Quantifying the Acidic and Basic Effects of Fifteen Floriculture Species Grown in Peat-based Substrate

in HortScience

Floriculture species differ in their effect on substrate-pH and the resulting substrate micronutrient availability in container production. The objective was to quantify effects of floriculture plant species on substrate-pH. In a growth chamber factorial experiment, 15 floriculture species were grown in 70%:30% by volume peat:perlite substrate and fertilized with nutrient solutions containing 100 mg·L−1 N and NH4+-N:NO3-N nitrogen ratios of 0:100, 20:80, or 40:60. The relationship between substrate-pH and milliequivalents (meq) of acid or base per unit volume of substrate was quantified by titration with hydrated dolomitic lime or HCl. After 33 days, species and solution type effects on substrate-pH and estimated meq of acid or base produced were evaluated. Final substrate-pH ranged from 4.83 for geranium in 40:60 solution to 6.58 for lisianthus in 0:100 solution, compared with an initial substrate-pH of 5.84. This change in substrate-pH corresponded with a net meq of acid or base produced per gram of tissue dry mass gain (NMEQ) ranging across solutions and species from 1.47 of base for lisianthus in the 0:100 solution to 2.10 of acid for coleus in the 40:60 solution. With the 0:100 solution, geranium produced the greatest NMEQ of acid (0.07), whereas lisianthus produced the greatest NMEQ of base (1.47). Because all N in the 0:100 solution was in the NO3 anion form, meq of both anions and cations taken up by plant roots could be calculated based on tissue analysis. With the 0:100 solution, species that took up more anions than cations into plant tissue tended to have a more basic effect on substrate-pH, as would be expected to maintain electroneutrality. Data were used to estimate the percent NH4+-N of total N in a nutrient solution that would be neutral (results in no substrate-pH change) for each species. This neutral percent NH4+-N of total N ranged from ≈0% (geranium) to 35% (pentas). Species were separated into three clusters using k-means cluster analysis with variables related to NMEQ and anion or cation uptake. Species were clustered into groups that had acidic (geranium and coleus), intermediate (dusty miller, impatiens, marigold, new guinea impatiens, petunia, salvia, snapdragon, and verbena), or basic (lisianthus, pansy, pentas, vinca, and zinnia) effects on substrate-pH. Evaluating the tendency to increase or decrease substrate-pH across a range of floriculture species, and grouping of plants with similar pH effects, could help predict NH4+:NO3 ratios for a neutral pH effect and assist growers in managing substrate-pH for container production.

Abstract

Floriculture species differ in their effect on substrate-pH and the resulting substrate micronutrient availability in container production. The objective was to quantify effects of floriculture plant species on substrate-pH. In a growth chamber factorial experiment, 15 floriculture species were grown in 70%:30% by volume peat:perlite substrate and fertilized with nutrient solutions containing 100 mg·L−1 N and NH4+-N:NO3-N nitrogen ratios of 0:100, 20:80, or 40:60. The relationship between substrate-pH and milliequivalents (meq) of acid or base per unit volume of substrate was quantified by titration with hydrated dolomitic lime or HCl. After 33 days, species and solution type effects on substrate-pH and estimated meq of acid or base produced were evaluated. Final substrate-pH ranged from 4.83 for geranium in 40:60 solution to 6.58 for lisianthus in 0:100 solution, compared with an initial substrate-pH of 5.84. This change in substrate-pH corresponded with a net meq of acid or base produced per gram of tissue dry mass gain (NMEQ) ranging across solutions and species from 1.47 of base for lisianthus in the 0:100 solution to 2.10 of acid for coleus in the 40:60 solution. With the 0:100 solution, geranium produced the greatest NMEQ of acid (0.07), whereas lisianthus produced the greatest NMEQ of base (1.47). Because all N in the 0:100 solution was in the NO3 anion form, meq of both anions and cations taken up by plant roots could be calculated based on tissue analysis. With the 0:100 solution, species that took up more anions than cations into plant tissue tended to have a more basic effect on substrate-pH, as would be expected to maintain electroneutrality. Data were used to estimate the percent NH4+-N of total N in a nutrient solution that would be neutral (results in no substrate-pH change) for each species. This neutral percent NH4+-N of total N ranged from ≈0% (geranium) to 35% (pentas). Species were separated into three clusters using k-means cluster analysis with variables related to NMEQ and anion or cation uptake. Species were clustered into groups that had acidic (geranium and coleus), intermediate (dusty miller, impatiens, marigold, new guinea impatiens, petunia, salvia, snapdragon, and verbena), or basic (lisianthus, pansy, pentas, vinca, and zinnia) effects on substrate-pH. Evaluating the tendency to increase or decrease substrate-pH across a range of floriculture species, and grouping of plants with similar pH effects, could help predict NH4+:NO3 ratios for a neutral pH effect and assist growers in managing substrate-pH for container production.

Controlling pH in soilless substrate is critical to managing nutrient availability in container production (Peterson, 1981). This can be a challenge considering that several factors interact and affect pH over time, including substrate components, limestone type and rate, applied nutrients and concentration, irrigation water alkalinity, and plant species (Argo and Biernbaum, 1996, 1997; Johnson et al., 2013). Floriculture species also differ in susceptibility to developing iron or manganese toxicity or deficiency symptoms if substrate-pH drifts too low or high during production (Argo and Fisher, 2002). A key grower decision is the selection of a water-soluble fertilizer formulation and concentration that stabilizes pH over time.

Fertilizer effects on substrate-pH are dominated by nitrogen form and concentration applied (Argo and Biernbaum, 1996; Barnes et al., 2014; Haynes, 1990; Huang et al., 2001; Johnson et al., 2013; Marschner, 2012). Fertilization with ammonium nitrogen (NH4+-N) produces an acidic reaction that decreases pH as a result of H+ efflux from roots during uptake and from nitrification. Nitrification can occur rapidly in container substrate above pH 5.5 and depends on factors that affect microbial activity such as pH, temperature, oxygen, moisture, crop duration, substrate components, nitrogen form, and concentration (Argo and Biernbaum, 1997; Lang and Elliot, 1991). Fertilization with nitrate nitrogen (NO3-N) usually produces a basic reaction that increases pH, resulting from the efflux of hydroxyl (OH) or bicarbonate (HCO3) ions from roots (Haynes, 1990; Marschner, 2012). Ammonium typically has a greater impact on substrate-pH compared with NO3-N when both forms are applied because NH4+-N uptake is energetically favored over NO3-N uptake (Engels and Marschner, 1995; von Wiren et al., 2001). The effect of urea nitrogen (urea-N) on substrate-pH varies depending on the state of hydrolysis, nitrification, and the subsequent uptake of NH4+-N vs. NO3-N (Verburg et al., 2003).

