EFFECTS OF SOAKING TEMPERATURE,STRATIFICATION, POTASSIUM NITRATE AND GIBBERELLIC ACID ON SEED GERMINATION OF LOQUAT TREES

The present study was carried out to increase loquat seed germination with treatments consisting of two soaking temperatures (24 ± 2°C and 38 ± 2°C), chemical agents [control, 0.5% potassium nitrate (KNO₃) and 250 mgL^?1 gibberellic acid (GA₃) each for 20 h], and different moist chilling (MC) periods (1, 2, 3 and 4 weeks under 4–5°C). Compared with 24 ± 2°C, soaking at 38 ± 2°C reduced germination%, mean daily germination (MDG), and mean germination time (MGT), plumule and radicle lengths. Germination percentage, days to 50% emergence, fresh weight and lateral root numbers significantly reduced as MC period increased. KNO₃ and GA₃ had no significant effect on germination percentage, MDG, MGT and lateral root numbers. KNO₃ reduced days to 50% emergence and radicle length, but increased fresh weight compared with control and GA₃. Finally, our results suggest the soaking at 24 ± 2°C followed by 0.5% KNO₃ each for 20 h plus 1 week of MC or soaking at 24 ± 2°C followed by 250 mgL^?1 GA₃ each for 20 h plus 2 week of MC.     

Effect of fertilizer,N rate and nitrapyrin on Ca and Mg nutrition of corn (zea hays,L.)

Abstract

Corn was grown with three rates (200, 400, 800 rng N/pot) of sewage sludge (Milorganite), KNO₃, or (NH₄)₂SO. application in the presence (10 ppm) or absence of nitrapyrin, a nitrification inhibitor. Bleached areas appeared on the lower leaves of plants at the lowest application of sludge when nitrapyrin was added. No other visible symptoms were noted.

Five‐week‐old seedlings were harvested, weighed and analyzed for Ca and Mg. Nitrapyrin restricted dry weight production of plants receiving sludge and increased growth in those receiving KNO₃. Concentrations of Ca and Mg were reduced in all plants receiving nitrapyrin except in those grown at the lowest rates of sludge application.     

Supplementary Potassium Nitrate Improves Salt Tolerance in Bell Pepper Plants

Abstract

The effect of supplementary potassium nitrate (KNO₃) on growth and yield of bell pepper (Capsicum annum cv. 11B 14) plants grown in containers under high root‐zone salinity was investigated. Treatments were (1) control, soil only and (2) high salt treatment, as for control plus 3.5 g NaCl kg^?1 soil. Above treatments were combined with or without either 0.5 or 1 g supplementary KNO₃ kg^?1 soil. Plants grown at high NaCl had significantly less dry matter, fruit yield, and chlorophyll than those in the control treatment. Supplementing the high salt soil with 0.5 and 1 g KNO₃ kg^?1 increased plant dry matter, fruit yield, and chlorophyll concentrations as compared to high salt treatment. Membrane permeability increased significantly with high NaCl application, but less so when supplementary KNO₃ was applied. High NaCl resulted in plants with very leaky root systems as measured by high K efflux; rate of leakage was reduced by supplementary KNO₃. These data suggest that NaCl status affect root membrane integrity. Sodium (Na) concentration in plant tissues increased in leaves and roots in the elevated NaCl treatment as compared to control treatment. Concentrations of K and N in leaves were significantly lower in the high salt treatment than in the control. For the high salt treatment, supplementing the soil with KNO₃ at 1 g kg^?1 resulted in K and N levels similar to those of the control. These results support the view that supplementary KNO₃ can overcome the effects of high salinity on fruit yield and whole plant biomass in pepper plants.     

