Microsoft Word - 17-Agra_42239 1153 Bioscience Journal Original Article Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 http://dx.doi.org/10.14393/BJ-v35n4a2019-42239 EFFECTS OF PHOSPHATE, CARBONATE, AND SILICATE ANIONS ON CO2 EMISSION IN A TYPICAL OXISOL FROM CERRADO REGION EFEITOS DOS ÂNIONS FOSFATO, CARBONATO E SILICATO NA EMISSÃO DE CO2 EM UM LATOSSOLO TÍPICO DA REGIÃO DO CERRADO Camila Silva BORGES1; Bruno Teixeira RIBEIRO1; Enio Tarso de Souza COSTA2; Nilton CURI1; Beno WENDLING2; 1.Departamento de Ciência do Solo, Universidade Federal de Lavras – UFLA, Lavras, MG, Brasil. camila.borges@estudante.ufla.br; 2. Instituto de Ciências Agrárias, Universidade Federal de Uberlândia – UFU, Uberlândia, MG, Brasil. ABSTRACT: The effects of agricultural practices on greenhouse gases emissions (e.g. CO2) at the soil-atmosphere interface have been highlighted worldwide. The use of ground limestone has been considered as the main responsible for CO2 emission from soils. However, liming is need as conditioner of acidic soils and the CO2 emission can be compensated due to carbon sequestration by plants. This study simulated under laboratory conditions the effects of two common agricultural practices in Brazil (P-fertilization and liming) on soil CO2 emission. Columns made of PVC tubes containing 1 kg of a typical Dystrophic Red Latosol from Cerrado region were incubated with CaCO3 (simulating liming), CaSiO3 (simulating slag), and different doses of KH2PO4 (simulating P-fertilization). The soil columns were moistened to reach the field capacity (0.30 cm3 cm-3) and, during 36 days, CO2 emissions at the soil surface were measured using a portable Licor LI-8100 analyzer coupled to a dynamic chamber. The results showed that CO2 emission was influenced by phosphate, carbonate, and silicate anions. When using CaSiO3, accumulated CO2 emission (36-day period) was 20% lower if compared to the use of CaCO3. The same amount of phosphate and liming (Ca-carbonate or Ca-silicate) added to the soil provided the same amount of CO2 emission. At the same P dose, as Si increased the CO2 emission increased. The highest CO2 emission was observed when the soil was amended with the highest phosphate and silicate doses. Based on this experiment, we could oppose the claim that the use of limestone is a major villain for CO2 emission. Also, we have shown that other practices, such as fertilization using P + CaSiO3, contributed to a higher CO2 emission. Indeed, it is important to emphasize that the best practices of soil fertility management will undoubtedly contribute to the growth of crops and carbon sequestration. KEYWORDS: Greenhouse gases. Tropical soils. Soil reaction. INTRODUCTION The CO2 released at soil-atmosphere interface comes from microbial activity (MARCELO et al., 2012), burning and decomposition of soil organic matter (JANZEN, 2004), and direct dissolution of carbonates (RAMNARINE et al., 2012). Soil management practices are strongly related to soil CO2 production in the soil (SMITH et al. 2008). The role of agricultural activities on CO2 emissions has been highlighted worldwide as a contributor to the greenhouse effect (global warming) (OERTEL et al., 2016; OZLU; KUMAR, 2018; CASTANHEIRA; FREIRE, 2013). However, this statement must be carefully revised since sustainable agriculture undoubtedly contributes to plant growth and, consequently, to carbon sequestration (SMITH et al., 2008; FORNARA et al., 2011). Brazil is ranked as one of the top world emitters of greenhouse gases, mainly due to the conversion of preserved areas into croplands for agriculture and livestock (CERRI et al., 2009; BENTO et al., 2018). However, there is some controversy if human activities are capable to promote the warming the Earth's atmosphere and changing the global climate (MOLION, 1995). Also, CO2 produced in soil is an indicator of biochemical processes, energy flow, carbon storage and decomposition, nutrient cycling, among others (VALLERO, 2014). Nowadays, the Cerrado Biome (∼ 200 million ha) concentrates the most part of the Brazilian agriculture (BATLLE-BAYER, et al., 2010). In the past (1970-80’s), this region was considered inappropriate for crop production due the occurrence of highly weathered-leached tropical soils (LOPES et al., 2012), mainly Latosols (almost 50% of the Cerrado). Liming, gypsum, P, K, and micronutrients build-up, and progressive adoption of Received: 15/05/18 Accepted: 05/12/18 1154 Effects of phosphate... BORGES, C. S. et al. Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 no-tillage were crucial for crop production on soils under Cerrado biome (LOPES; GUILHERME, 2016). In particular, the use of ground limestone to correct soil acidity has been frequently targeted as the main contributor to CO2 emission (BERNOUX et al., 2003). However, crop-livestock-forestry production would definitely be impossible without liming of Cerrado soils. Slags (Ca-silicates) has been successfully used to increase soil pH and as a source of Ca, similarly to the effect of ground limestone in the soil (RAMOS et al., 2006). In the soil environment, the direct dissolution of calcium carbonates acts in two opposite ways: i) releasing CO2 to the atmosphere, and ii) contributing to crop growth, which leads to increase the carbon sequestration. Thus, this study was carried out aiming to assess the CO2 emission under laboratory conditions in a typical Dystrophic Red Latosol from Cerrado region, as affected by two common and needed agricultural practices in Brazil: liming and phosphate fertilization. CaCO3 was used to simulate ground limestone and CaSiO3 for slag. MATERIAL AND METHODS Topsoil samples (0-20 cm) were used in this study. The soil is classified as a Dystrophic Red Latosol according to the Brazilian System of Soil Classification (EMBRAPA, 2013), and Hapludox according to the Soil Taxonomy Classification (SOIL SURVEY STAFF, 2014). The soil samples were collected nearby Uberlândia, Minas Gerais state, Brazil (18º59’40” S, 48º25’48” W, and 820 m altitude), then air-dried, ground and sieved (< 2 mm). Soil texture was determined by pipette method (DAY, 1965; DONAGEMMA et al., 2011) after dispersion of a soil suspension (10 g in 190 mL distilled water plus 10 mL 0.1 mol L-1 NaOH solution) in a 500-mL plastic bottle using Wagner’s shaker for 16 hours. Soil particle density was determined by volumetric flask method (BLACK; HARTGE, 1986). Chemical characterization involved the determination of the following properties: pH in water (ratio 1:2.5); Ca2+, Mg2+, and Al3+ exchangeable forms extracted with 1 mol L-1 KCl solution; K+, P, and micronutrient (Cu, Fe, Mn and Zn) extracted with Mehlich-1 solution; soil organic carbon (YEOMANS; BREMNER, 1988); effective cation-exchange capacity (sum of K+, Ca2+, Mg2+, and Al3+); potential cation-exchange capacity (sum of K+, Ca2+, Mg2+ and H+ + Al3+); and total oxides (SiO2, Al2O3, Fe2O3, TiO2 and P2O5) after sulfuric acid digestion analysis. The details of analytical procedures can be found in Donagemma et al. (2011). Table 1 shows the physical and chemical properties of the soil. Table 1. Physical and chemical properties of soil used in the experiment. Properties Value Clay (g kg-1) 380 Silt (g kg-1) 45.0 Sand (g kg-1) 575 Dp (g cm-3) 2.53 pH 4.80 K+ (mg dm-3) 11.0 Ca2+ (cmolcdm-3) 0.30 Mg2+ (cmolcdm-3) 0.10 Al3+ (cmolcdm-3) 0.40 H++Al3+ (cmolcdm-3) 1.30 SOC (g kg-1) 10.0 CEC1/ (cmolcdm-3) 1.73 CEC2/ (cmolcdm-3) 0.83 B (mg dm-3) 0.03 Cu (mg dm-3) 0.10 Fe (mg dm-3) 3.00 Mn (mg dm-3) 1.70 Zn (mg dm-3) 0,00 SiO23/ (g kg-1) 8.80 Al2O33/ (g kg-1) 77.0 Fe2O33/ (g kg-1) 55.0 P2O53/ (g kg-1) 0.10 1155 Effects of phosphate... BORGES, C. S. et al. Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 Soil columns were packed in PVC tubes (12-cm high and 10-cm internal diameter) filled with 1 kg of soil (oven-dried basis). The soil density was standardized at 1.2 g cm-3. Based on soil particle density (Table 1), the total porosity of soil columns was 0.53 cm3 cm-3. Before packing the columns, the soil samples were treated with phosphate, silicate, and carbonate, establishing the treatments described below. The sources of P and Si (treatments 4 to 8) were KH2PO4 and CaSiO3, respectively. Treatments 1) control; 2) 8.32 mmol kg-1 CaCO3; 3) 8.32 mmol kg-1 CaSiO3; 4) 8.32 mmol kg-1 P; 5) 8.32 mmol kg-1 P + 1.04 mmol kg-1 Si; 6) 8.32 mmol kg-1 P + 2.08 mmol kg-1 Si; 7) 8.32 mmol kg-1 P + 4.16 mmol kg-1 Si; 8) 8.32 mmol kg-1 P + 8.32 mmol kg-1 Si; 9) 8.32 mmol kg-1 P + 8.32 mmol kg-1 Si (as H4SiO4). During the entire experiment, soil moisture was maintained constant at field capacity (0.30 cm3 cm-3). The experiment was carried out under laboratory conditions, and