Floriculture species differ in their effect on substrate-pH, even when supplied with the same water-soluble fertilizer (Huang et al., 2001; Johnson et al., 2013). Huang et al. (2001) showed that seedlings of pansy (Viola ×wittrockiana Gams.), petunia (Petunia ×hybrid Vilm.-Andr.), and vinca (Catharanthus roseus G. Don.) increased the pH whereas celosia (Celosia cristata L.) and zinnia (Zinnia elegans Jacq.) decreased the pH in peat: perlite substrate. In both substrate (Johnson et al., 2013) and hydroponic nutrient solution (Dickson et al., 2016), geranium (Pelargonium ×hortorum Bailey L.H.) was acidic and decreased the pH compared with petunia which was basic and increased the pH, whereas impatiens (Impatiens wallerana Hook. F.) had intermediate effects to geranium and petunia.

A major process by which plants affect root zone pH is through imbalanced uptake of cation and anion nutrients (Haynes, 1990; Lea-Cox et al., 1996; Marschner, 2012; Rengel, 2003). Roots maintain charge balance either by equal uptake of cations and anions or by the efflux of ions equal to the net charge taken up by roots. Net cation uptake is balanced by efflux of H+ ions whereas net anion uptake is balanced by efflux of OH or HCO3 from roots (Kirkby and Knight, 1977; Lea-Cox et al., 1996; Marschner, 2012).

Some agronomic crop species that are labeled “iron-efficient” acidify the root zone as a strategy to improve iron solubility and uptake when grown in calcareous soil (Marschner, 2012). Geranium is a floriculture species that is referred to as “iron-efficient” because of high susceptibility to iron or manganese toxicity at low pH and also has the tendency to decrease substrate-pH over time (Argo and Fisher, 2002; Johnson et al., 2013). Other floriculture species susceptible to iron or manganese toxicity may also decrease pH, possibly as a means to increase iron uptake.

Johnson et al. (2013) modeled the interaction between three floriculture species (geranium, impatiens, and petunia) fertilized with 18 water-soluble fertilizers differing in applied nitrogen forms (NH4+-N, NO3-N, and urea-N) and concentration. The acidity or basicity of a fertilizer could be manipulated by adjusting nitrogen forms and concentrations to balance species root zone effects and stabilize pH. For example, the model predicted that geranium, impatiens, and petunia would require 0%, 10%, and 31% of total N as NH4+-N, respectively, with the remainder of N as NO3-N. This ratio would be expected to maintain a stable pH over time when these species were grown with zero alkalinity irrigation water and without residual lime in the substrate.

Commercial bedding plant operations typically grow a wide range of plant species, often in the same greenhouse, that may differ in effects on substrate-pH. Species diversity is therefore an important consideration in pH management. However, it is also not feasible to provide separate fertilizer regimes to hundreds of cultivars grown at a single location, and grouping of plants is necessary. The objective was to quantify the effects of plant species on substrate-pH for floriculture species fertilized with different NH4:NO3 nitrogen ratios. Floriculture species common in container production were selected, where species also differed in reported susceptibility to iron or manganese deficiency or toxicity and optimum pH (Argo and Fisher, 2002; Whipker et al., 2003).

The objective of this study was to quantify effects of floriculture plant species on substrate-pH. In a factorial experiment conducted in a controlled environment growth chamber, 15 floriculture species were grown in peat:perlite substrate and were irrigated with modified 0.5× Hoagland’s nutrient solutions with NH4+:NO3 nitrogen ratios of 0:100, 20:80, and 40:60. After 33 d, substrate-pH was measured and meq of acid or base produced per L of substrate was estimated using an acid–base substrate titration (Johnson et al., 2010). Nitrogen is taken up in different forms that vary in their charge (including NH4+ and NO3), and without isotope labeling (which was not used in this study), total N level in tissue cannot distinguish between the original fertilizer nutrient form. Dry tissue was harvested from plants irrigated with the 0:100 solution, and tissue nutrient data were used to estimate net uptake of anions minus cations, and cation or anion uptake ratio, assuming that all N was taken up in the anionic NO3 form. Species and solution NH4+:NO3 ratio were evaluated for effects on substrate-pH and meq of acid or base produced per L of substrate. Species were separated into clusters that corresponded to species overall acidic, intermediate, and basic effects on substrate-pH, and linear regression was used to predict species-specific NH4+:NO3 ratios expected to result in a stable pH. We hypothesized that species fertilized with 100% NO3-N that had greater net anion minus cation uptake would result in greater basicity than species that favored cation uptake. We also hypothesized that floriculture species that are reportedly susceptible to iron or manganese toxicity at low pH may tend to decrease substrate-pH, possibly acidifying the root zone as an iron-efficiency mechanism (Marschner, 2012).

Materials and Methods

The experiment was a factorial randomized complete block design with 15 species and three fertilizer NH4+:NO3 nitrogen ratios (0:100, 20:40, and 40:60) from a 0.5× Hoagland’s solution (Hoagland and Arnon, 1950), supplied at 100 mg·L−1 N, and organized in six blocks (benches) with 270 total replicate containers. On 5 Feb. 2015, seedling plugs of 15 floriculture species were transplanted from 144-cell trays (supplied by Knox Nursery, Winter Garden, FL) into four-cell plastic bedding plant containers (FG12047, 88 mL per cell or 350 mL per container) at four plants per container. Each four-cell container was considered as one replicate.

Plants were grown for 33 d on benches in a controlled environment growth chamber located at the University of Florida in Gainesville, FL. Growth chamber lighting was supplied by cool white fluorescent bulbs (32 W, 6500 K). Photosynthetically active radiation was measured at the plant canopy level using a quantum sensor (Apogee Instruments, Inc., Logan, UT), where light intensity averaged 175 µmol·m−2·s−1 for a daily light integral of 11.3 mol·m−2·d−1 across species. Daily air and substrate temperatures measured during the experiment with external temperature sensors connected to data loggers (Onset Computer Corporation, Bourne, MA) were 22.5 ± 1.5 °C and 23.1 ± 1.6 °C (mean ± sd), respectively.

Floriculture species consisted of geranium (Pelargonium ×hortorum Bailey. L.H.) ‘Ringo 2000 Deep Red’, impatiens (Impatiens wallerana Hook. F.) ‘Super Elfin Orange Bright’, petunia (Petunia ×hybrid Vilm.-Andr.) ‘Ultra Red’, coleus (Solenostemon scutellariodes L.) ‘Premium Sum Chocolate Covered Cherry’, pentas (Pentas lanceolata Forssk.) ‘Butterfly Red’, snapdragon (Antihirrum majus L.) ‘Snapshot Yellow’, verbena (Verbena ×hybrida L.) ‘Quartz White XP’, vinca (Catharanthus roseus L.) ‘Titan Dark Red’, lisianthus (Eustoma grandiflorum Salisb.) Florida Sky Blue’, African marigold (Tagetes erecta L.) ‘Taishan Orange’, dusty miller (Senecio cineraria L.) ‘Maritima Silverdust’, pansy (Viola tricolor D.C.) ‘Matrix Clear Yellow’, salvia (Salvia splendens Sellow ex Roem. & Schult.) ‘Vista Red’, New Guinea impatiens (Impatiens hawkeri L.) ‘Divine White Blush’, and zinnia (Zinnia elegans L.) ‘Zahara Double Fire’. Most species had open flowers at the end of the experiment, except for coleus, dusty miller, and lisianthus, which appeared vegetative with no visible flower buds.

