Contribution of the Incorporation of Poultry Litter and Limestone for the Fertility of Sandy Soil in the Brazilian Amazon ()
1. Introduction
The southern region of Rondônia comprises the transition between the Cerrado and the Amazon. In general both have highly weathered soils, deep, low fertility and high acidity [1] . Added to these characteristics there are areas in this region with soils of sandy texture, classified as Quartzipsamments [2] , which, from the agricultural point of view, have problems with the management and conservation of both soils, as well as the local water resources.
The Quartzipsamments of southern Rondônia are formed in geological-environmental domains, predominantly sandstone and have low water and moisture retention capacity as well as retention, fixation and assimilation of nutrients and OM (organic matter). They are lands mechanized in flatter areas and are able to be agricultured, by applying limestone and fertilizer; however, they may respond poorly to fertilization and lose water quickly when the rains cease [3] . These aspects give these soils low productive capacity under natural conditions; one should therefore adopt practices that increase their quality and productivity of the system.
The sandy soils have low natural fertility, frequent presence of Al (aluminum) in toxic form and low OM content. The OM is responsible for most of the CEC (cation exchange capacity) in these soils. Therefore, generally recommended the practice of liming, which aims to eliminate soil acidity and provide a supply of calcium and magnesium for plants, followed by the fertilization of nitrogen, phosphorus and potassium. However, due to the low CEC and high capacity for water infiltration, the leaching of these nutrients can be high, especially N (nitrogen) and K (potassium). P (phosphorus) can also be lost in large quantities, especially when conditions are favorable to the erosion process, but also by the process of leaching of this nutrient because sandy soils have low P adsorption capacity, and the application of fertilizers rich in P, the fast sorption sites are saturated by increasing its availability and its ability to losses to the environment [4] .
In this context, to increase the fertility of sandy soils they aren’t enough, being the practices of isolated liming and fertilization even risky. Therefore, one should highlight the important role of OM in the soil that among the numerous advantages, it can be shown the retention and availability of nutrients, elevated CEC and the stabilization of soil moisture, avoiding the heat exchanges harmful to the system roots of plants. Thus, the proper functioning of the soil does not occur without a fairly significant amount of organic matter, mainly in the tropics where soils are subject to higher rates of mineralization when compared to temperate regions.
The OM stands out as a key factor for the elevation and/or maintenance of soil quality [5] . The OM has the ability to hold two to three times their volume in water, which in turn, will be supplied to plants and to the fauna in the soil, as well as maintain its temperature under conditions suitable for life. In addition to the nutrients found in the organic fertilizer, plants can absorb large amounts of organic molecules such as amino acids, proteins, enzymes, vitamins, and others. These products promote greater vitality and resistance to plants, and results of soil biological activity and decomposition of OM [6] .
The management of OM in cropping systems has increased substantially in Brazil [7] and organic fertilizers have become vital for supplying nutrients to plants. Among the different organic wastes currently used as a source of OM. The poultry litter is a good alternative for improving the physical, chemical and biological soil properties. This occurs because of its physic-chemical characteristics and the expressiveness of the poultry industry in Brazil that produces large amounts of waste, making its application to soil a practical and economical method [4] . However, a waste-based organic fertilization should not be done randomly, because high doses of organic fertilizers with C/N and N/P can result in an unbalanced availability of nutrients [8] and fertilizers rich in P applied to sandy soils may lead to environmental pollution [4] . Therefore, it is necessary to evaluate the effect of doses of organic manure on soil fertility.
The concept of soil fertility, proposed by Liebig in the mid-nineteenth century, is inefficient in several contexts. Soil fertility, conceptually, is the ability of soil to provide nutrients in adequate quantity and proportion to the plants in the absence of toxic elements for their development and productivity. The ineffectiveness of this concept is demonstrated when comparing direct and conventional planting systems [9] .
For sandy soils, it is also extremely dangerous to treat fertility only in the mineral point of view, because nutrient availability within a farm crop in a soil with low buffering capacity may be easy, but keeping these nutrients in a cycle can become much more complex. Thus, it is an interesting strategy to incorporate indicators of fertility, microbiological variables, which act directly on nutrient cycling [10] . Microorganisms can be used as indicators for recovery of soils of different textures and the absence of microbial biomass in sandy soils indicates the irreversible nature of human disturbance [11] .
