Livestock in Hoophouses

Fall of 2007 we decided to try an experiment. Based on our desire not to pump fossil fuels for heat into our hoophouses in order to keep winter crops alive, but knowing that without supplemental heat the crops would freeze, we wanted to explore alternative heat sources.

We raise animals on our farm, including pigs, sheep, and meat rabbits. Livestock animals produce a considerable amount of heat. Hoophouses need heat. Hoophouses provide shelter. Animals need shelter. It wasn't hard to see the potential combination. Since this project sounded like research that could benefit other producers, we decided to apply for a grant from Western SARE.

What follows is a version of our final report to Western SARE covering this project.

Project Summary

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 less 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 have 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.

Objectives

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.

Results

In brief, the project went generally according to plan and confirmed the above hypothesis. Project activities included the following:

• Pens were installed inside one hoophouse in January, 2008, and a total of 15 feeder pigs were moved in.

• Data acquisition equipment was purchased and installed in both hoophouses, including temperature sensors at five locations in each house and a humidity sensor in each house. Data acquisition equipment utilizes 1-Wire components from Embedded Data Systems.

• A computer was set up in the farm house, gathering data from the sensors in the hoophouses via a wireless network.

• An outdoor weather station was installed. The system is a Davis Vantage Pro, with outdoor sensors and a wireless connection to the data gathering computer.

• Temperature and humidity data inside the hoophouses was gathered on a continual basis beginning in February.

• Weather data was gathered from the outdoor weather station beginning in late January.

• Materials for an in-vessel composter were purchased, a design was developed, and the composter built and tested.

• Feeder pig growth was observed through the winter, with no discernible performance difference between pigs raised outdoors vs pigs raised in the hoophouse.

• The producer prepared and presented a poster at the Western SARE subregional conference in October in Cheyenne, WY.

• A website was developed including project details and results.

The east hoophouse contained the animals. The west hoophouse was the control hoophouse, with no animals inside.

Consistent results were observed throughout last winter. During the night, with no solar radiation, we generally observed about a 7-8 °F temperature gain due to the animals in the east hoophouse. For example, the minimum outdoor temperature recorded was 6 °F, at 5:32 AM on March 6, 2008. Temperature inside the west hoophouse dropped to 14 °F, while the temperature in the east hoophouse was 22 °F. The pigs inside the east hoophouse contributed 8 °F to the temperature, over and above the moderation provided by the control hoophouse. The moderation provided by the control hoophouse was generally 4-8 °F above ambient nighttime temperatures.

The chart below shows selected data for a typical day in winter: February 18, 2008. East Temp and East Humidity refer to conditions in the east hoophouse. West Temp and West Humidity refer to conditions in the west hoophouse.

The table below contains the data from which the chart was built.

This data shows expected temperature and humidity patterns during a winter day. The outside temperature starts out at midnight at 14 °F, while the temperature in the West hoophouse is about 18 °F and the temperature in the east hoophouse is a little more than 25 °F. Since this is midnight, there is no heat contribution due to solar radiation. The west hoophouse, without the animals, had moderated the outside temperature by about 4 °F. The presence of the animals in the east hoophouse had contributed another 7 °F to the temperature.

The following are a few other interesting observations about the data:

• The temperature in the East hoophouse spikes downward at around 11:00 AM. This is when we rolled up the side panels to provide the pigs with ventilation.

• Humidity and temperature vary inversely, due to the fact that cold air can contain a lower moisture content and therefore becomes saturated with less moisture.

• The west hoophouse reaches a maximum temperature of about 87 °F while the outside temperature is only 36 °F. Solar radiation has a profound impact on inside temperature, even when the hoophouse is made of materials with low insulating value (polycarbonate, poly sheeting, steel, and aluminum).

• A minimum nighttime temperature of 20-25 °F is high enough not to damage many cold weather crops, including Japanese greens, some lettuces, spinach, root vegetables, etc. Even during the coldest night last winter, the temperature in the east hoophouse did not drop below 22 °F.

This winter (2008-2009), we have seen a minimum nighttime temperature of -6 °F, much colder than the minimum recorded temperature of 6 °F the previous winter. We did not have animals in the hoophouse this winter, and the temperature in the hoophouses dropped to 2 °F when the outside temperature was -6 °F. We have observed our Japanese greens surviving at hoophouse temperatures as low as 14 °F. If animals were able to provide a 7 °F temperature gain, this would bring the hoophouse to only 9 °F, possibly causing damage to the crops. Supplemental heat would be needed in these extreme conditions, albeit minimal.

Another part of the project, the in-vessel composter, was completed in January, 2009. The vessel for the composter is a re-purposed 500 gallon diesel tank. The frame is welded from steel box beam, and the vessel rests on heavy-duty casters welded to the frame. See the attached photos below. The drive mechanism includes a hydraulic motor powered from a skid loader connected to a drive wheel and tire typically used on a go-kart.

This initial attempt at a drive mechanism is only partially successful. Friction between the tire and vessel shell is not great enough to rotate the vessel if it is more than about 1/3 full of compost materials. There is enough friction to rotate a ½ full vessel back and forth about ½ way around, which is sufficient to mix the compost materials somewhat, but the tire begins to skid and will not rotate the vessel completely.

A new drive mechanism has been designed and parts are currently on order. The new drive mechanism will consist of a pulley on the hydraulic motor shaft and an adjustable belt going around the circumference of the vessel. This drive mechanism will provide significantly more friction on the vessel, hopefully enabling the motor to rotate the drum completely.

Benefits/Impacts

In our part of Colorado, we rarely experience temperatures below 0 °F. If an unheated hoophouse is able to moderate the ambient temperature 7 °F, and animals are able to increase the temperature by an additional 7 °F, to a minimum of about 14 °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 °F temperature moderation, could mean a minimum winter temperature at plant level of about 16-18 °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 reasons:

• We bed our pigpens with straw or cornstalks. We typically clean out our outdoor pens on a regular basis with 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.

• Wheat 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 °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 °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.

Recommendations or New Hypotheses

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.

Additionally, the roll-up sides included with our hoophouses does not seal very well at each end. There is a wide gap between the roll-up side material and the end-wall polycarbonate. We would like to find a cost-effective, reliable means to close this gap.

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 (minimum 130 °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 130 °F, decomposition is active. When it declines to below 130 °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.

This project was supported through a Farmer/Rancher grant from Western SARE (Sustainable Agriculture Research and Education). For more information on Western SARE, click on the logo.

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