Poinsettia growth,tissue nutrient concentration,and nutrient uptake as influenced by nitrogen form and stage of growth

Growth, development, and uptake of essential nutrients as influenced by nitrogen (N) form and growth stage was evaluated for ‘Freedom’ poinsettias (Euphorbia pulcherrima Willd. Ex Klotz.). Treatments consisted of five nitrate (NH₄ ⁺):ammonium (NO₃ ^‐) ratios (% NH₄ ⁺:% NO₃ ^‐) of 100:0, 75:25, 50:50, 25:75, and 0:100 with a total N concentration of 150 mg L^‐1. Plants were grown in solution culture for ten weeks under greenhouse conditions. Nutrient uptake data was combined into three physiological growth stages. Growth stage I (GSI) included early vegetative growth (long days). Growth stage II (GSII) began at floral induction and leaf and bract expansion (short days). Growth stage III (GSIII) was from visible bud through anthesis and harvest. Dry weights for all plant parts and height increased as the ratio of NO₃ ^‐ increased. Leaf area and bract area were maximized with 25:75 and 50:50 N treatments, respectively. Nitrogen treatments significantly affected foliar nutrient concentrations with calcium (Ca⁺⁺) and magnesium (Mg⁺⁺) being highest when NO₃ ^‐ was the predominant N form. Uptake of each macronutrient was averaged across all treatments and divided into physiological growth stages (GS) to identify peak demand periods during the growth cycle. The greatest uptake of NH₄ ⁺ and NO₃ ^‐ was from the early vegetative stage to floral induction (GSI). Phosphorus (P), potassium (K⁺), and Mg⁺⁺ uptake were greatest from floral induction to visible bud (GSII) and Ca⁺⁺ uptake remained relatively unchanged through GSI and GSII. Uptake was lowest for all nutrients from visible bud to anthesis (GSIII). Results from this study clearly indicate that peak demand periods for macronutrient uptake existed during the growth cycle of poinsettia.     

Tomato growth and nutrient uptake patterns as influenced by nitrogen form and light intensity 1

Tomato plants were grown in sand culture with NH₄ or NO₃ forms of N and at two levels of light. Plants were harvested at 0, 5, 9, or 12 days after starting treatments. NH₄‐N nutrition reduced growth, suppressed K, Ca, and Mg accumulation in shoot, increased P and N content and markedly reduced K, Ca, and Mg uptake per unit of root surface. Reduced light level decreased the toxic effects of NH₄ and markedly decreased NH₄ accumulation in shoots.     

Mineral composition of peanut tissue as influenced by irrigation water quality and irrigation method

Abstract

Peanut (Arachis hypogaea L.), is produced in the Virginia and North Carolina coastal plain where sodic deep well water sources are more readily available than high quality shallow well sources. The objective of this work was to determine the effect of irrigation water quality and irrigation method on the mineral composition of peanut tissue. Virginia‐type peanuts were grown on a Kenansville loamy sand (loamy, siliceous, thermic Arenic Hapludult) in Suffolk, VA from 1985 to 1987. Peanuts were irrigated with either overhead sprinklers or deep buried trickle lines using sodic deep‐well (142 m) and nonsodic shallow‐well (10 m) water. Trickle lines were buried 350 to 410 mm below each row. Sodic water had 220 mg Na/L, a pH of 8.5, and a sodium adsorption ratio (SAR) of 103. Non‐sodic water had 4.8 mg Na/L, a pH of 4.8, and an SAR of 3.1. Sodic water did not affect soil levels of Ca and Mg. Soil Na and pH were both higher to a depth of 900 mm in soil irrigated with sodic water. Sodic water appeared to reduce the concentration of Mg and increase the concentration of K in plant tissue. Plants from plots irrigated with sodic water concentrated Na in the stems and roots. Only in 1987, which was the driest year of the study, did seed concentration of plants irrigated with sodic water differ significantly from non‐sodic irrigated and non‐irrigated concentrations. Trickle irrigation reduced the amount of Na in the plants and may be the best way to use sodic irrigation water for peanut production.     

