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.     

Transformation of urea and ammonium sulphate in different soils

Summary The transformation of urea and ammonium sulphate in Ladwa sandy loam and Balsamand sand was studied in laboratory. Urea took at least one week in sandy loam and 2 weeks in sandy soils to hydrolyse completely. The process of hydrolysis was faster in finer soil with high organic matter than in coarse soil having low organic matter. There was no nitrification upto 3 days in sandy loam and upto 7 days in sandy soils, respectively, but there was immobilization of NO₃-N during these initial periods. The NO₃-N content at the end of incubation period (35 days) was more in case of urea than in case of ammonium sulphate treated samples in sandy loam soil and reverse was true in sandy soil. The hydrolysis of urea did not follow zero or first order kinetics as proposed in previous studies.     

Nitrogenous fertilizer transformations in the Sudan Gezira soil

Summary and conclusions 1. Studies of the transformation of urea and ammonium sulphate in the Sudan Gezeira soil, when incubated under field conditions in polythene bags, were carried out with two rates of nitrogen, different moisture levels and frequency of wetting and drying during the winter and summer months.2. The pattern of the transformation was nearly the same for the two levels of nitrogen added but there was a difference in magnitude. Urea hydrolysis was arrested during the first week in the open-bag system in the summer months. A low recovery of ammonia with ammonium sulphate and urea was associated with early ammonia volatilization losses.3. There was a marked accumulation of nitrite in the first two weeks especially in moist closed bags, thereafter it decreased to low values.4. Nitrate accumulated gradually under winter conditions, more so with closed bags than open ones. By contrast, little nitrate nitrogen was formed during the hot summer months, this being associated with high ammonia accumulation throughout the incubation period.     

The role of bacterial motility in the survival and spread of Pseudomonas fluorescens in soil and in the attachment and colonisation of wheat roots

Motile and non-motile strains of Pseudomonas fluorescens SBW25 were constructed using different combinations of the lacZY, xylE and aph marker genes which allowed their detection and differentiation in soil, root and seed samples. The survival of motile and non-motile strains was investigated in both non-competitive and competitive assays in water and non-sterile soil. Although there was no difference between strains in water, the motile strain survived in significantly greater numbers than the non-motile strain after 21 days in soil. There was no significant difference between competitive assays, where motile and non-motile cells were co-inoculated into soil, and non-competitive assays where strains were inoculated separately. Bacterial survival decreased as matric potential increased from -224 to -17 kPa but matric potential had no significant effect on motile compared to non-motile strains. Vertical spread of both motile and non-motile strains was detected 6.4 mm from the inoculum zone after 14 days in the absence of percolating water. There was no significant difference, for either strain, in distance moved from the inoculum zone after 14, 26 or 40 days. The motile strain had a significant advantage in attachment to sterile wheat roots in both non-competitive and competitive studies. When the spatial colonisation of wheat root systems was assessed in non-sterile soil, there was no significant difference between the motile and non-motile strain from either seed or soil inoculum. However, when the whole root system was assessed as one sample unit, differences could be detected. Bacterial motility could contribute to survival in soil and the initial phase of colonisation, where attachment and movement onto the root surface are important.     

The growth of saprophytic fungi on root surfaces

Summary Data are provided on the growth of non-pathogenic soil fungi on root surfaces. By growing roots from non-sterile soil into sterile vermiculite, and by regular isolation of fungi from the roots which had grown into the sterile vermiculite, it was shown that fungal growth down roots is slow. It is suggested that in the colonization of roots by non-pathogenic fungi successive lateral colonization from the soil is of greater importance than the growth of fungi down roots.     

