Effect of chromium and nitrogen form on photosynthesis and anti-oxidative system in barley

The effect of nitrogen forms on photosynthesis and anti-oxidative systems of barley plants under chromium stress was studied in a hydroponic experiment. The treatments comprised three chromium concentrations (0, 75, and 100 μM) and three N forms (NH₄)₂SO₄, urea, and Ca(NO₃)₂. In comparison with the urea or (NH₄)₂SO₄ fed plants, the Ca(NO₃)₂ fed plants had higher net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, transpiration rate, photosynthetically active radiation utilization efficiency, variable to maximum chlorophyll fluorescence ratio, and the content of chlorophylls and carotenoids. Cr toxicity caused oxidative stress in all plants but the Ca(NO₃)₂ fed plants had the least oxidative stress. Moreover, the Ca(NO₃)₂ fed plants had higher activities of anti-oxidative enzymes and content of non-enzymatic antioxidants than the urea or (NH₄)₂SO₄ fed plants. In addition, the Ca(NO₃)₂ fed plants had higher N and lower Cr content in all plant tissues than the urea or (NH₄)₂SO₄ fed plants. The current results indicate that the reasonable choice of N fertilizer is important for barley production on the Cr-contaminated soils.     

Effects of nitrogen fertilisers on the Javanese root-knot nematode Meloidogyne javanica and its interaction with cucumber

The influence of different nitrogen salts at five electrical conductivity levels (EC 2, 4, 6 and 8 mmhos/cm) on the Javanese root-knot nematode (RKN) (Meloidogyne javanica) and its interaction with cucumber was evaluated under in vitro, growth chamber and greenhouse conditions. Percentages of egg-hatching and second-stage juvenile viability of M. javanica were greatly reduced when NH₄Cl, (NH4)₂SO₄ and NH₄NO₃ were used especially at the higher levels of EC and accompanied with reduction in cucumber root galling. The lower root galling (less than 2.5) was accompanied with NH₄Cl, (NH₄)₂SO₄ and (NH₄)₂HPO₄, while KNO₃ and NH₄NO₃ resulted in moderate root galling. In contrast to the nitrogen salts, NaCl caused a reduction in both nematode infection and root growth especially at higher EC levels and this could be due to salinity effect. Diammonium phosphate was superior over the tested salts in increasing plant and root fresh and dry weights and cucumber phosphorus content, while KNO₃ was superior in increasing in plant content of potassium.     

Foliar applications of nitrogen to slash pine seedlings

Summary The absorption of N from foliar applications of various N sources by pine seedlings was studied under greenhouse conditions. Needles dipped into solutions of 4,000 ppm N from Ca(NO₃)₂ were burned slightly at the tips at two weeks. Although higher concentrations of (NH₂)₂CO and (NH₄)₂SO₄ could be used without plant damage, a uniform concentration of 3,000 ppm was used in all comparative tests of sources. The level of tissue N, brought about by soil fertilization 6 weeks previously, did not significantly influence absorption of foliarly applied N¹⁵. Soil moisture maintained at near 100, 60 to 70, and 25 to 35 per cent of water-holding capacity of the Leon fs did not significantly affect the absorption of tagged N. Greater quantities of N¹⁵ were absorbed as urea than as Ca(NO₃)₂ or (NH₄)₂SO₄. The use of a spreader-sticker increased the N¹⁵ uptake, regardless of the N compound used. However, the magnitude of the increased absorption associated with use as a sticker varied from 490 per cent with (NH₄)₂SO₄ to 260 per cent with urea. It was calculated that approximately 71, 45, and 39 per cent of foliar applied N was absorbed into needles within 24 hours from urea, Ca(NO₃)₂, and (NH₄)₂SO₄, respectively. Journal Paper No3588 of the Florida Agricultural Experiment Station, Gainesville, Florida.     

