Manure application at long-term in no-till: Effects on runoff, sediment and nutrients losses in high rainfall events

Manure application in agricultural systems has demonstrated improvement on physical, chemical and biological soil properties as well as on crop production, however, it may generate environmental problems, such as transport of pollutants associated with surface runoff. The aim of this work was to evaluate if the improvement on soil properties with the long-term liquid dairy manure (LDM) application can reduce the water, soil and nutrients losses by surface runoff under intense simulated rainfall. The intense simulated rainfall (60 mm h(-1)) was applied once before winter sowing over maize harvested residue (straw), three months after the harvest and eight months after the last application of LDM (0, 60, 120 and 180 m(3) ha(-1) year(-1)), which was continually applied on the surface mulch with no incorporation (no-till system) during twelve years, twice a year, in the summer and winter crops with three replicates. The surface runoff was evaluated up to 90 min at different time intervals and sediments, nitrogen, phosphorus, and carbon were analyzed. In general, the results indicated an increase on runoff and sediment losses and on nutrient concentrations and losses with LDM application (120 m(3) ha(-1) year(-1)). The expected positive effect on soil physical, chemical and biological properties by long-term LDM application was not enough to reduce the losses through runoff in heavy rainfall, even with the presence of straw and the absence of surface sealing (simulated rainfall was applied eight months after LDM application). However, the expected high concentration of nutrients on the soil surface increased the concentration of nutrients in runoff. The high proportion of bioavailable phosphorus indicates a major contribution on losses of readily available phosphorus for aquatic life. These results suggest the need for complementary conservation practices in no-till to prevent the input of runoff in watercourses during events of intense precipitation, even in the unmanured soil.