Funded by the Placer County Solid Waste Management Division and managed by the UCCE Placer County Office, the Placer County Master Composters have continued their march on source reduction of solid wste. The time is right to approach community members about this issue as they are receptive and willing to participate for the sake of their environment, their gardens, and especially their personal and community pocketbooks. Response to our outreach efforts have been excellent and we estimate that we have been instrumental in reducing waste as its source by about 2000 tons over this short two year period. (This equates to about a $225,000 collection cost savings.)
Outreach into the elementary schools has also been well received
and will continue. Teacher involvement and education will be a
major thrust this coming year.
Land application is one of the most effective methods of disposal of sewage sludge. Land application of sewage sludge and dewatered biosolids may also be beneficial in improving soil physical and chemical conditions, water holding capacity, and water penetration rate. However, the presence of heavy metals and pathogens in sewage sludge may make their use undesirable in lands used for the production of fruits and vegetables. Disposal of sewage sludge will be more likely on lands planted to field crops. California EPA and local county governments are the permitting authorities in California. Several attempts have been made by Publicly Owned Treatment Works (POTWs) to explore the possibility of applying biosolids to agricultural lands in California. Local county governments across the state have expressed concern about health and environmental issues associated with bulk application of sewage sludge despite the fact that sludges meet the general requirements of 40 CFR 503.12 and the management practices in 40 CFR 503.14.
Biosolids contain considerable amount of nitrogen (Kelling et al., 1977). Biosolids have been primarily used as a source of nitrogen, the amount of sludge nitrogen varies from 4 to 50% (Magdoff and Amadon, 1980). Most of the published research on biosolids has dealt with nitrogen availability from sewage sludge (Sommers, 1977) and plant uptake of metals in corn and wheat. A considerable amount of work has been done on the rate of accumulation of Se and other heavy metals in field crops in the San Joaquin Valley (SJV) in California (Severson and Gough, 1992). Drainage water from part of the SJV was transported to Kesterson Reservoir via the San Luis drain canal. Evaporation of water at Kesterson resulted in a high concentration of Se and other metals in Kesterson soil. Research has been done on the distribution of Se and other elements in soils (Tidball et al., 1989) and in groundwater (Deverel and Gallanthine, 1989), and their uptake by alfalfa and other crops (Wan et al., 1988). The uptake of heavy metals and trace elements by plants depends on the concentration of theses elements in soil as well as on complex sets of other factors related to soil geochemistry (Tidball et al., 1989). The most important soil factors that influence plant uptake of elements are pH, clay content, soil texture, root depth, organic matter content and the presence of competitive ions (such as S for Se uptake). In addition, plant species vary in their ability to accumulate and tolerate trace elements and heavy metals. The beneficial uses of sewage sludge and the other aspects such as nutrients, trace metals, organic compounds, and public health has been discussed in detail by Page et al. (1983).
Dewatered biosolids contains nitrogen, macro and micro nutrients, and organic matter with a high fertilizer value. Issues such as quality of drainage and surface water, groundwater pollution, and plant uptake of metals such as Mo, As, Se, and Cr are of great concern to the general public. Little is known about the environmental issues, such as quality of drainage and surface water, associated with the application of dewatered biosolids in irrigated regions in the United States. Sludge materials may contain heavy metals and trace elements such as lead (Pb) and selenium (Se). However, in the Imperial Valley and elsewhere, selenium has been found in drainage water in California at concentrations that already exceed the EPA standard for wetlands. Field crops account for almost 80% of the 500,000 acres of irrigated land in the Imperial Valley. Alfalfa and sudangrass ranked 1st and 2nd in total acreage, respectively in 1993 in Imperial Valley (Imperial County Agricultural Crop and Livestock report). These two major field crops were grown on more than 236,000 acres of irrigated lands in Imperial Valley in 1993. This proposed research will apply Class B biosolids at 0, 4, 8, 12 dry tons per acre of dewatered biosolids. This research will be directed toward evaluating the effect of different application rates of biosolids on soil physical characteristics, groundwater quality, plant uptake of metals that are identified in part 40 CFR 503.13 Table 4, and hay yield and quality aspects. No work has been done addressing the above issue after the full implementation of 40 CFR 503 in February of 1994 regarding the uses of sewage sludge or the environmental aspects associated with biosolids applications on irrigated lands. This project is designed to address these issues in addition to providing information relative to some of 40 CFR 503 data gaps.
