Potassium nutrition effects on seed alkaloid concentrations,yield and mineral content of lupins (Lupinus angustifolius)

To ensure that narrow-leafed lupin (Lupinus angustifolius L.) meets feed quality standards, the concentration of alkaloids must be kept under the maximum acceptable limit of 200 mg kg^–1 DM. One of the factors that may affect seed alkaloid concentration is soil nutrient deficiency. In this paper, we report the results of glasshouse and field experiments that tested the effect of potassium (K) deficiency on seed alkaloid concentrations. In the glasshouse, seed alkaloid concentrations increased by 385, 400 and 205% under severe K deficiency in sweet varieties (Danja, Gungurru and Yorrel, respectively) of L. angustifolius. The concentration of alkaloids in Fest, the bitter variety, was always high regardless of soil K status. At all levels of applied K (0–240 mg kg^–1 soil), lupanine was the predominant alkaloid in sweet varieties, whereas 13-hydroxylupanine prevailed in the bitter variety. Seed yield of all varieties increased exponentially with increasing amounts of applied K, reaching a maximum at 60 mg K kg^–1 soil. In the field, application of K to deficient soils decreased seed alkaloid concentration at Badgingarra, Western Australia (WA) but not at Nyabing, WA, in 1996. In both field trials, seed yield and mineral content were not affected by the amounts of K fertiliser applied. These findings highlighted the need for adequate K fertilisation of deficient soils in WA to avoid the risk of producing low quality lupin seed with high alkaloid concentrations. K deficiency is involved in stimulating alkaloid production in sweet varieties of L. angustifolius.     

Varying phosphorus supply and development,growth and seed yield in narrow-leafed lupin

Narrow-leafed lupin (Lupinus angustifolius L.) is usually grown in sandy, acidic and phosphorus (P) deficient soil with low yield and variable harvest index. This study aimed to examine the effects of varying P supply on lupin growth, seed yield and harvest index. Non-abscission plants (cv. Danja) were grown in Lancelin sand at seven rates of P supply (5, 10, 15, 20, 25, 30 or 40 mg kg^–1) in a naturally-lit glasshouse. The rate of leaf emergence, flowering time and flower number were decreased or delayed by low P supply (5, 10 or 15 mg kg^–1), with no differences at P rates higher than 20 mg kg^–1. High P supply (25, 30 or 40 mg kg^–1) increased plant seed yield and harvest index largely by increasing the number of pods and consequently yield on the lateral branches, but had less effect on the number of seeds per pod and seed size. Seed yield and seed P concentration continued to increase up to 40 mg P kg^–1but harvest index plateaued at 25 mg P kg^–1, indicating that low P supply decreased reproductive growth more than vegetative growth in narrow-leafed lupin.     

Effect of phosphorus,potassium and zinc fertilizers on iron toxicity in wetland rice (Oryza sativa L.)

During the period January–August 1996, an investigation was carried out in La Mata, Cotuí, Dominican Republic with the objective to study the effect of P, K and Zn fertilizers on Fe toxicity in the rice varieties JUMA-57 (sensitive to Fe toxicity), ISA-40 and PSQ-4 (both tolerant to Fe toxicity). The rate of fertilizer application was 22 and 62 kg P ha^–1; 58 and 116 kg K ha^–1; 3 and 7 kg Zn ha^–1 and a constant dose of 140 kg N ha^–1 and 40 kg S ha^–1 on all fertilized plots. The control received no fertilizer. JUMA-57 was the only variety that showed symptoms of Fe toxicity. The observed symptoms showed a yellow to orange colour. Symptoms of Fe toxicity appeared first one week after transplanting (WAT), decreased at the fourth WAT, but returned six WAT and continued until the end of the experiment. Fertilizer application reduced symptom intensity and increased grain yield in all varieties, but only JUMA-57 did not reach the maximum yield typical for that variety. Fertilizer application did not completely overcome the toxicity effect, i.e. in symptom intensity and grain yield. The positive effect of fertilizer application could not be attributed to a specific nutrient. Intensity of symptoms was not related to Fe concentration in the leaves. The average Fe concentration of 108 mg kg^–1 was not high enough to be considered toxic. Symptoms could not be explained through Mn toxicity (average Mn concentration in the leaves was 733 mg kg^–1) nor Zn deficiency (average Zn concentration in the leaves was 20 mg kg^–1). There was a clear relationship, though, between soil DTPA extractable Fe and symptom intensity or grain yield. The toxic effect was observed when the DTPA extractable Fe in the flooded soil was above 200 mg kg^–1. From these results, we concluded that the Fe toxicity resulted from high Fe in the root zone and not from high Fe concentrations in the leaves.     

