Straw Burning - 72



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Project Leader and Principal UC Investigators

G.E. Miller, J.R. Goss, Combustive Disposal of Rice Straw and Stubble

H.B. Schultz

J.F. Williams

Mark Engstrom

I. Akpan

Jim Thompson

Al Arkrush


Protection of the environment has involved us all, particularly in the last few years. New awareness of the problem has been generated by the press, candidates for office, new agencies, individual ecological groups, and the general public - with some attention (and irritation) directed at smoke from rice-straw burning in the central valley.

The rice growers, taking responsible positive action, have funded a number of projects that deal with the production and management of rice crop residues. Combustive and noncumbustive methods of disposal have been investigated for about 2 1/2 years, with some substantial progress. Information on the presence, extent, and potentials for crop loss from stem rot (developed by Dr. Robert K. Webster) has made the studies of combustive disposal of substantial interest.

The work has been divided into the areas of open-field burning and mobile incineration.


Field and laboratory monitoring of rice-straw bums has revealed that careful management of fuel and fire to reduce moisture content and rate of burn, increasing fuel consolidation, and burning under prescribed meteorological conditions can minimize production of visible emissions from open-field burning. Backfiring residue of low moisture can reduce the quantity of smoke particles to one-tenth that produced by headfiring high-moisture straw. Under conditions of median moisture, reductions can easily be 50%. Backfiring will require additional cost and effort. Current studies are being made to determine the economics and practical aspects of utilizing the principles developed.


Trials have been made of two mobile incineration units to date: one on a cooperative project with the Agricultural Engineering Department at Oregon State University; and the other with Ben Thompson of Live Oak, California. The current state of the art has not produced a machine that is economically feasible or physically possible to operate in the rice fields of California. (RM8)


New information on suitable conditions for burning residues and applying chemicals from the air was obtained from UC research on wind patterns in the Sacramento Valley (funded by the State Air Resources Board).

Wind recordings made in previous years in the valley were available from 9 surface stations for 6 years. Analysis of data shows that afternoon and evening winds in July and August were southerly 95% of the time at Sacramento, 85% at Biggs, and 80% at Red Bluff. Frequencies were assumed to be quite low in October and November, but they are now shown to be still substantial (respectively 50, 40, and 30%). This is very significant since such winds contribute to the dispersion of air pollutants by developing strong velocities aloft at night. These were recorded at two well exposed stations in the strategically located Sutter Buttes area. Very useful information was developed from those data, especially when related to conditions at the TV tower at Walnut Grove, which was studied in previous years. At an important 500-foot knoll on the west side of the Sutter Buttes the frequency of southerly winds in July and August is 95% at night, with velocity over 10 mph during 75% of those hours. The 2,000-foot peak at Sutter Buttes had conditions surprisingly similar to those at the TV tower, about 60 miles to the south: southerly winds 60% of the time before midnight and 30% after midnight in summer, respectively declining to 40 and 21% in October-November. More relevant in these fall months are winds at the 500-foot level (closer to the low-level jet height). There, southerly winds occurred on 40% of the afternoons and on 60% of the nights. Observations by night balloons released at various locations by crews of the Agricultural Engineering Department revealed that maximum winds were sometimes 30-40 mph at 500-1,000 feet. Such "vacuum-cleaner" conditions provided by the nocturnal low-level jet wind are commoner and faster on the east side of the valley, however, decreasing westward toward Glenn and Norman. (RM8)


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