Seed priming improves seedling emergence and reduces oxidative stress in Nigella sativa under soil moisture stress

Nigella sativa seeds have multiple industrial and pharmaceutical uses for the diseases treatment such as bronchitis, rheumatism, high blood pressure, cough, eczema, inflammation, and influenza. Although semi-arid areas are suitable for production of annual medicinal plants because they receive favorable amounts of solar radiations, the establishment of these plants' seedling requires frequent irrigations because their seeds are small and the climate is hot at the time of planting. When the irrigation sources are limited, poor establishment and inadequate production will result. Therefore, in order to improve nitrogen (N) in N. sativa seedling establishment, different effects of seed priming treatments were evaluated under drought stress. Different levels of soil moisture (irrigation after 11, 22, 33, and 44 mm of evaporation as no water stress, mild water stress, moderate water stress, and severe water stress, respectively) and seed priming treatments [no priming, potassium nitrate (KNO₃), zinc sulfate (ZnSO₄), polyethylene glycol 6000, and gibberellic acid (GA)] were evaluated as the main plot and subplot factors, respectively. The results showed that under mild water stress condition, seed priming significantly increased proline content and the highest percentage of emergence was obtained with ZnSO₄. Furthermore, the highest amount of soluble protein was observed in the KNO₃ treatment and the catalase enzyme content increased in all priming treatments, except polyethylene glycol treatment. Under moderate water stress condition, the KNO₃ treatment raised the rate and percentage of emergence and the seedling length. However, under severe water stress condition, the highest percentage of emergence was achieved by GA and ZnSO₄ treatments. Moreover, hydropriming and GA produced the highest proline content and seedling dry weight. Under moderate and severe water stress conditions, the hydropriming and ZnSO₄ treatments showed a significant increase in catalase activity. It can be concluded that priming of N. sativa seeds with ZnSO₄ and GA can alleviate drought stress in the early stages of seedling growth by increasing the antioxidants in the seedlings. Farmers in semi-arid regions can prime N. sativa seeds with these compounds before planting to increase production of this valuable medicinal plant and reduce water consumption.     

Evaluating the effect of liming on N<Subscript>2</Subscript>O fluxes from denitrification in an Andosol using the acetylene inhibition and <Superscript>15</Superscript>N isotope tracer methods

We assessed the effect of liming on (1) N₂O production by denitrification under aerobic conditions using the ¹⁵N tracer method (experiment 1); and (2) the reduction of N₂O to N₂ under anaerobic conditions using the acetylene inhibition method (experiment 2). A Mollic Andosol with three lime treatments (unlimed soil, 4 and 20 mg CaCO₃ kg^?1) was incubated at 15 and 25 °C for 22 days at 50% and then 80% WFPS with or without 200 mg N kg^?1 added as ¹⁵N enriched KNO₃ in experiment 1. In experiment 2, the limed and unlimed soils were incubated under completely anaerobic conditions for 44 h (with or without 100 mg N kg^?1 as KNO₃). In experiment 1, limed treatments increased N₂O fluxes at 50% WFPS but decreased these fluxes at 80% WFPS. At 25 °C, cumulative N₂O and ¹⁵N₂O emissions in the high lime treatment were the lowest (with at least 30% less ¹⁵N₂O and total N₂O than the unlimed soil). Under anaerobic conditions, the high lime treatment showed at least 50% less N₂O than the unlimed treatment at both temperatures with or without KNO₃ addition but showed enhanced N₂ production. Our results suggest that the positive effect of liming on the mitigation of N₂O evolution from soil was influenced by soil temperature and moisture conditions.     

Comparison of hydroponic solutions for poinsettia nutritional studies 1

Poinsettia cultivars Supjibi and Freedom were grown in eight hydroponic solutions to develop a baseline solution for further nutritional studies. Four solutions contained nitrogen (N) from Ca(NO₃)₂‐4H₂O and KNO₃ (denoted as ‐NH₄) and four contained Ca(NO₃)₂‐4H₂O, KNO₃, nitric acid, and NH₄NO₃ as the N sources (denoted as +NH₄). The four ‐NH₄ and +NH₄ solutions were further divided by an IX or 2X rate of micronutrients [boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn)] (denoted as IX or 2X). A factorial of these four solutions at 2 concentrations (100 mg L¹ of N and potassium (K) and 15 mg L¹ phosphorus (P), or 300 mg L¹ of N and K and 46 mg L^‐1 P) was studied. Greater leaf and stem dry weight for both ‘Supjibi’ and ‘Freedom’ was observed in plants grown with the +NH₄ solutions, with a larger increase occurring with’ Supjibi’. Leaf NH₄‐N content for both cultivars was higher for both the 100 and 300 mg L^‐1 N and K fertilization rates when NH₄‐N was included. The leaf K content was highest for the plants grown with the +NH/2X solution for ‘Supjibi’, for both fertilization rates, and leaf K content increased as the K application rate increased. Results indicate that for nutritional studies with poinsettias, hydroponic solutions should include between 12.5% to 33% of the N in the NH₄ form, a calcium magnesium (Ca:Mg) ratio of 2:1, and a micronutrient concentration of (mg I/¹) 0.5, 0.02, 6.6, 0.5, 0.1, and 0.05, respectively, for B, Cu, Fe, Mn, Mo, and Zn, for adequate plant growth.     

