Potassium→ammonium exchange of two benchmark soils from Botswana and its implication for nitrogen economy of the soils

Ion exchange preferences for NH₄⁺ and K⁺ by soil exchanger surface can greatly affect the NO₃^? leaching into groundwater and nitrogen-use efficiency in agricultural production. Since NH₄⁺ and K⁺ salts are usually applied together as fertilizers, the binary K→NH₄ exchange of two benchmark Botswana soils, Pellustert and a Haplustalf, was studied to determine the selectivity coefficients and the thermodynamic exchange constant with special reference to N economy. The Vanselow and the Gaines and Thomas coefficients indicated preference for NH₄⁺ by the Pellustert and K by the Haplustalf across the exchanger phase composition. The equilibrium constant (K_ex) was 1.807 for the Pellustert and 0.174 for the Haplustalf. The exchange free energy (ΔG_ex⁰) was ?1.467 kJ mol^?1 for the Pellustert and 4.334 kJ mol^?1 for the Haplustalf. Negative ΔG_ex⁰ for the Pellustert is consistent with preference for NH₄⁺ to K⁺ in contrast to positive ΔG_ex⁰ for the Haplustalf. The greater stability of NH₄X than KX complex in the Pellustert, and KX than NH₄X in the Haplustalf, would mean increased residence time of NH₄⁺ in the Pellustert than the Haplustalf. The implication of short residence time of NH₄⁺ in soil is rapid nitrification, thereby leading to NO₃^??N leaching losses and possible groundwater contamination.     

Influence of organic compounds on nitrogen‐fertilizer solubilization

Abstract

In the attempt to find new products which release nutrients in gradual forms, the behavior of two commercial fertilizers was studied, Nitrophoska® (N) and urea (U), covered with two organic materials, humic acid (HA) and alginic acid (AA). The release of nitrogen from the fertilizers was determined by electroultrafiltration (EUF). These applied materials on the fertilizer surface resulted in a slowing of the release of nitrogen, although strictly speaking, these compounds do not function as coated fertilizers. Their effectiveness depends on the fertilizer, for with Nitrophoska®, the addition of alginic acid was more effective, while for urea, the addition of humic acid slowed the release of nitrogen.     

Does nitrogen concentration affect relative uptake rates of nitrate,ammonium, and glycine?

Plant roots are exposed to a variety of nitrogen forms (e.g., nitrate, ammonium, amino acids) and take up these forms at different rates. Many studies have investigated whether plants prefer nitrate, ammonium, or amino acids; but studies may not be comparable because they used substrate concentrations between 100 and 2000 μmol L^–1. This study tests the hypothesis that substrate concentrations from 10 to 1750 μmol L^–1 affect plant preference for N forms. Nitrogen uptake by the herb Ocimum basilicum and the evergreen tree Eucalyptus regnans was examined by placing roots of intact seedlings in equimolar mixtures of nitrate, ammonium, and glycine in which one of the N forms was ¹⁵N‐labelled (and ¹³C‐labelled in the case of glycine). In both species, preference for N forms was affected by substrate concentration. At 10 μmol L^–1 (O. basilicum) or 10 and 50 μmol L^–1 (E. regnans), rates of N uptake did not differ among N forms. At substrate concentrations of 50 μmol L^–1 and greater O. basilicum took up ammonium the fastest, glycine the slowest, and nitrate at an intermediate rate. At substrate concentrations from 100 to 1750 μmol L^–1, E. regnans took up ammonium the fastest with glycine and nitrate taken up at slower rates. The absence of significant differences at lower concentrations was a true biological effect rather than a function of larger relative errors. This study demonstrates that substrate concentration has a large effect on plant preference for N forms, and sounds a warning for studies of N nutrition that do not consider the concentration‐dependence of plant preference for N forms.     

Effects of rice cropping intensity on soil nitrogen mineralization rate and potential in buried ancient paddy soils from the Neolithic Age in China’s Yangtze River Delta

Purpose

Rice cropping density, rice cropping duration, and fertilization can affect soil nitrogen (N) supply, but rice cropping intensity (RCI) on soil N fertility is not fully understood, particularly for ancient paddy soils without N fertilization.

