Carbon and nitrogen in particle-size fractions of organic matter of soils fertilised with surface and injected applications of pig slurry

The injection of pig slurry in the soil, associated with the no-tillage system and the reduction of carbon and nitrogen losses through volatilisation, can positively influence the carbon and nitrogen contents in the soil organic matter (SOM) fractions. The objective of the present study was to evaluate the effect of surface and injected applications of pig slurry to soils under a no-tillage system on soil organic carbon (SOC) and soil total nitrogen (STN) contents in particle-size fractions of the SOM. The no-tillage system included a crop rotation with grass species, summer maize, and winter black oat and wheat grown from 2011 to 2015. The treatments consisted of injected application of pig slurry, surface applications of pig slurry, application of chemical fertiliser (NPK), and a control with no soil fertiliser application. The 0-5, 5-10, and 10-20 cm soil layers were evaluated for SOC and STN contents, and for particle-size fractions: particulate organic carbon, particulate organic nitrogen, mineral-associated organic carbon, and mineral-associated organic nitrogen. We also evaluated the carbon and nitrogen contents and mass in the light organic matter. The injection of pig slurry increased carbon and nitrogen contents of all SOM fractions compared to surface application of pig slurry. These results suggest that the use of injected pig slurry to the soil under crop rotation in no-tillage reduces carbon and nitrogen losses by volatilisation and emissions to the atmosphere. We recommend the application of pig slurry by injecting in soil because it promotes higher increases in the SOM fractions. This form of application of pig slurry to the soil was shown as an effective and environmentally sustainable method for the conservation and improvement of soil quality.