Effect of trickle fertigation with three forms of nitrogen on soil pH,levels of extractable nutrients below the emitter and plant growth

The effects of application of nitrogen as calcium nitrate, urea or ammonium sulphate at two rates through the trickle irrigation system on pH and nutrient status of the wetted volume of soil below the emitters and on growth and nutrition of courgette (zucchini) plants (Cucurbita pepo L.) was investigated. Soil acidification, caused by nitrification, occurred to a large extent in the volume of soil immediately below the emitters in the urea and ammonium sulphate treatments. Acidification was greater at the high rate of N addition and more pronounced with ammonium sulphate than urea. A significant amount of applied urea appeared to move through the soil as urea and consequently, at the same rate of N addition, levels of ammonium were lower directly below the emitter and those of nitrate were higher further away from the emitters for the urea than ammonium sulphate treatments. Soil acidification below the emitters resulted in significant decreases in levels of exchangeable Ca, Mg and K and increases in levels of exchangeable Al, EDTA-extractable Fe, Mn, Zn and Cu and bicarbonate-extractable P. Vegetative growth and harvestable yields of courgettes were increased by both irrigation and nitrogen applications. Vegetative growth was generally greater at the low rate of N addition than at the high one and generally followed the order calcium nitrate > urea > ammonium sulphate. However, fruit yields followed the order urea > ammonium sulphate > calcium nitrate and were larger at the high rate of N for urea and ammonium sulphate treatments and unaffected by rate for the calcium nitrate treatments. It is suggested that with fertigation, the form of applied N can have significant physiological effects of plant growth and yields because N may be applied into the root zone on numerous occasions during the growing season.     

Top and root growth and nutrient absorption of Prunus avium L. at two soil pH and P levels

One-year-old Prunus avium L. were grown under greenhouse conditions in a Countesswells soil in all combinations of 2 pH and 2 P levels. The soil, obtained from a long-term liming and fertilizer experiment, provided pH values throughout the experiment of 3.75–3.99 (pH 1) and 4.81–5.41 (pH 2). The P treatments had 0.43% acetic acid extractable P of 31–44 g g^-1 (P1) and 145–173 g g^-1 (P2). The trees were harvested 92 (H1), 134 (H2), and 168 (H3) days after initiation of growth.Top (leaf+new stem) dry weight was significantly increased for pH 2 and P2 at H2 and H3. P2 also increased leaf weight (H1), the weight of the original stem-root (H2 and H3), and root length but decreased root diameter at both soil pHs (H2 and H3). Total tree uptake of N, P, K, Ca, and Mg was also increased by pH-P combinations which had significantly greater dry matter production and root length. Total Mn uptake decreased at pH2. Root nutrient inflows (uM m^-1 day^-1) were increased for Ca at pH2 and for P at P2. Mn inflow decreased at pH2 and at pH1 P2 although the increased root length associated with the latter treatmen resulted in increased total tree Mn uptake. In general, high nutrient inflows occurred in all trees at H1 and in severely stunted trees at pH1 P1; both had larger than average root diameters.     

Effects of liming and boron fertilization on boron uptake of Picea abies

The effects of liming on concentrations of boron and other elements in Norway spruce [Picea abies (L) Karst.] needles and in the mor humus layer were studied in long-term field experiments with and without B fertilizer on podzolic soils in Finland. Liming (2000+4000 kg ha^-1 last applied 12 years before sampling) decreased needle B concentrations in the four youngest needle age classes from 6–10 mg kg^-1 to 5 mg kg^-1. In boron fertilized plots the corresponding concentrations were 23–35 mg kg^-1 in control plots and 21–29 mg kg^-1 in limed plots. Both liming and B fertilizer decreased the Mn concentrations of needles. In the humus layer, total B concentration was increased by both lime and B fertilizer, and Ca and Mg concentrations and pH were still considerably higher in the limed plots than controls. Liming decreased the organic matter concentration in humus layer, whilst B fertilizer increased it.The results about B uptake were confirmed in a pot experiment, in which additionally the roles of increased soil pH and increased soil Ca concentration were separated by means of comparing the effects of CaCO₃ and CaSO₄. Two-year-old bare-rooted Norway spruce seedlings were grown in mor humus during the extension growth of the new shoot. The two doses of lime increased the pH of soil from 4.1 to 5.6 to 6.1, and correspondingly decreased the B concentrations in new needles from 22 to 12 to 9 mg kg^-1. However, CaSO₄ did not affect the pH of the soil or needle B concentrations. Hence the liming effect on boron availability in these soils appeared to be caused by the increased pH rather than increased calcium concentration.     

