

 

Crop trials were run in the early to mid Spring 2008 period under standard greenhouse conditions using 4 separate wide channel NFT systems filled with each of the growing media/pad treatments. Each treatment system had a separate nutrient tank and irrigation system. Nutrient solution was applied after germination at an EC of 0.5 mS.cm-1 and a pH of 5.8. Wheatgrass seed was soaked in water for 24 hours, then sown at a high rate of 3376 g/m2 (dry seed weight) and misted as required during the germination phase. Channels with covered with fine horticultural cloth to maintain humidity for the first 72 hours. Trials were run over two successive planting dates and treatments randomly assigned to channels for each sowing. Average day temperatures during these trials were 16 – 24o C (61 – 75o F) day and 12 – 16o C (54 – 61o F) night with a mix of cloudy overcast and bright days. Humidity level ranged from 70 – 92% with air movement across the crop assisted by a greenhouse fan. During the trial factors such as time taken to install and remove each media treatment, effect of treatments on solution EC and pH, disease occurrence, media moisture and temperature levels and general plant appearance were noted.

 

During these trials, samples of 100 seedlings from each treatment were taken every 3 days for relative growth rate assessment. Fresh and dry weight was recorded for each treatment and an analysis of relative growth rate expressed in grams/day of fresh and dry weight was determined. A 100 g sample of harvested foliage was taken at trial completion for a full foliar mineral analysis to determine if treatment differences in mineral uptake had occurred.

 

At harvest, fresh weight from each plot was recorded, along with an assessment of the overall quality from each treatment. Samples were taken for shelf life determination and visible signs of product deterioration over time were noted.

 

RESULTS AND CONCLUSIONS

 

 

The main findings of this trial were:

 

Perlite consistently performed the poorest of all 4 media evaluated in terms of plant growth rate and yield. Perlite plants were shorter and due to the particles on the bed surface, needed to be cut higher up on the plant at harvest, which may have reduced fresh yields. As with relative growth rates, yield differences are affected by planting date as well as by growing media treatment and by the interaction of these variables. Chi square analysis of the yield data showed differences observed in yield were greater than would be expected, so are therefore caused by treatment.

 

Harvested product quality was inconsistent in perlite – in planting one the wheatgrass was shorter, but darker green than the other treatments and resisted post harvest yellowing. However in planting two, perlite leaf blade yellowing and some tip burn developed in the production system which reduced harvest quality. STG produced the most consistent shelf life results with minimal yellowing and absence of any post harvest rots, although the perlite treatment from planting one had the highest quality at the end of shelf life assessment due to a darker green color.

 

The vermiculite was the only treatment to experience any root rot disease towards the end of the trial, this may have been due to the high water holding capacity of this media which may have pre disposed the plants to pathogen attack.

 

Foliar mineral levels did not show any major deficiencies or toxicities between treatments. The Peat-Lite treatment had higher foliage levels of some elements, which is most likely the result of additional fertilisers in the Peat-Lite mix which added to the nutrients applied via the nutrient solution. STG and perlite had low foliar potassium levels in both planting dates, while vermiculite, an inert media, and PeatLite which had additions of potassium nitrate in the mix, ran higher than expected levels. These differences are difficult to explain, given the nutrient solution was not recirculated and had sufficient potassium in the formulation for growth and development.

 

STG had a clear advantage in the efficiency and management of NFT wheatgrass production systems including greatly reduced set up time, ease of irrigation management, and effective control of root zone moisture levels.

 

Dr Lynette Morgan PhD

Suntec International Hydroponic Consultants

New Zealand

 

November 2008

 

 

Private and Confidential – Report prepared for Sure to Grow®, 6062 Holdings, LLC, Beachwood, Ohio USA

 

A COMPARISON OF SURE TO GROW® PADS

TO 3 OTHER MEDIA FOR THE PRODUCTION OF

WHEATGRASS IN A STANDARD NFT TRAY, GREENHOUSE SYSTEM, INCLUDING RELATIVE GROWTH RATE ANALYSIS and POST HARVEST ASSESSMENT

 

INTRODUCTION

 

Some sprouted seeds and seedlings species are grown specifically for their healthy compounds and properties and these have found a niche market within the health food industry. The most well known of these is wheatgrass, which has been grown for many years as a fresh or frozen health supplement after juicing. Wheatgrass is considered to be a highly nutritious and cleansing food source rich in vitamins, minerals, amino acids, antioxidants and enzymes.

 

Various hydroponic systems are currently used for wheatgrass production with the `long tray’ system growing in popularity. These are often modified, wide NFT channels into which hydroponic nutrient solution is supplied via emitters. These channels are typically either filled with a granular growing media or grow pad which holds the seed in place during the germination phase and provides a reserve of moisture. Nursery tray and bed systems are also in use for smaller scale wheatgrass production, many of which incorporate the use of overhead watering which poses an additional disease risk through wetting of the foliage. Many commercial growers have adapted NFT channels and technology to wheatgrass production, although there are now a range of specific wheatgrass production systems on the market that incorporate tiered systems and flood and drain tables.

