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  1. 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: 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: (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 2352-5509/ c⃝ 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
  2. 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. 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. 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.
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