Composting for Blueberry Production Progress Report 2009/2010 Blueberry Field Day - July 14 th, 2010 Author: Ryan Costello, graduate student in Crop and Soil Sciences and Horticulture, OSU, Corvallis, OR Email: ryancost@gmail.com Graduate Advisors: D. Bryla, B. Strik, D. Sullivan, J. Owens Project Assistance: C. Evans, R. Hamlyn, K. Pool, A. Shireman, P. Sturman, E. Vollmer Project Funding: USDA-NIFA Integrated Organic Program; In-kind support from Fall Creek Nursery Color Version of Report: http://groups.hort.oregonstate.edu/content/organic-blueberry-production Introduction In Oregon, highbush blueberry has traditionally been grown with a mulch or with pre-plant soil incorporation of Douglas-fir sawdust. Sawdust use in blueberries began when sawdust was abundant and inexpensive, but now sawdust is more costly and scarce. Applying sawdust as a mulch or soil amendment increases the need for nitrogen fertilizer, because soil microbes consume plant-available nitrogen during the decomposition process. The scarcity and cost of sawdust, combined with interest in improving plant and soil health, has stimulated some Oregon farmers to consider compost as an alternative organic input. Substitution of compost for sawdust may also provide savings in fertilizer input costs. Blueberry grows best on well-drained soils that have high organic matter content and acidic ph. Target soil ph for blueberry is near ph 5 (acidic). Blueberry plants are intolerant of high salt content, as indicated by electrical conductivity (EC). Compost generally has a ph near neutral (6 to 8), and may have relatively high salt content. The organic materials that compost is made from (feedstocks) and the composting process itself can produce finished composts with very different characteristics, including ph, salt content, bulk density (lb/cubic yard), and nutrient content. Composts made with high-nutrient feedstocks (e.g., manure) contain more nitrogen in the finished compost but also generally have higher salt content and higher ph. The Organic Systems Trial at NWREC utilizes a yard debris compost from a local commercial composter. We are not certain if this is the best compost for blueberry. The purpose of the ongoing research described here is to evaluate wide range of composts for suitability in blueberry production. Objectives: Evaluate composts created from locally available feedstocks to determine the best characteristics for blueberry production, and determine whether acidification of composts with elemental sulfur is beneficial. Experimental Design: Acidification with Sulfur In order to determine the amount of sulfur which would need to be added to acidify the composts, the composts were titrated in the laboratory with increasing amounts of sulfuric acid and measured at ph stabilization, the point at which the ph was no longer changing, which was found to occur at 72 hours. Ground elemental sulfur was then added to the composts 70 days prior to the initiation of the experiment in the average amount needed to drop the compost ph by 2 units, as determined by the titration.
Greenhouse Plant Response Experiment The initial plant response experiment was conducted in the USDA greenhouse at Oregon State University from February 9 th to May 4 th, 2010. One year old Duke were planted into one gallon pots containing 60% NWREC soil (ph 5.5), 10% screened pumice, and 30% compost by volume. The experiment was laid out in a two-way factorial randomized complete block design with five repetitions, with a total of 120 plants. The treatments were comprised of 10 different composts made from locally available feedstocks, as well as sawdust and soil only treatments for controls, and each treatment was applied in its acidified and non-acidified form. Acidification was achieved by adding elemental sulfur at an amount which would drop the ph of each compost by approximately 2 units. The plants were watered three times per week with a fixed amount of 150ml. They were fertilized with a complete acid-loving solution, Miracle-Gro Water Soluble Azalea Camelia and Rhododedron (30% N, 10% P, 10% K; N composed of 3% Ammonia and 27% Urea), at a rate of.014g N per plant bi-weekly. ph and EC (salinity) measurements, which are a snapshot of the soil solution at a given time, were done on Day 13 and Day 56. The plants were destructively harvested at Day 85. Nitrogen Incubation In order to determine the nitrogen that would be released or immobilized by the composts, an incubation was begun on January 20 th, 2010. 20g of wet compost was mixed with 300g of NWREC soil (gravimetric moisture of 23) and aerobically incubated at 22C. After 30 days the soil was then dried and measured for NO3 content. Initial Results: Greenhouse Plant Response Experiment The harvest data showed large differences in plant responses to the composts. The plants produced the most growth above and below-ground to the horse manure, grass hull, leaf, yard debris and biosolids composts. However, the plants grown in the grass hull composts showed visual evidence of possible herbicide damage (see image). The plants grown in the fir sawdust placed a significant amount of their energy into root growth, with very little above-ground growth. This could be explained by the tie-up of nitrogen by the sawdust, causing the plant to put out more roots in search of nitrogen. The mint hay and the dairy solids composts both produced very little root growth outside of the original root ball, and during the trial several plants died in the mint hay treatment and one in the dairy solids treatment (see images). Both of these composts had high ph and high salinity (see attached table). Sulfur Acidification The acidification with sulfur produced a positive effect for most of the treatments on leaf growth, and all of the treatments on root growth. Although the sulfur addition increased the salinity of the treatments (see attached table), the universally positive response of the plants to sulfur indicate that high ph was a greater inhibition to plant growth than high salinity. Nitrogen Incubation The incubation of the composts with soil showed that the composts varied significantly in their capacity to supply nitrogen to the plants. Incubation with sawdust tied up the nitrogen that was inherently available in the soil, producing a net nitrogen loss.
