José Miguel Reichert

Surface and subsurface microbial biomass, community structure and metabolic activity as a function of soil depth and season

Microbial biomass, size and community structure along with an estimate of microbial activity and soil chemical parameters were determined at three depths in two soils (e.g. sandy loam Ultic Hapludalf and silt loam Mollic Hapludalf ) replicated three times under one winter and summer season. Microbial biomass and community structure were estimated from phospholipid-PO4 content and fatty acid methyl ester (FAME) measurements. Microbial activity and assimilative capacity were estimated using a 3 H-acetate incorporation into phospholipids and by incubating the soil samples at the average winter and summer temperatures, 3 and 20 ◦ C, respectively. We found that the size of the microbial biomass in both the surface and the subsurface soils was not significantly affected by the seasonal variation but activity increased by as much as 83% at the summer temperatures in the surface soil. We demonstrated using FAME analysis that for both soils seasonal changes in the subsurface microbial community occurred. These findings suggest that winter conditions will shift the population activity level in both the surface and subsurface systems and the biochemical structure of the community in the subsurface. In all cases, the inorganic chemical properties of the soil, as a function of season, remained constant. The greatly increased activity of microbial population at the higher temperature will favor the capacity of the system to utilize nutrients or organic materials that may enter soil. During low temperature seasons the capacity of either surface or subsurface soils to assimilate materials is generally diminished but the reduction reflects changes in metabolism and not a reduced biomass size.

Suscetibilidade à compactação de um latossolo vermelho-escuro e de um podzólico vermelho-amarelo

Soil compaction of the agricultural soils is a result of soil machine interactions, which influence physical and biological soil properties and their relations with crop growth and yield. The objective of this study was to determine the compression index, the preconsolidation pressure and the soil strain of a Haplortox (LE) and a Paleudalf (PV), with different initial state of compaction and water saturation. Undisturbed soil samples were collected in two soils and at two depths, at no tillage and conventional tillage, at several locations and different times to obtain a natural variation of bulk density, corresponding to different initial levels of compactness and water saturation. For the uniaxial compression test, successive static loads of 12.2; 25; 50; 100; 200; 400 and 800 kPa were used, during five minutes for each load. This was determined at previous tests, where 99% of the soil strain had occurred at the time. Soil strain showed differentiated behaviors for each soil. For soil Haplortox, under low water saturation ( 60%) water saturation, whereas for the intermediate saturation (30 to 60%) the model was linear. The compression index correlated negatively with the initial bulk density and with water saturation in PV. For high initial bulk density (> 1.45 Mg m-3), the Haplortox had greater susceptibility to compaction when water saturation was near 70%, whereas when the same soil had low compaction (bulk density < 1.30 Mg m-3), the major susceptibility occurred under lower water saturation (near 50%). Multiple regression equations for preconsolidation pressure, using initial bulk density and water saturation, had low determination coefficient (0.28 for PV and 0.32 for LE), although significant, which indicates the need for incorporation of more variables in these models.

Densidade do solo, atributos químicos e sistema radicular do milho afetados pelo pastejo e manejo do solo

