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Agronomic Efficiency of Indian Rock Phosphates in Acidic Soils Employing Radiotracer A‐Value Technique a
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Manoj Shrivastava , B. M. Bhujbal & S. F. D'Souza
a
a
Nuclear Agriculture and Biotechnology Division , Bhabha Atomic Research Centre , Trombay, Mumbai, India Published online: 17 Feb 2007.
To cite this article: Manoj Shrivastava , B. M. Bhujbal & S. F. D'Souza (2007) Agronomic Efficiency of Indian Rock Phosphates in Acidic Soils Employing Radiotracer A‐Value Technique, Communications in Soil Science and Plant Analysis, 38:3-4, 461-471, DOI: 10.1080/00103620601174288 To link to this article: http://dx.doi.org/10.1080/00103620601174288
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Communications in Soil Science and Plant Analysis, 38: 461–471, 2007 Copyright # Taylor & Francis Group, LLC ISSN 0010-3624 print/1532-2416 online DOI: 10.1080/00103620601174288
Agronomic Efficiency of Indian Rock Phosphates in Acidic Soils Employing Radiotracer A-Value Technique Manoj Shrivastava, B. M. Bhujbal, and S. F. D’Souza Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Mumbai, India
Abstract: A greenhouse pot culture study was conducted to evaluate the agronomic efficiency of two rock phosphates from Mussoorie (MRP) and Purulia (PRP) in two acidic soils from Dapoli (Maharashtra) and Aruvanthklu (Karnataka), India, by growing maize (cv. Ganga) as the test crop and using 32phosphorus (P) single superphosphate (32P ¼ SSP) as a tracer (A-value technique). Dry-matter yield and P uptake increased significantly with the application of P fertilizers compared to control treatment (without P) in both the soils. There was no significant difference with respect to dry-matter yield among the P fertilizer treatments. However, P uptake by the shoots was found to be significantly higher in the PRP treatment in only Dapoli soil compared to other P fertilizer treatments. Phosphorus derived from fertilizer decreased in rock phosphate treatments compared to standard 32P-SSP treatment in both the soils, indicating an excess availability of P from the rock phosphates. A-values of soil and rock phosphate indicate a relatively higher P availability from Aruvanthklu soil compared to Dapoli soil; A-values for the rock phosphates were in the order PRP . MRP. The substitution ratio showed that the availability of P from both the rock phosphates were less than SSP in both the soils. Keywords: A-value, substitution ratio
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P, %Pdff, P uptake, rock phosphate, single superphosphate,
Received 8 December 2003, Accepted 3 May 2005 Address correspondence to Manoj Shrivastava, Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India. E-mail:
[email protected] 461
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INTRODUCTION Acidic soils in India are widespread and occupy about 30% of the cultivated area (Panda 1998). Phosphorus (P) deficiency is an important soil fertility problem in acidic soils because of its higher fixation and very low recovery from conventional high-soluble phosphatic fertilizer applied to the soil. Rock phosphates (RPs) can be utilized as a direct-application fertilizer in acid soils because of their low cost and slow release of P (Casanova, Perez, and Flores 1993; Marwaha, Kanwar, and Tripathi 1981; Sale and Mokwunye 1993). It is necessary to examine the agronomic effectiveness of RPs for an efficient use of RP as a P source (Kato, Zapata, and Axmann 1995). Radio-tracer techniques have been used for the agronomic evaluation of phosphatic fertilizer. These can be labelled with a radioisotope (32P or 33 P) during the manufacturing process (Fried and Dean 1952; Reddy, Saxena, and Srinivasulu 1982). However, labelling of RP cannot be done in a similar way because this process would drastically change the physicochemical characteristics of the RP (Fried and Mackenzie 1949; Mackenzie and Borland 1952). An isotopic dilution technique, the A-value approach, is very useful in distinguishing between P availability from RP and soil to the plant, and it can serve as a tool for evaluating agronomic effectiveness of RPs (Zapata and Axmann 1991; and Zapata and Axmann 1995). The objective of the present investigation was to evaluate the agronomic efficiency of two Indian RPs in two acid soils by employing the A-value (available nutrient) technique. MATERIALS AND METHODS Soils Two acidic soils from Dapoli (Maharashtra) and Aruvanthlku (Karnataka), India, were used in this study. Some physicochemical characteristics of the experimental soils are shown in Table 1. Phosphorus Fertilizers Standard P Fertilizer Single superphosphate (SSP) labelled with 32P containing 9.0% P with an initial specific activity of 32 MBq 32P g21 P was used as a tracer. Rock Phosphates Two RPs from Mussoorie (MRP) and Purulia (PRP) were used in this study. Rock phosphates were analyzed as per the procedures outlined by Bhujbal and
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Table 1. Some characteristics of the experimental soils Sr. no.