The non-enzymic reduction of nitrite by benzyl viologen (free-radical) in the presence and absence of ammonium sulphate

Some similarity is inferred between the reaction or reduced benzyl viologen with undissociated nitrous acid, which is significant at pH values below 7 and that with the undissociated product of nitrite ion and ammonium sulphate; presumably ammonium nitrite. This would explain why the presence of ammonium sulphate appreciably offsets the effects of decreasing pH and also the exponential relationship between rate of nitrite loss and ammonium sulphate concentration. There are other features of the reaction which cannot be explained at present, especially with regard to the degree of reduction of benzyl viologen. It is nevertheless apparent that a complex non-enzymic reaction yielding several products occurs when ammonium sulphate is present and that the presence of likely residual quantities after its use in enzyme purification may cause serious errors in enzyme assay.     

Effect of inoculation method and plant growth medium on endophytic colonization of sorghum by the entomopathogenic fungus <Emphasis Type="Italic">Beauveria bassiana</Emphasis>

A study was conducted to determine the effect of inoculation method and plant growth medium on colonization of sorghum by an endophytic Beauveria bassiana. Colonization of leaves, stems, and roots by B. bassiana was assessed 20-days after application of the fungus. Although B. bassiana established as an endophyte in sorghum leaves, stems, and roots regardless of inoculation method (leaf, seed, or soil inoculation), plant growth medium (sterile soil, non-sterile soil, or vermiculite) apparently influenced colonization rates. Seed inoculation with conidia caused no stem or leaf colonization by the fungus in non-sterile soil but did result in substantial endophytic colonization in vermiculite and sterile soil. Leaf inoculation did not result in root colonization, regardless of plant growth medium. Endophytic colonization was greater in leaves and stems than roots. Endophytic colonization by B. bassiana had no adverse effects on the growth of sorghum plants. Leaf inoculation with a conidial suspension proved to be the best method to introduce B. bassiana into sorghum leaves for plants growing in either sterile or non-sterile soil. Further research should focus on the virulence of endophytic B. bassiana against sorghum stem borers.     

Re-sorption of organic compounds by roots of Zea mays L. and its consequences in the rhizosphere

The exudation of soluble carbon compounds from Zea mays roots was investigated over a 10 day growth period under sterile and non-sterile solution culture conditions. The results showed that plants grown in sterile static solution culture, where C was allowed to accumulate, released 8 times less C than plants grown under culture conditions in which the solutions were replaced daily. The increased C loss from plant cultures in which exudates were removed daily was attributable to, (a) the reduced potential for root re-sorption of previously lost C, and (b), increasing diffusion gradients between the root and the surrounding bathing solution increasing passive leakage of exudates from the roots. In treatments where C was removed daily from the root-bathing solution, 86% of the total C lost was of a soluble low molecular weight nature, whereas, in sterile and non-sterile static cultures, allowing the accumulation of C over 10 days, this was reduced to 67.5 and 48% respectively. The main C fluxes operating in a solution culture system (efflux and influx of C by both roots and microorganisms) were examined using a computer simulation model to describe movement of soluble sugar-C in both sterile and non-sterile conditions. In sterile static cultures where C was allowed to accumulate in solution over a 10 day growth period, 98% of the C exuded was re-absorbed by the plant. Where C was removed daily from the root-bathing solution this was reduced to 86%. The predicted patterns of C accumulation were similar to those found in the experiments. Simulations showed that the pattern of accumulation and final equilibrium concentrations were dependent on the rate of exudation, the spatial characteristics of exudation, solution volume, root growth rate and the presence of a microbial population. Simulations under non-sterile conditions showed that roots can compete with microorganisms for exudates in solution indicating the possible importance of re-sorption in a soil environment. The results clearly indicate that roots are capable of regulating the net amount of C released into a solution culture with the amount of C collected being highly dependent on the experimental conditions employed. The possible implications of soluble C influx on processes operating within the rhizosphere and in experimental systems is discussed.     