Potassium Chloride Enhances Fruit Appearance and Improves Quality of Fertigated Greenhouse Tomato as Compared to Potassium Nitrate

Abstract

The effects of potassium chloride (KCl) as a potassium (K) source in fertigation solution on growth, yield and quality of tomato (cv. Durinta) in a controlled greenhouse were compared with potassium nitrate (KNO₃)—the conventional K source for vegetable fertigation. The treatments consisted of four levels of KCl: (1) 0% KCl (100% KNO₃), (2) 40% KCl (40% KCl and 60% KNO₃), (3) 60% KCl (60% KCl and 40% KNO₃), and (4) 100% KCl (0% KNO₃) in fertigation solution in the season 1999–2000. In 2000–2001, early (12 days after planting) and late (47 days after planting) applications of 100% KCl and 0% KCl were tested. The concentrations of K and other major nutrients were similar in all the treatments. Ammonium nitrate (NH₄NO₃), calcium nitrate [Ca(NO₃)₂] and nitric acid (HNO₃) were used as nitrogen (N) sources in KCl treatments. Electrical conductivity (EC) of all solutions ranged from 1.8 to 2.1 dS m^?1; pH range was from 6.6 to 7.1. Perlite was used as a neutral growing medium. Plant height, time to anthesis, time to harvest, and leaf nutrient content were monitored. Total yield, average fruit weight and number, and fruit size were measured after harvest. The appearance and quality of the fruits were rated following cold storage simulation for export conditions. None of the plants showed chloride (Cl) toxicity symptoms. No significant differences in yield components and plant growth were recorded among the treatments. Fruit dry matter, total soluble solids (TSS), glucose, titrable acidity (TA), pH, and EC of juice after simulation storage were not affected by the K source. Interestingly, fruit firmness, and freshness of calyx were significantly improved, while the number of rotten and blotchy fruits was significantly decreased in KCl treatments. The fruit nitrate (NO₃) content was decreased whereas iron (Fe) content was significantly increased in KCl treatments. The results show that KCl can be used as a substitute for KNO₃ without detrimental effects on plant development and yield, while significantly improving some important quality parameters. It is concluded that KNO₃ can be replaced fully or partially (depending on water quality) by KCl in tomato production while improving the quality of fruits.     

Greenhouse Gas Emissions from Paddy Soils Respond to Different Crop Root Residues and N Fertilizer Types

Greenhouse gas emissions from paddy soils respond differently to different combinations of crop root residues and N forms. An incubation experiment was carried out to explore the effect of four crop residues (milk vetch, ryegrass, winter wheat, and rape) and four nitrogen treatments (without fertilizer, urea, (NH₄)₂SO₄, and KNO₃) on CH₄, CO₂, and N₂O emissions in a paddy soil. Except in KNO₃ application treatments, CH₄ emissions of milk vetch residue treatments were significantly higher than those of the rest residue treatments. In the presence of milk vetch and ryegrass residues, urea application significantly increased CH₄ emissions in comparison to treatments without fertilizer. Urea significantly promoted CO₂ emissions, whereas (NH₄)₂SO₄ and KNO₃ significantly inhibited CO₂ emissions at all root residue treatments. Urea did not increase N₂O emissions, but (NH₄)₂SO₄ and KNO₃ promoted N₂O emissions at all residue treatments. In addition, KNO₃ had more effects on the increase of N₂O emissions than (NH₄)₂SO₄ in milk vetch-amended soils. Urea addition had no effect on global warming potentials, and (NH₄)₂SO₄ and KNO₃ addition significantly increased global warming potentials at all residue treatments except KNO₃ + winter wheat residue combination. Our results indicated that urea application had no additive effect on global warming when root residues were left in paddy soils, whereas (NH₄)₂SO₄ and KNO₃ application could increase the risk of global warming.     