Characteristics
Aruvanthklu soil
Dapoli soil
1 2 3 4 5 6 7
Texture pH (1:2.5 soil – water) Organic carbona (g kg21) Cation exchange capacityb (cmol(pþ) kg21) Bray I P (mg kg21)c P-fixing capacity (%)d 0.02 M CaCl2-extractable Ale (mg kg21)
Sandy clay 4.8 20.4 8.0 5.85 72.0 2.58
Clay loam 6.1 2.0 19.3 4.7 75.0 0.42
a
Walkley and Black (1934). Chapman (1965). c Bray and Kurtz (1945). d Singh, chhonkar, and Pandey (1999). e Dong et al. (1999). b
Mistry (1981). The characteristics of RPs (Table 2) indicate that MRP is a carbonate apatite type with small substitution of carbonate (CO3) for phosphate (PO4) in the apatite structure, whereas PRP is a fluroapatite with a negligible amount of substitution of CO3 for PO4 in the apatite structure.
Greenhouse Experiments Greenhouse experiments were carried out on samples of soil sieved at 2 mm. The soil (2.5 kg pot21) in the pots were subjected to four different treatments, namely (i) unfertilized control soil, (ii) soil þ 32P-labelled SSP, (iii) soil þ 32P-labelled SSP þ MRP, and (iv) soil þ 32P-labelled SSP þ PRP, and thoroughly mixed. Rock phosphates were added at the rate of 250 mg P kg21 soil, and 32P-labelled SSP was added at the rate of
Table 2. Some characteristics of the rock phosphates Citrate-soluble P (% of rock)
Chemical composition (g kg21)
Rock phosphate CaO SiO2 Al2O3 Fe2O3 MgO K2O P2O5 Mussoorie 440 Purulia 356
125 106
18 33
34 89
4 2
4 4
194 263
Neutral Molar ammo- 2% ratio nium citric CO3:PO4 citrate acid in apatite 0.309 0.401
0.760 1.623
0.052 0.013
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50 mg P kg21 soil. Each treatment was replicated four times in a complete randomized block design. The soils were kept at field-capacity moisture status for 2 days, and then basal nutrients nitrogen (N) and potassium (K) were applied at the rate of 60 mg N kg21 soil as urea and 30 mg K2O kg21 soil as KCl, respectively. Maize (Zea mays L. cv. Ganga) plants (four per pot) were grown for 42 days and harvested. Harvested plant materials (shoots) were washed with deionized water and oven dried at 708C to constant weight, and the drymatter yield (DMY) was recorded. Dried plant materials were wet ashed using a 5:1 HNO3 –HClO4 mixture, total P in the acid digest was determined colorimetrically (Koeing and Johnson 1942), and the radio assay of 32P was carried out using a Geiger Muller (GM) counter.