A integracao lavoura-pecuaria e uma alternativa de renda dos produtores no sul do Brasil. Entretanto, o pisoteio animal e, ou, o preparo de solo podem compacta-lo, prejudicando o crescimento radicular e a produtividade das plantas. Estudaram-se os efeitos do pisoteio animal em regime de pastejo continuo durante o inverno/primavera e do impacto do plantio direto e do preparo convencional de solo no estado de compactacao, atributos quimicos e distribuicao radicular. Em Podzolico Vermelho-Amarelo de textura superficial franca, foi implantada uma pastagem de estacao fria composta por aveia (Avena strigosa Schreb) e azevem (Lolium multiflorum L.). A carga animal variou conforme o crescimento da pastagem. Em dezembro de 1996, foi implantada a cultura do milho (Zea mays L.) para a producao de silagem, usando os seguintes tratamentos: plantio direto na area nao pastejada, plantio direto apos o pastejo, preparo convencional de solo na area nao pastejada e preparo convencional de solo apos pastejo. As avaliacoes apresentadas neste estudo sao referentes ao terceiro ano de cultivo, no qual houve um periodo de pastejo de 107 dias. Aos 45 dias da emergencia do milho, foram abertas trincheiras (100 x 40 cm) para visualizar a distribuicao do sistema radicular e coletar amostras de solo, a cada 5 cm, para caracterizacao quimica e determinacao da densidade do solo e de raizes. Ao longo do perfil (0-40 cm), o desenho da distribuicao de raizes indicou maior quantidade de raizes no preparo convencional de solo, concordando com os resultados de densidade de raizes. O pisoteio animal nao teve efeito sobre as caracteristicas fisicas, possivelmente pelo fato de o residuo da pastagem permanecer proximo a 1,0 Mg ha-1 de materia seca. A densidade do solo no plantio direto, na camada de 5-10 cm, foi de 1,41 Mg m-3, tanto na area pastejada como na nao pastejada. No preparo convencional de solo, esses valores foram de 1,15 Mg m-3, na area pastejada e de 1,12 Mg m-3, na area nao pastejada. A produtividade de graos de milho (4,55 Mg ha-1) e de silagem (34,66 Mg ha-1) nao foi afetada pelo pastejo ou pelo preparo do solo. O sistema de manejo do solo teve maior influencia na densidade do solo do que o pisoteio animal, considerando o controle da carga animal ajustado ao crescimento da pastagem.

Variabilidade temporal da resistência à penetração de um latossolo argiloso sob semeadura direta com rotação de culturas

Root growth is affected by mechanical soil resistance and affects the crop yield potential. This study evaluated the soil penetration resistance on a clayey Oxisol under distinct no-tillage cropping systems. The experiment was carried out at the technological field of Cotrijui in southern Brazil. The soil was a Haplorthox with a clay content of 0.68 kg kg-1 and it has been under four no-tillage cropping systems: succession soybean/wheat; corn/black oat/corn + velvet bean/wheat/soybean/wheat; velvet bean/wheat/soybean/ wheat/soybean/black oat; and crotalaria/wheat/soybean/black oat/corn/wheat. Soil penetration resistance (PR), soil moisture, and soil bulk density were evaluated at different times and soil depths. For all four cropping systems on this clayey Oxisol under no-tillage, the highest compaction state was observed at about 0.1 m depth and the lowest in the surface layer (0 to 0.07 m). The PR showed great temporal variation and was associated with soil moisture for each soil bulk density or compaction state. PR values restrictive for plant root growth were found at depths varying from 0.03 to 0.23 m, at soil moistures between 0.14 and 0.28 kg kg-1. The effect of inclusion of warm-season cover crops, which have an aggressive rooting system responsible for biological pore formation, was not observed for the studied time.

Qualidade física do solo na produtividade da cultura do feijoeiro num Argissolo

In this work, soil properties and least limiting water range (LLWR) were determined for an Alfisol under three states of compaction with black beans crop. Three experiments were used, comprising the following treatments: 12 years of no-tillage - NT; 12 years, of no-tillage compacted by four passes of a bucket loader - NTc; and chiseling of soil previously under no-tillage for 12 years - Ch. Throughout the plant cycle, bulk density, total porosity, volumetric water content, air filled porosity and soil resistance to penetration were evaluated. Plant root distribution and yield were also evaluated. The critical bulk density obtained by LLWR was 1.75 Mg m-3. In the NTc the bulk density was higher than critical value for most soil layers, whereas the PD and Ch presented higher value in a few layers. Soil water content was out of LLWR range for most part of plant cycle. Soil resistance to penetration in the NTc was higher than critical value in all evaluated dates, while in roots concentrated superficially. For the three experiments, higher compaction levels (NTc) induced yield reduction from 30 to 62% and soil chiseling (Ch) induced yield reduction from 2 to 12% compared to crops under no-tillage (PD). Compaction alleviation by chiseling was not necessary to improve crop yield for soil physical conditions of this area.

