ABSTRACT Conservation management practices with minimum soil mobilization, maintenance of amounts of straw in the soil, and chiseling of ratoons interrows can be beneficial to soil quality, nutrition and sugarcane yield; however, the combination of these practices and their influence over the culture cycle should be better understood. This study aimed to assess the effects of levels of remaining straw and chiseling in the cultivation of ratoons on soil fertility, nutritional status and yield of stalks and sugar in one sugarcane cycle (five ratoons), under no-tillage and conventional tillage systems. The study was performed in Dourados municipality, Mato Grosso do Sul, Brazil, in areas with a Oxisol (Latossolo) with very clayey texture. Design in randomized blocks was adopted, with four repetitions, in a subdivided portions scheme. Portions were composed of levels of remaining straw (0, 50 and 100 %), annually, and collected alternately in odd years (0I) and even years (0P) established after the plant harvest; sub-portions were composed of systems with and without chiseling. In the fourth ratoon, leaf diagnosis was made with quantification of macro-nutrient contents, and during the fifth ratoon soil samples were collected for chemical analyses. By the end of the cycle, accumulated yields of stalks and sugar were determined. In both management systems, keeping 100 % of straw improved soil fertility and kept higher yield levels in one sugarcane cultivation cycle, while chiseling did not influence soil fertility, nutrition and sugarcane yield. The use of no-tillage farming for sugarcane cultivation proved to be feasible in corrected environments, and did not reduce stalk and sugarcane yield. Straw removal influenced nutrient leaf contents, regardless of soil management.

ABSTRACT The Least Limiting Water Range (LLWR) is an indicator of soil physical quality, contributing in information to propose soil management systems in agricultural farming process. This work aimed to assess the usage of LLWR and critical soil bulk density for physical-water quality evaluations, as well as its effect on sugarcane farming under no-tillage and reduced-tillage, in Oxisol. Undisturbed soil samples were collected in 0.00-0.10 and 0.10-0.20 m soil layers, to determine the following attributes: soil bulk density, soil penetration resistance (PR), volumetric water content at field capacity and permanent wilting point and minimum aeration porosity. The LLWR proved to be a good soil physical water quality indicator in sugarcane farming under conservation tillage system. No-tillage presented a greater range of the LLWR when compared to the reduced-tillage, regardless to the PR value adopted as restrictive for sugarcane roots development, increasing the yield of stalks and sugars contents. The critical soil bulk density under no-tillage is between 1.48 and 1.53 Mg m-3 at the RP of 2 and 4 MPa, while under reduced-tillage it is between 1.44 and 1.51 Mg m-3.

ABSTRACT This study aims to evaluate the growth and yield of the sugarcane plant cultivars, and their correlation to soil mechanical penetration resistance in a Dystroferric Red Oxisol submitted to reduced tillage and, no-tillage systems. Eight sugarcane plant cultivars (RB965902, RB985476, RB966928, RB855156, RB975201, RB975242, RB036066 and RB855536) were in each soil preparation system, and the trial was conducted in a completely randomized design and eight treatments and four replications. The trial evaluated: number of tillers per meter, stalks height and diameter, and stalks yield and sugar content. Additionally, were evaluated the soil mechanical penetration resistance (PR) and soil moisture. The highest rates of daily elongation, yield of stalks and sugar content were observed under no - tillage, due to the lower soil mechanical penetration resistance and higher soil moisture. The cultivar RB966928 presented higher values for growth, yield of stalks and sugar content, while RB855536 and the medium to late maturity cultivars RB975201, RB975242, RB036066, which had either a lower stalk growth rate or presented lower number at the end of the cycle in both soil tillage.

RESUMO A compactação do solo é uma das principais causas de perdas de produtividade em culturas forrageiras, especialmente àquelas destinadas à produção de silagem, devido ao intenso tráfego de máquinas nas operações de semeadura, manejo e colheita. A escarificação do solo poderia ser uma alternativa para contornar o problema. Assim, objetivou-se avaliar os efeitos da escarificação mecânica nos atributos físicos de um Argissolo Amarelo, bem como os componentes agronômicos do capim elefante, cultivado em área com intenso tráfego de máquinas. O trabalho foi conduzido no Campus de Ciências Agrárias - UNIVASF, Petrolina, PE, no Submédio do Rio São Francisco, em blocos ao acaso, com quatro repetições; constituídos por profundidades de escarificação: ESC 0 - sem escarificação, ESC 15 - escarificação de 0,00 a 0,15 m e ESC 30 - escarificação de 0,00 a 0,30 m. Avaliaram-se os atributos físicos do solo antes e após a escarificação, sendo: densidade do solo, porosidade total e resistência do solo à penetração; e os componentes agronômicos do capim elefante: altura de planta e produção de biomassa. A densidade do solo, a porosidade total e a resistência do solo à penetração, bem como a produção de biomassa não foram influenciadas pela profundidade de escarificação, provavelmente pela textura arenosa do solo. A resistência do solo à penetração mostrou ser o atributo mais sensível para identificação da compactação e do efeito da escarificação mecânica. Não se verificaram alterações nas propriedades físicas do solo, densidade e porosidade total do solo, para os tratamentos sem escarificação, escarificação de 0,00 a 0,15 m e escarificação de 0,00 a 0,30 m. As profundidades de escarificação do solo não afetaram os componentes agronômicos do capim elefante.

