Using Compost as a Soil Amendment in Red Raspberries
Volume 6 Issue 10
Chris Benedict, Betsy Schacht, Jessica Shaw, Meijun Zhu, Chad Kruger, Georgine Yorgey
An on-going study is evaluating the annual application of compost derived from dairy manure as a top-dressed soil amendment to improve soil quality. The results reported herein are a subset of a larger trial evaluating the use of manure derived soil amendments in small fruit production. The objective of this study is to determine if annual applications of compost would impact soil quality, maintain plant growth and fruit yield, and not pose a food safety risk in red raspberry production.
Applications of compost made, in part, from local dairy manure occurred at 10 T/A (DW) in early April in 2016 and 2017 to ‘Meeker’ red raspberries planted in 2011. Prior to treatment assignment, plots were setup in a complete randomized block to control for soil texture variations throughout the field. Compost (COM) plots were compared to a standard synthetic fertilizer (CON) (2016 & 2017) as well as a nonfertilized control (CHK) (2017 only) through monthly soil nutrient monitoring, foliar nutrient content, plant growth, fruit yield, and various soil health assessments. Additional synthetic fertilizer applications were made to compost plots to deliver similar total macronutrients as the CON treatment.
Soil samples (surface) were taken to monitor for zoonotic pathogens (E. coli O157:H7, Listeriamonocytogenes, Salmonella, spp.) from all plots prior to compost application, 14 days after application, prior to harvest and in early fall. Additional leaf samples from primocanes and fruit samples from early ripening fruit were sampled for pathogens.
Spring floricane diameter and primocane height were similar across treatments (COM vs. CON).
Yield (total and fruit weight) was similar across treatments in 2016 (data not shown)
and 2017 (Figure 2).
In 2016, soil nitrogen levels (nitrate) were consistently higher in CON plots as compared to COM plots (Figure 3).
In 2017, soil nitrogen levels (nitrate) at 3” fluctuated throughout the monitoring period with COM and CON levels consistently higher than CHK. Early season (4/22/17) levels were higher in COM than CON, but this changed for the remaining of the sampling period (Figure 3).
No significant differences existed across treatments for all soil health indicators (bulk density, infiltration, penetrometer, plant parasitic nematodes) in 2016 or 2017.
No coli O157:H7 or L. monocytogeneswas detected from compost, soil, foliar, or fruit samples in 2016 (2017 samples have not been analyzed to date).
Application of compost combined with synthetic fertilizers maintained similar yield and plant growth as compared to a standard fertilizer program. Though, to date, no changes in physical soil properties (bulk density, compaction, or infiltration) have been observed. Based on a previous trial in red raspberries, top dressing compost required three years of applications before reductions in bulk density, compaction, and infiltration time were observed (Benedict unpublished data). To date, this trial has documented no food pathogen risk with the use of compost in red raspberries based on our application date and methods. It should be noted, that application of compost in red raspberries is complicated by the fact of the handling the bulky material and cost associated with distribution within a raspberry field.
We thank the grower cooperator involved in this project and the funding sources including NRCS Conservation Innovation Grants Program and WSDA Specialty Crop Block Grant Program.