Aggregate stability and rain-impacted sheet erosion of air-dried and prewetted clayey surface soils under intense rain

Stability of aggregates at the immediate soil surface affects the detachment, transport, and deposition of soil particles. The aggregate stability (expressed as mean weight diameter, MWD) and erosion rate were tested for clayey surface soils at two different water contents. The soils consisted of six Oxisols, one Ultisol, three Vertisols, one Alfisol, and one Aridisol. The MWD was determined by wet sieving of 4.76 to 8.00 aggregates, which were either air-dried (MWDd) or capillary prewetted at −0.5 kPa for 24 h (MNDw). Air-dried and prewetted (saturated from the bottom up for 2 h) soils were subjected to a 110-mm h−1 rain until a steady-state infiltration was reached. Runoff, sediment loss, and infiltration (for prewetted soil only) were monitored throughout the rain. The MWDd ranged from 0.18 to 4.80 mm, and the MWDw ranged from 0.44 to 5.66 mm. Prewetting increased the MWD for the oxidic or kaolinitic Oxisols and Ultisols and for one smectitc/kaolinitic Vertisol. The MWDw was positively related to CEC for highly weathered soils and negatively related for swelling soils, whereas base saturation was negatively related for both groups of soils. The ΔMWD, which expresses the increase in stability caused primarily by a decrease in slaking, was greatest for soils rich in kaolinite and Fe and Al oxyhydroxides and low in organic carbon. The steady-state infiltration rate (Is) ranged from 1.8 (illitic soil) to 54.8 mm. h−1 (sandy loam kaolinitic soil). The Is was consistently less for swelling than for highly weathered soils, and it was related to the sand/clay ratio, sand, and water retained between −33 and −1500 kPa. The increased aggregate stability with prewetting was generally not reflected in smaller amounts of erosion and runoff, possibly because of the faster rate of wetting than for the stability test, a higher water table for the prewetted soil than for the air-dried soil, and the inclusion of smaller aggregates in the erosion tests. Prewetting decreased the time to ponding for three highly weathered Oxisols and the illitic Alfisol, increased steady-state runoff rate (Qw) for five highly weathered soils, increased sediment loss rate (Qs) for the illitic and for one highly weathered soil, and increased Qs on a stable Oxisol. Soil textural properties (usually clay and sand/clay) and “binding” agents (organic carbon and Fe and Al oxyhydroxides) were the significant independent variables included in the stepwise multiple linear regressions for Is, Qs, and Qw

Dinâmica da agregação de um solo franco-arenoso em cinco sistemas de culturas em rotação e em sucessão

SUMMARY : AGGREGATION DYNAMICS OF A SANDY SOIL UNDER FIVECROPPING SYSTEMS IN ROTATION AND IN SUCCESSION Cover crops along with proper soil management recover or maintain soil physicalproperties such as aggregation. The objective of this study was to determine the effect ofcropping systems, cover crops, and soil organic matter (SOM) content on the temporalvariation of soil aggregation in an Hapludalf in its natural state and under different croppingsystems. The experiment was conducted at the experimental station of the Soil Departmentof the UFSM, Brazil. Undisturbed soil samples were collected in 60 day-intervals throughoutan year (Ocotober/1997 to October/1998) from a depth of 0–0.05 m and analyzed foraggregate stability, SOM content, and selected physical and chemical properties. The greateststructural stability was observed under grassland and the smallest stability for bare soildue to the intense soil tillage and reduction in SOM, increasing the proportion of smallaggregates. Cover crops formed and stabilized soil aggregates directly, and the stabilityand proportion of aggregates were greater under cultivation systems that increase SOMand cover the soil during the whole year. Different cropping sequences affect soil aggregationdistinctly, depending on the time of the year and time of establishment of the crops.Index terms: soil structure, aggregate stability, cover crops, soil management.

