Fertigation rate,leaching fraction,and growth of potted poinsettia

Single‐pinched poinsettia (Euphorbia pulcherrima ’V‐14 Glory') in 15‐cm pots received constant fertigation with 50, 100, 200, and 300 mg.L^‐1 nitrogen (N) from a 20N‐4.4 phosphorus (P)‐16.6 potassium (K) fertilizer with a leaching fraction (LF) of 0, 0.2, or 0.4. Plants received 25 irrigations during the 13‐week study. The shoot fresh and dry masses with 50, 100, and 300 mg.L^‐1 N at the 0.4 LF were 30% larger than at the 0 LF. The 300 mg.L^‐1 N fertigated plants had approximately 15% more leaf area and almost 122% more bract area than the 50 mg.L^‐1 N fertigated plants. The leaf N concentration of plants fertigated with 100, 200, and 300 mg.L^‐1 N was near or in the normal range of 4 to 6%, but was below the critical level of 3.5% with 50 mg.L^‐1 N fertigation. In contrast, the leaf P concentration approached or exceeded the toxic level of 0.9% with 100 to 300 mg.L^‐1 N. The N fertigation of 100 to 200 mg.L^‐1 is adequate for producing a quality poinsettia crop. Quality poinsettias can be grown at a 0 LF if quality irrigation water is available. With 11 mg.L^‐1 P via fertigation, the leaf P concentration was in the acceptable range. The P concentration in the 20N‐4.4P‐16.6K complete fertilizer was excessive for poinsettia and would contribute to unnecessary P leaching.     

Phosphorus dynamics in peat‐based substrates

The mobility of nutrients in soils is well characterized, whereas little information is available for common horticultural substrates based on peat. Aim of the current study was to investigate the mobility and dynamics of phosphorus (P) as well as the parameters involved in P transport to plant roots in peat‐based substrates. A series of experiments was run to determine the impedance factor (f) and the buffer power (b). The impedance factor was determined for black peat and black peat mixed with 20% and 40% (v/v) of mineral component at volumetric water content (θ) of 40%, 50%, 60%, and 70% and at different diffusion time. Buffer power was calculated for black peat and black peat mixed with 20% (v/v) of seven different mineral components. Phosphorus was applied at rates of 0, 35, and 100 mg (L substrate^–1), respectively. The impedance factor was not affected by addition of the mineral component to peat. However, f increased from 0.03 to 0.2, by increasing θ from 40% to 60%, indicating that water content has a significant effect on this parameter. Substrate‐solution P ranged from 0.3 to 27 and from 1 to 95 mg P (L solution)^–1 for the P‐application rate of 35 and 100 mg P (L substrate)^–1, respectively. Buffer power of the substrates ranged from 1 to 17.25 depending on the mineral component, and it was positively correlated with oxalate‐soluble Fe and Al in the substrate. The calculated effective diffusion coefficient for P in the substrate was in the range of 10^–7 to 10^–8 cm² s^–1. This high value could be attributed mostly to the low buffer power rather than to the high impedance factor.     

Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

Peat is commonly used as the main component of horticultural substrates, but it has a very low buffering capacity for the anionic macronutrient phosphorus (P), which can be increased by the addition of clays. The aim of this study was to characterize the P adsorption capacity of different substrate clays and to evaluate its significance for plant P uptake. Substrate clays were characterized with a single‐point batch experiment and adsorption and desorption isotherms. The data were fitted to the Langmuir equation for a calculation of the maximum adsorption capacity. Additionally, the contents of oxalate extractable Fe and Al (ΣFe_ox + Al_ox) were determined. The influence of a varying P adsorption capacity of the clays on the P availability to plants in the respective peat–clay substrates and pure peat was investigated in a growth experiment with Impatiens walleriana fertigated with 0, 17, and 35 mg P L^?1 solution, respectively. The observed and calculated (Langmuir) P adsorption capacity of the clays could be well‐characterized by both the batch experiment and the adsorption isotherms and was highly correlated with the ΣFe_ox+Al_ox. A higher P adsorption capacity of the clay amendment in mixed substrates resulted in a lower P concentration in the substrate solution, while the CAT extractable P concentration (P_CAT) was the same. Plant growth and shoot P concentrations were enhanced in the substrates, showing a higher P adsorption capacity, since plants were able to take up the whole amount of P_CAT, and also part of the non‐CAT extractable P. However, the release rate was too low to ensure optimal plant growth, which was in accordance with the result of the desorption experiment. The absolute extent of P release was increased with the increasing P adsorption capacity of the clays and higher degree of P saturation (DPS).     

