The effect of subsurface aluminium on the growth and uptake of surface‐applied phosphorus by wheat seedlings 1

Seedlings of four cultivars of wheat (Triticum aestivum L.) differing in tolerance to aluminium (Al) were grown for 14 to 20 days using a split‐root sand/solution culture technique. Each culture tube was divided horizontally into two compartments by a root‐permeable paraffin wax barrier, so that phosphorus (P) and aluminium (Al) supply could be varied in the upper 0–80 mm (surface) and lower 80–180 mm (subsurface) compartments, respectively.

Root growth into the subsurface zone was enhanced by increased P supply to surface roots, but only in the absence of subsurface Al. Where subsurface Al was present, increased P supply to surface roots had no effect on the penetration of roots into the subsurface zone. Tolerance to Al in the cultivars used was therefore not related to the ability to translocate P to sites of Al injury.     

Fall‐ Versus spring‐applied urea for spring‐sown barley: Influence of nitrogen rate

Abstract

Field experiments with barley were conducted on stubble of cereal grains in northcentral and central Alberta to determine the effect of N rate (25, 50, and 100 kg N/ha) on yield, N recovery and the relative efficiency (RE) of fall versus spring application of incorporated urea to barley. In most instances fall‐applied N was inferior to spring‐applied N and there were large differences in yield and N uptake of barley grain between fall‐ and spring‐applied N. The differences generally increased with increasing N rate for yield and N uptake, but decreased substantially for N use efficiency and % N recovery. As the N rate increased from 25 to 100 kg N/ha average RE of fall‐ versus spring‐applied N increased from 47 to 73% for yield increase and from 42 to 69% for N recovery. The increased RE with increasing N rate did not imply that the greatest level of N reduced the quantity of over‐winter N loss. Instead the results indicated that a lower proportion of the yield or N uptake was lost from fall application when the greatest rate of N was applied.     

Adsorption‐desorption of zinc in mollisols and their relationship with uptake of fertilizer‐applied zinc by rice

Abstract

Zinc (Zn) adsorption in mollisols conformed to the linear form of Freundlich equation. The log K values were positively correlated with silt, clay, and carbonate contents and soil pH, but negatively correlated with sand content. Sequential desorption of adsorbed Zn in 0.05M Ca(NO₃)₂, 0.1M Mg(NO₃)₂, 0.005M DTPA, and 0.1M HCl revealed that weakly and specifically bound fractions of added Zn, which could easily equilibrate with soil solution, were low and decreased with silt and carbonate contents and soil pH. Weakly bound fraction increased with sand content. Strongly bound and complexed fraction of applied Zn was the maximum and increased with clay, soil organic carbon and carbonate contents and specific surface area, but decreased with sand content. The mineral bound fraction of applied Zn was intermediate and increased with silt, clay and carbonate contents, and soil pH and specific surface area. Zinc uptake due to added Zn fertilizer by rice crop (Y) negatively correlated with log K, but positively related to Zn content in the equilibrium soil extract and Zn desorbed in 0.05M Ca(NO₃)₂. Both log K and l/n values together explained 59.5% of the total variation in Y, while Zn content in the equilibrium soil extract, Zn desorbed in 0.05M Ca(NO₃)₂, 0.005M DTPA and 0.1M HCl collectively accounted 79.6% of the total variation in Y.     

Assimilation of ammonia by the azolla‐anabaena symbiosis

¹⁵N‐labeled ammonia was rapidly assimilated by Azolla caroliniana and incorporated into plant material even though sustained growth of the fern‐algae symbiosis cannot be maintained with ammonia as nitrogen source. During ammonia uptake, the nitrogenous pool of the fern rapidly increases and contains large amounts of free ammonia and glutamine. N₂ fixation activity of the algal symbiont declines during assimilation of ammonia, but it is restored to a high level upon transfer of plants to nitrogen‐free media, as the pool ammonia content decreases. During growth of the fern on N₂, the algal symbiont supplies ammonia in a manner permitting sustained growth of the plant. Exogenous ammonia, therefore, appears to interrupt regulation of inorganic nitrogen metabolism of the plant‐algal symbiosis.     

