RESUMO Os extratores de fósforo (P) Mehlich 1 (M-1), Mehlich 3 (M-3) e Resina Trocadora de Ânions (RTA) apresentam sensibilidade ao conteúdo de argila do solo. Ainda, o uso de equações para conversão do P disponível extraído por M-3 em valores equivalentes de M-1 pode não ser adequado para um conjunto de solos contrastantes. O objetivo do trabalho é avaliar a influência do conteúdo de argila na extração de P por M-1, M-3 e RTA, bem como avaliar a efetividade de utilização de equações para conversão dos teores por M-3 em valores equivalentes de M-1. Foram selecionadas 301 amostras de solo no laboratório de rotina do CAV/UDESC, distribuídos em quatro classes de argila: 0-20, 21-40, 41-60 e > 60% de argila. As amostras foram preparadas e foi extraído o P disponível por M-1, M-3 e RTA. Os extratores M-3 e RTA extraíram quantidades de P 12 e 11% superiores ao M-1, respectivamente. M-1 extraiu menos P que M-3 e RTA em solos de textura arenosa e extraiu mais P que os demais extratores em solos de textura argilosa. A equação sugerida pela CQFS - RS/SC (2016) para conversão dos teores de M-3 para equivalentes em M-1 subestimou os valores de P em até 24%. Com isso, alternativamente, se propõe a utilização da equação P-M1eq (mg dm-3) = (P-M3 / (1,38-0,01*Arg)). Os métodos avaliados apresentam sensibilidade ao teor de argila do solo, devendo ser realizada a classificação da disponibilidade P por faixas de textura.

Changes in soil physical properties due to different management systems occur slowly, and long-term studies are needed to assess soil quality. The objectives of this study were to evaluate the effects of soil management systems and liming methods on the physical properties of a Latossolo Bruno Alumínico típico (Hapludox). A long-term experiment that began in 1978 with conventional and no-tillage systems was assessed. In addition, different liming methods (no lime, incorporated lime, and lime on the soil surface) have been applied since 1987 and were also evaluated in this study. Moreover, an area of native forest was evaluated and considered a reference for the natural condition of the soil. Soil physical properties were evaluated in layers to a depth of 1.00 m. Compared to native forest, the conventional tillage and no-tillage systems had higher soil bulk density, penetration resistance, and microporosity, and lower aggregate stability and macroporosity. Compared to the conventional tillage system, long-term no-tillage improved the structure of the Hapludox, as evidenced by increased microporosity and aggregate stability, especially in the soil surface layer. In no-tillage with lime applications sporadically incorporated, soil physical properties did not differ from no-tillage without lime and with lime applied on the soil surface, indicating that this practice maintains the physical quality of soil under no-tillage. Liming in a conventional tillage system improved soil aggregation and reduces penetration resistance in the soil layers near the soil surface. No-tillage was the main practice related to improvement of soil physical quality, and liming methods did not influence soil physical properties in this soil management system.

Cultivated soils, when submitted to agricultural practices, tend to compact due to the pressure exerted by agricultural machines and implements, a process that compromises soil quality and system sustainability. Specific properties of each soil, such as particle size and organic matter content, interfere with the process and degree of compaction and, consequently, plant growth. This study aimed to analyze the effect of different degrees of compaction (DC) on soil physical properties and black oat (Avena strigosa Schreb) growth. For this purpose, four soils were collected: Latossolo Vermelho distrófico retrático (Ferralsol LV CN), Cambissolo Húmico alumínico típico (Cambisol CH LG), Nitossolo Bruno distrófico típico (Nitisol NB PA), and Nitossolo Bruno distrófico húmico (Nitisol NB SJ). They were submitted to five degrees of compaction (bulk densities corresponding to 80, 85, 90, 95, and 100 % DC), defined by their relation to the maximum density obtained by the Normal Proctor Test. For each DC, porosity, soil water retention curve, penetration resistance, hydraulic conductivity, and aeration capacity were determined. In a greenhouse, the oats were cultivated in the four soils with five different degrees of compaction. The experiment was carried out in a completely randomized design, factorial scheme, and five replications. Crop measurements included the growth rate, shoot dry matter, and forage quality analysis. Soil compaction changed the physical properties of soils. In all tested soils, macroporosity and total porosity decreased, more intensely at LV CN. It had macroporosity below the critical level (0.10 m 3 m-3) from DC 85. Hydraulic conductivity also decreased in all soils, which is evidence of significant environmental degradation from DC 90 onwards. Microporosity increased in the four soils due to compaction effect, and it is one of the reasons why permanent wilting point has increased. It resulted in a problem at NB SJ , mainly because it reduced the available water volume at DC 90, 95, and 100. Penetration resistance has also increased from DC 80 to 100 at all soils, exceeding the limit of 2 MPa in DC 80 for NB SJ , DC 85 for NB PA and LV CN , and DC 95 for CH LG , representing a risk to root development. Regarding black oat crop, there was a reduction in shoot dry matter only in Cambisol and in the higher DC, fiber content keeps within a satisfactory amount, without affecting forage quality in all soils and DC, thus showing that black oat is tolerant to compaction.

In Brazil extensive areas are covered with pine forests, planted for pulp and paper production. This industry generates solid alkaline waste, such as dregs. The application of this dregs to forest soils is an alternative for soil acidity correction and plant nutrient supply, as well as a solution for its proper disposal. The purpose of this study was to compare the residual effect of surface application of dregs and dolomitic lime on (a) changes in the physical and chemical properties of an acidic soil and (b) pine tree development. The experiment was carried out in 2004 in Bocaina do Sul, Santa Catarina, consisting of the application of increasing dreg and lime rates to a Pinus taeda L. production area, on a Humic Cambisol, in a randomized block design with four replications and 10 x 10 m plots. The treatments consisted of levels of soil acidity amendments corresponding to the recommendations by the SMP method to reach pH 5.5 in the 0-20 cm layer, as follows: no soil amendment; dregs at 5.08 (1/4 SMP), 10.15 (1/2 SMP) and 20.3 Mg ha-1 (1 SMP); and lime at 8.35 (1/2 SMP) and 16.7 Mg ha-1 (1 SMP). Soil layers were sampled in 2010 for analyses of soil chemical and physical properties. The diameter at breast height of the 6.5 year old pine trees was also evaluated. Surface application of dregs improved soil chemical fertility by reducing acidity and increasing base saturation, similar to liming, especially in surface layers. Dregs, comparable to lime, reduced the degree of clay flocculation, but did not affect the soil physical quality. There was no effect of the amendments on increase in pine tree diameter. Thus, the alternative to raise the pH in forest soils to 5.5 with dregs is promising for the forestry sector with a view to dispose of the waste and increase soil fertility.

Agricultura. 2. Ciências ambientais. 3. Pesquisa agrária -Brasil. 4. Tecnologia sustentável. I. Santos, Carlos Antônio dos. CDD 630 Elaborado por Maurício Amormino Júnior -CRB6/2422 DOI O conteúdo dos artigos e seus dados em sua forma, correção e confiabilidade são de responsabilidade exclusiva dos autores. 2019 Permitido o download da obra e o compartilhamento desde que sejam atribuídos créditos aos autores, mas sem a possibilidade de alterá-la de nenhuma forma ou utilizá-la para fins comerciais.