The Inducible Formation and Stability of Nitrate Reductase in Higher Plants: I. EFFECTS OF NITRATE AND MOLYBDENUM ON ENZYME ACTIVITY IN CAULIFLOWER (BRASSICA OLERACEA VAR. BOTRYTIS)

The enzyme nitrate reductase could not be detected in leaf tissuesof cauliflower plants grown in sterile cultures with glutamicacid or ammonium sulphate if nitrate was absent. Excised leaftissues from these plants formed the enzyme for several hoursat a steady rate when infiltrated with nitrate. Plants starvedof nitrate for short periods lost enzyme activity which wasrestored in excised tissues upon infiltration with nitrate butnot with ammonium sulphate or nitrite. Molybdenum-deficientplants grown with nitrate also lacked enzyme activity whichwas restored in excised tissues after infiltration with molybdenum.Both nitrate and molybdenum were required to produce maximalrates of enzyme formation in excised tissues of plants grownwith ammonium sulphate and no molybdenum. Apparent Michaelisconstants for nitrate and molybdenum were found to be about10^-5 and 10^-7 respectively. The capacity of excised tissuesto respond to the inducer varied with their age and leaf positionon the plant and was exercised under conditions where growthwas unlikely. Increases in specific activities were similar.There was no evidence of a lag in response to nitrate or molybdenumwith tissues of plants grown with ammonium sulphate or glutamicacid in sterile cultures but lag periods were observed withtissues from plants deprived of nitrate. Cell-free preparationswere unable to respond to either factor. The results are interpretedas evidence for induced enzyme formation in vivo in responseto the substrate or the constituent metal.     

No accession-specific effect of rhizosphere soil communities on the growth and competition of Arabidopsis thaliana accessions

Soil communities associated with specific plant species affect individual plants' growth and competitive ability. Limited evidence suggests that unique soil communities can also differentially influence growth and competition at the ecotype level. Previous work with Arabidopsis thaliana has shown that accessions produce distinct and reproducible rhizosphere bacterial communities, with significant differences in both species composition and relative abundance. We tested the hypothesis that soil communities uniquely affect the growth and reproduction of the plant accessions with which they are associated. Specifically, we examined the growth of four accessions when exposed to their own soil communities and the communities generated by each of the other three accessions. To do this we planted focal accessions inside a ring of six plants that created a "background" soil community. We grew focal plants in this design in three separate soil treatments: non-sterile soil, sterilized soil, and "preconditioned" soil. We preconditioned soil by growing accessions in non-sterile soil for six weeks before the start of the experiment. The main experiment was harvested after seven weeks of growth and we recorded height, silique number, and dry weight of each focal plant. Plants grown in the preconditioned soil treatment showed less growth relative to the non-sterile and sterile soil treatments. In addition, plants in the sterile soil grew larger than those in non-sterile soil. However, we saw no interaction between soil treatment and background accession. We conclude that the soil communities have a negative net impact on Arabidopsis thaliana growth, and that the unique soil communities associated with each accession do not differentially affect growth and competition of study species.     

The effects of micro-organisms on plant growth

Summary Subterranean clover, tomato, phalaris, and radiata pine were grown with a complete plant- nutrient solution in sterile sand and agar and inoculated with soil suspensions prepared from unsterilized and from sterilized soil.The presence of micro-organisms reduced primary-root growth in all plants and total root growth in most plants. The total numbers of secondary roots were lower in non-sterile treatments but there was a tendency for an increase in the concentrations of secondary roots with the non-sterile plants. Under the test conditions only radiata pine grown in sterile sand produced significantly greater top growth than those grown in the presence of micro-organisms. Root-stunting micro-organisms were shown to occur in each of four different soil types used in the studies but the extent of stunting varied with the soil. In agar, root stunting was observed at 5 days and 9 days after planting (and inoculation) with subterranean clover and tomato respectively.Production and growth of root hairs by subterranean clover was markedly reduced by organisms from all four soils tested, the reduction varying with the soil. In contrast to root-stunting organisms, root-hair suppressing micro-organisms were abundant in soil. Root-hair suppression was apparent in sand after 3 days and is an inhibition of root-hair development rather than microbial digestion of existing root hairs. Only slight root-hair reduction was observed for tomato and phalaris.     