Besides the management of OM for maintaining the fertility of sandy soils, it is important to work with the concept of the agricultural capability of the land. Because, the lack of land use planning based on its limitations and potential has often caused negative environmental impacts [12] . In this manner, classifying the agricultural capability of the land is as important as knowing the soil fertility and recommending the appropriate fertilizer for the plant and soil. The Quartzipsamments have low agricultural potential. However, after 1970, these soils were incorporated into the agricultural exploration, primarily for the grazing system and subsequently for the grain production [13] .
Given the above, the present study aimed to evaluate the contribution of the incorporation of poultry litter and limestone in the fertility of sandy soils in the Brazilian Amazon, as guidance for further cultivation of Brachiaria pasture.
2. Materials and Methods
The experiment was conducted in municipality of Colorado do Oeste located in the southern region of Rondônia, in the Brazilian Amazon, Line 155, Gleba Corumbiara, Lot 96-A, 28 km (latitude―13˚00'08.43"S and longitude―60˚34'23.82"). The regional climate is classified as Aw (hot and humid tropical with well-defined dry and rainy season) according to Köppen’s Climate Classification with a mean annual rainfall of 2400 mm [14] . The local vegetation was classified as Tropical Savanna (Cerradão tropical subperinifólio) [15] and the soil as Neossolo Quartzarênico Órtico típico [16] , which amounts in soil classes of high-level categorical to Quartzipsamments in the Soil Taxonomy [16] .
The design of the experiment was a completely randomized block design (RBD) in a 4 × 4 × 2 factorial scheme, corresponding to four doses of poultry litter (0, 5, 10 and 15 mg∙ha−1), four times of incorporation (0, 75, 110 and 145 days) in the presence and absence of 2 mg∙ha−1 of limestone, with six replications. Each plot had a size of 3 m2.
Poultry litter had the following attributes: pH 7.01; 251.3 g∙kg−1 organic carbon; 39.8 g∙kg−1 calcium; 10.5 g∙kg−1 Mg; 6.9 g∙kg−1 K; 33.8 g∙kg−1 C and 31.2 g∙kg−1 P.
The incorporation of the different doses of poultry litter in a 20 cm deep soil layer occurred in November 2013. As the experiment was installed, the first sampling was held, which consisted at 0 at the time. Once the area was left fallow, sampling was held again at 75, 110 and 145 days after incorporation. In all samples it was collected in each plot three simple random samples in a zigzag pattern for the formation of a composite sample, for the variables to be determined. The time of 75 days was chosen for the limestone reaction and the primary mineralization of the OM.
From these samples, it was determined in laboratories the variables that are consisted of: CaCl2 pH, TOC (total organic carbon), available P and K, Ca (calcium), Mg (magnesium), H (hydrogen) and Al contents; and calculation was used to determine the CEC, the V% (base saturation) and the m% (Al saturation) [17] . The following were determined as microbiological variables: the MBC (carbon from the soil microbial biomass) [18] , BSR (basal soil respiration) [19] , and by calculation, the qMIC (microbial quotient) [20] and quotient qCO2 (metabolic) [19] .
Land suitability classification [21] and fertilizer recommendation for the harvest of Brachiaria was also performed. As there isn’t a manual for recommendations of fertilizers for the state Rondônia, it was used as base the fertilizer recommendation for the State of Acre [22] , which is also in the Amazon biome.
The statistical analysis consisted in checking outliers by the Grubbs test, followed by the Bartlett and Shapiro- Wilk test to test the homogeneity of variances and normality of residuals, respectively. The normal data obtained was analyzed using the ANOVA (analysis of variance) technique. The Tukey’s test, with a probability level of 0.05, was used to determine significant differences between treatment means of the variables that were isolated or double effect interaction. For the variables that showed the effect of the triple interaction the Scott-Knott test was applied. For variables with non-normal distribution of the data a transformation was performed. For P, K, Ca, Mg and MBC the transformation was performed with the equation x =
. For Al, m% and qMIC constructed the data with the equation x = x + 1. qCO2 for the metabolic transformation the equation x = x + 10 was used.
