Chelating resin method for estimation of sludge‐cadmium bioavailability

Abstract

A chelating resin procedure was developed to predict the plant uptake of Cd by municipal sewage sludges applied to land. Seventeen anaerobically digested sludges were sampled to give a range of total Cd content of 0.07 to 2.02 mmol/kg. Sludge suspensions [20 g in 100 mL 0.05 M Ca(NO₃)₂] were equilibrated with 1 g Chelex 100 resin placed in dialysis tubing and shaken at 200 rpm for 16 h. Resin‐extractable Cd was compared with sludge solution Cd (CdT and Cd²⁺) in equilibrium with 0.05 M Ca(NO₃)₂, and 0.05 M Ca(NO₃)₂ containing 50 (μM Na‐EDTA (ethylenediaminetetraacetate). Resin extractable Cd was correlated with Cd uptake by sudax, a sorghum/sudangrass hybrid (Sorghum bicolar), grown in Spinks loamy sand (Typic Udipsamment) amended with each of the sludges to give a constant Cd concentration of 22 μmol/kg soil.

Resin extractable Cd ranged from < 0.1 to 48 μmol/kg. Resin extracted between zero and 5.3% of total sludge Cd. Resin extractable Cd was highly correlated with CdT and Cd²⁺ in 0.05 M Ca(NO₃)₂ (R² = 0.97 and 0.98, respectively), and with 0.05 M Ca(NO₃)₂ containing 50 μM NaEDTA (R² = 0.97 and 0.98, respectively). There was a lower correlation with total sludge Cd and soil solution Cd (R² = 0.53 and 0.63, respectively). Cadmium concentration in sudax was highly correlated with resin extractable sludge Cd (R² = 0.92). When the two sludges with highest total sludge Cd were dropped, the correlation dropped (R² = 0.57), but resin extractable Cd predicted Cd uptake as effectively as CdT and Cd²⁺ in Ca(NO₃)₂ or Ca(NO₃)₂/EDTA. Resin extraction appears to be a promising method of assessing the potential bioavailability of sludge Cd.     

Comparing Nutrient Availability in Low-Fertility Soils using Ion Exchange Resin Capsules

Assessing the nutrient status of low-input, low-fertility desert soils poses some unique challenges. Commonly used soil analysis procedures and resin capsules generally assess nutrient status of fertile agricultural soils. Ion-exchange resin capsules (Unibest Company, Bozeman, Mont.) provide a viable alternative. A study was conducted to determine effectiveness of resin capsules to extract low levels of nutrients applied to native soils. Loamy sand and sandy clay loam desert soils from Utah were treated with combinations of four rates of nitrogen (N) as ammonium nitrate (34–0–0), three rates of phosphorus (P) as phosphoric acid (0–72–0), and two rates of iron sulfate (FeSO₄·7H₂O) and zinc sulfate (ZnSO₄·7H₂O) (include an untreated control). Each soil treatment was implanted with a resin capsule placed into either 250 or 1000 cm³ of soil after addition of water equivalent to 50% field capacity and incubated for either 60 or 120 days at 25 °C. After the appropriate incubation time, capsules were washed and extracted using 2 M hydrochloric acid (HCl), and the extract was used to measure iron (Fe), ammonium (NH₄)-N, nitrate (NO₃)-N, sulfur (S), and zinc (Zn). Conventional soil tests were completed on incubated soils (60 or 120 days). Resin capsules reflected NH₄-N and P fertilizer applied at low rates in the loamy sand but not in the sandy clay loam. Neither Fe nor Zn application was reflected in resin capsules, but the accompanying S was clearly quantified. In comparison to conventional soil test procedures, resin capsule NH₄-N was clearly a better indicator than KCl-extractable NH₄-N; resin capsule NO₃-N was effective, but not as good an indicator as water extraction; and resin capsule P was reflective of soil applied P in loamy sand but not in sandy clay loam, whereas sodium bicarbonate was effective in both soils. Resin capsules show promise for use in low-input conditions, but additional understanding of interactions in variable soils is needed.     