Materials and methods

Eight buried ancient paddy soils from the Neolithic Age in China’s Yangtze River Delta, and its parent material, and seven present paddy soils in the same fields were used to investigate the effects of RCI on soil nitrogen mineralization rate and potential. In the present study, concentration of phytolith of rice in soils was used to indicate the RCI.

Results and discussion

Soil N content was obviously greater in the buried Neolithic paddy soils than in the parent material. Total soil N increased with increasing phytolith from 5,200 to 60,000 pellets g^?1, but tended to decrease with increasing phytolith from 60,000 to 105,000 pellets g^?1. A possible reason for RCI-induced increase of soil N was due to biological N₂ fixation in the rice field because there was a significant negative relationship between total N and δ¹⁵N in the buried Neolithic soils. The mineralization rate constant (k) ranged from 0.0126 to 0.0485 d^?1 with an average of 0.0276 d^?1, which was similar to that of the parent material, but lower than those in the present paddy soils. The k value increased with increasing RCI in the Neolithic paddy soils. There was a significant positive relation between RCI and the percentage of cumulative mineralizable N in the 14 d of that within 103 d incubation.

Conclusions

Soil N content tended to increase with the increasing intensity of rice cropping and then decreased under the high intensity of rice cropping; the excessive high intensification of rice cropping could facilitate fast N mineralization (labile N) fraction in the cumulated mineralized N. The unfertilized paddy field could only meet soil N supply under the low intensification of cropping rice in the Neolithic Age. The N fertilization is necessary in order to improve soil fertility for sustaining the present high-yield rice production.     

The determination of ammonium and chloride by an auto‐analyser for the measurement of cation exchange capacity of soils

Abstract

An auto‐analyser method has been developed for the simultaneous determination of NH₄ ⁺ and Cl^‐ in Ca(NO₃)₂/KNO₃ extracts of NH₄Cl treated soils for cation exchange capacity measurements. The method gives satisfactory agreement with manual titration procedures.     

Does acidification increase the nitrogen fertilizer replacement value of bio‐based fertilizers?

Acidification of manure, digestate and their processed derivatives has been proposed as a technique to, amongst others, mitigate ammonia emissions related to application in the field. The current study investigated whether acidification of (1) pig slurry (PS), (2) liquid fraction of pig slurry (LFPS), (3) digestate (DIG), and (4) liquid fraction of digestate (LFDIG) increases their nitrogen (N) fertilizer replacement value (NFRV) as compared to non‐acidified counterparts, a synthetic N fertilizer (calcium ammonium nitrate; CAN) and an unfertilized control. Product performance was evaluated from the perspective of (1) crop development (yield, nutrient uptake, and crop quality assessment) via a pot experiment with Lactuca sativa L. and (2) soil N dynamics [net N release (N_rel,net) and net N mineralization] via a soil incubation experiment. Crop yield of pots receiving bio‐based fertilizers performed ‘on par' with CAN as compared to unfertilized control, implying that bio‐based fertilizers derived from digestate or manure could potentially play a role in replacing synthetic N fertilizers. However, our findings also suggest that acidification did not result in an increased use efficiency of applied N. NFRVs of acidified products were below those of non‐acidified products and CAN, with crop yield on average 6–13% and 11–18% lower compared to non‐acidified products and the CAN treatment, respectively. A possible explanation for lower performance as compared to non‐acidified products could be an inhibitory delay in the N_rel,net, which in our experimental design proved to be negative for crops with short production cycles. This pattern was revealed in the incubation experiments in which N_rel,net in acidified products remained below that of non‐acidified, in this study tentatively attributed to immobilization of mineral N. However, this negative effect on N availability should be reaffirmed in crops with longer production cycles. Finally, some interesting findings with regard to plant composition also warrant further in‐depth investigation, e.g ., Zn uptake by lettuce in acidified treatments was significantly higher than that of non‐acidified treatments. This implies that product pre‐treatment may play a future role in biofortification and amelioration of (trace) element composition of crops (arguably for crops with longer production cycles). Improving crop nutritional value by increased uptake of micronutrients is receiving increasing attention.     

