Determination of Available Macronutrients, Na, Cl, ph and EC in Coir Substrate Incubated with Mineral Fertilizers

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1 Determination of Available Macronutrients, Na, Cl, ph and EC in Coir Substrate Incubated with Mineral Fertilizers A.M.C. Furlani, M.F. de Abreu, C.A. de Abreu, P.R. Furlani and O.C. Bataglia Instituto Agronômico, Centro de Pesquisa e Desenvolvimento de Solos e Recursos Ambientais, C.P Campinas, SP Brazil Keywords: water extraction methods, substrates, salinity, nutrient diagnosis Abstract Coconut fiber has been considered an adequate alternative material as substrate for soilless potted plants under semi or protected cultivation. Several water extracts are used for the determination of ph, EC and available nutrients in substrates for plants, but there is little information about the relations among them for a more correct plant nutrient evaluation. The objective of this research was to compare current procedures of water extraction for the chemical analysis of coir substrate incubated with conventional NPK and slow-release fertilizers (SRF). Samples were collected at 20, 60 and 120 days of incubation and submitted to the following water extraction methods: 1:1.5 v/v; 1:2 v/v; 1:5 v/v; 1:10 m/v; and saturation extract. NPK showed a faster nutrient-releasing rate compared to the SRF. The substrate did not present excess sodium or high electrical conductivity (EC). However, ph decreased with period of incubation independently of treatment. The initial ph was increased in the conventional NPK-fertilizer and decreased in the SRF treatments. Ammonium and nitrate presented a different behavior along the time, according to fertilizer source. Phosphorus concentrations were not influenced, however, EC and all other macronutrients in the coir substrate were significantly affected by the water extraction methods. The best methods for the substrate analysis were the saturation and 1:1.5 water extracts for nutrient evaluation purposes. INTRODUCTION The plant production system in substrates under semi or protected cultivation has been actually considered an important agribusiness activity in Brazil. There is an increasing demand for substrates and techniques for improving plant management, yield and product quality. Coir has been considered an adequate material as substrate for potted plants due to its exceptional physical properties, although it sometimes may present salinity. This material has in Brazil a large availability and low price, since it is a by-product of the coconut industry (Kämpf, 2002). One of the main difficulties in the soilless production system is the nutrient management, which depends on adequate evaluation of substrate nutrient availability. The substrate chemical analysis faces a lack of standard procedures for results and interpretations accuracy. Different extraction methods have been currently used for the determination of ph, EC and available nutrients in substrates for plants: saturation extract (SE) is adopted in the USA (Warncke, 1986) and water extracts with fixed water volumes is adopted in Europe - 1:1.5 v/v; 1:2 v/v, 1:10 m/v; and 1:5 v/v (CEN, 2001; Sonneveld et al., 1974; Sonneveld and Elderen, 1994; Sonneveld et al., 1990). These methods provide proportionally unequal concentration values for the same treatment in function of different procedures, such as extraction time, shaking and dilutions, what turns difficult the