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

Root proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)^–1, whereas the adjoining compartment (B) had 4 mg P kg^–1 with a vertical high‐P strip (44 mg kg^–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg^–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)^–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g^–1 compared with 1.7–1.9 mg g^–1 in the 14 mg P kg^–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g^–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg^–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg^–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.     

Soil testing of horticultural substrates for cyclamen and poinsettia

Abstract

The 1: 1.5 water, Spurway and saturated media extract procedures were evaluated for cyclamen and 1: 1.5 water extract for poinsettia growing in bark, peat and peat + soil using nutrient uptake as the criterion. In addition, the N, P, and K desirable values (DV) to give maxi Timm dry wt in two harvests and to give maximum growth rate for various growing periods, in samples taken at the start of the trial and midway through the trial, were determined using a quadratic function for both crops. The relationships between N, P and K uptake and the soil test values were generally very good, although the methods overestimated N uptake and underestimated P uptake in bark‐relative to peat. Underestimation of P uptake in peat + soil was even greater. The initial desirable N soil test value in relation to midterm harvest (IDVM) for cyclamen in peat varied from 100–104 ppm for water, 303–312 ppm for saturated media and 44–46 for Spurway extraction. The midterm soil test value in relation to final harvest (MDVF) values varied from 125–136 ppm for water, 471–502 for saturated media and 44–53 ppm for Spurway extraction. Corresponding values in bark were generally higher. The IDVM and MDVF values using the water extract for poinsettia were 180–225 ppm and 155–215 ppm in peat and bark respectively. It was not possible to determine phosphorus IDVM values for cyclamen due to the poor fit of the response curve. The phosphorus MDVF values in peat for cyclamen were 8.1–8.8 ppm for water, 24.5–26.7 ppm for saturated media and 3.2–3.5 ppm for Spurway extraction. The corresponding values in bark were about half of those values and even lower in peat + soil. The phosphorus MDVF values in peat for poinsettia were 14–19 ppm and in bark 4–4.5 ppm for the water extraction. It was not possible to determine K desirable values for cyclamen because of lack of adequate plant response from K application. Potassium IDVF and MDVF values for poinsettia in peat were 100–136 and 80–126 ppm respectively. The DV obtained using growth data were broadly similar to those using plant dry wt. The desirable plant nutrient levels for maximum dry wt of cyclamen at final harvest varied from 1.9–2.4% for N, 0.10–0.17% for P and 1.0–1.7% for K. The DV values for poinsettia at mid harvest were 3.6–4.6% N, and at final harvest 2.7–3.6% N and 0.18–0.37% P.     