 

The majority of wheatgrass producers use climate-controlled greenhouses for year round production. Wheatgrass requires careful attention to nutrition as factors such as nutrient ratios, EC and pH can influence not only yields, but also quality and shelf life of the harvested product. Wheatgrass is different from sprouts in nutritional requirements and requires a dilute nutrient solution to be applied to maintain foliage quality and growth rates. Initially, wheatgrass seed can be germinated in water, however once the young shoot is visible and starting to develop chlorophyll, the seedling will have exhausted the reserves contained in the grain. At this stage, the young plant is starting to photosynthesize and produce its own assimilate, and nutrient ions will be absorbed by the root system. EC levels are typically run at seedling strength for wheatgrass, although they may be adjusted for season. The moisture holding capacity of the growing media used in wheatgrass production will also influence product quality and disease occurrence. Media with a high moisture holding capacity are likely to produce softer growth which may wilt more rapidly post harvest. Free draining media will produce a `harder’ plant, but may not hold sufficient moisture between irrigations.

 

Currently, a number of different substrates are used for wheatgrass production, these include paper towel, burlap sheets, perlite, vermiculite, peat based media, organic mixes and matting such as the Sure to Grow® Pads. All granular media pose a contamination risk with particles of substrate which may get carried with the seedlings at harvest while some media are more prone to disease outbreaks which can be common at the high density wheatgrass seed is sown at.

Perlite

Perlite is a natural volcanic material produced by heating the ground material to 1000oC. Perlite is often used as a component of potting mixes and as a hydroponic growing media for a wide range of crops such as tomatoes, cucumbers and melons. Expanded perlite is very light with bulk density of 0.1 g cm-3. Perlite is porous and can hold 3 – 4 times its weight of water. Perlite is netural with a pH of 7.0 – 7.5, and has little buffering capacity and is considered to be inert (contains no mineral nutrients). Perlite is sterile after manufacture and can be steamed between crops.

 

Vermiculite

Vermiculite is formed by heating a natural clay mineral to 1000oC, during which the water contained within the mineral becomes a vapour and expands the particles. As a results light weight particles are formed which have a high porosity. Vermiculite is typically used as a germination media or as a component of potting mixes. The bulk density of expanded vermiculite is 0.1 g cm-3 with a strong capacity action and an ability to hold 3 -4 times its own weight in water. Vermiculite is neutral with a pH of 7.0 – 7.5 and low EC. It retains a permanent negative charge and consequently it has a CEC (Cation exchange value) of 150 – 210 mmolc Kg-1 . Vermiculite has the ability to adsorb ions such as phosphate due to its high surface area and some positive charged sites on the edges of the mineral it is composed of.

 

Cornell Peat-Lite Mix

This is a growing media comprised of 50% sphagnum peat moss and 50% vermiculite with additional fertilisers. A number of different Cornell mixes exist for different applications from seedling production through to ornamental container mixes. Cornell Peat-Lite mixes can be purchased pre made or produced by growers on site. Peat is an organic material formed as a result of partial decomposition of plants, including species of sedges, grasses and mosses, under cool temperatures and anaerobic or semi-anaerobic conditions. Peat has a very high water holding capacity and is included in container mixes for this reason. Wetting agents are often used with peat to over come its hydrophobic nature. Sphagnum peat contains at least 95% organic matter and has a fibrous structure with a high surface charge density including cation exchange capacity. Sphagnum is usually characterised by an acidic pH (pH 3 – 5) and in most cases lime or dolomite is added to increase the pH up to the range 5 – 6. Although sphagnum moss has been found in some cases to contain specific fungistatic substances, it is generally considered as a substrate conducive to numerous soilborne diseases. The sterilisation of peat, although possible, does not alleviate the problem, as it leaves a biological vacuum that can easily be filled by pathogenic fungi (Raviv et al, 2002).

 

BACKGROUND

The Sure to Grow® Pads are a unique product for the production of short-term crops such as wheatgrass and microgreens which has been designed to provide a moisture retentive, sterile seed bed for use in a range of hydroponic production systems. The product is lightweight, clean, easy to install and remove and provides both aeration and moisture for the germinating seed and nutrient uptake by the young seedling.

 

The main objective of this study was to compare the growth, yields and quality of wheatgrass grown in STG pads with other commonly utilised substrates.

 

OBJECTIVES

 

  1. To compare the relative growth rate of wheatgrass sown into 4 different pad/media products used in US commercial production.

 

  1. To compare harvested fresh weight and quality of wheatgrass grown in 4 different pad/media products, including post harvest shelf life assessment.

 

  1. To assess various aspects of wheatgrass production in each of 4 media/pad products including occurrence of root disease, changes in nutrient pH, ease of use, salt build up, time required for set up and crop removal and disposal of spent product.

