# Root System and Its Relations with Soil Physical and Chemical Attributes in Orange Culture
## 4 Discussion  
Among the attribute selection methods used, the best option for both Utisol and Oxisol was the Wrapper method. This method has been used by several authors and [29] found good performance when comparing it with others, such as correction (CFS) and chi-square (\(\chi^{2}\)), using data mining techniques in their results to predict CO\({}_{2}\) emissions in the soil. [PERSON] et al. [31] also comparing methods of selection of variables, concluded that the most satisfactory was the Wrapper method, resulting in a model with greater general precision and Kappa coefficient in all the algorithms applied in their study. For greater development of citrus trees and higher fruit production, soils should be deep and permeable, with good fertility and have pH values between 5 and 6 [32]. However, when analyzing the decision tree generated for the Utisol area, it was found that pH was the main predictive attribute for orange root volume, in which a value of 4.2 provided high root volume. According to [33], soils with pH below 5 suffered acidification due to the release of metals into the medium such as Al, Fe and Zn derived from the dissolution of clay minerals and oxides. According to the same authors, under these conditions the availability of basic nutrients such as Ca, Mg and K may decrease. However, Cu, Fe, Mn and Zn contents may remain at favorable levels for plant development. The reduction of pH in an area of orange cultivation under Utisol was also observed by [9], comparing it with a native forest area in which the decrease was of 1.66 units presenting a value of about 4.1 after conversion of land use. The authors related the decrease in pH to the application of fertilizers and correctives used in citrus cultivation. In addition to pH, other chemical attributes influenced the prediction of root volume of orange culture such as phosphorus, magnesium and manganese, producing different  
Figure 5: Decision tree resulting from the use of the Wrapper attribute selection method and the J48 algorithm, using a minimum number of objects per sheet equal to four, to predict the growth of orange roots under Oxisol in an experimental area located at Avaré, São Paulo, Brazil. levels of root volume depending on the contents present in the soil. At depths greater than 0.50 m, it was observed that these nutrients, when present in adequate concentrations, provided high root volume to orange plants. According to [34], micronutrient consumption in Brazilian agriculture has increased, allowing a positive balance between input through fertilizers and correctives and output through harvesting, improving soil fertility and promoting increased productivity and, consequently, increased agricultural production. Among micronutrients, citrus fruits require zinc, manganese, boron and iron, and deficiency may limit productivity and fruit quality in Brazil [35]. The response of different cultivars to phosphorus levels depends on the amount of this nutrient present in the soil, which in tropical and subtropical soils can be inherently very low due to the strong interaction with the solid phase restricting nutrient mobility and the root absorption process [35]. Plant adaptation to low availability of phosphorus present in the soil occurs due to more efficient use of the nutrient for biomass production or by means of higher capacity for retention directly from the soil [36]. Absorption capacity is related to differences in root morphology and physiology, which alter the characteristics of nutrient absorption and capacity for efficient phosphorus conversion into biomass between different cultivars, and also to the use of different rootstocks [37]. Soil tillage systems were also determinants for orange root volume, and the triple tillage implement induced high root volume. By comparison, minimum tillage or subsoiler tillage provided medium root volume. The triple tillage implement operates to simultaneously effect furrow fertilization, subsoiling and construction of patches for planting.