Evaluating Nutrient Availability in Semi-arid Soils with Resin Capsules and Conventional Soil Tests,II: Field Studies

Commonly used soil analyses and resin capsules are employed to assess nutrient status in agriculture soils, but their validity in semi-arid ecosystems is unknown. Field studies with six rates of nitrogen (N) and phosphorus (P) application were established on crested wheat stands in both Rush Valley and Skull Valley, Utah. Resin capsule and conventional soil tests for nitrate (NO₃)-N, ammonium (NH₄)-N, and P were administered, and plant nutrient status was examined. Resin capsules were removed and replaced, and soil samples were taken every 90 d for 1 year. Concentration of P in resin capsules was not related to P rate but sodium bicarbonate (NaHCO₃)-extracted P was, and resin NH₄-N, resin NO₃-N, potassium chloride (KCl)–extracted NO₃-N and KCl-extracted NH₄-N were all related to N rate. Only KCl-extracted NO₃-N and NH₄-N levels related to plant tissue N. Overall, traditional soil tests are more effective than resin capsules in semi-arid field conditions, but resin capsules have potential for use in N assessment.     

The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

Purpose

This study examined the usefulness of ¹⁵N natural abundance (δ¹⁵N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L^?1 NO₃^?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ¹⁵N of NH₄⁺-N and NO₃^?-N in the top 5 cm soil before and after the incubation, and δ¹⁵N of NO₃^?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ¹⁵N of NH₄⁺-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ¹⁵N of NH₄⁺-N and significant increase in δ¹⁵N of NO₃^?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.

Conclusions

The δ¹⁵N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ¹⁵N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.

     

Evaluating Nutrient Availability in Semi-arid Soils with Resin Capsules and Conventional Soil Tests,I: Native Plant Bioavailability under Glasshouse Conditions

Resin capsule technology developed for nutrient analysis in agriculture soils recently has been expanded to semi-arid soils without knowledge of effectiveness. This study determined if resin nutrient adsorption is correlated to plant uptake and yield in semi-arid soils. Two soils were treated with five rates of nitrogen (N) and four rates of phosphorus (P), placed in pots with resin capsules, seeded with squirreltail grass (Elymus elymoides), and grown in a glasshouse for 120 d followed by biomass determination and nutrient analysis of capsules, soils, and tissues. Yield and total nutrient uptake were highly correlated to fertilizer application rates, resin ammonium (NH₄)-N, and sodium bicarbonate (NaHCO₃)–extracted P; marginally correlated to resin and potassium chloride (KCl)–extracted nitrate (NO₃)-N, and unrelated to KCl-extracted NH₄-N and resin P. Use of resin capsules to estimate N bioavailability is promising, but P bioavailability is not effectively estimated with resin capsules; instead traditional NaHCO₃ extraction is recommended.     

Effects of Nitrogen Levels and Nitrate/Ammonium Ratios on Oxalate Concentrations of Different Forms in Edible Parts of Spinach

Two hydroponic experiments were carried out to investigate the effects of nitrogen (N) levels and forms on the oxalate concentrations of different form in edible parts of spinach. Nitrogen was supplied at five levels (4, 8, 12, 16, 20 mM) in Experiment 1 and five ratios of nitrate (NO₃ ^?) to ammonium (NH₄ ⁺) (100/0, 75/25, 50/50, 25/75, 0/100) at a total N of 8 mM in Experiment 2. Biomass of spinach increased markedly from 4 mM to 8 mM N and reached the flat with further increase in N. The total oxalate and soluble oxalate in leaves and shoots (edible parts) increased significantly with increasing N levels from 4 to 12 mM, while the total oxalate and insoluble oxalate decreased markedly when N level was further increased from 12 to 20 mM. Oxalates of different forms in petioles increased first and then decreased and elevated again with increasing nitrogen levels. In the second experiment, decreasing NO₃ ^?/NH₄ ⁺ ratios markedly increased at first and then significantly decreased the biomass of spinach plants and the maximum biomass was recorded in the treatment of the NO₃ ^?/NH₄ ⁺ ratio of 50:50. The oxalate concentrations of different form in leaves and shoots were all decreased obviously as the ratio of NO₃ ^?/NH₄ ⁺ decreased from 100:0 to 0:100. Concentrations of total oxalate and soluble oxalate in petioles could be reduced by increasing ammonium proportion and were the lowest as the ratio of NO₃ ^?/NH₄ ⁺ was 50:50 and insoluble oxalate decreased as nitrate/ammonium ratio decreased. The concentrations of oxalate forms in leaves were all higher than those in petioles and soluble oxalate was predominant form of oxalates in both trials. It is evident that high biomass of spinach can be achieved and oxalate concentrations of different forms can be reduced by modulating N levels and NO₃ ^?/NH₄ ⁺ ratio, so this will benefit for human health especially for those people with a history of calcium oxalate kidney stones.     

