Final Report for FW07-031
The front range of the Colorado Rockies presents the vegetable farmer with significant production challenges. Much of the area experiences a short growing season - generally shorter than 120 days - resulting from elevations ranging between 6,000 and 9,000 feet.
Added to this are weather-related challenges, including wide temperature swings, extremely low humidity, hailstorms, and desiccating winds. Amid these challenges, outdoor cultivation of staple crops like tomatoes is essentially impossible, and many other crops are at risk.
Hoophouse cultivation is a potential solution to many of these challenges, protecting crops from the wind and hail, and somewhat moderating temperature swings. However, without supplemental heat, season extension is minimal, except possibly for cold-tolerant
crops. With the continually rising prices of fossil fuels, traditional propane or oil heat for greenhouses can be so costly as to significantly reduce or totally eliminate profits, since the vegetables grown locally in greenhouses must be price competitive with vegetables trucked in from warmer zones.
Livestock animals produce heat in two primary ways: body heat, and heat resulting from composting of manure and urine. This project confirmed that livestock inside a hoophouse has a positive impact on temperature. Harnessing this heat by raising animals inside a hoophouse may provide enough heat to raise the temperature inside the
hoophouse to a level sufficient to sustain production through the winter.
While the increased temperature may not be sufficient to protect warm weather crops, selection of winter-hardy crops and further protecting them by row covers inside the hoophouse may enable winter production without added heat.
The hypothesis of this project is that crops can be raised and harvested through the winter months in the front range of Colorado in hoophouse structures without added artificial heat. Heat energy produced by livestock as body heat and through composting manure
will keep the temperature at crop level in an unheated hoop structure at a temperature able to sustain cold weather greenhouse crops. To test this hypothesis, the project will undertake the following activities:
1. Explore the microclimate impact of raising hogs inside a hoophouse, comparing the temperature and humidity through the winter months inside two identical hoophouses, one with animals and one without.
2. Compare performance of hogs raised inside a hoophouse vs hogs raised in the farm's conventional manner, outside in dirt lots.
3. Design and construct a small-farm sized in-vessel composter, to reduce the animal waste to compost for vegetable production inside the hoophouses.
4. Document the project's results by developing a website, and by developing a seminar to offer to the Colorado State University Extension Service.
In our part of Colorado, we rarely experience temperatures below 0 degrees F. If an unheated hoophouse is able to moderate the ambient temperature 7 degrees F, and animals are able to increase the temperature by an additional 7 degrees F, to a minimum of about 14 degrees F, this contributes significantly to the survivability of cold weather crops. The animals' heat contribution augmented further by floating row covers, which should provide another 2
4 degrees F temperature moderation, could me an a minimum winter temperature at plant level of about 16-18 degrees F, within the survivability range of many cold weather crops. Minimal supplemental heat may be required on extremely cold nights.
This combination of temperature moderating contributors could enable a producer to grow certain crops through the winter along the front range with little or no expenditure on heating the hoophouses. This could improve the profitability of farmers by enabling the production of cash crops year round.
While the data indicate that the basic hypothesis of the project is proven, the project presented a number of challenges that we intend to work though in coming years. Pigs were perhaps a difficult choice of species to be raising in hoophouses, for the following
- We bed our pigpens with straw or cornstalks. We typically clean out our outdoor pens on a regular basis wi th our skid loader. Cleaning pens in this manner is impossible with crops growing in one half of the hoophouse.
- Pigs produce a significant amount of dust through their rooting and pawing of the soil. This dust settles on any crop growing in the hoophouse. Although we have not tested the dust, it could contain manure particles, which would be a concern if the dust contacted edible vegetable crops.
- Pigs are natural diggers and rooters. At one point during the winter they dug a hole almost two feet deep in one area of their pen. This created a problem in leveling the ground off for planting crops in the spring.
- Pigs tend to defecate and urinate in one area of the pen. The nitrogen concentration in the soil in this area has proven to be too great to allow germination of crops following removal of the pigs.
- Whe at seeds mingled with the straw bedding have created a weed problem in subsequent crops. Also, undigested corn seeds from the pig feed have contributed to the weed problem.
