Critical Zn concentration for essential oil yield and menthol concentration of Japanese mint

The effect of different concentrations of Zn nutrient application on Japanese mint (Mentha arvensis L.) was studied under glasshouse conditions. Zn application stimulated the dry matter production, essential oil concentration and menthol concentration of Japanese mint. Zn supplies of 0.05µg ml^–1 were required for maximum responses in dry matter yield and oil concentration. Significantly positive interrelationships were observed among fresh herb yield, dry matter yield and menthol concentration in the oil. Graphical analyses of Cate and Nelson model indicated the critical Zn concentration in leaves to be 28µg g^–1 on a dry matter basis and in the solution culture 0.0475µg ml^–1 on the basis of Zn concentration in leaves.     

Recycling of nutrients in Japanese mint - assessment of soil fertility and crop yield

The efficiency of mint-residue, composted alone and amended with starter nutrients, microbial culture and soil suspension (hereafter termed amended compost) was compared with farm yard manure and inorganic fertilizer on the yield of Japanese mint (Mentha arvensis L.) and improvement of soil fertility. Herbage, essential oil yield, nutrient uptake of Japanese mint and soil available nutrients were significantly enhanced due to application of amended compost as compared to nonamended compost, farm yard manure and inorganic fertilizer. Organic fertilized soils maintained significantly higher available nutrients throughout the crop growth period as compared to inorganic fertilized soils. No additional improvement in yields and soil fertility was recorded with combined application of compost and inorganic fertilizer in 1:1 ratio as against addition of compost alone. Advantage of such combinations was recorded in case of farm yard manure. Results of the study suggested possibilities for nutrient recycling through composted mint-residue for supplementing the fertilizers requirement of Japanese mint.     

Effect of the nitrification inhibitors dicyandiamide,nitrapyrin and thiourea onNitrosomonas europaea

Effects of the inhibitors dicyandiamide (DCD), nitrapyrin (N-Serve, NS), and thiourea (TU) on growth and metabolism ofNitrosomonas europaea were tested under laboratory conditions. Growth of a pure culture was completely suppressed by 10 ppm NS and 0.5 ppm TU; inhibition by 300 ppm DCD was 83%. Ammonia oxidation and respiration of Nitrosomonas cell suspensions were reduced by 93% (10 ppm NS), 95% (0.5 ppm TU), and 73% (300 ppm DCD).Hydroxylamine oxidoreductase was not affected by high concentrations of inhibitors (200 ppm DCD, 100 ppm NS, 100 ppm TU). Cytochrome oxidase activity was increased by 10% with 200 ppm DCD, not affected by 100 pm TU, and inhibited by 52% with 100 ppm NS.The modes of action thus differed among the tested inhibitors. The merely bacteriostatic effect of dicyandiamide was demonstrated by the reversibility of growth inhibition.     

Effect of nitrification inhibitors on N-fixing bacteriaRhizobium leguminosarum andAzotobacter chroococcum

The nitrification inhibitor dicyandiamide [DCD] did not inhibit growth and respiration of N-fixing bacteria (Rhizobium leguminosarum andAzotobacter chroococcum) in cell suspensions with concentrations of 400 ppm DCD. Growth ofRhizobium leguminosarum was inhibited by 17% with 100 ppm nitrapyrin (N-Serve), but respiration was not affected. Growth ofAzotobacter chroococcum was inhibited by 10 ppm (10%) and 100 ppm nitrapyrin (50%); in the latter case, respiration was also impaired (36%). Thiourea only caused a minor growth inhibition ofAzotobacter chroococcum with 100 ppm (8%) and had no effect onRhizobium leguminosarum.     

Effect of gamma irradiation on allelopathic potential ofSorghum bicolor against weeds and nitrification

The effect of low doses of gamma irradiation on the allelopathic potential ofSorghum bicolor against weeds and nitrification was investigated. The results revealed that all test doses (500, 1000 and 1500 rad) significantly increased the allelopathic activity of root exudates, aqueous extracts, and decaying residues aganst seed germination and seedling growth ofAmaranthus retroflexus. The results also indicated that all test doses stimulated the allelopathic potential of aqueous extracts and decaying residues against nitrification activity. The possible application of this approach in biological control is briefly discussed.     

Influence of straw mulching on fertilizer nitrogen use efficiency,moisture conservation and herb and essential oil yield in Japanese mint (Mentha arvensis L.)