Toxic Effect of Cadmium on Rice as Affected by Nitrogen Fertilizer Form

A nutrient solution experiment was conducted to determine the influence of N forms on growth, oxidative stress, and Cd and N uptake in rice plants. The treatments were consisted of two Cd levels (0 and 1 μmol) and three N forms (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results indicated that without Cd addition in the culture solution, the N forms had no significant effect on all measured parameters, including plant growth, photosynthetic traits, malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, and Cd and N concentration, while Cd addition in the medium resulted in significant differences in measured parameters among the three forms of N fertilizers. The least inhibition of growth was noted in (NH₄)₂SO₄-fed plants, and the largest in Ca(NO₃)₂-fed plants, when plants were exposed to Cd stress. The highest photosynthetic rate and chlorophyll content was also recorded in (NH₄)₂SO₄-fed plants. Addition of Cd caused a remarkable increase in SOD activity and MDA content in plants, and the extent of increase varied with N form, with (NH₄)₂SO₄-fed plants being smallest. In comparison with the control plants, the N concentration in roots and shoots was not significantly affected in (NH₄)₂SO₄-fed plants, but significant decrease in root N concentration was found for the NH₄NO₃ and Ca(NO₃)₂-fed plants under Cd stress. Moreover, the significant differences were also noted among the three N forms in both root and shoot Cd concentrations, with (NH₄)₂SO₄-fed plants being the lowest. The results indicated that the toxic effect of Cd on rice varied with the form of N fertilizer.     

Evaluation of thiosulfate as a nitrification inhibitor for manures and fertilizers

Nitrogen from poultry manure (PM) and ammoniacal fertilizers undergoes rapid nitrification upon addition to soils, making it highly susceptible to leaching and thus creating a potential for groundwater contamination by nitrate-N. Any management technique that could delay nitrification would be desirable. A laboratory incubation study was conducted to determine the effect of thiosulfate, a known nitrification inhibitor, on nitrification in a loamy sand soil amended with five N sources, including two poultry manures and three N fertilizers [(NH₄)₂SO₄, NH₄NO₃, CO(NH₂)₂]. The manures or fertilizers were added to a soil-sand mixture alone or in combination with Na₂S₂O at a rate of 100 mg N kg^-1 for the inorganic N sources and 147 mg N kg^-1 and 122 mg N kg^-1 for PM-1 and PM-2 respectively. All treatments were incubated for 12 weeks and analyzed periodically for NO₃-N and NH₄-N.Thiosulfate was most effective with NH₄NO₃, maintaining 100% inhibition of nitrification throughout the 12 week study, and with (NH₄)₂SO₄ (89% inhibition at 12 weeks). Thiosulfate also inhibited nitrification from urea and poultry manure, but the inhibitory effect diminished later in the incubation. Urea had 81% inhibition of nitrification after eight weeks, decreasing to 26% by week 12, while the manures averaged 89% inhibition after four weeks and 20% at week 12. Net mineralization of organic N from PM was also reduced by the use of thiosulfate, particularly for PM-1 where the percentage of organic N mineralized decreased from 42% after four weeks incubation to 3% at week 12. Therefore, while thiosulfate can reduce nitrification from manures, and thus the potential for nitrate leaching, the timing of manure application will influence the effect of thiosulfate on the availability of manure N for plant uptake or leaching.     

Yield and nitrogen uptake of rapessed (Brassica campestris L.) with ammonium and nitrate