 

 

TREATMENTS:

 

  1. Sure to Grow® Pad product (STG)
  2. Horticultural grade perlite
  3. Horticultural grade vermiculite
  4. Cornel peat-light mix (peat moss/vermiculite/fertilizers)

 

 

 

MATERIALS AND METHODS

 

Each of the four growing pads/media treatments were installed in separate NFT, (4 m long x 24 cm wide / 13 feet long x 9 inches wide) channels, seedling systems complete with individual reservoirs, channels and nutrient solutions. This was to determine the potential effect of each media/pad product on the nutrient solution EC and pH over the course of the trial and to assess any problems (such as particle blockages) which each treatment may create. Each separate NFT system consisted of 2 x 4 meter/ 9” x 13’ long standard wide based channels through which water, then nutrient flowed during the course of crop development.

 

A given weight of wheat seed (3376 g/m2,11 oz/ft2/ ) was pre soaked in water for 24 hours and then sown in the channels onto the surface of each of the 4 media/pad treatments. The grain was misted with water and covered with light frost cloth material and left to germinate for 48 hours with intermittent misting as required. After germination, channels were irrigated via a small submersible pump in each system reservoir. Drip irrigation was applied after 72 hours; a complete hydroponic seedling nutrient solution was applied to each system at an EC of 0.5 mS.cm-1 and pH of 5.8. This was adjusted and maintained daily until completion of each trial. Wheatgrass nutrient solution was irrigated and drained away during this trial as the wheatgrass grain, sown at high density, released large amounts of organic compounds into the solution which would have resulted in overgrowth of microbes and bacteria if permitted to recirculate continually within the system.

 

Once germination had occurred, relative growth rate assessment (RGR) was carried out in each media/pad treatment. RGR is a method of assessing the increase in plant dry weight/per day and is an important determinant of crop productivity. A random sample of plants from each treatment was collected every 3 days – fresh and dry weight of these seedlings was determined at each assessment date.

 

Wheat grass was grown through to harvest maturity – approximately 5 inches (12 – 14 cm) tall. At this stage, each plot was harvested by cutting at the base of the plants just above the roots, with some allowance for avoiding contamination with substrate particles. Plots were assessed for total fresh weight and quality. At harvest a sample of 100 g of wheatgrass from each treatment was sent to RJ Hill analytical laboratories for a full foliar mineral level analysis including N, P, K, Mg, Ca, S, Na, Fe, Mn, Zn, Cu and B.

 

Shelf life assessment: At harvest, 3 samples from each media/mat treatment (total of 12 samples) were collected for post harvest shelf life assessment. 30 g (1 oz.) of foliage was packaged into sealed polyethylene bags and stored under refrigeration (2o C, 35.6o F). Appearance, including rots, fungal growth, yellowing or other loss of colour, and turgidity was assessed until samples reached the end of their acceptable shelf life. Photographs were taken of each sample, after removal from the bags, at trial completion.

 

During the course of this trial, each media treatment was monitored for the presence or development of disease/root rot symptoms, root health, salt build up on the surface of the media or other production problems. Time taken to set up each separate media/mat treatment system was recorded, as well as time taken to remove each media/pad product post harvest from the hydroponic system.

 

The first sowing commenced on 16 September and was harvested on 7 October 2008. The second sowing commenced on 17 October 2008 and was harvested on

11 November 2008. These dates were during the early – mid spring period with average day temperatures of 16 – 24o C(61 – 75o F) and night temperatures of 12 – 16o C (54 – 61o F).

 

 

RESULTS

 

CROP OBSERVATIONS

Planting one (sown 16 September)

Sowing density of the soaked wheatgrass was high and grains formed a solid layer, often 2 – 3 grains deep on each of the treatment beds. By day 3, germination was similar in all treatments. It was noted that the grain heated up during the germination phase due to microbial activity. No differences in wheatgrass shoot size or stage of development was noted between treatments. By Monday 29 September all wheatgrass treatments were approximately 8 cm tall. The nutrient solution draining from all wheatgrass channels was not recirculated as this contained large amounts of organic matter which originated from the high density sowing of grain (possibly proteins and other compounds originating from the surface of the grain which could develop an overgrowth of microbes in solution which could result in a high biological demand in the system if recirculated). As the wheatgrass developed and the canopy thickened, some yellowing developed at the base of the vermiculite treatment. The perlite treatment had some particles lifted into the canopy, although these were few. Root systems developed rapidly and formed a thick mat on the base of the NFT channels in all treatments. Roots in all treatments were white and healthy.

 

Planting two (Sown 17 October)

Planting two was very similar to planting one in growth and development rate. A few plants on the outer edges of the channels developed some tipburn in the perlite treatment towards the end of this crop – this may have been due to the drier surface media this treatment continually ran. The perlite wheatgrass appeared slightly shorter from around day 7 until harvest. STG, Peat-Lite and vermiculite were similar in height and thickness. Roots appeared white and healthy during the trial, although one spot of disease was found in the lower channel area of the vermiculite treatment when the wheatgrass was cut for harvest.

