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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

Location: Application Technology Research Unit

2010 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 overall goals of the project are to quantify the amount of acidity released into the root substrate by a plant system during culture and to explore the use of mature dairy manure compost for adjusting and stabilizing substrate pH during crop production. We developed a technique for titrating peat moss substrate that allows us to assess plant acidification and the pH buffering capacity of compost. We also completed a comparative assessment of the Rhizon vacuum substrate solution sampler against conventional systems to develop a minimally invasive means for procuring un-altered solution for our substrate pH study. Thirteen floral crops when fertilized with neutral reaction fertilizer lowered pH between 4 and 78 days after transplant by the following amounts: petunia (0.14), begonia (0.19), osteospermum (0.43), pansy (0.51), impatiens (0.79), New Guinea impatiens (0.89), geranium (0.97), vinca (1.00), tomato (1.17), Reiger begonia (1.46), pot mum (1.56), sunflower (2.44), and kalanchoe (2.45). Substrate pH was successfully adjusted up to 6.5 from a starting point under 4 with compost and no other liming material and was stabilized to the same degree as obtained alternatively with agricultural limestone. The impact of compost on physical properties of a peat moss-base substrate was the same at the start as at the end of an 11 week pot mum crop. Over the 11 week crop time, dry bulk density and total pore space remained the same while air space diminished and container capacity rose. Substrate shrinkage in the pot due to compost was insignificant over the 11 weeks. Within each point in time, compost raised dry bulk density and container capacity, had no effect on total porosity, and lowered air space. Tissue analysis of pot mum leaves at the end of the crop indicated that compost resulted in increased concentrations of potassium, sulfur, copper, iron, and manganese, lower, but adequate, calcium and magnesium, and similar nitrogen, phosphorus, boron, and zinc concentrations. Leaching tests showed that the greatest release of nutrients from compost is at time zero and declines in an asymptotic fashion thereafter, suggesting that adjustments in crop fertilization will affect pre-plant fertilizer formulated into the substrate more than post-plant fertilization. Work to be undertaken this next year includes the following: the time-course rate of acid release into substrate by the plant system will be further quantified; a set of suitability parameters will be developed for evaluating the usefulness on candidate composts in container substrates; a means will be sought for lowering the dry bulk density of compost containing substrates which includes lighter components in the mix; the minimum required shipping bulk density of compost substrate that ensures acceptable wetability of the mix will be compared to that of conventional peat-lite substrate and; required adjustments in fertilization practices to accommodate nutrient release from compost will be identified. Activity was monitored through a site visit, face-to-face meetings at two conferences, frequent email communication, and once-a-month phone calls.


Last Modified: 7/25/2014
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