1. S U S T A I N A B L E P R O D U C T I O N A N D C O N S U M P T I O N 6 ( 2 0 1 6 ) 6 2 – 6 6
Contents lists available at ScienceDirect
Sustainable Production and Consumption
journal homepage: www.elsevier.com/locate/spc
Low-grade rock phosphate enriched human urine as novel
fertilizer for sustaining and improving agricultural
productivity of Cicer arietinum
M. Ganesapillaia,∗, Prithvi Simhab,c, Sumedh Sudhir Beknalkard, D.M.R. Sekhare
a Mass Transfer Group, Chemical Engineering Division, VIT University, Vellore – 632 014, Tamil Nadu, India
b Department of Environmental Sciences and Policy, Central European University, Nádor u. 9, 1051 Budapest, Hungary
c School of Earth, Atmospheric and Environmental Sciences (SEAES), The University of Manchester, Oxford Road, Manchester, M13 9PL,
United Kingdom
d Complex Fluids Engineering, Chemical Engineering Department, Doherty Hall, Carnegie Mellon University, Pittsburgh, PA 15213, USA
e M/s. Xanthate Technologies, Visakhapatnam, India
A B S T R A C T
In order to sustain food production in a resource-scarce scenario it is vital that maximum utility is derived from
available reserves while simultaneously promoting their recycling. Further, substantial value can be sourced if
approaches are devised that utilize resources that were erstwhile considered wastes. To look towards alternative
fertilization techniques, this study suggests a novel fertilizer combination of two waste products: low-grade Rock
Phosphate (RP) tailing and human urine. It is demonstrated that the combined use of urine (nitrogen) and low-grade
RP (phosphorous) can indeed act as a substitute to synthetic inorganic fertilizers. Crop trials were carried out for Cicer
arietinum using RP enriched urine at various application rates on a red loamy soil (pH of 8.11). Observations made
from plant growth response indicated that direct application of this fertilizer combination resulted in performance
equivalent to mineral fertilizer Di-Ammonium Phosphate added in the same ratio. The use of RP enriched urine
thus holds a lot of promise for simultaneous waste minimization, waste utilization, and improved resource-use
efficiency.
Keywords: Alternative fertilizer; Sustainable agriculture; Crop productivity; Waste utilization; Waste minimization
c⃝ 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction
The continual harvesting of crops from arable land for
human consumption affects the natural supply and balance
of nutrients in soil. In order to ensure long-term soil fertility
and good harvest, cultivated fields require timely addition
of soil improving supplements. Commercial agricultural
production has achieved this through the external application
of synthetic inorganic fertilizers. In recent years, urea and
ammonium nitrate have been by far, the most popular
∗ Corresponding author. Tel.: +91 97902 99447; fax: +91 462 24 30 92.
E-mail address: drmaheshgpillai@gmail.com (M. Ganesapillai).
Received 13 August 2015; Received in revised form 5 December 2015; Accepted 11 January 2016; Published online 28 January 2016.
sources of nitrogen (N) for soil supplements in crop
fertilization. However, in comparison to other N sources,
ammonium nitrate is relatively expensive and its production
is likely to decline over the coming decades (Erisman et al.,
2008). In such a scenario, urea is becoming more widely used
as an N source for crop production. Conversely, in many
countries, phosphorous (P) is the principal growth limiting
soil nutrient; phosphate fertilizers have indeed played a
crucial role in spurring agricultural productivity to move
global food production to the levels seen today. However, as
http://dx.doi.org/10.1016/j.spc.2016.01.005
2352-5509/ c⃝ 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

2. S U S T A I N A B L E P R O D U C T I O N A N D C O N S U M P T I O N 6 ( 2 0 1 6 ) 6 2 – 6 6 63
Elser and Bennett (2011) point out the utilizable or mineable
deposits of Rock Phosphate (RP) are extremely limited.
Moreover, highlighting the inherent dependency of food
production on soil supplements like P, in an alarming fore-
cast, Cordell et al. (2009) predict a global peak in P production
to occur by 2030. Even the fertilizer industry acknowledges
the decline in both quantity and quality of global reserves as
well as the rising costs of extraction, processing and trans-
portation of P (Driver, 1998; Smil, 2000; Childers et al., 2011).
In addition to these issues, there is a growing recognition of
the environmental costs of the current system of food pro-
duction. Poor nutrient management of soils and continued
use of synthetic fertilizers have had deleterious effects on soil
health (Sarkar et al., 1997). To sustain food production over
time and to ensure efficient utilization of available resources
with greatest efficiency, it is vital that improved methodolo-
gies and techniques for supplementing crop productivity are
envisioned and adopted (Ganesapillai and Simha, 2015).