 

Thermal readings

Temperature readings were taken during planting 1 and 2 using a non-destructive infra-red thermometer to record air, canopy and media temperature between the different treatments – a summary of which is provided below:

 

Conditions: Warm, high radiation, mid afternoon temperatures Crop stage: one week before harvest, good canopy cover.

 

Air temperature (greenhouse average) 23.4o C (74.1 oF)

Peat-Lite canopy 25o C (77 oF)

Peat-Lite root zone 21.7o C (71.1 oF)

 

STG canopy 25o C (77.0 oF)

STG root zone 27o C (80.6 oF)

 

Vermiculite canopy 24o C (75.2 oF)

Vermiculite root zone 25.2o C (77.4 oF)

 

Perlite canopy 22o C (71.6 oF)

Perlite root zone 23o C (73.4 oF)

 

 

System Observations

 

During the course of both plantings, differences in the moisture holding capacity between irrigations of the different growing media were noted. The Peat-Lite and vermiculite treatments became over-saturated rapidly and held moisture for longer than the STG mats or the perlite treatment. Perlite had a tendency to be well irrigated on the base of the channel and drier towards the top of the seed bed – i.e capillary action was not as great as in the vermiculite media. The STG pads drained well between irrigations, but held sufficient moisture for plant growth without over saturation. Maintaining good moisture status of the STG treatment was relatively simple as the mats could be pulled back to check root moisture levels (and root health) and the rate of drainage ensured that over watering was not a problem. The STG treatment was however observed to heat up the nutrient solution more than the other treatments during warm growing conditions.

 

 

SYSTEM SET UP AND MEDIA REMOVAL

 

The time required by one person to prepare and install the individual growing media into each NFT system (2 x 4 meter length, 13 foot long channels).

 

Media treatment Time taken for installation

 

Peat-Lite 4.5 minutes installation (does not include 30

minutes to weigh out fertilisers and manufacture the mix).

 

Vermiculite 4.3 minutes to install

 

Perlite 4.3 minutes to install

 

STG Pad Less than 1 minute to install

(unrolled and cut at end)

 

 

 Installation included scooping or pouring media into channels, levelling and wetting up to run off with a hand held sprinkler. Removal times were the same for each treatment as the root system has formed a solid mat in each of the channels and was cut and rolled up for removal.

 

 

RELATIVE GROWTH RATE

 

Relative growth rate is a measure of fresh and dry weight production expressed as grams per day per 100 seedlings. Note – the vertical lines in the centre of each bar are the standard error of that sample, for a result to be statistically significantly different, the vertical standard deviation lines must not vertically overlap those of another sample.

 

Figure 1 – Relative growth rate, fresh weight for planting 1 and 2

 

Relative Growth Rate – Wheatgrass fresh weight

0

0.2

0.4

0.6

0.8

1

1.2

Perlite

Vermiculite

Sure to Grow ®

PeatLite

Treatment

Fresh Weight g per day (100 plants)

Planting 1

Planting 2

 

Figure 1 shows that the vermiculite, STG and Peat-Lite treatments have a significantly higher fresh weight accumulation than the perlite treatment in planting 1. For planting 2, no significant differences in fresh weight accumulation existed between treatments.

 

Figure 2 Relative growth rate, dry weight for planting 1and 2

 

Relative Growth Rate – Wheatgrass dry weight

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Perlite

Vermiculite

Sure to Grow ®

PeatLite

Treatment

Dry Weight g per day (100 plants)

Planting 1

Planting 2

 

 

Figure 2 shows the Peat-Lite, STG and vermiculite had significantly higher dry weight accumulation than the perlite treatment for planting one. For planting two, no significant differences in dry weight accumulation existed between treatments.

 

FOLIAR ANALYSIS AT HARVEST

 

Treatment Element Planting 1 Planting 2 Optimum range
(wheat)
Peat-LiteN %4.44.83.5 – 5 %
P %1.01.10.2 – 0.7 %
K %4.64.61.8 – 3.5 %
Mg %0.300.320.2 – 0.5%
Ca %0.370.330.2 – 0.5 %
S %0.840.910.15 – 0.55%
Na %0.01<0.01
Fe mg/kg697125 – 100 ppm
Mn mg/kg12016035 – 475 ppm
Zn mg/kg557415 – 70 ppm
Cu mg/kg13135 – 25 ppm
 

 

B mg/kg4183 – 20 ppm
STGN %4.84.83.5 – 5 %
P %0.710.840.2 – 0.7 %
K %0.901.11.8 – 3.5 %
Mg %0.220.280.2 – 0.5 %
Ca %0.350.780.2 – 0.5 %
S %0.360.440.15 – 0.55 %
Na %<0.01<0.01
Fe mg/kg799325 – 100 ppm
Mn mg/kg566035 – 475 ppm
Zn mg/kg534915 – 70 ppm
Cu mg/Kg12135 – 25 ppm
 

 