Growth and mineral composition of tomato under various regimes of nitrogen nutrition 1

Five‐week‐old tomato plants were transplanted into pots containing 10 kg of potting compost which was amended with 0, 0.1, or 0.3 g of nitrapyrin and 4 g of N from KNO₃, (NH₄)₂SO₄ or sewage sludge and were grown in a greenhouse. After 2 to 3 weeks, leaves of the plants grown on any nitrapyrin x N source combination were curled with reduced laminae. Symptoms were most severe with the nitrapyrin x sludge regimes and least severe with the nitrapyrin x KNO₃ treatments. With (NH₄)₂SO₄ and sludge, growth was depressed linearly by nitrapyrin additions but was unaffected with KNO₃ fertilization. The concentrations of Ca and Mg in the shoots were lowered linearly or curvilinearly by nitrapyrin combination with any fertilizer whereas that of K was unaffected. Levels of Mn in leaves rose with nitrapyrin additions to the (NH₄)₂SO₄ or sludge treatment but were stable with any of the nitrapyrin x KNO₃ combinations. Cation antagonism among NH₄ ⁺, Ca⁺⁺, and Mg⁺⁺ is suggested as affecting the concentrations of these ions in tissues, whereas acidification of the medium and a restriction in dry matter production may account for the elevated levels of Mn in the tomato shoots grown in the presence of nitrapyrin.     

Effects of Forms and Rates of Zinc Fertilizers on Cadmium Concentrations in Two Cultivars of Maize

Abstract

A pot experiment was conducted to investigate the effects of three soluble zinc (Zn) fertilizers on cadmium (Cd) concentrations in two genotypes of maize (Zea mays): Jidan 209 and Changdan 374. Zinc fertilizers were added to soil at four levels: 0, 80, 160, and 240 mg kg^?1 soil as nitrate [Zn(NO₃)₂], chloride (ZnCl₂), and sulfate (ZnSO₄). Cadmium nitrate [Cd(NO₃)₂] was added to all the treatments at a uniform rate equivalent to 10 mg kg^?1 soil. The biomass of maize plants was increased with the application of three zinc fertilizers, of which Zn(NO₃)₂ yielded more than others. Under ZnCl₂ treatment, plant growth was promoted at the lower level and depressed at the higher one. All the three fertilizers decreased Cd concentration in shoots in comparison with treatments without Zn, but there were variations with different forms, especially in plants treated with Zn(NO₃)₂, which had the minimal value. The orders of average Cd concentration in shoots with different zinc fertilizers were ZnSO₄>ZnCl₂>Zn(NO₃)₂ for Jidan 209 and ZnCl₂>ZnSO₄>Zn(NO₃)₂ for Changdan 374, respectively (P<0.001). There was no significant difference between ZnSO₄ and ZnCl₂ treatments. The lowest Cd concentration in shoots was found in the 80‐mg‐kg^?1 soil or 160‐mg‐kg^?1 soil treatment. Cadmium concentration in roots in the presence of ZnCl₂ was the lowest and under ZnSO₄ the highest. The mechanism involved needs to be studied to elucidate the characteristics of complexation of Cl^? and SO₄ ^2? with Cd in plants and their influence on transfer from roots to shoots.     

Growth and mineral composition of radish under different nitrification inhibitors and nitrogen sources

Abstract

Captan [N‐(trichloromethylthio)‐4‐cyclo‐hexene‐l, 2‐dicarboximide] and benomy¹[methyl 1‐(butylcarbamoyl)‐2‐benzimidazolecarbamate] were evaluated as nitrification inhibitors and compared with nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine]. Nitrapyrin, captan, and benorayl were applied at 0, 20, 40, and 60 mg/kg with three nitrogen sources, KNO₃, (NH₄)₂SO₄, and urea, at 300 mg N/kg to ‘Cherry Belle’ radish (Raphanus sativusL). Nitrapyrin and captan inhibited nitrification effectively, but benomyl was not an effective inhibitor. Growth of radish roots and shoots was restricted with application of nitrapyrin and captan combined with (NH₄)₂SO₄or urea relative to the comparable KNO₃treatments. The concentrations of Ca, Mg, and NO₃‐N in plants, especially in shoots, fell, and the percentage of ? was increased with the addition of nitrapyrin and captan. Benomyl did not affect plant growth or composition     