Nitrogen nutrition of ginger (Zingiber officinale)

Summary Two fertilizer experiments were conducted in the field at Beerwah, South-East Queensland. In the first experiment leaf nitrogen concentrations, and the yield of ginger shoots and rhizomes at early and late harvests increased both with the total amount of nitrogen applied up to the highest level studied (336 kg N/ha as ammonium nitrate) and with the number of applications making up the total. At all levels of nitrogen application the apparent recovery of fertilizer nitrogen increased in the order 1 application <2 applications <4 applications. At 33.6 kg N/ha there appeared to be no advantage in dividing the total N applied into more than 4 applications but the data suggested higher recoveries of nitrogen with 8 applications at 112 kg N/ha and 336 kg N/ha. In the second experiment, ammonium nitrate, urea, and ammonium sulphate were found to be equally effective as nitrogen fertilizers for ginger when applied at equal rates of nitrogen per hectare. However, in terms of cost effectiveness they rated in the order urea > ammonium nitrate > ammonium sulphate.All three nitrogen sources acidified the soil, the decrease in soil pH during the growing season increasing with increasing rate of application. In Experiment 1 split applications, which increased the recovery of applied nitrogen in the crop, also increased the extent of acidification. In Experiment 2 ammonium sulphate tended to be more strongly acidifying than the other fertilizers but the difference was statistically significant only at the highest rate of nitrogen application. Because of the strong effects of nitrogen supply on both yield and soil pH, the highest yields were associated with end-of-season pH values below 5.0.     

Effects of ammonium sulphate application on the rhizosphere,fine-root and needle chemistry in aPicea abies (L.) Karst. stand

Rhizosphere, fine-root and needle chemistry were investigated in a 28 year old Norway spruce stand in SW Sweden. The uptake and allocation pattern of plant nutrients and aluminium in control plots (C) and plots repeatedly treated with ammonium sulphate (NS) were compared. Treatments started in 1988. Current year needles, one-year-old needles and cylindrical core samples of the LFH-layer and the mineral soil layers were sampled in 1988, 1989 and 1990. Compared to the control plots, pH decreased significantly in the rhizosphere soil in the NS plots in 1989 and 1990 while the SO₄-S concentration increased significantly. Aluminium concentration in the rhizosphere soil was generally higher in the NS plots in all soil layers, except at 0–10 cm depths, both in 1989 and 1990. Calcium, Mg and K concentrations also increased after treatment with ammonium sulphate. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment significantly reduced Mg concentrations in fine roots in all layers in 1990. A similar trend was found in the needles. Ca concentrations in fine roots were significantly lower in the NS plots in the LFH layer in 1990 and the same pattern was found in the current needles. The N and S concentrations of both fine roots and needles were significantly higher in the NS plots. It was suggested that NS treatment resulted in displacement of Mg, Ca and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

Absorption of Nitrogen, Phosphorus, and Potassium from Nutrient Sprays by Leaves

Barley, Brussels sprout, French bean, tomato, and sugar-beetplants grown in soil in pots and sprayed, usually daily, forseveral weeks, with nutrient solutions containing nitrogen,phosphorus, potassium, and a spreader, with precautions to preventthe spray solution falling on the soil, had higher nutrientcontents and dry weights than control plants sprayed with waterand spreader only. Increase in nutrient content occurred withhigh or low levels of nutrient supply to the roots and was approximatelyproportional to the concentration of spray and to the frequencyof spraying. The nitrogen content of sugar-beet plants was increased equallyby spraying with solutions supplying ammonium sulphate, calciumnitrate, or urea in equivalent concentrations. Nutrient uptake from solutions sprayed on leaves influenceduptake by the roots so that the additional amounts of nutrientcontained in sprayed plants may be greater or smaller than theamount absorbed from the spray by the leaves.     