Geiger Muller Counter A GM counter was used for the 32P radio assay. The GM counter consisted of a gas-filled end window mica (2 mg cm22 thickness) tube. Neon was used as the ionization gas with a small amount of halogen (bromine) as the quenching agent to extinguish the continuous discharge in the tube. A characteristics curve (applied voltage vs. counting rate) of the GM counter (Figure 1) showed that counter starting, threshold, and operating voltages are 425, 465, and 525 volts, respectively. Further, the curve has a plateau length of 90 volts with a slope of 0.10% volt21. Counting efficiency of the counter for 32 P is 17.4% with a paralysis time of 250 ms.
Figure 1.
GM characteristics curve.
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A-Value Technique The evaluation of RPs was performed in terms of a standard fertilizer, SSP, using the A-value technique. This technique is based on the A-value determination using 32P-labelled superphosphate first proposed by Fried (1954). This technique is further modified by Broeshart (1974), IAEA (1976), Zapata and Axmann (1986), and Zapata (1990). This evaluation is made in terms of equivalent units of SSP, which can be estimated from the difference in uptake of P from 32P-SSP by the crop in the presence and absence of RPs. For the agronomic evaluation, the substitution ratio (i.e., kg P as RP sources equivalent to 1 kg P of the fertilizer standard) were estimated (Zapata 1990).
Calculations Isotopic parameters namely, %Pdff (percent P derived from fertilizer) and A-values of soils, RPs, and substitution ratios were calculated as described by Zapata and Axmann (1986) and Zapata (1990). 1. Total P uptake (mg P pot21) UT is DMY %P/100. 2. %Pdff: Fraction of P in the plant derived from the fertilizer (32P-SSP): %Pdff ¼
Specific activity of plant ðdpm mg P1 Þ 100 Specific activity of fertilizer ðdpm mg P1 Þ
3. 32P-SSP uptake (mg pot21) Uf is (UT %Pdff)/100. 4. Percentage utilization of 32P-SSP (Utf) is (Uf 100)/[P rate applied as 32 P-SSP (mg pot21) (Rf)]. 5. A-value: The A-value expresses the availability of the P in the soil system relative to that of the 32P-SSP in units of the carrier (mg P pot21). A-value of the soil (mg Pot21) (AS) is [(100 2 %Pdff)/%Pdff] Rf. From the A-value of the RP-treated soils, an A-value of the RP is calculated: A-value of rock phosphate (mg pot21) ARP is A-value(SOILþRP) (mg pot21) 2 AS (mg pot21). 6. Partitioning of the P-uptake according to source of origin: i.
Plant P derived from
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P-SSP (mg pot21) Pf: Pf ¼
ii.
Rf Utf : 100
Plant P derived from soil (mg pot21) PS: Ps ¼
AS Utf : 100
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M. Shrivastava, B. M. Bhujbal, and S. F. D’Souza
Plant P derived from RP (mg pot21) PRP:
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PRP ¼
ARP Utf : 100
7. Percentage utilization of the RP is [PRP (mg pot21) 100]/[P rate as RP (mg pot21) RRP]. 8. Substitution ratio (SR): The effectiveness of the RPs was compared by calculating the amount of kg P as RP equivalent to 1 kg P as SSP (known as substitution ratio, SR): SR ¼
RRP ðmg pot1 Þ : ARP ðmg pot1 Þ
Statistical Analysis Data were analyzed statistically by a one-way analysis of variance (ANOVA) procedure. The ANOVA was performed on the yield and isotopic parameter (%Pdff and A-value), and comparisons between means of the treatments for the various measured parameters were made by the least significance difference (LSD) test (P 0.05) (Hoshmand, 1993).
RESULTS AND DISCUSSION Shoot Dry-Matter Yield (DMY) and Phosphorus Uptake Data reported in Table 3 indicated that application of P fertilizers significantly increased both DMY and P uptake of plants compared to the control treatment in both the soils. In the Dapoli soil, P uptake by the shoots was significantly enhanced by the combined application of PRP and SSP compared to the other treatment. In the Aruvanthklu soil, P uptake was not significantly affected by either of the combined application treatments, indicating that the availability Table 3.