Coluna de areia para medir a retenção de água no solo: protótipos e teste

Soil water retention curve (SWRC) has been built using several strategies and methodologies. For low tension the use of tension tables has predominated. This paper presents prototypes and test the use of sand suction columns to measure soil water retention from 0 to 100hPa tension. An initial test was set up in a sand column instrumented with tensiometers every 0.1m from top to 1.0m depth. The column was set in a plastic tube 0.25m diameter with devices to have water inlet and to allow water table level. The column was filled with sieved sand, saturated and drained till a given water table depth. The total water potential distribution inside of column and water tension variation at sand surface indicated that, after hydrostatic equilibrium, the depth of water table regulates the potential distribution and the water tension at sand surface is equal to depth of water table. Sand column models (low and high cost) were set up and tested. In these columns a tensiometer was installed at sand surface and saturated soil samples in cylinders with tensiometers inside were set on top of sand and on top of filter paper laid on sand. Tensiometers located at sand surface and inside of soil samples indicated that tension targets were achieved from 8 to 12 hours at both, sand surface or inside of soil samples.

Soil strength as affected by combine wheel traffic and two soil tillage systems

A resistencia mecânica do solo a penetracao pode limitar o crescimento do sistema radicular e a produtividade das plantas. O estudo objetivou avaliar a resistencia mecânica do solo a penetracao nas zonas de trafego e entre trafego de uma colhedora de graos, em dois sistemas de manejo do solo e duas condicoes de umidade do solo. Os tratamentos foram: plantio direto, nao trafegado pelas rodas da colhedora e no rastro do pneu dianteiro da colhedora; na area com preparo do solo, nao trafegado pelas rodas da colhedora e no rastro do pneu dianteiro da colhedora. Determinaram-se a resistencia mecânica do solo a penetracao com um penetrografo, realizando leituras eletronicas de resistencia a cada 0,15cm de profundidade, e a umidade do solo, ate uma profundidade de 40cm, em duas condicoes de umidade do solo (seco e umido), num Latossolo Vermelho-Escuro, argiloso. Nesses mesmos locais, foram coletadas amostras para determinacao da umidade do solo. O peso distribuido no eixo dianteiro da colhedora foi de 5,0Mg, sendo a area de contato com o solo igual a 0,283m2, exercendo uma pressao de contato com o solo de 0,0884MPa. Com maiores conteudos de agua no solo, a resistencia mecânica a penetracao foi baixa (menor que 2MPa) entre os diferentes tratamentos, nao limitando o crescimento radicular. Porem, na segunda avaliacao, quando o solo estava mais seco, verificou-se que o trafego da colhedora causou compactacao na camada de 5 a 17cm. O conteudo de agua do solo influenciou os valores absolutos de resistencia mecânica a penetracao. Valores de resistencia mecânica a penetracao considerados como criticos ao desenvolvimento das plantas (maiores que 2,0MPa) foram observados, principalmente, para o sistema de plantio direto. Os maiores valores de resistencia a penetracao foram encontrados no sistema de plantio direto que apresentou maior estado de compactacao na camada de 7,5 a 17,0cm. O sistema de plantio direto possui um estado de compactacao mais elevado, causado pelo acumulo de pressoes mecânicas a que o solo e submetido anualmente. Entretanto, a produtividade da cultura da soja nao diferiu entre os sistemas de manejo do solo, permanecendo em torno de 3,15Mg ha-1.

Estimation of water retention and availability in soils of Rio Grande do Sul

Dispersed information on water retention and availability in soils may be compiled in databases to generate pedotransfer functions. The objectives of this study were: to generate pedotransfer functions to estimate soil water retention based on easily measurable soil properties; to evaluate the efficiency of existing pedotransfer functions for different geographical regions for the estimation of water retention in soils of Rio Grande do Sul (RS); and to estimate plant-available water capacity based on soil particle-size distribution. Two databases were set up for soil properties, including water retention: one based on literature data (725 entries) and the other with soil data from an irrigation scheduling and management system (239 entries). From the literature database, pedotransfer functions were generated, nine pedofunctions available in the literature were evaluated and the plant-available water capacity was calculated. The coefficient of determination of some pedotransfer functions ranged from 0.56 to 0.66. Pedotransfer functions generated based on soils from other regions were not appropriate for estimating the water retention for RS soils. The plant-available water content varied with soil texture classes, from 0.089 kg kg-1 for the sand class to 0.191 kg kg-1 for the silty clay class. These variations were more related to sand and silt than to clay content. The soils with a greater silt/clay ratio, which were less weathered and with a greater quantity of smectite clay minerals, had high water retention and plant-available water capacity.