Ozone,acidic precipitation,and soil Mg impacts on soil and loblolly pine seedling nutrient status after three growing seasons

Recent studies have suggested that the growth of loblolly pine (Pinus taeda L.) has declined in the southeastern United States, possibly due to acidic deposition and air pollutants, especially under conditions of low nutrient availability. Consequently, the potential for individual and synergistic impacts of O₃, acidic precipitation, and soil Mg status on the nutrient status of loblolly pine seedlings and soil was investigated over a 3 yr study period. Thirty-six open top chambers equipped with a rainfall exclusion/addition system were utilized to administer three levels of O₃ (subambient, ambient, or twice ambient) and two acidic precipitation treatments (pH 3.8 or 5.2) to seedlings growing in 24-L plastic pots containing soil having either 35 or 15 mg kg^?1 of exchangeable Mg. Each chamber contained 36 pots, and each treatment combination was replicated six times for a total of 1296 individual pots. After three seasons, throughfall and foliar nutrition data indicated that foliar leaching was not accelerated by increasing the acidity of precipitation from pH 5.2 to 3.8 and that increasing O₃ did not act to exacerbate foliar leaching. Further, foliar nutrient concentrations were not significantly affected by precipitation pH or O₃ treatments. Soil and soil solution data also indicate no accelerated soil leaching associated with chronic acidic precipitation. Differences in soil Mg treatments were reflected in soil solution and seedling Mg contents, but the 15 mg kg^?1 soil Mg treatment was not sufficiently low enough to induce Mg deficiency in the seedlings.     

Effects of acidic precipitation,O3, and soil Mg status on throughfall,soil, and seedling loblolly pine nutrient concentrations

The individual and combined impacts of acidic precipitation, O₃, and soil Mg status on nutrient concentrations of throughfall, soil solution, soil, and seedling components were evaluated after one growing season. Loblolly pine seedlings were planted in a sandy loam soil having approximately 15 or 35 mg kg^?1 of exchangeable Mg and were exposed to subambient, ambient, or twice ambient concentrations of O₃ in open top chambers from May through October. Seedlings also received ambient amounts of simulated precipitation at pH 4.0 or 5.3 during this period. Concentrations of nutrients analyzed increased slightly in throughfall, but did not respond significantly to precipitation pH treatments. No increased nutrient leaching and no soil acidification were evident in soil exposed to low pH precipitation after one growing season. Ozone treatments had no significant effects on tissue nutrient concentrations. Interaction responses were very limited and do not suggest any significant synergisms.     

N2-fixation and growth promotion in cedar colonized by an endophytic strain of Paenibacillus polymyxa

Inoculation of western red cedar with Paenibacillus polymyxa P2b-2R, an endophytic diazotroph of a pine, was previously shown to result in biological nitrogen fixation (BNF) in seedlings grown under N-limited conditions, but biomass accumulation was reduced after a 9-month growth period. To determine if the seedling growth reduction was temporary, we inoculated cedar seed with strain P2b-2R and grew seedlings for up to 13 months in a N-limited soil mix containing 0.7 mM of available N labeled as Ca(¹⁵NO₃)₂. P2b-2R developed a persistent endophytic population comprising 10²–10⁶?cfu g^?1 plant tissue inside pine roots, stems, and needles. At the end of the growth period, P2b-2R had reduced ¹⁵N foliar N abundance by 36 % and increased shoot biomass by 46 % compared to controls. Our results indicate that inoculated seedlings derived 36 % of foliar N from the atmosphere and suggest that BNF by P. polymyxa can significantly enhance growth of cedar in a N-limited soil if seedlings are grown for a sufficient amount of time. These findings support the hypothesis that endophytic diazotrophs may facilitate regeneration and growth of western red cedar at N-poor sites.     