B mg/kg5123 – 20 ppm
VermiculiteN %4.54.53.5 – 5 %
P %0.640.610.2 – 0.7 %
K %4.03.01.8 – 3.5 %
Mg %0.330.290.2 – 0.5 %
Ca %0.140.140.2 – 0.5 %
S %0.350.360.15 – 0.55 %
Na %<0.01<0.01
Fe mg/kg9910525 – 100 ppm
Mn mg/kg836535 – 475 ppm
Zn mg/kg514415 – 70 ppm
Cu mg/kg12135 – 25 ppm
 

 

B mg/kg373 – 20 ppm
Perlite N %5.25.13.5 – 5 %
P %0.790.770.2 – 0.7 %
K %0.90.91.8 – 3.5 %
Mg %0.280.310.2 – 0.5 %
Ca %0.330.490.2 – 0.5 %
S %0.390.420.15 – 0.55 %
Na %0.03<0.01
Fe mg/kg898125 – 100 ppm
Mn mg/kg505735 – 475 ppm
Zn mg/kg535015 – 70 ppm
Cu mg/kg14145 – 25 ppm
B mg/kg4123 – 20 ppm

 

Slight differences in foliar mineral levels between planting one and planting two for each treatment will be due to differences in environmental conditions (temperature, light and humidity) which influence nutrient ion uptake and incorporation into leaf tissue, as the same nutrient formulation and strength was used for both sowing dates. The foliar mineral levels in the Peat-Lite treatment are also likely to be different from those of the other 3 treatments as the Peat-Lite media had fertiliser incorporated at the time of mixing – these being dolomite (Mg and Ca), super phosphate (P, Ca and S), potassium nitrate (N and K), Gypsum (Ca), trace element mix (Mn, Zn, B, Cu, Mo) and iron chelate (Fe). These fertilisers combined with the addition of the hydroponic nutrient solution may account for the higher levels of some elements in the Peat-Lite foliar tissue. The vermiculite, STG and perlite are considered to be `inert media’ and should have little effect on nutrient ion uptake, although differences do exist between treatments. The most notable is potassium (K) which is present at a level in the foliage in the vermiculite treatment at 4.0 % (optimum is 2.5 – 3.0 %), and present at low levels of 0.9 % in the STG and perlite, the reason for these differences are not clear. The higher level of potassium in the Peat-Lite is most likely a result of the presence of potassium nitrate in the Peat-Lite media. The relatively low levels of calcium in the vermiculite treatment (0.14 %) compared to the other three treatments may be due to either the CEC (cation exchange value) of vermiculite binding calcium and making it less available for plant uptake or to pH differences. No visible mineral deficiencies were noted on the wheatgrass during growth in either planting date.

 

There were few differences in the levels of trace elements (all within acceptable ranges) or magnesium between all four treatments. Sodium levels were also low or below the detection limit indicating no media has a sodium contamination problem (sodium is an unwanted element in hydroponic production). Nitrogen levels were optimal in all treatments and were found at similar levels in the Peat-Lite, STG and vermiculite and slightly higher in the perlite. Phosphate was slightly higher in the Peat-Lite treatment, due to the presence of super phosphate in the Peat-Lite mix, although all phosphate levels were within a good range.

 

 

YIELDS

 

Table 1, gives the final yield data in grams of harvested product per area of bed sown/plot

(approximate area is 23 cm x 3.8 m, 9” x 47”), by treatment and planting.

 

Table 1

 

Wheatgrass (amount of seed sown per plot = 3038 g, 107.2 oz)

 

Treatment

 

Planting 1Planting 2
Peat-Lite8614 g (304.1 oz)7435 g (263.9 oz)
STG7311 g (258.1 oz)7549 g (266.5 oz)
Vermiculite7958 g (280.9 oz)7014 g (247.6 oz)
Perlite5982 g (211.2 oz)6187 g (218.4 oz)

 

 

A Chi square analysis of the final harvest data found that significant treatment differences (P = 0.05) in yield existed in the wheatgrass for both planting dates.

 

Figure 3

 

Wh

eatgrass fresh weight yields.

 

Wheatgrass yield (g)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

Peat lite

STG

Vermiculite

Perlite

Grams Fresh Weight

Planting1

Planting 2

 

HARVEST QUALITY

 

The quality of cut wheat grass from each treatment plot was assessed at the time of harvest. High quality wheatgrass should be well developed with long, clean blades and freedom from media particles. Color should be uniform and mid to dark green with no tipburn or significant yellowing. Some paler color can be expected at the base of the plant with grain sown at this density as light can not penetrate through the canopy to the base of the plants in the final stages of growth. Plants should not be overly succulent, thin, weak or pale as this results in a shorter post harvest shelf life. Packaged wheatgrass should be free of all fungal and bacterial pathogens which may cause post harvest rots during storage.

 

WHEATGRASS HARVEST QUALITY

Peat-Lite:

Planting one: Plants tall, some yellowing at base. Roots healthy and white, some slight blue mould present on seed bed.