In a field study, the influence of organic mulches viz. paddy straw and citronella (Cymbopogon winterianus Jowitt) distillation waste on herb and essential oil yield and fertilizer N use efficiency in Japanese mint (Mentha arvensis L.) were examined for two years. Herb yield (dry weight) increased by 17 and 31% with paddy straw and citronella distillation waste, respectively over the use of no mulch. Essential oil yield also significantly increased due to mulching. A significant response to N was observed with 200 kg N ha^–1 in unmulched plots as against 150 kg N ha^–1 in mulched plots. Mulched soils have been observed to contain 2 to 4% higher moisture as compared to unmulched soils. Nitrogen uptake by plants increased by 18 and 25% over no mulch with using paddy straw and citronella distillation waste, respectively.     

Effect of the nitrification inhibitors 1-amidino-2-thiourea and dicyandiamide in combination with urea and ammonium sulfate

The efficiency of the nitrification inhibitors dicyandiamide (DCD) and 1-amidino-2-thiourea (or guanylthiourea = GTU) in reducing losses from N fertilizers was investigated in two greenhouse experiments where leaching of nitrate-N was induced by percolation at 3 and 5 weeks after fertilization.At an application rate of 10% by weight of fertilizer-N (e.g. 10 kg GTU/ha), GTU in combination with ammonium sulfate (AS) had effects similar to those of DCD (e.g. 15 kg DCD/ha) with regard to nitrate leaching, plant yields and nitrogen uptake. However, in combination with urea (U), GTU was more effective than DCD when applied at the same ratio except with a humic sandy clay soil (pH 7.3, 4.4% organic C), where GTU did not perform as effectively. Nitrate leaching was reduced by as much as 50% using U/GTU instead of U/DCD, and plant yield increased by 30%.At temperatures between 17 and 25°C, the combination U/GTU could protect a high percentage of the nitrogen from being nitrified and leached over a 3 to 5 weeks period. The superiority of GTU over DCD was demonstrated especially in the treatments with 5 weeks of preincubation, despite the considerably lower application rate.     

Effect of superphosphate and nitrogen on yield and take-all of wheat

Wheat was grown continuously in soil amended with 5 levels of superphosphate and with 4 levels of urea at 3 sites. The incidence and severity of take-all, caused byGaeumannomyces graminis var.tritici, declined with increasing rates of application of both superphosphate and urea.In both years, the severity of take-all on plants receiving neither superphosphate nor urea was about 40% while at the highest level of superphosphate and urea supply the take-all severity was approximately halved at 22%.There was an increase in grain yield in response to applied superphosphate and urea to the highest level of each nutrient. There was also an increase in the 1,000-kernal weights with superphosphate and urea fertilizer application.     

Incorporation of nitrification inhibitors with urea and urea-ammonium nitrate for irrigated corn

Nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] has been shown to delay nitrification and may increase nitrogen (N) utilization efficiency of crops under N loss conditions. Current application recommendations suggest immediate incorporation. With fertilizer N sources such as urea and urea-ammonium nitrate (UAN) solution, immediate incorporation may not be practical. Experiments were conducted with irrigated corn (Zea mays L.) over 3 years to determine if nitrification inhibitor (NI) incorporation and contact with the fertilizer source was essential with urea and UAN to maintain efficacy of nitrapyrin and etridiazol [5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole]. Nitrogen at a rate of 134 kg ha^–1 was broadcast on a Hubbard loamy coarse sand (sandy, mixed Udorthentic Haploboroll) before planting. Nitrification inhibitors were applied at 0.56 kg ha^–1 either as coating on urea, mixed with UAN, or applied in a broadcast application separate from the application of the N fertilizer. Incorporation was conducted immediately after NI application. Leaching losses, reduced N availability each year of experimentation. Nitrogen uptake from urea with no NI applied was 26% higher than uptake from UAN and resulted in 11% higher grain yields. Volatilization of urea from either N source was not apparent. Nitrapyrin and etridiazol produced similar increases in N utilization and yield. Incorporation of nitrapyrin and etridiazol was essential to obtain efficacy with both fertilizer sources. Incorporation of both NIs (averaged over NI) increased grain yields 28% with urea and 16% with UAN. Separate applications of NI provided comparable results to application with the fertilizer material if the NI was incorporated immediately.Journal Paper No. 16074 Univ. of Minnesota Agric. Expt. Sta., St. Paul, MN 55108. Contribution from the Department of Soil Science. This work was supported in part by Dow Chemical U.S.A. and the Olin Corp.     

