Green Manure vs. Brown Manure in an Organic Vegetable System

Final Report for YENC10-023

Project Type: Youth Educator
Funds awarded in 2010: $1,991.00
Projected End Date: 12/31/2013
Region: North Central
State: Iowa
Project Manager:
Mark Quee
Scattergood Friends School
Expand All

Project Information


Project Duration: This is an on-going experiment, though for purposes of the grant, it will conclude on March 15, 2012

Background and description of previous sustainable agriculture activities: I have been the Farm Manager at Scattergood Friends School since 2003. We raise 10 acres of certified organic fruits and vegetables, as well as grass-finished, rotationally grazed beef and lamb for student consumption. I am also actively involved in Practical Farmers of Iowa and other local organizations promoting sustainable agriculture.

• Our primary goal was to employ students in setting up a long term experiment studying the differences in fertility maintenance using animal manure products and plant-based cover-cropping.
• This experiment was the outcome of an Advanced Biology class unit on experiment design, so another goal was to provide a real-world application of classroom curriculum.
• In addition to the design component, another goal was to get students actively involved in the organic gardens maintained by the school. Students were responsible for laying out the project, starting seeds and transplanting, weeding, collecting harvest data and livestock care.
• A final goal is to give students an opportunity to work with real data and to create meaningful statistics and documents describing processes and results.

B1 B2 B3
• Siting: One of our first decisions was where the experiment should be sited. We had just transitioned approximately 3 acres from organic pastures to garden use, and considered this an ideal site since the soil would be relatively uniform and free of the influences of organic vegetable production. Taking into consideration the dimensions of our machinery and the plot, we flagged and staked out an area approximately 100 feet east-west and 50 feet north-south, creating eight separate plots:

• Soil Testing: To get some baseline measurements on soil fertility, we combined 8 samples from each of the B, G and CONTROL areas and sent them to Midwest Labs for SC3 tests because it is thorough and affordable.
• Variety Selection: In addition to soil tests, we decided to collect harvest data and selected plants that have different fertility needs, as well as are industry standards, hopefully ensuring seed availability into the future. For a leafy green, we chose Packman Broccoli, for a fruiting plant we chose Raven Zucchini, and for a root crop, we chose Red Ace Beets.
• (Trans)planting: The zucchini and broccoli plants were started indoors and transplanted when weather conditions were appropriate. In order to have the proper number of plants at the correct time, two successions of each were started. Beets were direct sown.
• Weeding: All areas were weeded on the same day and the same way. This primarily involved a Glaser wheel hoe and hand tools.
• Harvesting: Each crop presented different challenges in data collection, though for each we disregarded edges and collected data only from interior plants. Zucchini: Since larger is not better, we could not weigh the fruit, but decided instead to count marketable fruit during the plants’ productive lifespans. For broccoli, we counted the number of plants that could produce a marketable head (at least 6 inches across) and collected individual head diameter data. For beets, we randomly selected an interior 10 linear feet from each row, washed the beets and weighed the row production with the leaves and stems on.
• Livestock and Covercrops: Using electric temporary woven fencing, we grazed three Katahdin rams on the Brown side from July 27-Aug 5. On Aug 5 we rototilled the crop and livestock residue and drilled in a cover crop mix of oats and field peas in all areas except the control plot. On Sept 1, we introduced turkeys to the Brown side, where they rotationally grazed until Nov 1.
• Gearing up for Year 2: In spring 2012 we will have the soil tested from each of the treatment areas, and repeat another production year, but rotating the cash crops to maintain good management practices.

• Sarah Harper-Smith and the Advanced Biology Class: Sarah’s class designed the experiment, helped site and plot it, and did the transplanting and sowing.
• Practical Farmers of Iowa provided technical assistance with transitioning the land from pasture to garden and have helped with information on cover cropping and grazing.
• Council of International Visitors to Iowa Cities (CIVIC) was visiting the farm and offered assistance with redesigning the control areas to take into account possible nutrient migration due to the slope of the land.
• Dana Foster, Sam Taylor, Caleb Smith and Sebastian Ashley are Scattergood Farm employees who assisted with maintenance, harvest and data collection.
• Mike Severino is the new Advanced Biology teacher at Scattergood who will continue this experiment in his classes in the future.

Since this was the first year of a longitudinal study, our results were primarily establishing the baseline of data with which to compare future data. So far, the only thing I will change in subsequent years is starting larger successions of the broccoli and zucchini in order to ensure a longer window of optimal transplants. Spring weather is fickle in Iowa.

A summary of the Data:
• Broccoli: Average head size ended up identical (6.83 inches), though the green side produced a higher percentage of success (green = 54/55; brown = 45/50).
• Zucchini: Again, the green side outperformed the brown side with 11.2 marketable fruit per plant versus 8.4 marketable fruit per plant.
• Beets: the results were reversed here with brown out producing green by averaging 14.532 pounds per 10 linear feet, versus 12.504 lbs/10feet. The control bed was almost perfectly consistent with the green plot averaging 12.576 lbs/10feet.

This project included many aspects of sustainable agriculture, beginning with the use of cover crops and rotational grazing in managing nutrients and improving soil quality in a certified organic vegetable system. The big question that we are trying to answer is whether cover cropping can maintain nutrients as well as manure applications. By collecting harvest data as well as soil testing, we can glimpse not only the importance of objective measures (NPK + micro nutrients), but also the natural systems that enable vegetables to grow. Since our trial beds have a gentle slope, it will also be interesting to see in which system nutrients are more likely to migrate. The future effects remain to be seen. Since we have livestock that can graze on our gardens, we will likely continue to do so, even if we discover that cover cropping alone can maintain fertility. However, we will certainly gain much experience with the effect on nutritional requirements of three very different crops and this may impact some of our practices in the future.

Scattergood Friends School Farm welcomes many visitors throughout the year and I have been asked to give several presentations which included brief descriptions of this experiment. For the most part, of the three directives above, our outreach has been restricted to a.) our project, since no specific activities were planned for this project and results are not yet determined.

Date/ Group Title/ # of people/ On-Farm visit or Presentation
May 23, 2011/ Council for International Visitors to Iowa Cities/10/ On-Farm Visit
August 9, 2011/Iowa City Chamber of Commerce Ag Subcommittee/25/ On-Farm Visit
September 18, 2011/ Iowa City Field to Family Festival Culinary Bike Ride/120/ On-Farm Visit
September 30, 2011/ Cedar Rapids Unitarian Universalist Fellowship/10 Presentation
October 1, 2011/ Practical Farmers of Iowa Field Day/ 80/ On-Farm Visit
October 22, 2011/ Scattergood Homecoming/20/ On-Farm Visit
November 4, 2011/ NCR-SARE Farmers Forum at National Small Farm Tradeshow & Conference/100+/ Presentation

One complication was the delay in starting due to the livestock safety clearance. Hopefully this step is now fully integrated into the application process and will not interfere with starting time-sensitive experiments in the early spring. Otherwise, everything was well-explained and clear.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.