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Content uploaded by Valtcho D Jeliazkov (Zheljazkov)
Author content
All content in this area was uploaded by Valtcho D Jeliazkov (Zheljazkov) on Jun 21, 2015
Content may be subject to copyright.
Content uploaded by Valtcho D Jeliazkov (Zheljazkov)
Author content
All content in this area was uploaded by Valtcho D Jeliazkov (Zheljazkov) on Jun 21, 2015
Content may be subject to copyright.
Human Hair as a Nutrient Source
for Horticultural Crops
Valtcho D. Zheljazkov
1,3
, Juan L. Silva
2
, Mandar Patel
2
,
Jelena Stojanovic
2
, Youkai Lu
2
, Taejo Kim
2
, and Thomas Horgan
1
ADDITIONAL INDEX WORDS. lettuce, feverfew, yellow poppy, wormwood, Artemisia
annua,Lactuca sativa,Glaucium flavum,Tanacetum parthenium, food quality,
phenolics, hair waste
SUMMARY. Two pot experiments were conducted to evaluate noncomposted hair
byproduct as a nutrient source for container-grown crops. Lettuce (Lactuca sativa
‘Green Leaves’) and wormwood (Artemisia annua ‘Artemis’) were grown in a
commercial growth substrate amended with 0%, 2.5%, 5%, or 10% by weight hair waste
or controlled-release fertilizer (CRF) or were watered with a complete water-soluble
fertilizer (WSF). After harvest, yellow poppy (Glaucium flavum) was grown in the
pots and substrate that previously grew wormwood, and feverfew (Tanacetum
parthenium) was grown in the pots and substrate previously containing lettuce. The
5% hair treatment and the commercial fertilizer rates were calculated to provide the
same amount of nitrogen (N) during production of lettuce and wormwood based
on 50% N availability from hair. Yields in treatments containing hair or CRF or
watered with WSF were higher than in the untreated control. The highest lettuce
and wormwood yields occurred with CRF followed by WSF and 5% and 10% hair
treatments. However, yield of yellow poppy was higher in the hair treatments
than yields in inorganic fertilizer treatments or in the untreated control. Feverfew
yields did not differ among fertility treatments, but yields in fertility treatments
were higher than those of control. Lettuce leaf moisture content was lower, but
soluble solids were higher in plants in the hair waste treatments than in the WSF
or CRF treatments. Total phenolics in lettuce did not differ among treatments.
Total aerobic and coliforms plate counts were similar for all samples, averaging 6.0
and 1.2 log cfu/g, respectively. Results from this study suggest that noncomposted
hair waste could be used as a nutrient source for container-grown plants. Hair waste
should not be used as a single nutrient source for fast-growing plants because of
the time needed for degradation of the hair before release of plant nutrients.
Anumber of waste materials and
byproducts (such as animal
manure, municipal solid waste
composts, and sewage sludge) are
used currently in agricultural crop
production. Human hair waste gen-
erated by barbershops typically would
be disposed of at waste sites,
landfilled, or composted along with
other municipal solid wastes. Pre-
vious research has demonstrated that
noncomposted human hair waste
with an addition of municipal solid
waste compost can be used as nutrient
source for crops (Zheljazkov, 2005).
However, there is no published
research on the use of human hair as
an exclusive nutrient source for
greenhouse container production,
although human hair waste based
products have been commercially
available to crop producers in the last
couple of years (SmartGrow, FL City,
FL).
The hypothesis of this study was
that commercially available noncom-
posted hair waste cubes would sup-
port plant growth and the
development of two consecutive
crops (double cropping) and could
be used as a sole nutrient source. The
objective was to compare the produc-
tivity of four crops grown in commer-
cial growth medium in pots with the
following treatments: untreated con-
trol, noncomposted hair cubes at
2.5%, 5%, and 10% by weight, a con-
trolled-release fertilizer (CRF), and
water-soluble fertilizer (WSF). As
model plants, we used four con-
tainer-grown crops: lettuce, worm-
wood, yellow poppy, and feverfew.
Materials and methods
PLANT GROWTH CONDITIONS.In
Mar. 2007, two to three lettuce or
wormword seeds were planted in each
cell of 48-cell (6 ·3.5 cm, 5 cm deep)
plastic trays filled with a commercial
growth substrate (Metromix 300;
Sun Gro Horticulture, Bellevue,
WA). After emergence, seedlings
were thinned to one plant per cell
and grown in a greenhouse under
natural daylight with day tempera-
tures of 22 Cto25C and a night
temperature of 18 C. The experi-
ment was initiated in Mar. 2007 and
continued through Sept. 2007, when
the second crops were harvested.