Carbon dioxide assimilation in urea‐treated wheat leaves

Application of 10 mM urea to the flag leaf of wheat plants enhanced in vivo urease activity several fold. Photosynthetic rate was also increased considerably. There were significant differences in the leaf internal carbon dioxide (CO₂) concentrations between the urea‐treated and untreated leaves. The finding that carbon (¹⁴C) was detected in the ethanol extract of the leaves fed with ¹⁴C‐urea suggests that CO₂ released from urea is re‐fixed by the leaves.     

Downward movement of surface‐applied P on established forage stands

Abstract

Field experiments were conducted on Black Chernozem and Gray Luvisol soils in Alberta to determine the downward movement of long‐term applications of surface‐broadcast P fertilizer on established forage grass or alfalfa stands. The majority of fertilizer P recovered in soil as extractable P remained in the top 5 cm layer. The amount and depth of movement of applied P increased with P rate, but little or none was recovered below 15 cm.     

Long‐term supply and uptake by plants of elements from coal fly ash

Abstract

To assess the mineral composition of plants growing in pure fly ash, grasses growing on lysimeters filled with alkaline, neutral, or acid fly ash were sampled several times in a 6‐year period. The samples were analyzed for elements essential for plants and animals as well as non‐essential, but environmentally significant, trace elements. Grasses were also sampled from ash dumps that were 20 and 30 years old. Fly ash is not a proper source of plant macronutrients N, P, and K. Plant growth on the alkaline fly ash can be influenced for some time by the high salinity of that ash. Grasses growing on unweathered fly ash were found to be high in Al, B, Co, Fe, Mo, Ni, Pb, and Se. Concentrations of several elements declined in time but levels of B, Fe, Mo, and Ni were still elevated in grasses on both fly ash dumps. All concentrations, except Al, were lower than toxicity levels for plants as found in literature. In plants growing on fresh fly ash concentrations of Mo, Pb, and Se can exceed the maximum tolerable levels for domestic animals. On weathered fly ashes (ash dumps) the Mo, Pb, and Se concentrations in grasses were below the maximum tolerable levels. Effects on animals by Mo in weathered ash may not be excluded because Mo concentrations can be high enough to induce Cu deficiency. Animals that feed on plants grown on fly ash could suffer from Ca, Mg, Na, and P deficiency.     

Direct and residual effects of fertilizers applied in wheat‐rice cropping system

Field experiments were made on a sandy clay loam Fluvent to determine direct effects of NPK applied to wheat and their residual effects on succeeding rice at the Indian Agricultural Research Institute, New Delhi. A significant response of wheat was recorded only for nitrogen which when applied at 120 kg N ha^?1 or more had also significant but only little residual effects on succeeding rice. Adequate ? fertilization of both wheat and rice is necessary. Application of ? and ? had no significant on wheat or succeeding rice but NPK application produced the highest grain yield. Wheat‐rice rotation removed 286.4 to 424.4kg ha^?1 of NPK, which is much more than the rates applied. Thus for sustaining good yields from the wheat‐rice cropping system balanced NPK fertilization is recommended.     

Tolerance of spring wheat to a salt‐fluxing residue containing potassium and magnesium

Abstract

Field and greenhouse studies were conducted in Idaho in 1985 to document the maximum levels of a salt fluxing residue (slag) material that can be safely applied to agricultural soils without reducing spring wheat (Triticum aestivum) growth. The slag material, which contains significant quantities of Mg and K, was applied to Mission (coarse‐silty, mixed, frigid Andic Fragiochrepts) and Palouse (fine‐silty, mixed, mesic Pachic Ultic Haploxerolls) silt loam soils at rates ranging from 0 to 40,000 kg/ha. Parameters evaluated included: (1) germination, (2) plant vigor, (3) yield, and (4) soil and plant tissue K, Ca and Mg.

