André Pellegrini

Nitrate and ammonium in soil solution in tobacco management systems

Os fumicultores do sul do Brasil seguem pacotes tecnologicos que impoem o uso de altas doses de fertilizantes, sem considerar os atributos do solo e do ambiente, representando grande risco para a degradacao dos recursos hidricos. O objetivo deste trabalho foi monitorar as concentracoes de nitrato e de amonio na solucao do solo da regiao do sistema radicular e abaixo deste, em Neossolo Litolico cultivado com fumo sob preparo convencional (PC), cultivo minimo (CM) e plantio direto (PD). O estudo foi conduzido na microbacia hidrografica do Arroio Lino, localizada no municipio de Agudo - RS. A adubacao de base foi de 850 kg ha-1 de 10-18-24, e a adubacao de cobertura, 400 kg ha-1 de 14-0-14. A coleta da solucao do solo foi com lisimetros de tensao durante o ciclo da cultura. A concentracao de amonio e de nitrato foi analisada pelo metodo da destilacao e titulacao. As concentracoes de nitrato, que variaram de 8 a 226 mg L-1, foram maiores apos a adubacao de base e decresceram ao longo do ciclo. As concentracoes medias de nitrato (N -NO3-) na zona radicular foram de 75 no PD, 95 no CM e 49 mg L-1 no PC. Abaixo das raizes, as concentracoes medias de nitrato foram de 58 no PD, 108 no CM e 36 mg L-1-no PC. Nao houve diferenca estatistica significativa na concentracao de nitrato e amonio nos sistemas de manejo. Entretanto, as concentracoes de nitrato encontrados representam um risco potencial para contaminacao da agua subsuperficial das fontes da mibrobacia em estudo. A concentracao de amonio (N-NH4+) decresceu no tempo em todos os sistemas de manejo. Essa reducao pode ter decorrido do processo de nitrificacao e da absorcao de parte do amonio pelas raizes das plantas em crescimento.

Contribuição das fontes de sedimentos em uma bacia hidrográfica agrícola sob plantio direto

Knowledge of the main diffuse sources of sediment production can enhance efficiency in use of public resources invested in management strategies that seek to mitigate sediment transfer to waterways from catchment areas. The aim of the present study was to evaluate the sediment sources in a rural catchment with predominance of annual crops under a no-tillage system and with intense and inappropriate exploitation of natural resources (soil and water) by quantifying the relative contribution of roads and croplands in the overall production of sediments. Inappropriate exploitation is a result of a lack of planning of crop production areas and access pathways, both from the point of view of their location in the landscape, and of management practices which are incompatible with the conditions of soil fragility and relief. The catchment is located in the municipality of Julio de Castilhos, State of Rio Grande do Sul. The period under study was from May 2009 to April 2011. For identification of the sources we used the fingerprinting method, which compares the soils from different sources and the sediments in suspension in the drainage canal using tracer elements. Inadequate soil management in croplands, the lack of planning of access roads, and the absence of control practices for surface runoff compatible with the fragility brought about by the soil and topography of the watershed have caused the emergence of accelerated erosion with negative effects for the farmer and society. Roads represent a high percentage of contribution to sediment transfer, but the contribution of cropland increases with rainfall of high magnitude. This shows that the magnitude of rainfall events affects the proportion of contribution among sources throughout the year in the catchment area, affecting the process of mobilization of sediments and nutrients towards the drainage system.