Shoot dry-matter yield (DMY g pot21) and P uptake (mg P pot21) Aruvanthklu soil
Dapoli soil
Treatments
DMY
P uptake
DMY
P uptake
Unfertilized control 32 P SSP 32 P SSP þ MRP 32 P SSP þ PRP LSD (0.05)
1.850 3.025 3.600 3.625 0.990
2.250 4.192 4.569 3.990 0.840
2.350 5.625 5.375 5.500 0.449
4.100 7.250 6.689 7.914 0.651
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of P from PRP to the plant was significantly higher than MRP in Dapoli soil. The lower DMY and P uptake by maize shoots in Aruvanthklu soil compared to Dapoli soil could be attributed to the lower pH (4.8) and higher amount of plant-available Al (2.58 ppm) present in Aruvanthklu soil. Rajan et al. (1991) reported similar findings with rye grass in field studies where, at higher pH and low Al content, the yield and P uptake of crop increased. Isotopic Parameters The isotopic parameters %Pdff and A-values of soils are reported in Table 4. Significant (P 0.05) decrease in %Pdff values in the RP treatments as compared to standard treatment (32P-SSP) was obtained in both the soils, which is may be due to extra availability of P to plants in RP treatments (dilution effect). This is further confirmed by the significant (P 0.05) enhancement of A-values (available amounts of P from soil expressed in SSP equivalent units) due to application of RPs over standard 32P-SSP treatment in both the soils. In general, the A-value of Aruvanthklu soil was higher than that of Dapoli soil, which showed a higher amount of plantavailable P than Dapoli soil. Agronomic Evaluation of Rock Phosphates Data on the A-values of the RPs, plant P derived from RPs, and percentage utilization of P from RPs (Tables 5 and 6) showed that A-values obtained for Aruvanthklu soil were higher than those obtained for RPs, indicating thereby higher availability of P from soil in comparison to RPs. However, in the Dapoli soil, there was less variation between the A-values of soil and RPs. Variation in A-values of the RPs and the soils clearly affected the fraction of P in plants from the soils and RPs in both the soils (Tables 5 and 6). Further, the A-values of the RPs were found to be higher in the Aruvanthklu soil than the Dapoli soil, indicating that P availability from the RPs was greater in the Aruvanthklu soil than the Dapoli soil. This may be attributed to the lower pH Table 4. Phosphorus in the plant derived from (mg P pot21)
