Paulo Leonel Libardi

Soil physical quality of a Brazilian Oxisol under two tillage systems using the least limiting water range approach

Abstract Plant growth is directly affected by soil water, soil aeration, and soil resistance to root penetration. The least limiting water range (LLWR) is defined as the range in soil water content within which limitations to plant growth associated with water potential, aeration and soil resistance to root penetration are minimal. The LLWR has not been evaluated in tropical soils. Thus, the objective of the present study was to evaluate the LLWR in a Brazilian clay Oxisol (Typic Hapludox) cropped with maize ( Zea mays L. cv. Cargil 701) under no-tillage and conventional tillage. Ninety-six undisturbed soil samples were obtained from maize rows and between rows and used to determine the water retention curve, the soil resistance curve and bulk density. The results demonstrated that LLWR was higher in conventional tillage than in no-tillage and was negatively correlated with bulk density for values above 1.02xa0gxa0cm −3 . The range of LLWR variation was 0–0.1184xa0cm 3 xa0cm −3 in both systems, with mean values of 0.0785xa0cm 3 xa0cm −3 for no-tillage and 0.0964xa0cm 3 xa0cm −3 for conventional tillage. Soil resistance to root penetration determined the lower limit of LLWR in 89% of the samples in no-tillage and in 46% of the samples in conventional tillage. Additional evaluations of LLWR are needed under different texture and management conditions in tropical soils.

Faixa de umidade menos limitante ao crescimento vegetal e sua relação com a densidade do solo ao longo do perfil de um latossolo roxo

When a soil is managed, its structure is affected, usually increasing the bulk density, decreasing the porosity and modifying the distribution of porous diameter distribution. This investigation was carried out with the objective of evaluating the effect of soil bulk density on water availability to the plants. The experiment was conducted in Guaira (SP), Brazil in an Oxisol (typic Acrorthox). Three adjacent areas under different management systems were selected: no-tillage-non-irrigated, no-tillage-irrigated and natural forest. Undisturbed soil samples were collected at soil depth increments of 0.1m up to 1.0m depth. These samples were submitted to different tensions to determine the water retention and, subsequently the penetration resistance. The least limiting water range concept was used, to calculate the available water, which is based not only on field capacity and permanent wilting point, but also on the limiting resistance to penetration and the limiting aeration porosity. Results indicated that the increase of the soil bulk density up to 1.11Mg m-3, increases the soil water storage and also the available water to the crops; higher values of bulk density decrease the soil water availability.

Parcelamento da adubação nitrogenada na cultura do milho e utilização do N residual pela sucessão aveia preta-milho

Com o objetivo de avaliar a eficiencia de utilizacao do N pela cultura de milho (Zea mays L.), usando-se fertilizante marcado com 15N, aplicado parceladamente (duas formas), e o efeito residual deste fertilizante nas duas culturas subsequentes em sucessao (aveia preta e milho), sob implantacao do sistema plantio direto, foi conduzido um experimento, no sudeste do Brasil, nos anos agricolas 2003/2004 e 2004/2005, sob um solo de textura areno-argilosa (Hapludox). Os tratamentos consistiram da dose de 120kg ha-1 de N, na forma de sulfato de amonio marcado (15N) e dois parcelamentos de N 30-90 e 60-60kg ha-1. Nas plantas de milho e aveia preta, avaliaram-se o N total acumulado, o N proveniente do fertilizante e a recuperacao de N-fertilizante. O incremento da dose de fertilizante nitrogenado aplicado na semeadura (60kg ha-1 de N), no ano agricola 2003/2004, proporcionou aumento no aproveitamento de N pela planta (65%) em relacao ao tratamento que recebeu 30kg ha-1 de N na semeadura (45%).

Formato de cápsula e modo de instalação influenciando determinações do potencial mátrico por tensiômetros

The objective of this work was to determine the measurement accuracy of the soil water matric potential (ψm) by puncture tensiometers with either rounded or pointed porous cups, installed with or without “soil mud”, and to compare the performance of these tensiometers with that of tensiometers equipped with mercury manometers. The experiment was conducted in a Ultisol, in a randomized complete block design, in a factorial arrangement with five replicates. Puncture tensiometers with rounded porous cups, installed with “soil mud”, present more elevated accuracy for ψm determination in a wider measurement range, resembling tensiometers equipped with mercury manometers in drying soil.

Effect of levels and splittings of nitrogen on chemical properties of a Latosol cropped with maize in succession to black oats, under the introduction of the no-tillage system.

The present study evaluated the effect of nitrogen levels and splittings on the chemical characteristics of a soil cropped with maize in succession to black oats at the establishment of the no tillage system. The experiment was carried out in a Red- Yellow Latosol (typic Hapludox), with 14% of clay in the 0-0.20 m soil layer. The work consisted of two maize crops (2003/04 and 2004/05) and a black oats one in between, as cover crop. The experimental design was randomized blocks in an incomplete factorial scheme, with four replications. Treatments consisted of nitrogen levels (60, 120 and 180 kg ha -1 ) and one control without nitrogen, besides the splittings (30 or 60 kg ha -1 at sowing, the balance in cover and 60 kg ha -1 at sowing, remaining top dressed). The following soil variables were evaluated: Ca, Mg, K, organic matter, P, H+Al, Al, sum of bases, CEC, pH and base saturation V(%). Ammonium sulfate fertilization top dressed promoted a pH decrease in all treatments after the second maize crop and the increase in the level of N decreased the contents of soil Ca, Mg and K.

Efeito da adubação nitrogenada nas propriedades químicas de um Latossolo, cultivado com milho em sucessão à aveia-preta, na implantação do sistema plantio direto

The present study evaluated the effect of nitrogen levels and splittings on the chemical characteristics of a soil cropped with maize in succession to black oats at the establishment of the no tillage system. The experiment was carried out in a Red- Yellow Latosol (typic Hapludox), with 14% of clay in the 0-0.20 m soil layer. The work consisted of two maize crops (2003/04 and 2004/05) and a black oats one in between, as cover crop. The experimental design was randomized blocks in an incomplete factorial scheme, with four replications. Treatments consisted of nitrogen levels (60, 120 and 180 kg ha -1 ) and one control without nitrogen, besides the splittings (30 or 60 kg ha -1 at sowing, the balance in cover and 60 kg ha -1 at sowing, remaining top dressed). The following soil variables were evaluated: Ca, Mg, K, organic matter, P, H+Al, Al, sum of bases, CEC, pH and base saturation V(%). Ammonium sulfate fertilization top dressed promoted a pH decrease in all treatments after the second maize crop and the increase in the level of N decreased the contents of soil Ca, Mg and K.