The substrate was 70%:30% (v:v) peat:perlite mixed at the University of Florida using Canadian Sphagnum peat (Sun Gro Horticulture, Bellevue, WA) with long fibers and little dust (Von Post scale 1–2; Puustjarvi and Robertson, 1975) and wetting agent (0.15 mL·L−1 of substrate; Aquatrols, Paulsboro, NC). Hydrated dolomitic limestone [Graymont Western Lime, Inc., Eden, WI, 97% Ca(OH)2·MgO of which 92% passed through a 45-µm mesh and had an acid neutralizing value of 140% calcium carbonate equivalents (CCE)] was incorporated at 1.67 kg·m−3 of substrate for a pH of 6.0. Hydrated dolomitic limestone was used to avoid residual lime buffering of substrate-pH after planting.

Plants were fertilized using 0.5× modified Hoagland’s nutrient solutions with NH4+:NO3 nitrogen ratios of 0:100, 20:80, and 40:60 mixed with reagent grade salts in zero alkalinity deionized water. Macronutrients were supplied at 100 N, 16 P, 117 K, 100 Ca, and 24 Mg in mg·L−1. Sulfate and Cl concentrations varied depending on solution NH4+:NO3 ratio, and S and Cl concentrations were (in mg·L−1) 38 and 0 for the 0:100 solution, 61 and 24 for the 20:80 solution, and 113 and 36 for the 40:60 solution, respectively. Macronutrients were derived from (NH4)2SO4 Ca(NO3)2·4H2O, (KH2PO4), (MgSO4·7H2O), (CaCl2·2H2O), (KNO3), and (K2SO4). Micronutrient concentrations at 100 mg·L−1 N were (mg·L−1) 2 Fe, 1 Mn, 1 B, 0.2 Cu, 0.5 Zn, and 0.04 Mo supplied from FeEDDHA (6.0% Fe, Akzo-Nobel, Holland), CuSO4·5H2O, MnSO4·H2O, (NH4)6MoO2·2H2O, H3BO3, and ZnSO4·7H2O.

At transplant, each replicate container was irrigated to container capacity with 150 mL of either 0:100, 20:80, or 40:60 solution at 200 mg·L−1 N. The remaining irrigations consisted of 100 mL at 100 mg·L−1 N. Plastic liners with gusseted bottoms were secured underneath each replicate container to collect leachate and allow for reabsorption into the substrate. Each replicate received a total of 1.15 L of nutrient solution during the experiment.

Initial substrate-pH and electrical conductivity (EC) were measured for each solution type on 12 replicate containers without plants using the plug squeeze method of Scoggins et al. (2002). Measurements were taken on the combined leachate squeezed from each of the four cells per replicate container. Initial substrate-pH was measured after the first irrigation at transplant and averaged 5.84 ± 0.04 (mean ± sd) across all NH4+:NO3 treatments. Initial substrate EC was 1.98 ± 0.02, 2.14 ± 0.03, and 2.27 ± 0.02 mS·cm−1 for 0:100, 20:80, and 40:60 NH4+:NO3 solutions, respectively. Containers used for initial measurements had the same substrate-pH and substrate-EC 14 d after transplant (data not shown), indicating that substrate-pH and EC were relatively stable in the absence of plants. Final substrate-pH and EC were measured at the end of the experiment for each treatment replicate.

Species effects on substrate-pH over time were related to meq of acid or base produced per L of substrate using the acid–base titration approach of Johnson et al. (2010). In a laboratory procedure, samples of the same substrate used for the experiment, but not for growing plants, were placed into plastic zip-lock bags at 250 mL of substrate per bag. The substrate in each bag was moistened with 150 mL of 20:80 nutrient solution at 200 mg·L−1 N. Hydrochloric acid (0.5060 N) was added at 0, 2.5, 5.0, 7.5, 10.0, or 12.5 mL per sample for an equivalent of 0, 10, 20, 30, 40, and 50 meq of acid added per L of substrate. Hydrated dolomitic lime (139% CCE) was added at 0, 0.18, 0.36, 0.54, 0.72, and 0.90 g per sample for an equivalent of 0, 10, 20, 30, 40, and 50 meq of base added per liter of substrate. There were four replicates for each acid and base titration level, and replicates were allowed to equilibrate for 7 days before measuring substrate-pH. A polynomial curve was fit relating the change in pH units (from initial pH 5.84) to the meq of acid or base added per L of substrate, which was used to estimate the meq of acid or base produced by each species when supplied with each of the three solution types.

The uptake of individual nutrients was measured for plants fertilized with the 0:100 solution. Root and shoot tissue was harvested from seedlings at the beginning of the experiment and from each final replicate that received the 0:100 solution. Tissue was rinsed with HCl (0.1 N) followed by de-ionized water and was oven-dried for 48 h at 70 °C. Roots were washed with phosphate-free soap before the HCl rinse to remove substrate particles from root surfaces. Plant growth was measured as total dry mass gain (roots and shoots), which was calculated by subtracting the average dry mass for four seedlings from the final dry mass per replicate for each species (four plants per replicate).

Dry root and shoot tissue from plants supplied with 0:100 solution was analyzed for concentration of macronutrient and micronutrient elements by inductively coupled plasma atomic emission spectrophotometry (Quality Analytical Laboratories, Panama City, FL). Tissue concentrations of macronutrient and micronutrient elements were within the general sufficiency ranges proposed by Vetanovetz (1996) for bedding plants (data not shown). The concentration of each element in the tissue was multiplied by the dry mass to determine the total nutrient mass. Nutrient uptake was calculated by subtracting the average nutrient mass for four seedlings from the nutrient mass of each replicate. The uptake of nutrients was converted to meq values for calculating net ion uptake and cation or anion uptake ratio.

Net ion uptake was calculated as meq total of anions minus cations taken up and cation or anion uptake ratio was calculated as meq of total cation divided by total anion uptake for plants supplied with 0:100 solution. Assumed forms of ions taken up by roots were NO3, H2PO4, SO42−, MoO42−, and Cl for anions and K+, Ca2+, Mg2+, Fe2+, Mn2+, Cu2+, Zn2+, Na+, and Al3+ for cations. Boron was not considered in cation and anion calculations because H3BO30 is taken up as an uncharged molecule below pH 7.0 (Marschner, 2012; Miwa and Fujiwara, 2010). For each species, net ion uptake was divided by the total dry mass gain (grams) to determine the net uptake per unit of plant growth. Species-estimated meq of acid or base produced per volume of container substrate (350 mL) was also divided by the total dry mass gain to determine the estimated meq of acid or base per unit of plant growth. Individual cation or anion uptake was calculated as a percentage of total cation or total anion uptake, respectively.