Since soil salinity and water management are affected by biosolids application, part of this study will be to quantify soil salinity, water infiltration rates, and heavy metal accumulations in soil and groundwater. To observe cumulative aspects of dewatered biosolids application on soil characteristics, this study is proposed for three years. A comprehensive guide to the application and management of dewatered biosolids in agricultural soils, video materials, and a slide set of 40 CFR 503 requirements will be developed. Several field days, seminars and short courses will be conducted by the PI's during the project. Findings from this research project will be published in local, statewide, and national agricultural magazines and scientific journals.
The specific objectives of this research and demonstration project are to:
Deverel, S. J., and S. P. Millard. 1988. Distribution and mobility of selenium and other trace elements in shallow groundwater of the western San Joaquin Valley, California. Environ. Sci. and Tech. 22:697-702.
Kelling, K. A., L. M. Walsh, D. R. Keeney, J. A. Ryan, and A. E. Peterson. 1977. A field study of agricultural use of sewage sludge: II. Effect on soil N and P. J. Environ. Qual. 6:345-352.
Magdoff, F. R., and J. F. Amadon. 1980. Nitrogen availability from sewage sludge. J. Environ. Qual. 9(3):451-455.
Page, A. L., T. L. Gleason, III, J.E. Smith, Jr., I. K. Iskander, and L. E. Sommers. Proceedings of the 1983 Workshop on Utilization of Municipal Wastewater and Sludge on Land. 480 p.
Sommers, L. E. 1977. Chemical composition of sewage sludges and analysis of their potential use as fertilizers. J. Environ. Qual. 6:225-232.
Tidball, R. R., R. C. Severson, C. A. Gent, and G. O. Riddle. 1989. Elements associations in soils of the San Joaquin Valley, California. p. 179-193. In L. W. Jacobs (ed.). Selenium in agriculture and the environment. SSSA Special Publication 23. ASA. Madison, WI.
Wan, H. F., R.L. Mikkelsen, and A. L. Page. 1988. Selenium uptake
by some agricultural crops from central California soils. J. Environ.
Qual. 17:269-272.
Only the 5.0 T/A compost treatment had a significantly greater
marketable yield than the untreated control. The 5.0, 10.0 and
20.0 T/A treatments had significantly fewer tons of Fusarium infected
bulbs and a lower percent of infected bulbs. Compost had no effect
on the number of roots infected by Pink root.
| Yield (T/A) | ||||||||
| Compost Treatment (T/A) |
Total Market Yield |
Jumbo | Med. | Pre-pack | Culls | Basal Rot | Basal Rot % | No. of roots infected with pink root |
| 0 | 18.0 | 3.9 | 12.8 | 1.3 | 0.2 | 5.2 | 22.2 | 2.8 |
| 2.5 | 22.8 | 2.8 | 18.5 | 1.6 | 0.3 | 2.9 | 10.9 | 3.4 |
| 5.0 | 24.8 | 6.8 | 15.9 | 2.0 | 0.4 | 1.8 | 6.6 | 2.3 |
| 10.0 | 21.0 | 4.0 | 15.5 | 1.5 | 0.1 | 2.4 | 10.3 | 2.5 |
| 20.0 | 24.2 | 4.0 | 18.8 | 1.5 | 0.2 | 1.5 | 6.1 | 1.8 |
| LSD (P=0.05) | 6.6 | ns | 6.1 | ns | ns | 2.7 | 11.2 | ns |
The following parameters have been evaluated: yield, disease incidence, insect damage, plant nutritional analysis, soil nitrate movement, trunk circumference, number of fruit per tree, fruit size, leaf water potentials, light bar readings, soluble solids content, acidity, fruit flesh pressure, postharvest characteristics related to storage, internal browning, etc. In addition to the cultural aspects and the postharvest storage aspects, a consumer taste test evaluation was performed on fruit which was harvested during the 1995 season. Two consumer taste tests were performed to evaluate fruit which was ripened for three days following harvest and on fruit that was held in cold storage for one week; then ripened to simulate shipments to the east coast.