Growth and nutrient uptake by cotton roots under field conditions

Abstract

The relationship between nutrient uptake and root growth of cotton (Gossypium hirsutum L.) was studied under field conditions. This basic information could be beneficial when making best management decisions concerning the time of application and placement of fertilizer. A field study was conducted in North Alabama on a fertile Dewey silt loam (clayey, kaolinitic, thermic Typic Paleudult). Aboveground whole plants were harvested at approximately 10‐day intervals beginning at 211 cumulative heat units (CHU) after planting (37 days after planting: 4‐true leaves). Root length of harvested plants was also measured by depth and distance from the plant. Maximum root length was obtained at 1174 CHU (117 days after planting), while dry matter continued to increase until a maximum was obtained at 1317 CHU (128 days after planting). Maximum root length density of 1.60 cm cm³ was obtained in the surface 0–15 cm layer in the in‐row position at 912 CHU (99 days after planting). After first bloom approximately 70% of the cotton root system was in the surface 30 cm of soil. Average daily influx of S per m of root length increased with plant age until 1317 CHU (near cut‐out), after which influx declined. Nitrogen (N), calcium (Ca), and iron (Fe) influx peaked very early in the season (291–469 CHU) followed by a general decrease with plant age. Maximum daily influx of potassium (K), phosphorus (P), magnesium (Mg), copper (Cu), manganese (Mn), and zinc (Zn) per meter of root occurred at approximately peak‐bloom (764–912 CHU, 87–99 days after planting) and decreased with plant age. Copper, Fe, Mn, and Zn influx rates were ～ 1000 times lower as compared to the other nutrients.     

Effect of constant versus adjusted commercial fertilizer concentrations on poinsettia 1

Five poinsettia (Euphorbia pulcherrima Willd.), ‘Freedom Red’, ‘Angelika Red’, ‘Nutcracker Red’, ‘Maren’, and ‘Red Splendor’ received the following treatments of a commercial fertilizer based on nitrogen (N) concentrations of: 75 mg L^‐1 to anthesis; 75 mg L^‐1 first 4 weeks then 125 mg L^‐1 to anthesis; 125 mg L^‐1 first 4 weeks then 200 mg L^‐1 to anthesis; and 200 mg L^‐1 to anthesis. Plants were fertigated to appearance of leachate from the bottom of the pot. Treatment concentrations greater than 125/200 and 200 mg.L^‐1 significantly increased plant width of ‘Red Splendor’, height of ‘Nutcracker Red’ and dry weight of ‘Angelika Red’, ‘Nutcracker Red’, and ‘Maren’. Tissue concentrations of N, phosphorus (P), magnesium (Mg), and sulfur (S) increased as fertilizer treatment concentration increased for some cultivars. Significant differences between elemental concentrations of poinsettia cultivars occurred, specifically ‘Nutcracker Red’. Although tissue nutrient concentrations were at or below the critical level, general observations of each cultivar indicated that all plants were of commercial quality and almost indistinguishable between treatments. Poinsettia stem strength was not significantly affected by any fertilizer treatment used in this study.     

Root growth and N‐uptake activity of oilseed rape (Brassica napus L.) cultivars differing in nitrogen efficiency

Nitrate‐N uptake from soil depends on root growth and uptake activity. However, under field conditions N‐uptake activity is difficult to estimate from soil‐N depletion due to different loss pathways. We modified the current mesh‐bag method to estimate nitrate‐N‐uptake activity and root growth of two oilseed‐rape cultivars differing in N‐uptake efficiency. N‐efficient cultivar (cv.) ‘Apex' and N‐inefficient cv. ‘Capitol' were grown in a field experiment on a silty clayey gleyic fluvisol near Göttingen, northern Germany, and fertilized with 0 (N₀) and 227 (N₂₂₇) kg N ha^–1. In February 2002, PVC tubes with a diameter of 50 mm were installed between plant rows at 0–0.3 and 0–0.6 m soil depth with an angle of 45°. At the beginning of shooting, beginning of flowering, and at seed filling, the PVC tubes were substituted by PVC tubes (compartments) of the same diameter, but with an open window at the upper side either at a soil depth of 0–0.3 or 0.3–0.6 m allowing roots to grow into the tubes. Anion‐exchange resin at the bottom of the compartment allowed estimation of nitrate leaching. The compartments were then filled with root‐free soil which was amended with or without 90 mg N (kg soil)^–1. The newly developed roots and nitrate‐N depletion were estimated in the compartments after the installing period (21 d at shooting stage and 16 d both at flowering and grain‐filling stages). Nitrate‐N depletion was estimated from the difference between NO ‐N contents of compartments containing roots and control compartments (windows closed with a membrane) containing no roots. The amount of nitrate leached from the compartments was quantified from the resin and has been taken into consideration in the calculation of the N depletion. The amount of N depleted from the compartments significantly correlated with root‐length density. Suboptimal N application to the crop reduced total biomass and seed‐yield formation substantially (24% and 38% for ‘Apex’ and ‘Capitol’, respectively). At the shooting stage, there were no differences in root production and N depletion from the compartments by the two cultivars between N₀ and N₂₂₇. But at flowering and seed‐filling stages, higher root production and accordingly higher N depletion was observed at N₀ compared to N₂₂₇. Towards later growth stages, the newly developed roots were characterized by a reduction of root diameter and a shift towards the deeper soil layer (0.3–0.6m). At low but not at high N supply, the N‐efficient cv. ‘Apex’ exhibited higher root growth and accordingly depleted nitrate‐N more effectively than the N‐inefficient cv. ‘Capitol’, especially during the reproductive growth phase. The calculated nitrate‐N‐uptake rate per unit root length was maximal at flowering (for the low N supply) but showed no difference between the two cultivars. This indicated that the higher N‐uptake efficiency of cv. ‘Apex’ was due to higher root growth rather than higher uptake per unit of root length.     

