Concentration of nutrients and chlorophyll index in pigeon pea fertilized with rock phosphate and liming in cerrado oxisol

Soil fertilization and the management of green manure are needed to maintain and increase the soil fertility of Cerrado. Thus, the objective of this study was to evaluate the concentration of nutrients in the shoots and roots of pigeon pea that was fertilized with phosphorus sources that are associated with liming in Cerrado Oxisol. This study was conducted in a greenhouse with a completely randomized design in a 3×2 factorial arrangement with twelve repetitions. The rock phosphate, triple superphosphate and control treatments were associated with the presence and absence of liming; the sources of phosphorus were evaluated. The chlorophyll index and the concentrations of nitrogen, phosphorus, potassium, calcium, magnesium and sulfur in the shoots and roots of pigeon pea that was grown for a period of 107 days were evaluated. In general, the chlorophyll index and nutrient concentration of pigeon pea did not differ when fertilized with phosphate rock and triple superphosphate. The fertilization with rock phosphate and triple superphosphate provides a greater nutrient absorption of pigeon pea in the presence of lime.


INTRODUCTION
The concentration of phosphorus in the soil solution of the Cerrado is generally reduced.This feature, coupled with the high adsorption capacity of phosphorus, is the main constraint on the development of any profitable farming without the use of large amounts of phosphate fertilizers to meet the crop needs in this region (Sousa and Lobato, 2003).
The sources of phosphatic fertilizers are more soluble at a high cost per unit due to their greater agronomic efficiency in the short term, but as alternatives to these sources, there are less-soluble phosphates, such as rock phosphates.However, these sources do not have nutrient availability, with a lower cost and higher residual effect on the soil, being gradually absorbed by the plants (Horowitz and Meurer, 2004).Rock phosphates are classified per their origin and may *Corresponding author.E-mail: embonfim@hotmail.comAuthor(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License belong to the group of volcanoes, where rocks are from the groups of apatite and sedimentary when derived from phosphorite rocks and phosphoric bauxites.Rock phosphates are natural phosphates of volcanic origin, due to their high degree of crystallization and low solubility, while those of sedimentary origin are more soluble (Chien 1977;Lehr and MCclellan, 1972).Kaminski and Peruzzo (1997) observed that the sums of crop production provided by rock phosphate (Arad and Gafsa) and superphosphate were virtually the same.However, rock phosphates require soil acidity to solubilize and increase their efficiency over time.Sousa and Lobato (2003) observed a decrease in the solubility of rock phosphate with lime application, especially when applied at greater recommended amounts, to increase the base saturation to 50% dose, thereby allowing a reduction in costs in the practice of liming.
According to Pott et al. (2007), pigeon pea (Cajanus cajan (L.) Millsp.) is a legume with greater absorption of phosphorus via root exudates organic acids.Therefore, pigeon pea is able to potentiate the solubilization of phosphorus sources that are poorly soluble, such as rock phosphates, in addition to being able to perform symbiosis with the root nodule bacteria of the group, allowing the process of N 2 fixation .
These features cause pigeon pea to be a cover crop, able to improve the availability of soil nutrients, particularly phosphorus and nitrogen, and favoring the development of succeeding crops (Moltocaro, 2007).The positive effect of the interaction between phosphorus and nitrogen can be studied by the indirect measurement of the chlorophyll index, possibly due to the role of phosphorus in plant nutrition through the participation of adenosine triphosphate (ATP), benefiting the active process of absorption nitrogen (Malavolta et al., 1989;Prado and Vale, 2008).
Among the rock phosphates, Bayóvar is from the region of Piura in the province of Sechura, Peru, being of sedimentary origin.Bayóvar is gray, with a mash physical nature and with a guaranteed 29% of total phosphorus, 14% citric acid, and 32% calcium (Faria, 2012).In the Cerrado region, there are few studies of phosphorus fertilization using this source; therefore, this study aimed to evaluate the concentration of nutrients in the shoots and roots of pigeon pea that was fertilized with the rock phosphate Bayóvar and that is associated with liming in Cerrado Oxisol.