3. Results and Discussion
Regarding the isolated effects of treatment, the dose of 10 mg∙ha−1 of poultry litter increased (p < 0.05) the content of Mg and CEC in the soil, though the latter did not differ (p > 0.05) from the dose of 0. The 5 mg∙ha−1 dose decreased (p < 0.05) the m%. However, pH, K, BMC, qMIC and BSR were not affected (p > 0.05) by different doses of poultry litter incorporated (Table 1). Soil pH and Mg were increased (p < 0.05) at 75 days after incorporation, while the m% decreased (p < 0.05). The content of K only increased (p < 0.05) at 145 days after incorporation. The effective CEC was higher (p < 0.05) at day 0. The BMC increased (p < 0.05) after 110 days of incorporation, while BRS declined (p < 0.05) in the same period (Table 2). The presence of limestone increased (p < 0.05) the pH, the content of Mg and V%, and its absence provided greater (p < 0.05) concentration of K (Table 3).
For P there was a significant interaction between doses of poultry litter applied and its time of incorporation and between the incorporation of doses of poultry litter and the application of 2 mg∙ha−1 of limestone (Table 4). The incorporation of 10 and 15 mg∙ha−1 of poultry litter at 75 days of incorporation was effective (p < 0.05) to raise the level of P to 57.53 and 79.08 mg∙dm−3, respectively, without statistical difference between them. The presence of limestone was superior (p < 0.05) to its absence in the dose of 15 mg∙ha−1 of poultry litter, increasing the P concentration to 54.05 mg∙dm−3 (Table 4).
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Table 1. Means of chemical and microbiological attributes of a Quartzipsamment due to the effect of different doses of poultry litter, obtained in the Brazilian Amazon, 2014.
Means followed by different letters in columns don’t differ significantly from the Tukey test at 5% probability. *mg C-CO2 kg∙soil−1∙h−1.
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Table 2. Means of chemical and microbiological attributes of a Quartzipsamment due to the effect time of incorporation of poultry litter, obtained in the Brazilian Amazon, 2014.
Means followed by different letters in columns don’t differ significantly from the Tukey test at 5% probability. *mg C-CO2 kg∙soil−1∙h−1.
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Table 3. Means of chemical and microbiological attributes of a Quartzipsamment due to the effect of the incorporation of 2 mg∙ha−1 of limestone, obtained in the Brazilian Amazon, RO, 2014.
CV: coefficient of variation. Means followed by different letters in columns differ significantly by the F test at 5% probability. *mg C-CO2 kg∙soil−1∙h−1; **mg C-CO2 g−1∙BMC∙h−1.
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Table 4. Means of phosphorus content (mg∙dm−3) Quartzipsamment due to the effect of the interaction between doses of poultry litter and its time of incorporation, and of the interaction between doses of poultry litter and incorporating 2 mg∙ha−1 limestone, obtained in the Brazilian Amazon, 2014.
Means followed by the same letters, uppercase on the rows and lowercase on the columns, don’t differ significantly from the Tukey test at 5% probability.
The content of Ca, H, Al, V% and qCO2 were influenced by the significant interaction between the doses of poultry litter applied and its time of incorporation (Table 5), being that with the application of 5 mg∙ha−1 of poultry litter followed by 75 days of its incorporation achieved a higher (p < 0.05) content of Ca and V% and lower levels of H and Al. This dose did not differ statistically from 10 and 15 mg∙ha−1. The highest levels of qCO2 were obtained with the application of the smallest doses of poultry litter, 0 and 5 mg∙ha−1, and with the highest time of incorporation, 145 days.
Considering the components of potential soil acidity, Al and H, the incorporation of 5 mg∙ha−1 for a period of 75 days, would be a good alternative to reduce it, and besides, this combination increased the Ca and V% contents (Table 5). The exchangeable aluminum content was reduced to 0.27 cmolc∙dm−3, below the level toxic to most crops 0.30 cmolc∙dm−3 [23] . The addition of organic waste is often related to the decrease of the phytotoxic effects of Al [23] [24] .
The incorporation of 2 mg∙ha−1 of limestone has managed to increase (p < 0.05) the pH, Mg and V% (Table 3), although the latterdid not reach very high levels (22.48%) improved fertility has been achieved. Thus, combining the incorporation of poultry litter with limestone would be an interesting strategy.