Effects of ammonium-N on development and infectivity of the take-all fungus

Effects of applications of a mixture of ammonium sulphate and mono-ammonium phosphate and of ammonium nitrate on the incidence of take-all disease of wheat (caused by Gaeumannomyces graminis var. tritici) and on subsequent inoculum levels were studied in field and glasshouse experiments. In a field experiment in Western Australia, on a sandy soil at pH 5·4, nitrogen applications had no detectable effect on disease severity at anthesis, but ammonium sulphate treatment increased the number of propagules of the pathogen in the soil. In a pot experiment, in which seed was sown in the field experiment soils, disease was greater in soil from plots treated with ammonium sulphate and least in soil from the nil-nitrogen plots, reflecting the respective inoculum levels in the field plot. However, treatment of the soils of lower inoculum with ammonium sulphate and ammonium nitrate during this pot experiment decreased disease. A second pot experiment confirmed the effectiveness of ammonium sulphate and ammonium nitrate in reducing take-all at lower inoculum levels, and their ineffectiveness at higher inoculum levels.     

Influence of ammonium on fine root development and rhizosphere pH of Douglas-fir seedlings in sand

Ammonium sulphate is a major component of the air pollutants deposited on forests in the Netherlands. Different amounts of NH₄ ⁺ were added to Douglas-fir seedlings grown in tall containers of sand, to study the influence of high concentrations of NH₄ ⁺ in the soil on the development of fine roots and the effects of nitrogen uptake on rhizosphere pH. At the end of this eight-month experiment part of the ammonium appeared to have nitrified into nitrate. High doses of ammonium negatively affected root length and root length per unit of dry matter (specific root length). Although Douglas fir shows a preferential ammonium uptake in nutrient solutions the increases in the pH of the rhizosphere in this experiment indicate that nitrogen was mostly taken up as nitrate. When the ammonium concentration in the soil is low, it cannot be taken up readily because of its low mobility in soil. Shoot growth was stimulated by high availability of nitrogen. The possible effects of high doses of ammonium on long-term forest vitality are discussed.     

Cd-tolerant arbuscular mycorrhizal (AM) fungi from heavy-metal polluted soils

Spores of arbuscular mycorrhizal (AM) fungi were isolated from two heavy-metal polluted soils in France via trap culture with leek (Allium porrum L.). Preliminary identification showed that the predominant spore type of both cultures (P2 and Cd40) belongs to the Glomus mosseae group. Their sensitivity to cadmium was compared to a laboratory reference strain (G. mosseae) by in vitro germination tests with cadmium nitrate solutions at a range of concentrations (0 to 100 mg L^–1) as well as extracts from a metal-polluted and unpolluted soils. Both cultures of AM fungi from heavy-metal polluted soils were more tolerant to cadmium than the G. mosseae reference strain. The graphically estimated EC₅₀ was 0.8 mg L^–1 Cd (concentration added to the test device) for G. mosseae and 7 mg L^–1 for P2 culture, corresponding to effective Cd concentrations of approximately 50–70 g L^–1 and 200–500 g L^–1, respectively. The extract of the metal-polluted soil P2 decreased germination of spores from the reference G. mosseae but not from P2 culture. However, the extracts of two unpolluted soils with different physico-chemical characteristics did not affect G. mosseae, whereas germination of P2 spores was markedly decreased in the presence of one of the extracts. These results indicate a potential adaptation of AM fungi to elevated metal concentrations in soil. The tested spores may be considered as metal-tolerant ecotypes. Spore germination results in presence of soil extracts show the difficulty of assessing the ecotoxic effect of metals on AM fungi without considering other soil factors that may interfere in spore germination and hyphal extension.     