MATERIAL AND METHODS
This experiment was conducted in a greenhouse at the Federal University of Mato Grosso, Campus Rondonópolis, Brazil, from May to August 2011.
We used completely randomized design in a factorial 3 (triple superphosphate, rock phosphate and control treatment) × 2 (liming: presence and absence) with twelve repetitions.
According to the results of the chemical analysis, liming was performed only for treatments with the presence of the same, to increase the base saturation to 60%.Irrigation was performed via the gravimetric method, and throughout the experimental period, the soil moisture was maintained at 60% of the maximum capacity of water retention.
Sowing was performed using 20 seeds per pot planted two inches deep.Then, the phosphorus was applied at 200 mg dm -3 P2O5 according to the availability of the sources triple superphosphate (44% P2O5) and reactive rock phosphate Bayóvar (29% total P), which were incorporated into the soil.
A micronutrient fertilizer was applied using a solution containing 1 mg dm -3 B and Cu, 3 mg dm -3 Zn and Mn and 0.2 mg dm -3 Mo from the following sources: H3BO3, CuCl2.2H2O SO4.H2O ZnCl2 and MoO3, respectively.Fertilization with potassium (80 mg dm -3 ) and sulfur (10 mg dm -3 ) was performed 14 days after sowing using as sources KCl and CaSO4, respectively.The applications were based on pilot experiments with pigeon pea grown in the same soil.
Thinning was performed on the tenth day after sowing, leaving five plants per experimental unit; and at 107 days, the chlorophyll index was determined, analyzing two leaves from the middle third of the plants, with the aid of the chlorophyll index SPAD-502 Minolta.At the end of the evaluation, the plants were cut at ground level, and the roots were separated from the soil through a 2-mm sieve using water elutriation.Then, the plant material was packaged in paper, identified and dried in an oven with forced air circulation at 65°C until obtaining a constant weight.The dried plant material was ground in a Willey mill and passed through a 2-mm sieve.Then, 5-g samples were collected to measure the nutrients (nitrogen, phosphorus, potassium, calcium, magnesium and sulfur) of the shoots and roots of pigeon pea according to the methodology of Malavolta et al. (1997).
All of the results were subjected to an analysis of variance and Tukey's test up to a 5% probability using the statistical program Sisvar (Ferreira, 2008).

RESULTS AND DISCUSSION
The significant effects were found only on the nitrogen content of the shoots and the roots of pigeon pea with fertilizing and liming, respectively.Higher nitrogen concentrations in the shoots were observed with triple superphosphate and the control treatment without fertilization and without liming and in the roots with triple superphosphate and rock phosphate in the absence of liming (Table 1).Lima et al. (2003) observed a reduction in the leaf nitrogen concentration as a function of the evaluation time and stated that the dilution effect, which occurs when an increase in the dry mass causes a decrease in the concentration of the nutrients in the plant, occurred.This effect was observed in the control treatment and in the absence of liming (Table 1).Triple phosphate produced higher nitrogen concentrations in the shoots Table 1.Nitrogen concentration in the shoot of pigeon pea when fertilized with phosphorus sources and liming and nitrogen concentration in the root of pigeon pea when fertilized with phosphorus sources and liming.