Influence of phosphorus on the growth and ergot alkaloid content of Neotyphodium coenophialum-infected tall fescue (Festuca arundinacea Schreb.)

Tall fescue (Festuca arundinacea Schreb.) plants infected by the fungal endophyte Neotyphodium coenophialum (Morgan-Jones & Gams) (Glenn et al., 1996) often perform better than noninfected plants, especially in marginal resource environments. There is a lack of information about endophyte related effects on the rhizosphere of grasses. In a greenhouse experiment, four endophyte-infected (E+) tall fescue clones (DN2, DN4, DN7, DN11) and their endophyte-free (E–) forms were grown in limed (pH 6.3) Porter soil (low fertility, acidic, high aluminum and low phosphorus content, coarse-loamy mixed mesic Umbric Dystrochrept) at three soil P levels (17, 50, and 96 mg P kg^-1 soil) for five months. Excluding the genotype effect, endophyte infection significantly increased cumulative herbage DM yield by 8% at 17 mg P kg^-1 soil but reduced cumulative herbage DM yield by 12% at 96 mg P kg^-1 soil. With increased P availability in the soil, shoot and root DM, and root/shoot ratio in E+ plants were significantly less when compared to E– plants. Endophyte infection increased specific root length at 17 and 50 mg P kg^-1soil. At soil P level of 17 mg P kg^-1soil, E+ plants had significantly higher P concentrations both in roots and shoots. Similar relationships were found for Mg and Ca. E+ plants had significantly higher Zn, Fe, and Al concentration in roots, and lower Mn and Al concentration in shoots when compared to E– plants. Ergot alkaloid concentration and content in shoot of E+ plants increased with increasing P availability in the soil from 17 to 50 mg P kg^-1 but declined again at 96 mg P kg^-1 soil. Ergot alkaloid accumulation in roots increased linearly with P availability in the soil. Results suggest that endophyte infection affects uptake of phosphorus and other mineral nutrients and may benefit tall fescue grown on P-deficient soils. Phosphorus seems also to be involved in ergot alkaloid accumulation in endophyte-infected tall fescue.     

Zinc phytotoxicity to oilseed rape grown on zinc-loaded substrates consisting of Fe oxide-coated and calcite sand

The risk of zinc (Zn) phytotoxicity in soils has increased in various regions following application of different anthropogenic materials. In order to assess the relative efficiency of Fe oxide and calcite in sorbing Zn and hence alleviating Zn phytotoxicity, we grew oilseed rape for 28 days in pots containing Zn-loaded model substrates consisting of Fe oxide (ferrihydrite)-coated sand (FOCS, 0.2–0.5 mm, 0.3 m² ferrihydrite g^–1 sand) and calcium carbonate (calcite) sand (CCS, 0.2–0.5 mm, 0.3 m² calcite g^–1 sand). Five substrates containing 5, 10, 20, 40, and 80% FOCS and supplied with ZnSO₄ at a rate of 30, 100, 300, and 1000 mg Zn kg^–1 were used in the cropping experiment and in an in vitro study of Zn desorption for 62 days. Plants exhibited good growth and a similar dry matter yield (DMY) at the 30 and 100 mg Zn kg^–1 rates. On the other hand, DMY was markedly reduced at the 300 and, especially, at the 1000 mg Zn kg^–1 rate, particularly for the substrates with the higher FOCS proportions. Symptoms of phytotoxicity (viz. chlorosis, purple colouration due to P deficiency) were apparent at such rates and were accompanied by high Zn concentrations in both shoot (average values >1000 and >1500 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively) and root (average values >2500 and >6000 mg Zn kg^–1 dry matter for the 300 and 1000 mg Zn kg^–1 rate, respectively). Total Zn uptake was maximal at 300 mg Zn kg^–1. The results of water extractable Zn in the substrate after cropping and the dissolved Zn concentrations measured in substrate–water systems (desorption experiment) suggest that, on a surface area basis, calcite is more effective than Fe oxide to retain Zn and thus alleviate phytotoxicity at high Zn loadings. However, the Zn-sorption capacity of the Fe oxide cannot be neglected, particularly at low Zn loadings, where Fe oxide seems to exhibit a higher affinity for Zn – but not a higher Zn-sorption capacity – than does calcite.     