Rice and common bean growth and nutrient concentration as influenced by aluminum on an acid lowland soil

Aluminum (Al) toxicity is a major limiting factor for crop production in many acid soils in Brazil. Two greenhouse experiments were conducted to evaluate response of rice (Oryza saliva L.) and common bean (Phaseolus vulgaris L.) to Al levels on a Low Humic Gley acid soil. The Al levels created by liming were: 0,0.03, 0.10, 0.23, 1.03, and 3.83 cmol_c kg^‐1 of soil. Rice dry matter and grain yield were significantly improved (P<0.05) with increasing Al levels in the soil solution. However, common bean dry matter as well as grain yield were significantly (P<0.01) decreased with increasing Al levels. At 3.83 cmol_c Al kg^‐1 of soil, bean did not produce any dry matter or grain yield. On an average, Al decreased nutrient concentrations in the tops of rice plant except zinc (Zn) and manganese (Mn), but in bean crop almost all the nutrients concentrations were increased with increasing Al levels. Rice showed tolerance to Al toxicity, whereas, common bean was susceptible to toxicity of this element. For successful intensive crops production lime application will be necessary in Varzea soils especially for legume production.     

Root growth,nutrient uptake and use efficiency by roots of tropical legume cover crops as influenced by phosphorus fertilization

The root is an important organ which supplies water and nutrients to growing plants. Data related to root growth and nutrient uptake by tropical legume cover crops are limited. The objective of this study was to evaluate root growth of tropical legume cover crops and nutrient uptake and use efficiency under different phosphorus (P) levels. The P levels used were 0 (low), 100 (medium) and 200 (high) mg kg^?1 of soil and 5 cover crops were evaluated. Root dry weight, maximum root length, specific root length were significantly influenced by P and cover crop treatments. Maximum values of these root growth parameters were achieved with the addition of 100 mg P kg^?1 soil. The P X cover crops interaction for all the macro and micronutrients, except manganese (Mn) was significant, indicating variation in uptake pattern of these nutrients by cover crops with the variation in P rates. Overall, uptake pattern of macronutrients was in the order of nitrogen>calcium>potassium>magnesium>phosphorus (N > Ca > K > Mg > P) and micronutrient uptake pattern was in the order of iron>manganese>zinc>copper (Fe > Mn > Zn > Cu). Cover crops which produced maximum root dry weight also accumulated higher amount of nutrients, including N compared to cover crops which produced lower root dry weight. Higher uptake of N compared to other nutrients by cover crops indicated that use of cover crops in the cropping systems can reduce loss of nitrate (NO₃^?) from soil-plant systems. Increase in root length and root dry weight with the addition of P can improve nutrient uptake from the soil and less loss of macro and micronutrients from the soil-plant systems.     

Mineral content of soft winter wheat as influenced by nitrogen fertilization and management

Abstract

Soft winter wheat is used to make cookies, cakes, crackers, donuts, etc., and as such, grain nitrogen content (as protein) is an important determinant of flour quality and eventually the quality of the products made from it. Intensive Cereal Management (ICM) techniques are being adapted throughout the midwestem United States to increase grain yield and crop profits. The effect of additional/altered management inputs on grain nutrient content is important since they may be detrimental to subsequent product quality. The objective of this study was to determine the effects of cultivars and ICM inputs on grain nutrient content Identical field studies were conducted in 1985 and 1986 at Columbus, OH, East Lansing, MI, and Madison, WI containing three cultivars subjected to each of three management treatments differing in seeding and nitrogen rates, and the use of a fungicide, Propiconazole (Tilt) and plant growth regulator, Ethephon (Cerone). Nitrogen in the form of urea was applied at specific growth stages, and rates adapted to the soil type and previous crop of each study location so that similar amounts of N would be available to the wheat crop at each location.

Both environment and cultivar had significant effects on the leaf content of some but not all nutrients. The combination of increased seeding and nitrogen rates had no effect on grain yield but increased grain nitrogen content, leaf N, Ca, Mg, Mn, and Fe content The use of Tilt and Cerone also increased grain yield and nitrogen content, but lowered leaf K, Ca, and Mg.     

