Influence of Manure Application Techniques on the Microbial Content of Grass and Grass Silage

ABSTRACT Field observations of visible dry manure residues in organically fertilised grassland, especially in drought areas in Bavaria (Germany), raised questions about whether different manure application methods influence the microbial composition in grass and in silages. Therefore, the aim of this study was to investigate if and to which extent three manure application methods (broadcast, trailing shoe and disc injector) and a control (mineral fertiliser) influence the microbial quality of grass and grass silage. The following samples were taken in two trial years (2020–2021): Soil ( n = 16), manure ( n = 10), wilted‐chopped grass ( n = 96) and grass silage samples ( n = 80). The laboratory methods used were cultivation and qPCR. The comparison between the test groups showed no significant difference in the number of aerobic bacteria, lactic acid bacteria, Lactobacillus spp., Enterobacteriaceae , E. coli and yeasts in all sample types. The Clostridia load in soil and grass before fertilisation was similar in all test groups. After fertilisation, grass samples from plots fertilised with the disc injector method had statistically significantly lower Clostridia (2.6 log 10 cfu/g) than samples from the trailing shoe (3.3 log 10 ) and the broadcast (3.2 log 10 ) but higher than the control group (1.7 log 10 ) ( p < 0.05). Clostridia counts in silages were between 3.7 and 3.9 log 10 for the manure treatments and 3.3 log 10 for the control. Except for the Clostridia levels in the grass, the results of this study indicate that the grass and silage from the three manure application methods were of similar microbial quality.