Phosphorus in sequentially extracted fen peat soils: A K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy study

The speciation of phosphorus (P) in native and degraded peat soils is an analytical challenge, and synchrotron‐based P K‐edge X‐ray absorption near‐edge structure (XANES) is a suitable method to gain information on P species in soils and organic materials. The objective of the present study was to test if P K‐edge XANES reflected differences in P fractions in fen peat due to sequential extraction and peat degradation. We investigated each one top‐ and subsoil sample of a Fibric Histosol, which differed in the degree of humification (H8 vs. H5) and concentration of total P (P_t) (1944 mg kg^–1 vs. 436 mg kg^–1). In the topsoil, residual P, H₂SO₄‐P, and NaOH‐P accounted for roughly the same proportions of P_t (≈30%). In the subsoil, residual P (64% of P_t) was more abundant than NaOH‐P (21% of P_t) and H₂SO₄‐P (10% of P_t). Among many different P reference standards, the P XANES spectra reflected differences in mineral P more distinctive than in organic P compounds. Phosphorus XANES spectra of the residues after each sequential extraction step all showed a prominent white‐line peak at around 2152 eV. Stepwise removal of resin‐P, NaHCO₃‐P, and NaOH‐P were reflected mainly by the peak intensity but scarcely by distinct spectral features. Extraction with H₂SO₄ led to the disappearance of spectral features of Ca and Mg phosphates which is a first direct hint to these compounds in the peat. In conclusion, a combined sequential fractionation and spectroscopic (³¹P NMR, P K‐ and L‐edge XANES with linear‐combination fits) approach is proposed to overcome limitations of the present study and gain more insight into the P species in peat soils.     

Coal fly ash–based synthetic aggregates as potential alternative container substrates for ornamentals

