CARNAUBA BAGANA IMPROVES THE SOIL QUALITY CULTIVATED WITH CORN IN THE SEMIARID PIAUIENSE 1

The Corn an important role in agriculture, and can be used in both human and animal food, production of ethanol, medicines and glue. However, is verified cultivation practices and soil inappropriate management have led to soil deterioration. Thus, the importance of vegetation cover and the incorporation of organic matter in these cultivated soils. The objective of this work was to evaluate the effect of Carnauba bagana maintained on the soil as mulch and incorporated in macrofauna and soil organic carbon, in the municipality of Itainópolis, in the semi-arid region of Piauí. The areas to be studied will be: corn area with carnauba bagana, as mulch and incorporated into the soil; corn area with uncovered soil and an area of preserved native vegetation. The epigean and edaphic macrofauna will be collected, sorted and identified at the order level. Soil samples will be collected to determine soil organic carbon. Carnauba bagana improved the macrofauna community and soil organic carbon content. The cultivation of corn on uncovered soil reduced the uniformity and diversity of the epigeal macrofauna, the Wealth and Abundance of the edaphic macrofauna and the soil organic carbon content. The variables Larvae, Abundance, Richness, Shannon and Pielou indices, and COS in layers 0.00-0.05 and 0.05-0.10 m were selected for future studies of the impact of maize cultivation in the region.


INTRODUCTION
Corn (Zea Mays L.) belonging to the Gramineae/Poaceae family is a plant native to Mexico (LOPES et al. 2019). This cereal is a source of carbohydrates, fats, proteins, vitamins and minerals, being used in human and animal food, in addition to being feedstock for the production of medicaments and biofuels (LANGNER et al. 2019;USDA 2021).
In the 2022/2023 harvest there was record production of 1.23 billion tons (CONAB 2023).
However, the Northeast region recorded the lowest productivity, with 3785 kg ha -1 , much lower than the national average, which was around 5617 kg ha -1 (CONAB 2023).
This reduction in productivity rates is associated with factors such as climate, characterized by infrequent and low-intensity rainfall, and cultural practices and inadequate soil management, which has led to soil deterioration in this region, resulting in nutritional deficiencies (BIRTHAL et al. 2015;HERNÁNDEZ et al. 2015;BEN et al. 2019).
With this, is verified the importance of using alternative management practices that preserve and/or restore the productive capacity of the soil and the sustainability of production. (OLIVEIRA et al. 2017), such as the increase in organic matter.
Covering and incorporating of soil organic matter provide habitat and food for fauna, preserving and improving the diversity and richness of invertebrates. In addition, it increases infiltration and water retention in soil, improves soil aggregation, reduces erosion and loss of organic matter, and provides nutrients for plants (WU & WANG 2019;LUCERO et al. 2020). However, poorly managed soil negatively impacts in habitat, richness and diversity of soil fauna, which undermines ecosystem services fundamental to soil health and agricultural activity (JIANG et al. 2018;WU & WANG 2019;LUCERO et al. 2020). Among the impaired activities are aeration, aggregation and soil structuring, fragmentation and decomposition of organic matter, cation exchange capacity and nutrient cycling (DOMÍNGUEZ et al. 2018;LUCERO et al. 2020).
In view of this, the use of carnauba bagana to protect the soil and increase organic matter in corn crops in the northeastern semi-arid region can be a promising alternative.
The municipality of Itainópolis in Picos-PI macro-region is a Carnauba producing region, from where the straw, stalk -caule, roots, wood and the dust of its straw are extracted, from which wax is Disciplinarum Scientia. Série: Naturais e Tecnológicas, Santa Maria, v. 24, n. 1, p. 33-46, 2023. 35 produced, a product in which the Brazil is the only exporter (ABRAÃO et al. 2021). This generates a byproduct known as Carnauba bagana. However, most of the time the bagana is discarded in nature, except in some local farmers where is used as mulch and incorporate in soil, usually in the cultivation of corn, commonly produced by family farmers in the region.
In this context, the objective of this study was to evaluate the effect of Carnauba bagana maintained on the soil as mulch and incorporated in macrofauna and soil organic carbon.

LOCATION AND CHARACTERIZATION OF THE STUDY AREA
The work was carried out in the village of Várzea Grande, belonging to the municipality of Itainópolis-PI. The climate, according to the Köppen climate classification, is semiarid, very hot, characterized by scarce and irregular rainfall distribution, with high average temperatures around 30 °C and average anual rainfall of 696,6 mm (MEDEIROS et al. 2020).
For this, three distinct areas were selected, but bordering and with similar topography and texture. Corn area with carnauba bagana (CCB) as mulch and incorporated into the soil; Corn area with uncovered soil (CUS) and an area of preserved native vegetation (PNV), considered as witness.
The data referring to the characterization of the areas are presented in table 1 and figure 1.