Effect of crop residues on root growth and phosphorus acquisition of pearl millet in an acid sandy soil in Niger

The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha^-1 yr^–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha^-1 yr^-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha^-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg^-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg^-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha^-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm^-3) than for +CR–F (4.5 cm cm^-3) and –CR+F (4.2 cm cm^-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm^-3 (30–60 cm soil depth) to 0.2 cm cm^-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw.     

Long-term changes in extractable soil phosphorus (P) in organic dairy farming systems

On five farms that have been managed organically for several years, all cultivated soils were sampled on two occasions. The time span between the first and second soil sampling varied from 6 to 12 years. At the first sampling the farms had been managed organically for 3, 4, 6, 11 or 53 years. The average phosphorus (P) concentrations in topsoil (0-20 cm) extracted by ammonium-acetate lactate solution (P-AL) decreased from the first to the second sampling on all farms. At the second soil sampling, the average topsoil P-AL concentrations on the five farms were 50, 64, 65, 75 and 119 mg P kg^–1, which is characterised as medium (26–65 mg P kg^–1) or high (66–150 mg P kg^–1). The decrease occurred mostly in soils with high and very high (>150 mg P kg^–1) P-AL concentrations at the first sampling. In these samples, the average value decreased from 100 to 87 and from 188 to 151 mg P kg^–1, respectively. In subsoil (20–40 cm), an increase from 15 to 27 mg P kg^–1 (P<0.01) in P-AL concentration was found in subsoil samples with low P-AL concentrations (0–25 mg P kg^–1) at the first sampling. This indicates P transfer from topsoil to subsoil. The pattern of decrease in topsoil was fairly well explained by farm level P balances. The average topsoil concentrations of P-AL were well below values for comparable conventional farms, but still at a level acceptable for crop production. Crop yields were acceptable, but the general pattern of decrease shows that in the future, some P should be supplied from external sources to avoid a further decrease, especially on the fields with lowest P-AL concentrations.     

Tolerance of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) to high soil and solution selenium levels

The fertilisation of wheat crops with Se is a cost-effective method of enhancing the concentration of organic Se in grain, in order to increase the Se intake of animals and humans. It is important to avoid phytotoxicity due to over-application of Se. Studies of phytotoxicity of Se in wheat grown in Australia, where rainfall and grain yield are usually relatively low, have not been reported previously, and overseas studies have had varied results. This study used trials conducted in the field, glasshouse and laboratory to assess Se phytotoxicity in wheat. In field trials that used rates of up to 120 g ha^–1Se as selenate, and in pilot trials that used up to 500 g ha^–1 Se soil-applied or up to 330 g ha^–1 Se foliar-applied, with soils of low S concentrations (2–5 mg kg^–1), no Se toxicity symptoms were observed. In pot trials of four weeks duration, the critical tissue level for Se toxicity was around 325 mg kg^–1 DW, a level attained by addition to the growth medium of 2.6 mg kg^–1 Se as selenate. Solution concentrations above 10 mg L^–1 Se inhibited early root growth of wheat in laboratory studies, with greater inhibition by selenite than selenate. For selenite, Se concentrations around 70 mg L^–1 were required to inhibit germination, while for selenate germination % was unaffected by a solution concentration of 150 mg L^–1 Se. Leaf S concentration and content of wheat increased three-fold with the addition of 1 mg kg^–1 Se as selenate to the growth medium. This effect is probably due to the induction of the S deficiency response of the main sulphate transporter. This study found wheat to be more Se-tolerant than did earlier studies of tobacco, soybeans and rice. We conclude that Se phytotoxicity in wheat will not be observed at the range of Se application rates that would be used to increase grain Se for human consumption (4–200 g ha^–1 Se as selenate, which would result in soil and tissue levels well below those seen in the above studies), even when – as is common in Australia – soil S concentration and grain yield are low.     

Effect of NPK on growth and nitrogen fixation of Sesbania rostrata as a green manure for lowland rice (Oryza sativa L.)