The data thus far indicates that green waste compost compares favorably to our standard orchard fertilizers, when applied at the same rate of nitrogen. Significant differences are developing in leaf nutrient levels, organic matter content in the upper six inches of soil, and in the movement of the nitrate ion in the soil. An interesting observation with regard to brown rot disease was noted where the green waste compost was applied. In 1993 and 1994, less storage brown rot developed on the peaches where the green waste compost had been applied. This reduction in disease incidences has been attributed to the presence of Aureobasidium pullalan spores located on the surface of the fruit. When there are 2,500,000 spores or more, there appears to be no brown rot developing in stored fruit. Why the green waste compost treatment seems to accumulate more of these spores on the surface of the fruit than the other treatments is still under study.
The consumer taste test evaluation included three of the treatments from this study. This evaluation included fruit from the ammonium nitrate plots (petroleum based fertilizer) and from the manure and the green waste compost treatments. All fruit were comparable in size, color, firmness, and soluble solid content. Consumers were allowed to handle, smell, and evaluate fruit from each treatment prior to their tasting of similar fruit from each treatment (from which the soluble solid content and pressure had been predetermined). The results indicated that the consumers could not determine differences among the fruit except for texture. The consumers determined that the fruit flesh from the petroleum based fertilizer treatment was firmer than either of the organic fertilizer treatments. This was validated through statistical analysis, by using a UC firmness tester on each fruit prior to it being tasted by the consumers. The consumers could not determine any differences in any of the other parameters of color, size, shape, texture, or soluble solids. Prior to tasting the fruit, the consumers were asked to choose which of the three peaches they would prefer to buy. After tasting the fruit they were told the fertilizers used and then asked which fruit they would prefer to buy. When shown information about the fertilizer treatment used on the peaches, 84% of those who initially selected the peach that was later identified as "grown with conventional, petroleum-based fertilizers," switched to one of the two peaches labeled as 4 6 grown with natural fertilizers." None of the respondents who initially preferred a peach grown with one of the two natural fertilizers switched to the fruit grown with petroleum based fertilizer.
Composting has been implicated in the degradation of various pesticides. A pilot study was designed to determine if degradation curves could be developed for the following pesticides: DDT, Kelthane and Aldrin. These pesticides were added to soil at the level of 60, 1200 and 8 ppm respectively and placed in 18.93 liter containers with 30% cow manure and a consortium of soil microorganisms with the dominant species being Pseudomonas fluridans , Bacillis subtillis, and Aspergillis sp. The test was conducted at ambient temperature ranging from 4.5 to 21 C. Each lot was mixed, sampled and a fresh source of soil microorganisms added weekly. At the end of five weeks, levels were reduced by: DDT 86%; Kelthane 55% and Aldrin 88%. Degradation did occur at ambient temperatures of 4.5 to 21 C. A greater degree of degradation would be expected at higher temperatures found during normal composting of poultry litter and mortality.
A second experiment involving the normal composting process using macerated broiler mortality is being conducted. In this experiment, we obtained some plastic commercially available minicomposters. These minicomposters have a maximum capacity of .65 cubic yard or about ½ cu meter of material. We consider this amount to be about the minimum for good composting activity.
We started the project by making a compost with 841 pounds of macerated broiler chicken, 860 pounds of broiler litter, 411 pounds of green waste, and 492 pounds of water. After one week of composting, we divided this compost into six units weighing 328 pounds each and placed them in the minicomposters. We have a pesticide control with DDT, kelthane and princep in it. We have a minicomposter with DDT, one with Kelthane, and one with princep. There is a bunker C control and a bunker C minicomposter. We used 10 ppm of DDT in the control and contaminated bin. For kelthane and princep we used 100 ppm and for both the contaminated bin and the control, we used 2500 ppm. All bins except the two controls have the above mentioned soil microorganism consortium (SMOC). One premise being evaluated is the ability of this particular SMOC for degrading pesticides and other contaminants such as oil.
So far with the second experiment, it is difficult to measure the ability of the compost process and/or SMOC to degrade pesticides and oil. At this point, it looks like the most difficult problem to overcome is the development of a sampling technique. The numbers are so small and the variation so large that it looks like it will either degrade it entirely or it won't.