This research was carried out to study the characteristics and the potential utilization of coal fly ash–based synthetic aggregates (CSA) with oil palm waste as an alternative container substrate for ornamental‐plant production. CSA only, oil palm waste only, and two mixing ratios of CSA with oil palm waste at the ratio of 1:5 and 1:10 (V/V) were utilized under this study. Zeolite was utilized as a standard substrate to compare characteristics of other substrates. The physical and chemical properties of all substrates were characterized. Scanning electron microscopy (SEM) of coal fly ash and CSA were conducted in order to study the structural configuration of the CSA. Developed CSA gave an alkaline pH (9.82), high electrical conductivity (96.1 mS m^–1), high cation concentrations, high water‐holding capacity, and low bulk density (0.56 g cm^–3) compared to zeolite. Mixing of CSA with oil palm waste at the ratio of 1:10 gave enhanced physical and chemical properties such as bulk density (0.25 g cm^–3), particle density (1.76 g cm^–3), air space (20.6%), total pore space (85.8%), total water‐holding capacity (652 mL L^–1), pH (6.18), and electrical conductivity (42.4 mS m^–1), which were in the established ideal substrate range. Moreover, SEM study revealed that CSA is a dual‐composite material, which had well enmeshed coal–fly ash particles in the fibrous paper‐waste matrix creating porous spaces within the aggregate. The growth of French marigold (Tagetes patula), which is a popular ornamental plant in Japan, was assessed using these newly developed substrates. The mixing ratio of CSA and oil palm wastes at 1:10 reported the best maximum growth and yield parameters of French marigold, with increase in shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, plant height, and number of flowers per plant by 51%, 93%, 54%, 150%, 19%, and 61%, respectively, compared to the zeolite. It is revealed that a mixture of CSA and oil palm waste at the ratio of 1:10 can be successfully utilized as an alternative container substrate for French marigold production.     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

Salinity effects on annual bedding plants in a peat‐perlite medium and solution culture

Annual vinca (Catharanthus roseus (L.) G. Don ‘Pink Carpet'), geranium (Pelargonium x hortorum L. H. Bailey ‘Jackpot'), and marigold (Tagetes erecta L. ‘First Lady') were grown in a sphagnum peat moss and perlite medium. Plants were irrigated with solutions of different salinity by the addition of 0.0, 1.0, 2.0, 4.0, and 8.0 g/1 of a NaCl and CaCl₂ mixture resulting in solution electrical conductivity (EC) values of about 1.3, 3.0, 4.5, 7.9, and 13.9 ds/m, respectively. In another experiment marigold and geranium were grown in solution culture containing the same salt mixture at 0.0, 1.0, 4.0, and 8.0 g/1 with EC values of 1.4, 3.0, 7.4, and 12.5 ds/m, respectively. All species showed some salinity tolerance up to 2.0 g/1 in peat‐perlite and 1.0 g/1 in solution culture as growth reductions were below 10% and no foliar injury occurred. Foliar injury occurred on marigold and geranium, but not annual vinca, at 4.0 and 8.0 g/1 in both growing media. On a concentration basis, recently mature leaves sampled from marigold grown in peat‐perlite contained more chloride (Cl) but less sodium (Na) than geranium and annual vinca. However results of the solution culture experiment showed that, with the exception of 1.0 g/1 treatment, geranium and marigold plants absorbed the same amount of Cl and Na when content was expressed on a mg/g dry weight basis. The low Na concentration in marigold leaves was a reflection of restricted translocation of Na from the roots to the shoots.     

Rate variables associated with P uptake,utilization and growth of mycorrhizal and nonmycorrhizal Leucaena leucocephala 1

A sequential harvest experiment was conducted in the greenhouse to determine relative growth rate (RGR), specific absorption rate (SAR) of P, P utilization rate (PUR) and P utilization efficiency (PUE) of vesicular‐arbuscular mycorrhizal (VAM) and nonmycorrhizal Leucaena leucocephala. Total P content, root length and total dry‐matter yield of mycorrhizal plants were significantly higher than those of nonmycorrhizal plants beginning on 15, 25 and 25 days after planting, respectively. The length of root colonized by Glomus aggregatum increased exponentially with time and leveled off 30 days after planting. In mycorrhizal plants, RGR of roots (based on total root length) was lower than those of RGR of infected roots till 30 days after planting, after which time the trend was reversed. Although, RGR based on dry‐matter yield was higher in mycorrhizal plants than in nonmycorrhizal plants, the differences observed were not statistically significant. SAR of P was higher in mycorrhizal plants than in nonmycorrhizal ones till 30 days after planting. Even though, total P contents and concentrations in mycorrhizal plants were higher than nonmycorrhizal plants, PUR and PUE were higher in nonmycorrhizal plants. These results indicate that, although VAM plants were very efficient in P absorption and accumulation, they were not superior to non‐VAM plants in P utilization. However, plant species forming effective symbiosis with VAM fungi are likely to be successful competitors in nutrient‐poor environments than plants not infected with the fungi.     