The stem-nodulating tropical legume Sesbania rostrata is a promising green manure species for low input rice-farming systems in lowland areas. However, its success as biofertilizer depends on its biomass production and N₂ fixation. Nutrient imbalances and soils low in available nutrients can considerably affect biofertilizer production. Use of mineral N, P, and K fertilizers in growing S. rostrata as biofertilizer for lowland rice was therefore evaluated in pot experiments, and in the fields in Central Luzon, Philippines. Two soils low in Olsen P (3–7.3 mg kg^–1) and exchangeable K (0.05–0.08 meq 100g^-1) were used. Increasing amounts of N (0, 10, 20, 30, and 40 mg kg^-1), P (0, 50, and 100 mg kg^-1), and K (0, 100, 200, and 300 mg kg^-1) were applied to S. rostrata grown in the greenhouse, whereas small amounts of N, P, and K fertilizers (30, 15, and 33 kg ha^-1, respectively) were applied in the field.Mineral N application depressed nodulation and N₂ fixation in roots. It however, stimulated nodulation and N₂ fixation in stems. Applying 30 kg N ha^-1 as urea increased total N accumulation by S. rostrata and yield of the subsequent rice crop (IR64). Applied P and K both stimulated growth, nodulation, and N₂ fixation of S. rostrata. Nitrogen accumulation in P- and K-fertilized S. rostrata was about 40% higher than that in nonfertilized green manure. Thus integration of mineral N, P, and K fertilizers in a green manure-based rice-farming system can considerably improve biofertilizer production and increase rice grain yield.     

Dynamics of phosphorus fractions during fallow with natural vegetation and planted Pueraria phaseoloides in south-western Nigeria

A study was conducted in 1998 and 1999 on a long-term fallow management trial, established in 1989 at the International Institute of Tropical Agriculture (IITA), Ibadan, in the derived savanna of southwestern Nigeria, to quantify P fractions under natural fallow (NF) and a Pueraria cover crop fallow. Plots with previous 1:1, 1:2, and 1:3 crop/fallow ratios before reverting to fallow in either 1998 or 1999 were considered. Biomass accumulation under the two fallow types was comparable and increased linearly with fallow age, reaching slightly above 7 t dry matter ha^–1 after 8 months of fallow. Phosphorus accumulation in the fallow vegetation ranged from 2.1 – 9.1 kg ha^–1 for natural fallow (NF) and from 1.5 – 6.6 kg ha^–1 for Pueraria. Magnesium was also higher under NF (9.1 – 21 kg ha^–1) than under Pueraria (4.4 – 13 kg ha^–1), whereas N, Ca, and K contents were higher in Pueraria biomass than under NF at 1 year after fallow. Pueraria fallow tended to lower soil pH compared with NF. However, plots with less frequent cropping (1:3 crop/fallow ratio) did not have significantly different pH irrespective of the fallow vegetation type. Olsen extractable soil P increased as fallow length increased irrespective of the fallow system and previous crop/fallow ratio. For example, under NF (0–5 cm depth, 1:1 crop/fallow ratio in1998) Olsen P increased from 12 mg kg^–1 to 17 mg kg^–1 after 1 year of fallow and under Pueraria, it increased from 8 mg kg^–1 to 15 mg kg^–1. Fallow type and previous crop/fallow ratio had no significant and consistent effects on soil P fractions. However, NaOH- and concentrated HCl- extractable organic P fractions increased with fallow length. In 1998, under NF, NaOH- extractable organic P increased from 12 to 21 mg kg^–1 (1:1 crop/fallow ratio) and from 10 to 19 mg kg^–1 for both 1:2 and 1:3 crop/fallow ratio. HCl- extractable organic P increased from 11 to 30 mg kg^–1 (1:1 crop/fallow ratio), from 13 to 27 mg kg^–1 (1:2 crop/fallow ratio) and from 18 to 35 mg kg^–1 (1:3 crop/fallow ratio). Similar trend was observed under Pueraria fallow. These results suggest that P was reallocated to non-readily available organic P fractions irrespective of fallow type and previous land use. These organic P fractions, which are usually more stable, reflect the overall change in soil organic P levels when the soil was stressed by cultivation and then reverted to fallow. These pools may thus represent an active reservoir (source and sink) of P in shifting cultivation under tropical conditions without inorganic fertilizer application.     