Degradation of the nitrification inhibitor 1-amidino-2-thiourea in soils,and its action in Nitrosomonas pure culture and soil incubation experiments

The degradation of guanylthiourea (GTU) via 3,5-diamino-1,2,4-thiadiazole (TDZ) to dicyandiamide (DCD) was studied in selected soils. All three compounds could be determined by HPLC. GTU decomposed rapidly (within hours-days), the reaction from TDZ to DCD continued more slowly (within days-weeks). Soil type and temperature had an essential effect on the rate of degradation; conspicuous was a more rapid breakdown of GTU in presence of ammonium sulfate (AS) than in combination with urea.Each compound is a nitrification inhibitor; inNitrosomonas cell suspensions, 0.5 ppm GTU and 10 ppm TDZ achieved an effect comparable to 200 ppm DCD.The combination of these two effects—degradation in soil and inhibition of nitrification—were studied in soil incubation experiments. The three substances had inhibitory effects also in soil, however at significantly different application rates (20 ppm GTU or TDZ and 30 ppm DCD). Using these concentrations, AS/DCD and urea/GTU showed similar effects.Urea/GTU retarded nitrification by the factor 1.7 as compared to urea/DCD. AS/GTU had no advantage over AS/DCD which can be explained by the more rapid degradation of GTU in presence of AS.Urea/GTU apparently presents a promising possibility to utilize N-fertilizers more efficiently.     

Effect of nitrogen and water uptake on yield of wheat

For 2 years, field experiments were conducted to study the direct and interactive effects of water and nitrogen uptake at different growth stages on grain yield of wheat, grown on coarse textured alluvial soil of Ludhiana. Twelve treatments comprising 3 irrigation regimes and 4 rates of N were imposed. The N and irrigation regimes showed significant interaction, especially during the drier year. Grain yield was better explained with water uptake and N uptake, when partitioned over different growth stages than with total uptake. The sensitivity factor for water uptake was higher at the reproductive stage ( = 1.60) than at the vegetative ( = 1.05) and maturation ( = 0.38) stages. Contrary, yield was more sensitive to N uptake during the vegetative stage than the reproductive and the maturation stages. Sensitivity of grain yield to water uptake was higher at higher N application rates. Yield predictability was much better (R² = 0.98) when N and water uptake at different growth stages were combined.     

Effect of liming and carbofuran on groundnut yield in sandy soils in Niger

One of the constraints to groundnut production in sandy soils of Niger is crop growth variability. In early 1989, a trial on the effect of lime and carbofuran on soil pH, Al toxicity, nematode population and groundnut yield was initiated to study crop growth variability. Groundnut was sown in the 1989 rainy season, followed by pearl millet (Pennisatum glaucum) in the 1989–90 dry season and again groundnut in the 1990–91 rainy, and dry seasons. In 1989 the carbofuran treatment increased the pod yield. Lime application did not change the pH and exchangeable Al⁺⁺⁺ contents in the soil and did not increase groundnut yield. In the 1990–91 rainy and dry season, however, the application of 10 t ha^–1 of lime increased pH, decreased exchangeable Al⁺⁺⁺, improved crop growth and increased the yield of groundnut to the same level as was achieved by the carbofuran treatment. Application of lime did not affect the nematode population, which were reduced by the carbofuran.International Crops Research Institute for the Semi-Arid Tropics (ICRISAT); Submitted as ICRISAT Journal Article No 1228(via Paris)     

Phenolic inhibitors inErica australis L. and in associated soil

Fifteen phenolic compounds were identified in methanolic extracts obtained from flowers, leaves, stems, and roots ofErica australis L. and the associated soil. It is possible that the compounds identified may be connected with allelopathic phenomena.     

Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil

Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH₃) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH₃ could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha^–1 in dry season and 3.0–4.1 Mg ha^–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The¹⁵N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH₃ volatilization was probably responsible for the poor efficiency of broadcast urea in this study.     

Effect of puffing on oil characteristics ofAmaranth (Rajgeera) seeds

Puffing or popping is a common method of processingAmaranthus cruentus (Syn.Amaranthus paniculatus L. or Rajgeera) grain. Investigations into the effect of this processing treatment have shown the percent unsaturation in the oil to decrease from 75.5% to 62.3%. The maximum effect is on linoleic acid, the quantity of which decreased sharply from 46.8% to 27.0%. Squalene also increased by 15.5%, due to puffing of amaranth seeds.     