Water culture, growth chamber, greenhouse and field experiments were conducted to compare the effect of NH₄−N and NO₃−N on yield and N uptake of rapeseed (Brassica campestris L.). In water culture, the yields of 28-day old rapeseed plants grown at 14 μg N ml⁻¹ were double with NO₃ compared to NH₄, but N uptake was little affected. There was no such effect when concentration was reduced to 3.5 or 7 μg N ml⁻¹. The yield and N uptake of 26-day old rapeseed grown on six soils (pH 4.6 to 6.5) in pots in a growth chamber were much greater with NO₃ than with NH₄, although N concentration was more in the NH₄- than the NO₃-grown plants. In a greenhouse experiment with rapeseed grown on 12 potted soils, the N uptake of applied N was greater with NO₃ than with NH₄ on all soils. Averages were 63% with NH₄ and 78% with NO₃. However, NH₄-fixation capacities of the soils were only weakly correlated with yield from the two sources of N (r=0.48) and the relation was similar with N uptake. In contrast to the behavior of water culture, growth chamber and greenhouse experiments, the 33 field experiments did not show consistent difference in seed yield with NH₄ and NO₃ applied at time of seeding. In nine field experiments where band application was used for Ca(NO₃)₂, (NH₄)₂ SO₄, NH₄ NO₃, yield tended to be greatest for (NH₄)₂SO₄. However, in 19 experiments on acid soils with and without lime, yields in most cases were similar with (NH₄)₂SO₄ and NH₄ NO₃. Nitrification inhibitors were added to spring banded NH₄-based fertilizers in five experiments, but the yields were not influenced. Scientific Paper No. 558, Lacombe Research Station, Agriculture Canada.     

The effect of C/N ratio on lipid production byRhodosporidium toruloides ATCC 10788

Summary An optimum initial molar C/N ratio of about 77 was found for maximum lipid production from glucose or fructose with a nitrogen source from either (NH₄)₂SO₄, NH₄NO₃ or urea. The fatty acid composition of the lipids was affected by the initial C/N ratio and by the type of sugar but not significantly by the type of nitrogen.     

INORGANIC NITROGEN NUTRITION OF THE SEEDLINGS OF THE ORCHID,CATTLEYA

When grown in vitro in a medium containing NH₄NO₃ as the sole source of nitrogen, seeds ro the orchid, Cattleya (C. labiata ‘Wonder’ X C. labiata ‘Treasure'), germinated readily and proceeded to form small plantlets. Development of the embryos was accompanied by an increase in their total nitrogen and a decline in the percent dry weight. Growth responses of the seedlings in other ammonium salts like (NH₄)₂SO₄, (NH₄)₂HPO₄, NH₄Cl, ammonium acetate and ammonium oxalate were similar to that in NH₄NO₃. However, when grown in a medium containing NaNO₃, development of the seedlings was drastically inhibited; KNO₃, Ca(NO₃)₂, KNO₂ and NaNO₂ also were poor nitrogen sources. Attempts to grow the seedlings in NaNO₃ by changing the pH or by addition of kinetin, molybdenum or ascorbic acid as supplements were completely unsuccessful. When seedlings growing in NH₄NO₃ for varying periods were transferred to NaNO₃, it was found that those plants allowed to grow for 60 or more days in NH₄NO₃ could resume normal growth thereafter in NaNO₃. Determination of the nitrate reductase activity in seedlings of different ages grown in NaNO₃, after NH₄NO₃, showed that the ability of the seedlings to assimilate inorganic nitrogen was paralleled by the appearance of the enzyme.     

Comparison of the efficiency of urea,aqueous ammonia and ammonium sulphate as nitrogen fertilizers

Summary Nitrogen-15 labelled urea, aqueous NH₃ and (NH₄)₂SO₄ were applied to soils contained in pots. The fertilizers were injected in 5 cm³ of solution, 3.5 cm below the soil surface, to simulate a fertilizer band in the field. Ryegrass (Lolium perenne) was planted, and several cuttings and roots were harvested. Efficiency was determined as the recovery of fertilizer-N in the plant tissues and soil.Total recovery varied from 94 to 100%. There was no significant difference between the total recovery of the 3 fertilizer forms, although recovery in the soil component was lower for (NH₄)₂SO₄ than for urea or NH₃. There was a significant difference in total recovery between soils due to the soil component. Only small amounts of¹⁵N were not recovered, whereas laboratory experiments reported elsewhere had demonstrated that substantial gaseous losses of N as N₂, N₂O and NO +NO₂ occurred in these soils during nitrification of added NH₃ fertilizer.     

