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Idesia (Arica)

versión On-line ISSN 0718-3429

Idesia vol.31 no.1 Arica abr. 2013

http://dx.doi.org/10.4067/S0718-34292013000100008 

Volumen 31, N° 1. Páginas 59-65 IDESIA (Chile) Enero-Abril, 2013

INVESTIGACIÓN

 

Critical levels for Brachiaria brizantha and Panicum maximum using different sources of phosphorus

Niveles críticos para Brachiaria brizantha y Panicum maximum utilizando diferentes fuentes de fósforo

 

José Tadeu Alves da Silva1, Inêz Pereira da Silva2*, Cleber Lázaro Rodas2, Janice Guedes de Carvalho2

1 Empresa de Pesquisa Agropecuária de Minas Gerais - EPAMIG/ CTNM.
2 Departamento de Ciência do Solo - Universidade Federal de Lavras, Campus UFLA, Lavras- MG, Brasil. Caixa Postal 3037-CEP 37.200-000.
* e-mail: inezps@yahoo.com.br.


ABSTRACT

Phosphorus critical level is influenced by soil physical and chemical attributes and characteristics of each plant species. The aim of this study was to determine the critical levels of phosphorus in soil and plants of Bracharia brizantha cv. Marandu and Panicum maximum cv. Tanzânia, using different doses and sources of P. The work was carried out under green house conditions using soil samples with different clay contents. In the experiment with the cultivar Marandu were applied 20 treatments in factorial scheme (5 x 4), corresponding to five P doses (0, 100, 200, 400 and 800 mg dm-3) and four P sources (monoammonium phosphate, triple superphosphate, simple superphosphate and Gafsa reactive rock phosphate). In the experiment with the cultivar Tanzânia was also applied magnesium termophosphate. The treatments were distributed in a complete block design with four replicates. No differences were observed among the effects of monoammonium phosphate, triple superphosphate, simple superphosphate, Gafsa reactive rock phosphate and magnesium termophosphate on the production of dry matter of grasses Marandu and Tanzânia. The triple superphosphate provided the lowest values of P critical level in soil, the Gafsa reactive rock phosphate provided the lowest values of P critical levels in grasses shoot.

Key words: remaining phosphorus, soil fertility, mineral nutrition.


RESUMEN

El nivel crítico de fósforo se ve influenciado por los atributos físicos y químicos del suelo y las características de cada especie vegetal. El objetivo de este estudio fue determinar los niveles críticos de fósforo en el suelo y las plantas de Bracharia brizantha cv. Marandu y Panicum maximum cv. Tanzânia, utilizando diferentes dosis y fuentes de P. El trabajo se llevó a cabo bajo condiciones de invernadero utilizando muestras de suelo con diferentes contenidos de arcilla. En el experimento con la hierba Marandu, 20 tratamientos se aplicaron en un diseño factorial (5 x 4), correspondiente a cinco niveles de fósforo (0, 100, 200, 400 y 800 mg dm-3) y cuatro fuentes de fósforo (fosfato monoamónico, superfosfato triple, simple superfosfato y fosfato natural de Gafsa). En el experimento con la hierba Tanzânia, se aplicó también termofosfato magnesiano. Los tratamientos se dispusieron en un diseño de bloques al azar con cuatro repeticiones. No se observaron diferencias entre los efectos de fosfato monoamónico, superfosfato triple, simple superfosfato, fosfato natural de Gafsa y termofosfato magnesiano en la producción de materia seca de gramíneas Marandu y Tanzânia. El súper triple proporciona valores más bajos de nivel crítico de P en el suelo, al paso que el fosfato natural de Gafsa proporcionó más bajos niveles críticos de P en los brotes de hierbas.

Palabras clave: fósforo restante, fertilidad del suelo, nutrición de las plantas.


Introduction

Among the investments, the more costly to establish a pasture with good productivity is phosphorus fertilization. The low natural fertility combined with no replenishment of nutrients to the soil and inadequate management, such as overcrowding of animals and soil conservation lack, cause large areas planted with pastures are degraded or are in degradation process. One option for the recovery of these pastures is the use of liming and fertilization.

Brazilian soils, Latosols among them, have generalized deficiency of phosphorus (P). In this situation the phosphorus fertilization is considered of vital importance, especially in the establishment phase of pastures. With the high cost of phosphate fertilizers and the evidence that forage species have sharp variations in P demand, few studies have been conducted to determine the P requirement in forage species to obtain subsidies for a suitable fertilizer recommendation (Fonseca, 1987). The P requirement for a given plant species varies from soil to soil. Some research studies have attempted to relate soil physical attributes with P critical levels in soil and the shoots (Fonseca, 1987; Silva, 1990; Bonfim, 2004), however, there is a need for more information about the P critical levels for forage crops in tropical soils.

Critical level corresponds to a nutrient concentration in a specific part of the plant at a certain stage of growth, below which plant development, production or product quality are significantly reduced (Battaglia et al., 1992).