Growth,yield and fruit quality of cherry tomato irrigated with saline water at different developmental stages

Water shortage is a serious environmental and agricultural problem and saline underground water has been widely used to make up the fresh water shortage in northwestern China. An open-field experiment was conducted to establish a proper irrigation scheme with saline water for cherry tomato in the Minqin oasis, where very severe salinization occurs. The experiment had four treatments including fresh or saline irrigation over the crop season (control, C, T3), fresh/saline-water irrigation change on days after thinning 50 (DAT 50, T1) and saline/fresh irrigation change on DAT 50 (T2). Leaf area index (LAI), photosynthesis rate (P_n), transpiration rate (T_r), leaf dry matter (LDM), stem dry matter (StDM), yield, marketable fruit and total soluble solids (TSS) of tomato were measured. Saline irrigation, irrespective of the timing, significantly decreased maximum LAI, LDM and StDM, P_n, T_r and stomatal conductance but significantly stimulated water use efficiency. The reduction in maximum LAI, LDM and StDM was lower in T2 than in T1 and T3. Harvest index (HI) and TSS were higher in T2 and T3 than in T1 and C. Marketable fruit had no significant change in T2 but significantly declined in T1 and T3. Maximum saturated soil conductivity without yield reduction (the salt tolerance threshold) was 3.69?dS m^?1. Total yield of tomato would decrease by 9.85% with one unit increase of soil salinityhigher than the threshold. Final yield significantly reduced by 24.6% and 23.1% in T1 and T3 treatments, respectively. Our results suggest that irrigation with saline water before DAT 50 and fresh water after DAT 50 should be advocated for cherry tomato plantation in water-scarce areas like the Minqin oasis.     

Mineral composition of bermudagrass as influenced by maturity and nitrogen in a cool,temperate environment

Abstract

Warm‐season grasses contribute substantially to herbage supply during summer in cool‐temperate environments, when the productivity of cool‐season grasses declines. Herbage digestibility as well as mineral concentration may limit the amount of essential nutrients available to meet grazing animal requirements. A field study was conducted to determine the productivity and quality of a new selection of bermudagrass [Cynodon dactylon (L) Pers.], RSl, which is capable of growth and persistence in areas where other cultivars of bermudagrass are likely to winterkill. Concentrations and uptake of mineral nutrients in RSl bermudagrass were determined in response to N levels (0, 120, 240, and 360 kg N/ha) and delayed initial harvest (advancing maturity) at 2, 4, and 6 weeks after active growth began. Concentrations of P, Ca, K, Mg, and S in early season growth generally declined with advancing maturity. Concentrations of elements showed mixed response to N levels, and generally were not affected by treatments late in the growing season. Early in the growing season, mineral uptakes increased with advancing maturity. Increasing N levels early and late in the growing season enhanced mineral uptake. Mineral ratios, such as N:S and K (Ca + Mg), were within critical limits for adequate animal nutrition, but the Ca:P ratio was less than 2:1 and could contribute to known mineral‐related disorders in male sheep. Herbage mineral concentrations of RSl generally met or exceeded mineral nutrient requirements for sheep and cattle in growing or lactating physiological states.     

Tillering,nutrient accumulation,and yield of winter wheat as influenced by nitrogen form 1

When grown with mixtures of nitrate‐nitrogen (NO₃‐N) and ammonium‐nitrogen (NH₄‐N) (mixed N) spring wheat (Triticum aestivum L.) plants develop higher order tillers and produce more grain than when grown with only NO₃. Because similar work is lacking for winter wheat, the objective of this study was to examine the effect of N form on tillering, nutrient acquisition, partitioning, and yield of winter wheat. Plants of three cultivars were grown to maturity hydroponically with nutrient solutions containing N as either all NO₃, all NH₄, or an equal mixture of both forms. At maturity, plants were harvested; separated into shoots, roots, and grain; and each part analyzed for dry matter and chemical composition. While the three cultivars varied in all parameters, mixed N plants always produced more tillers (by a range of 16 to 35%), accumulated more N (28 to 61%), phosphorus (P) (22 to 80%), and potassium (K) (11 to 89%) and produced more grain (33 to 60%) than those grown with either form alone. Although mixed N‐induced yield increases were mainly the result of an increase in grain bearing tillers, there was cultivar specific variation in individual yield components (i.e., tiller number, kernels per tiller, and kernel weight) which responded to N form. The presence of NH₄ (either alone or in the mixed N treatment), increased the concentration of reduced N in the shoots, roots, and grain of all cultivars. The effect of NH₄ in either treatment on the concentrations of P and K was variable and depended on the cultivar and plant part. In most cases, partitioning of dry matter, P, and K to the root decreased when NH₄ was present, while partitioning of N was relatively unaffected. Changes in partitioning between the shoot and grain were affected by N treatment, but varied according to cultivar. Based on these data, the changes in partitioning induced by NH₄ and the additional macronutrient accumulation with mixed N are at least partially responsible for mixed‐N‐induced increases in tillering and yield of winter wheat.     