Stimulation of N2‐fixation in chickpea by gamma irradiation as affected by different levels of ammonium sulfate fertilizer

Abstract

A pot experiment was conducted under natural climatic conditions to study the effect of low doses of gamma irradiation (0, 5, 10, and 20 Gy) on the performance of winter chickpea (Cicer arietinum L.) in the presence of increased supply of ¹⁵N labeled ammonium sulfate (0, 20, 50, and 100 kg N ha^‐1). Presowing seed irradiation produced a significant increase in dry matter production (up to 3 6%) and total nitrogen yield (up to 45%). The stimulative effect of irradiation was more pronounced with the application of NH₄ ⁺‐N fertilizer. Seed irradiation increased the amount of N₂‐fixation by 8–61% depending on the dose and level of NH₄ ⁺‐N fertilizer rate. A 10 Gy was found to be the optimal irradiation dose for enhancing N₂‐fixation. High levels of NH₄ ⁺‐N decreased the percentage and the amount of N₂‐fixation, but did not affect nodule formation. However, the presowing 10 Gy irradiation dose reduced the negative effect of ammonia‐N fertilizer on N₂‐fixation. Therefore, we recommend irradiating chickpea seeds with a 10 Gy dose before planting in soil containing high levels of mineral nitrogen to reduce its negative effect on N₂‐fixation.     

‘Non-exchangeable’ ammonium in soils from Swedish long-term agricultural experiments: Mobilization and effects of fertilizer application

Abstract

In intensive agricultural systems, efficient nutrient use is necessary for high crop yields as well as for sustainable environmental management. Recent studies in temperate regions indicate that non-exchangeable NH₄ ⁺-N (NEA), which is fixed in clay minerals, may affect crop productivity and soil N dynamics more than previously thought. To estimate the quantity and plant availability of NEA in Swedish soils, ryegrass (Lolium perenne) was grown in a pot experiment using 18 soils that were collected (0–20?cm depth) from two long-term agricultural experiment series at five locations. Initial NEA, total N and soil K contents were measured, as well as NEA content 56, 112 and 168?days after planting of ryegrass. The results show that the soils (0–20?cm) contained 21–217?mg?NEA?kg^?1 sieved soil (5–300?kg?NEA?ha^?1) estimated as corresponding to 0.1–5.1% of the total soil N. Long-term application of farmyard manure (FYM) did not increase contents of soil NEA. Long-term application of K fertilizer increased soil contents of AL-extractable K, but there was no significant correlation with NEA content. Concurrent with ryegrass growth, NEA content decreased on average by 16% between day 0 and day 112, indicating that NEA was released from the soil and taken up by the plants.     

Does the source of nitrogen affect the response of subterranean clover to prolonged root hypoxia?

Nitrogen (N) is taken up by most plant species in the form of nitrate (NO ) or ammonium (NH ). The plant response to continuous ammonium nutrition is species‐dependent. In this study, the effects of the source of N nutrition (NO , NH , or the mixture of NO and NH ) on the response of clover (Trifolium subterraneum L. cv. 45C) plants to prolonged root hypoxia was studied. Under aerobic conditions, plant growth was strongly depressed by NH , compared to NO or mixed N nutrition, as indicated by the significant decrease in root and shoot‐dry‐matter production (DW), root and shoot water contents (WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters (F₀, F_v/F_m). However, the N source had no effect on chlorophyll a–to–chlorophyll b ratio. Under hypoxic conditions, the negative effects of root hypoxia on plant‐growth parameters (DW and WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters were alleviated by NH rather than NO supply. Concomitantly, shoot DW–to–root DW ratio, and root and leaf NH concentrations were significantly decreased, whereas root and leaf carbohydrate concentrations, glutamine synthetase activities, and protein concentrations were remarkably increased. The present data reveal that the N source (NO or NH ) is a major factor affecting clover responses to hypoxic stress, with plants being more tolerant when NH is the N form used. The different sensitivity is discussed in terms of a competition for energy between nitrogen assimilation and plant growth.     