Phosphorus critical level (21 mg dm-3) for 80% of the maximum production of Tanzânia grass (Panicum maximum) was obtained by Corrêa et al. (1996), using as P extractant the resin. Santos et al. (1998) determined the P critical level for Panicum maximum cv. Mombaça and Brachiaria decumbens cv. Basilisk at 70 days after planting. The critical level values found using the Mehlich-1, were 21.4 mg dm-3 and 18.4 mg dm-3 for the grass Brachiaria and Mombaça, respectively. Gheri et al. (2000) determined P critical level for Tanzânia grass in 38 mg dm-3. Correa et al. (1996) evaluating four cultivars of Panicum maximum (Tanzânia, Mombaça, Vencedor and T21) and six P doses as granular triple superphosphate, found that critical levels in soil and plant to achieve 80% of the maximum production were 21 mg dm-3 and 2.3 g kg-1 of P, respectively.

Consolini et al. (1999) found that phosphorus fertilization promoted significant increases in shoots dry matter production of Panicum maximum cv. Mombaça. Gheri et al. (1999) found that among cultivars of Panicum maximum Jacq., Tanzânia is the cultivar that had the best performance in rich soils in phosphorus. On the other hand, the cultivar Mombaça would be, based on the results, that would provide best productions in poorer soils, without providing poor result in rich soils.

In general, the cultivars of Panicum maximum Jacq. have high response to fertilization with P. Rego et al. (1985) observed that, with the application of 200 ppm of P, 49.2% of the applied P remained available in the sandy soil and clayey and sandy-clay soils, only about 12%.

The aim of this study was to estimate the phosphorus critical levels in the grasses Brachiaria brizantha (Marandu) and Panicum maximum (Tanzânia), using different doses and sources of P in Red Latosol and Red-Yellow Latosol.

Material and Methods

Samples were collected from the clayey Red Latosol (RL) and Red-Yellow Latosol medium texture (RYL), in the Northern Minas Gerais, in the depth of 0-20 cm. The samples were passed through sieve with 4 mm of aperture, which were separate sub-samples were subjected to chemical and grain size analysis. The results of these analyzes are presented in Table 1.

Table 1. Chemical and physical properties of soils, 2007.

1Cation-exchange capacity; 2Base saturation; 3Remaining phosphorus; 4Organic matter.

In the experiment with Bracharia brizantha (Marandu), 20 treatments were applied in a factorial design (5 x 4), corresponding to five phosphorus doses (0, 100, 200, 400 and 800 mg dm-3) and four phosphorus sources (monoammonium phosphate - MAP; triple superphosphate - TS; simple superphosphate - SS and Gafsa reactive rock phosphate - GRP). The soluble P contents from MAP, TS, SS and GRP are 55%, 37%, 18% and 9%, respectively. In the experiment with Panicum maximum (Tanzânia), 25 treatments were applied in a factorial design (5 x 5), corresponding to five phosphorus doses (0, 100, 200, 400 and 800 mg dm-3) and five sources of phosphorus (monoammonium phosphate - MAP; triple superphosphate - TS; simple superphosphate - SS; Gafsa reactive rock phosphate - GRP and magnesium termophosphate - MT). This latter source has 18% P soluble in water. Phosphorus doses were calculated considering the soluble P2O5 content in each source. Treatments were arranged in a randomized block design with four replications.

After application of treatments in each pot containing 5 dm-3 of soil, Tanzânia and Marandu grasses were seeded. In each pot were cultivated 10 plants. The soil moisture was maintained near field capacity. In all pots, after each cut of grass, were applied nitrogen (150 mg dm-3), potassium (150 mg dm-3) and a micronutrients compound in solution (mg pot-1: 14.65 of zinc, 14.83 of copper, 15.03 of boron and 0.23 of molybdenum).

Three cuts were made in grasses, 6 cm above the soil, at intervals of 30 days between cuts. The harvested material was placed in an oven with forced air circulation at 70 oC for 72 hours. The dried samples was weighed, ground, mineralized and analyzed. The mineralization was performed by nitric-perchloric digestion. In the extract obtained, the P was determined according to the methodology described by Malavolta et al. (1997).

A soil sample was collected in each pot after the 3° cut of grasses. It was determined in this samples available phosphorus using Melich-1 extractor, soil solution ratio of 1:10, in accordance with Braga (1980).

Statistical analyzes were performed with the data averages collected in the three cuts of grass. With the data of dry matter production and analysis of soil and shoot P content were conducted analyzes of variance, tests of means and regression settings. The regression equations were used to estimate the amount of phosphorus to reach 90% of the maximum production and getting the phosphorus critical level in soil and plant shoot.

Results and Discussion

There were no significant differences between the effects of P sources on dry matter production of two species of grass grown in the RYL and RL, by Tukey test at 5% of probability (Table 2). There were not significant interaction between doses and P sources.

Table 2. Shoots dry matter production (g pot 1) of grasses Marandu and Tanzânia, grown in RYL and RL

 

Regression equations were fitted for shoots dry matter production of grasses as a function of P doses applied in soil. The regression model that best fit was the quadratic base square root (Table 3).

Table 3. Regression equations adjusted for shoot dry matter production of Marandu and Tanzânia grasses, in g pot 1 (Ỳ), as a function of P doses applied in RYL and RL (x), 2007.