Twenty days after emergence, lettuce
seedlings were transplanted to 6-
inch-diameter pots containing 600 g
of the same growth substrate used for
transplant production, and worm-
wood was transplanted to 11-inch-
diameter pots containing 2800 g of
growth substrate. Two different size
pots were used to correspond to
wormwood and lettuce plant sizes.
The experimental design was a
randomized complete block design
Units
To convert U.S. to SI,
multiply by U.S unit SI unit
To convert SI to U.S.,
multiply by
29,574 fl oz mL 3.3814 ·10
–5
29.5735 fl oz mL 0.0338
2.54 Inch(es) cm 0.3937
25.4 Inch(es) mm 0.0394
1 mmho/cm dSm
–1
1
28.3495 oz g 0.0353
0.1 ppm mg/100 g 10
1 ppm mgkg
–1
1
(F – 32) O1.8 FC(1.8·C) + 32
This is a contribution of the Mississippi Agricultural
and Forestry Experiments Station Journal article No
11266. This research was funded by USDA-ARS
Specific Coop. Agreement 58-6402-4-026 with CRIS
MIS-223010. The specific project was ‘‘Field Estab-
lishment of Medicinal Herbs and Potential for Com-
mercial Production’’ awarded to Dr. Jeliazkov
(Zheljazkov) and by MIS project awarded to Dr.
J.L. Silva.
We thank Dr. Crofton Sloan, Dr. Frank Matta, and
Dr. Normie Buehring of Mississippi State University
and the anonymous reviewers of the journal for
critically reading the manuscript and suggesting many
improvements.
1
Mississippi State University, North Mississippi
Research and Extension Center, 5421 Highway 145
South, Verona, MS 38879
2
Mississippi State University, Department of Food
Science, Nutrition, and Health Promotion, Box 9805,
Mississippi State, MS 39762
3
Corresponding author. E-mail: vj40@pss.msstate.
edu.
592 •October–December 2008 18(4)
with four replicates. Factors were
crop (at two levels) and fertility (at
six levels). Lettuce and wormwood
were treated as one experiment, and
second crops yellow poppy and fever-
few were treated as a second experi-
ment. Experimental treatments were
as follows: hair waste cubes (Fig. 1;
donated by SmartGrow) were incor-
porated and thoroughly mixed into
the growth medium at 0%, 2.5%, 5%,
or 10% by weight (0, 70, 140, or 280
g, respectively) to provide 0, 11.6,
23.1, or 46.2 g/pot total N, respec-
tively. The hair waste cubes contained
16.5% N, 0.01% phosphorus (P),
0.01% potassium (K), 0.27% calcium
(Ca), 0.05% magnesium (Mg), and
0.23% sulfur (S), as analyzed by the
Mississippi State University Soil Test-
ing Laboratory (Mississippi State,
MS) using the method of Jones and
Steyn (1973) and averaged from
three replicates. Commercial fertilizer
treatments included a topdress of
CRF (Osmocote Plus 15N–9P–12K;
Scotts-Sierra Horticultural Products,
Marysville, OH) or fertilization with
100 mgkg
–1
of N with 1100 mL of
WSF (greenhouse-grade 20N–8.8P–
16.6K general purpose fertilizer;
Scotts-Sierra Horticultural Products)
every 7 d. The 5% hair treatment and
the commercial fertilizer rates were
applied to provide the same amount
of N during the production cycle
based on 50% N availability from the
hair waste as determined from pre-
vious research (Zheljazkov, 2005;
Zheljazkov et al., 2008). CRF pro-
vided 2.5 g N, 1.5 g P, and 1.99 g K
to each 6-inch-diameter pot, and
11.5 g N, 6.9 g P, and 9.3 g K to
each 11-inch-diameter pot. WSF pro-
vided 2.5 g N, 1.08 g P, and 2.06 g K
to each 6-inch-diameter pot, and
11.5 g N, 5.06 g P, and 9.6 g K to
each 11-inch-diameter pot.
Plants were grown in a green-
house with an average day/night
temperature of 28/20 C without
supplemental lighting for 50 d. Plants
were watered daily as needed, by
hand, making sure no leaching
occurred. Lettuce and wormwood
were harvested at commercial (mar-
ketable) maturity stage (six to eight
fully developed leaves, about 12
inches tall). Plants were cut about
1 cm above the substrate, and height
and fresh weight were recorded.