Comparison of ammonium bicarbonate‐DTPA,ammonium carbonate,and ammonium oxalate to assess the availability of molybdenum in mine spoils and soils

Abstract

A variety of extractants has been used to assess the availability of molybdenum (Mo) in soils. Most of the extractants have been studied from a deficiency aspect rather than for soils with Mo toxicity, and none of them have been used to extract available Mo from mine spoils. The purpose of this study was to examine the potential of different chemical extractants for assessing the availability of Mo in mine spoils and soils. One mine spoil and three soils were treated with sodium molybdate and then subjected to wetting and drying cycles for two months. These spoil/soils were extracted with ammonium bicarbonate DTPA (AB‐DTPA), ammonium carbonate, and ammonium oxalate solution for available Mo. Crested wheatgrass (Agropyron cristatum) and alfalfa (Medicago sativa) were grown in the spoil/soils in a greenhouse to determine plant uptake of Mo. Additionally, four mine spoils and six soils were extracted and analyzed for available Mo as mentioned above. The results obtained by these three extractants were highly correlated. It was found that ammonium oxalate extracts the greatest amount of Mo among the three extractants from spoil/soils since it dissolves some adsorbed Mo from Fe‐oxide and Al‐oxide. The changes in pH of spoil/soils did not have a significant effect on the amount of Mo extracted by any of these methods. The relationships between Mo uptake and Mo extracted by each method were all significant at 1% level. None of the extractants were clearly better or worse than the others. All three methods can be used to assess Mo availability, and potential toxicity from plant uptake of Mo from reclaimed spoils.     

Can the agronomic performance of urea equal calcium ammonium nitrate across nitrogen rates in temperate grassland?

In temperate grassland, urea has been shown to have lower nitrous oxide emissions compared to ammonium nitrate‐based fertilizer and is less expensive. However, nitrogen (N) loss via ammonia volatilization from urea raises questions regarding yield performance and efficiency. This study compares the yield and N offtake of grass fertilized with urea, calcium ammonium nitrate (CAN) and urea treated with the urease inhibitor N‐(n ‐ butyl) thiophosphoric triamide (NBPT) at six site‐years. Five annual fertilizer N rates (100–500 kg N/ha) were applied in five equal splits of 20–100 kg N/ha during the growing season. On average, urea produced slightly better yields than CAN in spring (103.5% of CAN yield) and slightly poorer yields in summer (98.4% of CAN yield). There was no significant difference in annual grass yield between urea, CAN and urea + NBPT. Urea had the lowest cost per tonne of DM grass yield produced. However, the urea treatment had lower N offtake than CAN and this difference was more pronounced as the N rate increased. There was no difference in N offtake between urea + NBPT and CAN. While this study shows that urea produced yields comparable to CAN, urea apparent fertilizer N recovery (AFNR) tends to be lower. Urea selection in place of CAN will increase national ammonia emissions which is problematic for countries with targets to reduce ammonia emissions. Promisingly, NBPT allows the agronomic performance of urea to consistently equal CAN across N rates by addressing the ammonia loss limitations of urea.     

To what extent can multifractal measures provide an accurate model of the porosity of soils?

Over the last decades, several authors have suggested that multifractal measures, that is, self-similar measures defined on fractal or non-fractal objects, could be useful to describe soil properties, to model soil processes, and to deal with their extreme microscale heterogeneity. In this context, a key question relates to the extent to which multifractal measures can indeed fulfill all the expectations they have generated. To address this question, we discuss the possibility of generating a synthetic soil image exhibiting multifractal porosity. To this end, a simple geometrical multifractal model in 2D is developed, which helps us to better understand the concept of multifractality and to generate images. We show that it is possible to generate synthetic binary images over a limited range of scales, but that a pure multifractal model for the distribution of the solid or pore mass cannot be developed due to physical constraints. Moreover, in the generated images mimicking multifractal solid space, a higher degree of multifractality corresponds to a larger porosity, rendering it difficult to tune model parameters to match actual soil properties. In addition, simple statistics relying on power-law fits appear insufficient to characterize soil architecture even if they may capture some key multiscale indicators of observed spatial heterogeneity. We argue that the same conclusions would be reached in a three-dimensional space, as well as for grey-scales images.     

