Intervalo de dessecação de espécies de cobertura do solo antecedendo a semeadura da soja

Abstract

O objetivo deste trabalho foi avaliar intervalos de dessecação (2, 7, 14, 21 e 28 dias antes da semeadura da soja - DAS) de espécies utilizadas como cobertura (Brachiaria ruziziensis, Pennisetum americanum e Brachiaria brizantha) no desenvolvimento inicial, teor nutricional da soja e manejo de plantas daninhas. O delineamento experimental foi em blocos ao acaso, com quatro repetições. Na semeadura da soja, as espécies dessecadas aos 21 e 28 DAS foram controladas acima de 90%, porém a dessecação aos 2, 7 e 14 DAS mostrou controle inferior e distinto entre as espécies. Na dessecação aos 2 e 7 DAS, a emergência da soja ocorreu sob grande quantidade de biomassa verde, apresentando menor estande. Todavia, na dessecação aos 2 DAS, a palha se manteve por mais tempo no solo, reduzindo novos fluxos de emergência de plantas daninhas. Com o aumento do intervalo entre a dessecação de P. americanum e a semeadura da soja, houve acréscimo pronunciado no teor de fósforo da cultura. Os maiores teores de potássio na soja foram verificados com palha de B. ruziziensis e B. brizantha, e o teor de nitrogênio, quando B. brizantha e P. americanum foram dessecadas, aos 21 DAS.

Corn and soybean yields as affected by cover crops and herbicide timing under no-tillage system

“…In addition, millet and common bean are more sensitive to glyphosate and could be desiccated closer to soybean planting. Supporting this information, Monquero et al (2010) reported that millet dried much faster than B. brizantha after glyphosate application. Therefore, during this time, without being completely dried, the perennial grass could damage the soybean development.…”

“…Also Nascente and Crusciol (2012) reported that the amount of 7.6 Mg ha -1 of B. brizantha and 2.8 Mg ha -1 of millet did not affect soybean plant population. On the other hand, Monquero et al (2010) observed that desiccation done close to the soybean planting day caused reduction in the plant stand. Moreover, when the herbicide was applied near the seeding of soybeans, cover crops were not dry enough to allow the straw to be cut by the planter disks (Nascente and Crusciol, 2012).…”

“…These differences had significant effect on the grain yield and B. brizantha straw allowed the lowest yield (3,631 kg ha -1 ) differing from the cover crops millet (4,588 kg ha -1 ) and common bean (4,979 kg ha -1 ). This could be associated with the amount of straw on the soil surface, because a large amount of straw can affect plant growth and affect yield and yield components (Monquero et al, 2010;Nascente and Crusciol, 2012;Nascente et al, 2013b). Constantin et al (2009) found that soybeans emerging on soil with a big amount of cover crop biomass had their productivity reduced.…”

“…They showed that in addition to cover crops shadow, there are other factors such as the demand for nitrogen by the microorganism decomposing straw and allelopathic effects. Besides, according to Monquero et al (2010), B. brizantha is less sensitive to glyphosate application than millet and, therefore, it takes more days to dry completely. Yamada and Castro (2007) reported that the injury caused by the cover crops as a result of herbicide application close to planting the next summer crop could be aggravated by the higher dry matter production of the cover crops.…”

“…Furthermore, according to Coupland and Lutman (1982) in glyphosate applications near the planting time, there is the possibility of root exudation of herbicides from cover crops to corn or soybean, especially if the roots of cover crops treated with herbicide are numerous and close to the roots of crops. Research showed that the best time to dry out the weeds or cover crops ranges between seven and 20 days before planting soybeans or corn (Constantin et al, 2009;Nunes et al, 2009;Monquero et al, 2010;). …”