Organic and conventional agriculture: A comparison of conventional, manure, and legume systems on soil carbon, soil nitrogen, yield, and economic returns from a long term system in the Mid-Atlantic
Type of Document:
Thesis or Dissertation
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Abstract: This thesis explores the effects and interactions of three systems of agricultural production: 1) conventional grain, 2) organic grain where fertility is supported by manure from dairy cows, and 3) organic grain where fertility is supported by leguminous crops. The data set included 28 years of comparative farming observations from the Rodale Institute s Farming Systems Trial. Ordinary least squares (OLS) regressions were used to examine the effects of the cropping system on soil nitrogen and soil organic carbon. OLS regressions were used to examine the impact of the cropping systems on corn yield in conjunction with soil nitrogen and soil organic carbon. The manure and legume cropping systems were found to sequester more carbon than a conventional system.
Overall, corn yields in the manure and legume systems were found to be 92.7% and 91.0% of the conventional system respectively. Following a 5 year transition period, manure and legume system yields were 95.9% 93.8% of conventional yields respectively. Corn yield was also analyzed in conjunction with plant genetics, weed pressure, and weather using a model where the weather variables were constructed based on the corn plant s phenological stages of development. Conditional on these variables, the manure and legume systems were found to have 11.4% and 33.0% higher yields respectively, than the conventional system.
Three years of cost and revenue data were used to estimate the level of organic premium needed for the organic and conventional systems to have economically equivalent returns. A 47.4% and 44.0% price premium was needed for the manure and legume systems respectively to maintain economic equivalence with the conventional system. Significant differences between the cropping systems were detected with respect to soil fertility, productivity and economic profitability.