SAMPLING OF EDAPHIC MACROFAUNA
For the sampling of edaphic macrofauna, each sampling unit was subdivided into three homogeneous subunits, which represented the study area.

SAMPLING OF SOIL ORGANIC CARBON
In each sampling subunit, 10 simple samples were collected and formed a composite sample, in the 0.00-0.05m and 0.05-0.10 m layers, totaling three composite samples by cultivation area and layer.
After collection, the soil samples were dried, crushed, packed and sent to the laboratory for analysis.

DETERMINATION OF EPIGEAL AND EDAPHIC MACROFAUNA
To determine the invertebrates, the following variables were calculated, according to Odum Shannon diversity index was calculated by the formula: Where, pi = ni/N; ni = abundance of each order, N = total abundance.
Pielou uniformity index was calculated by the formula: Pielou = Shannon/log Richness.

DETERMINATION OF SOIL ORGANIC CARBON
Soil organic carbon was extracted through the oxidation of organic matter by potassium dichromate (K 2 Cr 2 O 7 ) at 0.020 mol L -1 and determined by titration with ferrous ammonium sulphate at 0.005 mol L -1 (YEOMANS & BREMNER 1988).

STATISTICAL ANALYSIS
The data were submitted to analysis of variance using the F test (P≤0.05). Atributes means, when significant, were compared by the Tukey's test at 5% probability. Principal component analysis was also applied, with the aim of selecting the variables most sensitive to the effect of management, correlating the variables with each other and with the areas and management evaluated.

RESULTS AND DISCUSSION
Among the 10 taxonomic groups described, in relation to the epigean macrofauna, the Hymenopteras, Coleopteras and Orthopteras were more representative in the studied systems (Table 2).   Table 2). This was due to the Formicidae family that stood out within the group, possibly by the high adaptation capacity in the different systems (MENEZES et al. 2009). This group stands out among the most important of soil fauna, due to its participation in the decomposition of organic matter and nutrient cycling as well as seed dispersal, soil structuring, predation, among others (BRITO et al. 2016;GUIMARÃES et al. 2021).
The frequency of this group in the CCB was approximately twice the PNV and five times more than in CUS. This can be attributed to the adaptation of this group to the most regulated ecosys-

tems (MARTINS et al. 2017), which shows a trend of good conservation of the
The Orthoptera group was the third most representative, with a relative frequency of 26.35%, 6.35% and 9.09% for the CCB, CUS and PNV systems, respectively ( Table 2). This can be attributed to the ecological importance this order. These organisms are defoliators and make food base of many vertebrates and invertebrates, and therefore contribute directly the incorporation of organic matter in the soil (SANTOS JUNIOR et al. 2021).
There was a significant effect of areas for the Shannon and Pielou indices, while than for abundance and richness there was no significant difference (Table 3). The CCB area obtained the highest Shannon and Pielou indexes, compared to the CUS area, without differing from the PNV (Table 4). This occurred, possibly due to the input of plant material in soil, there was a significant effect of the area with the highest plant input, for the Shannon and Pielou indixes.
As for the relative frequency of taxonomic groups of edaphic macrofauna (Table 5)  CCB: Corn area with carnauba bagana; CUS: Corn area with uncovered soil and PNV: Preserved native vegetation. * Means followed by the same letter in the column do not differ by Tukey test at 5% probability of error. CV -Coefficient of variation.   Santa Maria, v. 24, n. 1, p. 33-46, 2023. 40 In general, the CCB area obtained a greater diversity of taxonomic groups in relation to CUS and PNV (Table 5). All areas studied there was presence of larvae, where the highest occurrences were in CCB (52.05%) and PNV (37,74%). Several invertebrates have a preference for depositing their larvae in environments with a greater accumulation of decomposing plant matter, so that they can develop (ROSA et al. 2015;ARAÚJO et al. 2021), which may explain the above results.
The variables that explained with correlation highest were: Richness, Blattodea, Abundance, Shannon index, SOC 0-5, SOC 5-10, Larva, Pielou index and Coleoptera, with emphasis on Richness, Blattodea, Abundance, Shannon index, SOC 0-5, SOC 5-10, Larva and Pielou index that showed a correlation ≥ 0.9. This indicates these variables are more sensitive to the influence to management used in systems, and can be selected for monitoring in future studies.  Figure 2 shows that all variables were strongly associated with the CCB and PNV areas, and that none of these groups associated with the CUS area. This points to a positive influence of the organic matter present in these areas for these organisms. Environments that favor a greater accumu- In cluster analysis, two distinct groups (G1 and G2) were formed between the systems ( Figure   3). Group 1 was formed by CCB and PNV and group 2 was formed by CUS. This again shows the similarity between the CCB and PNV, a fact that again highlights the importance of vegetation cover and of the input of organic matter. The cultivation of corn on uncovered soil reduced the uniformity and diversity of the epigeal macrofauna, the Wealth and Abundance of the edaphic macrofauna and the soil organic carbon content.