Can Dairy Slurry Application to Stubble, without Incorporation into the Soil, Be Sustainable?

Abstract

In many countries, livestock slurry must be injected or incorporated into the soil to reduce nitrogen losses. However, when the injection is not feasible, farmers adopting conservation practices discard the use of slurry as fertilizer. New approaches related to slurry treatment or application management can stimulate the use of slurry in conservation agriculture (CA). This study aimed to evaluate the agronomic effects of some new management strategies to use dairy slurry for fertilization of ryegrass grown on stubble-covered soil, using as reference standard practices (slurry injection and mineral fertilizer application). The following treatments were considered: (i) bare soil: control (CB), mineral fertilizer (MB), injection (IN); (ii) stubble: control (CS), acidified dairy slurry (ADS), raw dairy slurry (RDS), irrigation following RDS (IR), mineral fertilizer (MS), RDS placed under the stubble (US), raw slurry applied 16 days after sowing (RDS T16). Effects on ryegrass yield, apparent nutrient recovery (ANR) and soil chemical properties were assessed. ADS reached 94% equivalence to MS and performed similarly to IN for productivity, ANR and soil parameters showing to be a sustainable alternative to replace mineral nitrogen and a potential solution to enable dairy slurry application in CA without injection or incorporation into the soil.

Dairy Slurry Application to Stubble-Covered Soil: A Study on Sustainable Alternatives to Minimize Gaseous Emissions

“…Carbon dioxide emissions, especially in the first days, result from the decomposition of organic matter promoted by the stimulus of fertilization, moisture and soil disturbance on soil microbial activity [60]. Ultimately, similar C emissions between slurry-based and mineral (without C input) fertilizers may indicate an accumulation of carbon in the soil promoted by slurry-based fertilizers (although it was not possible to detect in this 108-day experiment), as observed in [35,57]. Results reported in [61] complement this information, with an increase in soil organic carbon promoted by the long-term application of straw and manure.…”

“…Thus, high GWP may not necessarily imply high ys-GWP and vice versa [62]. For instance, the ryegrass yield [35] and GWP of ADS were 2.98 and 1.66 times greater than CS, respectively. Therefore, to compensate for the lower CS yield, it would be necessary to grow an area 2.98 times larger, which means that the new GWP of CS would be 100.19 g CO 2 -eq pot -1 (2.98 × 33.62), or 1.79 times greater than ADS.…”

“…The physicochemical characteristics of the soil, dairy slurry and stubble; ambient daily temperatures; and ryegrass cultivation and yield are described in detail in [35].…”

“…P and K were added to equalize their content in all treatments that received slurry or ammonium sulphate. More details can be found in [35].…”

“…where yield is the sum of the ryegrass yields (dry matter) after three harvests, as reported in [35], expressed in g CO 2 -eq g −1 .…”