Effect of dairy manure-based fertilizers on nitrous oxide emissions in a semi-arid climate

Manure treatment technologies are of interest to dairy operations to improve nutrient management, although there are little data related to nutrient availability and environmental impacts of these manure-based fertilizer products. This field trial experiment investigated the impact of two manure-based fertilizer sources (phosphorus enriched solids [PE] and mechanical vapor recompression solids [VR]) on soil nutrients, crop yields, and N2O emissions in a forage rotation. The study was a factorial random complete block design, with two main factors: manure history (with [M]; without [NM]) and manure-based fertilizer product (control [Con], PE, VR), under a continuous corn and triticale rotation. M had greater soil organic carbon, total carbon, total nitrogen, and M3-P (30%-128%) and reduced NH4-N (15%) than NM, with no other treatment differences. Corn silage yields were greater in NM versus M (7%) treatments only in 2021, while in 2022 VRNM was 17% greater than ConNM only. Triticale yields were 14% greater in M plots versus NM treatments only in 2021. In 2022, triticale yields were 1.7 times lower in ConNM versus all other treatments, and PENM was 71% greater than ConM. The greatest N2O fluxes occurred in May, June, and July with M having 69% greater average cumulative fluxes than NM, while average VR cumulative fluxes were 102% greater than PE and Con. Over both years, net loss of N-applied as N2O-N was 1.9%-2.2% for VR and 0.4%-0.8% for PE solids. While manure-based fertilizers performed well as a nutrient source, their susceptibility to N2O loss needs to be considered in management strategies. Plain Language Summary Manure treatment technologies can improve nutrient management, though there is little data related to crop and environmental impacts of manure byproducts. We investigated two manure-based fertilizer sources (Phosphorus Enriched Solids [PE] and Mechanical Vapor Recompression Solids [VR]), and application of solid dairy manure, on soil nutrients, crop yields and N2O emissions. Application of solid dairy manure had greater soil carbon, nitrogen and phosphorus in the topsoil compared to manure-based fertilizers. There were slight differences in corn silage and triticale yields which were greater in treatments with previous manure application. Over two years, net loss of N applied as N2O-N was 1.9-2.2% for VR and 0.4-0.8% for PE solids. Nutrient extraction technologies produce manure-based fertilizer products that are beneficial for crops but may be susceptible to N2O losses, which need to be considered when managing these products.