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg^–1 soil, leaf P content increased from 0.65 to 7.0 g kg^–1. Both A and DM had maximal values near 51.7 mg P kg^–1 soil, which corresponded to a leaf P content of 3.2 g kg^–1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (g_s) tripled, and mean leaf internal CO₂ concentration ([CO₂]_i) decreased from 260 to 92 L L^–1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both K_M, which is mathematically equivalent to quantum efficiency, and V_max, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg^–1, with peak values between 4 and 5 g P kg^–1. Polynomial equations relating K_M and V_max, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.     

Minimizing the effect of mineral nitrogen on biological nitrogen fixation in common bean by increasing nutrient levels

Although common bean (Phaseolus vulgaris L.) has good potential for N₂ fixation, some additional N provided through fertilizer usually is required for a maximum yield. In this study the suppressive effect of N on nodulation and N₂ fixation was evaluated in an unfertile soil under greenhouse conditions with different levels of soil fertility (low=no P, K and S additions; medium = 50, 63 and 10 mg kg^–1 soil and high = 200, 256 and 40 mg kg^–1 soil, respectively) and combined with 5, 15, 60 and 120 mg N kg^–1 soil of ¹⁵N-labelled urea. The overall average nodule number and weight increased under high fertility levels. At low N applications, nitrogen had a synergistic effect on N₂ fixation, by stimulating nodule formation, nitrogenase activity and plant growth. At high fertility and at the highest N rate (120 mg kg^–1 soil), the stimulatory effect of N fertilizer on N₂ fixation was still observed, increasing the amounts of N₂ fixed from 88 up to 375 mg N plant^–1. These results indicate that a suitable balance of soil nutrients is essential to obtain high N₂ fixation rates and yield in common beans.     

Decay rate and substrate quality of fine roots and foliage of two tropical tree species in the Luquillo Experimental Forest,Puerto Rico

Decomposition rates, initial chemical composition, and the relationship between initial chemistry and mass loss of fine roots and foliage were determined for two woody tropical species, Prestoea montana and Dacryodes excelsa, over a gradient of sites in two watersheds in the Luquillo Experimental Forest, Puerto Rico. At all locations, fine roots decayed significantly more slowly than foliage during the initial 6 months.Substrate quality of the initial tissue showed marked differences between roots and foliage when using cell wall chemistry, secondary chemistry and total elemental analysis as indices. Quantity of acid detergent fiber (ADF) (non-digestible cell wall fiber) and lignin content were higher for roots than leaves: D. excelsa roots had 55.3% ADF and 28.7% lignin while leaves had 36.2% ADF and 11.8% lignin; P. montana roots had 68.0% ADF and 26.8% lignin while leaves had 48.5% ADF and 16.1% lignin. Aluminum concentrations were higher in fine roots (843 mg kg^–1 in D. excelsa, 1500 mg kg^–1 in P. montana) than leaves (244 mg kg^–1 in D. excelsa, 422 mg kg^–1 in P. montana), while calcium concentrations were higher in foliage (5.5 mg g^–1 in D. excelsa, 7.8 mg g^–1 in P. montana) than roots (3.4 mg g^–1 in D. excelsa, 3.1 mg g^–1 in P. montana). Nitrogen did not show any trend with tissue or species type. A linear model between mass remaining after 6 months and initial tissue chemistry could be developed only for calcium (r²=0.64).     