Movement of urea and its hydrolysis products as influenced by moisture content and urease inhibitors

A laboratory experiment was conducted on an Aquic Udifluvent Belgian soil in order to study the movement of urea and its hydrolysis products. This study was carried out at two moisture levels (10 and 20%) upon the addition of three types of urease inhibitors: hydroquinone, phenylphosphorodiamidate (PPDA), and N-(n-butyl)phosphorothioic triamide (NBPT). The results clearly show the effects of the inhibitors in retarding the hydrolysis of urea. The highest effect was observed with NBPT, followed by hydroquinone, and PPDA. The effect was more pronounced at 10% than at 20% moisture content. It was clear that subsequent nitrification of the NH _inf4 ^sup+ formed was inhibited at the lower moisture level. At 10% moisture, from the 7th day of incubation on, some NH _inf4 ^sup+ moved about 3 cm and reached the top of the soil column. At 20% moisture, no NH _inf4 ^sup+ reached the surface as it was quickly nitrified. After 17 days of incubation and at 20% moisture, the total mineral N was more or less homogeneously distributed within the soil column. In contrast, at 10% moisture, the remaining urea and the hydrolysis products were still concentrated at the place of application. The distribution of urea and its hydrolysis products was comparable with 7 days of incubation at 20% moisture and 17 days at 10%.     

Mineral composition of kenhy tall fescue as affected by nutrient solution concentrations of Mg and K

Four greenhouse sand culture experiments were conducted with Kenhy tall fescue, a Lolium multiflorum X Festuca arundinacea hybrid derivative. These experiments were conducted to characterize mg accumulation and the chemical composition of Kenhy under various combinations of Mg, K, and N solution concentrations. Of primary interest was the shape and magnitude of response of tissue Mg concentration to solution K levels and potential for Mg accumulation that exists in Kenhy under low solution K levels. Analyses were made for Mg, K, Ca, Na, N, and nitrate.

Increased Kg concentrations were observed with increased solution Mg. Increased solution K was in all cases associated with lower concentrations of Mg. Under conditions of low solution K (0.125 mM) and adequate Mg (0.25 mM), Mg accumulation exceeded 1.0%. Increased solution N was associated with decreased Mg concentrations. Both the linear and quadratic components of Mg solution concentration contributed significantly to increased tissue Mg. Hawever, the linear component of K solution concentration was sufficient to account for decreased tissue Mg. The reduction of tissue Mg to solution K was greater at higher concentrations of K.

Potassium accumulation significantly increased with increased solution K. Increased solution Mg was associated with lower tissue K in which the greatest reduction in K accumulation occurred with the first Mg addition.

Calcium accumulation decreased with increased solution K. Higher solution Mg was associated with lower tissue Ca levels while higher levels of N were associated with increased tissue Ca. Sodium accumulation was significantly reduced by increased K concentrations but neither Mg nor N was effective in consistently altering tissue Na concentrations.

From these experiments it is evident that Kenhy tall fescue has the absorptive capability for high levels of Mg under conditions of low levels of solution K. However, even small increments of solution K were shown to be capable of substantially reducing the Mg content, Thus, the selection of forage grasses for Mg absorptive capability must be conducted under conditions of high solution K, if large improvements on present forage materials are to be obtained. In addition, the inverse relationship between Mg and K present in Kenhy seedlings confirms the need to consider K fertilization recommendations in attempting to increase forage Mg durirg the grass tetany period.     