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

A hydroponic experiment was conducted to examine the effect of Cd stress on anti-oxidative enzyme activities at heading stage, yield components, root exudation and Cd and N uptake of rice plants grew in different N source i.e. (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results show that the effect of Cd stress on all measured parameters were N source dependent. Cd stress (1 μM) caused a remarkable reduction in grain yield and shoot biomass, an increase in root exudation, glutathione content, Cd concentration and catalase (CAT) and peroxidase (POD) activities of rice plants. In the plants under the control (without Cd addition) N source had no distinctive effect on the above measured parameters, but the differences among the three N forms in these parameters became significant when plants were exposed to Cd stress. Cd stress significantly increased POD and CAT activities, and gultathione content, with Ca(NO₃)₂-fed plants having the greatest POD and CAT activities and lowest glutathione content, and (NH₄)₂SO₄-fed plants being just opposite. Moreover, organic acid exudation varied also with N form for the Cd-stressed plants. In comparison with other two N forms, (NH₄)₂SO₄,-treated plants had higher grain yield, N concentration and lower Cd concentration in plants. The current results indicated that (NH₄)₂SO₄ is a better fertilizer for use in Cd contaminated soil.     

Optimization of cell growth and poly(3-hydroxybutyrate) accumulation on date syrup by a Bacillus megaterium strain

Optimal growth and PHB accumulation in Bacillus megaterium occurred with 5% (w/v) date syrup or beet molasses supplemented with NH₄Cl. When date syrup and beet molasses were used alone without an additional nitrogen source, a cell density of about 3gl^–1 with a PHB content of the cells of 50% (w/w) was achieved. NH₄NO₃ followed by ammonium acetate and then NH₄Cl supported cell growth up to 4.8gl^–1, whereas PHB accumulation was increased with NH₄Cl followed by ammonium acetate, NH₄NO₃ and then (NH₄)₂SO₄ to a PHB content of nearly 42% (w/w). Cultivation of B.megaterium at 30l scale gave a PHB content of 25% (w/w) of the cells and a cell density of 3.4gl^–1 after 14h growth.     

Toxicity of nitrapyrin to sunflower under different N nutrition regimes

Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH₄)₂SO₄, NH₄NO₃ and NaNO₃ to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH₄)₂SO₄>NH₄NO₃>NaNO₃. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH₄)₂SO₄ and NH₄NO₃ than as with NaNO₃. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH₄ ⁺−N nutrition relative to NO₃ ⁻−N nutrition.     

Effects of parathion and malathion on transformations of urea and ammonium sulfate nitrogen in soils

Summary A study of the effects of malathion and parathion applied at 10 and 50 g/g of soil on transformations of urea and (NH₄)₂SO₄–N in a sandy loam showed that the insecticides retarded urea hydrolysis as well as nitrification of urea and (NH₄)₂SO₄–N. At 50 parts/10⁶ rate of the insecticides, inhibition of urea hydrolysis ranged from 44 to 61% after 0.5 week and from 7 to 21% after 3 weeks of application. The insecticides inhibited the conversion of NH₄ ⁺ to NO₂ ^– without appreciably affecting the subsequent oxidation of NO₂ ^– to NO₃ ^– –N. This resulted in accumulation of higher amounts of NH₄ ⁺–N in soil samples treated with ammonium sulfate or urea N.The results suggest that transformations of urea and NH₄ ⁺ fertilizers in soils may be influenced by the amount of organophosphorus insecticide present and this may affect plant nutrition and fertilizer use.     

Nitrification in a New Zealand grassland soil

Summary The nitrifying population of a low-fertility New Zealand grassland soil was found to be very small and the soil did not accumulate NO₃-N when perfused in the laboratory with (NH₄)₂SO₄. The population of nitrifying bacteria, and the ability of the soil to nitrify on incubation, could be increased by field treatment with urea. The increased population developed in the presence of urea appeared to persist longer if lime was also applied to the soil. The limiting effect of substrate concentration on the population of nitrifying bacteria, which was observed in this soil, may help to explain the failure of some other grassland soils to accumulate NO₃-N.     

