BioCycle November 2005, Vol. 46, No. 11, p. 46
In three-year trials with beets and carrots, yields from leaf compost applied annually at rates as low as 10 T/A were higher compared to unamended controls.
Abigail A. Maynard

IN CONNECTICUT, with 94 active municipal leaf composting facilities, the most abundant type of compost is … leaf compost. Yet relatively little research has been done on root crop production where yard trimmings compost has been applied. Since 1989, at our experiment station in New Haven, I have conducted experiments with a variety of vegetables and cut flowers, studying responses to compost amendments. Most emphasis was placed on determining the effect of compost on the fertilizer requirement of these crops. The fertilizer application rate varied while the amount of compost was held constant (50 T/A or 1 inch on the surface). The high application rate of compost was selected to ensure the compost would have an effect within the three-year time frame of the experiment. This rate, however, might be unrealistic for growers with high acreages. In our latest experiment, compost application rate varied downward from 50 T/A, while the amount of fertilizer was held constant. The objective was to determine the effect of different rates of leaf compost on the yield of carrots and beets and to ascertain whether application rates lower than 50 T/A would have an immediate effect on yields.
Experiments were conducted on Cheshire fine sandy loam, a loamy upland soil with moderate moisture holding capacity. A three-foot aisle separated each 12 by 10 foot plot, and each treatment was replicated four times in a Latin square design.
Unscreened leaf compost was applied at rates of 50 T/A (dry weight basis) (1 inch on the surface), 25 T/A, and 10 T/A. The compost was rotary tilled into the soil to a depth of six inches. Compost was produced in a passive pile turned four or five times yearly for two years. All compost-amended plots and control plots were fertilized preplant with commercial grade 10-10-10 (N-P2O5-K2O) at a rate of 1,300 lb/A. Yields from the compost-amended plots were compared to yields from the unamended control plots.
Beets and carrots were seeded by hand in rows three feet apart. After the plants were 2-3 inches tall, they were thinned to two to three inches apart. Weeds were controlled by cultivation. Overhead irrigation was used as needed. Carrots were weighed without tops, while beets were weighed with their edible tops.
Soil Characteristics
Even though there were virtually no differences in soil nutrients between the compost-amended plots and the control plots, there were major differences in organic matter percentage and pH. After one 50 T/A compost application in 2000, soil organic matter increased to 4.3 percent compared to 3.4 percent on the unamended controls, an increase of 26 percent. The pH value also increased from 5.7 to 6.1. There were no major differences in organic matter percentage and pH on the 25 T/A and 10 T/A plots compared to the control plots in 2000.
In 2001, soil organic matter was 4.0, 4.5, and 5.1 percent (10, 25, and 50 T/A, respectively), an increase of 14, 29, and 46 percent compared to the unamended controls. In 2002, soil organic matter was 4.8, 5.3, and 6.5 percent, an increase of 26, 39, and 71 percent compared to the unamended controls. Over the three-year period, organic matter percentage from the unamended controls remained relatively constant while, in the compost-amended plots, organic matter percentage averaged a 44 percent increase, indicating a cumulative effect.
The soil pH remained relatively constant (5.7-5.9) on the unamended controls over three-year period of the experiment while the soil pH of the compost-amended plots increased annually with one exception where the pH remained constant (at the optimum pH of 6.6). In all the compost-amended plots, the compost had a liming effect by raising the pH into the range considered optimal for both microbial activity and nutrient availability. While the pH values of the 10 T/A plots and the 50 T/A plots were different in 2000 and 2001, they were equivalent in 2002 (6.4-6.6), thus demonstrating the cumulative effect of the annual additions of compost, even at the 10 T/A rate of application.
Carrot Results
For all three years, yields from plots (lbs/10feet of row) amended with compost were greater than the unamended controls plots. Yields from plots amended with 10 T/A or 25 T/A were equivalent in all three years while yields from plots amended with 50 T/A were greater than the other two rates in two of three years. Carrot yields from plots amended with compost at 50 T/A ranged 7 to 46 percent greater than yields from the unamended controls while plots amended with compost at 10 or 25 T/A ranged 6 to 26 percent greater.
