Band application of acidified slurry as an alternative to slurry injection in a Mediterranean double cropping system: Agronomic effect and gaseous emissions

Abstract

Injection is the recommended technique for slurry application to soil in most European countries but its utilization at the farm scale is quite limited, namely in countries from southern Europe, due to the strong investment needed in machinery and problematic utilization in stony and/or heavy soils. Acidification of animal slurry has proved to be efficient at minimising NH3 emissions but little is known about its impact on other greenhouse gas (GHG) emissions or agronomic effect, particularly in Mediterranean conditions. In the present study, we evaluate the potential of band application of acidified slurry as an alternative to raw slurry injection, in terms of agronomic effects and NH3 and GHG emissions, for two different Mediterranean soils (a sandy and a sandy-loam soil) where a double-cropping system (oat during winter and maize during spring/summer) was run over 3-years. Five treatments were tested in 1 m2 field plots: 1) control (non amended soil); 2) injected slurry (IS); 3) band application of raw slurry followed by soil incorporation (SS); 4) band application of acidified slurry followed by soil incorporation (AS); 5) band application of acidified slurry with no soil incorporation (ASS). An amount of slurry equivalent to ∼90 and 170 kg N ha−1 was applied before oat and maize sowing, respectively.The dry matter yields obtained with the AS treatment, in both the maize and oat crops, were mostly similar to or higher than those of IS, while ASS led - on some occasions - to small decreases in dry matter yield relative to IS, namely in the sandy soil. Treatment AS led also to apparent N and P recovery values (ANR and APR, respectively) similar to or higher than those of IS, except in the sandy soil during oat growth. After six consecutive slurry applications, a significant decrease of pH and an increase of the extractable S content were observed in soil receiving acidified slurry, relative to soil amended with non-acidified slurry.Significant NH3 emissions were observed only in SS treatment during all the experiment. Of the total N applied, the amount lost as N2O did not differ significantly among the amendment treatments during the oat growth. However, the cumulative N2O emissions from IS were significantly higher, relative to SS, AS and ASS, during maize growth. Higher cumulative CH4 emissions were observed during maize growth relative to oat growth, namely from IS compared to all other treatments. Band application of acidified slurry without soil incorporation reduced the N2O and CH4 emissions by 65% and 40%, respectively, relative to IS. The soil characteristics had no significant effect on the gaseous emissions for the acidified slurry treatments.It can be concluded that band application of acidified slurry followed by soil incorporation is an efficient solution to provide nutrients to plants while minimising NH3 and GHG emissions and can thus be proposed as an alternative to injection. Nevertheless, the impact of acidified slurry application on soil properties needs to be monitored in the long term.