Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: February 9, 2000
Publication Date: July 24, 2000
Citation: Rotz, C.A., Sharpley, A.N., Satter, L.D. 2000. Management effects on nutrient loading and losses from dairy farms. Journal of Dairy Science. 83(1):234. Technical Abstract: Management decisions can impact the long-term sustainability of dairy farms. Computer models provide useful tools for evaluating these impacts before they are implemented. A representative farm with 400 Holstein cows (producing 11,000 kg/cow/yr) and their replacements on 300 ha of silt loam soil was simulated over 25 yr of Pennsylvania weather using a whole farm model (DAFOSYM). Multiple simulations predicted the effects of animal density, herd production, and feeding strategy on N loss, P balance, and farm profit. Reducing the land area to 200 ha nearly doubled N losses and increased soil P buildup by 15 kg/ha/yr with little change in farm profit. At 400 ha, the farm was near a long-term P balance with an N fertilizer requirement of 50 kg/ha. A 10% increase in herd production through the use of BST provided a small increase in N loss and soil P level; whereas, a 25% drop in production reduced N losses 10% and P buildup by 3.6 kg/ha/yr. Changing the breed to Jerseys while increasing animal numbers to maintain the same sale of fat corrected milk increased N losses 45% with a small increase (1.8 kg/ha/yr) in excess P. Compared to soybean meal as the sole protein feed, including a low RDP feed in rations, reduced N volatile loss 35%, reduced N leaching loss 20%, and increased production and profit with little effect on soil P. Increasing the feeding of P to 20% above the NRC recommended level (common practice) increased the long-term buildup of soil P by 8 kg/ha/yr; whereas, a 20% reduction provided concurrent farm balances of both N and P. Shifting from low forage rations to maximum use of forage increased N losses slightly with little effect on P balance and farm profit. For further analysis of dairy production systems, the DAFOSYM software is available at the Internet address http://pswmrl.arsup.psu.edu.