About half of the lettuce samples were
held at 4 ± 1 C until analyzed (less
than 4 d) or frozen (for phenolics).
The wormwood samples and remain-
ing half of the lettuce samples were
dried in a drying oven at 68 C for
72 h and weighed.
One week after the lettuce and
wormwood were harvested, feverfew
was planted into 6-inch-diameter
pots and yellow poppy was trans-
planted into 11-inch-diameter pots
containing the growth substrate from
the previous crop. CRF and WSF
were applied as described for the
previous crops. No additional hair
waste cubes were applied to the hair
treatments. The feverfew and yellow
poppy were grown for 20 weeks and
were harvested in the same way as the
previous crops.
Growth medium samples were
taken after the harvest of the second
crop, dried at room temperature, and
extracted for phyto-available nutri-
ents using the Lancaster soil test
method (Cox, 2001). Determination
of specific conductance (total soluble
salts) was done using a conductivity
meter (model 32; YSI, Yellow
Springs, OH) (Willard et al., 1968).
Nitrate-N was determined using a
nitrate electrode (Francis and
Malone, 1975).
Chemical and physical analysis
of lettuce was conducted in three
replicates from each treatment. Each
replicate was an average of three read-
ings. Water content of lettuce was
determined by drying at 65 C for
24 h [Association of Official Agricul-
tural Chemists (AOAC) method
930.04 (AOAC, 1997)]. The soluble
solids concentration (SSC; in per-
centage) in lettuce was evaluated
using a refractometer (Bauch &
Lomb, Rochester, NY). The temper-
ature was maintained at 21 C with
water circulating through the refrac-
tometer. The refractometer was cali-
brated using distilled water before
each reading. After calibration, 1
drop of filtered lettuce juice was
placed on a glass prism of the refrac-
tometer. The results were recorded
and expressed as percentage of SSC
(Stojanovic and Silva, 2007).
TOTAL PHENOLICS.Lettuce sam-
ples from each treatment and replica-
tion were ground by mortar and
pestle. A 5-g portion was homogen-
ized with 15 mL of high-performance
liquid chromatography-grade metha-
nol (Fisher Scientific, Fair Lawn, NJ)
in a homogenizer. The homogenizer
was washed with 5 mL of methanol,
which was combined with the first
homogenate. Samples were centri-
fuged at 10,000 g
n
for 15 min at
15 C. The volume of the supernatant
was recorded, and the pellet was
discarded. Total phenolics in let-
tuce extract were determined with
the Folin-Ciocalteu reagent by the
method of Singleton and Rossi with
gallic acid as the standard (Singleton
Fig. 1. Hair waste cubes used in this study. Coins are U.S. quarters ($0.25) with a
diameter of 24.26 mm (1 mm =0.0394 inch).
•October–December 2008 18(4) 593
and Rossi, 1965). Twenty microliters
of sample was mixed directly in the
cuvette with 1.58 mL of water and
100 mL of Folin-Ciocalteu reagent
(Fisher Scientific). The cuvette was
incubated between 1 and 8 minutes,
and 300 mL of 20% sodium carbonate
was added. Samples were incubated at
room temperature for 2 h, and
absorbance was recorded at 765 nm.
COLOR.The color of lettuce
leaves was evaluated using a spectro-
colorimeter (Labscan Model 6000
0/45; Hunter Associates Labora-
tory, Fairfax, VA). The instrument
was calibrated with two standard tiles
(black and white) using a quartz-
halogen lamp. Each lettuce sample
was placed on a 10-mm-diameter
port. Three readings were taken on
two sides of each sample. The reflec-
tance values of ‘L’ (brightness), ‘a’
(redness+/greenness–), ‘b’ (yellow-
ness+/blueness–) were measured. Hue
angle value (tan
–1
b/a) and chroma or
saturation index [SI = (a
2
+b
2
)
1/2
]
were calculated according to Silva
et al. (2005).