Nitrogenous fertilizer transformations in the sudan Gezira soil

Summary and Conclusions Direct measurements were made of losses of ammonia during the transformation of urea and ammonium sulphate, surface-applied to alkaline Gezira soil in containers incubated in the field, under different rates of nitrogen application and moisture conditions.The highest rate of ammonia loss occurred during the first week after application with both fertilizers, thereafter decreasing to lower values. The cumulative ammonia loss was higher with higher application of nitrogen. Ammonium sulphate gave consistently higher ammonia losses than urea and losses from open soil system were generally less than from soil in polythene bags.With lowest irrigation level used, ammonia loss attained a sizeable value throughout the incubation period with both fertilizers. With the higher moisture levels, the magnitude of ammonia loss decreased appreciably, much more so with urea than with ammonium sulphate. Induced drying and rewetting prolonged the duration of loss and increased the magnitude of cumulative loss. An appreciable loss of ammonia may take place from fertillzed Gezira Soil under warm conditions, low moisture levels and high fertilizer concentration; this may be the case with patchy fertilizer distribution and frequent light showers during early summer. It is advisable to apply the urea or ammonium sulphate when conditions are most favourable for nitrification.     

Ammonium Nutrition as a Strategy for Cadmium Mobilisation in the Rhizosphere of Sunflower

Ammonium nutrition of higher plants results in rhizosphere acidification due to proton excretion by root cells. The acidification induced by ammonium-fed plants can be exploited to promote a localised metal mobilisation in neutral to alkaline polluted soils and therefore to improve phytoextraction. The effects of ammonium uptake by sunflower (Helianthus annuus L.) plants on the external medium pH, aerial and root growth and tolerance to soluble Cd were studied in hydroponic culture. The ammonium-fed sunflowers induced a strong acidification of the solution and, compared to the nitrate-fed sunflowers, a small modification in mineral nutrition and a different Cd partitioning between root and shoot. Moreover, ammonium nutrition was found to induce a great mobilisation of a sparingly soluble form of cadmium (CdCO₃). A pot experiment studied the ability of different ammonium-based fertilisers (ammonium sulphate, ammonium thiosulphate, urea) to modify bulk and rhizo-soil pH, compared to the effect of calcium nitrate and to the unfertilised soil. Furthermore, in order to promote the persistence of ammonium in soil, a combined treatment of ammonium sulphate and DMPP, a nitrification inhibitor, was tested. Soil pH was strongly modified by chemical and biological processes involved in fertiliser transformations. In particular, due to nitrification, all ammonium-based treatments showed a bulk soil acidification of over 1.5 pH units and a relative increase in rhizo-soil pH as a consequence of nitrate uptake. The treatment with DMPP showed an opposite trend with a lower pH in rhizo-soil than in bulk soil. The ability of ammonium-fed plants to mobilise heavy metals from the non-labile pool was studied in another pot experiment using three soils with different properties and at different degree and type of heavy metal contamination. Whatever the soil, the metal concentrations in shoots were higher in plants fed with ammonium (ammonium sulphate plus DMPP treatment). Our results support the hypothesis that ammonium nutrition with nitrification inhibitors is a viable strategy to improve heavy metals phytoextraction while protecting bulk soil from acidification and presumably from metal leaching. An erratum to this article is available at .     

Effect of some fertilizers on hatching of cereal cysts nematode,Heterodera avenae

Experiments were conducted in laboratory and pot conditions to determine the effects of urea, di-ammonium phosphate (DAP), single super phosphate (SSP), muriate of potash (MOP) and zinc sulphate (ZnSO₄) on hatching of Heterodera avenae. Two concentrations of each fertilizer were tested in lab for which 10 cysts and 5 ml of each concentration were taken in 5 cm diameter Petri plates. Observations were recorded at weekly intervals up to six weeks. Urea, DAP, SSP and MOP inhibited hatching and ZnSO₄ increased it. After six weeks, hatching was least (5.45%) in higher dose of urea and greatest (46.9%) in higher dose of ZnSO₄. In pot experiment, two doses of urea and single dose of SSP, MOP, and ZnSO₄ were applied in H. avenae-infested soil and WH-1105 wheat was sown. Observations on nematodes in roots, soil and remaining cyst contents were recorded 40 days after sowing. Among all the fertilizers, least nematodes in soil and roots were found at higher dose of urea and greatest number in ZnSO₄.     