Effect of oxygen deficiency on uptake of water and mineral nutrients by tomato plants in soilless culture

The consequences of oxygen deficiency on the root system of tomato plants in soilless culture at the beginning of the flowering stage were assessed over a 72‐hour period. The study of water uptake and oxygen depletion in the medium was conducted using a process of continuous computerized data processing. Fluctuations in composition of the nutrient solution were monitored every two hours through an analysis of samples. Oxygen deficiency of the nutrient solution had immediate effects on the water and nutrient uptake of the whole plant. The root asphyxia of a tomato plant caused a 20 to 30% decrease of water uptake after 48 hours. After 10 hours it also leads to the end of the uptake process of the nutrients except nitrates. Potassium (K) was the nutrient most sensitive to oxygen deprivation since an efflux into the culture medium was observed after only 4 hours of deprivation. Nitrate uptake was the least affected by oxygen deficiency. The persistent appearance of nitrite in the culture medium 12 hours after the beginning of the asphyxia process could be caused by the reduction of nitrates by the root system of the tomato plant. The plant would use the oxygen from the reduction reaction to ensure the water and nitrate uptake processes which are the two most important limiting factors of plant nutrition. Thus it seems that under root asphyxia conditions the plant would adapt to the new condition by relying on a metabolism of the “nitrate respiration”; type.     

Yield responses and nutrient uptake of chive as affected by nitrogen,phosphorous, and potassium fertilization

Abstract

Field experiments were conducted on Maraval clay loam (fine, kaolinitic, isohyperthermic Oxic Tropudalfs) and River Estate sandy clay loam (fine loam, micaceous, isohyperthermic Fluventic Eutropepts) in Trinidad and Tobago to determine the effect of rate of nitrogen (N) in the presence and absence of phosphorus (P) and potassium (K) on the growth, yield, and plant tissue nutrient content for chive (Allium spp.) grown for the fresh market. Nitrogen had a significant effect (p<0.001) on the average number of tillers/plot, the average number of leaf blades/plot and subsequently on the marketable yield (p<0.05) of the crop. Application of low rates of applied N (67 kg/ha) gave the highest values although there being significant differences (p<0.005) between soils with higher values recorded on the River Estate clay loam. On the Maraval clay loam, application of increased N had no positive effect on tissue N except in the presence of P and K fertilizers. Significant differences (p<0.05) were obtained for the plant tissue nutrient content between treatment and between soils, except in the case of plant tissue K content where no significant differences were obtained between soils.     

Effect of calcium concentration in nutrient solution before and after inoculation with Ralstonia solanacearum on resistance of tomato seedlings to bacterial wilt

We previously reported that calcium (Ca) nutrition in tomato (Lycopersicon esculentum Mill.) significantly affected the resistance to bacterial wilt caused by Ralstonia solanacearum Smith. To elucidate the mechanisms underlying the Ca-dependent resistance, the effect of the Ca concentration in the nutrient solution applied before and after inoculation with the pathogen on the resistance of tomato seedlings to bacterial wilt was studied. One week before inoculation, seedlings were transferred to nutrient solutions containing Ca at concentrations of 0.4, 4.4, or 20.4 mM. Soon after inoculation, the seedlings that were treated with each concentration of Ca before inoculation were transferred to solutions containing the same three concentrations of Ca. Although the disease development was not affected by the concentration of Ca in the solution before inoculation, a higher concentration of Ca after inoculation reduced the disease severity. This result suggests that the concentration of Ca in the host, especially in the cell walls, before infection may not be directly involved in the Ca-dependent resistance of tomato seedlings to bacterial wilt.     