MICROBIOLOGICAL ANALYSIS.A
sample of 25 g of lettuce was placed
in a stomacher bag (whirl-pak
TM
;
Nasco, Fort Atkinson, WI) to which
225 mL of 0.1% sterile peptone water
was added and the contents were
massaged in a stomacher (Sweard
Medical Limited, London) for 30 s
(Allende et al., 2004; Kim et al.,
2000). This was done to remove cells
from the lettuce and place them into
the solution. Total aerobic plate
counts (APC) were determined by
the spread plate method by using
0.1 mL of sampling dilution (Amer-
ican Public Health Association,
1992). Plate Count Agar (Difco;
Becton, Dickinson & Co., Lawrence,
KS) was used as the growth medium.
The APC plates were duplicated from
each dilution and were incubated in
an incubator (Precision Scientific,
Champaign, IL) at 37 C for 48 h.
The colonies were counted, and the
microbial counts were reported as log
colony-forming units (cfu) per gram
of lettuce. Total coliform counts were
determined from the same dilution
using violet red bile agar (Difco) and
incubating at 37 C for up to 48 h.
Coliform counts were expressed as
log cfu per gram.
Data analyses were performed
using analysis of variance in Quattro
Pro 10 (Corel Corp., Ottawa,
Canada). Means, whenever different,
were separated by using Fisher’s pro-
tected least significant difference
(LSD) test. (SAS version 9.1 for Win-
dows; SAS Institute, Cary, NC).
Results
The addition of hair waste cubes
to the growth medium at 5% or 10%
by weight increased lettuce and
wormwood yields relative to the
untreated control (Table 1). How-
ever, yields in the 5% or 10% hair
waste treatments were lower than
yields in the inorganic fertilizer treat-
ments. The highest yields of lettuce
and wormwood were obtained in the
CRF treatments, followed by the
WSF treatment. The yield response
of the second crops yellow poppy and
feverfew to the treatments was differ-
ent from the first crops. Overall, the
yellow poppy yields were greater in
the hair treatments, lower in the
commercial fertilizer treatments
(CRF or WSF), and the lowest in
the untreated control (the 0% hair
treatment; Table 1). The highest
yields were obtained in the 5% and
10% hair treatments, and yields in the
CRF exceeded those in the WSF
treatment. Feverfew yields in the fer-
tility treatments were not different,
but all were higher than in the
untreated control (Table 1).
All hair-treated lettuce and the
untreated control samples had lower
(P£0.05) moisture and higher (P£
0.05) SSC than the CRF or WSF
samples. The SSC of the CRF samples
was higher than that of the untreated
control or hair-treated samples,
whereas the SSC value of WSF sam-
ples was not different from all others
(Table 2). Total phenolics, color sat-
uration or chroma, and ‘b’ color
values did not differ (P>0.05) among
samples. Other color values varied
among samples, with no clear differ-
ences between hair-fertilized samples
and other treatments. Aerobic plate
counts were about 6 log cfu/g,
whereas total coliforms ranged 1.0
and 1.9 log cfu/g, with no clear
differences due to hair fertilization
(Table 2).
In general, the addition of hair
waste to growth medium resulted in
lower pH than the untreated control
as measured after the harvest of the
second crop (Table 3). Residual
nitrate-N concentrations were higher
in the 2.5% and 5% hair treatments
and CRF treatments than in the WSF
or control treatments. There was
a significant amount of residual P
in the inorganic treatments (CRF
or WSF) relative to the other treat-
ments. Residual K concentrations
were greatest in the inorganic fertil-
izer treatments, lower in the hair
treatments, and lowest in the control.
Residual zinc concentrations were
higher in the 10% hair and the CRF
treatments relative to the other treat-
ments. Residual sodium was higher in
the CRF, lower in the WSF, 10%, and
5% hair treatments, and lowest in the
control. Overall, hair treatments
resulted in increased total soluble
solids (TSS) than in the other treat-
ments. Because TSS concentrations
in the hair treatments were below
or at 0.3 mmho/cm [below 2 is
Table 1. Yields of lettuce, wormwood, feverfew, and yellow poppy grown in pots
with different treatments of hair waste and fertilizers.
Treatment
z
First crop
y
Second crop
Lettuce Wormwood Yellow poppy Feverfew
----------------------- (g dry herbage/pot)
x
-----------------------
Control (0% hair) 108.7 e
w
85.3 e 5.2 e 9.4 b
2.5% hair 11.2 de 68.3 e 182.3 b 60.6
5% hair 121.2 cd 109.6 d 306.1 a 52.4 a
10% hair 132.9 c 163.1 c 344.1 a 55.2 a
CRF 486.7 a 418.6 a 113.0 c 80.2 a
WSF 326.4 b 243.3 b 44.2 d 48.9 a
z
Hair treatments were added once to the growth medium, at planting of the first crop. The 2.5%, 5%, and 10% hair
represent addition of hair to the growth medium by weight, whereas the control does not have hair addition.
