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ABSTRACT Various attributes are often required to build soil quality indicators. However, determining these attributes is time-consuming and requires several specific devices. Thus, it is desirable to develop indexes that express soil quality based on easily determined attributes. The objective of this study was to investigate the spatial variability of the S index and its correlation with other physical and chemical soil attributes to generate a pedotransfer function for estimating the S index. A georeferenced sampling mesh covering 1.4 ha and employing 71 points was installed. The soil samples were collected in 0.00–0.15 m and 0.15–0.30 m deep layers to determine the physical and chemical attributes. The results indicated that the S index was correlated with porosity, carbon stocks, cation exchange capacity, and particle size fractions. However, macroporosity, microporosity, and sand content were the most suitable attributes for the construction of pedotransfer functions. A principal component analysis indicated that the S index was representative of 9.4% and 11.5% of the total variability in the dataset in the respective soil layers. Spherical semivariogram models showed that the S index was spatially dependent and ranged between 84–188 m. The S index maps estimated by the pedotransfer function resemble the observed S values; therefore, the function can be applied in spatial variability studies.

ABSTRACT The least limiting water range (LLWR) is a soil physical quality indicator that receives much attention. It has been criticized and put to the test regarding mathematical models that compose it since they describe the behavior of soil physical attributes in a simplified way. This study aimed to assess the efficiency of some pedofunctions proposed in the literature and artificial neural networks on the accuracy in predicting soil water retention at potentials equivalent to field capacity (θFC) and permanent wilting point (θPWP). In other words, to apply the best models to LLWR of two soil types (Oxisol and Ultisol) and verify changes in their structure. The results indicated that pedofunctions using sand, silt, clay, bulk density, and soil organic matter contents are more efficient in estimating θFC and θPWP. However, the use of multiple linear regression models to predict θFC values below 0.20 m3 m−3 may present a slight tendency to overestimate it, which is not observed in the neural networks. As in R2, equations from neural networks were more efficient in estimating θFC and θPWP. Pedofunctions used to calculate LLWR differ in the establishment of the critical soil bulk density, exposing the limitations of the model.

ABSTRACT Assess the physical quality of agricultural soils it is important to establish the management more adequate for plant growth. In this study, the soil water retention curve and S index as indicators of soil physical quality were evaluated in five integrated production systems in the following forestry arrangements: Eucalyptus in a single line, double line and triple line (Eucalyptus I, II and III respectively), Balsa in triple line and Teak triple line. The density and arrangement of forest trees influence the soil physical properties. Less soil water retention was observed in the Teak and Balsa wood systems in the layers 0-0.10 and 0.10-0.20 m. The field capacity, permanent wilting point, and available water were lower under the projection from the treetops, providing less soil water retention at this site. This position suffers more influence of the animal's footstep, having greater alterations on the soil structure. Integrated production systems showed poor soil structural quality based on the S index, averaging 0.034 and 0.035 for layers 0-0.10 and 0.10-0.20 m respectively.

O experimento foi realizado em ambiente protegido, com o objetivo de avaliar o efeito do resíduo da mineração de bauxita nos teores de macronutrientes, no solo e em plantas de cana-de-açúcar. Foram utilizados vasos de 10 L que receberam as seguintes doses de resíduo de bauxita: 0; 28;56; 84; 112 e 140 t ha-1, utilizando-se do clone de cana-de-açúcar SP92 4221. A incorporação do resíduo de bauxita no solo proporcionou aumento nos teores dos macronutrientes do solo, sendo que apenas para o enxofre doses acima de 83 t ha-1 proporcionaram reduções desse nutriente. Já para os teores de macronutrientes determinados na folha, doses acima de 70,5; 125; 101 e 56 t ha-1 diminuíram os teores de nitrogênio, fósforo, potássio e enxofre, respectivamente. Entretanto, para o cálcio e o magnésio, a utilização do resíduo proporcionou a diminuição dos seus teores foliares. A dose do resíduo de bauxita que teve a maior produção de massa seca foi de 64 t ha-1.The experiment was carried out in green house with the objective of evaluating the effect of the bauxite mining residue in the rates of macronutrients in sugarcane and soil. Containers of 10 L were used. They received the following rates of bauxite residue: 0; 28; 56; 84; 112 and 140 t ha-1 . The used culture was the sugarcane (SP92 4221). The incorporation of the bauxite residue in the soil provided an increase in the levels of the soil macronutrients, and only for sulphur levels above 83 t ha-1, it was possible to provide reductions of this nutrient. For rates of determined macronutrients in the leaf, levels above 70, 5; 125; 101; 56 t ha -1 diminished the rates of nitrogen, phosphorum, potassium and sulphur, respectively. However, for calcium and magnesium the use of the residue provided the reduction of leaf rates. The level of the bauxite residue which had the largest production of dry mass was 64 t ha-1.

A resistência mecânica do solo à penetração exerce grande influência sobre o desenvolvimento vegetal, uma vez que o crescimento das raízes e a produtividade das culturas variam de forma inversamente proporcional ao seu valor. O objetivo do trabalho foi estudar a variabilidade espacial e a correlação entre a produtividade do milho (PG) e a resistência mecânica do solo à penetração (RP) de um Latossolo Vermelho sob preparo convencional, em área pertencente à Fazenda Experimental de Ensino e Pesquisa da Faculdade de Engenharia - FE/UNESP - Câmpus de Ilha Solteira. Foram definidos 133 pontos de amostragem no campo, segundo malha com espaçamento regular de 10,0 m, nos quais foram medidas a RP, a umidade gravimétrica (UG), nas camadas de 0-0,10; 0,10-0,20; 0,20-0,30 e 0,30-0,40 m, e a PG. O modelo exponencial mostrou-se adequado para descrever todos os semivariogramas experimentais construídos. A RP e a UG apresentaram moderada dependência espacial, com alcance variando entre 20,2 e 63,0 m. A PG apresentou forte dependência espacial com alcance de 15,3 m. A RP não apresentou correlação espacial com a PG. Valores de RP variando entre 0,9 e 2,0 MPa não restringiram a PG.The soil mechanical resistance to penetration shows high influence on vegetal development since the growth of the roots and the crops productivity change in the inversely proportional form with its value. The objective was to study the spatial variability and the correlation between maize yield (GP) and soil mechanical resistance to penetration (PR) of an Oxissol soil under conventional tillage, located at the Experimental Station of the Engineering College - FE/UNESP - Ilha Solteira, São Paulo State, Brazil. It was defined 133 points of sampling in the field, according to a grid with regular intervals of 10.0 m, for the attainment of PR, gravimetric moisture (GM), in the layers of 0-0.10; 0.10-0.20; 0.20-0.30 and 0.30-0.40 m, and the GP. The exponential model showed adequate to describe all the adjusted experimental semivariograms. The PR and GM showed moderate spatial dependence, with range varying between 20.2 to 63.0 m. The GP presented strong spatial dependence with range of 15.3 m. There was not a spatial correlation between PR and GP. Values of PR varying between 0.9 and 2.0 MPa did not limit the GP.