Three-year growth responses of Pinus taeda L. to simulated rain chemistry,soil magnesium status,and ozone

Height, diameter, and biomass were measured for loblolly pine (Pinus taeda L) seedlings grown in soil containing 15 or 35 Μg Mg g^?1 and exposed from May to October in 1987, 1988, and 1989 to three O₃ concentrations (sub-ambient, ambient, or twice-ambient) and to rain pH levels of 3.8 or 5.2. Reduction in biomass accumulation in seedlings exposed to twice-ambient O₃ vs sub-ambient O₃ was 14% (P = 0.03) in 1987, 11.4% (P = 0.002) by 1988, and 8% (P = 0.15) by 1989. The greatest height growth occurred in seedlings exposed to twice-ambient O₃, and the greatest stem diameter growth occurred in seedlings exposed to sub-ambient O₃. A comparison of stem volume (d²h) with stem biomass suggested that tissue density was reduced by elevated O₃. Biomass accumulation response to rainfall chemistry was small (5.5% reduction in the low pH treatment in 1989) and not statistically significant for most plant tissues. Growth response to soil Mg status was not significant. Hoewever, in 1989 treatment interactions between rainfall chemistry and soil Mg status were observed. Height was 5% greater (P = 0.02) and biomass was 6% greater (P = 0.10) in seedlings grown in higher-Mg soil and receiving higher-pH rainfall than seedlings grown in any of the other pH-Mg treatment combinations. The data suggest direct adverse effects of near ambient O₃ and indirect, slower acting and interacting adverse effects of rainfall chemistry and soil nutrient status on growth of loblolly pine.     

Short-term uptake of <Superscript>15</Superscript>NH<Subscript>4</Subscript><Superscript>+</Superscript> into soil microbes and seedlings of pine,spruce and birch in potted soils

Short-term competition between soil microbes and seedlings of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth) for N was assessed in a pot study using (¹⁵NH₄)₂SO₄ as a tracer. Seedlings were grown in organic and mineral soil, collected from a podsol soil; 3.18 mg (¹⁵NH₄)₂SO₄ per pot were injected into the soil, corresponding to 4 µg ¹⁵N g^-1 d.m. (dry matter) mineral soil and 17 µg ¹⁵N g^-1 d.m. organic soil. The amounts of N and ¹⁵N in the seedlings and in microbial biomass derived from fumigation-extraction were measured 48 h after addition of ¹⁵N. In the mineral soil, 19–30% of the added ¹⁵N was found in the plants and 14–20% in the microbial biomass. There were no statistically significant differences between the tree species. In the organic soil, 74% of the added ¹⁵N was recovered in the microbial biomass in birch soil, compared to 26% and 17% in pine and spruce soils, respectively. Correspondingly, about 70% of the ¹⁵N was recovered in pine and spruce seedlings, and only 23% in birch seedlings. In conclusion, plants generally competed more successfully for added ¹⁵NH₄ ⁺ than soil microbes did. An exception was birch growing in organic soil, where the greater amount of available C from birch root exudates perhaps enabled micro-organisms to utilise more N.     

Effect of exponential fertilization on growth and nutritional status in Buddhist pine (Podocarpus macrophyllus [Thunb.] D. Don) seedlings cultured in natural and prolonged photoperiods

Abstract

Slow growth rate limits the development of seedlings from the Podocarpaceae family. The extended photoperiod (EP) is well known to promote tree seedling growth, but it may also cause the possibility of nutrient dilution without a proper nutrient supply regime. Exponential fertilization (EF) has been proven to counter nutrient dilution within tree seedlings efficiently. However, no study has determined the response of Podocarpus seedlings to the interaction of EF and photoperiod. We fed 13-month old Buddhist pine (Podocarpus macrophyllus [Thunb.] D. Don) seedlings using EF applied at rates of 0 (control), 50 (E50), 100 (E100), and 150 (E150) mg nitrogen (N) seedling^?1 for 5 months, during which half of all seedlings were cultured in the natural photoperiod (NP) with the others exposed to EP. The longer photoperiod resulted in greater seedling height and biomass accumulation of Buddhist pine seedlings. Relative to NP, EP increased N content at the whole-plant level but decreased N concentration in the stem and root, which indicated the symptom of N dilution. However, both phosphorus (P) content and P concentration increased in response to the longer photoperiod. EF rates in the E100 and E150 treatments were evaluated to be the ‘sufficiency’ ones for both N and P in EP and NP, respectively. In conclusion, EP could stimulate the growth of Buddhist pine seedlings but caused N dilution within them at the same time, and photoperiod would change the nutritional response of these seedlings to EF.     

