The following is an abstract of a poster presented by student Véronique Ouellet, Université Laval, at the American Dairy Science Association meeting in Utah last summer.
Corn silage is recognized as a palatable and digestible source of energy for dairy cows. On the other hand, corn silage production is widely criticized as it may carry more environmental risks than perennial forages.
Our objective was to use the whole-farm model N-CyCLES to assess the effect of different crop rotations with varied levels of environmental risks on dairy farm profits, nitrogen (N) and phosphorous (P) balance, and greenhouse gas emissions, while optimizing the management practices required to achieve maximum profits. Adaptations made to the model, included modification to rotations, adjustment in the optimization constraints, evaluation of crop production cost, evaluation of forage nutritive value, and update in fertilization requirements.
Data representative of an average dairy farm from Centre-du-Quebec region in Quebec, Canada were used. Four crop rotation scenarios considered to have different environmental impact were built in the model, and compared: corn grain-soybean-corn silage-alfalfa-alfalfa (very high negative impact, +++); corn grain-soybean-corn silage-alfalfa/timothy-alfalfa/timothy-alfalfa/timothy (moderate negative impact, ++); cereal-alfalfa/timothy-alfalfa/timothy-alfalfa/timothy-naked oats (low negative, +); cereal-alfalfa/timothy-alfalfa/timothy-alfalfa/timothy-alfalfa/timothy-mixed grains (positive impact, -).
Results showed that the highest dairy farm profits (0.12 $/kg of FPCM) were associated with the (++) rotation, whereas the lowest profits (0.05 $/kg of FPCM) were associated with the (-) rotation. The lowest farm-gate to farm-gate greenhouse gas emissions allocated to milk production (0.98 CO2 eq./kg of FPCM) was predicted for the (+++) rotation, whereas the highest value (1.03 CO2 eq./kg of FPCM) was predicted for the (-) rotation. This result is mainly explained by the lack of cash crops sold and the lower NFC and higher N content in cow diets for the farm with (-) rotation. The highest N and P balances (20.1 g/kg of FPCM and 1.185 g/kg of FPCM, respectively) were predicted for the (-) rotation since more corn grain was bought (156.5 t/yr) to compensate for the absence of corn grain and corn silage produced on the farm. Moreover, the lowest N and P balances (12.8 g/kg of FPCM, 0.465 g/kg of FPCM) were predicted for the (++) rotation.
These results suggested that including corn silage in the crop rotation do not carry a greater environmental risk on the considered output than crop rotations without corn, and that growing corn silage is profitable when the whole farm is considered as a single unit of decision. Sound practices still need to be developed to improve other environmental considerations such as soil structure and erosion.
Authors: Ouellet, V. (Université Laval), D. Pellerin (Université Laval), M. Chantigny (AAFC), and E. Charbonneau (Université Laval)