Planting two: Some yellowing at base of plants, canopy very thick, good green color on tops. Roots healthy.

 

STG:

Planting one: Plants slightly shorter than Peat-Lite treatment, dark green and healthy, roots all white thick and healthy.

Planting two: Thick canopy, some slight lower yellowing on base of plants, roots healthy.

 

Vermiculite:

Planting one: Quality good, some yellowing on outer leaves noted. Roots healthy Planting two: Dark green coloration, one isolated area of rot on lower channel end affecting roots and lower stem area (affected seedlings not harvested)

 

Perlite:

Planting one: Shorter than other treatments and darker green color. Roots healthy.

Planting two: Some plants with yellow tips and tip burn on outer edges of channel. Plants shorter than other treatments. Roots healthy.

 

 

SHELF LIFE ASSESSMENT

 

WHEATGRASS

Planting 1 harvested 7 October – shelf life assessment on 20 October

Treatment Comments
Peat-Lite

 

Yellowing started to develop on foliage in sample packs by day 6 and progressed until assessment date.
Sure To Grow

 

STG remained fully green until day 9 when some slight changes in color were noted. Color still acceptable at end of shelf life trial.
Vermiculite

 

Vermiculite treatment showed yellowing on the lower ends of the blades by day 5, this became significant towards the end of assessment. 50% of foliage was affected by yellowing by trial completion.
PerliteThe perlite treatment, although shorter, remained a dark green color through out the trial.

 

 

Wheatgrass shelf life samples from planting one. From left to right, Peat-Lite, STG, vermiculite and perlite.

 

 

Product quality at completion of shelf life assessment – planting one.

 

 

 

Wheatgrass samples at end of shelf life assessment – 22

November 2008

 

 

Planting 2 harvested 11 November – shelf life assessment 22 November

Treatment

 

Comments
Peat-Lite

 

Some wet/brown rot on lower ends of wheatgrass in 2 samples developing by day 8. Wilting, loss of turgor and yellowing (50% of foliage) in all samples by day 11.
Sure to Grow®

 

Slight loss of green color (chlorophyll breakdown), shelf life still acceptable at completion
Vermiculite

 

Extensive rot in one sample by day 10. Loss of chlorophyll and moderate yellowing in all samples.
PerliteSome wilting by day 11. Mild yellowing with tip die back and yellowing on some blades (note harvested wheatgrass had tipburn before shelf life assessment).

 

CONCLUSIONS

 

Crop Observations

In both planting dates germination was rapid and vigorous and occurred within 48 hours of sowing. Few differences were noted in crop development between treatments, however the perlite treatment appeared shorter than the Peat-Lite, STG and vermiculite, particularly in planting one. The perlite treatment also appeared darker green in color in planting one, but not in planting two.

 

The dislodgment of perlite particles by the wheatgrass crop also meant that the seed bed became uneven and harvesting had to be carried out at a higher level, above the base of the plants, to prevent excessive contamination with perlite particles. This will also have reduced harvestable yield.

 

Problems were found with irrigation of the heavier media (Peat-Lite and vermiculite) which, having a high moisture holding capacity, became over saturated rapidly and drained slowly. Over-saturation of a seed bed can lead to problems with a lack of oxygen in the root zone, predisposing the plants to disease. The timing and volume of irrigation with these heavier media became critical to managing the crop and the irrigation system could not be run continuously as would be possible with perlite and STG. Grower skill would be required to determine the moisture status of these media and adjust the irrigation on a regular basis to prevent problems originating from over saturation of the seedling bed. The perlite media did not tend to become over-saturated and drained well, however it had poor capillary action and did not wick up moisture from the base of the channel to the surface of the seed bed in the early stages of growth, necessitating the use of water sprays to keep the media surface moist during the first few days of establishment. Also, the high density of the seed and vigorous germination meant that the top layer of lighter perlite particles were lifted slightly from the rest of the seed bed by the developing roots and shoots – this would have reduced the capillary action of the perlite media.

 

The Sure to Grow® pad product was the most straight forward media to manage, both in terms of installation and crop removal, but also with regards to irrigation. The pad product retained sufficient moisture between irrigations to keep the germinating seed moist, while providing sufficient aeration for radicle growth. The pad product drained well and made it difficult to over-water the crop in the wide channel NFT system used, at any stage of development. Furthermore with the STG pads it is possible to easily view the developing root systems by lifting the mats back to expose the underside. This would allow growers to check for early root rot signs and to assess root health at any stage of development. The only disadvantage seen during this trial with the STG treatment was that the root zone could heat up rapidly during days with high radiation to levels higher than the ambient air temperature and that this could also warm the nutrient solution to levels above those optimal for seedling growth. While this was only noted in the afternoon of 1 – 2 days during this early spring period, it is likely to be a greater problem in crops grown in warmer climates and for summer cropping. This problem however could be alleviated relatively easily with use of nutrient solution cooling, as is becoming common for NFT lettuce and vegetable production in warm climates.

