Abstract

We evaluated the effects of biannual surface applications of swine wastewater (SWW) for 11 years, on chemical and microbiological attributes of a clay-textured soil under no-tillage (NT) or conventional tillage (CT) in Palotina, Paraná, Brazil. The treatments consisted of SWW doses (split into autumn-winter/spring-summer seasons) totaling 30, 60, 90 or 120 m³ ha^-1 year^-1, and a control without application, under CT or NT soil managements (SM). The experimental design was in randomized blocks with a split-plot arrangement and four replications, with SM in the plots and the doses of SWW in the subplots. After 11 years of applications of SWW, soil samples were taken at 0-10, 10-20, 20-40, and 40-60 cm of depth by the end of the winter cover crop, 44 days after the second biannual application. The treatments had only minor effects on the assessed chemical and microbiological soil properties. Available P and NO₃^--N increased with the doses of SWW at the two upper soil layers, whereas NT decreased NO₃^--N at 10-20 cm and increased P at 0-10 cm. Zn²⁺ also increased with the doses of SWW, irrespectively the SM. NT increased the microbial biomass C (MBC) at 0-10 cm and 10-20 cm of soil depth, and the microbial quotient (qMic) at 0-10 cm. SM and SWW did not change the densities of heterotrophic bacteria, fungi, nitrite-oxidizers or ammonifiers at any soil depth. SM had single effects on organic C, MBC and qMic, whereas SWW had single effect only on Zn²⁺. Only available P and NO₃^--N were affected by both SM and SWW. The principal component analysis for chemical and microbiological attributes showed distinct groupings between CT and NT, and SWW rates at 0-10 cm and 10-20 cm of soil depths, the most influenced soil layers.

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