Microsoft Word - 28-Agra_42626-vet-pg 968 Bioscience Journal Original Article Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 PHOSPHORUS SOURCES RESIDUAL EFFECTS ON TIFTON 85 PRODUCTION AND NUTRITIVE VALUE CULTIVATED IN A TROPICAL WEATHERED SOIL1 EFEITO RESIDUAL DE FONTES DE FÓSFORO NA PRODUÇÃO E VALOR NUTRICIONAL DO TIFTON 85 CULTIVADO EM SOLO TROPICAL Henrique Coutinho Junqueira FRANCO2; Bernardo Melo Montes Nogueira BORGES3*; Sérgio Augusto Quassi de CASTRO3; Michele Xavier Vieira MEGDA4; Marcio Mahmoud MEGDA4; Alan L. GARSIDE5; Edson Luiz Mendes COUTINHO2 1. Part of first author master’s dissertation; 2. São Paulo State Univ. (Unesp), Campus Jaboticabal, Dep. of Soil Science, São Paulo, Brazil; 3. Brazilian Biorenewables National Laboratory (LNBR), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, SP, Brazil; 4. Soil and Plant Nutrition program – ESALQ/USP, Piracicaba, SP, Brazil; 5. James Cook University, Australia; *bernardo.borges@lnbr.cnpem.br ABSTRACT: Acid reactions and low available phosphorus in tropical soils limit forage yield. The aim was to evaluate soil chemical characteristics pH, P and Mg, forage nutritive values, critical soil and plant P levels and the residual effect of each source. The experiment was in a greenhouse with a Rhodic Haplustox, loam texture. Experimental design was a 5 x 4 factorial with five replicates which phosphate fertilizers were triple superphosphate, reactive rock phosphates Gafsa and Arad, and fused magnesium phosphate powder and coarse, applied at rates of 30, 60, 90 and 120 mg kg-1 P and a control treatment without P. The effectiveness of rock phosphates increased due to their residual effect. The coarse fused magnesium phosphate resulted in the lowest efficiency. The P critical level in soil and plant were 18 mg kg-1 and 2.4 g kg-1, respectively. The increase of phosphorus rates provided an increase in crude protein content. KEYWORDS: Pasture. Phosphate rock. Critical level. Bermudagrass. INTRODUCTION Tifton 85 (Cynodon spp.) is a grass that, when properly managed, constitutes an alternative to intensive production systems. It is a subtropical climate forage, that adapted to tropical conditions with no adverse consequences (SINCLAIR et al., 2003), presenting a great production potential under tropical climate (SOHM et al., 2014). Reasons why it was grouped amongst the most demanding soil fertility forages (WERNER et al., 1996). Demanding special attention related to the issue, highlighting phosphorus (P) as a major problem, especially in weathered soils (SANCHES; LOGAN, 1992), at present, information regarding Tifton 85 nutritional requirements in tropical conditions are still scarce. In order to correct the soil deficiency, it is necessary to supply the nutrient utilizing fertilizers, but, unlike other sources P-fertilizers present different solubility and consequently different availability what can influence its efficiency in specific conditions. Rock phosphates, for example, feature low water solubility or insoluble, fused magnesium phosphates (FMP) are another example, although this product is not water soluble, it presents a high solubility in neutral ammonium citrate and citric acid. Solubility of this fertilizers are not only influenced by their chemical characteristics but also physical, the smaller the particle size the greater will be the contact with the soil, increasing P release from these sources (TIECHER et al., 2014). Phosphorus sources, application methods and soil management, might impact on fertilizer contact with the soil. Determining this way different reaction degrees of the phosphate fertilizer, affecting nutrient availability and root distribution in soil profile (WALKER et al., 2012; KNOX et al., 2014). Another problem is the amount of phosphate required to correct the fertility in weathered soils considering the limited world phosphate supply and (COOPER et al., 2011), associated to an increase in costs of fertilizers, justifying studies to optimize the use efficiency of alternative phosphate sources. On one hand, there are the variations as for the nature and the solubility of the rock and industrialized phosphates, and, on the other hand, the interaction with edaphic components that sharply interfere on P availability to plants (PROCHNOW et al., 2003). Nevertheless, it is necessary to establish more precise criteria for P recommendation. Thus the possibility to apply rock phosphates at relatively Received: 04/04/19 Accepted: 20/12/19 969 Phosphorus sources… FRANCO et al. Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 low cost has been emphasized as a viable alternative to supplement P demand to the crops in tropical highly weathered soils (FAGERIA; MOREIRA; CASTRO, 2011; GUEDES et al., 2012; WALKER et al., 2012; KNOX et al., 2014; TIECHER et al., 2014; BARBOSA et al., 2015; BUSTAMANTE et al., 2016). The aim of this work was to evaluate soil chemical characteristics pH, P and Mg. P, Mg, and crude protein content were determined in the shoot and the data was used to set the critical P level in the soil and plant, dry matter yield and evaluated the residual effect of each source, expecting that alternative sources would be as efficient as triple superphosphate. MATERIAL AND METHODS The experiment was conducted in a greenhouse located at the Sao Paulo State, Brazil (21˚14’05”S 48˚17’09”W), 615 asl, utilizing pots (diameter = 0.22 m; height = 0.2 m) containing 2.8 kg of soil collected from a Rhodic Haplustox loam texture (SOIL SURVEY STAFF, 2014), presenting the following chemical characteristics in the arable layer (0-0.2 m): pH (CaCl2) = 3.9; Organic Matter = 15 g kg-1; P (resin) = 3 mg kg-1; K = 0.06 cmolc kg -1; Ca = 0.4 cmolc kg -1; Mg = 0.2 cmolc kg -1; H+Al = 5.8 cmolc kg -1; CEC = 6.46 cmolc kg -1 and base saturation = 10%. Treatments were arranged in a complete randomized design in a factorial scheme 5 x 4 (five P sources and four P rates), with five replicates. A control treatment without application of P was included. The P sources evaluated were: Triple superphosphate – TS (42.1% P2O5; 10% Ca); Arad rock phosphate (34.33% P2O5); Gafsa rock phosphate (29.1% P2O5); thermo-magnesium phosphate powder – FMP-powder (18% P2O5; 9% Mg; 20% Ca; 25% SiO4); and fused magnesium phosphate coarse – FMP-coarse (18% P2O5; 9% Mg; 20% Ca; 25% SiO4). Applied P rates were: 30; 60; 90 and 120 mg kg-1 of P and a control treatment without P, it was taken as basis for calculating the amount of total P of each source. The phosphate fertilizers presented different solubility (Table 1) and the following physical characteristics: TS with 100% passing through the 2-mm sieve, and 50% passing through 0.3 mm sieve; FMP-powder 80% passing through 0.15 mm sieve; FMP-coarse 100% passing through 0.84 mm sieve and Gafsa and Arad rock phosphates with 100% passing through 4.8 mm sieve and 80% passing through the 2.8 mm sieve. Table 1. Phosphate fertilizers solubility in citric acid (2%) in a 1:100 ratio and water (H2O). Phosphorus sources Total %P2O5 Citric acid (2%) 1:100 H2O -------- %P2O5 soluble -------- Triple superphosphate 41 100 90 FMP coarse 18 92 0 FMP powder 18 92 0 Arad 34 35 0 Gafsa 29 41 0 FMP - Fused magnesium phosphate Soil acidity correction was carried out with a liming application to increase soil base saturation to 60%. The, the lime rate utilized was defined in an incubation pre-experiment, in which the ratio between base saturation and lime rates was obtained. The soil corrective was thoroughly mixed through the total volume of the soil in each pot and, 450 mL of deionized water was added, with the objective to maintain water holding capacity of the soil at 80%. The soil was left incubating for 20 days. After this period, soil from each pot was air dried and sieved, proceeding the application of the phosphorus fertilizers and basic fertilization. Basic fertilization, performed in all pots including control treatments, constituted of: N = 60 mg kg-1 (ammonium nitrate), K = 150 mg kg-1 (potassium chloride), S = 62 mg kg-1 (potassium sulfate), B = 0.5 mg kg-1 (boric acid), Cu = 0.5 mg kg-1 (coper sulfate) and Zn = 3.0 mg kg-1 (zinc sulfate). The products were dissolved in 100 mL distilled water, applied as solution in the total volume of the soil with manual homogenization. After this period, 300 g soil samples of each treatment were collected, and chemical analysis was performed to determine soil fertility. Tifton 85 (Cynodon spp.) was planted by vegetative propagation, utilizing four stolons of 0.1 m long, with two buds each. Fifteen days after planting a standardization clipping at 0.1 m from soil surface was carried out. During experimental period three manual shoot harvests were conducted (scissors were utilized) at 0.1 m from soil surface, in 970 Phosphorus sources… FRANCO et al. Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 30-days intervals. After each growth (including standardization clipping) topdressing was performed applying 160 mg kg-1 of N and 50 mg kg-1 of K, as ammonium nitrate and potassium chloride, respectively. Fertilization was performed in all treatments, including control, with the objective to evaluate residual P effect on the second and third harvest. During experimental period, all pots were watered daily with distilled water. The amount of water added was determined by the daily weighting of the pots. After the first harvest, two replicates were deactivated to proceed with soil sampling. At the end of the third harvest soil samples were collected from each treatment determine pH values in a calcium chloride solution (0.01 mol L-1), P and Mg available in the soil were extracted utilizing the ion- exchange resin procedure and determined by colorimetric method. Subsequent to the harvests, shoots were washed, and oven dried at 65 oC. Dried, materials were weighted in order to quantify dry matter production of each pot. Dry shoots were ground and analyzed for total N-Kjeldahl, Mg and P content by nitro-perchloric extraction. The crude protein (C.P.) content was calculated by multiplying total N content (g kg-1) by the constant 0.625, expressed in % in shoot dry matter. Using the evaluated variables, we attempted to established critical P levels for the plant and soil. The treatments’ effects on P sources and rates were submitted to a two-way ANOVA utilizing F test. Posteriorly for the significant causes of variation a Tukey test (P ≤0.05) was applied to compare source effect. When significant, the interaction source x rate was deployed for each variable separately and regression calculations performed utilizing the statistical package SigmaPlot version 11.0 (Systat Software, San Jose, CA). RESULTS AND DISCUSSION Forage dry matter yield Phosphate fertilization promoted an increase in Tifton 85 shoot dry matter yield during the whole experimental period (Fig. 1). The increase in dry matter yield when utilizing phosphate fertilizers has been mentioned by several authors (HILLARD; HABY; HONS, 1992; GUEDES et al., 2012; TIECHER et al., 2014; FAN et al., 2016) in forages, thus re-enforcing the importance of P in the nutrition of forage species. P rates (mg kg -1 ) 30 60 90 120 S h oo t d ry m at te r (g /p ot ) 0 10 20 30 40 TS: y = 2.34 + 0.261x - 0.0001x2 (R2 = 0.96**) Arad: y = 1.65 + 0.165x - 0.0007x2 (R2 = 0.99**) Gafsa: y = 2.15 + 0.163x - 0.0009x2 (R2 = 0.92**) FMP-powder: y = 1.90 + 0.243x - 0.0013x2 (R2 = 0.99**) FMP-coarse: y = 2.21 + 0.234x - 0.0014x2 (R2 = 0.94**) First harvest P rates (mg kg-1) 30 60 90 120 S h oo t d ry m at te r (g /p ot ) 0 10 20 30 40 Third harvest yield Second harvest yield Cumulative yield y = 3.87 + 0.19x - 0.0009x 2 (R 2 = 0.98**) y = 3.79 + 0.14 x - 0.0008x2 (R2 = 0.98**) y = 9.63 + 0.57 x - 0.0029x 2 (R 2 = 0.97**) Figure 1. Effect of P sources and rates on Tifton 85 shoot dry matter yield during experimental period. The initial growth of the forage was superior for TS compared to the other sources, contrary results were found in the literature, in which, FMPs promoted an initial effect similar or at times superior to the TS (MOREIRA et al., 2014; BARBOSA et al., 2015). Although soil acidity and the incorporation of fertilizers into the soil increase rock phosphates solubilization (BUSTAMANTE et al., 2016), it was not able to supply enough P in order to positively affect forage dry matter yield in the first harvest. Arad rock phosphate presented higher efficiency on P utilization by grasses when cultivated in an Oxisol, indicating favorable and residual conditions for reactive phosphate solubilization (RAMOS et al., 2009). The residual effect of the reactive rock phosphates is due to its gradual dissolution, that contributes to a lower P adsorption (KNOX et al., 2014), with an important residual effect (GUEDES et al., 2012). As a result of its geological origin, Arad releases the P from its crystallographic structure in a shorter period of time than the 971 Phosphorus sources… FRANCO et al. Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 Brazilian rock phosphates. The technical recommendations for the use of reactive rock phosphates possess some uncertainties, there is a consensus that more soluble phosphates provide greater response in the year of application, while rock phosphates are less efficient initially (ROSOLEM; MERLIN, 2014). The lowest residual effect of the coarse FMP on Tifton 85 dry matter yield in the second harvest, differ from a series of studies in the literature (FAGERIA; BARBOSA FILHO, 2007; FAGERIA; MOREIRA; CASTRO, 2011; MOREIRA et al., 2014; BARBOSA et al., 2015) which FMP presented a superior residual effect compared to a soluble source (TS). As for FMPs, the process of P dissolution is slow, since it depends on chemical reactions with the soil (BUSTAMANTE et al., 2016). Cumulative dry matter yield on TS and FMP-powder were similar. The FMP in powder, presented a residual effect similar to TS; FMP coarse resulted in a lower recovery of P residual, the contact to soil is minimized causing a non-optimal condition to P solubilization (FAGERIA; BARBOSA FILHO, 2007; BUSTAMANTE et al., 2016). Soil and forage attributes Phosphorus level in the soil decreased along the experimental period (Fig. 2), similar results with different forages species were reported (KUWAHARA et al., 2016), soil P levels significantly decreased, due to the large nutrient extraction by the forage. P rates ( mg kg-1) 30 60 90 120 P s o il ( m g k g -3 ) 0 20 40 60 80 100 Arad: y = 2.44+0.49x (R2=0.99**) Arad Gafsa Gafsa: y = 3.04+0.33x (R2=0.99**) TS: y = 2.24+0.73x (R2=0.99**) FMP-powder: y = 2.68+0.46x (R2=0.99**) TS FMP-powder FMP-coarse FMP-corase: y = 4.92+0.51x (R2=0.99**) (a) P rates (mg kg-1) 30 60 90 120 P s o il ( m g k g -3 ) 0 20 40 60 80 100 Arad FMP-powder FMP-coarse Gafsa TS FMP-coarse: y = 0.2 + 0.375x (R2= 0.96**) FMP-powder: y = 0.7 + 0.243x (R2= 0.99**) Gafsa: y = 2.4 + 0.227x (R2= 0.97**) TS y = 0.7 + 0.328x (R2= 0.99**) Arad: y = 0.01 + 0.367x (R2= 0.99**) (b) Figure 2. Effect of P sources and rates on levels of P soil before (a) and after (b) first harvest. The TS was the source that promoted the highest P level in the soil after its application and before the planting of the crop, however, after the first harvest the soil treated with FMP-coarse presented the highest P level. Sources with high water solubility such as TS promptly provide P to the plants, though, in acid and weathered soils, in a short period of time after fertilizer application, P adsorption occurs and posterior fixation on the surface of the Fe/Al oxides (OBERSON et al., 2001) and/or precipitation as a P secondary mineral linked to iron and aluminum, decreases available P content in the soil. On the other hand, results of FMP-coarse for P soil (Fig. 2) contradicts forage yield, in which this source presented the lowest performance. This observation suggests that the result of FMP-coarse P soil availability was overestimated and, thus, it can be inferred that the anion exchange resin method extracts P from the FMP-coarse treatment not as the roots of the plants. The Gafsa rock phosphate present P content value (Fig. 3a), at the first harvest, lower than the considered adequate 1.5 to 3.0 g kg-1 P for Cynodon grasses (KELLING; MATOCHA, 1990; WERNER et al., 1996). In the second harvest, P sources were similar on shoot P content and it is in the range, 1.5 to 3.0 g kg-1 P, considered sufficient (KELLING; MATOCHA, 1990). 972 Phosphorus sources… FRANCO et al. Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 P rates (mg kg-1) 30 60 90 120 P s h o o t ( g k g -1 ) 0 1 2 3 (a) TS: y = 1.13 + 0.037x - 0.0002x 2 (R 2 = 0.86**) FMP-powder: y = 1.07 + 0.035x - 0.0002x 2 (R 2 = 0.94**) Gafsa: y = 0.88 + 0.026x - 0.0001x 2 (R 2 = 0.96**) Arad: y = 0.92 + 0.029x - 0.0001x 2 (R 2 = 0.98**) FMP-coarse: y = 1.09 + 0.036x - 0.0002x 2 (R 2 = 0.91**) FMP-coarse Gafsa TS FMP-powder Arad P rates (mg kg-1) 30 60 90 120 P s h o o t (g k g -1 ) 1 2 3 Arad: y = 0.94 + 0.039x - 0.0002x2 (R2 = 0.91**) Gafsa: y = 0.89 + 0.033x - 0.0002x2 (R2 = 0.96**) TS: y = 0.86 + 0.032x - 0.0002x2 (R2 = 0.98**) FMP-powder: y = 0.75 + 0.028x - 0.0001x2 (R2 = 0.98**) FMP-coarse: y = 0.71 + 0.029x - 0.0001x2 (R2 = 0.96**) Arad Gafsa FMP-powder FMP-coarse TS (b) Figure 3. Effect on P sources and rates on Tifton 85 shoot P content in the first (a) and third (b) harvest. Although no effect on C.P. were noticed when varying P sources differences on P rates were noted for the second (y =-0.0006x2+0.105x+10.7; R2 =0.89; P <0.001) and third (y=- 0.0003x2+0.072x+10.05; R2=0.99; P <0.001) harvest, as mentioned by Souza et al. (1999) working with Brachiaria brizantha in a low fertility soil, after a 90 days growing period, also reported that phosphorus fertilization (P rates 50, 100 200 e 300 mg kg-1 as TS) resulted in an increase of C.P. content on forage shoot. Phosphorus critical level The soil P critical level corresponded to 18 mg kg-1 P (Fig. 4). This value represents soil P level that above it, yields’ response to P fertilization is probably low, P critical level. This value is slightly over the superior limit (7 - 15 mg kg-1) of the low P soil class, which was stablished in calibration insights with annual crops in the field (WERNER et al., 1996). However, when considering the values proposed by Kelling and Matocha (1990) ranging from 3 to 21 mg kg-1, it might be inferred that the critical level obtained in our study lies in the praised range aiming to execute a phosphorus fertilization with precision and sustainability. P soil (mg kg-1) 0 15 30 45 60 75 90 105 S h o ot d ry m a tt er ( g /p o t) 0 3 6 9 12 15 18 y = 1.56 + 0.575x if P < 18 R 2 = 0.90** C.L.= 18 mg kg-3 (a) P soil (mg kg-3) 0 15 30 45 60 75 90 105 P p la n t (g k g- 1 ) 0 1 2 3 C.L. = 2.4 g kg-1 C.L. = 18 mg kg-3 y = 0.56 + 0.101x if P (soil) < 18 y = 2.4 if P (soil) > 18 (R2 = 0.95**) (b) Figure 4. Soil (a) and Plant (b) phosphorus critical level. The P shoot content associated to the soi P level was 2.4 g kg-1 P which lies in the range 1.5 – 3.0 g kg-1 considered adequate for Cynodon cultivars (WERNER et al., 1996) and, close to the critical level of 2.2 g kg-1 P for Coastal bermudagrass (HILLARD; HABY; HONS, 1992). CONCLUSIONS Phosphorus fertilization promoted an increment on Tifton 85 shoot dry matter yield. The increase of rates up to 90 mg kg-1 P presented an increase on shoot dry matter yield, 973 Phosphorus sources… FRANCO et al. Biosci. J., Uberlândia, v. 36, n. 3, p. 968-975, May/June 2020 http://dx.doi.org/10.14393/BJ-v36n3a2020-42626 wherein triple superphosphate (TS) was the source with the highest agronomic efficiency. The efficiency of reactive phosphates (Arad and Gafsa) increased when it was considered its residual effect, whereas the coarse granulometry of the FMP resulted in a lower agronomic efficiency than the FMP-powder. The increment on P rates provided increase on P content and crude protein in Tifton 85 shoot. The P critical level in the soil and plant was 18 mg kg-1 and 2.4 g kg-1, respectively. ACKNOWLEDGEMENTS To the estimate Professor Dr. Luiz Roberto de Andrade Rodrigues (In memorian) for his suggestions during the conduction of the experiment. RESUMO: Reações ácidas e baixo fósforo disponível em solos tropicais limitam a produção de forragem. O objetivo foi avaliar as características químicas do solo pH, P e Mg, valores nutritivos das forragens, níveis críticos de P no solo e nas plantas e o efeito residual de cada fonte. O experimento foi realizado em casa de vegetação com Latossolo vermelho distrófico, textura média. O delineamento experimental foi inteiramente casualisado em fatorial 5 x 4, com cinco repetições cujos adubos fosfatados eram superfosfato triplo, fosfatos de rocha reativa Gafsa e Arad e fosfato de magnésio em pó e grosso, aplicados nas doses de 30, 60, 90 e 120 mg kg-1 de P e um tratamento controle sem P. A eficácia dos fosfatos rochosos aumentou devido ao seu efeito residual. O fosfato de magnésio fundido grosso resultou na menor eficiência. O nível crítico de P no solo e na planta foi de 18 mg kg-1 e 2,4 g kg-1, respectivamente. 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