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Format:
Print
Author:
Ford, Russell Flack
Dept./Program:
Natural Resources
Year:
2012
Degree:
MS
Abstract:
Until the 20th century, American agricultural commonly suffered from depletions of soil nutrients, including phosphorus. Depleted farmland could be replaced with newly-cleared land during westward expansion. However, in some cases, mixed farming systems (ruminant livestock, grains, and perennial grasses) retained and cycled soil fertility in a sustainable manner for many decades. Before the 20th century Vermont farm soils were perceived as 'impoverished' and 'exhausted' because nutrient losses from soil erosion and crop export had long exceeded nutrient imports to the state. Importation of grain and commercial fertilizers was recommended to reverse the depletion. Modem markets and transportation made possible a specialized fluid milk industry in Vermont by the 1920s. Farmers quickly adopted the feeding of grain to dairy cows and the use of commercial fertilizers. Grain and fertilizer were both produced outside the state, resulting in a positive net balance for phosphorus within the state.
Agricultural imports of phosphorus into the Missisquoi Bay watershed now contribute to cultural eutrophication in northern Lake Champlain. We estimate current and historic agricultural P mass balances for the Vermont portion of the Missisquoi Bay watershed, using Franklin County Vermont as a proxy boundary for that watershed. Major P imports include feed and mineral supplements and fertilizer. Major P exports include milk and milk products.
The phosphorus surplus 1924 to 2007 totaled 48,000 tons, growing from 14 tons/ yr in 1924 to 821 tons/ yr in 2007 due to the adoption of superphosphate fertilizer, and steadily increasing amounts of grain fed to milk cows. The 2007 P surplus is 30% greater than it was prior to 1970, when Missisquoi Bay moved from mesotrophic to eutrophic status. The surplus is projected to reach 1050 tons in the year 2030 if long-term increases in per-cow milk production and corn silage acreage continue. A 63% reduction in the current annual surplus is achievable from best management practice fertilizer and feeding strategies. Further reductions are possible from organic and grazing-based dairy farming. This study can guide agricultural and environmental planners in choosing attainable phosphorus reduction goals and strategies.