Controlled-release fertilizer (CRF) was surface applied at planting of the first crop and again with the planting of
the second crop, whereas the water-soluble fertilizer (WSF) fertilizer was added on weekly basis.
y
First, lettuce and wormwood were grown in the treated pots. After harvest, yellow poppy was grown after
wormwood and feverfew after lettuce.
x
1 g = 0.0353 oz.
w
Means with the same letter within a column are not significantly different by Fisher’s protected least significant
difference test at P£0.05.
594 •October–December 2008 18(4)
RESEARCH REPORTS
considered low (Bernstein, 1975)],
no further spot-plate screen was con-
ducted to identify specific salts in the
extract.
Discussion
Results from this study suggest
that once the degradation and miner-
alization of hair waste starts, it can
provide sufficient nutrients to con-
tainer-grown plants and ensure sim-
ilar yields to those obtained with the
commonly used fertilizers in horticul-
ture. However, it takes time for the
hair to start degrading and releasing
nutrients, as is reflected in lower
yields in the hair treatments relative
to the inorganic fertilizers for the
first crops, lettuce and wormwood.
Hence, this and previous research
(Zheljazkov, 2005) suggests that
unless sufficient time is allowed for
nutrient mineralization, hair waste
may not be suitable for fast-growing
vegetables such as lettuce unless
mixed with compost or other sources
of easily available nutrients. Human
hair is a keratinaceous substance that
is very resistant to degradation by
proteolytic enzymes such as trypsin
and pepsin due to the cross-linking
by disulfide bonds, hydrogen bond-
ing, and hydrophobic interactions
(Ignatova et al., 1999). Plausibly, that
resistance to mineralization is the
reason why this ‘‘waste’’ nutrient-rich
product is not used in production
of greenhouse crops as a nutrient
source. Because of the high N content
of human hair (16.5% N in the hair
used in this experiment), land filling
or surface disposing of hair waste,
especially on sandy soils, could result
in leaching of nitrates into surface
or groundwater. Human hair waste
could be composted, as has been
demonstrated with sheep wool (Das
et al., 1997; Plat et al., 1984; Verville,
1996), another similar keratinaceous
product. Composted wool has been
used in chickpea and wheat produc-
tion as a N source (Tiwari et al.,
1989a, 1989b). A major disadvantage
of composting of protein-rich feed-
stocks such as wool, however, is the
significant loss of N (Epstein, 1997).
Hence, there are environmental and
economic benefits for the use of non-
composted protein-rich materials as
N source for crops over the compost
prepared with such materials.
The major impact of hair fertil-
ization on lettuce quality was lower
moisture and higher SSC. This result
could lead to a ‘‘sweeter’’ flavor in
Table 2. Chemical analyses, leaf surface color, and microbial counts of lettuce grown at different fertility regimes.
Treatments
z
Water SSC
y
Phenolics
(mg/100 g)
x
L
w
a
v
b
u
Hue
t
Chroma
s
APC
r
TCC
r
--------(%) ------- ---- (cfu/g)----
Control
(0% hair) 90.4 b
q
5.9 a 33.7 ns 61.5 a –9.7 a 21.8 ns 113 b 24.2 ns 6.2 a 1.4 ab
2.5% hair 90.6 b 5.8 a 31.5 51.4 b –13.5 ab 21.0 123 a 25.0 6.0 ab 1.2 ab
5% hair 91.4 b 5.2 a 38.7 56.9 ab –13.2 ab 22.1 120 ab 25.8 6.0 a 1.0 b
10% hair 90.0 b 6.1 a 49.9 52.3 b –15.5 b 23.7 123 a 28.3 5.6 b 1.0 b
CRF 94.1 a 4.2 b 28.4 50.7 b –15.0 b 21.6 125 a 26.3 6.4 a 1.9 a
WSF 94.4 a 4.9 ab 25.5 54.7 ab –14.1 ab 21.9 123 a 26.0 6.2 a 1.3 ab
z
Hair and controlled-release fertilizer (CRF) were added once to the growth medium, and the water-soluble fertilizer (WSF) was added on weekly basis. The 2.5%, 5%, and
10% hair represent addition of hair to the growth medium by weight, whereas the control does not have hair addition.
y
SSC = soluble solids content.
x
1 mg/100 g = 10 ppm.
w
L = brightness value; the higher, the brighter.
v
a = redness value.
u
b = yellowness value.
t
Hue = atan (b/a).
s
Chroma = saturation index = (a
2
+b
2
)
1/2
.
r
APC = aerobic or total plate counts, TCC = total coliform counts (1 cfu/g = 28.3495 cfu/oz).
q
Means with the same letter within a column are not significantly different by Fisher’s protected least significant difference test at P£0.05.