Above: Blueberry plant response to the compost, sawdust and soil only treatments; plants were destructively harvested on Day 85. Error bars represent standard error. Left: Nitrogen (NO3-N) recovered after compost incubation with soil for 30 days. Baseline (0mg N) is the amount of nitrogen recovered from the soilonly controls. Error bars represent standard error.
Above: Root response was determined by measuring cm of root growth beyond the initial root ball at planting, with the highest at 7cm and the lowest at 1cm. Above: Symptoms of herbicide toxicity in the grass hull compost treatment, showing thin, leathery leaves. Above: Symptoms seen in the mint hay treatment. The older leaves first showed inter-veinal necrosis which was followed by whole plant death. Above: Above-ground plant growth was limited in the sawdust treatment (left); plants grew well in the horse manure treatment (right).
Treatment # 1 2 3 4 Compost description 80% dairy solids, 20% spent hops 45% horse manure with bedding, 45% spoiled hay, 10% spent hops locally produced manure-based mixture 80% grass hull, 20% mint hay 5 100% mint hay 6 100% horse manure with bedding 7 100% dairy solids 8 100% chipped leaves Compost Source Age of Compost Compost Analyses ph (10:1) EC (10:1, ms/cm) Sulfur per kg dry matter to drop compost ph by one unit (g) Total Inorganic N (g/dry kg) Total C (%) Total N (%) Made onsite at NWREC <1 yr 7.8 0.64 1.95 0.30 15.25 1.10 14 Made onsite at NWREC <1 yr 7.7 1.69 2.25 0.71 14.55 1.29 11 Corvallis organic blueberry farmer 2 yr 7.9 1.65 2.84 0.88 18.98 1.90 10 Monroe grass seed/mint farmer 2 yr 5.7 2.19 2.77 0.80 17.94 2.18 8 Monroe grass seed/mint farmer 2 yr 8.1 4.28 3.40 2.69 39.76 5.21 8 Oregon City stable 3 yr 6.4 1.13 2.05 1.08 9.59 0.98 10 Made onsite at NWREC <1 yr 8.0 5.00 5.09 5.75 27.76 2.45 11 Hillsboro onfarm leaf compost 1 yr 7.2 0.43 2.11 0.26 12.58 0.71 18 9 100% chipped yard debris City of Corvallis Unknown 7.7 0.77 2.23 0.08 21.23 1.41 15 10 100% biosolids City of Tacoma Unknown 5.4 0.93 3.40 0.84 22.59 1.45 16 11 100% fir sawdust NWREC N/A 4.0 0.04 N/A 0.01 47.45 0.20 237 Above: Analysis of composts/amendments used in the winter plant response experiment. The sulfur requirement to drop the ph by one unit was determined by laboratory titration with H2SO4. Total inorganic N calculated by total NO3 + total NH4. C:N ratio
Greenhouse Plant Response Experiment Treatments Treatment # Treatment Composition Amendment Description 1 2 3 4 5 6 7 8 9 10 11 Non-acidified ph EC/salinity (ms/cm) Acidified ph EC/salinity (ms/cm) 80% dairy solids, 20% spent hops compost 6.58 0.67 5.46 1.94 45% horse manure with bedding, 45% spoiled hay, 10% spent hops compost 6.36 1.70 5.42 3.53 locally produced manurebased mixture compost 7.00 1.00 5.70 3.54 80% grass hull, 20% mint hay compost 6.02 2.17 4.98 3.91 100% mint hay compost 6.70 2.10 5.50 5.26 100% horse manure with bedding compost 6.12 1.64 4.98 3.30 100% dairy solids compost 7.08 4.09 7.06 4.82 100% chipped leaves compost 6.52 0.45 5.62 1.72 100% chipped yard debris compost 6.58 0.71 5.86 2.44 100% biosolids compost 5.98 1.06 4.54 2.43 100% fir sawdust 5.84 0.10 5.82 0.18 12 90% soil, None 6.18 0.18 5.62 0.50 Above: Greenhouse Plant Response Experiment Treatments. ph and EC values measured on Day 13 of the experiment.