Oxygen and nitrate reduction kinetics of a nonflocculating strain of Zoogloea ramigera

The oxygen and nitrate reduction kinetics of a nonflocculating strain of Zoogloea ramigera were determined. Axenic, nitrate-reducing bacterial suspensions were acclimated to various oxygen levels in a chemostat while measuring nitrate reduction in the presence of high ammonium nitrogen concentrations. Significant nitrate reduction was observed at oxygen concentrations up to 8 mg L^–1. Oxygen consumption was inhibited by oxygen concentrations in excess of 2 mg L^–1.     

Selenium uptake by plants as a function of soil type,organic matter content and pH

In pots containing sandy soils at two levels (pH 5 and 7) to which 0.5 mg Se L^-1 soil had been added, an increase in the proportion of clay soil or peat soil led to a decrease in the uptake of Se by spring wheat grain (Triticum aestivum L., var. Drabant) and winter rape plants (Brassica napus L., var. Emil). The effect was most pronounced for the smallest additions of clay and peat soils. Differences in Se uptake between the two pH levels were greatest in treatments where the additions of clay and peat soils were small. At the high pH, an increase in clay content from 7% to 39% resulted in a decrease in Se uptake of 79% for wheat and 70% for rape. At the low pH, the uptake decreased by 72% and 77%, respectively. At the higher pH, an increase in the content of organic matter from 1.4% to 39% resulted in decreases in Se uptake of 88% for wheat grain and 69% for rape. At the low pH, Se uptake decreased by 63% and 48%, respectively. Adding peat soil to clay soil had little effect on Se uptake. Among the limed, unmixed clay, sand and peat soils to which Se had not been added, uptake was highest from the sandy soil, i.e. 8.3 ng Se/g wheat grain and 42 ng Se/g rape. The lowest uptake rates were obtained in the clay soil, i.e. 3.0 ng Se/g for wheat grain and 9.0 ng Se/g for rape.     

Different nitrogen sources and growth responses of Spirulina platensis in microenvironments

Spirulina platensis was cultivated, in comparative studies, using several sources of nitrogen. The standard source used (sodium nitrate) was the same as that used in the synthetic medium Zarrouk, whereas the alternative nitrogen sources consisted of ammonium nitrate, urea, ammonium chloride, ammonium sulphate or acid ammonium phosphate. The initial nitrogen concentrations tested were 0.01, 0.03 and 0.05 M in an aerated photobioreactor at 30 °C, with an illuminance of 1900 lux, and 12 h-light/12 h-dark photoperiod over a period of 672 h. Maximum biomass was produced in medium containing sodium nitrate (0.01–0.03–0.05 M), followed by ammonium nitrate (0.01 M) and urea (0.01 M). The final biomass concentrations were 1.992 g l^–1 (0.03 M sodium nitrate), 1.628 g l^–1 (0.05 M sodium nitrate), 1.559 g l^–1 (0.01 M sodium nitrate), 0.993 g l^–1 (0.01 M ammonium nitrate) and 0.910 g l^–1 (0.01 M urea). This suggested that it is possible to utilize nitrogen sources other than sodium nitrate for growing S. platensis, in order to decrease the production costs of scaled up projects.     

Interactions between aluminium,phosphorus and pH in the response of barley to soil acidity

Summary Two acid soils showing different Al solubility as a function of pH were limed to a range of pH values (in 10^–2 M CaCl₂) between 4.1 and 5.6. The apparent critical pH for the growth of barley in pots was 0.25 lower in the soil showing lower Al solubility. The addition of phosphate reduced exchangeable and soluble Al in the soils, and lowered the apparent critical pH by 0.35 while maintaining the difference between the soils. The Al concentration at the critical pH, measured after cropping to take account of the treatment effects on soil Al, also varied with soil and with phosphate addition. These apparent critical values of both pH and soluble Al varied linearly with available phosphate, over the range 18 to 73 mg P/kg soil, as follows: pH from 4.9 to 4.3; soluble Al, from 0.010 mM to 0.056 mM; and the soluble Ca/Al mole ratio, from 1270 to 214.     

Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride

Summary Following the addition of 0–75 mole N g^–1 as ammonium chloride or ammonium sulphate to a sandy loam soil the nitrate formed was measured daily for a period of 15–17 days. The nitrate produced as a function of time was described using the Monod equation for microbial growth. An optimisation technique is described for obtaining, from the nitrification time course data, the maximum specific growth rate, the affinity constantant and an index limited by the concentration of ammonium in soil solution. Additions of more than 7.3 moles N g^–1 soil as ammonium chloride were found to inhibit nitrification. The inhibition was interpreted as being caused by osmotic pressure or by chloride ion. A similar effect was not found with ammonium sulphate, because the salt concentration in the soil solution was restricted by the precipitation of calcium sulphate. The model developed was capable of accounting for nitrate production in the soil under non-steady state conditions of substrate concentrations and nitrifier biomass.     

Removal of nitrate, nitrite, ammonium and phosphate ions from water by the aerial microalga Trentepohlia aurea

The aerial microalga Trentepohlia aurea has beeninvestigated in relation to removal characteristics of nitrate, nitrite,ammonium and phosphate ions. When the alga was cultured in medium with veryhighconcentrations of ammonium, nitrate and phosphate ions, it showed relativelyhigh growth and removal rates. It also grew quite well with high nitriteconcentration (< 141 mg NO₂-N L^–1).The removal rate was 0.28 mg NO₂-N L^–1day^–1 in the 40-day culture, when it was cultured in modifiedBold's basal medium with added 51 mg NO₂-NL^–1. In addition, we examined simultaneous removal of nutrientions. The biomass was 1.5 times higher in medium which N- and P-sourcesufficient than in ordinary medium. Higher removal ratios of nitrite andnitratefrom medium were shown in a 30-day culture, reaching 37% and 32%, respectively.It is concluded that T. aurea has the potential for use inthe purification of wastewater.     

A15N tracer study to compare nitrogen supply by Azolla and ammonium sulphate to IR8 rice plants grown under flooded conditions

Summary A pot experiment was carried out using a Bangladesh sandy loam paddy soil of pH 6.9 to compare the rates at which nitrogen from Azolla and ammonium sulphate was available to a high yielding rice variety, IR8, grown for 60 days in pots with 4 cm standing flood water.¹⁵N tracer studies confirm that nitrogen from ammonium sulphate was more available to the rice plants than from Azolla. An application of 6, 9 and 18 mg N of Azolla pot^–1 (each pot contained 250 g soil) increased shoot dry matter yields by 13, 29 and 49% for an uptake of 19, 36 and 85% more nitrogen; the corresponding increases on using ammonium sulphate were 33, 54 and 114% for an increased uptake of 57, 90 and 177% more nitrogen, respectively. About 34% of applied¹⁵N of Azolla was taken up by the rice plants in 60 days but 61% of¹⁵N of the ammonium sulphate was absorbed during this period. About 45% of the Azolla-N was released in 60 days, 55% remained in the soils as undecomposed material and 11% was lost as gas. The gaseous loss of¹⁵N from ammonium sulphate was 14%; 25% remained in the soils.     

Soil pH Effects on Uptake of Cd and Zn by Thlaspi caerulescens

For phytoextraction to be successful and viable in environmental remediation, strategies that can optimize plant uptake must be identified. Thlaspi caerulescens is an important hyperaccumulator of Cd and Zn, whether adjusting soil pH is an efficient way to enhance metal uptake by T. caerulescens must by clarified. This study used two soils differing in levels of Cd and Zn, which were adjusted to six different pH levels. Thlaspi caerulescens tissue metal concentrations and 0.1 M Sr(NO₃)₂ extractable soil metal concentrations were measured. The soluble metal form of both Cd and Zn was greatly increased with decreasing pH. Lowering pH significantly influenced plant metal uptake. For the high metal soil, highest plant biomass was at the lowest soil pH (4.74). The highest shoot metal concentration was at the second lowest pH (5.27). For low metal soil, due to low pH induced Al and Mn toxicity, both plant growth and metal uptake was greatest at intermediate pH levels. The extraordinary Cd phytoextraction ability of T. caerulescens was further demonstrated in this experiment. In the optimum pH treatments, Thlaspi caerulescens extracted 40% and 36% of total Cd in the low and high metal soils, respectively, with just one planting. Overall, decreasing pH is an effective strategy to enhance phytoextraction. But different soils had various responses to acidification treatment and a different optimum pH may exist. This pH should be identified to avoid unnecessarily extreme acidification of soils.     