San Joaquin Composting $500 + ad-hoc contribution, in-kind. Thermo,
in-kind. Hondo, inkind. (Kearney & DANR proposals submitted--funding
denied.)
No significant difference was found in the quantity of runoff
or preliminary neutron probe data the first year. The grower then
installed a double-line drip system. Yields were recorded the
second year and showed no significant difference in tonnage or
quality. Infiltration has shown no significant benefit as a function
of subsurface water content changes during the season. 1995 tissues
showed no nutrient differences.
Much cotton in the San Joaquin Valley is grown on loamy to heavy
clay ground with impaired drainage and marginal sodicity. As infiltration
can be adversely impacted leaching suffers and total salts or
specific ions can cause crop stress. In this setting does an ash-stabilized
sludge provide fertility and reclamation benefits superior
to traditional gypsum application?
Harrison (Ohio State), Doug Munier (UC Kern), Wayne Hall Farms.
$2,254 American N-Viro, (plus commercial lab expense -$9,000)
Salt loads were not diminished in any treatment. No significant differences were found with respect to metals accumulation. Seed cotton yields were available for only one block due to harvester error and were less than I bale/ac due to high salt loads (ECe 6.2 to 7.8 dS/m). Infiltration during the last irrigation was low for all treatments but still significantly greater for the N-Viro treatment over the gypsum or the control; 1.34, 0.78, and 0.55 inches in 12 hours, respectively. Possibly, organic binders and microbial polysaccharides may have maintained some better soil structure.
Cost of the material could be less than available gypsum. The
company decided not to pursue setting up an operation in Kern
County and the mixture is currently not available.
Urban greenwaste is the single largest category of solid waste
targeted for landfill reduction mandates in Assembly Bill 939.
Large-scale facilities in the state are making this bulk compost
available for $5 to $20/ton. Both government and private enterprises
in Kern County are gearing up to produce a total of 400 to 600
tons/day of finished compost. Costs for a 5 ton/acre application
run $35-50 for trucking and spreading alone without any material
cost. At this loading rate green waste facilities alone will need
30,000 acres for spreading in 1995. Past studies have focused
on heavy loading rates and results are variable. Is this material
a profitable amendment alternative for agriculture
in Kern County?
$7,380 Community Resource Recycling and Recovery (plus in-kind and lab expense -$8,000).
Also submitted 3/31/94 for competitive grant in a larger version
with expanded impact to the CA Integrated Waste Management Board
in cooperation with Kern County Waste Management for $ 100,000.
Funding denied.
There was significantly improved emergence in late-planted alfalfa
for all amendments, but no difference in final stand or first
year yields. Levels of soil phosphorous and zinc were found to
be significantly greater in the top 3 cm. of composted plots after
emergence. Slightly improved packout of US No. 1 Large garlic,
but not significant. Seed cotton yields were unaffected. No plant
nutritional differences seen in tissue sampling for all crops
during season; even on the course sandy loam planted to garlic
where %N of leaves was low all season. 1996 early season soil
samples of 0-12" showed some trend toward increased P and
K after a second season compost application. Infiltration in alfalfa
was unaffected. Water use appeared unaffected in all crops. (Cotton
and garlic were sprinkler irrigated.)
In addition to traditional manuring/amendment programs and the
use of urban waste strewn materials, some cotton growers have
begun serious composting efforts with gin trash. Is this a profitable
amendment program for San Joaquin cotton growers and how does
it compare to alternative materials?
$24,000 Cotton Inc.
