Resumo A longa duração do sistema plantio direto tem causado limitações para o solo, como a compactação e a acidez subsuperficiais. O objetivo deste trabalho foi avaliar os efeitos de estratégias de manejo sobre os atributos do solo e a produtividade da soja. O experimento foi realizado em um Latossolo nas safras agrícolas de 2016/17 e 2017/18 e seu delineamento experimental foi de blocos ao acaso com três repetições. Os tratamentos foram constituídos pela aplicação de estratégias de descompactação (escarificação e subsolagem) e de melhoria química (óxido de cálcio e magnésio, calcário e gesso), utilizadas de forma isolada e combinada. As amostragens de solo para análise química e a determinação da resistência à penetração do solo foram realizadas 6 e 18 meses após a aplicação dos tratamentos. A escarificação e a subsolagem foram eficientes na redução da resistência à penetração, mas apresentaram efeito temporário no solo. A subsolagem intensa associada à aplicação profunda de óxido de cálcio e magnésio, após 18 meses da aplicação, incrementou os valores de pH e os teores de cálcio e magnésio, além de neutralizar a saturação por alumínio até 60 cm. Em ambas as safras avaliadas, não houve efeito significativo dos tratamentos sobre a produtividade da soja.

Abstract The long term use of the no-tillage system has caused limitations to the soil, such as the subsurface compaction and acidity. The aim of this study was to evaluate the effect of management strategies on soil attributes and soybean yield. The experiment was carried out in the 2016/17 and 2017/18 crop seasons and its experimental design was a randomized blocks with three replications. The treatments were constituted by strategies of physical improvement (chiseling and subsoiling) and chemical improvement (calcium and magnesium oxide, limestone and gypsum), isolated or combinated. Soil samplings for chemical analysis and determination of resistance to soil penetration were performed 6 and 18 months after application of treatments. The chiseling and subsoiling were efficient in reduction compaction, but presented temporary effects in the soil. The intense subsoiling associated with the deep application of calcium and magnesium oxide, 18 months after the application, increased the pH values and the calcium and magnesium contents in addition to neutralizing the aluminum saturation to the depth of 60 cm. In both evaluated seasons, there was no significant effect of treatments on soybean productivity.

ABSTRACT Improvement of soil chemical properties in dystrophic Oxisols managed under long-term no-tillage system (NTS) with surface broadcast lime has been, frequently, restricted to a shallow topsoil layer. As a consequence, a sharply-defined chemical quality gradient is created, with deterioration from the surface towards deeper layers in Oxisols in southern Brazil. The aim of this study was to assess the temporal effects of gypsum, applied alone or in combination with lime, on Ca2+ content and Al3+ saturation in the rooting zone (RZ) (0.00-0.40 m). Four experiments were conducted from 2009 to 2014 in Typic Hapludox soils with distinct chemical qualities in the RZ managed under a long-term NTS (over 20 years) in Rio Grande do Sul (subtropical region). A randomized block experimental design with three replications was used. Experiments I and II were implemented in 2009, with treatments consisting of gypsum rates ranging from 0.0 to 6.5 Mg ha-1. The other two experiments were implemented in 2011. In experiment III, a split-plot design was used, with plots received gypsum rates ranging from 0.0 to 5.0 Mg ha-1, and the subplots received two lime rates (0.0 and 2.0 Mg ha-1). A split-plot design was also used in experiment IV, with plots receiving gypsum rates ranging from 0.0 to 6.0 Mg ha-1, and subplots receiving four lime rates, ranging from 0.0 to 4.8 Mg ha-1. Soil samples were stratified in layers at depth from 0.00 to 0.60 m and taken during the period of the experiment. The use of gypsum increased the Ca2+ and SO42−-S contents, proportional to the rate applied, and lowered Al3+ saturation throughout the soil profile evaluated. However, an increase in base saturation of the subsoil (0.25-0.60 m layer) was only observed at high rates of gypsum (>5.0 Mg ha-1) in the medium-term and through accumulation of a high rainfall volume. A faster and more pronounced effect of subsoil improvement was observed when the chemical quality of the topsoil layer was already high and when gypsum and lime were applied in combination. Greater improvement in subsoil chemical quality induced by gypsum, alone or in combination with lime, was found in a period exceeding 30 months (Experiments III and IV), remaining for up to 54 months (Experiments I and II). The combination of gypsum with lime was an effective strategy to increase vertical movement of bases in the RZ, mitigating the gradient of chemical quality in dystrophic Oxisol, avoiding discontinuity in the NTS.

RESUMO: A pesquisa teve por objetivo testar a hipótese de que sob condições de confinamento das raízes em um volume limitado, os efeitos negativos no crescimento e produtividade da planta de alface podem ser compensados aumentando a disponibilidade de N no meio radicular. O experimento foi realizado entre 11 de agosto e 23 de setembro de 2011. Mudas de alface da cultivar Stella com cinco folhas foram plantadas em vasos empregando areia como substrato. Os tratamentos foram constituídos por três níveis de confinamento do sistema radicular e cinco concentrações de nitrogênio na solução nutritiva, em esquema fatorial 3x5, em parcelas subdivididas, inteiramente casualizado com quatro repetições e 22 plantas por sub-parcela. O confinamento das raízes foi simulado usando tamanhos de vasos de 2,5 dm3 (sem confinamento, controle); 1,0 dm3 (moderado) e 0,4 dm3 (severa). As concentrações de nitrogênio foram: 5,55 (C1), 8,05 (C2), 10,55 (C3), 13,05 (C4) e 15,55 (C5) mmol/L. Houve interação entre os dois fatores, de forma que plantas sob confinamento severo das raízes na concentração de 10,55 mmol/L de N apresentaram crescimento de folhas similar àquelas sem confinamento (controle) na dose de 5,55 mmol/L de N. O aumento da concentração de N favoreceu o crescimento da parte aérea da planta, porém, reduziu o crescimento das raízes. Em plantas de alface cultivadas em condições de confinamento radicular, o seu crescimento é reduzido e não é compensado pelo aumento da concentração de nitrogênio. Tanto no sistema de produção convencional ou fora do solo, práticas de manejo para estimular o crescimento de raízes devem ser consideradas para maximizar o crescimento das plantas de alface e a eficiência de uso do nitrogênio.

ABSTRACT: The objective of this research was to test the hypothesis that when lettuce plants grow under root confinement, development and yield is reduced and that such negative effects may be compensated by increasing nitrogen availability in the rooting media. The experiment was conducted between August 11st and September 23rd 2011. Lettuce transplants, cultivar Stella, bearing five leaves, were planted in pots using sand as substrate. Treatments were three root confinement levels and five N concentrations in the nutrient solution, in a 3x5 factorial randomized experimental design with four replications. Root confinements were simulated by pot sizes of 2.5 dm³ (no confinement, the control); 1.0 dm³ (moderate) and 0.4 dm³ (severe). Nitrogen concentrations were: 5.55 (C1), 8.05 (C2), 10.55 (C3), 13.05 (C4) and 15.55 (C5) mmol/L. Interactions were observed between confinement levels and N concentrations. Plants grown under severe root confinement supplied by the nutrient solution at the concentration of 10.55 mmol/L of N reached leaf growth similar to those under no root confinement at 5.55 mmol/L of N. Increasing the N concentration in the nutrient solution enhanced shoot growth but decreased root growth. In lettuce plants grown under root confinement, plant growth is reduced and it is not compensated by increasing N fertilization rates. In both horticultural conventional or soilless production systems, managing practices for stimulate root growth has to be considered to maximize lettuce plant growth and nitrogen use efficiency.