CSU, Chico

In-vessel Composting Report (Rice Straw & Dairy Manure)

In-vessel Composting Report (Rice Straw & Dairy Manure)

Objectives:

Compost siteThe proposed study will examine the feasibility of an in-vessel composting process for agricultural waste products as an alternative waste management strategy in an effort to address air and water quality issues at the agriculture/urban interface. The project was designed to develop a commercial-scale composting facility in Colusa County in an effort to convert rice straw into a "value-added" product suitable as a soil amendment or organic fertilizer. This was made possible through funding made available by the California Air Resources Board to mitigate air quality concerns associated with the traditional practice of rice straw burning.

Burning has its benefits because it's inexpensive and effective in removing fungus, while replacing macro and micronutrients to the soil. However, burning also increases particulate matter in the air, thus alternative uses are being sought. Suitable alternatives should not compromise soil fertility or enhance fungal pathogens. Compost production provides a very sustainable alternative to conventional burning practices, because it builds soil profile and adds organic matter, nutrients and beneficial microorganisms to the soil. The feasibility depends greatly on the level of commitment by the grower.

FeedlotBroken Box also proposed to develop a cattle backgrounding facility that would use rice straw as feed in a variety of cattle rations. Considerable energy has been placed on this particular aspect of the project. Over the last 12 months, over 4,000 head have been fed in the facility. Current capacity is 3,000 head.

The ultimate goal of the project was to find effective, lost cost end-uses for rice straw.

table1

*Both the compost and rice straw feed require additional processing (costs) not reflected in this table.

FeedingCurrently, the most profitable alternative for straw utilization at Broken Box Ranch is direct sales as baled straw for feed or as a part of a complete ration fed through the backgrounding lot. As the hay market drops, sales for baled rice straw (sold as feed) may also drop as customers look for better nutrient value for cattle supplementation. Thus, a diversified product line will be needed to withstand fluctuations in the commodity markets.

Overall, compost production at Broken Box has been slow due to the development and setup of other enterprises, as well as the current favorable cost/return on baled straw sold as feed. Details regarding each aspect of the business are as follows:

Enterprise Development:

1. Feedlot Enterprise

Cattle eatingCurrently, the feedlot has a one-time capacity of 3,000 head and employs 5 full-time employees, 2 seasonal employees, in addition to the owners, Jerry and Sherry Maltby. Over the last 12 months, the facility has fed over 4,000 head, consuming 2,500 tons of straw, approximately 1,250 lbs of straw/head.

The content of rice straw in the ration varies depending on the animal's nutritional needs. Rations have been formulated with straw content ranging from 50 to 100% with the remaining portion composed of tomato pumice and other byproducts. Byproducts are purchased on a contract basis, stored in bags or in commodity bays for use in least cost ration formulation.

The facility incorporates mounded dirt pens, separated by pipe and cable. Cattle are fed twice a day and have access to fresh water at all times. Capital investments include the loader, mixer/feed truck and the construction of the facility itself, i.e., pipe, cement, cable and labor. This enterprise has used 27% of the total rice straw consumed by the ranch during the startup phase of the project. Estimated rice straw utilization at the current 3,000 head capacity is approximately 4000 tons for 2002 - 2003. As utilization of the facility increases, so will the consumption of rice straw.

2. Composting Enterprise

CompostThe composting enterprise has been slow with the development and expansion of the backgrounding lot. A composting surface was put in place in the spring of 2001 using road-base as the primary hardening material. Even with rollers and packing equipment, the base was not hard enough to run the large commercial scale Ag-Bag machine for the purposes of in-vessel composting. Without a firm surface, the machine bogs and cannot advance forward as the bag fills. Under these circumstances, lime stabilization or asphalt may be required to harden the surface. Lime stabilization has been shown to run about a 1/3 of the cost of cement or asphalt and requires the incorporation of a combination of calcium oxide, cement, and fly ash.

