A Process-Based Nutrient Model for the Bedpack Manure of Confined Beef Systems

View the project final report

• 2013 annual report

Commodities

• Animals: bovine

Practices

• Animal Production: manure management
• Crop Production: nutrient cycling
• Sustainable Communities: sustainability measures

Manure management is a concern for beef cattle producers and the general public. However, the manure and bedding material mixed with manure can be a valuable fertilizer. We conducted a lab-scale experiment to investigate how manure storage time, bedding material, and temperature affect ammonia (NH₃), greenhouse gases (carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)), moisture content, and nutrient content (nitrogen (N), phosphorus (P), and potassium (K)) in lab-scaled simulated beef cattle bedded manure packs. The study showed that NH₃ and GHG concentrations were higher under hot conditions (approaching 104°F) compared to moderate conditions (at temperatures around 50°C). Storage time did not affect NH₃ and N₂O losses, whereas CH₄ and CO₂ emissions are expected to increase with longer storage. During hot, dry summer months, bedded manure packs are expected to be drier and have less N content because of increased gaseous loss of N. Ammonia emission and K concentration are expected to be higher when corn stover bedding is used compared to soybean stubble. Results of the lab-scaled study inform a model of N, P and K transformations and movements in bedded manure packs with respect to different manure storage time, bedding material, and ambient air temperature. A survey with beef producers and consultant/planners in Minnesota, South Dakota, Iowa, and, Nebraska was conducted to identify the most useful format of input and output parameter to this model. A process-based model has been conceived that predicts amount and volume of manure produced, fertilizer (N-P-K) content and monetary value, and NH₃ and N₂O emissions. Using this model, manure storage space and nutrient losses as gaseous emission can be estimated, and manure over- and under-application can be reduced. In the future, producers can use this information to make best decisions on manure management practices and obtain sustainable beef cattle manure management.

Introduction:

Traditionally, beef cattle have been kept outside on pasture or in open or partially covered feedlots. In the Northern Great Plains, there is an increasing interest in raising beef cattle in confined housing, such as hoop and mono-slope barns. As reasons for building confinement facilities, producers cite the ability to mitigate extreme weather conditions, complete containment of feedlot runoff, and/or high land prices that make it cost prohibitive to build additional open feedlots. A variety of management styles are used in these confined facilities. Typically, beef producers apply bedding material once per week or every other week to manage manure and moisture, and to provide comfort for the animals (Doran et al., 2010). Some producers let the manure and bedding build up to a bedded manure pack that is compacted over time by cattle activity. In this management style, manure is only removed from the bunk apron once or twice weekly to establish a bedded pack in the center of the pen. The bedded pack might be removed between groups of cattle (once or twice per year) or may be maintained for several years (Doran et al., 2010). Other producers remove all bedding and manure as frequently as once per week to avoid a bedded pack. Either way, removed manure with bedding needs to be managed properly and is either stored, applied directly to cropland as fertilizer, or treated (e.g. by composting) prior to field application.

Improved understanding of the nutrient composition of manure from bedded beef facilities provides beef producers with information to guide manure management decisions that reduce nutrient losses to the environment. Spiehs et al. (2011) provided baseline information on nutrient composition (nitrogen (N), phosphorus (P), potassium (K), and dry matter) of beef cattle bedded manure packs. Yet, it is unknown how storage temperature and bedded manure characteristics affect manure nutrient composition, nutrient value, and moisture content over time. There is limited information on how manure management practices impact ammonia (NH₃) and greenhouse gas emissions from beef cattle bedded manure. A better understanding of nutrient transformations and movements will help optimize nutrient and moisture management practices of bedded packs and increase profitability and crop yields.

Modeling can help describe the processes occurring in manure and predict the fate of nutrients in the manure. The advantage of a process-based model over an empirical model is that it can also be applied for conditions that diverge from the original data which was used to develop the model. There are only limited models available that predict GHG and NH₃ emissions from livestock farms relating to environmental factors: the Manure-DNDC model (Li et al., 2012) and the Integrated Farm System Model (IFSM) (Rotz et al., 2014). These accessible models lack prediction capabilities for manure quantity and nutrient content from bedded beef systems. In addition, no data from mono-slope barns were used to calibrate these models. A model is needed that describes the combined processes occurring within a bedded beef barn system with respect to both different bedding material and manure removal frequencies. The model should predict manure quantity, nutrient content, and fertilizer (N-P-K) value for a sustainable beef cattle facility.

References:

Doran, B. E., Euken, R., & Spiehs, M. J. (2010). Hoops and Mono-slopes: What we have learned about management and performance. Feedlot Forum 2010.

Li, C. S., W. Salas, R. H. Zhang, C. Krauter, A. Rotz, and F. Mitloehner. 2012. Manure-DNDC: a biogeochemical process model for quantifying greenhouse gas and ammonia emissions from livestock manure systems. Nutrient Cycling in Agroecosystems 93(2):163-200.

Rotz, C.A., Corson, M.S., Chianese, D.S., Montes, F., Hafner, S.D., Bonifacio, H.F., Coiner, C.U., 2014. The Integrated Farm System Model Reference Manual, Version 4.1. USDA-Agricultural Research Service. Avaialble at: http://www.ars.usda.gov/sp2UserFiles/Place/80700500/Reference%20Manual.pdf. Accessed 25 February 2015.

Spiehs, M. J., Woodbury, B. L., Doran, B. E., Eigenberg, R. A., Kohl, K. D., Varel, V. H., Berry, E. D., & Wells, J. E. (2011). Environmental conditions in beef deep-bedded monoslope facilities: a descriptive study. Transacttions of the ASABE, 54(2), 663-673.

The objective of my research was to develop a process-based model that estimates manure quantity, nutrient content, fertilizer (N-P-K) value, and gaseous emission (NH₃, N₂O) for the bedded manure mixture. The model should simulate the physical, chemical and biological transformations and movements of N, P and K from the bedded manure pack surface with respect to different storage length, bedding material, and ambient air temperature. The important and relevant input variables include bedding material, manure storage time, bedded pack depth, and ambient temperature. Output parameters include amount, fertilizer (N-P-K) and monetary value of manure produced, and NH₃ and N₂O emissions.

Physical, chemical, and biological transformations of N, P, and K from simulated bedded packs have been measured. However, model development is still progressing. A framework, inputs and outputs to the model exist. Calculations still have to be fine-tuned before the model can be calibrated and validated with data from the experimental study. The model performance will be evaluated with different measures to detect bias and errors in the model that might cause wrong predictions. The utility of the model will be validated with NH₃ emission and manure N-P-K concentration estimates from field-scale studies.