Use of waste must respect application intervals on crops, research shows

The Paraná AgroResearch and Applied Training Network (Rede AgroParaná), which has financial support from SENAR-PR and the State government, is developing a subproject in the Campos Gerais region to assess the implications for soil, water and nutrient losses on from the application of liquid bovine manure, in the long term, in areas with a Direct Planting System (SPD). The region was chosen to implement the study based on its capacity to generate cattle waste, given that Campos Gerais is a hub for dairy production in confinement and semi-confinement systems. In the same region, the soil has been managed under SPD for more than 30 years and, in many areas, it already receives intensive applications of manure from dairy farms.

For research, two experiments are being conducted with the application of liquid bovine manure in direct planting with crop rotation (soybeans, corn, wheat and black oats). The experimental stations belong to Fundação ABC and were installed in 2005 in conditions that represent the most used production system in the region.

According to Nerilde Favaretto, professor at the Department of Soils and Agricultural Engineering at the Federal University of Paraná (UFPR) and coordinator of the project, the focus of the research is the reduction of environmental impacts, especially on water resources. “We identified recommendations that provide benefits from the application of waste while reducing the environmental problems that may be caused,” she explains.

The researcher emphasizes that organic fertilizer brings several benefits in terms of productivity and the physical, chemical and biological attributes of the soil, increasing the accumulation of carbon and nitrogen in the soil – as long as management is carried out appropriately. “It is essential to adopt complementary soil conservation practices to prevent surface runoff from reaching water bodies,” says Nerilde.

Recommendations

One of the conclusions of the study is that successive applications of cattle manure can increase the risk of eutrophication of water bodies, due to the increase in phosphorus in the soil and the possibility of runoff into the water system. Eutrophication occurs when there is an accumulation of nutrients and the proliferation of algae in the surface layer of water, preventing photosynthesis and reducing oxygen levels. This causes the death of several animal and plant species, damaging aquatic ecosystems.

Another aspect observed was that, with the application of up to 120 m³/hectare/year of liquid cattle manure, there was a reduction in the volume of runoff and losses of soil and nutrients. “If the producer applies up to 60 m³ in winter and up to 60 m³ in summer, the possibility of contamination decreases, while the benefits remain”, points out the researcher.

According to Nerilde, it is recommended to apply manure at least seven days before a rain event. This minimizes the so-called surface sealing effect of the soil, which reduces water infiltration and increases surface runoff. “The interval between the application of manure and the occurrence of rain influences the capacity for water infiltration into the soil and the possibility of this manure being transported into nearby watercourses”, he concludes.