Unlocking fixed soil phosphorus upon waterlogging can be promoted by increasing soil cation exchange capacity

Phosphorus (P) adsorbed by iron (Fe) oxyhydroxides in soil can be released when the Fe(III) minerals are reductively dissolved after soil flooding. However, this release is limited in tropical soils with large Fe contents and previous studies have suggested that P sorbs or precipitates with newly formed Fe(II) minerals. This hypothesis is tested here by scavenging Fe²⁺ in flooded soils by increasing the cation exchange capacity (CEC) of soil through resin application (30 cmol_c kg^?1; Na‐form). Three soils from rice paddies with contrasting properties were incubated in aerobic and anaerobic conditions with or without resin and with or without addition of organic matter (OM) to stimulate redox reactions. Dissolved Fe was 0.1–1.1 mm in unamended anaerobic soils and decreased to less than 0.07 mm with resin addition. Anaerobic soils without resin and aerobic soils with or without resin had marginal available P concentrations (<2 mg P kg^?1; anion‐exchange membrane P). In contrast, available P increased 3‐ to 14‐fold in anaerobic soils treated with resins, reaching 16 mg P kg^?1 in combination with extra OM. Application of Ca‐forms of resin did not stimulate P availability and dissolved Ca concentrations were larger than in unamended soils. Resin addition can increase P availability, probably by a combination of reducing solution Fe²⁺ (thereby limiting the formation of Fe(II) minerals) and increasing the OM solubility and availability through reducing dissolved Ca²⁺. The soil CEC is a factor controlling the net P release in submerged soils.     

The significance of plant energy status for the uptake and incorporation of NH4-nitrogen by young rice plants

Uptake and assimilation of inorganic N in young rice plants has been studied with labelled N (N-15). Depletion of the plants' carbohydrate content, obtained by a preceding dark period, resulted in a drastic reduction of NH₄ ⁺-N uptake. Plants exposed to low light intensity showed diminishing NH₄ ⁺-N uptake rates as compared with plants exposed to full light intensity, the latter showing constant NH₄ ⁺-N uptake rates during the whole experimental period. The percentage of labelled insoluble N in total labelled N was not significantly affected by a preceding dark period, whereas the low light intensity resulted in a lower proportion of insoluble N in roots and shoots. The incorporation of labelled N into the insoluble fraction (proteins, nucleic acids) was higher in plants fed with NH₄ ⁺-N than in those fed with NO₃ ^-.

The uptake of NH₄ ⁺-N was not significantly affected by NO₃ ^-, whereas the NO₃- uptake rate was considerably reduced in the presence of NH^{4 +}-N. Low energy status of plants affected the nitrate uptake more than the uptake of NH₄ ⁺-N. The results show that uptake and assimilation of inorganic N depend much on the energetic status of plants. Nitrate uptake and assimilation is more sensitive to low energy conditions than NH₄ ⁺-N.     

Symbiotic N nutrition, C assimilation, and plant water use efficiency in Bambara groundnut (Vigna subterranea L. Verdc) grown in farmers’ fields in South Africa, measured using 15N and 13C natural abundance