Phosphate fertilizer
Triple Means followed by the same letter within a first line compare the fertilization and do not differ by Tukey's test at a 5% probability.Means followed by the same letter within a second line compare the liming and do not differ by Tukey's test at a 5% probability.and roots of pigeon pea but, however, equaled those produced by the rock phosphate Bayóvar in the roots.The roots of pigeon pea, being closer to the supply source, absorbed phosphorus from the rock phosphate Bayóvar at triple the amount from superphosphate, a source of greater solubility.
Bonfim-Silva and Monteiro (2010) evaluated the concentration of nitrogen and sulfur in the roots of Brachiaria, similar to most of the research on forage plants, emphasizing the development of the shoots, leaving the roots as a "hidden" component and not addressing the interdependence between these parts of the plant.
For green manure, the root characteristics serve as parameters for the selection of suitable species because a vigorous root system can explore and absorb nutrients from deeper soil layers, making these nutrients available to the successor cultures.Therefore, studies that address the nutritional characteristics of the root system of pigeon pea are of great importance, especially with regard to the correct practice of green manuring.
For the contents of chlorophyll in the leaves of pigeon pea, significant effects were found for fertilization and liming.The effect rock phosphate tripled that of superphosphate, promoting the chlorophyll index, as well as in the presence of lime (Table 2).
The sources of phosphate fertilizer triple superphosphate and rock phosphate were equal and allowed the highest phosphorus uptake by pigeon pea, promoting a greater concentration of nitrogen in the leaves, reflecting the results of the chlorophyll index analysis and corroborating the results in the concentrations of nitrogen in the aerial parts of pigeon pea (Table 1).Means followed by the same letter within a line compare the fertilization within the liming interaction and do not differ by Tukey's test at a 5% probability.Means followed by the same uppercase letter within a column compare the liming and fertilization interaction and do not differ by Tukey's test at a 5% probability.
Bonfim-Silva et al. ( 2012), in a study with doses of Bayóvar rock phosphate in Cerrado Oxisol, observed a chlorophyll index of 48.4 in Crotalaria juncea plants, higher than that in this study.
There was an interaction between phosphorus fertilization and liming for the phosphorus concentrations of the shoots and roots of pigeon pea (Table 3).Due to the dilution effect, lower concentrations of phosphorus in the shoots and roots were observed when plants were subjected to treatments with triple superphosphate and rock phosphate, regardless of setting.
Therefore, there was no significant difference in liming when rock phosphate was used, but the response of the crop to accumulate phosphorus in the tissues was positively influenced by liming when triple superphosphate was used as a source.It is most likely that in these treatments the plants were able to absorb and metabolize necessary phosphorus loads faster due to the higher solubility of the source and the possibility of the non-existence of a root system hampered by the presence of aluminum.
Due to the concentration effect, higher concentrations of phosphorus in the shoots and roots of pigeon pea were observed when submitted to the control treatment, regardless of setting.This result, which was also observed by Fernandes et al. (2007), in which the plants retained a greater amount of phosphorus in the roots under conditions of low nutrient supply, maintained the root growth at the expense of shoots.According to these authors, one explanation for this result is that the roots, being closer to the supply source, use the limited influence of this nutrient for maintenance and growth.Fernandes et al. (2007) studied the velvet bean, Mucuna cochinchinensis and jack bean observed that the phosphorus content in plants increased with increasing doses of phosphorus and lime, with the most significant effect being the interaction between the factors, suggesting that the good performance of these species as accumulators and the later recycling of nutrients depend on a minimum supply of phosphorus and liming.
The results for the concentration of potassium in the shoots and roots of pigeon pea indicate that the interaction was highly significant among the factors of fertilization and liming (Table 4).
For the shoots, triple superphosphate in the presence of lime resulted in higher concentrations of potassium, along with the treatment without phosphorus fertilization in the absence of liming (Table 4).Because the results of control treatment occurred due to the effect of concentration, as confirmed by the reduced plant growth, the results were inversely proportional to those with triple superphosphate.
In the control treatment, liming decreased the potassium content by approximately 7 g kg -1 when compared with the absence of liming.According Vilela et al. (2004), the influence of liming on increasing the availability of potassium is related to the increased soil cation exchange capacity, providing more exchange sites for retention, reducing leaching and promoting a greater uptake of potassium by the plants.The results of this study demonstrate the importance of the practice of liming on soils with low phosphorus availability.Ernani et al. (2000) found that the response to lime decreased with the increase of phosphorus fertilization.Thus, the observed results are close to those of these authors; in the control treatment, there was an increased response to liming, demonstrating the importance of a proper relationship, which may result in an economy of limestone in the soils with a high content of available phosphorus and phosphorus in soils having high pH, being particularly important for the plant species in which nutrition is a high percentage of the total production cost.
For triple superphosphate, there was no significant difference for liming, but for rock phosphate in the absence of liming, there were high concentrations of potassium in the shoots of pigeon pea.
Rock phosphates are derived simply by grinding phosphate rock, may or may not pass physical processes Means followed by the same letter within a line compare the fertilization within the liming interaction and do not differ by Tukey's test at a 5% probability.Means followed by the same uppercase letter within a column compare the liming and fertilization interaction and do not differ by Tukey's test at a 5% probability.
Table 5. Calcium concentration in the shoots of pigeon pea when fertilized with phosphorus sources and liming and calcium concentration in the roots of pigeon pea when fertilized with phosphorus sources and liming.Means followed by the same letter within a first line compare the liming and do not differ by Tukey's test at a 5% probability.Means followed by the same letter within a first line compare the fertilization and do not differ by Tukey's test at a 5% probability.Means followed by the same letter within a second line compare the liming and do not differ by Tukey's test at a 5% probability.

