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

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.

Effects of Soil pH on Gaseous Nitrogen Loss Pathway via Feammox Process

The application of N fertilizer is one of the most critical soil acidification factors in China, and soil acidification significantly alters biogeochemical processes such as N loss. Anaerobic ammonium oxidation coupled with iron reduction (Feammox) is an important biological process for N loss in natural environments, with the end-products of N2, NO2− and NO3−. However, the response of Feammox pathways to soil pH fluctuation has not been thoroughly studied. In the current study, Feammox pathways and microbial communities were explored through a slurry culture experiment with an artificially adjusted pH combined with a 15N isotope tracing technique and molecular biotechnology. Results showed significant differences in the gaseous N loss through Feammox (0.42–0.97 mg N kg−1 d−1) under different pH conditions. The gaseous N loss pathways were significantly affected by the pH, and Feammox to N2 was the predominant pathway in low-pH incubations. The proportion of N loss caused by Feammox coupled with denitrification increased as the soil pH increased. The gaseous N loss through Feammox increased by 43.9% when the soil pH decreased from 6.5 to 5.0. Fe-reducing bacteria, such as Ochrobactrum, Sphingomonas, and Clostridium increased significantly in lower pH incubations. Overall, this study demonstrated the effects of soil pH on Feammox pathways and extended the understanding of the N biogeochemical cycle in acidic soil.

Effects of rumen undegradable protein sources on nitrous oxide, methane and ammonia emission from the manure of feedlot-finished cattle

Here, the effects of sources of rumen undegradable protein (RUP) in diets on methane (CH4), nitrous oxide (N2O) and ammonia (NH3) emissions from the manure of feedlot-finished cattle were evaluated. We hypothesized that the use of different RUP sources in diets would reduce N loss via urine and contribute to reduced N2O, CH4 and NH3 emissions to the environment. Nellore cattle received different diets (18 animals/treatment), including soybean meal (SM, RDP source), by-pass soybean meal (BSM, RUP source) and corn gluten meal (CGM, RUP source). The protein source did not affect the N and C concentration in urine, C concentration in feces, and N balance (P > 0.05). The RUP sources resulted in a higher N2O emission than the RDP source (P = 0.030), while BSM resulted in a higher N2O emission than CGM (P = 0.038) (SM = 633, BSM = 2521, and CGM = 1153 g ha− 2 N-N2O); however, there were no differences in CH4 and NH3 emission (P > 0.05). In conclusion, the use of RUP in diets did not affect N excretion of beef cattle or CH4 and NH3 emission from manure, but increased N2O emission from the manure.

20 Years nitrogen dynamics study by using APSIM nitrogen model simulation for sustainable management in Jilin China

The tremendous increase in industrial development and urbanization has become a severe threat to the Chinese climate and food security. The Agricultural Production System Simulator model was used to simulate soil nitrogen in black soil in Yangling Jilin Province for 20 years. The observed values are consistent with the simulated values. The predicted values of total soil NO3−–N and NH4+–N nitrogen are 10 kg ha−1 and 5 kg ha−1 higher than the observed values. The total soil NO3−–N loss has the same trend as the rainfall, and it increases with the number of rainfall days over the years. The average 20 years losses of NO3−–N and NH4+–N observed were 1375.91 kg ha−1, and 9.24 kg ha−1, while in the simulation increase was 1387.01 kg ha−1 and 9.28 kg ha−1, respectively. The difference between the observed and simulated values of NO3−–N and NH4+–N of mean loss was 11.15 kg ha−1 and 0.04 kg ha−1 respectively. Moreover, our findings highlight the opportunity further to improve management policies (especially for nitrogen) to maintain crop yield.

