José Eloir Denardin

Distribution of phosphorus fractions in a Brazilian Oxisol under different tillage systems

Abstract Changes in residue management resulting from adoption of conservation tillage systems have the potential to alter the concentration and distribution of phosphorus (P) in the soil surface. The objective of this study was to determine the effect of methods of tillage management on the distribution and concentration of organic and inorganic forms of soil P near the soil surface (0–10 cm depth) for an Oxisol in southern Brazil. The tillage systems included zero tillage (ZT) (seeding directly onto the standing stubble of the previous crop), minimum tillage (MT) (seeding the crop after chisel plowing to 15-cm depth and disk harrowing to 7.5 cm), or conventional tillage (CT) (seeding after disk plowing to 20-cm depth with nearly total soil inversion plus two disk harrowings to 10-cm depth). After a period of five years, reducing tillage through adoption of MT or ZT practices increased total P in the surface 10 cm by 15% when compared to CT. Although there were no differences in amounts of total P between MT and ZT systems, under ZT management larger amounts of labile organic and inorganic forms of P accumulated close to the soil surface, followed by a reduction below the 6-cm depth. Under MT, the labile organic and inorganic forms of P were uniformly distributed within the surface 10 cm of soil. The accumulation of high levels of labile P near the soil surface under ZT followed a distribution pattern similar to the accumulation of organic residues in the soil. This would help explain why other workers have found increased P uptake by crops grown under ZT, and why more available P can be extracted by common soil testing methods from the surface 7 to 10 cm of soils under ZT than under CT management.

Persistência dos efeitos da escarificação sobre a compactação de Nitossolo sob plantio direto em região subtropical úmida

O objetivo deste trabalho foi avaliar a persistencia dos efeitos da escarificacao sobre a compactacao de Nitossolo Vermelho, manejado sob plantio direto (PD), na regiao subtropical umida do Brasil. O experimento foi realizado em blocos ao acaso, com quatro repeticoes e seis tratamentos, constituidos pelo tempo de manutencao do solo sob PD apos escarificacao: PD continuo por 24 meses apos escarificacao, realizada em setembro de 2009; PD continuo por 18 meses apos escarificacao, realizada em marco de 2010; PD continuo por 12 meses apos escarificacao, realizada em setembro de 2010; PD continuo por seis meses apos escarificacao, realizada em marco de 2011; plantio realizado em solo recem escarificado, em setembro de 2011; e PD continuo e sem escarificacao (testemunha). As especies cultivadas na area foram: milho, safra 2009/2010; trigo, em 2010; soja, safra 2010/2011; centeio, em 2011; e milho, safra 2011/2012. Os efeitos dos tratamentos foram avaliados a partir de parâmetros fisicos do solo e de parâmetros morfologicos e produtivos da cultura do milho, na safra 2011/2012. A escarificacao do Nitossolo sob plantio direto, em regiao de clima subtropical umido, nao aumenta a produtividade de graos de milho, e os seus efeitos sobre a estrutura do solo nao persistem por mais de 18 meses.

Efeito de semeadora com haste sulcadora para ação profunda em solo manejado com plantio direto

The adoption of no-till in the humid subtropical region of Brazil based on only two precepts of conservation agriculture, soil disturbance restricted to the crop row and crop residue maintained as soil cover, has led to stratification of soil chemical properties in the 0-20 cm soil layer and physical degradation of the subsurface layer (from approximately the 5-20 cm depth), which may make for lower yields during short term droughts. The aim of this study was to evaluate the residual effect of a seed drill/fertilizer applicator equipped with fixed shanks, set at four different depths, for the sowing of maize (Zea mays L.), in mitigation of chemical and physical problems in a Latossolo Vermelho distrofico humico (Rhodic Hapludox) under no-till for more than ten years. The treatments were: T1 = shank extremity at 5 cm depth; T2 = shank extremity at 10 cm depth; T3 = shank extremity at 15 cm depth; and T4 = shank extremity at 17 cm depth. The crop profile method was used to evaluate soil physical properties (bulk density, total porosity, macroporosity, and soil resistance to penetration) at eight and ten months after sowing the maize. The chemical properties (pH in water; available P and K; exchangeable Ca, Mg, and Al; potential acidity; and organic matter) were evaluated in layers every 2.5 cm from the 0-22.5 cm depth. The seed drill/fertilizer applicator equipped with fixed shanks for ripping the soil was able to mitigate soil physical and chemical problems, both at eight and 12 months after sowing.

