Abstract
Many measures have been proposed to mitigate gaseous emissions and other nutrient losses from agroecosystems, which can have large detrimental effects for the quality of soils, water and air, and contribute to eutrophication and global warming. Due to complexities in farm management, biological interactions and emission measurements, most experiments focus on analysis of short-term effects of isolated mitigation practices. Here we present a model that allows simulating long-term effects at the whole-farm level of combined measures related to grassland management, animal housing and manure handling after excretion, during storage and after field application. The model describes the dynamics of pools of organic carbon and nitrogen (N), and of inorganic N, as affected by farm management in grassland-based dairy systems. We assessed the long-term effects of delayed grass mowing, housing type (cubicle and sloping floor barns, resulting in production of slurry and solid cattle manure, respectively), manure additives, contrasting manure storage methods and irrigation after application of covered manure. Simulations demonstrated that individually applied practices often result in compensatory loss pathways. For instance, methods to reduce ammonia emissions during storage like roofing or covering of manure led to larger losses through ammonia volatilization, nitrate leaching or denitrification after application, unless extra measures like irrigation were used. A strategy of combined management practices of delayed mowing and fertilization with solid cattle manure that is treated with zeolite, stored under an impermeable sheet and irrigated after application was effective to increase soil carbon stocks, increase feed self-sufficiency and reduce losses by ammonia volatilization and soil N losses. Although long-term datasets (>25 years) of farm nutrient dynamics and loss flows are not available to validate the model, the model is firmly based on knowledge of processes and measured effects of individual practices, and allows the integrated exploration of effective emission mitigation strategies.
Highlights
During the last century, in many agricultural systems the inputs of nitrogen (N) bound by the Haber-Bosch process have largely replaced N from sources like symbiotic fixation and mineralization from manures, crop residues and soil organic matter [1]
N soil losses were strongly linked to available inorganic N, these soil losses from solid cattle manure (SCM) system were initially lower than from the slurry-based system, but were larger than for the slurry system after 75 years (Fig. 4e)
The simulation results demonstrated that individual emission mitigation measures were often insufficient to reduce N losses at the farming systems level
Summary
In many agricultural systems the inputs of nitrogen (N) bound by the Haber-Bosch process have largely replaced N from sources like symbiotic fixation and mineralization from manures, crop residues and soil organic matter [1]. Management should focus more on incorporation of legumes like clovers to fix atmospheric N2, cropping and animal housing systems that optimize crop residue and manure utilization, and on slow processes of build-up of organic matter (OM) and N stocks in soils [11]. The interactions among these biological processes are complex and prone to environmental variability, and as a consequence farmers often struggle to develop a coherent new management strategy at lower input levels [10]
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