The effect of mineral fractions on physical and phosphorus-related chemical properties of peat-based substrates for pot plants

Physicochemical traits of peat-based pot substrates prepared from mixing of 20 or 40?vol.% of some different mineral fractions (sub. 1 to 7, subjected to decreasing amount of clay content of 66.1, 61.2, 49.7, 38.5, 26.0, 23.7 and 19.4%, respectively) with black peat were evaluated and then phosphorus uptake of poinsettia (Euphorbia pulcherima) simulated mechanistically as a case study pot plant. For preparation of substrate number 8, pure peat was mixed with 40?vol.% of the same mineral component as substrate number 6 (with 23.7% clay). Result revealed that adding different mineral fractions up to 40?vol.% to pure peat, water-holding capacity and total pore volume were reduced only by 11 and 15?vol.%, respectively. It was found that keeping the moisture content of peat-based substrates with 20?vol.% of mineral soils around 60%–70%, the optimum ventilation and enough free space of about 15%–25% will be provided around the root system. In addition, simulated P uptake did not change significantly with addition of 20?vol.% of different mineral components in peat-based substrates. As a result, P uptake mainly was dependent on the amount of plant available P level than different mineral fractions.     

EFFECT OF PHOSPHORUS APPLICATION ON HIERARCHICAL LATERAL ROOT MORPHOLOGY AND PHOSPHORUS ACQUISITION IN SOYBEAN

Root growth systems are hierarchical and sensitive to nutrient availability in soil. Lateral roots are an important component of plant root morphology. Phosphorus (P) availability regulates root branching in plants such as Arabidopsis thaliana, barley (Hordeum vulgare), and rice (Oryza sativa L.). However, little information is available for soybean (Glycine max L.). A pot experiment was conducted to determine the morphological characteristics of lateral roots of different orders and P acquirement of soybean seedlings under three levels of applied P of 0, 50 and 100 mg P kg^?1 soil. Root length, an important parameter of root characteristics, differed in four orders. Lateral roots in the second and third order contributed 39.4 and 34.2% of total root length, respectively. Moreover, since most of lateral roots were fine roots (roots having a diameter 0.5 mm), fine roots had a frequency distribution of 58.5 to 61.4% in the second and third orders. Phosphorus application significantly increased dry weight, total length and number of lateral roots in the four orders with the ranking of fourth > third > second > first (P ≤ 0.05), but did not affect the average length of a lateral root. Phosphorus application reduced the frequency distribution of fine lateral roots in the first and second orders, while increased in the third and fourth orders (P ≤ 0.05). Compared with the medium P application (50 mg P kg^?1 soil), the high P application (100 mg P kg^?1 soil) inhibited lateral root growth with decreases in root dry weight, root length and root number at all orders. Phosphorus concentration and content increased with the increase in P application. The correlation between characteristics of lateral root and P status in the plants varied among root orders. The length of lateral roots from first to third order had a positive correlation with P concentration in root and shoot, and had a good relationship with P content. Lateral root numbers at the second, third and fourth orders were significantly correlated with P content while no correlation was found with the average length of a lateral root. It is proposed that the main effect of P application appears to be on the lateral root initiation rather than on lateral root elongation, and P favors the lateral root formation of the higher orders. The total length and number of lateral root at the second and third orders play a more important role in P content than those at other lateral root orders.     

