Abstract Background Goosegrass is one of the most troublesome weed species in Brazil due to its wide dispersion and the ability to evolve herbicide resistance. Objective Investigate the response of goosegrass accessions from Mato Grosso, Brazil to glyphosate, clethodim, and haloxyfop. Methods Goosegrass seed samples were collected from seventeen production fields (accessions) in Mato Grosso and screened with the recommended label rates of clethodim, haloxyfop-methyl, and glyphosate. Six accessions withstood the label rate of the evaluated herbicides and were subjected to a dose-response study. Out of the six accessions, two were selected for further F1 dose-response investigations due to their ability to survive the label rate of the three herbicides individually. All studies were conducted under greenhouse conditions in a completely randomized design with four replications, and the F1 dose-response study was replicated in time. Results All six accessions investigated in the dose-response study presented ED50 values higher than susceptible plants for control and biomass reduction. Haloxyfop-methyl had the highest resistance ratios, followed by clethodim and glyphosate. The two accessions investigated in the F1 dose-response study were confirmed to be cross-resistant to clethodim and haloxyfop-methyl and showed low-level resistance to glyphosate. Conclusions The continuous reliance of POST herbicides for weed management in Mato Grosso cropping systems has selected goosegrass accessions that can withstand high rates of ACCase-inhibiting herbicides, particularly haloxyfop-methyl. Moreover, two accessions with resistance to ACCase-inhibiting herbicides, clethodim and haloxyfop-methyl, and low-level resistance to glyphosate were identified, suggesting the presence of multiple resistance in goosegrass accessions from Mato Grosso, Brazil.

Espécies com via fotossintética C4 são mais eficientes na assimilação de N que plantas C3, o que resulta em diferentes resistências do N do tecido à possibilidade de lavagem por chuva. Essa diferença pode alterar a ciclagem de N em sistemas agrícolas onde essas espécies são utilizadas como plantas de cobertura. O presente trabalho teve como objetivo estudar a produção de fitomassa em resposta ao N e à lavagem do nutriente da palha de gramíneas com diferentes vias de assimilação de carbono. Milheto (Pennisetum glaucum) e braquiária (Brachiaria ruziziensis), com via C4, e aveia-preta (Avena strigosa) e triticale (X. Triticosecale), com via C3 de assimilação de C, foram cultivados por 47 dias. Foi determinada a produção de matéria seca e tomadas amostras para determinação de N e C no tecido. Em seguida, foi simulada uma chuva de 30 mm, aplicada sobre o equivalente a 8 t ha-1 de matéria seca de resíduos. Foram determinadas as quantidades de amônio e nitrato lavadas dos resíduos. As gramíneas C4 responderam a doses mais altas de fertilizante, mas os teores de N no tecido foram menores. A quantidade de N lavada dos resíduos foi menor para as plantas C4 provavelmente porque sua relação C/N foi maior e o N estava mais fortemente ligado aos compostos orgânicos da planta. No planejamento de uma rotação de culturas é importante ter em conta as diferenças na liberação de N dos resíduos, uma vez que isso pode alterar a nutrição nitrogenada da próxima cultura.

Crop species with the C4 photosynthetic pathway are more efficient in assimilating N than C3 plants, which results in different N amounts prone to be washed from its straw by rain water. Such differences may affect N recycling in agricultural systems where these species are grown as cover crops. In this experiment, phytomass production and N leaching from the straw of grasses with different photosynthetic pathways were studied in response to N application. Pearl millet (Pennisetum glaucum) and congo grass (Brachiaria ruziziensis) with the C4 photosynthetic pathway, and black oat (Avena Strigosa) and triticale (X Triticosecale), with the C3 photosynthetic pathway, were grown for 47 days. After determining dry matter yields and N and C contents, a 30 mm rainfall was simulated over 8 t ha-1 of dry matter of each plant residue and the leached amounts of ammonium and nitrate were determined. C4 grasses responded to higher fertilizer rates, whereas N contents in plant tissue were lower. The amount of N leached from C4 grass residues was lower, probably because the C/N ratio is higher and N is more tightly bound to organic compounds. When planning a crop rotation system it is important to take into account the difference in N release of different plant residues which may affect N nutrition of the subsequent crop.

O manejo correto da adubação potássica pode minimizar perdas assim como evitar o esgotamento de K do solo. Objetivou-se estudar a dinâmica do K no perfil do solo em função do teor de argila e do teor do nutriente resultantes da adubação da soja. Foram coletados solos de texturas média e argilosa, que vinham sendo adubados com 0, 60, 120, e 180 kg ha-1 de K2O na soja por 6 anos. O experimento foi conduzido em casa de vegetação, em tubos de PVC estratificados nas profundidades de 0-5, 5-10, 10-20, e 20-40 cm. Na superfície das colunas, aplicaram-se mais 80 kg ha-1 de K2O. Durante 16 semanas, foi aplicada, semanalmente, água em quantidade equivalente a 100 mm de chuva. Em cada aplicação, o volume de solução percolada foi determinado, assim como as quantidades de K contidas nessa solução. Após a desmontagem das colunas de solo, foram determinados os teores de K trocável e não-trocável nas diferentes profundidades. A percolação de K foi maior no solo de textura argilosa, que tinha mais K disponível devido ao maior efeito residual da adubação potássica anterior. A intensidade de lixiviação foi proporcional ao teor de K disponível, mas inicialmente a lixiviação foi mais intensa no solo mais arenoso, decrescendo com o tempo. No argiloso, as perdas foram mais constantes. Houve proporcionalidade entre teor inicial e lixiviação no perfil do solo, nas duas formas de K e nos dois tipos de solo. Conclui-se que o efeito residual da adubação potássica aumentou as quantidades de K percolado. A movimentação de K no perfil do solo teve boa relação com o teor inicial de K no solo, resultante da adubação potássica anterior nos dois tipos de solo. A passagem de K considerado não-trocável para trocável foi rápida e influenciou na lixiviação.

A correct potassium fertilization management, using adequate fertilizer amounts, can minimize K losses and avoid soil K depletion. The objective of this study was to evaluate potassium dynamics in the soil profile as affected by different textures and exchangeable K levels resulting from previous soybean fertilizations. Soils with sandy loam and clayey texture previously planted with soybean and fertilized with 0, 60, 120 and 180 kg ha-1 K2O were sampled during 6 years. The experiment was carried out in a greenhouse, using 40 cm high and 5 cm diameter PVC tubes, where it was stratified the 0-5, 5-10, 10-20 and 20-40 cm soil layers. On the column surface, 80 kg ha-1 of K2O was applied as KCl and 100 mm water was applied weekly, for 16 weeks. At each application, the drainage solution volume and the K concentration in the leacheate were determined. After the disassembly of the soil columns, exchangeable and non-exchangeable K contents were determined for each layer. Potassium leaching was higher in the clay soil, where available K was higher due to the residual effect of previous K fertilization. Leaching intensity was proportional to available K contents. In the sandy soil initial leaching intensity was higher but decreased along time, whereas in the clayey soil K losses were more constant. The soil K level and leaching in soil profile were proportional to the exchangeable and non-exchangeable K for both soils. The residual effect of K fertilizer during the years under soybean, increasing its availability, can result in intensive exchangeable K losses, irrespective of soil texture. Potassium transformation from non exchangeable to exchangeable K is very fast, and affects the amount of leached K.