use of substrate analysis as a reliable nutrient diagnosis tool for a better nutrient management. The objective of this research was to compare laboratory current procedures of water extraction for the chemical analysis of available macronutrients, Na, ph and EC in coir substrate incubated with mineral fertilizers. MATERIALS AND METHODS An experiment was carried out in the greenhouse, in Instituto Agronômico, at Campinas, State of São Paulo, Brazil, with coir incubated with conventional (NPK) and slowrelease fertilizers (SRF). The treatments were applied as follows: (1) control; (2) NPK + S; Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS

2 (3) NPK + S + micronutrients; (4) SRF + S and; (5) SRF + S + micronutrients. The SRF (formula N- P 2 O 5 - K 2 O = ) presents a releasing period of three to four months and it was applied at a rate of 6 g L -1 of coir. The conventional fertilizer was applied at the same rate, using the sources: urea, potassium chloride and triple superphosphate. Sulfur (S) was added as CaSO 4.2H 2 O at the rate of 40 mg L -1 of coir. The micronutrients were applied in the nutrient solution as follows (mg L -1 of coir): 0.6- B (H 3 BO 3 ); 1.5- Cu (CuSO 4.5H 2 O ); 2.1- Zn (ZnSO 4.7H 2 O); 2.1- Mn (MnSO 4.H 2 O); 2.1- Fe [Fe (NH 4 ) 2 (SO 4 ) 2.6H 2 O]. The fertilizers were thoroughly mixed to the coir that was incubated up to 120 days. Substrate samples were collected at 20, 60 and 120 days for the chemical analysis, using the following methods of water extraction: 1:1.5 v/v water extract (Sonneveld et al., 1974; Sonneveld and Elderen, 1994) - this method is currently used in The Netherlands for ph, EC, macro and micronutrients determination in substrates. The procedure consisted of: 200 ml of substrate sample was moisturized with deionized water, enough to drip when slightly hand pressed. The sample was then submitted to 10 kpa in a pressure ring; thereafter, 100 ml previously treated sample was added to 150 ml deionized water, shake during 15 minutes at 220 rpm and filtered through paper filter; 1:2 v/v water extract (Sonneveld et al., 1990) - method used by some Brazilian substrate producing companies for ph and EC evaluation according the following procedure: 100 ml sample (without previous prepare) is added to 200 ml of deionized water, shake for 20 minutes at 220 rpm and filtered through paper filter; 1:5 v/v water extract (CEN, 2001) method adopted by the Comité Européen de Normalization (CEN), which consists of adding 250 ml of water to 50 ml of substrate sample (without previous prepare), shake for 20 minutes at 220 rpm and filtered through paper filter; 1:10 m/v water extract method originally used in Germany and adopted by the research group of the Universidade Federal do Rio Grande do Sul, Brazil, for EC, ph and macronutrient determinations. This procedure requires moisture standardization (by oven drying at C or addition of water) when sample humidity is different from 50%: 20 g of material with 50% humidity is added to 200 ml of deionized water, shake during 3 hours and filtered after a 24-hour rest period; saturation extract (SE) (Warncke, 1986) - distilled water was added to about 400 ml of substrate and stirred with a spatula, until the mixture showed a glittering surface or until a spatula-made ridge vanished rapidly. After one-hour rest, the mixture was again adjusted to saturation and thereafter transferred to a Buchner funnel with paper filter connected to a