PROC GLM ANOVA in SAS 9.4 (SAS Institute, Cary, NC) was used to evaluate floriculture species and solution NH4+:NO3 ratio main and interaction effects on substrate-pH, dry mass gain, and meq of acid or base produced per gram of dry mass gain. ANOVA with PROC GLM was also used to evaluate species main effects on cation or anion uptake ratio, net meq of anions minus cations taken up, meq anions minus cations taken up per gram of dry mass gain, meq of individual nutrients taken up, and Fe2+ and Mn2+ concentration in tissue for plants supplied the 0:100 solution. Linear regression was used to calculate the NH4+:NO3 expected to result in a stable pH for each species, where percent NH4+-N of total N supplied with each of the three solution types and meq of acid or base produced per container volume of substrate (350 mL) were independent and dependent variables, respectively. PROC FASTCLUS k-means cluster analysis was used in combination with PROC FREQ to separate species into three clusters that corresponded to the species about acidic, intermediate, and basic effects on substrate-pH. Clusters were based on the percent NH4+-N of total N estimated for a stable pH, the mean values for meq of acid or base produced per gram of dry mass gain for each of the three solution types, meq of anions minus cations taken up per gram of dry mass gain (0:100 solution), and cation or anion uptake ratio (0:100 solution) for each species. ANOVA with PROC GLM was used to evaluate the differences between the three groups for each variable used in clustering. Tukey’s honestly significant difference at α = 0.05 significance level was used for mean separation.

Results and Discussion

Final substrate-pH was affected by plant species (P < 0.0001), solution NH4+:NO3 ratio (P < 0.0001), and their interaction (P < 0.0001), and ranged from 4.83 to 6.58 between species and solution types (Fig. 1). When fertilized with the 0:100 NH4+:NO3 solution, 13 species resulted in final substrate-pH greater than the initial pH of 5.84. When fertilized with the 40:60 NH4+:NO3 solution, all 15 species resulted in final substrate-pH lower than the initial pH. Substrate-pH least-square means were 6.24, 5.75, and 5.25 for the 0:100, 20:80, and 40:60 NH4+:NO3 solutions, respectively.

Fig. 1.
Fig. 1.

Substrate-pH after 33 d for floriculture species grown in peat: perlite substrate and irrigated with nutrient solutions containing 100 mg·L−1 N and NH4+:NO3 nitrogen ratios of (A) 0:100, (B) 20:80, and (C) 40:60. Data are species least-square means of six replicates. Error bars indicate ±95% confidence intervals using Tukey’s honestly significant difference at α = 0.05. Dashed lines represent the initial substrate-pH (5.84) at the beginning of the experiment.

Citation: HortScience horts 52, 8; 10.21273/HORTSCI11926-17

Species effects on substrate-pH can be compared on the basis of the meq of acidity or basicity produced per gram of plant growth (NMEQ). For example, Rengel (2003) showed that 37 agronomic species differed in NMEQ, ranging from 0.3 to 2.0 meq of acidity produced per gram of shoot dry mass (original reported units were centimoles of acid per kilogram of shoot dry mass). To calculate NMEQ, plant growth was measured as the change in total dry mass over 33 d, which differed by species (P < 0.0001) but not by NH4+:NO3 ratio (P = 0.8018) (data not shown). In addition, change in substrate-pH over time was converted to units of meq of acid and base produced in the substrate using an acid-base titration (Johnson et al., 2010). In a laboratory procedure, meq of acid (HCl) and base (hydrated dolomitic limestone) applied to samples of substrate was correlated with change in pH units (from initial pH 5.84). Substrate-pH decreased as much as 3.34 units when titrated with acid and increased as much as 2.58 units when titrated with base (Fig. 2). A polynomial response curve was generated and used to estimate meq of acid (negative values) and base (positive values) produced per L of substrate corresponding to a specific change in pH units. For example, a substrate-pH change of −1 pH units would equal −9.72 meq (acid) using the equation in Fig. 2. Initial substrate-pH (5.84) was subtracted from final values in Fig. 1 to determine change in pH units, which were converted to meq of acid or base produced per L of substrate. Acid or base (meq) per L of substrate was scaled to the volume of substrate per replicate (350 mL) for meq of acid or base produced per container and divided by total dry mass gain for meq of acid or base produced per unit of growth.

Fig. 2.
Fig. 2.

Relationship between mineral acid (0.5060 N hydrochloric acid) or base (hydrated dolomitic limestone with 139% neutralizing value) and change in substrate-pH (ΔpH), quantified using the acid–base titration. The polynomial equation milliequivalents (meq) of acid (− value) or base (+ value) per L of substrate = 0.8780 × ΔpH3 + 1.3369 × ΔpH2 + 9.9856 × ΔpH − 0.2569, with P < 0.0001.

Citation: HortScience horts 52, 8; 10.21273/HORTSCI11926-17

There was an interaction between species and NH4+:NO3 ratio (P < 0.0001) on NMEQ. The NMEQ of acid (negative value) or base (positive value) ranged between species and solution types from 1.47 meq of base for lisianthus (0:100 solution) to −2.10 meq of acid for coleus (40:60 solution) (Fig. 3). In the 0:100 solution, geranium and marigold produced an NMEQ not different from zero, whereas other species produced base up to 1.47 meq of base for lisianthus (Fig. 3A). These levels of NMEQ are similar to the 0.3–2.0 of acidity reported by Rengel (2003) in field soil conditions with an unspecified fertilizer regime. In the 20:80 solution, pentas and lisianthus were the only species to produce base (Fig. 3B). Most species produced acid in the 40:60 solution, except for pentas which was not different from zero (Fig. 3C). Although commercial water-soluble fertilizers are labeled as “acidic,” “neutral,” or “basic” in their effects on pH based on calcium carbonate equivalents (Pierre, 1933), results in Fig. 3 show that fertilizer effects on substrate-pH depend on the plant species grown.

Fig. 3.
Fig. 3.

Milliequivalents (meq) of acid or base per gram of plant dry mass gain after 33 d for floriculture species grown in peat:perlite substrate irrigated with nutrient solutions containing 100 mg·L−1 N and NH4+:NO3 nitrogen ratios of (A) 0:100, (B) 20:80, and (C) 40:60. Data represent species least-square means of six replicates. Error bars are ±95% confidence intervals using Tukey’s honestly significant difference at α = 0.05.