The adoption of soil management systems aiming for higher activity of soil microbes and increased OM and soil pH, can reduce P adsorption [25] . These affirmations are corroborated by the results of this work.
The incorporation of limestone combined with 15 mg∙ha−1 of poultry litter was able to raise the level of P to 54.05 mg∙dm−3. Handling this, which could be replaced by the incorporation of 10 and 15 mg∙ha−1 of poultry litter at 75 days of incorporation, which was effective (p < 0.05) to raise the level of P to 57.53 and 79.08 mg∙dm−3, respectively, with no statistical difference between them (Table 4). According to the interpretation of the level of P with relation to clay content, these yields available are considered high [26] . As P is a nutrient that limits crop productivity in many regions of the world, particularly in areas with highly weathered acidic soils [27] these results are of paramount importance for the fertility and productivity of the soil.
The TOC was the only variable influenced by the interaction of the three factors. The best combination was the application of 15 mg∙ha−1 of poultry litter with 75 days of incorporation in the presence of limestone (Table 6).
The significance of the OM on many soil properties is evidenced in the presence of macro and micro-organ- isms whom affect the formation of the aggregates in the soil, because in conjunction with root fungi and filaments, they segregate and exude the mucilage that stick the soil particles, and the smaller aggregates, thus becoming larger aggregates, which makes the soils stable for several years, preventing leaching and erosion from occurring [28] . The application of poultry litter can contribute to soil aggregation in the order of 34% after three years of implementation [29] . The greater stability of aggregates in water and larger size aggregates are desirable
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Table 5. Means of the content of calcium, hydrogen, aluminum (cmolc∙dm−3), base saturation (%) and metabolic quotient (mg C-CO2 g−1∙BMC∙h−1) Quartzipsamment due to the effect of the interaction between doses of poultry litter and its time of incorporation, obtained in the Brazilian Amazon, 2014.
Means followed by different letters, uppercase and lowercase lines in columns, differ significantly by the Tukey test at 5% probability.
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Table 6. Means content of total organic carbon (g∙kg−1) Quartzipsamments due to the effect of the interaction between doses of poultry litter, its incorporation time and presence and absence of 2 mg∙ha−1 of limestone, obtained in the Brazilian Amazon, 2014.
Means followed by different letters, uppercase and lowercase lines in columns, differ significantly by the Scott-Knotttest at 5% probability.
properties in cultivated soils, since they are directly linked to erosion. Thus, besides being a source of nutrients, OM protects the soil against erosion.
The nutrient cycling is fully linked to the quantity of microorganisms present in the soil, and these, the quantity and quality of OM. BMC is the living soil fraction consisting of bacteria, fungi, actinomycetes, algae and protozoa. The BMC can be used as a biological indicator, or as an index of sustainability adequacy for a production [20] system. The qMIC indicates the availability of TOC for microbial biomass [30] . The soil microbiota acts in the process of decomposition of OM, participating directly in the biogeochemical cycling of nutrients, thereby mediating its availability in the soil [10] . Thus, raising the level of nutrients available to plants without increasing microbial biomass tends to the rapid loss of fertility and the unsustainability of cultivation.
There was no effect (p > 0.05) of increased doses of poultry litter in content BMC and qMIC (Table 1), only the time of incorporation (Table 2). This is probably due to the effect of the soil texture on soil microbial biomass, which shows to be more significant than planted vegetables substrates [30] . Therefore, the same could be true for increasing the amount of organic waste. Considering that the studied soil is sandy, the increased microbial biomass, corresponds to the greater nutrient cycling and reduced losses of soil/plant system, these results demonstrate that the added nutrients by the poultry litter will be cycled through the microbial biomass. Increases in BMC is 28% higher with the application of poultry litter when compared to fertilization with urea were obtained on a clay soil [31] . Increased BMC is usually accompanied by a decrease in metabolic activity [32] , represented by BSR (Table 2), which was found by [10] and also in this work.