Results:No significant differences in field trial from
last year. No results yet from second year. Shafter plots spread
3/26/96. Cotton planted 4/12. Severe lack of emergence occured
in the 20 ton manure and sludge/greenwaste compost plots. Rhizoctonia
and pythium was found on damaged seedlings. Established
plants in these plots have remained less vigourous than other
treatments.
| MANURES | COMPOSTS | SLUDGE | |||||
| Fresh Dairy | Fresh Chicken | Dairy | Gin Trash | Green Waste | Sludge/Grn Wste | For land applic.) | |
| Dry Weight | 42% | 35% | 66% | 68% | 68% | 68% | 20% |
| N | 19 | 28 | 18 | 32 | 17 | 23 | 23 |
| P | 5 | 19 | 8 | 5 | 8 | 31 | 8 |
| K | 25 | 19 | 31 | 42 | 25 | 5 | 1 |
| *Equiv.Fert.$ | $11 | $15 | $13 | $17 | $11 | $14 | $7 |
| Calcium | 13.4 | 13.8 | 28.6 | 23.1 | 14.0 | ||
| Magnesium | 5.1 | 2.6 | 5.2 | 3.3 | 1.9 | ||
| Sodium | 7.1 | 3.6 | 3.4 | 3.8 | 2.0 | ||
| Chloride | 5.6 | 1.4 | |||||
| Sulfur | 2.4 | 2.9 | 5.9 | 19.7 | 2.9 | 7.2 | |
| Zinc | 0.07 | 0.08 | 0.33 | 0.27 | 0.38 | ||
| Iron | 0.19 | 0.56 | 3.30 | 6.53 | 10.00 | ||
| Boron | .07 | 0.02 | 0.10 | 0.11 | 0.02 | ||
| Copper | 0.02 | 0.04 | 0.07 | 0.20 | 0.26 | ||
| *Using the following values per unit: N @ $0.20, P @ 0.27, and K @ 0.22. | |||||||
|---|---|---|---|---|---|---|---|
| Max Increase (ppm) | |||||||||
| Regulatory Limits | Calif. Title 22 | Federal 503 | Mined Gypsum | Ash/Sludge Mix | Sewage Sludge | Green Waste Compost | Kern Lake Soil | Sludge | Compost |
| Metal
% solids | Total mg/kg | Total mg/kg | 84.3 | 54.9 | 66.0 | 70.0 | 85.8 | 10 t/ac | 10 t/ac |
| Antimony | 500 | 3.6 | **ND | 3.1 | ND | 0.5 | 0.016 | ND | |
| Arsenic | 500 | 75 | 4.7 | 3.9 | 15.8 | 2.5 | 8.7 | 0.079 | 0.013 |
| Barium | 10,000 | 47.1 | 551.0 | 515.6 | 86.0 | 137.0 | 2.578 | 0.430 | |
| Beryllium | 75 | 0.6 | ND | ND | ND | 1.2 | ND | ND | |
| Cadmium | 100 | 85 | 0.6 | ND | 15.5 | ND | 0.3 | 0.078 | ND |
| Chromium | 2,500 | 3,000 | 7.8 | 41.3 | 131.2 | 12.0 | 4.7 | 0.656 | 0.060 |
| Cobalt | 8,000 | 3.6 | 9.4 | 7.6 | ND | 13.4 | 0.038 | ND | |
| Copper | 2,500 | 4,300 | 6.9 | 149.0 | 674.8 | 54.0 | 26.3 | 3.374 | 0.270 |
| Led | 1,000 | 840 | 3.6 | 51.8 | 100.7 | 40.0 | 11.4 | 0.504 | 0.200 |
| Mercury | 20 | 57 | 0.1 | 0.7 | 3.1 | ND | 0.1 | 0.016 | ND |
| Molybdenum | 3,500 | 75 | 1.2 | ND | 30.9 | ND | <1.2 | 0.155 | ND |
| Nickel | 2,000 | 420 | 4.9 | 40.9 | 84.9 | 16.0 | 31.0 | 0.425 | 0.080 |
| Selenium | 100 | 100 | 0.4 | ND | 5.5 | ND | 1.4 | 0.028 | ND |
| Silver | 500 | 0.6 | 13.0 | 111.1 | ND | 0.2 | 0.556 | ND | |
| Thallium | 700 | 44.2 | ND | ND | ND | 0.6 | ND | ND | |
| Vanadium | 2,400 | 17.4 | 49.3 | 16.0 | 15.0 | 47.2 | 0.080 | 0.075 | |
| Zinc | 5,000 | 7,500 | 23.8 | 334.0 | 1,000.8 | 163.00 | 93.9 | 5.004 | 0.815 |
| *From analyses taken in Kern County | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Average from Hyperion Treatment Plant. | |||||||||
| **None detected. | |||||||||
Much of this material is collected separately from municipal solid waste and is processed at privately operated facilities into mulch or compost. Average chemical and physical properties of non-composted, semi-mature or partially composted , and fully composted green wastes are shown in Table 1. Properties of an agriculturally-derived compost, cotton gin trash compost, are also shown.