Bambara groundnut (Vigna subterranea L. Verdc) is the second most important indigenous food legume in Africa. The aim of this study was to evaluate plant growth, N₂ fixation, N contribution, C accumulation, and plant water relations of Bambara groundnut grown in 26 farmers’ fields in Mpumalanga Province of South Africa. The data revealed marked (p?≤?0.05) differences in plant dry matter (DM) yield, N concentration and content, δ¹⁵N, the proportion of N derived from symbiotic fixation (%Ndfa), and actual amounts of N-fixed between and among the 26 farms surveyed. Bambara groundnut plants obtained 33–98 % (mean?=?72 %) of their N nutrition from symbiotic fixation and contributed 4–200 kg N-fixed ha^?1 (mean?=?102 kg N-fixed ha^?1). Plant density correlated positively with %N (r?=?0.31***), δ¹⁵N (r?=?0.126***), and amount of N-fixed (r?=?0.15*), indicating that the high %Ndfa values obtained for Bambara groundnut in this study and the low symbiotic N yield associated with some farms were due to low plant density rather than poor symbiotic functioning. Bambara groundnut obtained more N from soil (e.g., 173 kg N ha^?1) than from symbiosis (e.g., 135 kg N-fixed ha^?1) in some fields, implying that the N₂-fixing efficacy of the microsymbionts nodulating Bambara groundnut was low at some locations in South Africa. The data from this study showed δ¹³C values ranging from ?28.01 to ?26.20?‰, which indicates differences in plant water use efficiency on the different fields studied. Furthermore, the positive correlations between δ¹³C and N-fixed (r?=?0.15*) and between δ¹³C and N content (r?=?0.14*) suggest a functional relationship between water use efficiency and N₂ fixation, just as the positively significant correlations between δ¹⁵N and DM yield (r?=?0.24***), N-fixed and DM weight (r?=?0.76**), and N content and DM yield (r?=?0.99*), as well as N-fixed and C content (r?=?0.76**) also indicate a functional relationship between N₂ fixation and photosynthesis. In the same way, the positive correlation between δ¹³C and DM weight (r?=?0.14*), or δ¹³C and C content (r?=?0.15*), also implies a functional link between water use efficiency and plant growth. Thus, an increase in water use efficiency in Bambara groundnut, whenever it occurs, seems to functionally enhance plant growth, symbiotic N₂ fixation, and photosynthetic activity, just as N₂ fixation in nodules also seems to stimulate leaf photosynthesis.     

Comparison of DTPA and resin extractable soil Zn to plant Zn uptake

Abstract

Extraction of soil zinc with routine chemical extractants does not always reflect differences in Zn availability as detected by plant uptake. This study was undertaken to explore and compare the use of an ion exchange resin and diethylenetriaminepentaacetic acid (DTPA) for extracting soil Zn as related to plant Zn uptake. Beans were grown in 1989 following differential cropping with corn and beans or fallow in 1988 on a Portneuf silt loam near Kimberly, Idaho. Two Zn fertilizer treatments were imposed across previous cropping treatments. A batch method for determining resin extractable soil Zn was established.

Both plant Zn concentration and Zn uptake by beans in 1989 were significantly higher in Zn fertilized than unfertilized treatments regardless of previous crop; and higher in plots previously cropped with corn than beans or fallow, regardless of Zn treatment. DTPA and resin extractable soil Zn were significantly higher in Zn fertilized plots compared to unfertilized plots but did not differ between previous cropping treatments. Resin and DTPA extractable soil Zn concentrations were positively correlated. Resin extracted soil Zn correlated better with plant Zn concentration and Zn uptake throughout the growing season than DTPA extracted soil Zn, particularly in plots that had been fallowed or previously cropped with corn. Resin may be extracting labile soil Zn not extracted with DTPA and, therefore, be better simulating plant uptake. Both extraction methods correlated better with Zn uptake when evaluated within cropping treatments, emphasizing the need to consider previous crop when calibrating soil tests.     

Characterization of recently 14C pulse-labelled carbon from roots by fractionation of soil organic matter

The inability of physical and chemical techniques to separate soil organic matter into fractions that have distinct turnover rates has hampered our understanding of carbon (C) and nutrient dynamics in soil. A series of soil organic matter fractionation techniques (chemical and physical) were evaluated for their ability to distinguish a potentially labile C pool, that is ‘recent’ root and root‐derived soil C. ‘Recent’ root and root‐derived C was operationally defined as root and soil C labelled by ¹⁴CO₂ pulse labelling of rye grass–clover pasture growing on undisturbed cores of soil. Most (50–94%) of total soil + root ¹⁴C activity was recovered in roots. Sequential extraction of the soil + roots with resin, 0.1 m NaOH and 1 m NaOH allocated ‘recent’ soil + root ¹⁴C to all fractions including the alkali‐insoluble residual fraction. Approximately 50% was measured in the alkali‐insoluble residue but specific activity was greater in the resin and 1 m NaOH fractions. Hot 0.5 m H₂SO₄ hydrolysed 80% of the ¹⁴C in the alkali‐insoluble residue of soil + roots but this diminished specific activity by recovering much non‐¹⁴C organic matter. Pre‐alkali extraction treatment with 30% H₂O₂ and post‐alkali treatment extractions with hot 1 m HNO₃ removed organic matter with a large ¹⁴C specific activity from the alkali‐insoluble residue. Density separation failed to isolate a significant pool of ‘recent’ root‐derived ¹⁴C. The density separation of ¹⁴C‐labelled roots, and roots remixed with non‐radioactive soil, showed that the adhesion of soil particles to young ¹⁴C‐labelled roots was the likely cause of the greater proportion of ¹⁴C in the heavy fraction. Simple chemical or density fractionations of C appear unsuitable for characterizing ‘recent’ root‐derived C into fractions that can be designated labile C (short turnover time).     