As an alternative, large static piles or cribs were assembled last fall. Aeration tubes were placed at the base of each pile to force air throughout the crib. These static piles were allowed to compost all winter. In the spring of 2002, the cribs were disassembled and windrowed with a compost turner to improve compost texture. The material tested 1.4% N (primarily organic N), .4% P (phosphorus) and 1.1% K (potassium). A portion of this material has been used for marketing purposes in the form of a research trial to establish yield and soil fertility data (see section 4).

Rice strawCost projections using real numbers generated from actual expenses show that optimal profitability can be achieved at 12,500 tons of production annually to offset the cost of equipment/pad and raw material charges. The project will need to invest in a compost turner and pad stabilization to stay on track with compost production projections. Table 1 shows the importance of scale to this particular component of the operation. One ton of straw is required for each ton of compost produced because of the reduction in mass, approximately 1000 pounds of manure is used/ton of compost produced.

Seasonal composting can be accomplished on the road-base during the summer/fall months. Cribs will be used during the winter months. The key component is moisture and proper aeration. Without these components, the material will not heat up and breakdown into the humus-like material.

table2

Labor was assessed at $14/hr and capital costs included pad stabilization and a large compost turner that was expensed over a five year period. The biggest cost associated with the compost is baling and rice straw removal from the field. If this is considered a cost of rice production, then the return on the bulk compost sales increases considerably.

table3

In addition, rice straw should be classified as grade 1, 2 and 3. Grade 1 straw is suitable for sale as feed off site to other producers at $30/Ton. Grade 2 straw is intermediate in quality for use in the feedlot, as the roughage component of the ration, assessed at $20/T. Grade 3 straw is poor quality straw that is damaged or left over from last year and not suitable for other purposes, assessed at $10/T. At this rate, the return on compost is $14.84/T and the composting process is adding value to this raw material.

Potential for straw utilization is 15,000 T/yr when equipment and capital costs are used optimally.

Composting Research:

Black bagsThe University Farm at California State University Chico has developed a site that is now producing 250 tons of compost from dairy manure and rice straw annually using conventional windrow methods primarily for research purposes to support the commercialization of Broken Box Compost. The following studies have been conducted:

1. Compost quality assessment

  • Crop productivity
  • Phytotoxcity

2. Economic evaluation of windrow vs. in-vessel
3. Plant pathogen suppression

Compost Quality (Marketing label shown below)

Compost PilesNutrient Composition: NPK: 1.2: 0.5: 1.5 as an average value
Approximately 30% is Organic Matter
pH is 8
Fecal coliforms: 0 counts
E. coli: 0 counts
Salmonella: 0 counts
Heavy metals: Arsenic, Lead and Mercury all negative.


Conclusions:

Compost production from rice straw and dairy manure is feasible and can be profitable under the right management scenario. The marketability outlook for this product is excellent and will continue to grow as the organic movement gains momentum in the U.S. and as air and water quality laws continue to strengthen and become enforced.

Any dairy with 300 or more dairy cows produces enough cow manure to offset the cost of composting equipment. These types of dairies are in an excellent position to work with local rice growers in a cooperative arrangement.

Both air and water quality laws and regulations will continue to limit the application of raw manures, thus compost will provide a low cost, easy alternative, as a soil conditioner that is weed seed and pathogen free.

Assessing the real value added to manure and straw from this process is difficult, in lieu of the economic figures to accurately assess the benefit of full compliance with state air and water quality laws. Perhaps, on average, the typical dairy is in violation once or twice in a lifetime for example, the cost of that fine and required modifications to the existing facilities for compliance purposes is of significant value.

The question on everyone's mind is "What is it worth to do the right thing?" i.e., never leach contaminants into the ground water and never blow particulate matter into the atmosphere? These are values that do not have a readily available price tag, and therefore difficult to factor into the profitability equation.

Recommendations for Broken Box Ranch:

1. Harden existing surface with fly ash and cement for windrow compost production
2. Develop crib structures for static pile aeration during winter months
3. Purchase turner for 12 month compost production
4. Develop water source for easy access to windrows for proper moisture maintenance
5. Explore bagging options to increase product value and enhance marketability
6. Maintain website
7. Advertise on the CCOF website
8. Develop relationship with local nurseries and landscapers for ongoing contracts
9. If compost production begins to take off, hire sales staff to move product