Evaluation of Pine Bark or Pine Bark with Goat Manure or Sewage Sludge Cocomposts As Growing Media for Vegetable Seedlings

The suitability as growing media of composts made from pine bark or pine bark cocomposted with goat manure or sewage sludge and either inoculated or not inoculated with effective microorganisms, was evaluated under greenhouse conditions with and without fertilization using cabbage as the test crop. The treatments were replicated three times and arranged in a randomized complete block design in a fibre glass covered greenhouse. Cabbage seedlings were grown in cavity trays for five weeks, after which plants were harvested and fresh and dry weights determined. Samples were also analyzed for N, P, K and selected heavy metal concentrations. Results revealed that pine bark-goat manure cocomposts supported good seedling growth and could thus be good substitutes for pine bark alone as a growing medium where goat manure or similar manures are available. The results also showed that despite the superior nutritional value of these alternative growing media, nutrient supplementation may still be necessary where seedlings are kept in the nursery for extended periods due to nutrient exhaustion through plant uptake and leaching. Pine bark-sewage sludge compost also had positive effects on seedling growth but could only be recommended as a growing medium for nonfood plants because its composting did not reach the thermophillic temperatures necessary for adequate pathogen kill. Inoculation with effective microorganisms improved seedling growth in sewage sludge and goat manure based composts but the mechanisms involved remain to be established.     

15N foliar dilution of western red cedar in response to seed inoculation with diazotrophic Paenibacillus polymyxa

Diazotrophic bacteria previously isolated from internal tissues of naturally regenerating lodgepole pine (Pinus contorta var. latifolia (Dougl.) Engelm.) seedlings were tested for their ability to fix N in association with western red cedar (Thuja plicata Donn.). Surface-sterilized cedar seed was sown in glass tubes containing an autoclaved sand/montmorillonite clay mixture that contained a N-free nutrient solution labeled with ¹⁵N as 0.35?mM Ca(¹⁵NO₃)₂ (5?% ¹⁵N label). After sowing, seed was inoculated with one of three bacterial strains: Paenibacillus polymyxa P2b-2R, P. polymyxa P18b-2R, or Dyadobacter fermentans P19a-2R. At the end of the 27-week plant growth period, P2b-2R was the only strain detected in the cedar rhizosphere. No bacteria were found inside plant tissues. Cedar foliar N concentrations were significantly enhanced (26–33?%, P?<?0.05) in response to inoculation with all three bacterial strains but ¹⁵N dilution (23?%, P?<?0.05) was observed only in seedlings treated with strain P2b-2R. This strain also reduced seedling dry weight (27?%, P?<?0.05). We observed similar trends in a second experiment with slight modifications to the protocol, but the magnitude of foliar ¹⁵N dilution was greater (56?%, P?<?0.05). Based on our results, we conclude that cedar seedlings inoculated with strain P2b-2R derived 23 and 56?% of their foliar N from bacterial N fixation in two seedling growth experiments.     

Medium‐term effects of poultry manure on pine nitrogen uptake in a 15N‐labeled burnt soil§

The effects of poultry manure (PM), used for the reclamation of a ¹⁵N‐labeled burnt soil, on N nutrition of pine seedlings were evaluated during one year in a pot experiment. Six treatments were used: ¹⁵N‐labeled soil (LS), ¹⁵N‐labeled burnt soil (BLS), and BLS+PM at doses equivalent to 1, 2, 4, and 8 t ha^–1 of dry PM (PM1, PM2, PM4, and PM8, respectively). Either in the whole tree or the different organs, N concentration: (1) decreased (p 0.05) in the order LS > BLS, BLS+PM1, BLS+PM2, BLS+PM4 > BLS+PM8 and (2) was negatively correlated with phytomass production (p < 0.05 to p < 0.01). The two highest amounts of assimilated N per kg dry soil were found in LS and BLS (130–134 mg) and the lowest in BLS+PM8 (87 mg), the other treatments being in an intermediate range (108–115 mg). Irrespective of the soil treatment, 56%–66% of the pine‐N were accounted for by needles, 29%–32% by roots, and 8%–12% by stems, the differences among organs being always significant (p < 0.05). The percentage of pine‐N derived from PM (%PNDFM) increased steadily with PM dose, from 1.7% in BLS+PM1 to 13.3% in BLS+PM8, reaching values for the two highest PM doses within the range found for ¹⁵N mineral fertilizers in forests. From 8.2% to 16.9% of the PM‐N was assimilated by the pines. Although differences among treatments were not significant, the two highest values were found in BLS+PM4 and BLS+PM8. Therefore, the ¹⁵N data showed clearly that there is a positive medium‐term effect of PM on pine N nutrition during the reafforestation phase of burnt‐forest reclamation. The lower total N uptake by pine seedlings in the PM treatments was explained in terms of lower levels of soil available N due to its exportation with the phytomass of the preceding ryegrass culture, used for the early protection phase in the burnt soil–reclamation procedure.     