Samples of these materials were provided by participants in the California Integrated Waste Management Board's compost demonstration projects, 1994-96. Participants include Will Gehr (City of San Jose Agriculture in Partnership project), Jesus Valencia (Stanislaus Co.), Marc Buchanan and Richard Smith (UC Santa Cruz/San Benito Co.), Harry Andris (Fresno Co.), and Carol Frate (Tulare Co.). Additional samples of yard trimmings were provided by Ron Ganiatts, Valleys Pride. John Texiera and Rick Wegis provided cotton gin trash compost samples.
| Non-composted yard trimmings | Semi-mature composted yard trimmings | Mature composted yard trimmings | Composted cotton gin trash | |
| n = | 8 | 8 | 18 | 3 |
| Organic matter* | 68 | 59 | 40 | 49 |
| C | 33 | 29 | 19 | 24 |
| C:N | 25 | 20 | 14 | 10 |
| C:OM | 0.48 | 0.48 | 0.48 | 0.48 |
| N | 1.38 | 1.43 | 1.42 | 2.40 |
| P | 0.20 | 0.20 | 0.27 | 0.30 |
| K | 0.85 | 0.84 | 1.00 | 1.58 |
| NO3-N,mg/kg | 18 | 11 | 98 | 618 |
| NH4-N,mg/kg | 158 | 140 | 62 | 8 |
| EC,dS/m (5:1) | 4.2 | 4.0 | 3.9 | 8.2 |
| Bulk density, lb/yd3 | 186 | 381 | 1061 | 998 |
| Particles >3/8 inch | 43 | 27 | 5 | 2 |
| *All values are percent dry weight basis except where noted. Organic matter content=100-%ash. | ||||
|---|---|---|---|---|
The 32-acre trial consists of three treatments replicated three times. Each plot is 120 ft wide by 1300 ft. There are three treatments:
In the first year of the trial, chicken manure was applied at 2.5 dry tons/acre and compost was applied at 3.5 dry tons per acre. A low rate of compost was chosen because it was felt that the rate should be one that could be economically included in an annual crop budget. The only difference in fertilization was that plots with either compost or manure were sidedressed with 70 pounds/acre nitrogen (applied as anhydrous ammonia) and the "conventional" plots received 130 pounds/acre.
Maxxa cotton was planted in April 1995. During the season stand counts, gypsum block readings, pressure bomb readings, crop nutrient levels determined by plant tissue analyses, plant growth using plant mapping, and insect pests were monitored. No significant differences occurred among treatments. Plant tissue samples from compost plots were lower in nitrogen than those from the other two treatments at the "cut-out" stage, but that is not surprising as the compost did not have as much nitrogen content as the manure yet compost plots still received 60 pounds less nitrogen than the "conventional" plots.
1995 was not an outstanding year for cotton yields in general and this field was not exception. Yield results are listed in Table 1. Although the compost plots produced slightly less cotton per acre than the other two treatments, the difference was not statistically significant.
Following cotton in 1995, the grower had to change cropping plans and instead of planting cotton in 1996, his landlord insisted he plant wheat for winter forage. Plants were sampled during the season for tissue analysis but lab results are not back at this time. There were no differences in yield.
Following wheat, compost and turkey manure were applied to their respective plots. In addition, on either side of the trial an 80-foot strip received compost at 20 tons per acre dry weight. Although data from these strips will not be analyzed as part of the trial, soil and plant measurements will be taken from these areas.
To date, no obvious benefits from green waste compost have been documented; however, it is of benefit to know that there have been no negative impacts noted. The compost handled very nicely and was spread without problems by a conventional manure spreading truck. No foreign objects were found in the compost and analyses at Davis showed no weed seeds or detrimental levels of nutrients, salts, or metals.