 

Using NFT wide channel systems provides a major advantage in that the crop should not need over-head irrigation and hence the foliage can remain dry. Many foliar pathogens need damp foliage and/or high humidity levels to attack the crop, thus sub-surface irrigation can assist with disease prevention. While sterilised water (heated to 80o C / 175o F for 15 minutes), and channels were used during this trial, one small isolated disease outbreak did occur in the vermiculite growing media towards the end of planting one. This appeared to be a root rot pathogen which developed in an isolated patch towards the end of the growing channel which resulted in brown roots and some lower stem rot. It is possible that despite being considered to be `sterile’ media, that it may have had contamination with disease spores or that disease spores entered the crop in the usual way (on wind currents, as dust contamination or seed borne as all wheat seed utilized was untreated with fungicides).

 

 

Relative growth rates

Relative growth rate, expressed as both fresh and dry weight accumulation per day are an indication of how the media treatment affects plant biomass production and development. While fresh weight determines final yield, dry weight is the more important parameter as it determines factors such as shelf life and quality.

 

Generally there were no significant differences found in fresh or dry weight accumulation during this trial in the Peat-Lite, vermiculite and STG treatments. However the perlite treatments had significantly lower fresh and dry weight accumulation in planting one and this also resulted in significantly lower yields in the perlite for this planting date. It could be concluded from this data that the physical properties of perlite are not as optimal for wheatgrass growth and development as that of the Peat-Lite, vermiculite and STG, although the influence of environmental conditions may play a role in yield and growth rate results from perlite.

 

 

Yields

As with relative growth rates, yield differences were affected by planting date as well as by growing media treatment and by the interaction of these variables. Chi square analysis of the yield data showed differences observed in yield were greater than would be expected, so could be therefore caused by treatment.

 

The differences in yield between growing media treatments may be due to a number of reasons. Perlite did not have the strong capillary action of the other media in the NFT channel systems and the dryer surface of this media may have been responsible for the lower yields and smaller seedlings. Peat-Lite contains humic acids and possibly other organic growth promotant compounds which may have assisted development and yields. The STG Pads provided an excellent physical environment for the seedling growth with good drainage and high aeration in the system used, all of which play a role in growth and yield.

 

 

Harvested quality

The productivity of wheatgrass crops should not just be assessed based on fresh weight yields. Plant quality and post harvest life are of equal or even greater importance as wheatgrass typically have a limited shelf life and can develop a number of post harvest problems. Plant quality is influenced by a number of factors including density, genetics, environmental conditions, root zone factors, nutrition, disease presence and growing media.

High quality wheatgrass should be uniform in height and developmental stage, with good color development, no foliage yellowing or leaf spots and blades of a reasonable length, however not overly thin and elongated. The presence of fungal or bacterial pathogens in the production channels at the time of harvest can carry over and cause rots in the harvested product. Plants which are overly tall, thin, light for size and succulent generally have a lower shelf life compared to those which are more compact.

 

Harvested wheatgrass quality from both planting one and planting two was similar, apart from some slight yellowing noted mostly in the Peat-Lite and vermiculite treatments. The perlite treatment developed some tipburn and yellowing in the second planting, possibility due to higher light and temperature levels in the second planting date. The perlite cut product was noticeably shorter than the other three treatments and a darker green color in planting one, which was indicative of the dryer root zone that the perlite treatment created. STG wheatgrass was consistent in both planting dates with good color which was darker green in planting one, possibility due to cooler temperature conditions with some slight yellowing on the base of the plants in planting two. There was no sign of root rot or root browning on the lower surface of the mats.

 

 

Shelf life

An acceptable shelf life period is vital for wheatgrass which are still in the seedling stage and highly prone to desiccation and tissue breakdown. The respiration rate is also high in harvested wheatgrass and post harvest problems can occur. The most common reasons for limited shelf life in wheatgrass are yellowing due to a loss of chlorophyll. Fungal and bacterial pathogens can also cause wet rots which cause a rapid breakdown of leaf tissue inside the pack, even under refrigeration.

 

There were some trends evident in the shelf life assessment trial. Generally yellowing of the foliage was the most common cause for loss of shelf life in planting one and two. However wet rots which caused foliage disintegration inside the pack were noted in planting two on the Peat-Lite and vermiculite. It is likely that fungal and/or bacterial pathogens were present in the production system (although only one isolated outbreak of root rot was found in the vermiculite at harvest) and these carried through to the harvested product causing post harvest rots after 10 days in storage. The STG treatment did not develop any wet rots or fungal pathogens post harvest and had only a slight loss in color over the shelf life period. The perlite treatment, despite its lower yield, consistently produced a good shelf life and maintained chlorophyll levels and an acceptable green color for the majority of the post harvest life for planting one. However in planting two the tip burn noted on the plants at harvest worsened in storage and resulted in some die back of the blades.

 

 

 

SUMMARY

The main findings are:

 

Perlite consistently performed the poorest of all 4 media evaluated in terms of plant growth rate and yield. Perlite plants were shorter and due to the particles on the bed surface, needed to be cut higher up on the plant at harvest, which may have reduced fresh yields.