Phosphorus and sulphur requirements of blackwood (Acacia melanoxylon R.BR.) seedlings

Abstract

The effects of varying phosphorus (P) and sulphur (S) supply on the dry matter production, height growth, foliage type, nutrient content and nutrient composition of blackwood seedlings were examined in a fractional, factorial experiment with 12 levels each of P and S in 29 treatments.

Regressions of final height at age 6 months, and seedling dry weight respectively on P and S supply level gave quadratic response surfaces with maxima occurring at the combinations P_15.1 S_12.7 and P_15.8 S_14.6 (where P₁ S₁ = a total dose of 5 mg each of P and S). This result suggests that requirement for s is closely comparable to that for P in blackwood seedlings. Interaction (P × s) was not significant for any variable.

At harvest, seedlings grown with the P‐S treatment combination closest to the predicted optimum supply for maximum productivity had concentrations of 2.7% N, 0.23% P, and 0.16% S in their tops, or 2.4% N, 0.20% P. and 0.17% S in the whole seedling. These seedlings were well proportioned with a tops:roots dry weight ratio of 1.2. In seedlings raised with only a token supply of P or S, top growth suffered at the expense of root growth and the ratio was always < 1.

The results of the trial suggest that superphosphate with its balanced P and S content (N‐P‐K‐S rating: 0–10–0–11) would be the most cost effective fertiliser for use in nursery production of blackwood where a need for supplementary P and S exists.     

Seasonal Biomass Accumulation and Nutrient Uptake of Pea and Lentil on a Black Chernozem Soil in Saskatchewan

ABSTRACT

Close relationships usually exist among biomass accumulation, nutrient uptake, and seed yield during the growing season. Field experiments with pea (Pisum sativum L.) and lentil (Lens cultinaris L.) were conducted in 1998 and 1999 at Melfort, Saskatchewan, Canada, to determine relationships of biomass accumulation and nutrient uptake with days after emergence (DAE) or growing degree days (GDD). For both biomass accumulation and nutrient uptake, maximum rates and amounts increased with time at early growth stages and reached a maximum value at late growth stages. The R² values for cubic polynomial regressions were highly significant, indicating their suitability to estimate the progression of biomass accumulation and nutrient uptake as a function of days after emergence (DAE). Both pulse crops followed a similar pattern in biomass accumulation and nutrient uptake, which increased in the early growth stages and reached a maximum late in the growth cycle. Pulse crops usually reached their maximum biomass accumulation rate and amount at early to late bud formation (42–56 DAE or 390–577 GDD) and at medium pod formation to early seed filling (75–82 DAE or 848–858 GDD) growth stages, respectively. Maximum biomass accumulation rate was 175–215 kg ha^{? 1}d^?1 for pea and 109–140 kg ha^{? 1}d^{? 1} for lentil. Maximum nutrient uptake rate and amount usually occurred at branching to early bud formation (28–49 DAE or 206–498 GDD) and at the flowering to seed filling (66–85 DAE or 672–986 GDD) growth stages, respectively. Maximum uptake rate of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S), respectively, was 4.6–4.9, 0.4–0.5, 5.0–5.3 and 0.3 kg ha^{? 1}d^{? 1} for pea, and 2.4–3.8, 0.2–0.3, 2.0–3.4 and 0.2 kg ha^{? 1}d^{? 1} for lentil. In general, maximum nutrient uptake rate and amount occurred earlier than maximum biomass accumulation rate and amount, respectively; and the maximum accumulation rates of both biomass and nutrients occurred earlier than maximum amounts. The findings suggest that adequate supply of nutrients from soil and fertilizers at early growth stages, and translocation of biomass and nutrients to seed at later growth stages are of great importance for high seed yield of pulse crops.     

