Abstract Root growth is crucial in crop production and is influenced by soil attributes, but also affects soil chemical, physical and biological quality, along with management and conservation practices. In this paper, soybean root growth data from a field study at Guarapuava, Paraná State, Brazil are examined. In 2019, at a farm with over 35 years of no-tillage system (NT) adoption, three management sets were established in 1,1 ha macroplots: 1) farmer's NT standard (FNT), without terraces, with downhill farming and with autumn fallow; 2) autumn cover crops and contour farming added to FNT, as best management practices (BMP); 3) terraces and contour farming (TC) added to FNT. Soybean was sowed in November 2020 and 2021, and minirhizotron tubes (1 m long, 7 cm wide) were installed into the soil just after soybean emerged in 2020. Root length, area, volume, and diameter were evaluated with the help of a root scanner. Data were submitted to descriptive statistics. The added conservation practices improved root length, area and volume, significantly for BMP in the subsoil (40-60 cm) compared to FNT standard. Minirhizotron enabled the study of roots in the field, but data variability was high, so that for annual crops with pivoting roots like soybean, root observation points (6 per plot) must be increased, and crop stand close to the observation points is a critical font of error.

ABSTRACT The effects of machinery traffic and cover crops on soil physical properties have been underexplored under no-till agricultural production in subtropical environments. The objective of this study was to quantify the soil water infiltration rate and related soil physical properties in response to tractor traffic levels (0, 2, 5, and 20 passes) and the presence or absence of cover crops in a Xanthic Hapludox soil over two growing seasons under no-till conditions. The experiment was carried out in a randomized block design arranged in a factorial scheme with four replications. The traffic factor was constituted by the number of passes with a 6 Mg weight tractor. The winter crop management practices factor consisted of the cover crops (i) black oat (Avena strigosa) in 2017 and turnip (Raphanus sativus var. oleiferus) in 2018 compared with (ii) fallow with spontaneous vegetation. The soil water infiltration rate increased with cover crops when compared to fallow. Regarding tractor traffic levels, shortly after soil compaction, there was a lower water infiltration rate at 20 passes, 45 mm h-1 lower than the absence of tractor traffic. The soil water infiltration rate was positively correlated with macroporosity and negatively correlated with soil bulk density. After 14 months of soil compaction caused by tractor traffic, an improvement in the soil physical properties and the water infiltration rate was found, which were enhanced by the inclusion of cover crops.

RESUMO A compactação do solo pode reduzir a produtividade potencial das culturas e é frequentemente encontrada no sistema plantio direto, mas há pouca informação sobre os limites críticos das propriedades físicas do solo nessas condições, especialmente em solos subtropicais. Os objetivos deste estudo foram avaliar a influência do tráfego de tratores nas propriedades físicas do solo e identificar limites críticos de densidade do solo, grau de compactação do solo, macro e microporosidade no rendimento das culturas de milho e aveia preta avaliados in situ em um Latossolo Bruno no Sul do Brasil. O tráfego de trator agrícola (0, 2, 5 e 20 passagens) foi estabelecido em sistema plantio direto para criar diferentes níveis de compactação do solo. Amostras indeformadas de solo foram coletadas em profundidades de 0,00-0,05; 0,07-0,12 e 0,17-0,22 m logo após o tráfego do trator em dois momentos: antes do cultivo de milho e, antes do cultivo de aveia preta. Nas condições deste experimento, os rendimentos 10% maiores de milho e aveia preta foram obtidos com macroporosidade acima de 0,10 m3 m-3 e 0,13 m3 m-3, respectivamente. Da mesma forma, o grau de compactação do solo de 90% e 86% foi considerado crítico para o milho e aveia-preta, respectivamente. Além disso, a compactação do solo pelo tráfego de máquinas reduziu o rendimento do milho em até 33% e o rendimento da biomassa de aveia preta em até 44%. Nossos resultados demonstram que os produtores devem estar atentos às consequências do tráfego de máquinas nas propriedades do solo, pois pode comprometer severamente o rendimento a produtividade das culturas, principalmente do milho e da aveia preta cultivados em solo muito argiloso como o avaliado neste estudo.

ABSTRACT Soil compaction can decrease potential crop yield and is frequently found in no-till cultivation systems, but there is little information on the critical limits of soil physical properties in these conditions, especially in subtropical soils. The objectives of this study were to evaluate the influence of tractor traffic on soil physical properties and identifies critical limits of soil bulk density, soil compaction degree, macro, and microporosity on crop yield of corn and black oat assessed in situ in a Xanthic Hapludox in Southern Brazil. Tractor machine traffic (0, 2, 5 and 20 passes) was established in no-till soil to create different soil compaction levels. Undisturbed soil samples were collected at depths of 0.00-0.05, 0.07-0.12 and 0.17-0.22 m just after tractor traffic in two moments: before corn cultivation, and then before black oat cultivation. Under the conditions of this experiment, the 10% higher yields of corn and black oats were obtained with macroporosity above 0.10 m3 m-3 and 0.13 m3 m-3, respectively. Similarly, the soil compactness degrees of 90% and 86% were considered critical for the corn and black oat, respectively. In addition, soil compaction by machine traffic reduced maize yield up to 33% and black oat biomass yield up to 44%. Our results demonstrate that growers should be aware of the consequences of machine traffic on soil properties, as it can severely compromise crop yields, especially of corn and black oats cultivated in very clayey soil like the one evaluated in this study.

Resumo A poluição da água causada por nitrogênio é originada por fontes difusas e pontuais. Em sistemas aquáticos superficiais, o nitrato é uma das formas mais problemáticas de nitrogênio, causando crescimento de fitoplâncton e de macrófitas e consequentemente a eutrofização da água. Este estudo teve o objetivo de avaliar se o modelo Soil and Water Assessment Tool (SWAT) pode simular a carga de nitrato em uma bacia hidrográfica rural em séries diárias e mensais. Foram investigados 462 km² da parte superior da bacia hidrográfica do rio Stör, uma bacia de planície tipicamente rural localizada no norte da Alemanha. Os resultados mostraram que as simulações de carga de nitratos em incrementos mensais são melhores preditores de dados observados do que simulações diárias. As práticas mais efetivas para minimizar as cargas de NO3-N foram a redução da aplicação de fertilizante nitrogenado e o incremento de áreas de conservação, tal como as faixas filtro.

Abstract Water pollution by nitrogen originates at diffuse and point sources. In surface aquatic systems, nitrate is one of the most problematic forms of nitrogen, causing phytoplankton and macrophyte growth and consequently water eutrophication. This study evaluated whether the Soil and Water Assessment Tool (SWAT) model can simulate nitrate load in a rural watershed in daily and monthly time increments. The study investigated 462 km² of the upper part of the Stör catchment, a typical rural lowland catchment located in Northern Germany. The results showed that simulations of nitrate load at monthly increments are better predictors of observed data than daily simulations. The most effective practices to minimize the NO3-N load were the reduction of nitrogen fertilizer application and the increasing of conservation areas, such as field filter strips.