vacuum flask to which it was applied suction to obtain 25 ml extract. The nutrients and Na were determined in the extracts by ICP-OES (spectrometer model Jobin Yvon JY50P). The data was submitted to analysis of variance for a completely randomized design, in a 5x3x5 factorial arrangement (fertilizer, incubation period and extraction method) and the mean comparisons were made by Tukey test (0.05). RESULTS AND DISCUSSION Although the ph values showed variation among fertilizer treatments (means over treatments, Table 1) the differences within treatments were not statistically significant by any of the methods. Differences among methods were also not significant, maybe due to the significant interactions found for the variables, in spite of the low coefficient of variation for ph (CV = 6.8%). The average ph values increased according to the water extraction method in the following order: SE 1:1.5 = 1:2 = 1:10 < 1:5. Addition of SRF significantly decreased the initial ph values (Table 1), which also decreased with the period of incubation for all treatments (Table 3), whereas NPK increased them (Table 3); ph decreased with incubation period in all treatments, and at 60 and 120 days no significant ph differences were found within treatments with added fertilizers. The EC values expressed total ionic activity in the solution and were differentiated among treatments in the SE, 1:1.5, 1:2 and 1:10 water extracts, but differences were not detected by the 1:5 method (Table 1). Low sodium (Na) concentrations were found in coir, which were lowest in the control and highest in the SRF-treatments (control< NPK< SRF), indicating that the original material contained small amount of sodium and that the fertilizers contributed to add the element as a contaminant (Table 1). The low Na concentrations evidenced also that the EC values were much more affected by chloride (Cl), firstly, and potassium (K), secondly, than by sodium contained in the fertilizers, since higher EC values were observed in NPK- 110

3 treatments (Tables 1 and 2), which showed higher K but much higher Cl concentrations (control < SRF<< NPK) (Table 1). There were significant differences among treatments and periods of incubation for the N-NH + 4, N-NO - 3, P, K, Ca, Mg and S concentrations in the water extracts (Tables 2 and 3). The average values of N-NH + 4 and N-NO - 3 showed differences among the control and the fertilization treatments for all methods, but these were not statistically significant, probably due to the high CV% for N-NH (61.7) and N-NO 3 (41.3), what probably interfered with the mean comparison test used (Tukey test, 0.05). For N-NH + 4, the values were significantly different only by the SE method, and for N-NO - 3, only by the 1:1.5 (Table 2). Besides, a different behavior was observed for N-NH and N-NO 3 between the conventional (NPK) and slow-release fertilizer (SRF) treatments, along the periods of incubation. In the NPK-treatments, N-NH + 4 decreased with time, and N-NO - 3 increased, what probably indicates that nitrification occurred. This effect was not observed in the SRFtreatments, in which both N-NH + 4 and N-NO - 3 values increased with the period of incubation (Table 3). These interaction effects might also have influenced the coefficient of variation and consequently the least significant mean value for the methods comparison. All water extraction methods showed the same efficacy in differentiating P- concentrations among