32
P-SSP (%Pdff) and A-values
Aruvanthklu soil Treatments 32
P-SSP P-SSP þ MRP 32 P-SSP þ PRP LSD (0.05) 32
Dapoli soil
%Pdff
A-value
%Pdff
A-value
47.5 36.1 34.3 5.9
141 222 242 42
60.3 45.5 43.6 6.7
83 151 162 32
468 Table 5.
M. Shrivastava, B. M. Bhujbal, and S. F. D’Souza Agronomic evaluation of rock phosphate (RP) in Aruvanthklu soil A-value (mg P pot21)
Treatments 32
P-SSP P-SSP þ MRP 32 P-SSP þ PRP
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32
Soil þ RP
Soil
RP
— 222 242
141 141 141
— 81 101
Partitioning of P content in plant (mg P pot21) 32
P SSP
2.009 1.653 1.362
Soil
RP
Utilization of P from RP (%)
2.181 1.841 1.536
— 1.072 1.101
— 0.172 0.180
of Aruvanthklu soil as compared to Dapoli soil. A positive effect of lower soil pH has also been reported by Kanabo and Gilkes (1987) and Bolan and Hedley (1990). Higher dissolution of RPs at lower soil pH can be ascribed to excess Hþ ion in soil solution, which may neutralize the hydroxide (OH2), PO32 4 , 2 CO22 , and fluoride (F ) ions released into the solution by the hydrolysis of RP 3 (Chien 1993; Rajan, Watkison, and Sinclair 1996). Apart from the lower pH, higher concentration of soil organic matter may also account for the higher A-values of the RPs in the Aruvanthklu soil. The beneficial effects of organic matter on RP solubilization are reported by various workers (Chien, Sale, and Hammond 1990; Drake 1964; Ramachandran, Bhujbal, and D’souza 1998). Chelation of calcium (Ca2þ) present in RPs by the hydrolyzing product of soil organic matter such as citrate and oxalate could reduce the activity of Ca2þ in the system, thereby allowing more dissolution of the apatite mineral from RPs in accordance with solubility product principle (Chien, Sale, and Hammond 1990; Chaudhary and Mishra 1980a; Hammond, Chien, and Mokwunye 1986). Although the A-values of the RPs were higher in the Aruvanthklu soil, utilization of P from RP was found to be higher in Dapoli soil. The possible reason could be the influence of two opposing processes, namely dissolution and reaction of dissolved phosphate with soil matrix components such as aluminum and hydrogen ion species, on agronomic effectiveness of RPs (Rajan, Watkison, and Sinclair 1991). Therefore, dissolution of RPs increased in Aruvanthklu soil, but acidity [hydrogen (Hþ) and Al3þ] adversely affected P availability and plant growth, thereby reducing the utilization of P from the RP as compared to
Table 6.
Agronomic evaluation of rock phosphate (RP) in Dapoli soil A-value (mg P pot21)
Treatments 32
P-SSP P-SSP þ MRP 32 P-SSP þ PRP 32
Soil þ RP
Soil
RP
— 151 162
83 83 83
— 68 79
Partitioning of P content in plant (mg P pot21) 32
P SSP
4.360 3.041 3.450
Soil
RP
Utilization of P from RP (%)
2.890 1.994 2.284
— 1.654 2.180
— 0.265 0.349
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Table 7. Substitution ratio (kg P as rock phosphates equivalent to 1 kg P as SSP) A values (mg P pot21)
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Rock phosphates
Substitution ratio
P rate (mg P pot21)
Aruvanthklu
Dapoli soil
Aruvanthklu soil
Dapoli soil
625 625
81 101
68 79
7.72 6.19
9.19 7.91
MRP PRP
Dapoli soil. Of the RPs assessed in this report, the A-value and percentage utilization of P from PRP was found to be higher compared to MRP, which may be related to differences in their citrate soluble P content. The present results agree with the findings of Engelstad, Jugsujinda, and DeDatta (1974), Chaudhary and Mishra (1980b), and Chien, Hammond, and Leon (1987). The substitution ratio results (Table 7) showed that 1 kg P as SSP was equivalent to 7.72 kg MRP and 6.19 kg PRP in Aruvanthklu soil and 9.19 kg MRP and 7.91 kg PRP in Dapoli soil, respectively. Relatively higher values of the substitution ratio of RPs in both the soils confirmed the low P availability from the RPs as compared to the SSP.
CONCLUSIONS It is very important to measure the P availability from the RP sources to provide a useful basis for investigating the efficacy of RPs as P nutrient sources for crops. The results of this study showed that the isotopic A-value technique is very useful in quantifying the P availability from RPs in different soil types and provides basic information on RP sources, which can be used as recommendations in field trials. In general, this short-term study revealed that although the availability of P from RPs (A-values) was higher at lower pH (Aruvanthklu soil), utilization of P from RPs was higher in the Dapoli soil. The PRP performed better than MRP in both soils. The substitution ratio of RPs showed that both the RPs were less effective than the SSP. Hence, efforts are required to enhance the fertilizer use efficiency of the RPs through suitable means such as RP composting, microbial solubilization, addition of sulfur, and partial acidulation with mineral acids.
ACKNOWLEDGMENT We thank the Board of Radiation and Isotope Technology, Mumbai (Department of Atomic Energy, Government of India) for the supply of 32P-labelled SSP. We also thank V. Ramachandran for his valuable suggestions and A. K. Kadam for his assistance in conducting the pot culture experiment.
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