Grain yield,stalk rot,and mineral concentration of fertigated corn as influenced by N P K

Peanut (Arachis hypoaaea L.) is a major cash crop in Georgia. Corn (Zea mays L.) is the preferred rotation crop, but is often not profitable because of large inputs costs. Fertilizer comprises approximately 50% of the variable production costs of irrigated corn. There is interest in reducing fertilizer inputs, in particular N, to reduce variable costs and decrease nitrate leaching to groundwater, but yields may suffer. Our objective was to investigate the effect of N, P, and K fertilizer rates on the yield of N‐fertigated corn in a corn/peanut rotation. Field experiments were conducted during 1987 and 1988 on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudult) at Tifton, GA. Treatments were three rates each of N, P, and K fertilizer in a complete factorial. Nitrogen, P, and K rates were 168, 252, 336 kg N ha^‐1 yr^‐1; 44, 73, 103 kg P ha^‐1 yr^‐1; and 84, 223, and 363 kg K ha^‐1 yr^‐1, respectively. Grain yields were large, 12.6 and 10.4 Mg ha^‐1 in 1987 and 1988, respectively, but not affected by N, P, or K rate. Since the lower rates of N, P, and K were less than recommended, fertilizer use efficiency for fertigated corn can be improved, for at least one year, by reducing N, P, and K fertilizer rates to less than current recommendations. Rates of N, P, and K did not result in a substantial difference in the concentration of essential nutrients. Stalk rot was limited (< 15%), but decreased with increasing K fertilizer rate.     

Encapsulation of lycopene extract from tomato pulp waste with gelatin and poly(gamma-glutamic acid) as carrier

Tomato pulp waste, a byproduct obtained during the processing of tomato juice, has been shown to be a rich source of lycopene. The objectives of this study were to use gelatin and poly(gamma-glutamic acid) (gamma-PGA) as coating materials for the encapsulation of lycopene extract from tomato pulp waste. Initially, lycopene was extracted with supercritical carbon dioxide, followed by microencapsulation using an emulsion system consisting of 4.5% gelatin, 10% gamma-PGA, and 4.8% lycopene extract. Analysis of differential scanning calorimetry revealed that the thermal stability of the coating material could be up to 120 degrees C, with a mean particle size of 38.7 microm based on Coulter counter analysis. The total weight of microencapsulated powder was 617 microg with the yield of lycopene being 76.5%, indicating a 23.5% loss during freeze drying. During storage of microencapsulated powder, the concentrations of cis-, trans-, and total lycopene decreased along with increasing time and temperature. A fast release of lycopene in the powder occurred at pH 5.5 and 7.0, while no lycopene was released at pH 2.0 and 3.5.     

Manganese toxicity in bush bean as affected by concentration of manganese and iron in the nutrient solution

An experiment was conducted to clarify the relationship between Mn toxicity and Fe deficiency in bush snap bean (Phaseolus vulgaris L. cv. ‘Wonder Crop No. 2'). Seedlings were grown in full strength Hoagland No. 2 solution at pH 6.0 for ten days. Six concentrations of Mn as MnCl₂.4H₂O were used in combination with three concentrations of Fe as FeEDTA.

Toxicity symptoms, induced by low levels of Mn (0.1 ppm and above), included: small brown necrotic spots and veinal necrosis on primary leaves; necrosis on primary leaf petioles; interveinal chlorosis, with or without brown necrotic spots, on trifoliate leaves; and brown necrotic spots on stipules. Manganese toxicity symptoms were alleviated or prevented by increasing Fe concentration in the nutrient solution.

Manganese concentration in the leaves increased with increasing Mn and decreased with increasing Fe concentration in the nutrient solution, Iron concentration in the roots increased with increasing Fe concentration in the nutrient solution; however, Fe concentration in the leaves was not significantly affected by increasing Mn concentration in the solution culture. Manganese toxicity symptoms developed when Mn concentration in the leaves reached about 120 ppm.

A decrease in the Fe/Mn ratio in the nutrient solution resulted in a proportionate decrease in that of the leaves. Manganese toxicity symptoms occurred when the Fe/Mn ratio in the solution was 10.0 and below, or when the ratio in the leaves was less than 1.5. The ratio of Fe/Mn in the solution required for optimum growth of ‘Wonder Crop No. 2’ bean, without Mn toxicity symptoms, was in the range of 20.0 to 25.0.

Results indicate that the chlorosis on bush bean leaves induced by excessive Mn in the nutrient solution was due to excessive accumulation of Mn and not to Fe deficiency.     