Some chemical and physical factors affecting the rate and dunamics of nitrification in urine-affected soil

The effects of urinary chloride and nitrogen concentration and osmotic pressure on the nitrification of ammonium in a calcareous soil treated with cow urine were examined. Urinary chloride concentrations of up to 7.4 g L^–1 had no effect on the rate of nitrification, as determined by the accumulation of soil nitrate. Osmotic stress, generated using a mixed salt solution, had an inhibitory effect on nitrification at soil osmotic pressures lower than or equal to –1.0 PMa. Nitrification was completely inhibited at a soil osmotic pressure of –2.6 MPa. Accumulation of nitrate after a lag phase of 18 days was noted in the –2.0 MPa soil osmotic pressure treatment, indicating some degree of adaptation or osmo-regulation within the nitrifying population at this stress level. High urine-N concentrations resulted in considerable nitrite accumulations and reduced nitrification activity through the effect of free ammonia. It is concluded that in most temperate grassland soils at near-neutral pH, urinary chloride and nitrogen are unlikely to reduce nitrification rates, except where urine-N concentrations exceed 16 g N L^–1. Inhibition due to osmotic stress will be directly related to soil moisture status and may be particularly severe in dry, light-textured soils.     

Buckwheat (Fagopyrum esculentum Moench) has high capacity to take up phosphorus (P) from a calcium (Ca)-bound Source

Two experiments were carried out in a growth chamber to investigate the phosphorus (P)-uptake efficiency of Fagopyrum esculentum Moench (buckwheat) and Triticum aestivum (spring wheat) from a Ca-bound form. The first experiment was based on a sand-culture system with either rock phosphate (RP) or CaHPO₄ (CaHP) as the P source and nitrate or ammonium nitrate as nitrogen source. A highly calcareous soil was used in the second experiment. Buckwheat was shown to be highly efficient in taking up Ca-bound P compared to spring wheat. When plants were supplied with nitrate, the total P uptake by buckwheat from RP was nearly 10-fold higher than that of spring wheat (20.1 compared with 2.1 mg P pot^–1). Changing nitrogen source from nitrate only to ammonium nitrate increased P uptake by spring wheat substantially, but not buckwheat. High P-uptake efficiency of buckwheat was also demonstrated using the field soil, but to a lesser extent, which may be related to the difference in Zn supply between sand culture and field soil. It is suggested that buckwheat may be included in intercropping or crop rotation systems to activate P sources in calcareous soils. The principal mechanism of P uptake efficiency of buckwheat may be its ability to acidify the rhizosphere; however, further study is needed to unravel the regulation of root excretion of H⁺ and its molecular basis in order to exploit buckwheat's genetic capability to utilise sparingly soluble P from soil.     

Nodulation potential of soils from red alder stands covering a wide age range

Red alder (Alnus rubra Bong.) stands in the Pacific Northwest are the common first stage in succession following disturbance. These stands are highly productive and contribute a large amount of N to the soils as a result of their N₂-fixing symbiosis with Frankia. As these alder stands age, the soils not only increase in total N, but concentrations of NO^– ₃ increase and pH decreases as a result of nitrification. The objective of this study was to determine how the nodulation capacity of Frankia varies as red alder stands age and if differences in nodulation capacity are related to changes in soil properties. Nodulation capacity was determined by a red alder seedling bioassay for soils from red alder stands in the Oregon coast range covering a wide range of ages. Six chronosequences were sampled, each containing a young, an intermediate, and an older alder stand. Soil total N, total C, NO^– ₃, NH⁺ ₄, and pH were measured on the same soil samples. These factors as well as alder stand characteristics were compared with nodulation capacity in an attempt to identify soil characteristics typical in developing alder stands that most strongly affect nodulation capacity. Soil pH and NO^– ₃ concentration were highly correlated with nodulation capacity and with each other. Cluster analysis of the sites using these two variables identified two groups with distinctly different nodulation capacities. The cluster with the higher nodulation capacity was lower in NO^– ₃ and higher in pH than the other cluster, which included the majority of sites. There was substantial overlap in the age ranges for the two clusters and there was no significant correlation between age and nodulation capacity. Thus nodulation capacity appears to be most closely related to soil properties than to stand age.     