金盏菊栽培中园林废弃物堆肥与牛粪替代泥炭的效果分析

  【目的】   探究园林废弃物堆肥和牛粪有机肥替代进口泥炭用于金盏菊 (Calendula officinalis L.) 无土栽培的可行性。   【方法】   在添加10% 珍珠岩和10% 蛭石 (体积比) 不变的条件下，将园林废弃物堆肥和牛粪有机肥按照V_{园林废弃物堆肥}∶V_{牛粪有机肥} = 4∶0 (T1)、3∶1 (T2)、2∶2 (T3)、1∶3 (T4) 和0∶4 (T5) 配制栽培基质，并以T0处理 (10% 珍珠岩 + 10% 蛭石 + 80% 进口泥炭) 作为对照，总计6种栽培基质，用于金盏菊无土栽培。在180 天的温室培育后，测定并分析金盏菊总鲜质量、根鲜质量、地上部分鲜质量、根长、花朵数、冠幅以及株高等指标，利用冗余 (RDA) 分析探究影响金盏菊各形态指标的主要因素，并根据植株形态指标综合评价体系来评估金盏菊生长状况，最终确定不同配比的栽培基质品质的优劣。   【结果】   T0处理与T1处理的金盏菊根系发育优于T2～T5处理；T1～T5处理的金盏菊地上部分生长情况均优于对照组T0处理，其中T5处理的金盏菊株高、冠幅生长效果最优，T2处理的金盏菊花朵数增多效果最优；T1～T5处理金盏菊生物量积累均高于对照组T0处理。通过RDA分析可知，金盏菊地上部分的生长、总鲜质量和地上部分鲜质量主要受栽培基质的速效磷、速效钾、全氮、pH、电导率 (EC值) 和容重影响；金盏菊地下部分生长情况主要受栽培基质的EC值、有机质、总孔隙度、通气孔隙和持水孔隙影响。通过综合评价可知，T1处理栽培基质条件下金盏菊综合评价指数最高 (0.72)，金盏菊的综合生长状况最优。   【结论】   园林废弃物堆肥和牛粪有机肥替代进口泥炭进行金盏菊无土栽培可以有效提高金盏菊品质，降低我国花卉无土栽培对进口泥炭的依赖。其中，以10% 蛭石 + 10% 珍珠岩+80% 园林废弃物堆肥对金盏菊生长最为有利，既可利用廉价的有机固体废弃物，又可提高金盏菊的生产效益。      

Manganese in substrate clays—harmful for plants?

Mixtures of peat and substrate clays are commonly used as growth media for horticultural plant production. A quality protocol for substrate clays defines a threshold value of active manganese (Mn_act = sum of exchangeable and easily reducible Mn) in substrate clays of < 500 mg kg^–1 to prevent toxic reactions of plants. This threshold value was tested in experiments with peat‐clay blends under various growth conditions, and nutrient solution experiments were additionally conducted to investigate the effects of silicic acid and dissolved organic matter on the occurrence of Mn toxicity. Common bean (Phaseolus vulgaris L.) and hydrangea (Hydrangea macrophylla) plants were cultivated in different peat‐clay substrates and in peat under different moisture and pH levels. The clays varied in their Mn_act content from 4–2354 mg kg^–1. The results of the substrate experiments reveal that a threshold value for Mn in substrate clays is not justified, as plants grown in all peat‐clay substrates did not develop any Mn toxicity even at high substrate moisture or low pH conditions which are known to increase the Mn availability. The extraction of active Mn did not well reflect the Mn concentrations in plant dry matter and substrate solution. As plants tolerated high Mn concentrations in the substrate solution compared to the nutrient solution without toxicity symptoms, the influence of silicic acid and dissolved organic matter (DOM) on Mn toxicity was characterized in a nutrient‐solution experiment. Manganese toxicity was clearly diminished by silicic acid application, but not by DOM. The former effect probably explains the tolerance of bean plants in peat substrates where high silicon concentrations in the substrate solution were observed. Peat‐clay blends even provided up to five times more silicon to plants than pure peat.     