In 2002, there was a decrease in yields compared to 2001 in the unamended controls while yields in the compost-amended plots progressively increased from year to year illustrating a cumulative effect of the annual compost amendments.
The average number of carrots per plot indicates the effect of the compost on germination and survivability of the young seedlings. Plots were thinned after germination so the density reflects gaps in the 10 foot row exceeding the thinning rate of two to three inches. The average number of carrots per 10 feet in the compost-amended plots averaged 24 in 2000, 34 in 2001, and 51 in 2002 compared to 20, 29, and 33 in the unamended control plots. Plant density of carrots from compost-amended plots increased 112 percent from 2000 to 2002, while density from the control plots increased 65 percent. This also indicates a positive effect of the annual compost amendments.
Applying leaf compost at a rate as low as 10 T/A had an impact on numbers of carrots and yield, even in the first year. The number of carrots and yield from plots amended with 10 T/A compost annually was greater than the number and yield from the control plots in all three years. Increasing the application rate to 25 T/A had no effect on yield but increasing it further to 50 T/A increased yield as much as 12 percent.
Beet Results
In all three years, all the compost-amended plots had greater yields (lbs/10 feet of row) than the unamended control plots. Beet yields from all the compost-amended plots averaged 29, 58, and 149 percent greater than the unamended control plots, in 2000, 2001, and 2002 respectively. This suggests a cumulative benefit of compost amendments.
In the first year of compost application, there was little difference in yield between the various application rates. However, in 2001 and 2002, beet yields increased as the compost application rate increased. In 2001 and 2002, as the application rate increased from 10 to 50 T/A, yields increased 39-41 percent compared to the unamended controls.
The average number of beets/10 ft row from the compost-amended plots increased, with one exception, from 21 to 317 percent compared to the average number from the unamended controls. In the first year of compost application, there was little difference in density between application rates. In 2001, the average number of beets increased as the application rate increased with the greatest density found on plots amended with 50 T/A compost. In 2002, there were major differences in density between the application rates; however, the greatest number of beets was found on plots amended with 25 T/A compost.
Like carrots, a compost rate as low as 10 T/A had a positive impact on numbers of beets and yield. In the first year, yield increased 22 percent compared to the unamended control plots, while the density increased 27 percent. After three years of compost applications, yield was 103 percent greater than the control plots with the density increasing 133 percent.
For unknown reasons, yields decreased in 2002 in all amended and unamended plots. Compost, however, appeared to mitigate the losses. There was an average 50 percent decrease in yield from 2001 to 2002 from the compost-amended plots compared to a 137 percent decrease from the control plots. In addition, density in the compost-amended plots decreased 90 percent compared to a 417 percent decrease in the unamended control plots. Apparently, the yield and density losses in 2002 were not due to the compost amendments but to an unknown environmental factor, such as poor seed viability, unfavorable seedbed conditions, or weed competition.
Summary Of Trials
For three consecutive years, leaf compost was applied to plots on a loamy upland soil at rates of 50 T/A, 25 T/A, and 10 T/A. Yields of beets and carrots from the compost-amended plots were compared to yields from unamended control plots. For both beets and carrots, leaf compost applied annually at rates as low as 10 T/A resulted in greater density and yields compared to unamended controls. The differences between compost-amended plots and the unamended control plots occurred in the first year of compost application.
For carrots, in all three years, all compost-amended plots had greater yields (up to 46 percent) compared to the unamended control plots. Increasing the application rate to 25 T/A from 10 T/A had little effect on yield but increasing it to 50 T/A from 10 T/A increased the yield as much as 12 percent.
For beets, in all three years, all compost-amended plots had greater (up to 149 percent) yields compared to the unamended control plots. Increasing the application rate to 25 T/A from 10 T/A increased beet production 9 to 30 percent while yields from plots amended with compost at a rate of 50 T/A increased as much as 42 percent compared to plots amended with 10 T/A in the final two years.
Greater yields of carrots and beets were not due to increased nutrients in the compost-amended soils but were probably related to the effects of greater organic matter contents and higher pH values. There was a cumulative effect of compost additions over three years in both carrot and beet yields compared to the unamended controls.
Abigail Maynard is in the Department of Forestry and Horticulture at the Connecticut Agricultural Experiment Station in New Haven.