Effect of Nitrogen Fertilizer Forms on Growth,Photosynthesis, and Yield of Rice Under Cadmium Stress

ABSTRACT

A pot experiment was conducted to study the influence of four nitrogen (N) fertilizer forms [Urea; calcium nitrate, Ca(NO₃)₂; ammonium sulfate, (NH₄)₂SO₄; and organic N] on growth, photosynthesis, and yield of rice under two cadmium (Cd) levels (0 and 100 mg Cd kg^?1 soil). Cadmium addition significantly reduced photosynthetic rate, and the reduction varied with N fertilizer form, with ammonium (NH₄ ⁺)-N and urea treated plants having more reduction. Nitrogen form had a distinct effect on SPAD value, and the effect was also dependent on Cd level and growth stage. Cadmium-stress significantly reduced flag leaf area, but for the second leaf, only the plants supplied with organic N showed the reduction. There was a significant difference in plant height among four N forms, with NH₄ ⁺- and nitrate (NO₃ ^?)-treated plants having the highest and lowest height, respectively. Cadmium stress caused significant reduction in grains per panicle and total plant weight, and the reduction varied with N form, with organic N treatment showing more reduction. There were significant differences among N forms in N and Cd concentrations of the plants subjected to Cd stress, with NH₄ ⁺-N treated plants having highest N and lowest Cd concentrations and NO₃ ^?-treated plants having lowest N and highest Cd uptake. The results showed that the inhibition of Cd stress on growth and yield formation of rice is closely related to N fertilizer form.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Effect of nitrogen form ratio on pansy growth and nutrition and the palatability to white‐tailed deer

Abstract

Pansies are one of the most popular annual bedding plants in the United States. Growth and uptake of essential nutrients as influenced by N‐form ratio was evaluated in pansy as well as what role pansy nutrition plays in the protection of pansy against feeding damage by white‐tailed deer provided by selected repellents. Plants were grown under three N‐form ratios: 100:0, 50:50, and 0:100NO₃:NH₄. Dry weight was highest for pansy treated with 100:0 and lowest for plants treated with 0:100 NO₃:NH₄ Mean quality ratings were 4.07 for pansies grown with 100:0,1.80 for pansies grown with 50:50, and 0.78 for pansies grown with 0:100. Potassium (K), magnesium (Mg), and manganese (Mn) content was lower in plants treated with 0:100 than in those treated with 100:0. Ammonium may have competed with these cations for uptake. Boron (B), copper (Cu), molybdenum (Mo), and aluminum (Al) content was highest in plants treated with N‐NH₄. There was no significant difference shown in nutrient levels caused by repellent treatments. Feeding damage was shown to be affected by N‐form ratio only on Day 3 of the study. Of the three repellent treatments [Deer and Rabbit Repellent (Thiram), Deer Away purrescent egg spray, and no spray], Thiram provided the greatest protection to pansies over the study period.     

Differential responses of soybean and dry bean to zinc deficiency 1

Whether a legume obtains its nitrogen (N) from the air, through dinitrogen fixation, or from the soil, as nitrate (NO₃), may influence its susceptibility to zinc (Zn) deficiency. The influence of N source [potassium nitrate (KNO₃)+ native soil N versus rhizobium‐inoculated seed + native soil N] and phosphorus (P) (0 and 200 mg P/kg), and Zn fertilizers (0, 1, and 8 mg Zn/kg) on growth and nutrient composition of soybean (Glycine max L. cv. McCall) and navy bean (Phaseolus vulgaris L. cv. Seafarer) grown on a calcareous soil were studied under greenhouse conditions. Inoculated plants, but not their KNO₃‐treated counterparts, had root nodules. However, due to N deficiency resulting from suboptimal N fixation, growth of these inoculated plants, especially of navy bean, was poorer than that of similarly treated KNO₃‐fed plants. As a consequence of this restricted growth, responses to P and Zn fertilizers were generally greater in KNO₃‐treated plants. Added P decreased the yield of KNO₃‐treated navy bean in the absence of added Zn, but P‐induced Zn deficiency had little effect on the growth of similarly treated inoculated plants. Plant excess bases (EB)/total plant N ratios [EB = 1/2 Ca + l/2Mg + Na + K ‐ Cl ‐ total S (S = divalent) ‐ total P (P = monovalent)] were less in KNO₃‐treated soybean than in correspondingly treated navy bean. Therefore, rhizosphere pH values around navy bean roots were probably less than those around soybean roots. Despite the hypothesized lower rhizosphere pH values, KNO₃‐treated navy bean was more susceptible to Zn deficiency than soybean. This greater susceptibility of navy bean to Zn deficiency was apparently at least partly due to poor translocation of Zn from the roots to the tops.     