Soil testing of horticultural substrates (ii) Desirable nitrogen values for the 1: 1.5 water extract

Abstract

The initial nitrogen desirable value (DV) to give maximum dry weight and maximum growth rate for various growing periods has been estimated for the 1: 1.5 water extraction procedure by regressing dry weight and net growth rate against soil test values using a quadratic function. The DV for dry weight and growth rate has been estimated for chrysanthemum and verbena (2 trials each) and for dry weight for tomato (1 trial) in a number of substrates.

The DV for maximum dry weight of chrysanthemum, grown for 48 days under winter conditions, were: Peat 151–211 ppm and greater, Bark 140‐168 ppm and Peat and Sawdust and Sand (PSS) 135–162 ppm. Under summer conditions and grown for 35 days, the DV were as follows: Peat 134 — 172 ppm, Peat and Pumice (PP) 142 ‐170 ppm, Bark 168–202 ppm and PSS 152–172 ppm.

The DV for maximum dry weight of verbena grown for 42 days under spring conditions were as follows: Peat 57 ppm, Bark 41 ppm and PSS 48–52 ppm and greater. Under summer conditions and grown for 38 days, the DV for verbena were: Peat 77–90 ppm, PP 70–85 ppm, Bark 67–73 PPm and greater, and PSS 72 ppm.

For the chrysanthemum and verbena trials, the DV for maximum growth rate over various periods were generally in the range of DV found for maximum dry weight. However, the values did tend to increase later in the life of the crop.

The DV for maximum dry weight of tomato were as follows: Peat 260–290 ppm, PP 211–240 ppm, Bark 220–254 ppm, PSS 186–236 ppm and Sawdust and Sand 190–220 ppm. This trial, in contrast to the others, was not conducted in conditions free from leaching and this may have given a higher DV.     

Growth of Loblolly Pine and White Pine after Enrichment by Nutrient Loading

Low nutrient availability often constrains the growth of young trees following planting to fields or forests. Nutrient loading of young tree seedlings increases their growth in outplanting. Loblolly pine (Pinus taeda L.) and white pine (Pinus strobus L.) were grown for one year on nutrient-loading regimes that varied from 13 to 410 mg N L^?1 in sand culture. Other nutrients varied in proportion to the nitrogen (N) concentrations. Resulting plant growth showed that an array of nutritional regimes from deficient to excessive was applied. The young plants were transplanted into containers of sandy loam and were grown for one year without fertilization. Growth of each species increased with enhanced nutrient loading. The optimum concentration of N for nutrient loading was about 1.5 to 1.8% leaf dry weight for either species. Nutrient loading during nursery culture imparts transplants with nutrient levels that will enable growth for at least a year after outplanting.     

Light and temperature influence phosphorus absorption by slash pine

Abstract

One‐year‐old slash pine seedlings (Pinus elliottii Engelm.) accumulated more radioactive phosphorus in needles at a 15–10°C day‐night temperature and 2500 foot candles than at higher temperatures and reduced light. Rate of phosphorus uptake was related to concentrations of ethanol‐soluble carbohydrates but not to those of starch or all carbohydrates. Results suggest that temperature and light can be important for optimum phosphorus nutrition of slash pine.     

Early detection of phosphate deficiency in plants

Abstract

At 3, 7 and 10 days after planting, uptake of ³²P‐ orthophosphate over 15 minutes by pine seedlings grown in phosphate deficient soil was 3.0 4.8 and 5.2 times that of seedlings growing in phosphate amended soil. At 4 days and 7 days uptake over 15 minutes by phosphate deficient wheat was 1.2 and 2.4 times that of plants grown in phosphate amended soil. A rapid, sensitive, very early bioassay of available soil phosphate is suggested.     

Nutrient Indexing in “‘Kinnow” Mandarin (Citrus deliciosia Lour.× Citrus nobilis Tanaka) Grown in Indogangetic Plains

