Searching for livestock production systems with a high energy utilization is of interest because of resource use andpollution aspects and because energy use is an indicator of the intenstjication of production processes. Due to interactions between crop and livestock enterprises and between levels of dtflerent input factors and their eflects on yields, it is proposed to analyze agricultural energy utilization through system modelling of data from farm studies. Energy use in small grains, grass-clover andfodder beets registered in organic and conventional mixed dairy farms was analyzed and used together with crop yields in order to model energy prices on three Danish soil types. Conventional crop yields were higher but they also used more indirect energy with input factors, especially fertilizers. The conventional yields were not suficiently higher to compensate for the extra use of energy compared with the organic crops. The organic crops had lower energy prices on all soil types, with the smallest dtflerence on irrigated sandy soils. Sensitivity analyses were made for the effects of changes in irrigation and fertilizer levels. One conclusion was that better energy utilization in grain crops might be found at intermediate levels offertilizer use, especially on irrigated soils. Actualfarm diesel use was on average 47% higher than expected from standard values, suggesting that care should be taken when basing energetic analysis of farming methods on experimental data alone. On the same farms, the energy use in firy production registered in organic and conventional mixed dairy farms was analyzed and used together with milk and meat yields in order to model energy prices for three direrent feeding strategies and two soil types. Conventional dairy production is more intensive with a greater feeding ration and a higher proportion of high-protein feed, but has also higher yields. The conventional yields were not suficiently higher to compensate for the extra use of energy compared with the organic feeding ration. However, the lower energy price in organic dairy production is dependent on the composition of the feeding strategy. Substitution of 5OOSFU of grain with grass pellets makes an ordinary organic feeding ration based on conventional crop production competable. In general, the crop energy price models can be used together with the dairy production to model the eflects of direrent feeding and crop rotation strategies on the overall energy utilization in mixed dairy production systems. 0

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