To this effect, human urine has been advocated as a
safe, high quality–low cost alternative fertilizer that can
provide a rich source of nutrients to supplement agricultural
productivity (Ganesapillai et al., 2016; Kirchmann and
Pettersson, 1994; Wohlsager et al., 2010). Relative to fossil-fuel
sourced mineral fertilizers, human urine comprises of the
products of metabolism and hence contains very low levels
of heavy metals (Jönsson et al., 1997). Moreover, 75%–90%
of the N in urine is excreted as urea and the remainder as
ammonium and creatinine (Lentner et al., 1981). Urease in
soils quickly coverts urea into ammonium (NH+
4
) and carbon
dioxide through hydrolysis and increasing its pH to 9–9.3
(Vinnerås et al., 2003). Ammonium is a directly available
source of N for growing plants; microbial activity in soils
transforms ammonium into nitrate (NO−
3
), the other form in
which N is taken up by plants. Further, potassium (K) ions
excreted in the urine as ions become directly plant-available
when applied to soils.
However, the large concentration of N in the urine results
in a lower P:N and K:N ratio than most inorganic fertilizers
manufactured for commercial agricultural practices. This ne-
cessitates the external addition of P and K. P is the second
limiting nutrient after N in soils that influences and deter-
mines crop growth. However, the cost of applying conven-
tional water-soluble P fertilizers like single super phosphate
(SSP) and triple super phosphate (TSP) in developing coun-
tries is high as their manufacturing requires import of high-
grade RP and Sulfur (Van Kauwenbergh, 2011). Nonetheless,
many developing countries have substantial and untapped
low-grade RP deposits. Further, RP mining produces substan-
tial quantities of ‘tailings’, the fractions created and discarded
as ‘uneconomic’ during the mineral processing. Togo, the fifth
largest producer of RP dumps nearly 2.5 million tons of RP
tailings along its coastline which not only mobilizes consider-
able quantities of P but also results into environmental exter-
nalities such as bioaccumulation and heavy metal pollution
(Gnandi et al., 2006).
In a resource-scarce scenario recycling is of paramount
significance. Resource-use efficiency is another dimension to
consider in addition to recycling. Acknowledging the need
to sustain the use of our available resources, it is vital
that maximum utility is derived from what is available.
In this vein, devising new ways to utilize resources that
were erstwhile considered unusable or whose production and
application were considered unfeasible could be an approach.
Both low-grade RP and human urine are examples of such
resources. This study presents a novel approach to increase
soil fertility through the combined application of low-grade
RP and human urine. Although the use of RP-enriched
composts has been the subject of recent studies (Biswas
and Narayanasamy, 2006), there have been very few reports
on the direct application of low-grade RP in neutral and
basic soils. Hence, in the present work, the direct application
of low-grade RP enriched human urine on the plant
growth response parameters of Chickpea (Cicer arietinum) was
investigated.
2. Materials and methods
Human urine was obtained from twenty healthy young male
volunteers (in their early twenties) with well-balanced di-
ets. Fresh urine samples were collected in plastic air-tight
containers and refrigerated at −20 ◦C to avoid ammonia
volatilization (see Table 1). The frozen urine samples were
thawed, mixed completely before the experimental runs and
were characterized for its major constituents as described
elsewhere (Ganesapillai et al., 2014). RP tailings with 43.8%
tri-calcium phosphate (20.05% P2O5) were obtained from Es-
hidiya mines of the Jordan Phosphate Mines Company Lim-
ited, Jordan. Commercial grade Di-Ammonium Phosphate
(DAP) with 46% P2O5 was procured from the local market (Vel-
lore, India) and was used without further purification. Prior
to the study, DAP was ground and sieved to size less than
2.5 mm.
Plant growth studies were performed at the VIT University
Research Farm, Vellore, India (12◦55
′
12.79
′′
N–79◦7
′
59.9
′′
E;
216 m above sea level). The temperatures of the site
varied between 22.6 ◦C and 34.5 ◦C with relative humidity
of 47%–65%, mean annual rainfall of 795 mm and average
sunshine of 12–13 h day−1
, respectively. Composite soil
samples were collected from depth of 0.2 m from the surface
and sieved through a 6 mm aperture. The soil used was
red loam with 4.33% gravel, 92.84% sand and 2.83% fines.
