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.

ABSTRACT There is little information on how different spatial arrangements affect modern maize hybrids under irrigation in the maize second growing season in Brazil. The objectives of this study were to evaluate the performance of maize genotypes with different canopy architecture as a function of different spatial arrangements in the Southeast Brazil. Two maize hybrids with semi-erect (DKB 390) and erect (DKB 230) leaves were cultivated during the second season and evaluated for different plant densities (4, 7 and 10 × 104 plants?ha?1) and row spacings (0.25, 0.50 and 1.00 m), under irrigation in a tropical environment. The increase in plant density increased plant height and ear insertion height, but reduced stalk diameter. The absorbed photosynthetically active radiation and the leaf area index also increased in higher plant densities, with a reduction of the SPAD index. The increase in plant density enhanced grain yield, however, there was no difference of yield between different row spacings. The hybrid DKB 230 (upright leaves) showed greater yield potential compared to DKB 390 (semi-upright leaves). The critical leaf area index was 5.2 and 4.3 for the hybrids DKB 230 and DKB 390, respectively. The estimated plant density that provides the maximum yield are 9.7 × 104 and 8.8 × 104 plants?ha?1 for the hybrids DKB 230 and DKB 390, respectively.

Resumo: A interação de diferentes tratamentos químicos de sementes com atributos de germinação, vigor e metabolismo de estresse em plântulas de soja precisa ser melhor compreendida. Os objetivos deste estudo foram avaliar o vigor, a germinação e atributos bioquímicos das sementes de soja em função de diferentes tratamentos químicos das sementes. Adotou-se o delineamento experimental inteiramente casualizado, com 8 tratamentos de sementes e 4 repetições. As sementes foram avaliadas quanto à germinação, vigor (primeira contagem de germinação, baixa temperatura, envelhecimento acelerado, índice de velocidade de emergência) biomassa de plântulas, atividade de enzimas e análise de SVIS®. Os tratamentos avaliados não diferiram em relação ao controle na germinação e vigor das sementes. Por meio da análise de imagens, o índice de uniformidade das plântulas tende a aumentar devido ao tratamento químico das sementes, embora os índices de vigor e crescimento não tenham apresentado diferença. A biomassa da parte aérea das plântulas tende a diminuir com os tratamentos químicos das sementes, e a biomassa da raiz não apresentou diferença. Os tratamentos químicos das sementes aumentaram a atividade do peróxido de hidrogênio nas plântulas entre 6 a 40% em relação ao controle; a atividade da catalase aumentou entre 87 a 184% em relação ao controle; e nenhum efeito foi observado na peroxidação de lipídios. De maneira geral, o tratamento químico das sementes beneficiou a atividade fisiológica das plântulas de soja e melhorou a atividade do metabolismo antioxidante. Nenhum dos tratamentos químicos de sementes usados foi fitotóxico.

Abstract: The interaction of different seed chemical treatment with seedlings germination, vigor and stress metabolism attributes needs to be better understood in soybean crop. The objectives of this study were to evaluate seed vigor, germination, and biochemical attributes of soybean seedlings as a function of different seed chemical treatments. A completely randomized experimental design was adopted, with 8 seed treatments and 4 replicates. Seed germination, vigor (first germination count, cold test, accelerated aging, emergence speed index), seedling biomass, enzimes activity and SVIS® analysis were evaluated. The evaluated treatments had no difference relative to control on seed germination and vigor. Through image analysis, the seedling uniformity index were equal or higher than control with the seed chemical treatment, while vigor and growth indexes had no difference. Shoot biomass of seedlings tends to decrease with seed chemical treatments, and root biomass had no difference. Seed chemical treatments increased the activity of hydrogen peroxide in seedlings by 6 to 40% compared to control; the activity of catalase increased by 87 to 184% compared to control; and no effect was observed in lipids peroxidation. Overall, seed chemical treatment benefited the physiological activity of soybean seedlings and improved antioxidant metabolism activity. None of the seed chemical treatments used were phytotoxic.