Quadratic coefficients linear and square root base are significant at and *5% of probability.

From these equations were estimated P doses to provide 90% of the maximum shoot dry matter production. Considering all sources, P average dose to provide 90% of the maximum shoot dry matter production of grasses was 408 mg dm-3. The Marandu grass grown in RL had the highest average value of 90% of the maximum shoot dry matter production (Table 4). The values of 90% of the maximum shoot dry matter production of grasses showed up very close in the different phosphorus sources used (Table 4).


Table 4. Estimated phosphorus doses (PD) to provide 90% of the maximum shoot dry matter production (MSDMP) of Marandu and Tanzânia grasses, 2007.

The TS provided lower values of P critical level in soil. It was hoped that the lowest value of critical level in the soil was where we applied the GRP as a fertilizer had the lowest content of water-soluble P, where P is the major limitation for the plant, inducing the plant to absorb and use P with greater efficiency (Novais et al., 2007).

P critical level of the RL cultivated with Marandu grass (19.7 mg dm-3) had a lower value than grown with grass Tanzânia (21.1 mg dm-3) (Table 5). Mesquita et al. (2004) in work with grasses at greenhouse conditions, obtained values of P critical level in soil of 26 and 29 mg dm-3, for Panicum maximum cv. Mombaça and Brachiaria brizantha. cv. Marandu, respectively. Bonfim et al. (2004) found a significant correlation between the P critical levels of soil and remaining P, in other words, soils with lower remaining P value had lower value of critical level. The values of the remaining P from RYL and RL used in this work were 33.2 and 18.4 mg L-1, respectively, corroborating the statements of the authors mentioned above.

Table 5. Regression equations between available P and applied P to the soil and P critical levels (CL) in RYL and RL cultivated with Marandu and Tanzânia grasses with different P sources, 2007.

** and *, significant at 1% and 5% of probability, respectively.

Replacing estimated P doses to provide 90% of the maximum production (Table 4) in the equations of tables 6 and 7, P critical levels of grasses shoot were estimated. The critical levels of grasses grown in RYL showed higher values in relation to those grown in RL. Bonfim et al. (2004) found that phosphorus critical levels in Brachiaria brizantha (Marandu) plants were lower in soils with the highest phosphorus buffering capacity.

Several factors influence P foliar critical level, among these factors is the soil physical characteristics that reflect the soil P buffering capacity. According Novais et al. (2007), soil P critical level correlates with soil characteristics which reflect the phosphorus buffering capacity, as the remaining phosphorus, which is a measure of the amount of phosphorus that stays in equilibrium solution in response to a concentration of phosphorus added to the soil. Lower the amount of phosphorus remaining of given soil, greater the phosphorus potential adsorption.

According to Muniz (1983), the influence of the soil P buffering capacity on the foliar critical levels acquires fundamental importance in the interpretation of results of leaf analysis. According to Silva (1990), plants generally use more efficiently the P, when this is in reduced availability. This author cites that the absorbed P in clay soils with high buffering capacity factor, is used more efficiently. Muniz (1983) mentions that the use of plants more efficient in absorbing or using P must be considered.

According to Novais & Smyth (1999), competition between plant and soil by P applied as fertilizer causes the plant to adjust and use more efficiently the available P, so P critical levels in soil and shoot plants tend to reduce as this increases competition. Bedin et al. (2003) found lower P foliar contents in soybean plants grown in soil with high buffering capacity and higher foliar contents in plants cultivated in sandy soil with low buffering capacity. According to the authors, this apparent adjustment of the absorption indicates sensitivity of the plant to the soil buffer capacity.

The lower values of critical levels in the shoots were obtained with GRP application. This fertilizer is the one with the least amount of P soluble in water (9% P2O5). In other hand, the largest values of critical levels were obtained with application of MAP and TS (Tables 6 and 7) which are fertilizers with higher concentrations of P soluble in water. Results obtained by Resende et al. (2006), in a study with application of P in corn showed that the lower the phosphorus supply, greater was corn plants efficiency to use it.

Table 6. Regression equations between shoot P content and applied P to the soil and P critical levels (CL) on Marandu grass with different P sources applied in RYL and RL, 2007.

Linear and quadratic coefficients are significant to 1% of probability.


Table 7. Regression equations between shoot P content and applied P to the soil and P critical levels (CL) on Tanzania grass with different P sources applied in RYL and RL, 2007.

Linear and quadratic coefficients are significant to 1% of probability.

Conclusions

No differences were observed among the effects of monoammonium phosphate, triple superphosphate, simple superphosphate, Gafsa reactive rock phosphate and magnesium termophosphate on the dry matter production of Marandu and Tanzânia grasses.

The triple superphosphate provided lower values of phosphorus critical level in soil.

The Gafsa reactive rock phosphate had the lowest content of phosphorus soluble in water provided lower values of phosphorus critical levels in grasses shoot.

 

Literature cited

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Fecha de Recepción: 23 Enero, 2012. Fecha de Aceptación: 19 Octubre, 2012.

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