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Farm scale study: Results from 2008

April 24, 2009

In 2008 we grew corn, soybean, sweet potato, and sweet sorghum organically at three different farming scales:

  1. Biointensive plots were managed according to methods recommended by John Jeavons, in his book How to Grow More Vegetables…, using only human labor and hand tools. Each biointensive plots covered 20 m2 (215 sq. ft.).
  2. Market garden plots were managed with hand tools and walk-behind tractors. Each market garden plot covered 126 m2 (1356 sq. ft.).
  3. Small farm plots were managed primarily with conventional 4-wheeled tractors, supplemented with hand tools and walk-behind tractors for tasks that weren’t suited to the larger machines. Each small farm plot covered 836 m2 (9000 sq. ft.).
Research plots at the Kentucky State University farm, growing sweet potato, soybean, corn, and sweet sorghum at different production scales. A small farm plot is in the foreground; biointensive and market garden plots are in the background. These three plots represent one of four replicates of the farm scale study. This picture was taken on August 25, 2008, just before the soybean harvest began.

Research plots at the Kentucky State University farm growing sweet potato, soybean, corn, and sweet sorghum at different production scales. A small farm plot is in the foreground; biointensive and market garden plots are in the background. These three plots represent one of four replicates of the farm scale study. This picture was taken on August 25, 2008, just before the soybean harvest began.

We recorded the labor used to manage each plot through the season, and divided this figure by the plot size. The biointensive plots used the most labor (26 minutes per square meter) and the small farm plots used the least (3.7 minutes per square meter.).

We recorded the intensity of our labor in order to estimate the metabolic (food) energy needed to support the laborer while working. We multiplied the volume of fuel used for machinery by the energy density of the fuel to estimate the fossil fuel energy consumed. The small farm plots used the most energy (0.75 megajoules per square meter) and the biointensive plots used the least (0.10 megajoules per square meter).

Labor and energy use at three farming scales. Only human labor and hand tools were used at the biointensive scale. Hand tools were supplemented with a gasoline-powered walk-behind tractor and attachments at the market garden scale. These were supplemented with conventional four-wheeled tractors and attachments at the small farm scale. Each bar shows the mean of four replicated plots near Frankfort, KY in 2008. Error bars denote standard error.

Labor and energy use at three production scales. Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

 

Metabolic energy accounted for all of the energy invested in the biointensive plots. Fuel energy accounted for most of the energy invested in the market garden and small farm plots.

Metabolic and fuel energy used to grow crops at three production scales. Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

Metabolic (red) and fuel (black) energy used to grow crops at three production scales. Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

 

Plot preparation (cultivation) accounted for most of the energy use at all farm scales.

Energy used to produce crops for a growing season at three production scales. Bars are color-coded to show proportion of energy used to prepare the land, plant the crops, manage the crops during the growing season, harvest the crops, and process the crops.crops.

Energy used over the course of a growing season at three production scales. Bars are color-coded to show proportion of energy used to prepare the land (pale pink); plant the crops (hot pink); manage weeds, pests, and irrigation (maroon); harvest the crops (purple); and process the crops for sale and establish winter cover crops after harvest (black). Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

 

Plot preparation (“double digging“) accounted for most of the labor use at the biointensive scale, but weed management and post-harvest processing accounted for the largest components of labor use at the market garden and small farm scales. Hand tools were frequently used for in-row weed management at all production scales. Post-harvest processing tactics differed little between treatments because we did not have access to the combine harvestors or threshing machines that would typically be used at the small farm scale.

Labor use by farm scale

Labor used over the course of a growing season at three production scales. Bars are color-coded to show proportion of labor used to prepare land (pale pink); plant crops (hot pink); manage weeds, pests and irrigation (maroon); harvest (purple); and process crops for sale and establish winter cover crops after harvest (black). Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

 

Soybean yield was highest at the market garden scale. Sweet potato yields were similar across scales. Field corn and sweet sorghum yields were highest at the small farm scale.

farmscale-yields

Yields of four energy crops at three production scales. Figures for field corn and field soy represent dry grain yield; all others are fresh weight. Two varieties of each crop except sweet potato were grown. Darker bars represent varieties bred for food; lighter bars are intended for commodity sales (animal feed, processing, biofuel feedstock etc.). Each bar represents the mean of four plots. Error bars show standard error of the mean. See text for details.

 

Efficiency of land (top), energy (middle) and labor (bottom) use at three production scales.

Efficiency of land (top), energy (middle) and labor (bottom) use at three production scales.

Small farm plots used land and labor most efficiently; biointensive plots were the most energy-efficient.

These results are from the first year of a four-year study. 2008 was a drought year. Our corn and soy yields were well below national averages at all scales, but sweet sorghum yield for the fuel variety (M81E) was well above the national average at the small farm scale.

We plan to make some changes in 2009, based on the results in 2008:

 

  • We will try different varieties of corn and soybean;
  • We will transplant corn and sweet sorghum into biointensive plots, instead of direct seeding;
  • We will not double dig biointensive plots, but will incorporate compost with a broadfork;
  • We will use a smaller tractor to cultivate the small farm plots.

 

For more information see:

 

 

Thanks to Tony Silvernail for managing the study, as well as Brian Geier, John Rodgers, Joelle Johnson, the KSU farm crew, and student volunteers from the CASS program for their many hours of help. Comments and feedback regarding this study are most welcome.

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