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Janet F. M. Rippy and Paul V. Nelson

Measurement of substrate pH entails procurement of the substrate solution and measurement of the solution pH. Acid-base reactions are completed at the time of testing. Determination of substrate pH during development of a titration curve is more complex because it involves initially the reaction of a base with the substrate. Five factors that can influence the resulting pH values were investigated in this study and include amount of water added to substrate, method to procure substrate solution for pH determination, chemical form of base used, time allowed for acid-base reaction and the addition of CaSO4. Substrate in this study consisted of 3 sphagnum peatmoss: 1 perlite (by volume) amended with wetting agent. Dolomitic limestone (6 g·L-1 substrate) was added to substrate for the water amount and solution procurement method experiments. Except for the water amount experiment, deionized water was added by weight to achieve 95% container capacity. Dishes were incubated at 20 °C for specified times. To identify the minimal level of water necessary to ensure complete contact between base and substrate for neutralization, additions equivalent to 95%, 100%, 120%, and 150% container capacity were tested. The 95% level proved adequate. The saturated media extraction and pour-through bulk solution displacement methods for pH determination resulted in higher pH measurements in the incubated substrate than the squeeze bulk solution displacement method. This indicated that the former two methods diluted the soil solution. The squeeze method was deemed most effective. NaOH resulted in higher pH endpoints than Ca(OH)2. This was apparently due to a higher affinity of Ca2+ for peatmoss exchange sites. Since Ca2+ is the predominant cation associated with liming materials for soilless substrates, Ca(OH)2 is more appropriate for titration. From the tested incubation times of 0, 2, 4, 8, 24, 48, and 96 hours, the duration of 24 hours was found to be adequate to allow complete reaction of base with substrate acidity. The best procedure for determining pH in a substrate titration situation included a water level of 95% container capacity, Ca(OH)2 base, an incubation time of 24 hours and the squeeze solution displacement method. The additional CaSO4 was not necessary. Chemical names used: calcium sulfate (CaSO4), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2], calcium ion (Ca2+).

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Robin A. DeMeo and Thomas E. Marler

Two studies were conducted to determine the influence of pH on papaya seed germination and seedling emergence. The germination test was conducted with `Waimanalo' and `Tainung 1' seeds, using a double layer of filter paper disks in plastic petri dishes placed within a growth chamber. Each dish received 40 seeds, and germination was defined as when the radicle was visible. Disks were wetted daily with nutrient solution adjusted to pH of 3, 4, 5, 6, 7, 8, or 9. Germination began on day 5, and the study was terminated on day 23. Solution pH did not influence germination rate or ultimate germination percentage. `Waimanalo' exhibited 58% germination and `Tainung 1' exhibited 64% germination in this test. The seedling emergence study was conducted with `Waimanalo' seeds using sand culture within a growth chamber. Thirty seeds were planted in 10-cm containers, and the sand was irrigated daily with the solutions from the first study. Emergence was defined as when the hypocotyl hook was visible above the sand. Emergence began on day 10, and the study was terminated on day 30. Solution pH did not influence seedling emergence, and mean emergence was 69% in this study. The results indicate that the seed germination and seedling emergence stages of papaya seedling growth are adapted to a wide range of substrate pH.

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H. Melakeberhan, G.W. Bird and A.L. Jones

This study was conducted as part of a stone fruit decline project to determine the effects of soil pH (3.9 to 7.0) on soil and plant nutrient imbalance and mortality of standard (Mazzard and Maheleb) and new (GI148-1 and GI148-8) rootstocks. Seedling mortality and soil Ca in all rootstocks and soil K and leaf Ca, K, Al, and Mn contents in all rootstocks but GI148-8 were higher at below optimum than at optimum soil pH. The nutrient imbalance suggests that the adaptation of these rootstocks to biotic and abiotic factors needs to be considered.

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Joseph P. Albano, James Altland, Donald J. Merhaut, Sandra B. Wilson and P. Chris Wilson

Dissolved carbonates and bicarbonates are major contributors to irrigation water alkalinity. Irrigation water alkalinity (i.e., buffering capacity), not pH, has the major influence on substrate (the term “substrate” is interchangeable with “media

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Michael R. Evans, Johann S. Buck and Paolo Sambo

determine and compare the substrate pH, EC, and primary macronutrient status of three ground PBH products to sphagnum peat over time in a greenhouse environment and to determine if these chemical properties were within acceptable ranges for use in substrates

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Linda L. Taylor, Alexander X. Niemiera, Robert D. Wright and J. Roger Harris

capacity, rate of N immobilization, and the presence of an allelopathic chemical in recently manufactured substrate as explanations for growth differences. A pH decrease has been observed in both stored PTS and loblolly pine logs (R. Wright, unpublished

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Warren E. Copes, Haibo Zhang, Patricia A. Richardson, Bruk E. Belayneh, Andrew Ristvey, John Lea-Cox and Chuanxue Hong

pH, alkalinity, nutrient content, oxygen demand, soluble and suspended sediment, and algal populations ( Chen et al., 2003 , 2004 ; Hem, 1985 ; Majsztrik et al., 2011 ; Moss et al., 2003 ). Levels of residual chemical biocides, such as fungicides

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Linda L. Taylor, Alexander X. Niemiera, Robert D. Wright, Gregory K. Evanylo and Wade E. Thomason

nitrite (NO 2 – ) while nitrite-oxidizing bacteria oxidize NO 2 – to NO 3 – . Ammonia-oxidizing bacteria grow in a pH range of 5.8 to 8.5 and have growth optima in the range of 7.5 to 8.0 ( Prosser, 1989 ). The generally accepted reason for this

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Pauline H. Andrews and P. Allen Hammer

Three cultivars each of zonal geranium (Pelargonium ×hortorum `Candy Lavender', `Fireball', and `Patriot Red') and ivy geraniums (Pelargonium pelatum `Global Deep Lilac', `Global Salmon Rose', and `Global Soft Pink') were grown in root media with pHs varying from 4.3 to 7.8. In Expt. 1, a mixture of sphagnum peat, fine perlite, and fine pine bark was modified with limestone and hydrated lime at the following rates: 0, 1.2, 3.0, 4.7, and 11.9 kg·m–3 limestone; 11.9 limestone plus 5.9 hydrated lime; 11.9 limestone plus 8.3 hydrated lime; and 11.9 kg·m–3 limestone plus 10.7 kg·m–3 hydrated lime to give the various root medium pH treatments. Plants were grown for 11 weeks in glass greenhouses. In Expt. 2, plants were grown in two commercial soilless mixes with one being modified with the addition of 0 kg·m–3 limestone, 6.0 kg·m–3 limestone plus 0.6 kg·m–3 hydrated lime, and 6.0 kg·m–3 limestone plus 2.4 kg·m–3 hydrated lime. In both experiments, greatest dry weight was recorded in zonal and ivy geraniums plants grown at root medium pHs above 6.4. This study showed a root medium pH of 6.4 to 6.5 should be recommended for the greenhouse production of both zonal and ivy geraniums.

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Ka Yeon Jeong and James E. Altland

trends in how moisture content and temperature affect pH, EC, and nutrient dynamics in stored substrates, they do not provide specific information on 1) how quickly nutrients are released from a CRF, 2) how much nutrients are immobilized, and 3) how N