Under field conditions slag application rates of 4,000 and 8,000 kg/ha reduced wheat stands and vigor; however, yields were not adversely affected when compared with the control. Application rates in excess of 8,000 kg/ha resulted in reduced germination, plant vigor, and yield and are consequently not recommended. Greenhouse studies provided further evidence to substantiate the field results.     

Long‐term root uptake of radiocesium by several crops

Abstract

A greenhouse study was conducted to evaluate the long‐term availability of radiocesium (Cs‐137) to various crops grown on contaminated soil that were limed to pH 6.8 (LIME) or were limed and Zn‐ and Mn‐EDTA chelates added (LIME + CHELATE). Crops were grown either continuously or followed a cropping sequence. Continuously grown clover and bahiagrass accumulated the most Cs‐137 with levels exceeding 2,000 pCi/g dry weight in bahiagrass. Uptake of Cs‐137 was depressed by both the LIME and LIME + CHELATE treatments. Uptake was usually greatest during the first three years but only in unlimed soil. Cesium‐137 is about 3 to 8 times higher in soybean beans than in wheat grain. Uptake of Cs‐137 by plants from contaminated soil can be expected to be high in acidic soils, especially in the absence of lime treatment.     

Effect of N‐(n‐butyl)thiophosphoric triamide added to peat and leather in urea‐based fertilizers on urea hydrolysis and ammonia volatilization

Abstract

A laboratory experiment evaluated the rate of urea hydrolysis and ammonia volatilization from urea (U) mixed in organo‐mineral (O‐M) fertilizers. These fertilizers were incubated in soil in the presence or absence of N‐(n‐butyl)thiophosphoric triamide (NBPT) as a urease inhibitor. Two organic matrices, leather (L) and peat (P), were used to prepare the O‐M fertilizers. In the absence of NBPT, the highest ammonia losses and the fastest rate of urea hydrolysis were in the soil treated with the fertilizer containing leather (UL₅₀). Significantly lower ammonia losses occurred with peat‐based fertilizers. Although the fertilizer containing peat (UP₅₀) stimulated the rate of urea hydrolysis with respect to the urea alone, no increase in ammonia volatilization was detected. NBPT‐containing fertilizers were stored for different times (0,7, 30, and 60 days) and temperatures (25°C and 40°C), and the NBPT recovery was monitored by extraction and analysis by HPLC. The NBPT recovery decreased by increasing either the storage time or the storage temperature. Differences among the fertilizers occurred after storage at 40°C for 30 or 60 days. With UN, in spite of about 25% extracted amount of NBPT, the ammonia losses did not increase with respect to the non‐stored fertilizer. On the contrary, no inhibitor was recovered from either of the O‐M fertilizers (UNL and UNP). However, in the presence of leather, NBPT reduced the volatilization losses by 35 to 40%, whereas in the presence of peat, a complete loss of NBPT efficiency occurred. In general, either the inhibitor recovery or efficiency were affected by the storage conditions or the type of organic matrix.     

Localized root growth in soil induced by controlled‐release urea granule and barley nitrogen uptake