Diagnosis and remediation of nutrient constraints in perennial fruit crop like citrus are the two important pillars of an effective nutrient management program. Efforts were made to develop nutrient indexing (NI) criteria based on generated leaf and soil analysis dataset for “Kinnow” mandarin (Citrus deliciosia Lour. × Citrus nobilis Tanaka) grown on illitic soils of Indogangetic plains (Entisol, Inceptisol, and Aridisol). NI through diagnosis and recommendation integrated system (DRIS) using leaf analysis data showed optimum value of leaf nutrient concentration as 2.22–2.32% nitrogen (N), 0.11–0.15% phosphorus (P), 1.10–1.41% potassium (K), 2.32–2.79% calcium (Ca), 0.38–0.61% magnesium (Mg), 22.4–58.3 ppm iron (Fe), 26.3–56.2 ppm manganese (Mn), 4.2–7.2 ppm copper (Cu), and 21.3–26.9 ppm zinc (Zn) vis-à-vis a fruit yield of 32.4–56.1 kg tree^?1. Using these NI criteria, Zn was observed as most deficient (64.7%) followed by Fe (61.5%), Mn (57.6%), N (96.1%), and P (38.5%) using percentage of orchards as basis. While, optimum NI (mg kg^?1) using soil analysis data was determined as 114.3–121.2 potassium permanganate (KMnO₄-N), 7.8–12.3 Olsen-P, 96.4–131.3 ammonium acetate (NH₄OAc)-K, 189.4–248.6 NH₄OAc-Ca, 72.3–89.9 NH₄OAc-Mg, 5.8–11.1, DTPA-Fe, 4.3–6.9 diethylenetriaminepentaacetic acid (DTPA)-Mn, 0.45–0.69 DTPA-Cu, and 21.3–26.9 DTPA-Zn for the optimum yield of 32.4–56.1 kg tree^?1. Soil analysis-based NIs displayed a good complementary with leaf analysis-based NIs evident from the diagnoses indicating Mn (52.2%) as most dominant constraint Zn (61.2%) followed by Mn (48.3%), N (41.2%), and P (35.6%). The recommended DRIS-based NIs would lay a scientific basis in formulating citrus fertilization program.     

Growth and nutrient uptake dynamics of Mytilaria laosensis seedlings under exponential and conventional fertilizations

The growth characteristics and nutrient uptake dynamics of Mytilaria laosensis Lec. seedlings treated weekly with conventional and exponential fertilizations were investigated at intervals of 3 weeks for 12 weeks in a greenhouse. Leaf area and pigment compositions were also examined at the final harvest. The fertility treatments (mg nitrogen seedling^–1) included two conventional (50C and 100C) and four exponential (50E, 100E, 200E and 400E) fertilizations, and no fertilization (0) as control. The biomass and nutrient contents of M. laosensis seedlings increased exponentially with time. Steady-state nutrition of nitrogen (N) and phosphorus (P) were achieved under exponential fertilization treatment of 50?mg?N?seedling^?1 (50E) and conventional fertilization treatment of 100?mg?N?seedling^–1 (100C), resulting from simultaneous increase of their biomass and nutrient contents. The nutrient uptake efficiency continuously increased over time in conventionally fertilized seedlings, but it increased initially and declined or remained stable from 11 weeks after transplanting in the exponentially fertilized seedlings. At the end of the experiment, the conventionally fertilized seedlings performed remarkably better than all exponentially fertilized seedlings except for seedlings in the exponential treatment of 200?mg?N?seedling^–1 (200E) in height, root collar diameter and biomass. The optimum N and P uptake occurred in 200E seedlings because their N and P contents were 71%/60% and 14%/9% higher than both conventionally fertilized seedlings (50C/100C) without significant differences in growth performance between them. The leaf areas and chlorophyll contents of seedlings increased significantly with the increase of fertilizer levels and nearly peaked at the range from 100 to 200?mg?N?seedling^–1, whereas the delivery schedule (conventional and exponential) had little effect on leaf areas and chlorophyll contents of seedlings at the same nutrient level (50 or 100?mg?N?seedling^–1). These findings will provide evidence to make guidelines on fertilization for nursery production of M. laosensis, and help understand the nutrient demands for this species and further benefit the development of its plantations.     

Growth and chloroplast ultrastructure of two citrus rootstock seedlings in response to ammonium and nitrate nutrition 1

