Effect of Compost Applications on Soil-Plant Characteristics and Yield of Broccoli and Cucumbers - Year Three of a Three Year Study; and Three Year Summary of the Effects of Compost Applications on the Soil and Plant Growth

 

Richard Smith, Farm Advisor, U.C. Cooperative Extension, San Benito County and Marc

Buchanan, Consulting Agronomist, Santa Cruz

 

(Note:  extensive tables and figures are available by contacting Richard Smith or Marc Buchanan.)

 

Introduction

 

The goal of this three-year trial was to examine the effect of compost applications on crop growth, nutrient dynamics in the plant and soil and observe microbial populations in plots that were amended with various rates of compost. The 10 and 20 ton compost per acre rates of compost used in this trial were higher than growers would normally be able to afford; however it was felt that it was important to use higher rates in order to bring on changes in the soil and plant during the three years of the trial. The composts used in this study were made in part with green wastes from municipalities. These materials were mixed with dairy manure, straw as well as wastes from packing sheds and canneries.

 

We wish to acknowledge the cooperation and assistance of Joe Tonascia, grower;  Pat Herbert and Don Cranford, compost suppliers; Joel Wiley, John Pryor Fertilizer Company; Don McFadden, trucker; and the California Integrated Waste Management Board, project funders.

 

Methods

 

This trial was conducted at Tonascia Farms, Hollister, on a Sorrento Silty Clay Loam. Compost was applied at the rates of 0, 10 and 20 tons per acre prior to planting each crop (see analyses of compost below). The following are specifics about applications and crops grown over the three years: 1995 - Applied on April 3 for spring head lettuce crop and July 17 for fall broccoli crop; 1996 - no compost was applied to the spring head lettuce crop (missed the application due to wet soil conditions) and June 12,  1996 for fall head lettuce crop; 1997- Applied December, 1996 for spring broccoli  (planted 2/15 and harvested 4/25) crop and May 27 for the fall cucumber crop (planted 6/15 and harvested 8/7 & 8/15). The same rate of compost was applied to the same plot over the three years. In total 5 compost applications had been made prior to the fall 1997 cucumber crop. Standard fertilizer applications were made to the broccoli and cucumber crops. The fields were minimum tilled with the Sundance system following each crop except prior to the fall 1996 crop the field was disked, ripped and land planed.

 

Soil nitrate and ammonium were measured in the soil by taking 2.0 M KC 1 extracts of the soil. The extracts, along with plant tissue and soil samples, were sent to the DANR Analytical Laboratory at U.C. Davis for analysis. Active soil fungus and bacterial levels were measured on March 12 using a plating and counting technique at the Soil Microbial Biomass Service at Oregon State University. Soil microbial biomass were measured on April 23, July 7, and 30, and August 19 in the lab of Dr. Louise Jackson, Dept. of Vegetable Crops, UC Davis using the soil fumigation technique.

 

 

Compost Composition:

 

Prior to the spring 1997 crop, applied 12/96 (from Herbert, Hollister)

 

Water Content	pH	EC	Ca	Mg	Na	Cl	B	Zn	Fe	N	C
			Meq/L			ppm				%
55%	8.1	6.3	7.4	6.5	26.0	24.1	2.0	11.8	240	0.99	11.6

 

 

 

 

Prior to the fall 1997 crop, applied 5/27/97 (from Herbert, Hollister)

 

Water Content	pH	EC	Ca	Mg	Na	Cl	B	Zn	Fe	N	C
			Meq/L			ppm				%
20%	7.2	7.6	5.28	9.0	9.4	17.9	26.8	1.7	7.3	424	0.67

 

 

 

 

Results - 1997

 

Spring Broccoli Crop: There was a reduction in the amount of magnesium in the tissue of the broccoli on the first sampling date (March 12) and no other differences were observed in the nutrient content of the broccoli on three sampling dates during the growing season.  There was a slight reduction in the amount of nitrate in the soil of the 10 T/A compost treatment on the first sampling date but no further differences in nitrate or ammonium levels in the soil were detected on three sampling dates.  Active soil fungus and bacteria levels were not significantly greater in the compost treatments on March 12.   Soil analyses indicated an increase in pH in the 10 T/A treatment, an increase in P in the 10 & 20 T/A treatments, an increase in K in the 20 T/A treatment and an increase in organic matter in both compost treatments. There was no significant increase in the yield of broccoli in any of the treatments.

 

Fall Cucumber Crop: There was less chlorine in the leaves of cucumbers in the 20 T/A treatment on July 29 and more phosphorous in the 20 T/A treatment on August 14. There was more nitrate-N in the soil of the 10 T/A treatment on July 29 and in the 20 T/A treatment on September 3.  There were strong trends for an increase in microbial biomass in both the 10 and 20 T/A treatments, however none of the values were statistically significant.  The levels of organic matter in the soil were higher in the 10 and 20 T/A treatments and total digestible nitrogen was higher in the 20 T/A treatment on July 20.  No yield differences were seen in either of the treatments.

 

 

Summary - Three Year Study

 

Over the three seasons there were few significant differences with regard to the nutrient levels in the tissue of the crops that were grown. There were increases in the levels of potassium and calcium in the early growth stages and occasionally magnesium was seen to be lower. The reduction in the levels of magnesium are of interest due to the high levels of magnesium that naturally occur in the Hollister area soils that can occasionally be problematic. Compost did increase the levels of organic matter in the soil on five sampling dates. Phosphorous was higher in the soil on three. In general, nitrate-nitrogen levels were lower at the beginning of the crop cycle  (closer to the application date of the compost); however, as the season continued the compost-amended treatments typically had higher levels of nitrate than the unamended plots. This could be due to immobilization of the nitrate immediately after application of the compost and mineralization of nitrate from the compost later in the growth cycle after a sufficient period of time. It is interesting to note that even though 884 and 1,768 lbs of nitrogen had been added as compost to the 10 and 20 ton per acre compost treatments over the three years of the trial, the nitrate pools in the soils of these two treatments were still relatively modest. The soil microbial biomass data, as mentioned above, does not provide statistically significant differences, but does have a strong trend indicating increased microbial activity in the compost amended treatments. No yield increases were seen in any of the treatments over the three years.