Influence of the nitrogen source and concentration on N fractions and free amino acid levels of grape vine explants

The influence of the source of inorganic nitrogen (KNO₃, (NH₄)₂SO₄ and NH₄NO₃) and its concentration (5, 10, 20 and 30 mM N) on total N incorporation, as well as on N distribution into different fractions (amminiacal, amino, amide and protein) and on free amino acid levels has been determined in grape vine explants cultured in vitro.Increasing concentrations of the nitrogen source resulted in increased total N content in tissues. This effect was small for KNO₃, higher for (NH₄)₂SO₄ and maximal for NH₄NO₃. In addition, nitrate promoted an increase in amino-N only, whereas ammonium increased both the ammoniacal-N and the amino-N fractions. Incorporation of N into amide-N and protein-N were not affected significantly by the N sources tested.The application of increasing quantities of N enhanced the accumulation of most free amino acids, especially arginine, alanine and proline, but to different extents, depending on both the N source and its concentration. The combination of ammonium and nitrate resulted in a higher accumulation of amino acids than that observed with either one of the two forms alone.     

Suppression of peatland methane emission by cumulative sulfate deposition in simulated acid rain

This field manipulation study tested the effect of weekly pulses of solutions of NH₄NO₃ and (NH₄)₂SO₄ salts on the evolution of CH₄ and N₂O from peatland soils. Methane and nitrous oxide emission from a nutrient-poor fen in northern Minnesota USA was measured over a full growing season from plots receiving weekly additions of NH₄NO₃ or (NH₄)₂SO₄. At this relatively pristine site, natural additions of N and S in precipitation occur at 8 and 5 kg ha^–1 y^–1, respectively. Nine weekly additions of the dissolved salts were made to increase this to a total deposition of 31 kg N ha^–1 y^–1 on the NH₄NO₃-amended plots and 30 and 29 kg ha^–1 y^–1 of N and S, respectively, in the (NH₄)₂SO₄-amended plots. Methane flux was measured weekly from treatment and control plots and all data comparisons are made on plots measured on the same day.After the onset of the treatments, and over the course of the growing season, CH₄ emission from the (NH₄)₂SO₄-amended plots averaged 163 mg CH₄ m^–2 d^–1, significantly lower than the same-day control plot mean of 259 mg CH₄ m^–2 d^–1 (repeated measures ANOVA). Total CH₄ flux from (NH₄)₂SO₄ treatment plots was one third lower than from control plots, at 11.7 and 17.1 g CH₄ m^–2, respectively. Methane emission from the NH₄NO₃-amended plots (mean of 256 mg CH₄ m^–2 d^–1) was not significantly different from that of controls measured on the same day (mean of 225 mg CH₄ m^–2 d^–1). Total CH₄ flux from NH₄NO₃ treatment plots and same-day controls was 16.9 and 15.1 g CH₄ m^–2, respectively. In general, stable, relatively warm and wet periods followed by environmental `triggers' such as rainfall or changes in water table or atmospheric pressure, which produced a CH<sub>4</sub> `pulse' in the other plots, produced no observable peak in CH₄ emission from the (NH₄)₂SO₄-amended plots. Nitrous oxide emission from all of the plots was below the detection limit over the course of the experiment.     

Effect of some nitrogenous salts on nitrogen transfer and protease activity in germinatingZea mays L. seeds

Maize seeds were allowed to germinate in the presence of different nitrogenous salts for 72 h. Changes in the ethanol soluble and insoluble nitrogen were studied in the embryo and in the endosperm. Supply of Ca(NC₃)₂ enhanced germination and protease activity in the endosperm resulting in greater solubilisation of protein to soluble nitrogen in the seeds. NH₄NO₃ and (NH₄)₂SO₄ were less effective as compared to Ca(NO₃)₂. Cycloheximide inhibited germination and protease activity. Pretreatment also resulted in increase in growth, soluble and insoluble nitrogen, and nitrate reductase activity in the primary leaves. Ca(NO₃)₂ was more effective than NH₄NO₃ and (NH₄)₂SO₄.     