temperature ranged from 20º to 22º C. The CO2 emission from soil columns was measurement using a portable LI-8100 analyzer (LiCor, EUA) coupled to a dynamic chamber (Figure 1), on the following days: 1st, 3rd, 5th, 8th, 10th, 12th, 15th, 17th, 22nd, 26th, 29th, 31nd and 36th. The treatments were compared for accumulated CO2 emissions, which were calculated using equation 1. (1) Where: Q is the accumulated CO2 (g m-2); q is the average CO2 emission rate (g m-2 s-1) for each considered time interval (Δt). Figure 1. Experimental design and CO2 measurement using a portable LI-8100 analyzer (LiCor, EUA) coupled to a dynamic chamber. Photo: Camila Silva Borges. RESULTS AND DISCUSSION Figure 2A shows the accumulated CO2 emission influenced by CaCO3 and CaSiO3. The control treatment represents the background CO2 emission from soil microbial activity after disturbance sampling, sieving (< 2 mm), and remoistening (0.25 g g-1). A significant difference between CaCO3 amended samples and the control ones was observed. After 36 days, the soil samples treated with CaCO3 emitted 130.7 g m-2 (± 13.8), while those of control emitted 64.1 g m-2 (± 2.9). The effect of CaCO3 on CO2 emissions from soils are related to the direct dissolution of CaCO3 in soil solution (equations 2 to 4) and also by the increase in soil pH, favoring microbial activity (soil respiration) (MARCELO et al., 2012; FORNARA et al., 2011). The soil pH increased from 5.2 (control) to 6.9 after CaCO3 application (data not shown). In a long-term field experiment on a Red Latosol (642 g kg-1 sand, 315 g kg-1 clay, and 43 g kg-1 silt), CO2 emission increased linearly with limestone dose (MARCELO et al., 2012). CaCO3 + H2O → Ca2+ + HCO32- + OH- (2) HCO32- + H2O → H2CO3 + OH- (3) H2CO3 → H2O + CO2 (4) After 36 days, the samples treated with CaSiO3 emitted 108.9 g m-2 (± 5.2). Compared to 1156 Effects of phosphate... BORGES, C. S. et al. Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 the control, accumulated CO2 was 70% and 104% higher in treatments using CaSiO3 and CaCO3, respectively. The CO2 is not produced by direct dissolution of Ca-silicates, as evidenced by equations 5 to 8. Under natural conditions, the weathering of Ca-silicate minerals is considered a sink of atmospheric CO2 (BRADY, 1991). The effect of CaSiO3 on CO2 emission is certainly related to microbial activity, which was also favored by the increase in soil pH. Similarly, soil pH also increased when CaCO3 was used, ranging from 5.2 (control) to 6.5 (with CaSiO3 application). CaSiO3 → Ca2+ + SiO32- (5) SiO32- + H2O → HSiO3- + OH- (6) HSiO3- + H2O → H2SiO3 + OH- (7) H2SiO3 + H2O → H4SiO4 (8) The CaSiO3 (e.g. slag) has been used in Brazilian agriculture (mainly in sugarcane crops) having the same effects of liming: source of Ca and increasing soil pH (BARBOSA FILHO et al., 2001), and promoting Al3+ precipitation (MATICHENKOV; BOCHARNIKOVA, 2001). The environmental benefits of Ca-silicates (slags) are their own reuse and less CO2 emission from soil (ALLEONI et al., 2009). After 36 days, the difference in CO2 emission between CaCO3 and CaSiO3 treatments was 20% (Figure 2A). Figure 2. Effects of carbonate and silicate (A) and phosphate (B) on accumulated CO2 emission of a Dystrophic Red Latosol under lab conditions. Error bars indicate the standard deviation (n = 3). The CaCO3 reaction in the soil released CO2 to the atmosphere (equations 2 to 4). However, Figure 2B shows that the application of 8.32 mmol kg-1 P (KH2PO4) + 8.32 mmol kg-1 Si (CaSiO3) produced 203.3 g m-2 (± 11.8) of CO2 (217% higher than the CaCO3 amended samples). The single application of 8.32 mmol kg-1 P produced the same amount of CO2 as that of the liming amended samples (CaCO3 or CaSiO3). Vinhal-Freitas et al. (2012) studied the effects of P doses (from 0 up to 600 mg kg-1) on the microbial activity of Cerrado soil areas (32-year pine plantation, 11-year no- tillage, and native Cerrado). As P doses increased, the CO2 production by soil microorganisms increased. This effect was more pronounced in non- cultivated soil (native Cerrado). As the concentration of Si (as CaSiO3 combined with P) increased, CO2 emission increased (Figure 3). In the presence of P (8.32 mmol kg-1), the increment of 1 mmol kg-1 Si increased by 8.61 g m-2 the CO2 emission. Considering the effect of P on CO2 production in 1157 Effects of phosphate... BORGES, C. S. et al. Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 soils (VINHAL-FREITAS et al., 2012), the effect of Si is certainly related to the increase in the P availability in the soil. The anions silicate and phosphate compete by the same adsorption sites on soil particles (POZZA et al., 2007). It is noteworthy to mention that when P + Si (as H4SiO4) was applied, CO2 emission was the lowest. H4SiO4 has low solubility (pKa ∼ 9.0). Thus, the anion silicate could not influence P availability. Figure 3. Increasing Si doses combined with a single P dose (8.32 mmol kg-1) on accumulated CO2 emission. Error bars indicate the standard deviation (n = 3). In general, the accumulated CO2 emission decreased as follows: 8.32 mmol kg-1 P + 8.32 mmol kg-1 Si (CaSiO3) > 8.32 mmol kg-1 P + 4.16 mmol kg-1 Si (CaSiO3) = 8.32 mmol kg-1 P + 2.08 mmol kg-1 Si (CaSiO3) > 8.32 mmol kgˉ1 P + 1.04 mmol kg-1 Si (CaSiO3) > 8.32 mmol kg-1 P = CaCO3 > 8.32 mmol kg-1 P + 8.32 mmol kg Si (as H4SiO4) = CaSiO3 > control (Figure 4). Figure 4. Accumulated CO2 emission after 36-day incubation period as affected by CaCO3, CaSiO3 and P addition. Error bars indicate the standard deviation (n=3) and the letters compare the treatments by Scott-Knott test (p<0.05). 1158 Effects of phosphate... BORGES, C. S. et al. Biosci. J., Uberlândia, v. 35, n. 4, p. 1153-1160, July/Aug. 2019 CONCLUSIONS The use of CaSiO3 contributed to decrease CO2 emission compared to CaCO3. However, the combination of P and CaSiO3 contributed to the highest CO2 emission. Based on this experiment, we could oppose the claim that the use of limestone is a major villain for CO2 emission from soils. Also, we could show that other practices, such as fertilization using P+CaSiO3, contributed to a higher CO2 emission. Indeed, it is important to emphasize that the best practices of soil fertility management will undoubtedly contribute to crop growth and carbon sequestration ACKNOWLEDGMENTS The authors are grateful to the following Brazilian funding research agencies: Fapemig (Project 04520-2010), Capes, and CNPq. Also, we thank CNPq (Process 141595/2018-3) supporting the costs of this publication. RESUMO: Os efeitos das práticas agrícolas nas emissões de gases de efeito estufa (e.g., CO2) na interface solo-atmosfera têm sido destacados em todo o mundo. O uso de calcário tem sido considerado o principal responsável pela emissão de CO2 em solos. Entretanto, a calagem é necessária como condicionador de solos ácidos e a emissão de CO2 pode ser compensada devido ao sequestro de carbono pelas plantas. Este estudo simulou, em condições de laboratório, os efeitos de duas práticas agrícolas comuns no Brasil (adubação fosfatada e calagem) na emissão de CO2 do solo. Colunas de tubos de PVC, contendo 1 kg de amostra de um Latossolo Vermelho Distrófico típico da região de Cerrado, foram incubadas com CaCO3 (simulando calagem), CaSiO3 (simulando escória) e diferentes doses de KH2PO4 (simulando fertilização com P). As colunas de solo foram umedecidas para atingir a capacidade de campo (0,30 cm3 cm-3) e, durante 36 dias, as emissões de CO2 na superfície do solo foram medidas usando um analisador portátil Licor LI-8100 acoplado a uma câmara dinâmica. Os resultados mostraram que a emissão de CO2 foi influenciada pelos ânions fosfato, carbonato e silicato. Ao usar CaSiO3, a emissão de CO2 acumulada (período de 36 dias) foi 20% menor se comparado ao uso de CaCO3. A mesma quantidade de fosfato e calcário (Ca-carbonato ou Ca-silicato) adicionado ao solo proporcionou a mesma quantidade de emissão de CO2. Na mesma dose de P, o Si aumentou a emissão de CO2. A maior emissão de CO2 foi observada quando o solo foi alterado com as maiores doses de fosfato e silicato. Com base neste experimento, nega-se que o uso de calcário em solos é um grande vilão para a emissão de CO2. Além disso, foi mostrado que outras práticas, como a fertilização usando P + CaSiO3, contribuíram para uma maior emissão de CO2. Assim, é importante enfatizar que práticas adequadas de manejo da fertilidade do solo, sem dúvida, contribuirão para o crescimento das culturas e o sequestro de carbono. PALAVRAS-CHAVE: Gases de efeito de estufa. Solos tropicais. Reação do solo. REFERENCES ALLEONI, L. R. F.; MELLO, J. W. V.; ROCHA, W. S. D. 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