Trays (0.44 × 0.32 × 0.14 m) were filled with air-dried soil
and studied with 8 replications. Trays were arranged as six
separate arrays. Each array comprised eight replicates of the
six soil treatments, on a grid containing 4 rows by 12 columns
of trays. Within each array, the soil treatments were allocated
positions according to a Randomized Complete Block (RCB)
design, so that groups of six pots within each row comprised
one replicate. Urine, RP and DAP were added to the respective
trays 2 days prior to seed sowing and watered to ensure
proper dissolution of fertilizers in the soil. Trays were divided
into four slots and 12 seeds were sowed in each slot at a depth
of 30 mm. Post germination, plants were thinned to 8 per slot
for all the trays. All trays were regularly watered with de-
ionized water throughout the study period. Upon maturity
(approximately 4 months after sowing the seeds) all trays
were harvested and the plants morphological properties and
biomass yield were determined.
Prior to the treatments the unamended soil (control), was
characterized for its major properties (see Table 2). Post-
harvesting, the soil from each tray was collected, air dried at
40 ◦C, and gently crushed to pass through a 2 mm sieve. All
soil samples were analyzed for total carbon, total nitrogen,
and exchangeable cations (P, K, Ca, Mg and Al); pH was
measured in 0.01 M CaCl2 (1:5) (Rayment and Higginson,
1992). Total carbon and nitrogen were measured using the
Dumas combustion method at 900 ◦C with an oxygen flow

3. 64 S U S T A I N A B L E P R O D U C T I O N A N D C O N S U M P T I O N 6 ( 2 0 1 6 ) 6 2 – 6 6
Table 1 – Major constituents and their concentration in
human urine.
Constituents Concentration (mg L−1)
Urea 19 700
Creatinine 985
Chlorides 5 955
Sodium 3 198
Potassium 1 482
Sulfates 810
Phosphates 685
Ammonium 513
Total Solutes 33 328
Table 2 – Major properties of the top soil.
Property Value
pH (CaCl2) 8.11
Bulk Density (g cm3) 1.02
Total Carbon (g kg−1) 20.3
Total Nitrogen (g kg−1) 1.81
Cation Exchange Capacity (cmol(+) kg−1) 7.21
rate of 125 mL min−1
. Percentage biomass increase for
various treatments was computed using absolute control as
the standard while DAP was considered as the standard for
determining relative agronomic efficiencies (Eqs. (1) and (2)).
Bt refers to the biomass of plants in treatment (g), while Bc
and BDAP represent the biomass of plants in control and in
DAP respectively.
Percentage Biomass Increase =

Bt − Bc
Bc

× 100 (1)
Relative Agronomic Efficiency =

Bt − Bc
BDAP − Bc

. (2)
The plant growth data was found to follow normal distribu-
tion showing homogeneity of variances. The data was statis-
tically analyzed through Microsoft R⃝ Excel 2010/XLSTAT c⃝ Pro
(Version 7.5, 2015, Addinsoft Inc., Brooklyn, NY, USA) at a level
of significance set at P < 0.05 using ANOVA followed by Tukey-
HSD as a post-hoc test.
3. Results and discussion
The treatments investigated and the responses of plant
growth parameters have been summarized in Tables 3 and
4. For all treatments, the performance of RP enriched urine
was found to be better than that of the control (Table 3,
Table 4; p < 0.05). In terms of shoot dry weight, following
trend was observed for the different treatments: T4 ≈ T2 >
T5 ≈ T6 ≈ T3 > T1. A similar trend was seen for root dry
weight with the control yielding the lowest value. In terms
of total plant biomass a distinct pattern was evident: T4 >
T2 > T5 > T6 > T3 > T1; significant increase in biomass
yield was demonstrated in treatments T2 (38.16%) and T4
(28.87%). However, enhancement of root dry weight was most
pronounced under T5 (∼30% of T1).
With phosphate input of 30 kg P2O5 ha−1
(kept constant)
to the soil, another trend was observed with increasing N
addition in the form of human urine. Most plant growth
response variables reacted favorably as N addition was
increased up to 30 kg ha−1
. Further supplementation with
N led to decline in growth parameters relative to earlier
treatments although the results were still better than that of
the control. Walley et al. (2005) reported similar findings for
chickpea where they suggested that, increasing application
of inorganic N fertilizer beyond 40 kg N ha−1
reduces
leguminous N2-fixation. They also suggest that for the
benefits of starter N to be realized and the productivity of
chickpea to be enhanced, rates as high as 30 kg N ha−1
may
be required to optimize the yields. While a low-grade RP input
of 30 kg P2O5 ha−1
yields favorable results in comparison to
the control for all treatments, further resource-use efficiency
could be ensured through the identification of optimal N
additive. This study reports ∼30 kg N ha−1
as a favorable
rate of application for Cicer arietinum. The results of the
present study are in concurrence with Lundström and Lindén
(2001) who reported similar findings with human urine as
an alternative organic fertilizer for wheat and barley. For
instance, considering pod number as the response variable;
treatment T5 (50 kg N ha−1
) relative to T4 (30 kg N ha−1
)
indicated that further N addition leads to fewer number of
pods (T5 is 87% of T4) but still significantly higher than
the control T1 (p < 0.05). Similar findings and observation
of trends for N addition to soils cultivating chickpeas and
soybeans was reported by Bahr (2007) and Caliskan et al.