One basic question is whether relatively low rates of compost as used in this trial will, under the high temperature and irrigated conditions of San Joaquin Valley agriculture, result in an eventual buildup of organic matter and/or nutrients that will cause a measurable difference in yield or soil conditions.
| Treatments | Gin Turnout (%) | Lint (lbs/ac) |
|---|---|---|
| "Conventional" | 35 | 971 |
| Chicken Manure | 35 | 977 |
| "Green Waste" Compost | 35 | 921 |
| LSD | NS | NS |
| CV% | 1.3 | 11.9 |
A major factor in the efficacy of beneficial microorganisms is the nutritional substrate available. Composted organic materials, already recognized as having value as potting mix amendments, can also serve as the nutrient base for beneficial microorganisms. A significant portion of my laboratory's research currently involves surveying a variety of potting mixes used commercially in California for horticultural production for naturally occurring plant disease suppressiveness. We are also testing several commercially available biocontrol agents for efficacy against plant pathogens in various compost-amended potting mix formulations. We have developed quick, short-term greenhouse bioassays for screening large numbers of container media, with and without commercial biocontrol agent fortification. These quick bioassays are also useful for determining consistency amongst batches of one type of potting mix. Longer term studies are also planned, to examine storage-life of disease suppressive effects, as well as efficacy during production of longer-term crops (e.g., 12-14 month woody crops). The goal of these disease suppression bioassays is to make information available to the horticultural industry that will offer growers new options for plant disease control as well as provide them, the compost end-users, with encouragement to use and demand high-quality compost amendments, for reasons of both organic waste management and plant disease management.
Napa County UCCE has been busy with a small start-up grant to teach composting. I believe six counties had similar grants from CAWMCB. We are in the middle of it all as we speak. Grant calls for training of Master Composters and their teaching of local residents. We patterned it after Placer/Nevada and Sonoma programs. Local grower group organizing into a 'Sustainable Growing Group' has some major corporate players. They ask provocative questions for which research does not yet exist. Terms are tossed around that need definition:
Examples:
These are used in advertisements and by in-speak agency folks. Local grower approach is not to use compost unless they get a benefit from it.
Unknown repeat application timing. Compost sources see it as disposal problem, but growers see it as a cash flow issue. With our wet winters and clay loam soils we have access with heavy equipment for only a short time after harvest. Research needs to be done about surface soil benefits over time. Clyde Elmore and I have talked about this with Pritchard, et al and may submit a DANR grant to explore this. I note Oregon St Univ seems to be studying impacts of weed management practices on surface biomass and microbe populations. Big grower fear up here is not heavy metals, but is soil active root pathogens such as Oak Root Fungus. Does it survive composting? Dr Raabe says nothing in literature about it,( but suspects it may be possible) this could be an excellent research project. Is green wast ebetter than compost? or vice-versa ?
The effects of repeated application of two composts differing in carbon / nitrogen (C/N) ratio on weekly soil nitrate nitrogen (NO3-N), weekly soil ammonium nitrogen (NH4-N), and leaf lettuce yield are being studied in trials near San Luis Obispo. One compost type (HiCN) is prepared primarily from yard wastes and has a C/N ratio of 29 - 32:1 The other compost (LoCN) is a compost prepared primarily from feedlot manures and has a C/N ratio of 10 -12:1. Prior to transplanting leaf lettuce, both composts are being applied and incorporated in the same plots repeatedly over four crop cycles at rates of 9, 18, 36, and 54 Mg ha-1 (dry mass) in each application. No other fertilizer is applied.
Education Summary: A meeting is being planned for September 1996 in Arroyo Grande (San Luis Obispo Co) on Compost and Mulch Utilization in Agriculture. The meeting is directed toward row crop and orchard growers, landscapers, and waste management professionals. Speakers include UC Specialists and Farm Advisors and a panel of growers.
This is the first year of a multi-year study on the effect of compost on vegetable production. The site was double cropped this year with lettuce followed by broccoli. Compost used at 10 and 20 T/A did not affect the yield of lettuce or broccoli in this study. Compost increased the content of N, K and Ca of lettuce early in the season but not later in the season. In addition, compost increased the content of P and Zn in broccoli early in the season but had no effect later.
