Why Examine Moisture Content of a Manure Pack?
Bedded manure is a valuable fertilizer source because it contains essential macronutrients (nitrogen (N), phosphorus (P), and potassium (K)) for crop production. Previous research with beef cattle bedded manure packs demonstrated that water-soluble macronutrients accumulated toward the bottom of the packs with water movement. Thus, predicting water movement in bedded manure helps to estimate nutrient composition throughout the bedded pack. This work presents a development of a process-based model of vertical water movement that considers percolation and diffusion as the main processes of water and vapor movements in bedded manure packs. Evaporation from the top zone to the atmosphere was considered a process of convective mass transfer. The model predicts the change in moisture content of the different zones in the bedded manure and assists in estimating nutrient composition.
Why Study Moisture Movement In a Bedded Pack?
Beef cattle producers that raise cattle in complete confinement, such as mono-slope or hoop barns, may apply bedding material to manage moisture and improve the environment for the animals. Some producers let the manure and bedding accumulate to form a bedded manure pack, which is compacted by cattle activity. The bedded manure contains valuable nitrogen (N), phosphorus (P), and potassium (K) that are essential for crop production and soil sustainability. Depending on temperature, bedding material, and storage time of the bedded pack, the concentration of water-soluble N, P and K compounds may increase in the bottom of the bedded pack where water accumulates. Thus, understanding and predicting water movements within the bedded manure is important to estimate fertilizer N-P-K content and distribution in the bedded manure.
What did we do?
The processes considered in this process-based model include evaporation, percolation, diffusion of water vapor and diffusion of liquid water for vertical water movement. The model by Seng et al. (2012) for static compost piles and a modified version of the Integrated Farm System Model (not yet released) by Rotz et al. (2014) for bedded manure were reviewed and compared. Ultimately, the model needs to be adaptable to estimate the water content of the pack over time for different environmental conditions, bedding materials, and storage times at varying depths within the bedded pack. Data for model calibration and validation were gained through laboratory-scale experiments by Ayadi et al. (in review).
What have we learned?
Percolation and liquid water diffusion are considered the main processes for vertical water movement between layers in the bedded manure. Evaporation occurs from the surface of the top zone of the bedded pack. The rates of percolation and liquid water diffusion are depth-specific and their rates therefore vary. The modified version of the Integrated Farm System Model (IFSM) is more adaptable to data gained through laboratory-scale experiments. Overall, IFSM is more applicable to producer-available data and thus more applicable to predict water movement for bedded manure packs in real-life conditions.
After predicting water movements in the bedded manure, the model will be used to estimate N, P and K movement through the different zones of the bedded manure pack as well as gaseous emission (ammonia and nitrous oxide) from the bedded pack surface. The final overall model will be a calculator that estimates fertilizer N-P-K content and value and ammonia and nitrous oxide emissions of the bedded manure packs from confined beef cattle facilities with respect to temperature, bedding material, storage time and depth of the bedded pack.
Erin Cortus, Ph. D., Assistant Professor, South Dakota State University, Brookings, SD
Ferouz Ayadi, M.S., Graduate Student, South Dakota State University, Brookings, SD; Mindy Spiehs, Ph. D., Animal Scientist, USDA‐ARS Meat Animal Research Center, Clay Center, NE
Ayadi, F. Y., M. J. Spiehs, E. L. Cortus, and D. N. Miller. In review. Physical, chemical and biological properties of different depths and ages of simulated beef bedded manure packs. Transactions of the ASABE.
Rotz, C.A., Corson, M.S., Chianese, D.S., Montes, F., Hafner, S.D., Bonifacio, H.F., Coiner, C.U., 2013a.
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
Seng, B., H. Kaneko, K. Hirayama, and K. Katayama-Hirayama. 2012. Development of water movement model as a module of moisture content simulation in static pile composting. Environmental Technology 33(15):1685-1694.
The support and assistance of Henry F. Bonifacio with the simulation of water movements in the bedded pack manure is very much appreciated. This project and all associated reports and support materials were supported by the Sustainable Agriculture Research and Education (SARE) program, which is funded by the U.S. Department of Agriculture- National Institute of Food and Agriculture (USDA-NIFA). Any opinions, findings, conclusions or recommendations expressed within do not necessarily reflect the view of the SARE program or the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. The mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA.
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