fertilization treatments, keeping relative proportional differences among them (Table 2). Potassium concentrations among fertilization treatments were well differentiated by both saturation and 1:1.5 extracts; however, in the other extracts only the control was different from the fertilization treatments. Since potassium seems to be the major element contributing to the EC values, these will be also influenced by the water extraction method (Table 2). Differences among treatments for the Ca, Mg and S concentrations were only significantly evident in the saturation extracts. None of the other methods were able to differentiate Ca, Mg and S concentrations even among the fertilization treatments, probably due to their lower concentrations in the coir fiber substrate and higher CV% (69.8, 47.7 and 37.3%, respectively) found for these elements (Table 2). Furlani et al. (2002) obtained similar results when comparing these methods for the analysis of macronutrients in Pinus bark. The SE and 1:1.5 were the best methods for the differentiation of fertilization treatments. Concerning the periods of incubation, the NPK- treatments released, on the overall, higher quantity of available nutrients at the initial 20-day-incubation period compared to the SRF- treatments that released higher quantity at 120-day-incubation, as expected. But, for most nutrients the concentration in the water extracts increased with time, although in the SRF-treatments the nutrient releasing occurred at a slower rate, since at 120 day-incubation period these nutrient values were still lower in the SRF- than in NPK- treatments, except for N-NH + 4 and N-NO - 3 as already discussed (Table 3). The results indicated clearly that for nutrient diagnosis purposes, the saturation and 1:1.5 extraction methods were more accurate in detecting differences in nutrient concentrations and EC values among substrate samples, allowing a better estimate of nutrient availability and the need for reposition. CONCLUSIONS The rate of nutrient release in the coir substrate water extracts varied with the incubation period and fertilizer source. The tested coconut fiber substrate did not present excess sodium or high EC. The NPK-fertilizer showed a faster nutrient-releasing rate compared to the SRF and higher Cl concentrations, what increased EC. Ammonium and nitrate concentrations varied along the time but the variation trend was opposite to each other and depended on the fertilizer source. Concerning the water extraction method comparison, the results of EC and all macronutrient concentrations, with exception of P, were significantly affected by the procedures. The best evaluations obtained for the treated coir substrate were in the saturation and 1:1.5 water extracts. ACKNOWLEDGEMENTS 111

4 Thanks to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial assistance and grants. Literature Cited Comité Europeén de Normalisation (CEN), EN Soil improvers and growing media - Extraction of water-soluble nutrients. Brussels. Kämpf, A.N O uso de substrato em cultivo protegido no agronegócio brasileiro. In: Furlani, AMC et al. (coords.). Documentos IAC, Campinas, n. 70, p. 89. Furlani, A.M.C., Abreu, C.A. de, Abreu, M.F. de, Furlani, P.R. and Bataglia, O.C Uso de soluções aquosas na extração de macronutrientes em casca de pinus compostada e adubada. Resumo n.13 apresentado no III Encontro Nacional de Substratos para Plantas, Campinas. Documentos IAC, Campinas, n. 70, p. 