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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPMENT OF A METHOD FOR STABILIZATION OF PH IN CONTAINER SUBSTRATE DURING CROP PRODUCTION
2011 Annual Report


1a.Objectives (from AD-416)
Development of a method for stabilization of pH in container substrate during crop production. This will be done by.
1)quantify the rate of release of acidity from the plant system throughout crop time,.
2)Determine the extent of change in substrate titration properties during the 11 week crop chrysanthemum,.
3)Determine how to draw an unaltered soil solution sample that is representative of the pH situation throughout the soil ball,.
4)Establish a titration method for testing substrate,.
5)Test the capacity of a stable, reproducible dairy compost to set initial substrate pH and to buffer it against later change,.
6)Establish the optimum proportion of compost in a peat moss:perlite base substrate for establishing and holding the target pH,.
7)Profile the pH buffering capacity of compost during an 11 week crop of chrysanthemums,.
8)Evaluate the impact of compost on substrate physical properties,.
9)Explore methods for lowering the bulk density of compost-containing substrates, 10) Lower the bulk density of compost by composting for a shorter time, just sufficient for complete nitrification of NH4+ to NO3- to avoid a later pH drop if nitrification were to occur, 11) Test the use of light weight components along with compost to compensate for weight, and 12) Measure the impact of compost on nutrient supply to establish a compensating fertility program.


1b.Approach (from AD-416)
We plan to use a physiologically neutral fertilizer, water with zero alkalinity (deionized water), and water soluble liming materials devoid of residual lime. The net effect will be pH depression caused by plant system respiration and chemical acidity of the fertilizer. The test crop will be potted chrysanthemum because it has a suitably long production time of 11 weeks, is available year-around, and is one of the most important potted crops world-wide. A substrate of 3 sphagnum peat moss and 1 perlite will be used. Nutrient solution will be applied with each irrigation. Acid release will be determined periodically by extrapolating between the initial and final pH points for a given period on a substrate pH titration curve for that period. Substrate will be titrated quarterly during the crop. This will enable us to determine if the initial pre-plant titration curve is adequate for measuring acid release throughout the crop or whether subsequent curves are needed in addition to the initial curve. It will also yield the subsequent curves in the event they are required. The pour-through extraction procedure will be used as a point of reference for a close examination of the efficacy of Rhizon porous plastic vacuum extractors. Parameters to be considered include: length of time for water sorption prior to titration, the balancing cation on the titrating base (Na vs. Ca), mixing time after each addition of base, and advisability of adjusting substrate from pH 3 to 11 and back to 3 prior to titration to open up exchange sites in the organic material.


3.Progress Report

The effects of mature dairy manure compost (DMC) on physical properties of a peat moss-perlite substrate before and after 12 weeks of plant growth were evaluated. In four substrates, DMC0, 1, 2, and 3, the ratio of DMC to peat moss was 0, 1, 2, or 3 on a dry weight basis, equivalent to DMC at 0, 16, 26, or 33% on a volume basis. In all mixes, the peat moss plus DMC was held constant at 75% volume and perlite at 25%. Two sets of cylinders with an inside diameter of 7.6 cm and height of 15.2 cm were filled with the test substrates. The first set remained fallow and after three top irrigations was used for the initial physical property tests. In the second set of cylinders, one rooted cutting of pot chrysanthemum ‘Macumba’ (Dendranthema x grandiflora (Ramat.) Kitam) was transplanted into each cylinder and grown for 12 weeks after which the substrates were tested for physical properties. The effects of addition of DMC to peat moss:perlite substrate were as follows. Addition of DMC to DMC0 nearly doubled initial and final dry bulk density (Db) from 0.08 gmL-1 to 0.14 - 0.15 gmL-1 in all three DMC containing substrates. Compared to DMC0, total porosity (TP) in DMC1 was similar whereas in DMC2 and 3 TP was lower. Addition of DMC generally resulted in a rise in initial and final container capacity (CC). The increase in CC was greatest in initial and final DMC1 followed by initial and final DMC2 and then initial DMC3. The CC in final DMC3 was similar to DMC0. Addition of DMC resulted in decreased air space (AS) at all levels of DMC. The effects of 12 weeks of crop cultivation on substrate physical properties were as follows. No change in Db occurred in any substrate; TP was similar in DMC0 and 1 but lower in final DMC2 and 3 by 3 and 5% of substrate volume, respectively, however all values were above 84%; CC was higher in all final substrates by 4-7% of substrate volume, with the highest rise in DMC0; and AS was lower in all final substrates by 5-7% of substrate volume. The distribution of particle sizes comprising the DMC0 substrate showed an increase in size by the end of the crop time while the DMC containing substrates showed no change in particle size. This indicated that little or no decomposition of DMC occurred during crop time. Plant shoot dry weight increased with additions of DMC to a maximum at DMC2 and then decreased to the second highest level at DMC3 which indicated that the DMC effects on physical properties were not adverse. This project was monitored by phone calls every other month, joint participation in journal and popular press articles, and frequent email communications. The project addresses Objective 3: Evaluate existing and alternative growth medium amendments to determine the potential to deliver Si and buffer pH without negatively impacting beneficial microorganisms or crop growth.


Last Modified: 11/23/2014
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