Citation: HortScience horts 52, 8; 10.21273/HORTSCI11926-17

Past research has shown that plants fertilized with 100% NO3-N typically have net anion uptake (shown as a positive meq anions minus cations per gram of dry mass gain) and cation or anion uptake ratios less than 1 (Haynes, 1990; Kirkby and Knight, 1977; Marschner, 2012). To calculate net anion uptake, the uptake of individual nutrients per gram of dry mass gain was first analyzed using ANOVA for each species in the 0:100 solution. There were species differences (P < 0.01) for all macronutrients, sodium, and chloride (data not shown). Uptake of cations and anions was dominated by NO3, which contributed between 38.0% and 43.8% of the total (meq) combined cations and anions. As a contribution of total meq of anion uptake, NO3 (75.9% to 87.3%) was followed by H2PO4 (4.4% to 9.2% depending on species), SO42− (3.3% to 14.2%), and Cl (1.5% to 6.7%). Cations taken up were predominantly K+ (28.0% to 59.2% of total cations), Ca2+ (10.8% to 40.6%), Mg2+ (19.6% to 36.6%), and Na+ (0.7% to 6.7%). Micronutrients represented <1% of total uptake. When the meq of all cations was subtracted from meq of all anions, the net anion uptake was lowest for zinnia (0.34 meq·g−1) and greatest for lisianthus (1.69 meq·g−1), and the ratio of cations or anions taken up into plant tissue ranged from 0.48 (lisianthus) to 0.85 (geranium) (Table 1). The observed trend, whereby all plants took up more anions than cations in the 0:100 solution, was consistent with published studies by Kirkby and Knight (1977) with hydroponically grown tomatoes in a nutrient solution with 100% NO3-N. A positive correlation was found between net anion uptake (based on tissue analysis) and NMEQ (based on substrate-pH change) when fertilized with 100% NO3-N (Fig. 4). Similarly, Rengel (2003) found that meq of acid produced by roots (NMEQ) was correlated with meq of excess cations taken up into plant tissue for 37 agronomic crop species grown in field soil.

Table 1.

Species main effects on milliequivalents (meq) net anions minus cations taken up, meq net anions minus cations taken up per gram of dry mass gain, and meq of acid or base produced per gram of dry mass gain when supplied 0:100 solution. Data are species least-square means of six replicates. Mean separation used Tukey’s honestly significant difference at α = 0.05. Percent NH4+-N of total N expected for a stable pH was calculated for each species using linear regression based on species meq of acid or base produced per container volume of substrate (dependent variable) and percent NH4+-N of total N supplied for each of the three nutrient solution (independent variable).

Table 1.
Fig. 4.
Fig. 4.

Relationship between milliequivalents (meq) net cation or anion uptake (shown as meq anions minus cations taken up) and meq acid or base produced per gram of dry mass increase for species fertilized with the 0:100 solution. Data represent least-square means of six replicates. The regression equation is meq acid or base produced per gram dry mass increase = 0.725 ± 0.408 * (meq anion minus cation uptake per gram dry mass increase) − 0.066 ± 0.377 with R2 = 0.531.

Citation: HortScience horts 52, 8; 10.21273/HORTSCI11926-17

The NH4+:NO3 ratios estimated to result in a neutral pH effect were calculated for each species using linear regression (Table 1). The percent NH4+-N of total N applied in the three nutrient solutions and meq of acid or base per L of substrate over 33 d were independent and dependent variables, respectively. R2 values were above 0.730 and averaged 0.856 for all species (data not shown). With the exception of geranium, species were estimated to require between 4.4% (coleus) and 35.1% (pentas) of total N as NH4+-N with the remainder of N as NO3-N to balance species and nitrogen effects and result in zero pH change over time (Table 1). Geranium produced meq of acid not different from zero when fertilized with the 0:100 solution, resulting in a negative predicted NH4+:NO3 ratio, and therefore would require fertilization with 100% NO3-N to minimize acidity. On average, species required greater NH4+:NO3 ratios for a neutral effect compared with the observations made by Sonneveld and Voogt (2009), who reported that most greenhouse crop species require NH4+-N between 5% and 10% of total N for a stable pH in soilless substrates.

In commercial horticulture production of diverse crops, it is not practical to have a specific fertilizer formulation to stabilize pH for each species. One possibility is to separate species into groups and manage pH for each group separately. Cluster analysis in combination with ANOVA was therefore used to determine grouping of species with similar effects on pH.

Species were separated into three clusters using k-means cluster analysis, using the neutral percent NH4+-N of total N, NMEQ for each of the three solutions, net anion uptake in the 0:100 solution, and cation or anion uptake ratio in the 0:100 solution as dependent variables. The contribution of each variable in terms of separating species into clusters was shown by the cluster analysis R2 values. The R2 equaled 0.871 for the neutral percent NH4+-N of total N, R2 = 0.530 for NMEQ in 0:100, R2 = 0.816 for NMEQ in 20:80, R2 = 0.580 for NMEQ in 40:60, R2 = 0.179 for net anion uptake, and R2 = 0.334 for cation or anion uptake ratio. Therefore, clusters differed more consistently in the neutral percent NH4+-N of total N than in other variables. Clusters were compared by each variable using ANOVA, where clusters differed in percent NH4+-N of total N (P < 0.0001) and meq of acid or base per gram of dry mass gain in 0:100 (P = 0.0108), 20:80 (P < 0.0001), and 40:60 (P = 0.0055) solution. There were no statistical differences for meq of anions minus cations taken up (P = 0.3054) or cation or anion balance (P = 0.0869) in 0:100 solution (Table 2).

Table 2.

Species listed by cluster (numbers one through three) from k-means cluster analysis with cluster main effects on percent NH4+-N of total N for a neutral pH effect, milliequivalents (meq) of acid and base per gram of dry mass gain for each of the three solution types (0:100, 20:80, 40:60), meq anions minus cations taken up per gram of dry mass gain with species supplied 0:100 solution, and cation or anion uptake ratio with species supplied 0:100 solution. Species were clustered based on each species percent estimated NH4+-N of total N for stable pH and mean values (n = 6) for each of the remaining variables. Data represent cluster least-square means of two (cluster 1), eight (cluster 2), and five (cluster 3) species. Mean separation used Tukey’s honestly significant difference at α = 0.05.

Table 2.

Species are summarized by cluster in Table 2. On average, species in cluster 1 had the greatest mean meq acid per gram of dry mass gain whereas species in cluster 3 had the greatest mean meq of base per gram of dry mass gain for each of the three solution types (Table 2), and overall were acidic and basic in effects on pH. For meq of acid or base (per gram of dry mass gain), species in cluster 2 were not different from cluster 1 in 0:100 solution or cluster 3 in 40:60 solution but differed from both clusters with 20:80 solution and were considered as intermediate in effects on pH. Each cluster differed in species mean percent NH4+-N expected to stabilize pH, averaging 0%, 13.1%, and 26.8% NH4+-N of total N for clusters 1, 2, and 3, respectively (Table 2). Supplying species clustered as acidic, intermediate, and basic with ≈0%, 13%, and 27% of total N as NH4+-N, respectively, would be expected to result in about stable substrate-pH across species.

