Soil Seed Bank Phytosociology in No-Tillage Systems in the Southwestern Amazon Region

Abstract

Understanding the ecological dynamics of weed populations in no-tillage systems is important to establish strategies for integrated weed control capable of increasing agroecosystem sustainability. This study sought to evaluate the effect of succession systems on the seed bank in a no-tillage system. The effects of fifteen succession systems, composed of seven grasses, seven Leguminosae, and a fallow condition, were evaluated on the seed bank at two soil depths (0 to 10 and 10 to 20 cm). The species found in the seed bank were quantified and identified by species and family. The precision of sampling, density, dominance, the indices of diversity of Simpson and Shannon-Weiner; index of sustainability; analysis of groupings of dissimilarities; and the value of importance of each species were calculated. High weed diversity was observed; 29 species were counted, including members of 12 different families. The highest expression of weeds was observed at soil depths of 0 to 10 cm. The Simpson and Shannon-Weiner coefficients indicated high diversity in both systems of succession. The index of sustainability did not indicate significant alterations in the different systems of succession. The coefficients of confenetic correlation were 0.74% and 0.82% for the 0-10 and the 10-20 cm soil depths respectively. It is concluded that there is a high diversity of weeds in the agroecosystems of Amazonia, and different cover crops promote modifications in the community and expression of the weeds' seed bank.

Intercropping maize and succession crops alters the weed community in common bean under no-tillage

“…The highest obtained common bean grain yield was for the crotalaria intercropping system, in relation to single maize (12.7 % higher), and the brachiaria intercropping system was intermediate to both (Figure 2B). Therefore, these observations are mainly attributed to changes in the community of weeds present in the seedbank area, due to the different managements adopted in the maize cropping (Cardina et al 2002, Cardoso et al 2017, Vargas et al 2017. Here, we hypothesize that it is not only important to think about reducing the density of weeds in the field, but also to ensure that the weeds present in a specific cropping system do not interfere with the cash crop yield.…”

“…Indeed, the rotation of at least three crops does not affect the crop grain yield and increase the weed community diversity by reducing the weed seedbank in the notillage system (Murphy et al 2006). On the other hand, it was found that the C. juncea crop rotation could increase the relative dominance and decrease the species diversity in the weed seedbank (Vargas et al 2017). However, more accurate and long-term studies need to be considered in order to elucidate the weed emergence flow in the field (experimental area conditions), since climatic conditions could affect the seedbank dynamics.…”

“…In this way, integrated crop management systems mitigate the use of herbicides, according to no-tillage system requirements (Bergtold et al 2017), allowing the use of long-term efficient strategies for weed control (Gomes Junior & Christoffoleti 2008). In fact, the dynamics of weed seedbanks is strongly regulated by the applied management (Murphy et al 2006, Cardoso et al 2017, Vargas et al 2017). However, intrinsic factors of weed species, such as morphological (seed size, shape and dispersal) and physiological (germination, dormancy type and resistance) characteristics also interact in the phytosociology of the weed community (Cardina et al 2002, Masin et al 2006, Feng et al 2015, Darmency et al 2017.…”

“…As observed by Lima et al (2014), the weed community changes during the cover crop development cycle, and the species with the highest importance value are controlled, as verified for E. indica at 90 days after sowing (DAS) of U. ruziziensis and at 135 DAS of Crotalaria spectabilis. Indeed, the results presented in the literature highlight the lack of phytosociological researches aiming to define integrated weed control strategies for the different cropping regions under no-tillage (Bybee-Finley et al 2017, Vargas et al 2017). Thus, this study aimed to evaluate the effect of maize intercropped with brachiaria or crotalaria on the phytosociological parameters of the weed seedbank along the succession of pearl millet, maize and common bean, under no-tillage.…”

Culturas de cobertura na supressão de plantas daninhas e atributos físicos do solo cultivado com café

“…Os resultados de precisão de amostragem de densidade e de precisão de amostragem de dominância (Figura 1) entre as plantas de cobertura e a escarificação mecânica do solo, avaliados na entrelinha e na projeção do rodado do trator, em área cultivada com a cultura do café estão acima do indicado por Concenço et al (2015), que considera como valor mínimo aceitável 1,00 %. Concenço et al, (2014) Coeficientes de diversidades mais altos normalmente são relacionados às áreas que tem maior amplitude de espécies de plantas infestantes (Vargas et al 2017). Em algumas situações se erra o termo de diversidade, com riqueza de espécies (Barbour et al 1987).…”