Influence of fungal isolates on germination and growth of perennial ryegrass

Summary The influence of fungi isolated from perennial ryegrass roots on the germination and development of seedlings of perennial ryegrass was investigated. The basic procedure employed was to sterilise the seed surface and then inoculate with fungi and plant in non-sterile soil. It was realised that the fungal isolate inoculated on to the sterile seed surface would not remain dominant in the root region of the host and would have an influence on the host which would decline with time from when the seed germinated. This was because it would have to face antagonism from the normal components of the root microflora present in the non-sterile soil.Trichoderma viride delayed the emergence of the seedlings and reduced the production of herbage, an observation consistent with results of some other investigators. A sterile hyaline fungus stimulated the emergence of the seedlings, but subsequent tests showed that the presence of the microflora of the seed coat, or the soil microflora, or the sterile hyaline fungus was effective in promoting the rate of germination of seed that had been surface sterilised. Leaching seed in water brought about an increase in the rate of seed germination, and it is suggested that there might be a germination inhibitor soluble in water present in the seed coat, which might be inactivated by saprophytic micro-organisms.     

Effects of ammonium sulphate application on the chemistry of bulk soil,rhizosphere, fine roots and fine-root distribution in a Picea abies (L.) karst. stand

The effect of ammonium sulphate application on the bulk and rhizosphere soil chemistry, elemental concentration of living fine roots (<2 mm in diameter), amounts of living and dead fine roots, root length density and specific root length density were investigated in a 28 year old Norway spruce stand in SW Sweden. The treatments started in 1988. Core samples of the LFH layer and mineral soil layers were sampled in control (C) and ammonium sulphate (NS) treatment plots in 1988, 1989 and 1990. Soil pH and NO₃-S and SO₄-S, Al, Ca, Mg, Mn and K concentrations were measured for both the bulk soil and rhizosphere soil.The pH-values of the bulk and rhizosphere soil decreased in 1989 and 1990 in NS plots compared to control plots, while the SO₄-S concentration increased. The Ca, Mg and K concentration increased in the NS treatment in almost all layers in the bulk and the rhizosphere soil. Ammonium ions may have replaced these elements in the soil organic matter. The NS treatment reduced Mg concentration in fine roots in all layers in 1990. The Al concentrations in the rhizosphere and bulk soil were higher in NS plots in all layers, except at 0–10 cm depth, both in 1989 and 1990. The Al content of living fine roots was higher in NS plots than C plots but the differences were not significant. The NS addition did not affect the P and K contents of fine roots in any soil layer, but the S concentrations of fine roots were significantly higher in NS plots in 1989 and 1990. The fine root necromass was higher in NS than in C in 1990, in the LFH layer, indicating a gradual decrease in the vitality of the fine roots. It was suggested that the NS treatment resulted in displacement of Mg and K from exchange sites in the LFH layer leading to leaching of these cations to the mineral soil. Further application of ammonium sulphate may damage the fine roots and consequently adversely affect the water and nutrient uptake of root systems.     

Mineralization and gaseous losses of nitrogen from urea and ammonium sulphate in salt-affected soils

Summary An incubation study on mineralization and gaseous losses of nitrogen was conducted on three soils with increasing levels (1.1 to 50 mmhos/cm) of salinity and two levels of urea and ammonium sulphate upto 6 weeks. Mineralization of nitrogen increased with time and decreased with the increase of salinity. It was more from ammonium sulphate than urea, and relatively more from the lower dose. The gaseous losses of NH₄-N increased with salinity. About 35±5 per cent of added N was lost in the gaseous form at maximum (ECe=45 to 50 mmhos/cm) salinity and losses were more from light than heavier soils. Salinity and pH, both were correlated negatively with the N mineralisation and positively with the gaseous losses of ammonia in these salt-affected soils. re]19751105