Generation of High Concentration Free Volatile Fatty Acids from Continuous Anaerobic Digestion of Chicken Manure by Suppressing the Decomposition of Nitrogenous Components.

Free volatile fatty acids (free VFA) play a crucial role in the inactivation of pathogens during the anaerobic digestion of animal manure. However, the decomposition of nitrogenous components can release alkaline ammonium-N, which might increase the pH and reduce the concentration of free VFA. In this study, continuous anaerobic digestion of high-solid chicken manure was conducted for 150 days. The results indicated the process stabilized at a pH of approximately 6.0, with total ammonia nitrogen (TAN) of around 7.0 g/L. The resulting concentration of free VFA was only about 3.1 g/L, which might not sufficiently effective for pathogen inactivation. On the 70th day, hydrogen chloride was added into the reactor to adjust the pH to 5.5. This led to a further decrease in pH to 4.3 and TAN to 2.3 g/L. As a result, the concentration of free VFA significantly increased, reaching up to 12.6 g/L. These findings support the potential for generating high levels of free VFA even for nitrogen-rich manure by implementing an appropriate process regulation.

Assessing the environmental sustainability of different soil disinfestation methods used in solar greenhouse vegetable production systems.

Overuse of fertilizers and irrigation and continuous monocropping is increasingly jeopardizing vegetable production in solar greenhouses as it causes serious soil degradation and the spread of soil-borne diseases. As a countermeasure, the practice of anaerobic soil disinfestation (ASD) has been recently introduced, which is carried out during the summer fallow period. However, ASD may increase N leaching and greenhouse gas (GHG) emissions when large amounts of chicken manure are applied. This study assesses how the use of different amounts of chicken manure (CM) combined with rice shells (RS) or maize straw (MS) affects soil O2 availability, N leaching, and GHG emissions during and following the ASD period. Application of RS or MS alone effectively stimulated long-lasting soil anaerobiosis without major stimulating effects on N2O emissions and N leaching. Seasonal N leaching and N2O emissions were in the ranges of 144-306 and 3-44 kg N ha-1, respectively, and were strongly increasing with increasing rates of manure application. Combining high rates of manure application with the additional incorporation of crop residues further increased N2O emissions by 56 %-90 % as compared to the standard practice of farmers (1200 kg N ha-1 CM). About 56 %-91 % of seasonal N2O emissions occurred during the ASD period, whereas N leaching mainly occurred in the cropping period (75 %-100 %). Our study shows, that for priming ASD incorporation of crop residue is sufficient and that the addition of chicken manure for ASD is not needed and should be reduced or even prohibited as it does not improve yields but stimulates the emission of the strong GHG N2O.

Anaerobic soil disinfestation with incorporation of straw and manure significantly increases greenhouse gases emission and reduces nitrate leaching while increasing leaching of dissolved organic N.

Greenhouse vegetable production in China mostly involves excessive N fertilization and flood irrigation. This causes serious soil degradation and spreading of soil borne diseases. As a countermeasure against soil borne diseases anaerobic soil disinfestation (ASD) is applied during the summer fallow period. Current practices involve the incorporation of organic C sources, covering of the soil with plastic film and flood irrigation. However, farmers not only apply straw but also organic manure in ASD which may result in significant greenhouse gas emissions and N leaching. A field experiment was conducted in a greenhouse during the summer fallow period to test the impact of three ASD practices on soil GHG (N2O, CO2 and CH4) emissions and N leaching: 1) control (CK), bare soil, no ASD; 2) ASD without straw incorporation (ASD-S); 3) ASD plus straw incorporation (ASD+S) and 4) ASD plus straw and chicken manure incorporation (ASD+SM). Applying any form of ASD resulted in an increase in N2O emissions from approximately 1 kg N ha-1 month-1 to 10.7 (ASD)-47.0 (ASD+SM) kg N ha-1 month-1. Furthermore, N leaching from treatments of ASD ranged from 24.1-54.2 kg N ha-1 month-1, with highest values in ASD-S. However, while N leaching in ASD-S was solely in the form of NO3-, DON leaching was with approximately 12-20% a significant component of total N leaching in ASD+S and ASD+SM. Overall, ASD+SM showed the highest environmental N losses, which were dominated by N2O emissions. This highlights the need to advise farmers and policy makers to ban the incorporation of chicken manure instead of straw only during the ASD period and to optimize irrigation schemes instead of flood irrigation to reduce environmental N losses. Putting in more environmental sound ASD practices will certainly help to improve the sustainability of greenhouse vegetable production.