Tendency to decrease root zone pH is a potential strategy used by some iron-efficient species to increase iron solubility and uptake (Marschner, 2012). Iron solubility is reduced as substrate-pH increases (Lindsay, 1979). Crop species are labeled as iron-efficient if they exhibit root strategies that specifically increase iron uptake, such as acidifying the rhizosphere, efflux of organic acids and chelating molecules, and greater ability to reduce iron at root surfaces (Bienfait, 1988; Marschner, 2012). Albano and Miller (1996) found that marigold responded to low substrate-iron concentration by acidifying the root zone and increasing iron reductase activity, which are iron-efficiency strategies. Albano and Miller (1996) also found that under iron-sufficient and excess conditions, root zone acidification and increased iron reductase activity was not expressed. Floriculture species that have been noted to decrease pH include geranium and marigold (Gibson et al., 2007; Johnson et al., 2013). Floriculture species that are susceptible to iron or manganese toxicity symptoms at low substrate-pH include geranium, marigold, lisianthus, pentas, and New Guinea impatiens (Argo and Fisher, 2002; Harbaugh, 1995; Whipker et al., 2003). However, this group of species sensitive to low substrate-pH differed considerably in this study in their effects on pH (Figs. 1 and 3). For example, lisianthus and pentas had among the most basic pH effects in this study (Fig. 3). Floriculture species sensitive to high pH and iron or manganese deficiency include pansy, petunia, salvia, snapdragon, vinca, and zinnia (Cavins et al., 2000; Gibson et al., 2007). Pansy, petunia, and vinca have also been noted to increase pH (Gibson et al., 2007; Johnson et al., 2013). Vinca, pansy, and zinnia in this experiment were considerably more basic compared with petunia, salvia, and snapdragon (Fig. 3). Categorizing species response in terms of susceptibility to micronutrient toxicity or deficiency at low or high pH therefore differs from the effect of species on substrate-pH, which was quantified in this study.

Accumulation of Fe2+ and Mn2+ in tissue was not related to species acid–base cluster (Table 3). As previously mentioned, marigold and geranium are susceptible to iron or manganese toxicity whereas zinnia and pansy are susceptible to iron or manganese deficiency (Albano et al., 1996; Argo and Fisher, 2002; Gibson et al., 2007). However, marigold and zinnia had the greatest tissue concentration of Fe2+ whereas geranium and pansy had the lowest concentration. Tissue concentration of Mn2+ was also greatest in zinnia and lowest in lisianthus (susceptible to iron or manganese toxicity). Differential uptake of individual macronutrients affects species cation or anion uptake balance and consequently the effect on root zone pH (Bekele et al., 1983; Haynes, 1990; Marschner, 2012). In addition, total tissue iron analysis does not differentiate between biologically active and inactive forms within plant cells, where high proportions of inactive iron have been linked with symptoms of iron deficiency in leaves (Marschner, 2012).

Table 3.

Species listed by cluster (numbers one through three) from k-means cluster analysis with species main effects on tissue concentrations of Fe2+ and Mn2+ when supplied with 0:100 solution. Data are least-square means of six replicates. Mean separation used Tukey’s honestly significant difference at α = 0.05.

Table 3.

Conclusions

The acidic and basic effects of plants on substrate-pH were quantified over a wide range of floriculture container crop species. When supplied with 100% NO3-N, species with greater net anion uptake produced greater basicity in the substrate compared with species with greater cation uptake. Commercial growers can adjust the ratio of NH4+-N and NO3-N in the applied water-soluble fertilizer to balance species acidic or basic effects and stabilize pH over time. Percent NH4+-N of total N supplied estimated to result in a stable pH ranged from 0% (geranium) to 35% (pentas) across species. However, it is not practical to supply a specific fertilizer formulation to stabilize pH for each species in commercial production. Using a k-means clustering and statistical approach, species in this study were separated into groups that corresponded to species about acidic, intermediate, and basic effects on substrate-pH. Supplying 0%, 13%, and 27% of total N as NH4+-N (remainder as NO3-N) would result in about stable pH for acidic, intermediate, and basic species. Growers can group floriculture species by their tendency to increase or decrease substrate-pH and adjust the fertilizer NH4+:NO3 for each group as a strategy to manage pH and reduce the risk of micronutrient disorders.

Floriculture species that are reportedly susceptible to micronutrient toxicity at low pH did not all exhibit the iron-efficiency strategy of acidifying the rhizosphere pH. For example, geranium was acidic and tended to decrease pH, whereas lisianthus and pentas had among the most basic effects on substrate-pH. In addition, accumulation of Fe2+ and Mn2+ in plant tissue was not related to the measured species effects on substrate-pH or reported susceptibility to micronutrient toxicity or deficiency. For example, marigold (susceptible to iron or manganese toxicity) and zinnia (susceptible to iron or manganese deficiency) had the greatest tissue concentration of Fe2+ whereas geranium (susceptible to iron or manganese toxicity) and pansy (susceptible to iron or manganese deficiency) had the lowest concentration.

Literature Cited

  • AlbanoJ.P.MillerW.B.1996Iron deficiency stress influences physiology of iron acquisition in marigold (Tagetes erecta L.)J. Amer. Soc. Hort. Sci.121438441

    • Search Google Scholar
    • Export Citation
  • AlbanoJ.P.MillerW.B.HalbrooksM.C.1996Iron toxicity stress causes bronze speckle, a specific physiological disorder of marigold (Tagetes erecta L.)J. Amer. Soc. Hort. Sci.121430437

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.BiernbaumJ.A.1996The effect of lime, irrigation-water source, and water-soluble fertilizer on root-zone pH, electrical conductivity, and macronutrient management of container root media with impatiensJ. Amer. Soc. Hort. Sci.121442452

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.BiernbaumJ.A.1997Lime, water source, and fertilizer nitrogen form affect medium pH and nitrogen accumulation and uptakeHortScience327174

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.FisherP.R.2002Understanding pH management for container-grown crops. Meister Publishing Willoughby OH

  • BarnesJ.NelsonP.WhipkerB.E.DickeyD.A.HesterbergD.ShiW.2014Statistical model for describing macronutrient impacts on container substrate pH over timeHortScience49207214

    • Search Google Scholar
    • Export Citation
  • BekeleT.CinoB.J.EhlertP.A.I.van der MassA.A.van DiestA.1983An evaluation of plant-borne factors promoting the solubilization of alkaline rock phosphatesPlant Soil75361378

    • Search Google Scholar
    • Export Citation
  • BienfaitH.F.1988Mechanisms in Fe-efficiency reactions of higher plantsJ. Plant Nutr.11605629

  • CavinsT.J.WhipkerB.E.FontenoW.C.HardenB.McCallI.GibsonJ.L.2000Monitoring and managing pH and EC using the PourThru extraction method. North Carolina State Univ. Hort. Info. Lflt. 590

  • DicksonR.W.FisherP.R.ArgoW.R.JacquesD.J.SartainJ.B.TrenholmL.E.YeagerT.H.2016Solution ammonium:nitrate ratio and cation/anion uptake affect acidity or basicity with floriculture species in hydroponicsSci. Hort.2003644