Resistência à penetração e rendimento da soja após intervenção mecânica em latossolo vermelho sob plantio direto

Compaction negatively affects a number of soil properties, e.g., resistance to root penetration and water and nutrient availability to plants, restricting the photosynthetic rate, shoot growth and consequently, the yield. When soil compaction becomes limiting to crop development, mitigation measures must be adopted. The purpose of this study was to evaluate the residual effect of mechanical soil plowing and chiseling, by a seeder with soil breakers (disks and disks plus short ripper) as mitigation practice of the soil compaction under no-tillage (NT), on soil penetration resistance and soybean yield. In 2001, a study was conducted in Coxilha, in northern Rio Grande do Sul, on an Oxisol, in an area with a sequence of NT management. In this field, every year a treatment of mechanical soil decompression was applied, consisting of plowing and chiseling the soil under NT, before sowing the summer crop, reassuming the NT management after this intervention. The experimental design consisted of randomized blocks in a split-plot design with three replications. The treatments consisted of a combination of 13 systems of soil management in the main plots and two seed drill devices in the subplots. Thus, the management systems were evaluated by the control, represented by the uninterrupted maintenance of NT for 16 years, six NT management periods (7.5, 6.5, 5.5, 4.5, 3.5, and 2.5 years) after one intervention with mechanical disc plow + disc harrow (A) and the same six NT management periods after one mechanical intervention with chiseling (E). The levels in the subplots consisted of the action of a no-till seeder equipped with double discs reaching a depth of 7 cm and a seeder equipped with double disks + short ripper reaching a depth of 13 cm. Results indicated that the mitigating effect on compaction and on the improvement of soil structure of the mechanical intervention in soil under consolidated NT consisting of soil chiseling or plowing is short-lived, with a residual effect of up to two and a half years for penetration resistance. The use of a no-till seeder drill equipped with short ripper + disc seeder has potential for mitigation of soil compaction, by reducing mechanical penetration resistance in the 7-15 cm layer. Nevertheless, the residual effect of mechanical intervention for soil decompaction and the adoption of different devices for fertilizer application in the plant furrow were not effective in altering the soybean yield in the 2008/2009 growing season.

Dispersão de argila em microagregados de solo incubado com calcário

Soil compaction limits grain yields. Among others factors, soil amendment with agricultural lime can contribute to micro-aggregate dispersion and the formation of compacted layers. The objective of this study was to evaluate the effect of lime on soil physical attributes related to soil compaction. The experiment was carried out in PVC columns, in a glass house, during 18 months. Sterilized and non-sterilized samples of a dystrophic Red Latosol (Hapludox) were incubated with 0, 1.9, 3.8, 5.7, 7.6 and 15.2 Mg ha-1. After the incubation period, the micro and macro porosity, soil density, clay dispersion, hydraulic conductivity and concentration of exchangeable Al, Ca and Mg and soil organic matter were evaluated. Soil density, clay dispersion, pH and Ca and Mg concentration increased with lime application, while macro porosity, hydraulic conductivity, soil organic matter, and Al decreased. The increase of pH and hydraulic conductivity were higher in the sterilized soil. Liming effects were more evident at a rate of 3.8 Mg ha-1. Soil sterilization increased the pH value and decreased the organic matter content and Ca, besides the hydraulic conductivity. Micro- aggregate dispersion in limed soils can, at least partially, contribute to soil compaction.

