The California Integrated Waste Management Board (CIWMB) funded a two-year project to demonstrate the use of composted lawn and landscape trimmings (referred to as green waste compost in this report) collected from the cities of Visalia, Tulare, and Kingsburg in commercial field crop production. The intent was to conduct the study in a field to be planted to cotton in both years, but due to economic circumstances wheat for winter forage was planted after the first year of cotton and corn is currently planted for the second year of the experiment.
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 |