Influence of compost of sewage sludge and low-quality water on pesticide uptake by tomato plants grown in an iron mine soil

Purpose

In mine soils, especially from arid or semiarid areas, the use of low-quality water for irrigation is a usual practice. Therefore to fill this gap, different experiments have been carried out to evaluate the effect of compost, pesticide and wastewater on the growth of tomato plants in a mine soil located at an iron extraction area.

Materials and methods

Soils proceeded from Alquife mine wastes whose most outstanding characteristics are alkaline conditions, low organic matter and electrical conductivity and high As concentration. The compost of sewage sludge (CSL) used to amend this soil had a slightly acid pH (6.8), EC 3.0?±?0.07 dS m^-1 (1/10 ratio, m/V) and 10 % organic carbon (OC) content. Irrigation was performed with distilled water (DW) or wastewater (WW) and two pesticides, the insecticide thiacloprid and the fungicide fenarimol, were applied to the soil. Tomato was grown directly from seeds on each pot. Four treatments with addition of pesticides were considered. For comparison purposes, two additional treatments without pesticides were also included.

Results and discussion

Addition of compost of sewage sludge led to a significant and sustained increase of soil OC content and dehydrogenase activity, while irrigation with wastewater had a slight or negligible effect on both properties. The plant species responded negatively to wastewater irrigation when this practice was undertaken with the application of both pesticides. No detectable amounts of thiacloprid, a relatively unstable and polar insecticide, were found in soil. The concentration of fenarimol in soil was higher after amendment with compost, but was not modified by irrigation with wastewater. In tomato shoots, the amounts of both pesticides were inversely correlated with final soil organic carbon, indicating that this soil property is relevant for their plant uptake. Besides, fenarimol concentrations in the soil and the tomato shoots were inversely related (r?=??0.836).

Conclusions

Tomato was not able to grow healthy in Alquife mine soil without compost addition. The irrigation with wastewater only reduced plant growth when used in combination with pesticides. Uptake of both pesticides by tomato plants was negligible according to the low bioaccumulation factor values, but was almost doubled for wastewater irrigation. Caution should be taken with the use of treated wastewater, because it may reduce plant growth in tomato that is a species sensitive to salinity.

     

Factors related to iron uptake by dicotyledonous and monocotyledonous plants. II. The reduction of Fe3+ as influenced by roots and inhibitors

In a companion paper (10), varieties of four plant species [two monocotyledons (oats and corn) and two dicotyledons (soybeans and tomato)] were shown to differ widely in their ability to respond to Fe‐stress. The ability of the more Fe‐efficient varieties was manifested by a lowering of the pH of the ambient medium of the root and/or by loss of reductants from the root. Both effects can enhance uptake of Fe by the roots, since Fe is taken up primarily, if not entirely, as Fe²⁺ ions. Thus, a given stressed plant has a means, under some degree of metabolic control, for modifying the root environment and, thereby, alleviating its chlorotic condition.

The present investigation deals with environmental factors, particularly chemical inhibitors, modifying the effectiveness of the stress response. Without inhibitors, excised root samples of the four species exhibited a wide range of abilities to reduce Fe³⁺ to Fe²⁺. Roots of the dicotyledonous species reduced about twice as much Fe³⁺ as did equal weights of the monocotyledonous species. Iron‐efficient tomato, soybean, and oat roots reduced more Fe³⁺ than did roots of the Fe‐inefficient varieties. The two corn varieties were about equal in their effectiveness.

Comparable samples of roots were also exposed to chemicals that induce or aggravate Fe chlorosis. Those found to be very effective inhibitors of Fe³⁺ reduction by the roots included: hydroxide, orthophosphate, pyrophosphate, Cu²⁺ and Ni²⁺. Other ions (includ ing Mn²⁺, Zn²⁺ and molybdate) and ethyl ammonium phosphate also inhibited Fe³⁺ reduction but to a lesser degree. Citrate, however, enhanced Fe³⁺ reduction. The degree of inhibition or enhancement differed for each of the varieties. In general, the Fe‐efficient plants were best able to reduce Fe³⁺ in spite of the inhibitory influence of the imposed treatments. Thus, our findings indicated that inhibition of the Fe³⁺ ‐reduction process at, or near, the periphery of the root is an apparent cause of Fe chlorosis.