Vertical mulching como prática conservacionista para manejo de enxurrada em sistema plantio direto

In regions of temperate and subtropical humid climate in Brazil, below the parallel of 24° latitude South, the rainfall characteristics potentially exceed the soil water infiltration rate and produce runoff, at any time of the year, independent of soil use and management system. The additional conservational practices have not been fully adopted in the no-tillage system as it would be required to control the erosion potential due to the soil conditions of these regions. Runoff results in chemically enriched sediments, which poses environmental risks, besides causing economical losses in the agriculture production system. The objective of this study was to evaluate the efficiency of vertical mulching as a conservation practice to restrict runoff in areas under no-tillage system, by evaluating the sediment enrichment rate based on double soil sampling in fields with presence and absence of the practice of vertical mulching. The double sampling covered representative soils of each plantation and the respective sediments generated by hydric erosion. Soil pH in water, SMP index, available P, exchangeable K, Ca, Mg and Al, and organic matter were determined, and the total and base saturation and cation exchange capacity in each sample were calculated. Results indicate that the conservation practice of vertical mulching reduces the degree of chemical enrichment of the sediments and mainly prevents the transport of these sediments away from plantations, minimizing economical losses and environmental risks. The no tillage system, without complementary conservation practices to control runoff, does therefore not represent a soil conservation practice capable of preventing environmental degradation.

Duração das alterações em propriedades físico-hídricas de Latossolo argiloso decorrentes da escarificação mecânica

The objective of this work was to determine the duration of the effects of soil decompaction, by mechanical chiseling, through physical and hydraulic indicators of a clayey Oxisol under no-tillage (NT). The treatments consisted of months (0, 6, 12, 18, 24, 30, and 36) after chiseling under NT and of a control treatment without chiseling under NT during 27 years. The following variables were evaluated: penetration resistance, infiltration rate, bulk density and relative density, pore size distribution, and saturated hydraulic conductivity. The duration of the effects of mechanical chiseling varied according to the evaluated soil property, lasting six months for bulk density and relative density, total porosity, and macroporosity; 18 months for penetration resistance; and 24 months for hydraulic conductivity and infiltration rate. Soil properties related to water transport, such as hydraulic conductivity and steady infiltration rate, maintain the effect of mechanical chiseling for a longer time and, therefore, are more suitable to measure the duration of mechanical decompaction.

Soil chemical management drives structural degradation of Oxisols under a no-till cropping system

Physical degradation of the subsurface layer of soils reduces the effectiveness of no-till (NT) as a sustainable soil management approach in crop production. Chemical factors may reduce the structural stability of Oxisols and thereby exacerbate compaction from machinery traffic. We studied the relationship between chemical management and structural degradation in Oxisols cultivated under NT at three sites in southern Brazil. The surface and subsurface layers of the soils were characterised chemically and mineralogically and three physical attributes related to soil structural stability (readily dispersible clay in water, mechanically dispersible clay in water, and water percolation) were quantified for each layer. The same characterisations were performed on Oxisols collected from adjacent non-cultivated areas, to provide reference data for non-degraded soil. The levels of dispersed clay in the cultivated soil from the surface layer matched those of the non-cultivated soil, but for the subsurface layer higher dispersed clay levels in the cultivated soil showed that it was physically degraded relative to the non-cultivated soil. Water percolation was found to be slower through the Oxisols cultivated under NT, irrespective of the soil layer. The relationships between the three indicators of soil structural stability and the measured chemical and mineralogical variables of the soils were explored through an analysis of canonical correlation. The principal variables associated with the lower stability of the cultivated vs non-cultivated Oxisols were the lower concentrations of organic carbon and exchangeable aluminium and, for the surface layer, the higher pH. It is argued that structural degradation of Oxisols cultivated under NT, observed predominantly in the subsurface layer, has been aggravated by the accumulation of amendments and fertilisers in the surface soil and reduced levels of organic matter, especially in the subsurface layer.