Table 3. Growth medium pH, residual nitrate =N, extractable nutrients, and conductivity at harvest of wormwood and
feverfew
z
as a function of addition of fertilizer of hair waste.
Treatments
y
pH
NO
3
-N
x
P
x
K
x
Ca
x
Mg
x
Zn
x
Na
x
EC
(mmho/cm)
w
----------------------------------------(mgkg
–1
)
x
---------------------------------------
Control
(0% hair) 7.4 a 0.8 c
v
28 c 254 d 4,713 1,108 3.8 b 99 c 0.1
2.5% hair 5.9 d 3.2 b 31 c 396 c 4,008 1,094 3.4 b 115 bc 0.3
5% hair 6.1 d 4.3 b 26 c 430 c 4,450 1,214 3.2 b 131 b 0.2
10% hair 4.5 e 1.8 bc 36 c 239 d 3,576 983 6.9 a 128 b 0.3
CRF 6.4 c 6.2 a 97 a 930 a 5,561 1,425 6.0 a 179 a 0.1
WSF 6.9 b 1.3 c 53 b 701 b 5,235 1,300 2.5 b 130 b 0.1
z
First, lettuce and wormwood were grown in the treated pots. After harvest, yellow poppy was grown after wormwood and feverfew after lettuce.
y
Hair and controlled-release fertilizer (CRF) were added once to the growth medium, and water-soluble fertilizer (WSF) was added on weekly basis. The 2.5%, 5%, and
10% hair represent addition of hair to the growth medium by weight, whereas the control does not have hair addition.
x
NO
3
N = nitrate nitrogen, P = phosphorus, K = potassium, Ca =calcium, Mg = magnesium, Zn = zinc, Na = sodium (1 mgkg
–1
= 1 ppm).
w
EC = EC (1 mmho/cm = 1 dSm
–1
).
v
Means with the same letter within a column are not significantly different by Fisher’s protected least significant difference test at P£0.05.
•October–December 2008 18(4) 595
lettuce, but the lower moisture may
result in decreased crunchiness. These
perceptions need to be determined
by a sensory panel. Total phenolics
did not differ, but there was a per-
ceived trend for hair-treated samples
to contain higher phenolics. Color
values had slight differences among
treatments, but not enough to be
discernible by the naked eye. This
observation tells us that consumers
may not be able to notice the differ-
ence among produce grown in these
different nutritional regimes. APC of
lettuce were average for this product,
about 6 log cfu/g (Valentin-Bon
et al., 2008), and hair treatment did
not have any effect. Total coliforms
were also below 2 log cfu/g (Gilbert
et al., 2000; Johnston et al., 2005),
indicating good handling practices
and the unlikelihood of enteropath-
ogens being present.
Overall, the amount of residual
nutrients in growth medium after the
harvest of the second crops was above
that of the control, indicating a pos-
sibility for additional cropping. Fur-
thermore, further mineralization of
hair waste would be expected in the
hair treatments, which might be able
to supply phyto-available nutrients
for a subsequent crop, as hair fibers
were visible in the growth medium at
the time of sampling. However, a
potential concern with the use of hair
as an amendment and nutrient source
for plants is the apparent decrease of
growth medium pH and increase
of TSS (Table 3). Similar reduction
of soil pH after the use of hair waste
addition has been previously reported
(Zheljazkov, 2005). The relatively
higher electrical conductivity in the
hair treatments might have been the
reason for the lower lettuce yields in
these treatments relative to the CRF
or WSF treatments, as lettuce is
known to be a salt-sensitive crop
(Kerns et al., 1999).
Further research is needed to
match nutrient release from hair
waste to crop requirements and to
estimate optimal rates of application
of hair waste to different container-
grown crops. Because human hair
may carry biohazards such as human
pathogens or chemicals, further
research is needed to address possible
health concerns of consumers and the
general public on the use of human
hair waste as nutrient source for edi-
ble crops.
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