Controlled‐release urea is a fertilizer which meters out urea over a long period of time. It can provide a favorable nitrogen (N) concentration for root growth, especially at the early stage of plant development. The objective of this study was to determine the interactions of urea or controlled‐release urea granules with barley roots and the resultant N uptake by plants. Two experiments (Experiment I and Experiment II) with treatments of Nil, non‐coated urea, Coated I and Coated II (Coated I and Coated II are controlled‐release urea products) were conducted in a greenhouse at 23±5°C. In both experiments, one barley (Hordeum vulgare L. cv. Duke) seed and one granule of urea or controlled‐release urea were placed in a pot (5.2‐cm height and 8‐cm diameter) containing soil low in mineral N. In Experiment I, shoot and soil samples were taken at 14, 28, and 46 days after seeding. Roots and fertilizer interaction were visually examined and photographed. In Experiment II, root samples both around the fertilizer granule and away from the granule were taken only at 28 days after seeding. In both experiments, dry matter mass and total N content of shoot and root, and mineral N in soil were determined. In Experiment I, at the 28‐day sampling roots proliferated around the controlled‐release urea granule but not around the urea granule. Shoot N uptake since the 28 days was higher with controlled‐release urea than with urea because of the root proliferation. In Experiment II, root dry mass and N content around the granule was higher with controlled‐release urea than with urea. In the controlled‐release urea treatments, root mass and N content away from the granule were also increased in comparison to the Nil. This shows a stimulus relationship between the two portions of the roots in the same plant, i.e., the roots being accessed to the N source increased growth of the other roots with no access to the source. Because only a small portion of roots was involved in N uptake in the controlled‐release urea treatments, the intensity of N uptake per unit of root mass was much higher with controlled‐release urea as compared to urea. In conclusion, root growth was enhanced around controlled‐release urea granule, and that portion of roots around the fertilizer granule played a major role in absorbing N. In addition, a stimulus relationship existed between roots grown around the granule and those grown away from the granule.     

Reduced‐till spring wheat response to fertilizer sources and placement methods

Abstract

Field studies were conducted to determine the effect of nitrogen (N) and phosphorus (P) fertilizer sources and placement configurations on spring wheat growth, yield and quality. Different standard and experimental N and P sources at two rates and in different placement methods provided 32 fertilizer treatments at three locations. Banding of N and P together resulted in the greatest yields. Of the fertilizer combinations where N and P were applied separately, only broadcast N with deep banded P gave similar yields to N and P together. Banding fertilizer with the seed at these levels damaged seedling growth and limited yield. Elevated protein levels, when found, were likely due to lower yields and subsequent concentration of N in grain protein. Careful consideration of fertilizer rate, source and placement strategies to optimize production and water utilization are essential in dryland environments.     

Extractability of previously‐applied zinc as influenced by properties of calcareous soils

Abstract

The recovery of applied zinc (Zn) by plants is relatively small. Coupled with lack of leaching, this leads to accumulation of Zn in topsoil which may result in unfavorable growth conditions for the subsequent plants. Different extractants may be used for assessing the Zn status of soils previously treated with Zn sources. The extractability of retained Zn is influenced by soil properties. This experiment was conducted to study the influence of selected properties of calcareous soils on extractability of Zn by three popular Zn soil tests. Twenty samples from surface horizons (0–20 cm) of highly calcareous soils of southern Iran (pH 7.9 to 8.5; calcium carbonate equivalent 16 to 58%) previously treated with three levels of Zn (0, 10, and 20 mg Zn kg^‐1 soil as ZnSO₄#lb7H₂O) in triplicate and under one crop of corn (Zea mays L.) were extracted with DTPA, EDTA‐(NH₄)₂CO₃ and Na₂‐EDTA. Extractability (EXT) in a particular extractant was defined as the slope of the regression line, relating extractable Zn of each soil to the rate of applied Zn, multiplied by 100. The EXT values of soils ranged from 24.9 to 73.0% for DTPA, 47.2 to 84.4% for EDTA‐(NH₄)₂CO₃, and 28.2 to 56.7% for Na₂‐EDTA. Stepwise regression equations showed that cation exchange capacity (CEC) and calcium carbonate equivalent (CCE) followed by clay content were the most influential soil properties in EXT of retained Zn of highly calcareous soils. The EXT values decreased with increase in CEC, and CCE but increased with increase in clay.     