(2008), respectively.
It is acknowledged that the objective of the study is not
merely to compare the agronomic yield of the waste-based RP
enriched urine and commercially available DAP. Instead, the
outcomes illustrated here from the crop trials are indicative
of the potential that can be harnessed from waste resources
such as low-grade RP and human urine towards providing
fertility to depleted soils. A relative agronomic efficiency of
1.2, calculated based on experimental observations carried
out in 8 replications confirms the feasibility of employing
these waste resources as recycled crop nutrients (Table 3).
Rodhe et al. (2004) in their study on the N effect of
fertilizers on barley in a Swedish setting find that crop yield
corresponding to 90% of that of equivalent ammonium nitrate
fertilizer can be obtained through the use of human urine.
Table 5 illustrates the influence of RP enriched urine on major
soil properties. Soil pH was found to increase slightly from
8.11 to 8.32 that was possibly due to urea hydrolysis following
the addition of urine in the soil. Al was not detected in the
control or in the soils subjected to treatments. No significant
difference was observed for the available Mg and Ca. However,
in comparison to the control, the Cation Exchange Capacity
(CEC) substantially improved for the treated soils due to
increased availability of K and Na. Total nitrogen content in
the soils increased due to the high nitrogen content of urine
and nitrogen fixing properties of Cicer arietinum. This is an
added advantage as the next cropping cycle would require
reduced application of fertilizers.
4. Conclusions
In a resource-dependent yet resource-scarce society, it is vital
that processes or approaches are developed to use waste
resources. To this effect, the present study demonstrated an
approach to fertilize crops through the combined use of two
waste resources; low-grade RP and human urine. Through
the observation of various plant growth parameters it can be
concluded that significant potential exists for such fertilizers
to act as alternatives to inorganic fertilizers currently in
use. This was validated through the high performance
observed in response parameters of Cicer arietinum as the

4. S U S T A I N A B L E P R O D U C T I O N A N D C O N S U M P T I O N 6 ( 2 0 1 6 ) 6 2 – 6 6 65
Table 3 – Response of plant parameters (Cicer arietinum) and effectiveness of different treatments.
Tmt.
No
Treatments Shoot dry
weight
Root dry weight Total biomass Biomass
increase
RAEa
(g plant−1
) (g plant−1
) (g plant−1
) (%)
T1 Control 4.1 ± 0.0655c 0.104 ± 0.0012d 4.641 ± 0.0040f – –
T2 DAP at (30 kg P2O5 ha−1 + 15 kg N ha−1) 5.8 ± 0.0463a 0.129 ± 0.0010b 5.929 ± 0.0023b 28.87 –
T3 RP at 30 kg P2O5 ha−1 + Urine at 10 kg N ha−1 5.2 ± 0.0906b 0.117 ± 0.0009c 5.317 ± 0.0022e 14.56 0.58
T4 RP at 30 kg P2O5 ha−1 + Urine at 30 kg N ha−1 5.9 ± 0.0707a 0.133 ± 0.0013ab 6.232 ± 0.0012a 38.16 1.21
T5 RP at 30 kg P2O5 ha−1 + Urine at 50 kg N ha−1 5.4 ± 0.0707b 0.135 ± 0.0008a 5.535 ± 0.0014c 24.07 0.73
T6 RP at 30 kg P2O5 ha−1 + Urine at 70 kg N ha−1 5.3 ± 0.0655b 0.108 ± 0.0008d 5.408 ± 0.0014d 21.23 0.64
Values are means ± SEM, n = 8 per treatment group.
Means in a column without a common superscript letter differ (P < 0.05) as analyzed by one-way ANOVA and the TUKEY test.
aRAE: Relative Agronomic Efficiency.
Table 4 – Plant growth parameter response to various treatments.
Tmt.
