Nitrous Oxide Emissions from Surface versus Injected Manure in Perennial Hay Crops

Abstract

Low‐producing alfalfa and tall fescue stands can benefit from the addition of manure. Injection of manure (slicing of soil) did not reduce yields of alfalfa or tall fescue. Impact of manure injection on N2O emissions is weather and species dependent. When injection of manure does not increase yield, surface application is more economical. Injecting manure can preserve N, but may mechanically damage the root systems of hay crops such as tall fescue (Festuca arundinacea L.) and alfalfa (Medicago sativa L.). Such damage could result in reduced yield. The objective of this study was to compare the effect of disk‐injected versus surface applied liquid dairy manure on (i) alfalfa and tall fescue dry matter (DM) yield and (ii) nitrous oxide (N2O) emissions. Two manure application methods (injection versus surface application) and two no‐manure controls (injection versus no soil disturbance) were replicated six times in 2014 and 2015 on established hay stands. Manure application increased alfalfa yield from 2.9 to 3.7 and from 4.2 to 5.1 Mg DM ha‐1 in 2014 and 2015, respectively, regardless of application method, suggesting no yield penalty or benefit from injection. Nitrous oxide emissions increased two‐ and six‐fold with manure addition, consistent with higher yields under manure application. Compared with the control treatments, manure addition to tall fescue increased yield by 0.8 and 3.3 Mg ha‐1 in 2014 and 2015, respectively, also with no yield benefit or penalty from injection. Injection of manure did not influence N2O emissions in 2014, but increased emissions by 35% compared with surface application in 2015, and this is consistent with differences in soil moisture that year. Our results indicate injection of liquid manure can be implemented without negatively influencing yield in hay crops, while the impact on N2O emissions can be crop and weather dependent. When injection does not increase yield, the surface application of manure to hay crops is more economical.

Nitrous oxide emissions are driven by environmental conditions rather than nitrogen application methods in a perennial hayfield

“…The previous corn silage trial adjacent to our trial generally did not experience such dry conditions, again suggesting that low soil moisture levels played a role in limiting N 2 O fluxes during our study. Alternatively, flux rate differences between our trial and the previous, adjacent corn silage trail may be due to the different cropping systems, as our N 2 O flux rates were comparable to rates observed in other perennial grass systems (Rodhe et al., 2006; Sadeghpour et al., 2018), but lower than the peak fluxes observed in some (Dittmer et al., 2020; Duncan et al., 2017), but not all (Cambareri et al., 2017), corn systems.…”

“…The previous corn silage trial adjacent to our trial generally did not experience such dry conditions, again suggesting that low soil moisture levels played a role in limiting N 2 O fluxes during our study. Alternatively, flux rate differences between our trial and the previous, adjacent corn silage trail may be due to the different cropping systems, as our N 2 O flux rates were comparable to rates observed in other perennial grass systems (Rodhe et al, 2006;Sadeghpour et al, 2018), but lower than the peak fluxes observed in some (Dittmer et al, 2020;Duncan et al, 2017), but not all (Cambareri et al, 2017), corn systems. Although daily precipitation was not an important predictor of N 2 O fluxes (Table 3), relatively large rainfall events the day before sampling appear to have contributed to the higher daily fluxes observed in the injection and broadcast treatments on August 5, 2020 (7.6 cm on August 4, 2020, the largest rainfall event of our study) and in the injection treatment on June 15, 2021 (2.4 cm on June 14, 2021; Figure 2a,b,d).…”

“…Given the importance of soil moisture in predicting N 2 O fluxes, the relatively small N 2 O fluxes and the minimal treatment differences we observed may be related to low soil moisture at the time of treatment application. Soil moisture was mostly low (mean = 12.4 ± 0.13%) within 30 days after all treatment applications, when fluxes were expected to peak (Figure 2c Sadeghpour et al, 2018;Sistani et al, 2010;Vallejo et al, 2005). In comparison, average daily N 2 O fluxes at the same site, but in corn silage (Zea mays L.), were 1.5 and 3.75 times greater than those we observed after manure broadcast and injection applications, when VWC was 20%-22% on average during and for a month after applications (Dittmer et al, 2020).…”

“…Incomplete denitrification is widely known as an important N 2 O source in agricultural systems (Butterbach‐Bahl et al., 2013; Dell et al., 2011). However, fluxes are spatially and temporally variable (Butterbach‐Bahl et al., 2013), and manure injection's effect on N 2 O emissions varies with application timing, precipitation, and year (Dittmer et al., 2020; Misselbrook et al., 1996; Sadeghpour et al., 2018). Thus, manure injection does not always generate more N 2 O emissions than alternative practices (Cambareri et al., 2017; Sadeghpour et al., 2018; Vallejo et al., 2005).…”

Conservation tillage is compatible with manure injection in corn silage systems

“…The adoption of no-till and reduced tillage and manure injection have been on the rise in the northeast dairy region of the United States in the last 30 yr. Surface application of manure is a relatively inexpensive and common method of manure application to corn silage (Sadeghpour, Ketterings, Vermeylen, Godwin, & Czymmek, 2017), but this practice can result in ammonia volatilization, nutrient runoff, and leaching (Ketterings et al, 2013;Maguire et al, 2011). Manure injection can increase the retention of plant-available N by reducing ammonia volatilization while decreasing environmental outcomes (Burcham et al, 2008;Duncan et al, 2017;Hansen et al, 2003;Misselbrook et al, 1996;Pote et al, 2003).…”