Abstract

It is important to understand the differential response of citrus rootstock to various rates of nitrogen (N) forms in order to evaluate the tree response to N availability under different production conditions. In this study, the effects of N sources (NH₄‐N or NO₃‐N), and rates (5, 15, 45, and 135 mg N L^?1) on two citrus rootstock seedlings (Swingle citrumelo, SC; Cleopatra mandarin, CM) growth (110 d) and N concentrations in various parts of seedling were investigated in a nutrient solution experiment. The effects of N nutrition on the chloroplast ultrastructure of leaves were examined at the end of the experiment. Rootstock and N sources significantly influenced the growth of leaves, stems, and roots. The growth of all seedling parts of both rootstocks decreased with an increase in concentration of NH₄‐N in the solution. In contrast, there was a positive relationship between the seedling growth and the concentration of NO₃‐N in the nutrient solution with marked response observed as the NO₃‐N concentration increased from 5 to 15 mg L^?1 The experiment demonstrated a distinct growth suppression effect with an increase in concentration of NH₄‐N in the nutrient solution, particularly SC rootstock. Chloroplast ultra‐structure of the leaves showed evidence of injury of the seedlings which received N entirely as NH₄ ⁺ form, but the injury was not seen when the seedlings received N as the NO₃‐N form. The disruption of chloroplast ultrastructure increased with increased rate of NH₄‐N. The most conspicuous characteristic of ammonium toxicity was the massive accumulation of strands granules and phytoferritin which is clearly an evidence of NH₃ toxicity. The results are important for understanding the implications of N source on seedling growth and chloroplast structure of citrus leaves.     

A greenhouse study of northern red oak seedling growth on two forest soils at different stages of acidification

The objective of this study was to determine whether or not Ca and P in soils from two forested sites at two different stages of acidification were limiting growth of red oak seedlings. The A and E horizons of a Berks soil from Watershed 4 at the Fernow Experimental Forest (cation exchange buffer range) and a Hazelton/Dekalb soil from Pea Vine Hill in Southwestern Pennsylvania (Al buffer range) were placed in pots and utilized as the growth medium for northern red oak seedlings in a greenhouse environment. Soil water NO₃-N, Ca, Mg, and K concentrations were significantly higher (α≤0.05) on the Berks soil. Soil exchangeable P and soil solution TP (total phosphorus) were significantly higher (α≤0.10) on the Hazelton/Dekalb soil. Both soils were amended with bone meal (CaPO₄) to determine the effects of Ca and P addition on the growth and nutrient uptake of the seedlings. Height growth of the control red oak seedlings was significantly (α≤0.05) greater on the Berks soil after 45 d, but amendment of Hazelton/Dekalb soil with bone meal eliminated this difference. Bone meal addition to the Hazelton/Dekalb soil resulted in significantly greater (α≤0.05) height growth of red oak seedlings when compared to red oak seedlings grown on unamended Hazelton/Dekalb soil, but did not have a similar effect for red oak seedlings grown on Berks soil. Bone meal addition to Hazelton/Dekalb soil resulted in greater (α≤0.05) concentrations of Ca and Mg in red oak leaves. Unfertilized Berks red oak seedling leaves had significantly higher (α≤0.05) concentrations of Ca and K than their Hazelton/Dekalb counterparts. Al/Ca molar ratios were significantly lower on the Berks soil. Red oak height growth was increased significantly by Ca addition to the Hazelton/Dekalb soil.     

Soil testing of horticultural substrates (v) Evaluation of 1: 1.5 water extract and ammonium acetate extract for potassium and desirable potassium values

Abstract

The 1: 1.5 water extraction of horticultural substrate for K was evaluated using K uptake as the criterion. Two crops, chrysanthemum (2 trials) and verbena (2 trials) were grown in peat, peat + pumice (PP), pine bark and peat + sawdust + sand (PSS). The ammonium acetate (NH₄OAc) extraction for K was evaluated in one trial. The number of K application rates varied from 9 to 23.

The relationship between both soil tests and plant uptake was very good for all substrates, although it was generally poorer in bark, particularly in the verbena trials. This was probably due to the relatively high level of native K in bark and the lower K requirement of verbena. The relationship between water extractable K and NH₄OAc extractable K was linear and very good.

Percentage maximum dry weight and net growth rate were regressed against soil test values using a quadratic function and desirable values (DV) were estimated from the response curve. The initial DV for water extractable K For maximum dry weight in the chrysanthemum trials varied from about 45 ‐ 139 ppm and for NH₄OAc extractable K in one chrysanthemum trial varied from 284 ‐ 469 ppm. The DV obtained from growth rate measurements were similar to those obtained using percent maximum dry weight. It was not possible to determine DV for plants growing in bark and in PSS in one trial.

The DV for verbena, which could be determined in peat in only one trial due to lack of response in the others was 10–11 ppm in the water extract.