An evaluation of anion exchange resin used to measure nitrate movement through soil

Abstract

The attribute that ion‐exchange resins remove ions from solutions moving through them can be used to measure nitrate transport through soils. The characteristics of nitrate adsorption by resins must be known to interpret nitrate accumulation on ion‐exchange resins embedded in soil. The extent to which anion exchange resins retain NO₃‐ from soil leachate was measured in 15.9 cm diam.by 60 cm long intact cores of Nolin (fine silty mixed mesic Dystric Fluventic Eutrochroept) soil. A NC₃ ^‐‐selective resin and a non‐selective resin were tested. Columns were fertilized at a rate of 300 kg N/ha and 150 kg Br/ha and leached with 50 cm of water. Under these conditions, both resins retained approximately 80% of the NO₃‐ and Br^‐ leached through the soil. This compared with greater than 95% retention in laboratory columns containing only resin. The difference in retention was attributed to different flow through the resin associated with the method of resin emplacement.     

Leaching of Nitrate,Ammonium, and Phosphate From Compost Amended Soil Columns

Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha^?1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha^?1 rate and leached with deionized water (300 ml day^?1, for five days; equivalent to 34 cm rainfall). The concentrations of NO₃-N, NH₄-N, and PO₄-P in leachate reached as high as 246, 29, and 7 mg L^?1, respectively. The amount of N and P leached accounted for 3.3-15.8 percent of total N and 0.2-2.8 percent of total P in the compost. The leaching peaks of NO₃-N occurred following the application of only 300-400 ml water (equivalent to 6.8-9.1 cm rainfall).     

Nutrients,Free Amino Acids,and Sugar Contents in Narcissus Roots Affected by N,P, K Deficiency during Winter

Non-rooted bulbs of Narcissus L. cv. “Garden Giant” were planted on October 25, 1993 and cultivated under N, P, or K deficiency or in complete medium (control). The roots emerged on November 5 and were sampled on March 7, 1994. The X-ray microanalyzer images showed the distribution of N, P, K, Ca, Mg, S, and Cl in a control root. The distribution of Cl was similar to that of K and also a similar distribution was found between Ca and S. There were significant differences in the concentration of N, P, K, Ca, Mg among treatments. Interaction among nutrient levels was observed. Control roots accumulated a large amount of nitrogen (84 mg g DW^-1) which was partitioned almost equally between the 80% ethanol soluble and insoluble fractions. N-deficient roots in the -N treatment, on the other hand, accumulated only about 12 mg g DW^-1 nitrogen, mostly in the insoluble fraction (83% of total N). Total amino acid contents responded to N, P, or K deficiency. Glutamine was a major free amino acid in control roots (17 mg N g DW^-1) and K-deficient roots (29 mg N g DW^-1), while arginine seemed to be the predominant amide in P-deficient roots. Content of total soluble sugars in the control, -P and -K treatments that was 49, 46, and 49 mg g DW^-1, respectively, was lower than in the -N treatment (137 mg g DW^-1). Mono- and disaccharides; fructose, glucose, and sucrose, were found in narcissus roots.     