No
Treatments Plant height Pod number Seed number Seed
weight
(cm) (nu plant−1
) (nu plant−1
) (g plant−1
)
T1 Control 34.7 ± 0.080e 16.4 ± 0.130e 19.7 ± 0.122f 8.27 ± 0.003e
T2 DAP at (30 kg P2O5 ha−1 + 15 kg N ha−1) 44.3 ± 0.128c 25.6 ± 0.120b 28.5 ± 0.073b 12.4 ± 0.011a
T3 RP at 30 kg P2O5 ha−1 + Urine at 10 kg N ha−1 38.8 ± 0.080d 23.2 ± 0.104c 27.8 ± 0.082c 11.7 ± 0.018b
T4 RP at 30 kg P2O5 ha−1 + Urine at 30 kg N ha−1 45.2 ± 0.132b 26.1 ± 0.075a 29.6 ± 0.092a 12.4 ± 0.019a
T5 RP at 30 kg P2O5 ha−1 + Urine at 50 kg N ha−1 45.8 ± 0.053a 22.8 ± 0.092c 26.2 ± 0.075d 11.0 ± 0.098c
T6 RP at 30 kg P2O5 ha−1 + Urine at 70 kg N ha−1 46.1 ± 0.080a 21.4 ± 0.107d 23.8 ± 0.070e 10.0 ± 0.062d
Values are means ± SEM, n = 8 per treatment group.
Means in a column without a common superscript letter differ (P < 0.05) as analyzed by one-way ANOVA and the TUKEY test.
Table 5 – Soil chemical analysis post-harvesting for different treatments.
Treatments pH Exchangeable cations
(cmol(+) kg−1
)
CECa TN TC
(CaCl2) Al Ca K Mg Na (cmol(+) kg−1
) (%) (%)
Control 8.11 ND 3.20 2.05 1.20 0.76 7.21 0.181 2.03
DAP at (30 kg P2O5 ha−1 + 15 kg N ha−1) 8.13 ND 3.21 2.07 1.20 0.77 7.25 0.185 2.04
RP at 30 kg P2O5 ha−1 + Urine at 10 kg N ha−1 8.21 ND 3.22 2.23 1.21 1.43 8.09 0.186 2.07
RP at 30 kg P2O5 ha−1 + Urine at 30 kg N ha−1 8.23 ND 3.23 2.41 1.22 2.11 8.97 0.188 2.11
RP at 30 kg P2O5 ha−1 + Urine at 50 kg N ha−1 8.29 ND 3.23 2.59 1.23 2.75 9.80 0.192 2.11
RP at 30 kg P2O5 ha−1 + Urine at 70 kg N ha−1 8.32 ND 3.24 2.73 1.23 3.14 10.3 0.198 2.12
aCEC: Cation Exchange Capacity; TN: Total Nitrogen; TC: Total Carbon.
result of treatment T4 (RP at 30 kg P2O5 ha−1
and urine
at 30 kg N ha−1
). Additionally, it was also shown that
the direct application of RP is possible in slightly alkaline
soils. Moreover, due to the addition of urine and inherent
nitrogen fixing character of Cicer arietinum, soil chemical
analyses following the harvest indicated an increase in total
soil nitrogen; this necessitates lesser fertilizer input during
subsequent cropping.
The use of human urine in agriculture through urine
diversion and its subsequent utilization as a N source for
enhancing productivity has a two-fold advantage; it reduces
health risks to humans by diverting urine from water systems
where it is a pollutant, while recycling nutrients back quickly
into food systems (Ganesapillai et al., 2015). Furthermore, the
use of low-grade RP provides a sustainable option to supply
P to plants, especially in countries with scarce high-grade
RP deposits. In this respect, use of RP enriched urine holds
a lot of promise for developing countries like India. Above
all, it ensures utilization of both low-grade RP and human
urine while acting as a relatively inexpensive substitute to
mineral fertilizers like DAP. It is further iterated that the
objective of the study was not to distinguish the fertilization
potential of commercially available DAP and the waste-based
RP enriched urine on agricultural productivity. Instead, the
results of the study are indicative of the substantial socio-
economic and environmental value that can be sourced from
waste resources. Indeed, this would only be possible if the
comprehension of two human constructs, ‘resources’ and
‘wastes’ are blurred to the extent that conventional wisdom
begins to acknowledge wastes to be resources of a natural
cycle that circulates biological nutrients.
Acknowledgments
The authors wish to acknowledge Dr. Prabhu Linghiah of
Eshidiya Mines, Jordan Phosphate Mines Company PLC,
Jordan for his insights and discussion during the study and
for providing the RP tailings. The authors also acknowledge
the financial support provided by VIT University (2040/VP-A-
31082012), Vellore, India for conducting the experiments.

5. 66 S U S T A I N A B L E P R O D U C T I O N A N D C O N S U M P T I O N 6 ( 2 0 1 6 ) 6 2 – 6 6
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