Calagem
of concentration (Kaminski and Peruzzo, 1997) and do not suffer any chemical treatment (sulfuric acid).Soil acidity favors the solubilization of phosphate, making it available for use by the plants.Thus, the increased absorption of potassium by pigeon pea may provide a greater availability of this nutrient in the soil by the decomposition of biomass, allowing the recycling of this nutrient.Richart et al. (2006) observed an increase in the foliar phosphorus concentration as a function of the dose of elemental sulfur and sulfur attributed to the influence of the reduction of the soil pH, favoring the solubility of rock phosphate.
The concentration of potassium in the roots of pigeon pea (Table 4), with higher concentrations of triple superphosphate and rock phosphate in the presence of lime and in control treatment in the absence of liming, was measured.The sources also equaled the absence of liming.According to Bedin et al. (2003), a greater reactivity of phosphates, being more readily available, would favor the absorption and utilization of nutrients, mainly for short cycle crops.Sorato and Crusciol (2007) observed that liming increased the concentrations of potassium in the shoots and that, among the cations available to the soil after application, potassium is the most soluble in the extracts of plant residues.
For the calcium concentrations, there was a significant effect of isolated liming on the shoot, isolated to the fertilization and liming of the roots of pigeon pea (Table 5).There were higher concentrations of calcium in the shoots in the presence of lime and in the roots with rock phosphate in the presence of lime.In addition to the benefit of phosphorus, the available phosphate rock Bayóvar provides calcium as a companion nutrient, directly influencing the development of the roots and stimulating microbial activity and the absorption of other nutrients, in addition to being required in large quantities by N 2 -fixing bacteria.Teixeira et al. (2005) evaluated the concentrations of nutrients in millet, jack bean and pigeon pea and observed that legumes had higher calcium concentrations.This fact is of great importance as it evidences the efficiency of legumes, such as pigeon pea, as recyclers of nutrients.
More efficient species in the uptake, translocation and utilization of nutrients may be more interesting for use in the management of soils with low fertility, which present a higher adaptability and better performance (Caldeira et al., 2002).
Significant effects were isolated to fertilization and liming for magnesium concentrations in the shoots and roots of pigeon pea, respectively (Table 6).
High concentrations of magnesium occurred in the shoots in the control treatment due to the effect of concentration and the presence of lime (Table 6).In the roots, the effects of triple superphosphate and rock phosphate were equal, providing higher magnesium concentrations in the roots, along with the treatment in the presence of lime (Table 6).
Teixeira and Malta (2012) observed magnesium concentrations of 2.80 and 1.60 g kg -1 for jack bean and Crotalaria juncea, respectively.Oliveira (2004) reported that the adequate magnesium concentration ranges from 2.0 to 5.0 g kg -1 for pigeon pea and that these values were observed in treatments with lime, demonstrating the importance of the practice of liming, being the form most recommended and efficient in providing the soil magnesium for plant uptake, although the authors used dwarf cultivars.However, the rate of release of nutrients from the crop residues during the process of decomposition depends on the characteristics of the species, in particular the carbon/nitrogen ratio and the location and manner in which these nutrients are found in plant tissue (Giacomini et al., 2003).
Magnesium exerts important functions in the aerial part of the structure of the chlorophyll molecule, in addition also being a cofactor of ATP hydrolysis, providing energy for nitrogen fixation (Malavolta et al., 1997).
The treatments affected the sulfur concentrations of pigeon pea.A significant interaction was detected in the fertilization and liming of the shoots (p<0.0001) and roots of pigeon pea (Table 7).
In bean shoots, high concentrations of sulfur with rock phosphate in the presence of lime and in the treatment without phosphorus fertilization in the absence of liming (Table 7) were observed.In the roots, triple superphosphate in the presence of lime and rock phosphate and the control treatment in the absence of liming were statistically equal and promoted higher concentrations of sulfur (Table 7), providing the roots of a higher sulfur concentration a high concentration of sulfur in the aerial parts of pigeon pea.
However, the appropriate concentration of sulfur for pigeon pea is 1.5 to 3.0 g kg -1 (Oliveira, 2004).Therefore, the results of this study are less than adequate for culture.

Conclusions
In general, the concentrations of nutrients and pigeon

Table 2 .
Chlorophyll index in the leaves of pigeon pea when fertilized with phosphorus sources and liming.
a Means followed by the same letter within a first line compare the fertilization and do not differ by Tukey's test at a 5% probability.Means followed by the same letter within a second line compare the liming and do not differ by Tukey's test at a 5% probability.

Table 3 .
Phosphorus concentration in the shoots of pigeon pea when fertilized with phosphorus sources and liming and phosphorus concentration in the roots of pigeon pea when fertilized with phosphorus sources and liming.

Table 4 .
Potassium concentration in the shoots of pigeon pea when fertilized with phosphorus sources and liming and potassium concentrations in roots of pigeon pea when fertilized with phosphorus sources and liming.

Table 6 .
Magnesium concentrations in the shoots of pigeon pea when fertilized with phosphorus sources and liming and magnesium concentrations in the roots of pigeon pea when fertilized with phosphorus sources and liming.Means followed by the same letter within a first line compare the fertilization and do not differ by Tukey's test at a 5% probability.Means followed by the same letter within a second line compare the liming and do not differ by Tukey's test at a 5% probability. b

Table 7 .
Sulfur concentrations in the shoots of pigeon pea when fertilized with phosphorus sources and liming and sulfur concentrations in the roots of pigeon pea when fertilized with phosphorus sources and liming.Means followed by the same letter within a line compare the fertilization within the liming interaction and do not differ by Tukey's test at a 5% probability.Means followed by the same uppercase letter within a column compare the liming and fertilization interaction and do not differ by Tukey's test at a 5% probability.peachlorophyll index did not differ by fertilization with rock phosphate and triple superphosphate.For the nitrogen concentration in the shoot pigeon pea bean triple superphosphate promotes greater concentration of nutrients in the plant in relation to the rock phosphate.Higher nutrient concentration is observed in the absence of phosphate and lime due to the dilution effect. aA