Nitrogen transformations in a flooded soil in the presence and absence of rice plants: 1. Nitrification

Nitrification rates (n) in the floodwater of an alkaline clay were measured in the absence or presence of rice plants by inhibition of ammonium oxidation and ¹⁵N-dilution techniques. Floodwater nitrate concentrations in control treatments showed a marked diurnal variation, and were higher than in the inhibitor treatments after the first day. Ammonium concentrations in floodwater declined exponentially in all treatments, being markedly affected by diffusion and NH₃ volatilization but little affected by nitrification and plant uptake. Nitrification rates in floodwater estimated by ¹⁵N-dilution were generally higher than the rates estimated by the inhibitor method. Estimates of n were generally higher during daylight hours than at night, and did not differ significantly between planted and unplanted pots. Microbial immobilisation of labelled ammonium and gross N immobilisation were not affected by addition of the nitrification inhibitor 2-ethynylpyridine.     

Biological suppression of nitrification by selected cultivars ofHelianthus annum L.

The allelopathic potential of different cultivars ofHelianthus annuus against nitrification was studied using the soil incubation method. The results indicated that aqueous extracts and residues of roots and shoots of all test cultivars significantly reduced the nitrification rate in soil. However, cultivars Local and Citosol were found to be more inhibitory to nitrification than others.     

Activation of soil respiration and shift of the microbial population balance in soil as a response to Lavandula stoechas essential oil

Lavandula stoechas, a native plant of Greece, is rich in essential oil and fenchone is its major constituent. We examined the effect of the essential oil and its main constituents on soil metabolism and microbial growth. Addition of the essential oil or fenchone to soil samples induced a remarkable increase in soil respiration. This was accompanied by an increase in the soil bacterial population of three orders of magnitude. This sizable population was not qualitatively similar to that of the control soil samples. One bacterial strain dominated soil samples treated with L. stoechas essential oil or fenchone. By use of the disk diffusion assay, we evaluated the capacity of three bacterial strains that we isolated from the soil samples, as well as Escherichia coli and Bacillus subtilis (reference strains), to grow in the presence of the essential oil and three of its main constituents (fenchone, cineol, -pinene). The substances tested did not inhibit the growth of the strain found to dominate the bacterial populations of treated soil samples; they severely inhibited B. subtilis. The other two isolated strains could also grow in liquid cultures in the presence of different quantities of essential oil or fenchone. Addition of fenchone at the end of the exponential phase increased the cell numbers of the strain that dominated the bacterial populations of treated soil samples, indicating use of the substrate added. On the basis of these results, we propose a scheme of successional stages during the decomposition process of the rich-in-essential-oil litter of aromatic plants that abound in the Mediterranean environment.     

Accelerated soil mineralization,nitrification, and revegetation of abandoned fields due to the removal of crop-soil phytotoxicity

In an abandoned corn field, clear-cutting of crop vegetation increased the productivity, species richness, and nonannuals in the following years after abandonment, as compared to the control plots from which crop vegetation was not removed. The increase in plant growth was apparently due to the elimination of allelopathic chemicals from the soil, which normally are released from the standing crop. Removal of vegetation also increased the soil mineralization of Ca²⁺, Mg²⁺, K⁺, NH₄ ⁺ and NO₃ ^–-N. This situation encouraged species having higher mineral requirements to rapidly invade the fields in the successive years. Clear-cutting also increased the nitrification process by removing the inhibitors of nitrification. The number ofNitrosomonas was always significantly higher in the harvested plots as compared to unharvested plots. Phenolic phytotoxins were isolated from the crop residue and soil. Further, these phytotoxins were significantly higher in the unharvested crops as compared to clear-cut plots, in most samples. Whatever the direct or indirect additional explanation for increased biomass, nonannuals and richness in successive years, it is clear that the removal of standing crop has a definite influence.     

Effect of prilled urea and modified urea materials on yield and quality of geranium (Pelargonium graveolens L. Her.)

Two field experiments were conducted to study the effect of prilled urea, neem cake coated urea, dicyandiamide treated urea and urea supergranules applied to a perennial aromatic herb, geranium (Pelargonium graveolens L. Her'.) grown on a sandy loam soil. Application of nitrogen increased the biomass and essential oil yields. Neem cake coated urea significantly increased the yields over prilled urea. There was no residual effect of N levels and N carriers. The concentration and quality of essential oil were not influenced either by levels or carriers of N.