High Carbon Amendments Increase Nitrogen Retention in Soil After Slurry Application—an Incubation Study with Silty Loam Soil

Abstract

Excess nitrogen (N) after animal slurry application is a persistent problem of intensive agriculture, with consequences such as environmental pollution by ammonia (NH3) and nitrous oxide (N2O) emissions and nitrate (NO3−) leaching. High-carbon organic soil amendments (HCAs) with a large C:N ratio have shown the potential of mitigating unintended N losses from soil. To reduce gaseous and leaching N losses after the application of slurry, a laboratory incubation study was conducted with silt loam soil. We tested the potential of three different types of HCA—wheat straw, sawdust, and leonardite (application rate 50 g C L−1 slurry for each of the three HCAs)—to mitigate N loss after amendment of soil with pig and cattle slurry using two common application modes (slurry and HCA mixed overnight with subsequent addition to soil vs. sequential addition) at an application rate equivalent to 80 kg N ha−1. Compared to the control with only soil and slurry, the addition of leonardite reduced the NH3 emissions of both slurries by 32–64%. Leonardite also reduced the total N2O emissions by 33–58%. Wheat straw reduced N2O emissions by 40–46%, but had no effect on NH3 emission. 15 N labeling showed that the application of leonardite was associated with the highest N retention in soil (24% average slurry N recovery), followed by wheat straw (20% average slurry N recovery). The mitigation of N loss was also observed for sawdust, although the effect was less consistent compared with leonardite and wheat straw. Mixing the slurry and HCA overnight tended to reduce N losses, although the effect was not consistent across all treatments. In conclusion, leonardite improved soil N retention more effectively than wheat straw and sawdust.

Improving nitrogen retention of cattle slurry with oxidized biochar: An incubation study with three different soils

“…Dissolved organic C and mineral N (NH 4 + and NO 3 − ) were extracted with 0.01 M calcium chloride (CaCl 2 ) solution (soil/solution ratio, 1:4 w/v) and shaken for 2 h at 200 rpm as described in Cao et al. (2022).…”

Nitrogen fertilization and liming increased CO2 and N2O emissions from tropical ferralsols, but not from a vertisol

“…The headspace was connected to the gas analyser (G2508, Picarro, Inc.) in closed‐loop mode. This allowed the change in CO 2 , CH 4 and N 2 O concentration to be quantified over a 10‐min period, as described by Cao et al (2021). The measurements of GHG fluxes were performed on incubation days 1, 2, 3, 5, 8, 15, 22, 29, 36, 43, 50 and 57.…”

“…Soil substrates (with and without N and CaCO 3 ) were thoroughly mixed, filled in incubation PVC tubes (150-mm height, 50-mm diameter) as described in Cao et al (2021) and recompacted to the original bulk density, as reported in Table 1. The soil moisture was adjusted to 50% of the water holding capacity, and the water content was adjusted by weekly weighing and replacing the evaporative water loss by using distilled water.…”

Leonardites Rich in Humic and Fulvic Acids Had Little Effect on Tissue Elemental Composition and Dry Matter Yield in Pot-Grown Olive Cuttings

“…There are regions of the Soil Syst. 2022, 6, 7 2 of 12 world where landless livestock production systems are dominant, which create complications in waste management, sometimes resulting in serious problems of environmental contamination [4,5]. In other regions, animals and their associated farmyard manures are practically nonexistent.…”