Nitrogen‐uptake by plants following soil incubation

Abstract

Many methods of evaluating organic soil nitrogen (N) mineralization and N availability indexes have been proposed. Chemical methods are more rapid but they do not measure the soil microorganisms and plant root activities. Incubation‐leaching procedure may remove some of the readily mineralizable soil organic N compounds. Continuous‐incubation procedure may sometimes increase soil acidity or cause toxins accumulation. The objective of this study was to determine, in a greenhouse experiment, the relative capabilities of 10 soils with organic matter (O.M.) content ranging from 2.38 to 8.63% to supply plant‐available N by combining two procedures, i.e., soil incubation and plant N‐uptake. In method one (M₁), N‐uptake by 3 successive oat crops of 8 weeks each, without soil preincubation was studied. Method two (M₂) involved a soil preincubation of 8 weeks, and the subsequent determination of N‐uptake by two successive crops of oats (Avena sativa L.) of 8 weeks each. No soil‐leaching was used. The results show that there was a large difference in plant N‐uptake according to soil organic matter. The highest correlation between soil O.M. and plant N‐uptake (r = 0.91**) was given by the first crop following incubation. The N‐uptake by the first crop in M₁ (without soil incubation) was much less correlated with soil O.M. (r = 0.74*) and was significantly influenced by soil initial NO₃ and NH₄‐N. The results of this study show that the preincubation of soil samples minimized the influence of soil initial mineral N and that a preincubation was necessary before the plant N‐uptake measurement, even on a 8‐week cropped soil period.     

Sulfate uptake by salinity‐tolerant plant species

Abstract

High soluble‐sulfate (SO₄) concentrations affect water quality, soil chemistry, plant sulfur (S) levels, and possibly ruminant‐animal health. The objective of this greenhouse pot study was to determine the potential for accumulating high levels of S by tansy mustard (Descurainia pinnata (Walt.) Britton), kochia (Kochia scoparia L. Schrad.), yellow sweet clover (Melilotus officinalis L.), slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners), and sunflower (Helianthus annuus L.). Plants were grown on both a Brinegar (fine‐loamy Ultic Argixeroll) and Portneuf (coarse silty Durixerollic Calciorthid) soil. Each species received five‐SO₄ levels. The saturation extract electrical conductivity (EC) of the cropped soils ranged from 6 to 16 dS/m, while the soluble SO₄ varied from 16 to 200 mmol_c/kg soil. Soil solutions were saturated or very nearly saturated with respect to gypsum at the conclusion of each study. Plant dry matter yield, except of grass growing on the non‐calcareous soil, was not reduced by SO₄ treatment nor by the sulfate‐induced decrease in mole fraction of calcium (Ca)/(sum cations) to values less than 0.10 for kochia and grass. Sulfur concentration in the plants ranged from 2.5 mg/g in grass to 10 mg/g in mustard and for each species was linearly related to the SO₄ treatment and soil‐SO₄ activity. Plant SO₄‐S values ranged from 70 μg/g in the grass to nearly 900 μg/g in mustard. Total nitrogen (N): organic S was 4.4, 7.5, 11.4, 16.5, and 5.8 for mustard, kochia, clover, grass, and sunflower, respectively. It was concluded that these species could accumulate high levels of S in the above ground tissue.     

The measurement of low concentrations of ammonia in the atmosphere by flow‐injection analysis

Abstract

A flow injection procedure, based on the reaction between ammonia, salicylate, nitroprusside and alkaline dichlorisocyanurate, was developed which enabled changes in the concentration of ammonia in the atmosphere to be monitored at 15 minute intervals. The detection limit was 10 ppb NH₃‐N in solution for a working range of 0 ‐ 1000 ppb, corresponding to a concentration in the air of 4 μg NH₃‐N/m³. Regression analysis revealed a complex inter‐relationship between the concentrations of the reagents. The method was validated by the close correlation obtained between the results with a cross‐check analysis by ion chromatography and its use demonstrated by following the volatilization of ammonia from a soil core treated with urine.     