- Pigs require ventilation, and go into stress if the temperature exceeds about 105 degrees F. Conversely, in poor weather conditions, ventilation is not necessarily the best thing for plants. During the winter months this is not typically a problem, but in the spring, the temperature inside a hoophouse can soar to above 140 degrees F very quickly. We learned that we had to be vigilant in tending the roll-up sides on our hoophouse so as not to endanger crops while providing enough ventilation for the pigs.
Education and Outreach
I prepared and presented a poster at the Cheyenne subregional conference for Western SARE. I spoke with at least a dozen producers there that expressed quite a bit of interest in the project and the preliminary results. There was significant interest in hoophouse production in our region, and the idea of raising livestock in the hoophouses intrigued
many. One producer who already had a hoophouse and also raised chickens said he was going to try moving chickens into his hoophouse this winter.
Primary outreach from this project includes the website developed specifically to provide the project details and results. An email link is provided on the website to facilitate communication.
The website includes an HTML version of this final report, with certain sections removed or modified, and other sections expanded. This is intended to be viewed and downloaded by other producers. Also, I will begin looking for opportunities to share the project
materials with other producers at other meetings and conferences.
The poster from the Cheyenne conference also provided limited outreach to conference participants.
Education and Outreach Outcomes
While the project's hypothesis seems to be validated, a species other than pigs may present fewer challenges. We raise meat rabbits and sheep commercially on our farm, and in future years we intend to experiment with raising them in half of a hoophouse while raising crops in the other half. Rabbits should not create the same challenges as pigs, although they will undoubtedly present their own challenges.
Automatic, thermostatically-controlled ventilation is a must. We have thermostatically controlled fans in our hoophouses, but in very sunny, windless conditions on warmer spring days, they do not provide enough ventilation for animals or crops. We also have roll-up sides on our hoophouses, which provide sufficient ventilation, but as mentioned
above, managing them requires diligence so as not to chill the crop or overheat the livestock on days when the weather changes rapidly. Adding thermostatically-controlled motors to the roll-up sides would simplify this management task and increase the comfort
for the livestock.
Roll-up sides, where the side plastic is attached to the hoophouse at the top and rolls up around a conduit from the bottom, may not be the best design, given the fact that, as the side is opened, a cold breeze can blow across plants at ground level, possibly causing
damage. Some manufacturers are offering roll-down sides, where the side plastic is attached to the hoophouse at the bottom and rolls down from the top around a conduit suspended from cables. This is similar to the curtains provided in many livestock shelters, and is reliable technology. Retrofitting our hoophouses with these roll-down sides could improve the temperature management in the hoophouses.
We are now experimenting with the in-vessel composter. Ideas for improving the composter include the following:
- As described earlier, the drive mechanism needs work, and we will experiment with a belt drive in coming weeks.
- We may consider coating the vessel with epoxy if rust seems to be an issue.
- Since proper composting requires elevated temperatures (about 150 degrees F), we may need to partially insulate the drum. Insulation would need to be applied so as not to allow moisture to accumulate in the insulation or against the vessel wall, to keep rust degradation controlled. Spray urethane seems to be an ideal product for this, since it does not absorb moisture and sticks firmly to metal surfaces.
- We may need to punch additional holes in the vessel if composting seems to be stagnating due to lack of air.
- Adding a thermocouple to the tank would help to monitor composting progress. Turning compost re-activates decomposition and the temperature begins to elevate. Then, as the microorganisms consume the nitrogen in their vicinity, decomposition activity starts to decline. Rotating the vessel would mix the microorganisms and the nitrogenous materials and re-activate decomposition. When mixing the compost ceases to cause a temperature increase, the compost is finished. The general idea would be to turn the drum and monitor the temperature.
When it increases to above 150 degrees F, decomposition is active. When it declines to below 150 degrees F we would rotate the vessel and mix the materials. If upon rotating the vessel the temperature does not increase, we would empty the finished compost and start with a new batch.
- Adding a loading chute - sort of like a funnel - would make loading easier. The door opening is not wide enough to accept dumping a full skid loader bucket. Loading only one side of the skid loader bucket helps, but there is still quite a bit of material that falls outside the compost vessel. A bottomless hopper a little wider than the skid loader bucket attached to the door opening would probably
help the loading process.