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers,a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg^?1 of Cd and 241 mg kg^?1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH₄)₂SO₄+DCD treatment produced higher NH₄⁺?N concentrations in soil solution than the (NH₄)₂SO₄ and NaNO₃ treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg^?1, respectively. The (NH₄)₂SO₄+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO₃ treatment. Plant shoots grown with NaNO₃ had higher Cd concentrations than (NH₄)₂SO₄+DCD treatment at 24.0 and 15.4 mg kg^?1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.     

Epidemiology of wheat take-all as influenced by soil pH and temporal changes in inorganic soil N

Summary Soil pH, NH ₄ ⁺ and NO ₃ ⁻ concentrations in soil, and take-all root rot of winter wheat grown in the field were measured concurrently from sowing to anthesis in order to relate disease development to liming and N fertilization practices. Experimental variables included soil pH (5.5 and 6.0) and three N sources (NH₄NO₃, (NH₄)₂SO₄, NH₄Cl) banded with the seed at sowing in factorial combination with the same three N sources topdressed in the spring. Take-all severity was increased by increasing soil pH and by fertilization with NO ₃ ⁻ . Disease severity on crown roots increased exponentially following spring N fertilization and was affected more by soil pH and N-form than was severity on seminal roots. Grain yield ranged from 4.70 Mgha⁻¹ with spring NH₄NO₃ at soil pH 6.0 to 7.65 Mgha⁻¹ with spring NH₄Cl at soil pH 5.5. Sixty-six percent of the variability in grain yield was explained by the number of take-all infected crown roots per tiller at anthesis. Oregon Agric. Exp. Stn. technical paper no. 7707.     

Effect of nitrogen forms on growth and chemical changes in the rhizosphere of strawberry plants

The experiment was set up to examine the influence of different nitrogen forms: (NH₄)₂SO₄, Ca(NO₃)₂ or NH₄NO₃ on growth response, root induced pH changes in the rhizosphere, root-borne acid phosphatase activity in strawberry plants cv. Senga Sengana. The plants grown on sandy mineral soil were fertilized with 3 forms of nitrogen, in concentrations of 46 mg N·kg⁻¹ soil. The plants were grown in rhizoboxes with removable plexiglass lids. To ensure the root growth along the plexiglass lids, the rhizoboxes were placed at an angle of about 50° with the lid on the lower side. In case of ammonium supply, the nitrification inhibitor DIDIN was added (10 mg·kg⁻¹ of moist soil) to prevent conversion of ammonium into nitrate. The growth response (roots and shoots) of strawberry plants were determined after 11 weeks of treatment with different N forms. The best development of the root system and shoots (root and shoot dry weight and root length) was obtained, when ammonium nitrate was supplied. It is suggested therefore, that NH₄NO₃ stimulates vegetative growth of strawberry plants cv. Senga Sengana. However, there were no statistical differences in a leaf and flower number of the plants grown under different forms of N-fertilization. Determination of rhizosphere pH, and acid phosphatase activity were executed using non-destructive techniques, which enabled weekly measurement of chemical changes in the rhizosphere. The results revealed that the form of nitrogen supplied had a predominant effect on chemical changes in the rhizosphere of strawberry plants. The highest pH values (average pH 6.8) were measured in the rhizosphere of individual plants supplied with Ca(NO₃)₂. Whereas the lowest pH values (average pH 5.8) were detected in the presence of (NH₄)₂SO₄. The curve of rhizosphere pH measured along individual roots of the plants treated with Ca(NO₃)₂ represents the highest pH values whereas the curve of rhizosphere pH under (NH₄)₂SO₄ treatment had the lowest pH values. The highest activity of acid phosphatase were observed in the rhizosphere of strawberry plants grown in the presence of (NH₄)₂SO₄, at pH 5.8.