Agricultural Residues

Types

Field and Seed Crop

Rice Hull Storage Area

Field and seed crop residues are the materials remaining above the ground after harvesting, including straw or stubble from barley, beans, oats, rice, rye, and wheat, stalks, or stovers from corn, cotton, sorghum, soybeans, and alfalfa. The moisture content (wet basis) of these residues ranges from 8 percent to 80 percent. The typical bulk density of loose straw and stover varies from 1-3 lb/ft3 and the bulk density of baled straw and stover varies from 7-12 lb/ft3. If pelletized, the bulk density increases to 35-45 lb/ft3.

Fruit and Nut Crop

Almond Hull Stockpile

Fruit and nut crop residues include orchard prunings and brushes. The types of fruit and nut crops include almonds, apples, apricots, avocados, cherries, dates, figs, grapefruit, grapes, lemons, limes, olives, oranges, peaches, pears, plums, prunes, and walnuts. The moisture content (wet basis) of these residues ranges from 35 percent to 55 percent. Hammermilled orchard prunings have a bulk density of from 9-12 lb/ft3.

Vegetable Crop

Windrows of Grape Pomace

Vegetable crop residues consist mostly of vines and leaves that remain on the ground after harvesting. The types of vegetable crops include such plants as artichokes, asparagus, cucumbers, lettuce, melon, potatoes, squash, and tomatoes. The moisture content (wet basis) of these residues is usually greater than 90 percent.

Nursery Crop

Nursery crop residues include the prunings and trimmings taken from the plants during their growth and in the preparation for market. There are more than 30 different species of nursery crops (e.g. flowers and indoor plants, etc.) that are grown. The moisture content of these residues is usually dependent on the type of crop that is being grown.

Waste Quantities and Uses

Quantifying the amounts and types of agricultural residues generated in each of the crop categories is extremely difficult, as it would require conducting comprehensive research throughout the state with continuous updates to the compiled data. Without ongoing data collection, any quantification estimates would only be valid for the time frame that the study was done and would be susceptible to ongoing market changes. Therefore, the quantification of agricultural residue tonnages should be viewed with these inherent limitations in mind and the tonnages quoted should not be considered absolute values.

In generating estimated quantities, three primary sources were used. The first data source was compiled by the IWMB through the submissions of Source Reduction and Recycling Elements (SRRE) by local jurisdictions throughout the state. The second source of information was the California Energy Commission?s (CEC) publication, 1991 Biomass Resource Assessment Report for California.

The last source of information was two joint reports from the California Air Resources Board (CARB) and the California Department of Food and Agriculture (CDFA): Report of the Advisory Committee on Alternatives to Rice Straw Burning, and Progress Report on the Phase Down of Rice Straw Burning in the Sacramento Valley Air Basin 1995-1996.

IWMB Data

The SRRE is part of each city's and county's countywide integrated waste management plan (CIWMP). The CIWMP is a plan developed by local jurisdictions outlining the course of action being taken to achieve the disposal reduction goals (reduce 50 percent of the waste going to landfills by the year 2000) mandated by the State.

The SRRE database consists of primary data compiled from local jurisdictions and has been periodically updated, with the current February 1997 report containing 94.9 percent of the jurisdictions reporting. The database contains separate fields for crop residues, manure, and miscellaneous organic. The only data applicable to this study is the crop waste category. Estimates are based on 1990 waste stream characterization (updated in February 1997), and indicate that 69,898 tons of crop waste was generated, with none being diverted from disposal. There is a factor of uncertainty attributed to the fact that each city or county may define crop residue differently in the survey.

CEC Data

The second source of information on quantities of different types of agricultural wastes generated is the CECs publication titled 1991 Biomass Resource Assessment Report for California. This report contains data on field and seed crops, fruit and nut crops, vegetable crops, and nursery crops (see Appendix A). The data were presented in bone-dry tons (BDT) because the main purpose of this report was to evaluate the potential quantities of biomass available to the biomass industry in California. A distribution of total potential of biomass resources in California is shown on a chart in Appendix B.

CARB and CDFA Data

The joint CARB and CDFA report gives estimated quantities of rice straw generated in California on an annual basis. From the data in this report, it was estimated that approximately 1.5 million tons of rice straw was generated from 514,720 acres in rice production during the 1996-97 season.

Approximately 883,794 tons from 294,598 acres (57 percent of production) was disposed of using on-farm methods. Off-farm disposal of rice straw was 0.6 percent of the total 1996-97 rice straw produced. It is estimated that approximately 8,800 tons or 2,933 acres of rice straw were diverted to environmental mitigation, erosion control, and livestock utilization. Estimates of current and projected off-farm, rice disposal/year are shown in Table A.

Recoverable and/or burnable rice straw production is typically estimated at 3 tons/acre. However, actual aboveground rice straw production is closer to 3.5 tons/acre.

Without major changes in the current marketplace, the low level of off-farm rice straw disposal will continue with little change during the next three years.

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Last updated: October 21, 2008

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