89. Sonneveld, C. and Elderen, C. W. van Chemical analysis of peaty growing media by means of water extraction. Commun. Soil Science and Plant Analysis 25: Sonneveld, C., Ende, J. van den and Dijk, P.A. van Analysis of growing media by means of a 1:1,5 volume extract. Commun. Soil Science and Plant Analysis 5(3): Sonneveld, C., Ende, J. van den and Bes, S.S. de Estimating the chemical compositions of soil solutions by obtaining saturation extracts or specific 1:2 by volume extracts. Plant and Soil 122: Warncke, D.D Analyzing Greenhouse growth media by the saturation extraction method. Hortscience, v. 21(2):

5 Tables Table 1. Effect of water extraction methods on ph, electrical conductivity (EC), Na and Cl values of coir incubated with fertilizers (average over periods of incubation). Treatments Water extraction method S E (1) 1:1.5 1:2 1:10 1:5 Means (2) ph Control 4.91 a A 4.69 a A 4.89 a A 5.09 a A 5.08 a A 4.93 NPK 4.98 a A 5.14 a A 5.21 a A 5.20 a A 5.40 a A 5.19 NPK+micro 4.73 a A 5.12 a A 5.24 a A 5.00 a A 5.40 a A 5.10 SRF (3) 4.16 a A 5.26 a A 4.31 a A 4.47 a A 4.50 a A 4.34 SRF+micro 4.17 a A 4.29 a A 4.28 a A 4.06 a A 4.51 a A 4.26 Means ( 2 ) Electrical conductivity (ds/m) Control 1.02 c A 0.33 c B 0.24 c B 0.24 c B 0.33 a B 0.43 NPK 6.13 a A 2.35 a B 1.79 abc 1.41 a C 0.82 a D 2.50 NPK+micro 6.54 a A 2.48 a B 1.91 a C 1.44 a C 0.83 a D 2.64 SRF (3) 4.88 b A 1.79 b B 1.40 b BC 1.08 abcd0.65 a D 1.96 SRF+micro 4.53 b A 1.82 b B 1.36 b B 0.84 b C 0.64 a C1.84 Means (2) Na (mmol L -1 ) Control 0.63 d A 0.22 b B 0.19 b BC 0.16 b BC0.07 a C0.25 NPK 1.45 c A 0.46 a B 0.38 a BC 0.27 abcd0.16 a D 0.54 NPK+micro 1.40 c A 0.46 a B 0.40 a BC 0.27 abcd0.26 a D 0.54 SRF (3) 2.01 a A 0.55 a B 0.49 a B 0.33 a C 0.20 a C0.72 SRF+micro 1.80 b A 0.53 a B 0.46 a B 0.27 abc0.19 a C0.65 Means (2) Cl (mmol L -1 ) Control 6.00 b A 1.91 b B 1.22 a B 1.37 b B 0.45 a B 2.19 NPK a A 9.87 a B 8.67 a BC 5.92 a C 2.88 a D NPK+micro a A a B 8.98 a BC 6.14 a C 2.92 a D SRF (3) 8.83 b A 2.83 b B 1.88 b B 1.58 b B 0.75 a B 3.17 SRF+micro 7.51 b A 2.17 b B 1.70 b B 1.13 b B 0.70 a B 2.74 Means (2) (1) S E = saturation extract; (2) Means followed by the same letters, small in the columns and capital in the lines, do not differ by Tukey test (0.05); ( 3 ) SRF = slow release fertilizer. 113

6 Table 2. Effect of water extraction methods on nutrient concentrations of coir substrate incubated with fertilizers (average over periods of incubation). Treatments Water extraction method SE (1) 1:1.5 1:2 1:10 1:5 Means (2) mmol L -1 Ammonium (NH + 4 ) Control 0.10 c A 0.16 b A 0.13 b A 0.43 a A 0.07 a A 0.18 NPK a A 6.80 a B 4.69 a BC 3.84 a BC 2.72 a C 6.94 NPK+micro SRF (3) aba b A 6.63 a B 4.33 a B 4.87 a BC 3.40 abb 3.66 a BC 3.37 a B 2.10 a C 1.45 a B SRF+micro b A 4.13 a B 3.37 abb 1.82 a B 0.86 a B 4.43 Means (2) Nitrate (NO - 3 ) Control 0.07 b A 0.04 c A 0.04 b A 0.08 b A 0.04 b A 0.66 NPK 6.16 a A 1.75 b B 1.22 b B 1.10 b B 0.55 abb 2.16 NPK+micro 5.15 a A 1.76 b B 1.36 b B 0.99 b B 0.56 abb 1.96 SRF (3) 6.18 a A 5.32 a A 4.00 a B 1.17 b C 1.78 a C 3.69 SRF+micro Means (2) 5.47 a A a A a B a BC a C Phosphorus (P) Control 0.38 c A 0.07 c A 0.06 c A 0.06 c A 0.03 c A 0.12 NPK a A 3.16 a B 2.49 a B 2.54 a B 1.36 abc 4.05 NPK+micro a A 3.15 a B 2.66 a B 2.71 a B 1.55 a C 4.19 SRF (3) 5.86 b A 1.32 b B 1.32 b B 0.99 b B 0.67 bcb 2.03 SRF+micro 5.26 b A 1.25 b B 1.26 b B 0.93 b B 0.63 c B 1.87 Means (2) Potassium (K) Control 6.83 d A 1.89 c B 1.42 