Models for relating pH measurements in water and calcium chloride for a wide range of pH,soil types and depths

Soil pH is commonly measured in water (pHw) or 0.01 M CaCl₂ (pH_Ca). The need to convert between these methods has led to the publication of linear, quadratic and cubic polynomial relationships for limited suites of soils. Concerns over the applicability of such relationships when mapping a wide range of soils and pH led to the establishment of a database of pH_W and pH_Ca values on each of 7894 samples from soil survey and field experimental sites in Queensland. The relationship between pH_W and pH_Ca across all soils was investigated and preliminary results examining the effect of soil depth and soil type on the relationship are presented.For all soils and depths, a linear regression accounted for 93.2% of the variation but did not predict pH_Ca well at very high or low pH_W values. The inclusion of second and third powers of pH_W accounted for significantly more of the variation (R²=0.94) in pH_Ca and the resultant curve matched the data better at high and low pH.Analysis of surface, sub-surface and subsoil groupings did not reveal any appreciable differences in the relationship between pH_W and pH_Ca attributable to depth. In contrast, differences in the relationship were evident between soil types. Generally, the mildly leached soils had linear relationships, while the weathered soils were distinctly curvilinear at low pH.     

Ground water flow paths in relation to nitrogen chemistry in the near-stream zone

Interactions between ground water flow paths and water chemistry were studied in the riparian zone of a small headwater catchment near Toronto, Ontario. Significant variations in oxygen — 18 and chloride indicated the presence of distinct sources of water in the ground water flow system entering the near-stream zone. Shallow ground water at the upland perimeter of the riparian zone had nitrate-N, chloride and dissolved oxygen concentrations which ranged between 100–180 µg L^–1, 1.2–1.8 mg L^–1 and 4.6–9.1 mg L^–1 respectively. Concentrations of nitrate — N in deep ground water flowing upward beneath the riparian wetland were < 10 µg L^–1, whereas chloride and dissolved oxygen ranged between 0.6–0.9 mg L^–1 and 0.4–2.2 mg L^–1 respectively. Ammonium — N concentrations (20–60 µg L^–1) were similar in shallow and deep ground water. Ground water was transported through the wetland to the stream by three hydrologic pathways. 1) Shallow ground water emerged as springs near the base of the hillslope producing surface rivulets which crossed the riparian zone to the stream. 2) Deep ground water flowed upward through organic soils and entered the rivulets within the wetland. 3) Deep ground water reached the stream as bed and bank seepage. Springs were higher in nitrate and chloride than rivulets entering the stream, whereas bank seeps had lower concentrations of nitrate and chloride and considerably higher ammonium concentrations than the rivulets. These contrasts in nitrate and chloride concentrations were related to initial differences in the ion chemistry of shallow and deep ground water rather than to element transformations within the riparian wetland. Differences in ammonium concentration between seeps and rivulets were caused by immobilization of ammonium in the substrates of aerobic rivulets, whereas little ammonium depletion probably occurred in deep ground water flowing upward through reduced subsurface organic soils around the stream perimeter.     

Seasonal variations of leaf water potential and growth in fertigated carob-trees (Ceratonia siliqua L.)

Variations of predawn and midday leaf water potential and relative growth rates were studied in mature carob trees (Ceratonia siliqua L. cv Mulata) submitted to a fertigation experiment. Three levels of irrigation were tested: 0%, 50% and 100%, based on daily standard evaporation values. For each irrigation level two nitrogen amounts were applied –21 and 63 kg N ha^-1 year^-1 as ammonium nitrate. The experiment was run between July 91 and August 1993. Measurements of leaf water potential and absolute branch length increments were made at monthly intervals, during the entire experimental period or during seasonal growth, respectively. Leaf water potential was related to soil volumetric water content, maximum and minimum air temperature and daily evaporation. Predawn leaf water potentials were always higher than –1.1 MPa. Midday leaf water potential values presented very large seasonal variations and very low values independent of treatments. The low leaf water potentials observed for the fertigated trees during summer, suggest that this parameter may be related not only to the evaporative demand but also to growth investment. The amount of fertigation was positively correlated with vegetative growth increment and fruit production. Practical implications for irrigation schedules of leaf water potential patterns together with drought adaptation mechanisms of carob tree are discussed.