Availability of fluoride to plants grown in contaminated soils

Two pot experiments were carried out to study uptake of fluoride (F) in clover and grasses from soil. Fluoride concentrations in t Trifolium repens (white clover) and t Lolium multiflorium (ryegrass) were highly correlated with the amounts of H₂O– and 0.01 t M CaCl₂–extractable F in soil when increasing amounts of NaF were added to two uncontaminated soils (r=0.95–0.98, t p<0.001). The amounts of H₂O– or 0.01 t M CaCl₂–extractable F did not explain the F concentrations to a similar extent in t Agrostis capillaris (common bent) grown in 12 soils (Cambic Arenosols) collected from areas around the Al smelters at Å: rdal and Sunndal in Western Norway (r=0.68–0.78). This may be due to variation in soil pH and other soil properties in the 12 soils. Soil extraction with 1 t M HCl did not estimate plant–available F in the soil as well as extraction with H₂O or 0.01 t M CaCl₂. Fluoride and Al concentrations in the plant material were positively correlated in most cases. Fluoride and Ca concentrations in the plant material were negatively correlated in the first experiment. No consistent effects were found on the K or Mg concentrations in the plant material. The F accumulation in clover was higher than in the grasses. The uptake from soil by grasses was relatively low compared to the possible uptake from air around the Al smelters. The uptake of F in common bent did not exceed the recommended limit for F contents in pasture grass (30 mg kg^–1) from soil with 0.5–28 mg F(H₂O) kg^–1 soil. The concentration in ryegrass was about 50 mg F kg^–1 when grown in a highly polluted soil (28 mg F(H₂O) kg^–1 soil). Concentrations in clover exceeded 30 mg F kg^–1 even in moderately polluted soil (1.3–7 mg F(H₂O) kg^–1 soil). Liming resulted in slightly lower F concentrations in the plant material.     

Isolation of bacterial strains capable of using lupanine,the predominant quinolizidine alkaloid in white lupin,as sole carbon and energy source

Seven Gram-negative bacterial strains, capable of using lupanine, the predominant quinolizidine alkaloid in white lupin, as sole carbon and energy source, were isolated from soil in whichLupinus albus andL. luteus had been grown. A metabolic profile system (BIOLOG) identified only three of the seven isolates, two asXanthomonas oryzae pvoryzae E and one asGluconobacter cerinus. The maximum specific growth rates of the seven isolates when incubated at 27°C in a medium containing as sole carbon source 2 g L^–1 of lupanine, ranged from 0.05 to 0.13 h^–1 and the concentration of dry biomass at the stationary phase ranged from 0.7 to 1.1 g L^–1. Unidentified strains IST20B and IST40D exhibited the highest maximum specific growth rates (0.13h^–1), removed 99% of the initial lupanine after 30 h of incubation, and the dry biomass yields did not exceed 0.4 g per g lupanine consumed. Strain IST20B is of potential use forL. albus debittering because, after 32 h growth in aqueous extracts ofL. albus, 85% of initial alkaloids were removed while the concentration of soluble protein was only reduced by 8%.     

Effects of soil cadmium on Pinus sylvestris L. seedlings

The effects of Cd on the growth and distribution of Cd and mineral nutrients within plant tissues were investigated for Pinus sylvestris L. seedlings grown in mineral forest soil with increasing levels of Cd addition (0–100 mg kg^–1). Approximately 20% of added Cd was found to be extractable from sandy loam forest soil. Root growth was less affected by Cd than shoot growth, which showed a significant reduction in the 100 mg Cd kg^–1 treatment. Cadmium accumulated in roots up to 325 mg kg^–1. Decreased concentrations of K in needles and Ca in stems with increasing Cd levels suggest a disturbance of mineral nutrition as a result of Cd addition.     

Influence of L-tryptophan and auxins applied to the rhizosphere on the vegetative growth of Zea mays L.

Glasshouse experiments were conducted to evaluate the influence of L-TRP in comparison with indole-3-acetamide (IAM), tryptophol (TOL) and indole-3-acetic acid (IAA) on the growth of Zea mays L. var. Early Sunglow. L-TRP (25 to 2.5×10^–5 mg kg^–1 soil), IAM (22 to 2.2×10^–5 mg kg^–1 soil), TOL (20 to 2.0×10^–5 mg kg^–1 soil), and IAA (22 to 2.2×10^–5 mg kg^–1 soil) were applied as a soil drench to established uniform seedlings. All treatments were applied in a completely randomized design with 10 replicates. IAM had no significant effect on the plant growth parameters. Shoot height, uppermost leaf collar base distance, internodal distance, and shoot dry and fresh weights were significantly improved upon the addition of TOL (2.0×10^–2 mg kg^–1 soil), however, the highest concentration (20 mg kg^–1 soil) caused a 14.6% reduction in leaf width. L-TRP (2.5×10^–3 mg kg^-1 soil) also had a significant influence on shoot height, uppermost leaf collar base distance, internodal distance and fresh weight of shoot compared with the control. The highest concentration of L-TRP (25=mg kg^–1 soil) had a negative effect on leaf width and dry weight of the shoot. The most pronounced response on the corn growth parameters was observed with the application of IAA at lower concentrations (2.2×10^–5 to 2.2×10^–2 mg kg^–1 soil) specifically improving root growth. The highest concentration (22 mg kg^–1 soil) of IAA had a significant negative effect on plant height, leaf width, stem diameter, shoot fresh and dry weight. These findings indicate that L-TRP applied at the appropriate concentrations can have positive effects on corn growth comparable to pure auxins (TOL and IAA).     