Where as increasing doses of poultry litter did not decrease the level of any component of fertility (Table 1), and that the incorporation of 10 and 15 mg∙ha−1 increased the P content without differing statistically from each other at 75 days incorporation (Table 4), and that 15 mg∙ha−1 increased the amount of TOC (Table 6) also after 75 days of incorporation, it is recommended the application of the highest dose, since it is not logistically impracticable, because its cost is low and its benefits go beyond soil fertility.
The time of 75 days of incorporation was effective to raise the pH, Mg (Table 2), P (Table 4) Ca and V% (Table 5), demonstrating the rapid mineralization effect of OM in tropical environments. Studies with less time of incorporation are needed to recommend the planting of crops before that period. Because in the beginning of decomposition of the OM there can be acidification of soil and immobilization of the nutrients, with productivity losses for the implanted harvest.
The presence of limestone did not demonstrate impressive results in fertility, but increased pH, Mg and V% (Table 3), and still had significant interaction with P availability (Table 4), being so that it is recommended its implementation. With surface application of limestone, similar results were obtained only after 18 months of application [33] .
In the area being studied Brachiaria brizantha cv. Marandu cultivated. No evaluation was made of the effect of treatments on the cultivate of Brachiaria, just the grazing was eliminated and after application of poultry litter and limestone the area was left fallow. However in possession of the results regarding soil fertility and based on the recommendation for the formation of new pasture for the State of Acre [22] , inferences about the culture can be made.
The fertility requirement of the forage is considered average and the recommended bases saturation is 40%. With the incorporation of 15 mg∙ha−1 of poultry litter for 75 days V% was elevated to 32.61% (Table 5), close to the recommended level. As the P concentration was increased to the range of high availability, it would require the application of only 10 kg∙ha−1 of P2O5. However, considering the very poultry litter as a source of input P, P fertilization would not be necessary. It is recommended the application of nitrogen and potassium in pasture establishment [22] .
The undesirability of phosphate fertilizers is due to concerns about the rising level of available P levels that cause environmental impacts. With the incorporation of poultry litter in sandy soils under grassland, weak bonds with the surface of the P microaggregates are formed, which can be easily lost by leaching occurrences, as well as the erosion losses that inorganic P and labile organic P linked to these microaggregates suffer [34] . All these forms can reach the water. Leaching and P loss of fertilizers applied to the soil may exceed the water extractable from source material amounts, because of organic P mineralization and competitive adsorption of the dissolved organic carbon [35] . The high loss of P occurs due to low binding energy of sandy soils, organic C increased and decreased exchangeable aluminum, so high application rates of poultry litter, or continuous applications can lead to desorption of P and percolation of the same, being that the tillage system allows longer applications than the conventional ones [4] .
According to the recommendation of fertilization [22] and the results of this study for Quartzipsamment the application of 15 mg∙ha−1, combined 2 mg∙ha−1 of limestone with incorporation of 75 days provides conditions for the establishment of a new pasture formed with the Brachiaria brizantha species. However, for the maintenance of fertilization from poultry litter or other sources new experiments must be conducted. With respect to nitrogen, for example, it is known that both broiler freshly applied as residual contribute to the supply of this element in grasses [36] . Therefore it is likely that doses of poultry litter can be reduced over time.
For the land suitability classification [21] it must be taken into account the agricultural practices adopted by farmers in order to diagnose the behavior of land in different technological levels. Thus, the studied soil was inserted in the land suitability classification, as the management level B (undeveloped), and group 4 subgroup P (land belonging to the class of good agricultural potential for planted pasture). Therefore, it is noticed that the use of the property is appropriate for its class agricultural capability, being able to improve soil fertility through the application of poultry litter and limestone.
4. Conclusion
The incorporation of 15 mg∙ha−1 of poultry litter combined with 2 mg∙ha−1 of limestone for 75 days of incorporation raises various components of fertility for Quartzipsamment, mainly being the available phosphorus. This management allows deployment of the cultivation of Brachiaria brizantha cv. Marandu replacing the fertilization formation. In sandy soils the concern about soil fertility is its lifting and handling, with the microbial biomass rising after 110 days of incorporation of the treatments, favorable conditions occur for nutrient cycling. However, the results correspond only to the first year of implementation in pasture fertilization.
Acknowledgements
Financial support from Federal Institute of Rondônia is highly acknowledged and appreciated.
NOTES
*Corresponding author.