Column studies of denitrification in soil

Small columns, 2.5 cm dia and of different lengths, were filled with an air-dried. Hanford sandy loam and leached with CaCl₂ (0.001 n) and nitrate (10–100 μg/ml N) for 3 weeks. The average NO₃ N concentration of the leachate during the last 12 days of the experiment was used to calculate denitrification rates. The net reaction of NO₃^? appeared to be zero order with the 50 and 100 μg/ml NO₃ N applications with a rate constant of 0.27 μg/ml/h N residence time for columns 5–50 cm long. Nitrate was not completely lost with the lower NO₃^? N applications; this implies that greater than zero order reactions can also occur. Although N₂ gas evolution was not measured, most N was doubtless volatilized since analysis of selected soil samples at the end of the experiment indicated no net assimilation of the NO₃ N.     

In situ Remediation of DDT-contaminated Soil Using a Two-Phase Cosolvent Flushing-Fungal Biosorption Process

The effectiveness of cosolvent soil flushing and fungal biosorption for the remediation of p,p′-DDT-contaminated soil was evaluated usingpacked soil columns in order to simulate an in situ soil flushing technique. Greater than 95% of p,p′-DDT (940 mg kg^-1) was desorbed from the soil by flushing with 40 or 80% 1-propanol. Increasing the cosolvent volume fraction increased the rate of p,p′-DDT removal from the soil, however, the extent of p,p′-DDT removal was not enhanced. A further enhancement in therate of p,p′-DDT removal was achieved by increasing the cosolventflow rate from 6 ml hr^-1 to 12 ml hr^-1 (pore water velocity from 18.9 to 37.8 cm hr^-1). The desorbed p,p′-DDT was removed from cosolvent wash solutions by partitioning onto fungal biomass. Biosorption of p,p′-DDT resulted in low concentrations of the organochlorine (3.3 μg ml^-1) remaining in thecosolvent effluent indicating that the cosolvent could be reused for further p,p′-DDT desorption. Using this technique, between 53 and 95 pore volumes were required to reduce p,p′-DDT concentrationsfrom 990 mg kg^-1 to below Australian and New Zealand Environmentaland Conservation Council (ANZECC) guidelines (50 mg kg^-1).     

A novel ambipolar‐resin membrane for extracting soil nutrients

We have synthesized a novel ambipolar membrane for the simple, rapid, and simultaneous extraction of key nutrients from soil. The membrane was made by adding an anion‐ and a cation‐exchange resin to a polyvinyl alcohol hydrogel in the presence of glutaraldehyde as a cross‐linking agent. The synthetic membrane was efficient in adsorbing (extracting) NO , PO , K⁺, Ca²⁺, and Mg²⁺ ions from soil simultaneously. The ion‐adsorption capacity of the membrane was related to the soil nutrient status, duration of membrane–soil contact, and soil water content. The importance of these factors followed the order: soil nutrient status > contact time > soil water content. Adsorption by the membrane of NO and Mg²⁺ ions from soil leveled off after 48 h of membrane–soil contact but uptake of Ca²⁺, PO , and K⁺ ions required a longer contact time for equilibrium to be established. When the soil water content exceeds 55% w/w, this factor ceased to influence ion adsorption by the ambipolar‐resin membrane. The synthetic membrane is potentially useful for the in situ assessment of the nutrient requirement of certain crops at a given point in time.     

Dissolved Organic Carbon in Association with Water Soluble Nutrients and Metals in Soils from Lake Okeechobee Watershed, South Florida