Polymers act as nitrogen carriers to fertilize greenhouse and field grown lettuce

Abstract

Two concentration levels for each of two polymer gels (polyacrylate and vinyl alcohol acrylic acid) were incorporated with urea, ammonium sulfate [(NH₄)₂SO₄], and potassium nitrate (KNO₃) fertilizer solutions and used as nitrogen (N) carriers to fertilize lettuce grown in a greenhouse and field study. Of the initial 1290 mg N applied, gel treatments contained up to 70 mg N after 43 days. The vinyl alcohol polymers retained significantly larger quantities of NO₃‐N from the (NH₄)₂SO₄ and KNO₃‐N sources than from the urea source. The N concentration in each gel treatment was an important factor and dependent on the polymer and fertilizer source. Both gels performed better when incorporated with (NH4)₂SO₄ and KNO₃ than with urea.     

Responses of physiological parameters,grain yield,and grain quality to foliar application of potassium nitrate in two contrasting winter wheat cultivars under salinity stress

An experiment was conducted to test whether foliar application of KNO₃ on wheat in the heading stage could reduce salinity‐induced injuries, produce high grain yield, and improve grain quality. Salt‐resistant DK961 and salt‐sensitive JN17 wheat cultivars under 0 or 100 mM–NaCl conditions were foliarly watered with distilled water or a 10 mM–KNO₃ solution. The four treatments included: T₁ (CK₁), 0 mM NaCl + distilled water; T₂, 0 mM NaCl + 10 mM KNO₃; T₃ (CK₂), 100 mM NaCl + distilled water; T₄, 100 mM NaCl + 10 mM KNO₃. The results indicate that there were no differences (p > 0.05) in plant growth, grain yield, and grain quality between T₂ and T₁ in both cultivars, but these response variables were significantly lower in T₃ than in T₁. K⁺ : Na⁺ ratio, chlorophyll content, photosynthetic capacity, grain yield, flour yield, water absorbance, ash content, dough‐development time and dough‐stability time were significantly higher in T₄ than in T₃, while protein concentration, wet‐gluten concentration, and antioxidant enzyme activities were lower. Although foliar application of KNO₃ on JN17 enhanced plant growth, grain yield, and grain quality, these parameters were still lower in T₄ than in T₁. Our findings suggest that cultivating the salt‐resistant wheat cultivar combined with foliar application of KNO₃ at heading stage may alleviate salinity injuries and produce higher grain yield and better grain quality under saline conditions.     

Effects of urease and nitrification inhibitors on the efficient use of urea for pastoral systems

Abstract

The humic substances contained in an animal organic waste were extracted and the total extract separated into three humic fractions with different molecular weights (low, F₁ <10³; medium, F₂, with molecular weights ranging from 10³ to 10⁴; and high, F₃ >10⁴). The C content was highest in F₂, the same fraction also showing the lowest N content. The molecular weight of the humic fractions influenced the electrical conductivity, the highest molecular weight resulting in the lowest degree of electrical conductivity. Membrane-controlled ultrafiltra-tion (the method used to separate the various fractions from the whole extract) was also suitable for purifying such enzymes as phosphatase and β-glucosidase: the total activity obtained from the three fractions was considerably greater than that determined in the whole extract, Pyrolysis-gas chromatography (Py-GC) applied to the whole extract and humic fractions showed that in the F₃ fraction (highest molecular weight) benzene was the major fragment while furfural was the major fragment of F₁ (lowest molecular weight). For this reason, the humification index benzene/toluene indicates that the fraction with the highest molecular weight was the most humified while the furfural/pyrrole ratio indicates that the fraction with the lowest molecular weight was the most degradable. The whole extract and the fraction F₁ had a negative effect on seed germination when the concentration was equivalent to 100 mg kg^?1 of C, while the germination index was higher than that of the control when only 10 mg kg^?1 were used. The F₂ fraction had a positive effect on germination regardless of the concentration used. When 10 mg kg^?1 of C of the humic substances studied were added to the nutrient solution for growth experiments with maize plants, F₃ led to increases in root weight and F₂ led to increases in shoot weight. An inhibitor effect was observed for fraction F₁.     