b B 1.36 b B 0.52 b B 2.40 NPK b A abb 6.80 a C 5.54 a CD 3.45 a D NPK+micro SRF (3) a A c A a B 8.17 abb 7.11 a C 5.80 a BC 5.78 a CD 4.43 a CD 3.49 a D 2.70 abd SRF+micro Means (2) c A b B a B abc abc Calcium (Ca 2+ ) Control 0.10 d A 0.01 b A 0.01 a A 0.01 a A 0.01 a A 0.03 NPK 3.04 b A 0.74 a B 0.41 a BC 0.25 a BC 0.11 a C 0.91 NPK+micro 3.67 a A 0.85 a B 0.49 a B 0.33 a B 0.28 a B 1.12 SRF (3) 2.28 c A 0.39 abb 0.22 a B 0.15 a B 0.19 a B 0.64 SRF+micro 1.99 c A 0.37 abb 0.20 a B 0.10 a B 0.18 a B 0.57 Means (2) Magnesium (Mg 2+ ) Control 0.08 d A 0.01 a A 0.01 a A 0.01 a A 0.01 a A 0.02 NPK 1.54 c A 0.39 a B 0.23 a BC 0.13 a C 0.06 a C 0.47 NPK+micro 1.66 bca 0.41 a B 0.26 a BC 0.15 a C 0.08 a C 0.51 SRF (3) 2.03 a A 0.40 a B 0.24 a BC 0.16 a BC 0.09 a C 0.58 SRF+micro 1.80 a A 0.38 a B 0.21 a BC 0.10 a C 0.07 a C 0.51 Means (2) Sulfur (S) Control 0.64 c A 0.20 b A 0.13 b A 0.12 a A 0.05 a A 0.23 NPK 4.74 b A 1.88 a B 1.22 a BC 0.90 a C 0.54 a C 1.86 NPK+micro SRF ( 3 ) 5.04 b A 7.76 a A 2.00 a B 2.79 a B 1.30 a BC 1.76 a C 0.94 a C 1.25 a C 0.61 a C 0.84 a C SRF+micro 7.51 a A 2.82 a B 1.83 a C 1.02 a CD 0.83 a D 2.80 Means ( 2 ) (1) SE = saturation extract; (2) Means followed by the same letters, small in the columns and capital in the lines, do not differ by Tukey test (0.05); (3) SRF = slow release fertilizer. 114

7 Table 3. Effect of incubation periods on ph and nutrient concentrations in coir substrate incubated with fertilizers (average over water extracts). Treatments Incubation period (days) Means( 1 ) ph Control 5.06 b A 5.09 a A 4.65 a B 4.93 NPK 7.10 a A 4.63 b B 3.83 b C 5.19 NPK + micro 6.97 a A 4.47 b B 3.86 b C 5.10 SRF(²) 4.57 c A 4.46 b A 3.98 b B 4.34 SRF + micro 4.53 c A 4.47 b A 3.78 b B 4.26 Ammonium (NH + 4 ), mmol L -1 Control 0.09 b A 0.35 c A 0.10 c A 0.18 NPK a A 6.66 a B 3.79 b C 6.94 NPK + micro 8.73 a A 7.12 a A 3.30 b B 6.39 SRF(²) 1.43 b C 3.71 b B 8.95 a A 4.70 SRF + micro 1.51 b B 3.48 b B 8.30 a A 4.43 Nitrate (NO - 3 ) mmol L -1 Control 0.04 c A 0.07 c A 0.06 c A 0.06 NPK 1.39 b B 2.37 b A 2.70 b A 2.16 NPK + micro 1.08 b B 2.26 b A 2.54 b A 1.96 SRF(²) 2.45 a C 3.88 a B 4.74 a A 3.69 SRF + micro 2.59 a C 3.51 a B 5.32 a A 3.80 Phosphorus (P) mmol L -1 Control 0.10 c A 0.16 d A 0.10 c A 0.12 NPK 3.53 a B 4.50 b A 4.11 a A 4.05 NPK + micro 3.60 a B 5.15 a A 3.83 a B 4.19 SRF 0.70 b C 2.33 c B 3.07 b A 2.03 SRF + micro 0.67 b C 2.17 c B 2.76 b A 1.87 Potassium (K) mmol L -1 Control 2.58 b A 2.29 c A 2.34 c A 2.40 NPK 9.12 a B 9.67 b B aba NPK + micro 7.84 a B a A a A SRF 4.43 b C 7.68 b B a A 8.17 SRF + micro 4.47 b C 7.79 b B b A 7.66 Calcium (Ca) mmol L -1 Control 0.02 a A 0.03 c A 0.03 c A 0.03 NPK 0.13 a B 0.40 bcb 2.18 a A 0.91 NPK + micro 0.15 a C 1.03 a B 2.18 a A 1.12 SRF 0.22 a B 0.52 b B 1.18 b A 0.64 SRF + micro 0.28 a B 0.50 b B 0.91 b A 0.57 Magnesium (Mg) mmol L -1 Control 0.02 b A 0.02 b A 0.02 c A 0.02 NPK 0.11 abb 0.23 a B 1.07 aba 0.47 a NPK + micro 0.10 abc 0.42 a B 1.02 aba 0.51 a SRF 0.25 a B 0.39 a B 1.11 a A 0.58 a SRF + micro 0.29 a B 0.36 a B 0.89 b A 0.51 a Sulfur (S) mmol L -1 Control 0.25 b A 0.24 c A 0.21 c A 0.23 c NPK 2.08 a A 1.53 b A 1.96 b A 1.86 NPK + micro 1.71 a A 2.29 a A 1.94 b A 1.98 SRF 1.35 a C 2.55 a B 4.74 a A 2.88 a SRF + micro 1.58 a C 2.51 a B 4.31 a A 2.80 a ( 1 ) Means followed by the same letters, small in the columns and capital in the lines, do not differ by Tukey test (0.05). ( 2 ) SRF = slow release fertilizer. 115