Urease Inhibitors Effects on the Nitrogen Use Efficiency in a Maize–Wheat Rotation with or without Water Deficit

The use of urease inhibitors in irrigated systems decreases both soil ammonium (NH4+) and nitrate (NO3−) availability, and, thus, could be an easy tool to reduce N loss due to ammonia volatilization and NO3− leaching. The main goal of this experiment was to assess the effect of urease inhibitors on N use efficiency, N losses, and their economic impact in a maize-wheat field experiment. In this study, 10 treatments were compared, combining the urea fertilizer with or without urease inhibitor, applied in one or two dressings, and under optimal or sub-optimal irrigation. A single application of urease inhibitor (IN1d), coupled with the conventional urea, helped to reduce the nitrate leaching risk both during the maize period (even when compared to the two dressing treatment) and after harvest. In addition, this improvement was achieved together with an increase in economic benefit, even when compared with the application of the same amount of regular urea split into two dressings. Under low water availability systems, the benefits of applying urease inhibitors increased with respect to the application of regular urea, making this technique a very promising strategy for adaptation to climate change in arid and semiarid regions.

Annual Nitrogen Balance from Dairy Barns, Comparison between Cubicle and Compost-Bedded Pack Housing Systems in the Northeast of Spain

The aim of this study was to determine N recovery and irreversible losses (i.e., through NH3-N volatilization) from manure in two different housing systems throughout a year using an N mass balance approach. Dietary, milk, and manure N were monitored together with outside temperatures in six dairy barns during six months, comprising two different seasons. Three barns were designed as conventional free stalls (cubicle, CUB) and the other three barns as compost-bedded packs (CB). All the barns were located in the Ebro’s valley, in the northeast of Spain. Mass N balance was performed simultaneously in the six barns, during two three-month periods (Season I and II) and sampling at a 15-day interval. Results of ANOVA analysis showed that annual N retained in manure (kg/head per year) from cows housed in CUB barns was significantly higher than in manure from cows housed in CB (133.5 vs. 70.9, p < 0.001), while the opposite was observed for N losses (26.9 vs. 84.8, for CUB and CB barn, respectively; p < 0.005). The annual mean proportion of irreversible N loss from manure in relation to N intake was much lower in barns using conventional free-stall cubicles than the mean ratio registered in bedded pack systems barns.

Effects of Zeolitic Urea on Nitrogen Leaching (NH4-N and NO3-N) and Volatilization (NH3) in Spodosols and Alfisols

Global use of urea nitrogen (N) fertilizer is increasing, but N losses are still very high (40–70%). Zeolites have the capability of holding NH4+, thus reducing N losses when applied as a soil amendment. However, application of a large quantity of zeolite is costly and inconvenient. In this study, zeolitic fertilizers were evaluated to select the best formulation with reduced leaching of NH4-N and NO3-N and NH3 volatilization in agricultural soils (Alfisol and Spodosol). The treatments included the following: T0 = control, T1 = urea fertilizer, T2 = zeo-urea (1:1), T3 = zeo-urea (2:1), T4 = zeo-urea (3:1), T5 = zeo-urea (1:2), and T6 = zeo-urea (1:3). Leaching was performed at 4, 8, 12, 19, 25, 32, 39 and 45 days after the soils were treated with the designated fertilizers, including control, and packed into columns. Leachate samples were collected after each leaching event and analyzed for the concentrations of NH4-N and NO3-N and the quantity of leachate. Ammonia volatilization was recorded at days 1, 5, 9, 13 and 20 of soil treatments. Results indicate that zeolitic fertilizer formulations effectively reduced N losses. NH4-N loss was reduced by 13% and 28% by zeo-urea (1:1) in Alfisol and Spodosol soils, respectively, whereas zeo-urea (2:1) and zeo-urea (3:1) effectively decreased NO3-N leaching in Alfisol. Volatilization loss of NH3 was reduced by 47% in Spodosol and 32% in Alfisol soil with zeo-urea (1:1) as compared with that of urea fertilizer. The results suggest that zeo-urea (1:1) is an effective fertilizer formulation for reducing N losses, especially in Alfisol, as compared with conventional urea fertilizer.