High-external input agriculture is one of the most disruptive human activities, which have been justified by the current economic paradigm due to high productivity and the need to feed a growing population. However, we are dangerously close to the edge of the planet resources and both hunger and food insecurity has increased. Limiting the use of non-renewable chemical fertilizers and pesticides, changing water management, enhancing diversity and considering the often-neglected social dimension of agriculture are the bases to other chemical and biological technologies to agriculture. Biological inputs can stimulate the substitution of chemical inputs without questioning the current fundaments or can be adopted as a turning point to intensify the harsh processes of transition to more environmental friendly agriculture. The debate is open and our contribution is to develop the scientific basis for biological inputs that, unlike soluble fertilizers and pesticides, depend on a number of factors for its success in promoting crop yield. In this review, we showed the results obtained with the combined use of diazotrophic endophytic bacteria and humic substances in diverse crops (sugarcane, maize, tomato, common beans and pineapple), presenting the main morphological and physiological changes induced by biological technology. A snapshot of the state of the art of the use of plant growth promoting bacteria together with humic substances was provided, showing their potential especially when plants are subjected to moderate to severe abiotic stress. The number of studies reporting the combined use of plant growth promoting bacteria and humic substances is surprisingly low. There is an open avenue for research and encouraging debate is the goal. To overcome the conventional agriculture, maintaining productivity levels is more than scientific challenge, is a humanitarian duty. The biological inputs can help in this purpose.

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The aim of this study was to assess the effect of N(2)-fixing and P-solubilizing bacteria during maturation of vermicompost on phosphorus availability. A bacterial suspension containing Burkholderia silvatlantica, Burkholderia spp. and Herbaspirillum seropedicae was applied at the initial stage of vermicomposting. At the end of the incubation time (120days), the nitrogen content had increased by18% compared to uninoculated vermicompost. Water-soluble P was 106% higher in inoculated vermicompost while resin-extractable P increased during the initial vermicomposting stage and was 21% higher at 60days, but was the same in inoculated and uninoculated mature compost. The activity of acid phosphatase was 43% higher in inoculated than uninoculated vermicompost. These data suggest that the introduction of the mixed culture had beneficial effects on vermicompost maturation.

ABSTRACT:Since the beginning of Human civilization, the soil organic matter has been used as plant growth promoter and/or regulator.Indeed, early in plant science history, even before the auxin concept has been established, the term "auximones" was coined to describe plant growth promoting humic acids derived from peat. Despite of this, until the end of the 20 th century, humic substances remained as some of the most neglected environment signals in plant physiology research. However, this scenario has changed in last decade with the discovery that the major systems of energy transduction of the plant cell membranes, the proton pumps, can be tightly orchestrated by humic substances just as elicited by a hormonal signaling. Differential activations of both plasma membrane (PM H + -ATPase) and vacuolar pumps (V-ATPase and H + -PPase) are modulated by humic substances triggering ion signatures related to specific patterns of plant growth and development. Phytohormones have been found to be associated with this humus bioactivity, and nitric oxide acting as a second messenger in a signaling pathway in which plants can sense the soil environment to cope with specific conditions. In this review, we discuss some of the most influential data available in literature, which have shaped this underexplored interface between the chemistry of the organic matter and the plant physiology. The key role of organic matter in the sustainable agriculture will also be highlighted from a biochemical perspective of the plant cell responses to biofertilization, specially in tropical environments.

RESUMOO objetivo deste trabalho foi avaliar o estoque e a qualidade da matéria orgânica (MOS) por meio de análises de ressonância magnética nuclear (RMN) de 13 C no estado sólido de amostras intactas de solo e de ressonância paramagnética eletrônica (RPE) e fluorescência dos ácidos húmicos (AH) isolados de um Cambissolo cultivado com cana-de-açúcar por longo tempo. Numa situação, a canade-açúcar foi cultivada por 55 anos sem a queima por ocasião da colheita. A outra situação envolveu uma área cultivada com queima da palhada, na qual em uma parte foi realizada a adição de vinhaça (120 m 3 ano -1 ) durante 35 anos e a outra não recebeu esse tratamento. O aumento no estoque de AH em 157 e 57 % nas camadas de 0-0,20 e 0,20-0,40 m, respectivamente, na área cultivada durante 55 anos com preservação do palhiço, correspondeu ao aumento observado no grau de aromaticidade e diminuição da acidez da MOS, obtido por RMN 13 C. Nas áreas com manejos que envolviam a preservação da MOS foram obtidos AH com maior concentração de radicais livres do tipo semiquinona, determinada por RPE, e maior intensidade de emissão de fluorescência. Mudanças significativas no processo de humificação da MOS e, portanto, na sua qualidade foram decorrentes da preservação do palhiço por ocasião da colheita. Por sua vez, a adição de vinhaça