Effects of water‐soluble constituents of plant residues on water uptake by seeds

Abstract

There has been strong support for the hypothesis that the adverse effects of plant residues on crop yields are due to phytotoxic compounds derived from these residues. This hypothesis is based largely on studies showing that, when compared with distilled water, aqueous extracts of plant residues have an adverse effect on seed germination and seedling growth. Because seed germination and seedling growth are reduced by a delay in germination resulting from slow uptake of water by seeds, we studied the possibility that the adverse effects of aqueous extracts of plant residues on seed germination and seedling growth might be at least partly due to water uptake by seeds being retarded by water‐soluble constituents of these residues. To test this possibility, we compared the rates of water uptake and germination of seeds of corn (Zea mays L.), soybean [Glycine max. (L.) Merrill], and wheat (Triticum aestivum L.) when these seeds were treated with distilled water and with aqueous extracts of corn, sorghum [Sorghum bicolor (L.) Moench], and wheat residues. We found that the rates of water uptake and germination of seeds treated with aqueous extracts of plant residues were appreciably slower than the corresponding rates for seeds treated with distilled water. This may be due to the water potentials of these extracts (ca. ‐50 kPa) because when seeds of corn, sorghum, and wheat were treated with a solution of polyethylene glycol 8000 having a water potential similar to that of the extracts of plant residues tested, the rates of water uptake and germination were also slower than the corresponding rates for seeds treated with distilled water. These observations suggest that the adverse effects of aqueous extracts of plant residues on seed germination and seedling growth when compared with distilled water may be partly due to constituents of these extracts inducing water potential effects that reduce water uptake by germinating seeds.     

The foliar absorption of urea‐N by tall fescue and creeping bentgrass turf

The absorption and assimilation of ¹⁵N‐labeled urea applied to the foliage of tall fescue (Festuca arundinacea Schreb.) and creeping bentgrass (Agrostis palustris Huds.) turf was examined under a controlled environment. Each source of N was dissolved in deionized water to a final concentration of 25 g N liter^‐1 and spray‐applied at a rate of 5 g N m^‐2. Absorption of the fertilizer‐N over a 72 hr period, as measured by ¹⁵N analysis of tissue digests, averaged 55% for the two species. Absorption was also estimated by a washing procedure which measured the urea remaining on the foliage, and by the increase in total N in the plant tissue.

There were no significant differences between the three methods in estimating absorption. Partitioning of the absorbed ¹⁵n between tissues averaged 37% in new leaves, 51% in old leaves and shoot tissue, and 11% in the roots. More than 90% of the absorbed urea‐N was hydrolyzed by 72 hr.     

Efficiency of h+‐atpase activity on cadmium uptake by four cultivars of lettuce

Cadmium (Cd) uptake by lettuce (Lactuca sativa L.) was studied in a hydroponic solution study at concentrations approaching the total concentration in contaminated soil solutions. Four cultivars of lettuce were tested (Divina, Reine de Mai, Melina, and J.44). Ten 12‐day old seedlings, pretreated in 0.5 μM CdCl₂ solution, were labelled with carrier free ¹⁰⁹CdCl₂ (from 0.05 μM to 5 μM Cd in nutrient solution) in the presence and absence of metabolic inhibitors, DNP and DCCD. Cadmium taken up by the roots was determined after a 30 min desorption in unlabelled CdCl₂ solution. In the absence of metabolic inhibitors and at 5 μM Cd, root absorbed from 2.5 to 8 mg Cd/g root dry weight. Exchangeable Cd measured after desorption represented less than 1% of the total Cd absorbed by the root. Cadmium absorption in presence of DNP showed that approximately 80% of the Cd enters the cell through an active process. This mechanism seems to be directly associated with H⁺‐ATPase as observed with DCCD inhibition. Varietal differences in shoot Cd uptake were only demonstrated at concentrations below 0.1 μM. Screening lettuce cultivars only by the Cd level in the tissue seems not to be possible for these cultivars except at concentrations close to that in the soil solution. But differences in relative contribution of uptake mechanisms in total Cd absorption were observed. High levels of Cd in roots were correlated with high contri‐ butions from H⁺‐ATPase in the active process of Cd uptake.