    • Search Google Scholar
    • Export Citation
  • EngelsC.MarschnerH.1995Plant uptake and utilization of nitrogen p. 41–82. In: P.E. Bacon (ed.). Nitrogen fertilization in the environment. Marcel Dekker Inc. New York NY

  • GibsonJ.L.PitchayD.S.Williams-RhodesA.L.WhipkerB.E.NelsonP.V.DoleJ.M.2007Nutrient deficiencies in bedding plants: A pictorial guide for identification and correction. Ball Publishing. Batavia IL

  • HarbaughB.K.1995Iron toxicity in Pentas lanceolataHortTechnology5306307

  • HaynesR.J.1990Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pHPlant Soil126247264

    • Search Google Scholar
    • Export Citation
  • HoaglandD.R.ArnonD.I.1950The water culture method for growing plants without soil. Calif. Agr. Expt. Sta. Circ. 347

  • HuangJ.NelsonP.V.LeeJ.2001Seedling effect on root substrate pHJ. Plant Nutr.2411331147

  • JohnsonC.N.FisherP.R.HuangJ.VetanovetzR.P.ArgoW.R.2010Quantifying the acidity of an ammonium-based fertilizer in containerized productionHortScience4510991105

    • Search Google Scholar
    • Export Citation
  • JohnsonC.N.FisherP.R.HuangJ.YeagerT.H.ObrezaT.A.VetanovetzR.P.ArgoW.R.BishkoA.J.2013Effect of fertilizer potential acidity and nitrogen form on the pH response in a peat-based substrate with three floriculture speciesSci. Hort.162135143

    • Search Google Scholar
    • Export Citation
  • KirkbyE.A.KnightA.H.1977Influence of the level of nitrate nutrition on ion uptake and assimilation, organic acid accumulation, and cation-anion balance in whole tomato plantsPlant Physiol.60349353

    • Search Google Scholar
    • Export Citation
  • LangH.J.ElliotG.C.1991Influence of ammonium:nitrate ratio and nitrogen concentration on nitrification activity in soilless potting mediaJ. Soc. Hort. Sci.116642645

    • Search Google Scholar
    • Export Citation
  • Lea-CoxJ.D.StutteG.W.BerryW.L.WheelerR.M.1996Charge balance—A theoretical basis for modulating pH fluctuations in plant nutrient delivery systemsLife Support Biosph. Sci.35359

    • Search Google Scholar
    • Export Citation
  • LindsayW.L.1979Chemical equilibria in soils. The Blackburn Press Caldwell NJ

  • MarschnerP.2012Mineral nutrition of higher plants. 3rd ed. Academic Press San Diego CA

  • MiwaK.FujiwaraT.2010Boron transport in plants: Co-ordinated regulation of transportersAnn. Bot.10511031108

  • PetersonJ.C.1981Modify your pH perspectiveFlorists’ Rev.169343592–93

  • PierreW.H.1933Determination of equivalent acidity and basicity of fertilizersInd. Eng. Chem.5229234

  • PuustjarviV.RobertsonR.A.1975Physical and chemical properties p. 23–38. In: D.W. Robinson and J.G.D. Lamb (eds.). Peat in horticulture. Academic Press London

  • RengelZ.2003Handbook of soil acidity. Vol. 94. CRC Press London

  • ScogginsH.L.BaileyD.A.NelsonP.V.2002Efficacy of the press extraction method for bedding plant plug nutrient monitoringHortScience37108112

    • Search Google Scholar
    • Export Citation
  • SonneveldC.VoogtW.2009Plant nutrition of greenhouse crops. Springer Dordrecht The Netherlands

  • VerburgK.BraschkatJ.HockmanZ.MooreA.D.HelyarK.R.ProbertM.E.HargravesJ.N.G.SimpsonR.J.2003Modeling acidification processes in agricultural systems p. 135–187. In: Z. Rengel (ed.). Handbook of soil acidity. Marcel Dekker Inc. New York NY

  • VetanovetzR.P.1996Tissue analyses and interpretation p. 197–220. In: D.W. Reed (ed.). Water media and nutrition for greenhouse crops. Ball Publishing Batavia IL

  • von WirenN.GojonA.ChaillouS.RaperD.2001Mechanisms and regulation of ammonium uptake in higher plants p. 61–77. In: P.J. Lea and J.F. Morot-Gaudry (eds.). Plant nitrogen. Springer New York NY

  • WhipkerB.E.CavinsT.J.GibsonJ.L.DoleJ.M.NelsonP.V.FontenoW.2003Plant nutrition p. 29–46. In: D. Hamrick (ed.). Ball redbook. Vol. 2. Ball Publishing Batavia IL

If the inline PDF is not rendering correctly, you can download the PDF file here.

Contributor Notes

We thank PanAmerican Seed, USDA-ARS Floriculture and Nursery Research Initiative #58-3607-8-725, and industry partners of the Floriculture Research Alliance at the University of Florida (floriculturealliance.org) for supporting this research. Thanks to James Colee from the Department of Statistics at University of Florida IFAS for providing statistical support.

Corresponding author. E-mail: pfisher@ufl.edu.

  • View in gallery

    Substrate-pH after 33 d for floriculture species grown in peat: perlite substrate and irrigated with nutrient solutions containing 100 mg·L−1 N and NH4+:NO3 nitrogen ratios of (A) 0:100, (B) 20:80, and (C) 40:60. Data are species least-square means of six replicates. Error bars indicate ±95% confidence intervals using Tukey’s honestly significant difference at α = 0.05. Dashed lines represent the initial substrate-pH (5.84) at the beginning of the experiment.

  • View in gallery

    Relationship between mineral acid (0.5060 N hydrochloric acid) or base (hydrated dolomitic limestone with 139% neutralizing value) and change in substrate-pH (ΔpH), quantified using the acid–base titration. The polynomial equation milliequivalents (meq) of acid (− value) or base (+ value) per L of substrate = 0.8780 × ΔpH3 + 1.3369 × ΔpH2 + 9.9856 × ΔpH − 0.2569, with P < 0.0001.

  • View in gallery

    Milliequivalents (meq) of acid or base per gram of plant dry mass gain after 33 d for floriculture species grown in peat:perlite substrate irrigated with nutrient solutions containing 100 mg·L−1 N and NH4+:NO3 nitrogen ratios of (A) 0:100, (B) 20:80, and (C) 40:60. Data represent species least-square means of six replicates. Error bars are ±95% confidence intervals using Tukey’s honestly significant difference at α = 0.05.

  • View in gallery

    Relationship between milliequivalents (meq) net cation or anion uptake (shown as meq anions minus cations taken up) and meq acid or base produced per gram of dry mass increase for species fertilized with the 0:100 solution. Data represent least-square means of six replicates. The regression equation is meq acid or base produced per gram dry mass increase = 0.725 ± 0.408 * (meq anion minus cation uptake per gram dry mass increase) − 0.066 ± 0.377 with R2 = 0.531.