The study was conducted with Tonascia Farms in Hollister, CA. The soil type was a Sorrento Silty Clay Loam. Each plot was eight 40" beds wide by 50 feet long. Compost was applied with a mechanical spreader on two occasions: prior to the lettuce crop on April 3 (lilliston incorporated on 4/4) and, over the same strips, prior to the broccoli crop on July 17 (lilliston incorporated on 7/19). The compost was applied at 0, 10 and 20 T/A and there were four replications of each compost treatment. The field was sprinkler irrigated. And pest control was conducted according to the growers standard practices.
Lettuce was planted on 4/17 and watered on 4/19. It received the following fertilizer treatments: preplant (3/31)- 400 lbs 5-17-17; lst sidedress (5/23) - 400 lbs 20-00-5; 2nd sidedress (6/3) - 400 lbs 20-0-0-5. Total N applied = 180 lbs. No preplant soil N03 analysis was taken. All fertilizer was applied by tractor and was shanked into the beds. The compost strips were split into preplanted and non-preplanted and sidedressed and non-sidedressed areas. Tissue samples for nutrient analyses were gathered on 5/22; 6/5; and 6/27. Fresh sap N03 was collected from the mid-ribs of the outer wrapper leaves on 6/6; 6/19; and 6/27. Soil nitrate and ammonium levels were determined by KCI extracts on 6/2; 6/19; and 6/27. Yield data was collected from the middle 20' of row on 6/27.
Broccoli was planted on 7/24 and watered on 7/26. It received the following fertilizer treatments: 0 preplant; 1st sidedress (8/31) - 420 lbs AN 34; 2nd sidedress (9/21) - 420 lbs AN 34; Total N applied = 285 lbs. Preplant soil N03 level = 21 ppm. All fertilizer was hand applied to the plots over the top of the middle of the beds and watered into the beds. The compost strips were split into sidedressed and nonsidedressed areas. Tissue samples for nutrient analyses and fresh sap analyses were gathered on 10/1 I- 10/25 and I 1/10. A soil microbial biomass samples were sent to Elaine Ingham's lab at OSU on I 1/10 for active fungus and bacteria analyses. Yield data was collected from the middle 20' of row on I 1/1 0, I 1/1 5 and 1 1/20.
| Bulk Den. |
H2O | Ash | C | C:N | NH4 | NO3 | N | P | K | |
|---|---|---|---|---|---|---|---|---|---|---|
| lb/yd3 | ---------%-------- | ----ppm---- | --------%-------- | |||||||
| Lettuce | 1480 | 32.1 | 77.2 | 10.9 | 11.0 | 10 | 170 | 0.98 | 0.27 | 0.94 |
| Broccoli | -- | 33.8 | -- | 11.2 | 10.2 | 10 | 220 | 1.1 | -- | -- |
| pH | EC | Na | Cl | B | Zn | |
|---|---|---|---|---|---|---|
| ------------meq/L----------- | -----------ppm---------- | |||||
| Lettuce | 8.8 | 3.4 | 9.2 | 14.9 | 32 | 265 |
| Broccoli | 8.6 | --- | --- | --- | --- | |
Nutrient content of the lettuce tissue was more affected by compost
and preplant applications earlier in the season. There was greater
N, K and Ca in the lettuce tissue with increasing compost and
less Mg at thinning (table 1). At heading and harvest compost
had no effect on the amount of nutrients in the tissue (tables
2 and 3). Compost also had no effect on the fresh sap N03
levels on three sampling dates (table 4). Compost had no effect
on the levels of N03 and NH4 in the soil
on three sampling dates (table 5). Compost also had no effect
on the yield but the preplant fertilizer contributed significantly
to the yield and size of the lettuce (table 6).
Potassium was higher in the 20 T/A treatment at the first sampling
date and phosphorous was lower (table 7). Magnesium was lower
in the IO and 20 T/A treatments and zinc was greater on the second
sampling date. Fresh sap N03 was also greater in the
20 T/A treatment (table 8). At harvest compost had no effect on
nutrient content (table 9). The compost did not affect the levels
of active fungi or bacteria in the soil (table 10). Compost or
sidedressed fertilizer did not affected yield (table 11) probably
due to residual nitrogen in the soil from the prior lettuce crop
(nitrate-N prior to planting 21 ppm).