 

Harvested product quality was also inconsistent in perlite – in planting one the wheatgrass was shorter, but darker green then the other treatments and resisted post harvest yellowing. However in planting two, leaf blade yellowing and some tip burn developed in the production system which reduced harvest quality. STG produced the most consistent shelf life results with minimal yellowing and absence of any post harvest rots, although the perlite treatment from planting one had the highest quality at the end of shelf life assessment due to a darker green color.

 

The vermiculite was the only treatment to experience any root rot disease towards the end of the trial, this may have been due to the high water holding capacity of this media which may have pre disposed the plants to pathogen attack.

 

Foliar mineral levels did not show any major deficiencies or toxicities between treatments. The Peat-Lite treatment had higher foliage levels of some elements, which is most likely the result of additional fertilisers in the Peat-Lite mix which added to the nutrients applied via the nutrient solution. STG and perlite had low foliar potassium levels in both planting dates, while vermiculite, an inert media and Peat-Lite which had additions of potassium nitrate in the mix, ran higher than expected levels. These differences are difficult to explain, given the nutrient solution was not recirculated and had sufficient potassium in the formulation for growth and development.

 

STG had a clear and significant advantage in the efficiency and management of NFT wheatgrass production systems including greatly reduced set up and removal times, ease of irrigation management, and effective control of root zone moisture levels.

 

 

Disclaimer: No responsibility is taken for the use or misuse of the data presented in this report or for sections of this report re published or re stated out of context. This report is private and confidential and can be distributed by the named client only.

 

Appendix one – Wheatgrass Nutrient Formulation

 

 

Standard complete, hydroponic nutrient formulation for wheatgrass production in NFT channels. For use with distilled or RO water only.

 

Amount of fertiliser salts in grams dissolved in two 10 litre stock solution tanks. A one in 400 dilution rate with water will give an EC of 0.5 mS cm-1 and TDS of 350. Solution diluted with sufficient water to achieve the correct working strength EC. pH level 5.8 – 6.0.

 

PART A

Calcium nitrate 1252.4 g

Potassium nitrate 144.4 g

Iron chelate (13%) 50 g

PART B

Potassium Nitrate 144.4 g

Monopotassium phosphate 202.7 g

Magnesium sulphate 424.8 g

Manganese sulphate 8 g

Zinc sulphate 1.1 g

Boric acid/Solubor 3.9 g

Copper sulphate 0.3 g

Ammonium molybdate 0.103 g

 

A one in 100 dilution rate will give the following levels of elements:

 

N = 16.7 mMole/l 233ppm

P = 1.5 mMole/l 47 ppm

K = 4.3 mMole/l 167 ppm

Mg = 1.7 mMole/l 42 ppm

Ca = 6.3 mMole/l 250 ppm

S = 1.7 mMole/l 55 ppm

Fe = 6.50 ppm

Mn = 2.18 ppm

Zn = 0.30 ppm

B = 0.66 ppm

Cu = 0.07 ppm

Mo = 0.04 ppm

 

Appendix two – Cornell Peat-Lite mix

 

Batch size = 75 litres

 

 

37.5 litres of peat moss

37.5 litres of horticulture grade vermiculite

 

613 g Dolomite

405 g Gypsum

102 g super phosphate

76.5 g potassium nitrate

3.2 g Iron chelate (13%)

10 g Trace elements

Wetting agent

 

REFERENCES

 

Raviv M., Wallach R., Silber A and Bar-Tal A., 2002. Substrates and their analysis. In `Hydroponic Production of Vegetables and Ornamentals. D Savvas and H Prassam (eds). Published by Embryo Publications, Athens, Greece.

Appendix Three

 

Crop Trial Photos

 

 

Wide NFT channels (Sure Grow Channels, manufactured in Australia)

 

Planting one – 16 September

 

 

Planting 1, September 22, 2008.

 

 

 

Below – planting one, 28 September 2008. Treatments from left to right: perlite (2 channels), vermiculite (2 channels), STG (2 channels) and peat lite (2 channels).

 

 

Wheat germination after 72 hours. Top left: STG, top right Peat-Lite, bottom left: vermiculite, bottom right: perlite

 

 

Above: Germination of STG treatment wheat.

 

Above: Gutation (water droplets forced from tips of blades in the early morning) on wheat grass indicating healthy root system and root pressure.

 

 

 

 

 

Vermiculite treatment on left

(2 channels), STG on right (2 channels). Note both treatments have similar growth and development – the STG pads are positioned lower down in the channel as they do not have the depth of media under the plants that the other treatments had.

 

Below: Planting 2, STG on left (2 channels), Vermiculite on right (2 channels)

 

 

Root systems: above perlite (Left) and Peat-Lite (right). Below STG (left) and vermiculite.

 

Above: STG wheatgrass at harvest.

 

Left: Harvesting Peat-Lite treatment

 

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