Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 2000
Publication Date: N/A
Technical Abstract: Computer models provide useful tools for evaluating management decisions 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 years 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 accumulation by 15 kg/ha/yr with little change in farm profit. At 400 ha, the farm was near a long-term P balance with a N fertilizer requirement of 50 kg/ha. Changing the breed to Jerseys while increasing animal numbers to maintain the same sale of fat-corrected milk increased N losses 45 percent with a small increase (1.8 kg/ha/hr) in excess P. Compared to soybean meal as the sole protein feed, including a low RDP feed in rations reduced N volatile loss 35 percent, reduced N leaching loss 20 percent, and increased production and profit with little effect on soil P. Increasing the feeding of P to 20 percent above the NRC- recommended level (common practice) increased the long-term buildup of soil P by 8 kg/ha/yr, whereas a 20 percent reduction provided concurrent farm balances of both N and P. Shifting from low forage rations to maximum use of forage increased the purchase of alfalfa hay and reduced grain imports, which increased N losses slightly with little effect on P balance and farm profit. Changing from a corn and alfalfa rotation to all corn reduced N volatilization loss 14 percent and increased leaching loss 22 percent with little effect on soil P.