Effects of Nitrogen Source on Growth and Development of Strawberry Plants

ABSTRACT

An experiment was conducted to study the effects of nitrate (NO₃ ^?) and ammonium (NH₄ ⁺) ratios in nutrient solutions on the growth and production of fruits, runners, and daughter plants of strawberry Fragaria x ananassa Duch., grown in a hydroponic system. Five treatments were applied, consisting of different proportions of NH₄ ⁺ and NO₃ ^? in the nutrient solution. The NH₄ ⁺:NO₃ ^? ratios were: T0 = 0:4, T1 = 1:3, T2 = 2:2, T3 = 3:1, and T4 = 4:0, at a constant nitrogen (N) concentration of 4 mol m^?3. Growth and morphogenesis were characterized by monitoring leaf-area increase, number of flowers and fruits per plant, and number of daughter plants of first and second generations. Nitrogen and carbon (C) content were measured at the end of the experiment in the organs of both mother and daughter plants. None of the variables related to the growth of the mother plant was affected by the treatments. However, the number of fruits increased with the proportion of NH₄ ⁺ in the nutrient solution. The number of daughter plants produced was affected only at high NH₄ ⁺ proportions, and their size (dry matter per daughter plant) and fertility (number of second-generation plants per first-generation plants) were reduced. The N or C content of the plants was not significantly affected by the treatments, but the C/N ratio in the crowns of mother plants was higher in treatments with 25% and 50% NH₄ ⁺ in the nutrient solution.     

Influence of the presence of nitrite and nitrate in soil on maize biomass production, nitrogen immobilization and nitrogen recovery

 When comparing nitrite (NO₂ ^–) and nitrate (NO₃ ^–) toxicity to maize (Zea mays L.) growth, it is important to know the fate of applied nitrogen (N). A pot experiment, using potassium nitrite (K¹⁵NO₂) and potassium nitrate (K¹⁵NO₃) was conducted to determine the fate of N (0, 75, 150, and 225 mg N kg^–1 soil) applied to a sandy loam soil collected from Gistel (Belgium). The total dry weight of the plants treated with NO₂ ^– was lower than that of the plants treated with NO₃ ^– at 15 and 26 days after N application (harvest 1 and harvest 2, respectively). Shoot and root biomass reduction started at a relatively low NO₂ ^– application rate (75 mg NO₂ ^–-N kg^–1). Biomass reduction increased, at both harvests with increasing amounts of NO₂ ^– to more than 55% at the highest application rate (225 mg NO₃ ^–-N kg^–1). In the NO₃ ^– treatment, a reduction of 16% in total plant dry biomass was recorded only at the highest application rate (225 mg NO₂ ^–-N kg^–1), at both harvest times. The ¹⁵N plant uptake (shoots plus roots) at harvest 1 decreased with increasing N application rates of both N forms (KNO₂ and KNO₃). Twenty-six days after the N application, the total ¹⁵N taken up by the plant increased in all treatments in comparison with 15 days after the N application. However, only at higher rates of N application (150 and 225 mg N kg^–1) was the ¹⁵N uptake by the NO₂ ^– fed plants significantly lower than by the NO₃ ^– fed plants. The percentage of immobilized N from the applied N was low (0–17.7%) at both harvests, irrespective of the N source. However, with relatively low N application rates (75 mg N kg^–1), the immobilized N in the soil decreased with time. This may be due to the re-mineralization of the applied N. The percentage of inorganic ¹⁵N in the soil in NO₂ ^– treatments was slightly lower than in equivalent doses of NO₃ ^–. This might be due to higher losses of N as N-oxides. Unaccounted for N from the applied N ranged from 21% to 52% for the NO₂ ^– treatments and from 3% to 38% for the NO₃ ^– treatments. Received: 17 July 1997