  • AlbanoJ.P.MillerW.B.1996Iron deficiency stress influences physiology of iron acquisition in marigold (Tagetes erecta L.)J. Amer. Soc. Hort. Sci.121438441

    • Search Google Scholar
    • Export Citation
  • AlbanoJ.P.MillerW.B.HalbrooksM.C.1996Iron toxicity stress causes bronze speckle, a specific physiological disorder of marigold (Tagetes erecta L.)J. Amer. Soc. Hort. Sci.121430437

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.BiernbaumJ.A.1996The effect of lime, irrigation-water source, and water-soluble fertilizer on root-zone pH, electrical conductivity, and macronutrient management of container root media with impatiensJ. Amer. Soc. Hort. Sci.121442452

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.BiernbaumJ.A.1997Lime, water source, and fertilizer nitrogen form affect medium pH and nitrogen accumulation and uptakeHortScience327174

    • Search Google Scholar
    • Export Citation
  • ArgoW.R.FisherP.R.2002Understanding pH management for container-grown crops. Meister Publishing Willoughby OH

  • BarnesJ.NelsonP.WhipkerB.E.DickeyD.A.HesterbergD.ShiW.2014Statistical model for describing macronutrient impacts on container substrate pH over timeHortScience49207214

    • Search Google Scholar
    • Export Citation
  • BekeleT.CinoB.J.EhlertP.A.I.van der MassA.A.van DiestA.1983An evaluation of plant-borne factors promoting the solubilization of alkaline rock phosphatesPlant Soil75361378

    • Search Google Scholar
    • Export Citation
  • BienfaitH.F.1988Mechanisms in Fe-efficiency reactions of higher plantsJ. Plant Nutr.11605629

  • CavinsT.J.WhipkerB.E.FontenoW.C.HardenB.McCallI.GibsonJ.L.2000Monitoring and managing pH and EC using the PourThru extraction method. North Carolina State Univ. Hort. Info. Lflt. 590

  • DicksonR.W.FisherP.R.ArgoW.R.JacquesD.J.SartainJ.B.TrenholmL.E.YeagerT.H.2016Solution ammonium:nitrate ratio and cation/anion uptake affect acidity or basicity with floriculture species in hydroponicsSci. Hort.2003644

    • Search Google Scholar
    • Export Citation
  • EngelsC.MarschnerH.1995Plant uptake and utilization of nitrogen p. 41–82. In: P.E. Bacon (ed.). Nitrogen fertilization in the environment. Marcel Dekker Inc. New York NY

  • GibsonJ.L.PitchayD.S.Williams-RhodesA.L.WhipkerB.E.NelsonP.V.DoleJ.M.2007Nutrient deficiencies in bedding plants: A pictorial guide for identification and correction. Ball Publishing. Batavia IL

  • HarbaughB.K.1995Iron toxicity in Pentas lanceolataHortTechnology5306307

  • HaynesR.J.1990Active ion uptake and maintenance of cation-anion balance: A critical examination of their role in regulating rhizosphere pHPlant Soil126247264

    • Search Google Scholar
    • Export Citation
  • HoaglandD.R.ArnonD.I.1950The water culture method for growing plants without soil. Calif. Agr. Expt. Sta. Circ. 347

  • HuangJ.NelsonP.V.LeeJ.2001Seedling effect on root substrate pHJ. Plant Nutr.2411331147

  • JohnsonC.N.FisherP.R.HuangJ.VetanovetzR.P.ArgoW.R.2010Quantifying the acidity of an ammonium-based fertilizer in containerized productionHortScience4510991105

    • Search Google Scholar
    • Export Citation
  • JohnsonC.N.FisherP.R.HuangJ.YeagerT.H.ObrezaT.A.VetanovetzR.P.ArgoW.R.BishkoA.J.2013Effect of fertilizer potential acidity and nitrogen form on the pH response in a peat-based substrate with three floriculture speciesSci. Hort.162135143

    • Search Google Scholar
    • Export Citation
  • KirkbyE.A.KnightA.H.1977Influence of the level of nitrate nutrition on ion uptake and assimilation, organic acid accumulation, and cation-anion balance in whole tomato plantsPlant Physiol.60349353

    • Search Google Scholar
    • Export Citation
  • LangH.J.ElliotG.C.1991Influence of ammonium:nitrate ratio and nitrogen concentration on nitrification activity in soilless potting mediaJ. Soc. Hort. Sci.116642645

    • Search Google Scholar
    • Export Citation
  • Lea-CoxJ.D.StutteG.W.BerryW.L.WheelerR.M.1996Charge balance—A theoretical basis for modulating pH fluctuations in plant nutrient delivery systemsLife Support Biosph. Sci.35359

    • Search Google Scholar
    • Export Citation
  • LindsayW.L.1979Chemical equilibria in soils. The Blackburn Press Caldwell NJ

  • MarschnerP.2012Mineral nutrition of higher plants. 3rd ed. Academic Press San Diego CA

  • MiwaK.FujiwaraT.2010Boron transport in plants: Co-ordinated regulation of transportersAnn. Bot.10511031108

  • PetersonJ.C.1981Modify your pH perspectiveFlorists’ Rev.169343592–93

  • PierreW.H.1933Determination of equivalent acidity and basicity of fertilizersInd. Eng. Chem.5229234

  • PuustjarviV.RobertsonR.A.1975Physical and chemical properties p. 23–38. In: D.W. Robinson and J.G.D. Lamb (eds.). Peat in horticulture. Academic Press London

  • RengelZ.2003Handbook of soil acidity. Vol. 94. CRC Press London

  • ScogginsH.L.BaileyD.A.NelsonP.V.2002Efficacy of the press extraction method for bedding plant plug nutrient monitoringHortScience37108112

    • Search Google Scholar
    • Export Citation
  • SonneveldC.VoogtW.2009Plant nutrition of greenhouse crops. Springer Dordrecht The Netherlands

  • VerburgK.BraschkatJ.HockmanZ.MooreA.D.HelyarK.R.ProbertM.E.HargravesJ.N.G.SimpsonR.J.2003Modeling acidification processes in agricultural systems p. 135–187. In: Z. Rengel (ed.). Handbook of soil acidity. Marcel Dekker Inc. New York NY

  • VetanovetzR.P.1996Tissue analyses and interpretation p. 197–220. In: D.W. Reed (ed.). Water media and nutrition for greenhouse crops. Ball Publishing Batavia IL

  • von WirenN.GojonA.ChaillouS.RaperD.2001Mechanisms and regulation of ammonium uptake in higher plants p. 61–77. In: P.J. Lea and J.F. Morot-Gaudry (eds.). Plant nitrogen. Springer New York NY

  • WhipkerB.E.CavinsT.J.GibsonJ.L.DoleJ.M.NelsonP.V.FontenoW.2003Plant nutrition p. 29–46. In: D. Hamrick (ed.). Ball redbook. Vol. 2. Ball Publishing Batavia IL

All Time Past Year Past 30 Days
Abstract Views 141 40 0
Full Text Views 129 75 5
PDF Downloads 46 36 2