ABSTRACT Soil compaction is one of the major causes of yield losses in forage crops, especially those for the production of silage, due to heavy machinery traffic in seeding, management and harvesting operations. The soil chiseling could be an alternative to solve the problem. Thus, this work aimed to evaluate the effects of mechanical chiseling on the physical attributes in a Yellow Argisoil, and agronomic characteristics of elephant grass grown, in area with intensive traffic of machines. The experiment was conducted at the Campus of Agricultural Sciences - UNIVASF in the Submedium of the São Francisco River, in randomized blocks design with four replications; consisting of three depths chiseling: ESC 0 - without chiseling, ESC 15 - chiseling 0.00 to 0.15 m and ESC 30 - chiseling 0.00 to 0.30 m. It was evaluated the physical attributes of the soil before and after chiseling scarification, and soil bulk density, porosity and penetration resistance; and agronomical components of elephant grass: plant height and biomass production. The bulk density, porosity and resistance to penetration as well as biomass production were not affected by the depth of chiseling, due to the sand soil texture. The mechanical resistance to penetration proved to be the most sensitive attribute to identify the compacting and the effect of mechanical chiseling. It was not observed change in the soil physical properties in the treatments with chiseling, chiseling in the depth of 0.00 to 0.15 m and 0.00 to 0.30 m. The chiseling depth evaluated not affect the agronomical components of the elephant grass.

RESUMO A conversão de uma condição natural para uma de uso agrícola pode impor mudanças em atributos, propriedades e processos do solo e trazer consequências ambientais para a região de sua abrangência. O objetivo deste trabalho foi avaliar a qualidade física do solo em áreas agrícolas de municípios do entorno do lago de Sobradinho, região semiárida do Estado da Bahia, tendo como ferramenta técnicas estatísticas de análise multivariada. Inicialmente, aplicaram-se as análises estatísticas descritiva e de correlação e o teste de normalidade, que serviram como pressupostos para realizar análise fatorial e estimativa dos escores fatoriais. Com base nesses, determinou-se o índice de qualidade física de solo para as profundidades de 0,00-0,10; 0,10-0,20; e 0,20-0,40 m, respectivamente, cujo principal objetivo foi classificar os solos como bom, regular e ruim, de acordo com o desempenho dos seus atributos físicos. Em seguida, realizou-se a análise discriminante para validação dos índices construídos a partir dos resultados da análise fatorial, bem como conhecer os atributos físicos do solo que influenciam e estão associados à qualidade desse na área agrícola da região. A densidade do solo (Ds), macroporosidade (Ma) e microporosidade (Mi) foram os atributos que se destacaram como indicadores de qualidade, pois apresentaram maior peso relativo nos modelos de discriminação dos sítios amostrados: Ds, Ma e Mi, nas camadas de 0,00-0,10 e 0,10-0,20 m; e Mi e Ds, de 0,20-0,40 m, sugerindo que nas condições estudadas essas variáveis são as principais responsáveis pela qualidade física dos solos. No geral, a qualidade física do solo não foi considerada ideal, fato que pode ser atribuído às práticas de manejo adotadas e, sobretudo, aos baixos teores de matéria orgânica e à textura extremamente arenosa, conferindo fragilidade aos solos da região.

ABSTRACT Conversion of a natural condition to agricultural use can impose changes in soil properties and processes and bring environmental consequences to the region this agricultural use encompasses. The aim of this study was to evaluate the physical quality of the soil in agricultural areas of municipalities around Sobradinho Lake, a semiarid region in the State of Bahia, using multivariate analysis statistical techniques as a tool. Initially, descriptive statistical analysis and correlation analysis techniques and the normality test were applied, which served as prerequisites for performing factor analysis and estimation of factor scores. Based on that, we determined the soil physical quality index for soil depths of 0.00-0.10, 0.10-0.20, and 0.20-0.40 m, the main objective being to classify soils as good, fair, and poor, according to the performance of their physical properties. Discriminant analysis was then carried out with the objective of validating the results obtained from the indices constructed with the results of factor analysis, as well as determining the physical soil properties that influence and are associated with soil quality in the agricultural areas of the region. Soil bulk density (Ds), macroporosity (Ma), and microporosity (Mi) were the properties that stood out as quality indicators, because they showed greater relative weight in the discrimination models of the sites sampled: Ds, Ma, and Mi in the 0.00-0.10 and 0.10-0.20 m layers, and Mi and Ds in the 0.20-0.40 m layer, suggesting that under the conditions studied, these variables are primarily responsible for the physical quality of the soil. Overall, the physical quality of the soil is not considered ideal, which may be attributed to the management practices adopted and, especially, to low levels of organic matter and the extremely sandy texture of the soil, rendering fragility to soils of the region.