Effects of host plant and cucurbitacin on growth of larval Diabrotica undecimpunctata howardi

The effects of host plant and dietary cucurbitacin on the growth of larval southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber (Chrysomelidae: Luperini), were investigated. SCR were reared on four hosts: corn, Zea mays; peanuts, Arachis hypogaea; and two squash varieties, Cucurbita pepo cv. Ambassador (containing cucurbitacin D (0.08 mg g^–1 fr.wt.) = bitter), and C. pepo cv. Early Yellow Crookneck (lacking cucurbitacin = non-bitter). Larval growth was significantly greater on corn and peanuts than on either squash variety. After four weeks, adults had emerged from corn and peanut plants, while squash-reared larvae had not yet entered the pupal stage. There was no difference in larval growth on the two varieties of squash. Primary metabolite measurements showed no nutritional differences between the two squash varieties. Artificial diet experiments were used to test the effect of three concentrations of cucurbitacin D (0.0, 0.1, and 0.6 mg g^–1 diet) on growth of larval SCR. Larvae reared on diet containing 0.6 mg g^–1 cucurbitacin weighed significantly less than larvae reared on diet containing 0.1 mg g^–1 or no cucurbitacin after 10 d. No significant difference in growth was measured between the 0.1 mg g^–1 diet and the 0.0 mg g^–1 diet. Results are discussed relative to theories about the relationship between diabroticites and cucurbitacins.     

Effect of soil-applied NPK fertilizers on severity of black spot disease (Alternaria brassicae) and yield of oilseed rape

Effect of soil application of eight combinations of NPK fertilizers on the severity of black spot disease (BSD), caused by Alternaria brassicae (Sacc.) Berk., and yield of short duration oilseed rape (Brassica campestris L) were investigated under both pot and field conditions in 1987–88, 1988–89 and 1990–91. The severity of BSD was significantly greater (36–48%) on plants grown in ground treated with NP (N 90 kg ha^–1+P 40 kg ha^–1) applied as urea and single superphosphate respectively than on plants from the unfertilized control (NoPoKo) (o). However, the severity of BSD was significantly smaller (25–33%) when K (40 kg ha^–1) was applied as muriate of potash than in plants from control and NP treatments. The effect of NK (N 90 kg ha^–1+K 40 kg ha^–1) in decreasing the severity of BSD was increasingly more pronounced than the effects of PK (P 40 kg ha^–1+K 40 kg ha^–1), NP and K (40 kg ha^–1) applications. The decrease in the severity of BSD due to K was due to increased production in plants of phenolics which inhibited conidial germination and decreased sporulation of A. brassicae.The decrease in the severity of BSD due to NK application gave consistently increased seed yield 68% more than those of control and other treatments. The K-fertilized plants also showed increased resistance to lodging, increased 1000-seed weight and decreased seed infection. Seeds obtained from K-fertilized plants showed good seed germinability and vigorous seeding growth.     

Response of corn (Zea mays L.) to manganese application on Atlantic Coastal Plain soils

Field research was conducted on four Atlantic Coastal Plain soils in the United States to evaluate response of corn (Zea mays L.) plants to Mn application. The soils under study were classified as either Aeric or Typic Ochraquults. Manganese application increased corn grain yields by an average of 1195 kg ha^–1 on the four soils. The average grain yields on the soils were 7955 kg ha^–1 for the control and 9150 kg ha^–1 for the +Mn treatment. A Mitscherlich plant growth model was used to establish relationships between percent maximum grain yield and Mn concentration in the ear leaf at early silk (r=0.87, =0.01) and in the mature grain (r=0.58, =0.01). Based on 90% of maximum yield as the definition of the critical deficiency level, the critical Mn deficiency levels calculated with parameters from the Mitscherlich model were 10.6 mg kg^–1 in the ear leaf and 4.9 mg kg^–1 in the grain.