Water quality of Lake Okeechobee has been a major environmental concern for many years. Transport of dissolved organic matter (DOM) in runoff water from watershed is critical to the increased inputs of nutrients (N and P) and metals (Cu and Zn). In this study, 124 soil samples were collected with varying soil types, land uses, and soil depths in Lake Okeechobee watershed and analyzed for water-extractable C, N, P, and metals to examine the relationship between dissolved organic carbon (DOC) and water soluble nutrients (N and P) and metals in the soils. DOC in the soils was in 27.64?C400 mg kg^?1 (69.30 mg kg^?1 in average) and varied with soil types, land uses, and soil depth. The highest water-extractable DOC was found in soils collected in sugar cane and field crops (277 and 244 mg kg^?1 in average, respectively). Water soluble concentrations of N and P were in the range of 6.46?C129 and 0.02?C60.79 mg kg^?1, respectively. The ratios of water-extractable C/N and C/P in soils were in 0.68?C12.52 (3.23 in average) and 3.19?C2,329 (216 in average), and varied with land uses. The lowest water-extractable C/N was observed in the soils from dairy (1.66), resident (1.79), and coniferous forest (4.49), whereas the lowest water-extractable C/P was with the land uses of dairy (13.1) and citrus (33.7). Therefore, N and P in the soils under these land uses may have high availability and leaching potential. The concentrations of water soluble Co, Cr, Cu, Ni, and Zn were in the ranges of?<?method detection limit (MDL)?C0.33, <MDL?C0.53, 0.04?C2.42, <MDL?C0.71, and 0.09?C1.13 mg kg^?1, with corresponding mean values of 0.02, 0.01, 0.50, 0.07, and 0.37 mg kg^?1, respectively. The highest water soluble Co (0.10 mg kg^?1), Cr (0.26 mg kg^?1), Ni (0.31 mg kg^?1), and Zn (0.80 mg kg^?1) were observed in soils under the land use of sugar cane, whereas the highest Cu (1.50 mg kg^?1) was with field crop. The concentration of DOC was positively correlated with total organic carbon (TOC) (P <0.01), water soluble N (P <0.01), electrical conductivity (EC, P <0.01), and water soluble Co, Cr, Ni, and Zn (P <0.01), and Cu (P <0.05), whereas water soluble N was positively correlated with water soluble P, Cu, and Zn (P <0.01) in soils. These results indicate that the transport of DOC from land to water bodies may correlate with the loss of macro-nutrients (N, P), micro-nutrients (Cu, Zn, and Ni), and contaminants (Cr and Co) as well.     

Release of carbon and nitrogen compounds by plant roots and their possible ecological importance+

The root-borne C- and N-flux in the plant/soil system was studied by determining the ¹⁴C- or ¹⁵N-balances in pot trials with soil as a substrate (¹⁴CO₂- or ¹⁵NH₃-application to the shoots, comparison of sterile and nonsterile treatments for quantification of root-borne substances). The following results were obtained: 1. The amount of (primary) root-borne carbon compounds released into soil was (besides root respiration) 11—20% of net-CO₂-assimilation or 13—32% of the ¹⁴C incorporated into the plants (= 1 t C · ha^—1). 5—6% of ¹⁵N assimilated by the plants were released as root-borne N compounds (= 15 kg N · ha^—1). 2. A considerable portion of the root-borne C (about 6% = 600 kg C · ha^—1) was found in the rooted soil zone at the end of the experiments (rhizodeposition). 3. (Primary) root-borne C and N compounds found in immediate vicinity of the roots (about 60—80%) were mainly water soluble, whereas most of the C and N compounds found in a greater distance were water insoluble. The water soluble exudates consisted mainly of neutral (carbohydrates) and acid fractions (organic acids). The basic fraction (amino acids) made up a small portion only. 4. The root-borne C and N compounds influenced the nutrient balance of soil and plant directly and/or indirectly via microbes (depending on species, variety and nutritional status of plants). 5. Microbes stimulated the release of C- and N-compounds, but rapidly respired 65—85% of the root-borne C-compounds, thereby putting a burden on the C-budget of the “host” plant. 6. It could be shown by the example of hup⁺ Rhizobium meliloti strains (tested by ³H₂-incorporation) and the wheat-Serratia-association, that energy efficient microbenplant systems can improve plant performance.     

Water Vapor Barrier Properties of Zein Films Plasticized with Oleic Acid

Water sorption, water vapor permeability, and tensile properties were evaluated for zein films plasticized with oleic acid. The effect of relative humidity on water vapor permeability and tensile properties of films was investigated. Samples were produced by two different methods: casting from a zein solution and stretching from a zein-fatty acid resin. Films were also coated with linseed oil. Results indicated that preparation method affected water sorption and permeability of zein films. Resin films showed lower water sorption than cast films, especially at high A_w values. Water vapor permeability was also lower for resin films. Coating with linseed oil further improved water vapor barrier ability of resin films. Permeability was affected by environmental relative humidity; higher relative humidity resulted in increased permeability. Environmental relative humidity also affected tensile properties of resin films. Toughness and elongation were improved when relative humidity increased from 50 to 85% rh. Tensile strength showed a maximum at 75% rh. Coating improved elongation and toughness of films. Maximum elongation and toughness were observed for coated samples at 85% rh. Zein resin films showed good tensile and water barrier properties that were maintained through environmental humidity levels from 50 to 98% rh.