Effects of decreasing soil water content on seminal lateral roots of young maize plants

Soil micropores that contain water at or below field capacity cannot be invaded by seminal or first‐order lateral roots of maize plants because their root diameters are larger than 10 μm. Hence, at soil‐water levels below field capacity plant roots must establish a new pore system by displacement of soil particles in order to access soil water. We investigated how decreasing soil water content (SWC) influences growth and morphology of the root system of young maize plants. Plants were grown in rhizotrons 40 cm wide, 50 cm high, and approximately 0.7 cm thick. Five SWC treatments were established by addition of increasing amounts of water to soil and thorough mixing before filling the rhizotrons. No water was added to treatments 1–4 throughout the experiment. Treatment 5 was watered frequently throughout the experiment to serve as a control. Seminal‐root length and SWC in soil layers 0–10, 10–20, 20–30, 30–40, and 40–50 cm were measured at intervals of 2–3 d on scanner images by image analysis. At 15 d after planting, for treatments 1–4 shoot dry weight and total root length were directly related to the amount of water added to the soil, and for treatments 4 and 5, total root length and shoot dry weights were similar. Length of seminal roots visible at the transparent surface of the rhizotron for all treatments was highest in the uppermost soil layer and decreased with distance from the soil surface. For all layers, seminal‐root elongation rate was at maximum above a SWC of 0.17 cm³ cm^–3, corresponding to a matric potential of –30 kPa. With decreasing SWC, elongation rate decreased, and 20% of maximum seminal root elongation rate was observed below SWC of 0.05 cm³ cm^–3. After destructive harvest for treatment 1–4, number of (root‐) tips per unit length of seminal root was found uninfluenced over the range of initial SWC from 0.10 to 0.26 cm³ cm^–3. However, initial SWC close to the permanent wilting point strongly increased number of tips. Average root length of first‐order lateral (FOL) roots increased as initial SWC increased, and the highest length was found for the frequently watered treatment 5. The results of the study suggest that the ability to produce new FOL roots across a wide range of SWC may give maize an adaptive advantage, because FOL root growth can rapidly adapt to changing soil moisture conditions.     

Growth and nutrient content of poinsettia (Euphorbia pulcherrima Willd. ex Klotz) in a soilless growth medium containing sewage sludge pellet fertilizer

The effectiveness sewage sludge pellet fertilizer (SPF) as a nutrient source for containerized poinsettia (Euphorbia pulcherrima Willd. ex Klotz) was determined by comparing the growth and nutrient element content of ‘Eckespoint Celebrate 2’ plants grown with SPF in the growth medium versus plants fertilized with conventional water‐soluble fertilizer (WSF). Plants were grown in 1.6‐L pots of soilless growth medium with SPF incorporated at planting at the rates of 1.0, 1.5, 2.0, 2.5, or 3.0 gm nitrogen (N) pot^‐1. Sludge pellet fertilizer plants received either no WSF or a dilute solution of 2ON‐4.3P‐16.6 potassium (K) (50 mg N L^‐1) twice a week. Control plants had no SPF and were fertilized with WSF at 250 mg N L^‐1 twice a week. At the end of the experiment plant growth measurements were made, leaves were analyzed for their nutrient element content, and growth medium was analyzed for pH and electrical conductivity (EC). Plants grown with SPF, with or without dilute WSF, were of commercially acceptable quality, but were somewhat smaller than the control plants. Plants growing with SPF alone and no WSF developed a chlorosis suggestive of N deficiency which was largely prevented by the application of WSF. Foliar analysis revealed that N in the leaves of plants receiving SPF alone was at the critical level for deficiency established for poinsettia. In treatments where dilute WSF was applied, the N content of the leaves was within the normal range. The foliar levels of all other nutrients fell within the normal ranges established for poinsettia in all SPF treatments. In addition to N deficiency, high growth medium EC at planting and low EC by the end of the experiment might also explain the inhibition of growth with SPF versus the WSF control. Results of this study suggest that poinsettia can be successfully grown using SPF as the sole source of nutrition, however the best growth is possible only when a dilute solution of N‐containing WSF is applied on a regular basis.