Temporal and spatial distributions of nitrate‐nitrogen in two furrow‐irrigated semiarid soils amended for sludge and fertilizer

Abstract

A statistical comparison of data collected from two cotton production fields with a history of either commercial fertilizer or sludge amendments showed significantly different nitrate‐nitrogen (N) concentrations in time and space. The sludge‐amended field had high nitrate concentrations in the root zone (1.5 m) throughout the season. Whereas, the fertilized field showed low nitrate‐N concentrations during the same period. Both fields showed significant increases in nitrate‐N following pre‐plant irrigation events, and significant decreases of nitrate‐N in the root zone during the growing season. Following harvest, the sludge‐amended field had very large reserve of nitrate‐N in the profile. The spatial variabilities, as determined by the % coefficients of variations (CVs) of eight cores per sampling event, of nitrate‐N distributions where large in both fields, 69% and 90% for the sludge and fertilizer field, respectively. The estimated nitrate‐N leaching losses were much higher in the sludge‐amended than the fertilized field. Significant leaching losses in the sludge‐amended field were likely the result of year‐to‐year sludge residue accumulations that mineralize and release nitrate‐N in the zone of incorporation (0–30 cm).     

Effect of an anionic surfactant on hydraulic conductivities of sodium- and calcium-saturated soils

The effect of sodium dodecylbenzenesulfonate （SDBS）, an anionic surfactant used widely in household products and industrial processes, on saturated hydraulic conductivities （Ksat） of an Anthrosol saturated with sodium （Na-soil） or calcium （Ca-soil） was analyzed in a laboratory experiment using the constant head method, and adsorption and dispersion experiments were also conducted to infer the possible mechanisms of Ksat fluctuations. The results showed that SDBS was more intensely adsorbed in the Ca-soil than in the Na-soil. With an increase in the SDBS concentration, the stability of the Na-soil suspensions decreased when the SDBS concentration was less than 1.2 mmol L^-1 and then above this concentration, increased markedly, while the stability of the Ca-soil suspensions increased gradually at all SDBS concentrations studied. With an increase in the SDBS concentration, the Ksat of the Na-soil increased, which resulted mainly from the increase of water channels in the soil because of the coagulation of the soil particles, while the Ksat of Ca-soil decreased mainly on account of the clogging of partial water channels by precipitated Ca（DBS）2 and the fine soil particles generated.     

Effects of supplemental‐nitrogen on the quality of rice proteins

A study was conducted on the effect of supplemental nitrogen (N) (20 hg/ha) applied as a foliar spray or to the soil on seed production, protein percentage, and protein fractions of rice. Plants were grown in a greenhouse over two different periods of time, i.e., August 1988 to January 1989 (Period I), and December 1988 to April 1989 (Period II). Nitrogen was applied to the leaves 10 and 20 days after anthesis (DAA), and to the soil at anthesis and at 15 DAA. Average temperature was 28.7°C during Period I and 32°C during Period II, corresponding to 18.7 and 22.0 growing degree‐day/day (GDD/day), respectively. The difference in GDD/day reduced the plant cycle from 130 days during Period I to 109 days during Period II. Plants grown during Period II had larger numbers of spikelets, a higher percentage of “full grown grains”;, and higher grain weight. Although percentage crude protein was about the same for the two periods, prolamin content was increased and the albumin+globulin fraction was decreased during Period II, but with no difference in glutelin content. The increase in number of spikelets, percent full grains, and grain weight appeared to result in a greater energy demand for plants grown during Period II. This may explain the increase in prolamins, since prolamin synthesis requires less energy than globulin or albumin synthesis. There was a simultaneous decrease in albumin and globulin synthesis during Period II. The content of glutelins, which represent the major reserve proteins in rice grains, was constant during both periods.     

The use of the 15N‐dilution technique for field measurement of symbiotic nitrogen fixation

Abstract

Quantitative distribution of ¹⁵N in artificially and naturally enriched field‐growing legume‐based pastures are presented and compared. The results are discussed in terms of the assumption of the ¹⁵N‐dilution technique as a means of measuring symbiotic nitrogen fixation under field conditions.     

Effect of ammonium chloride,ammonium sulphate,and sodium nitrate on take‐all and grain yield of wheat grown on soils in South‐western Australia

Five field experiments are described which measured the effect of three sources of nitrogen (N) fertilizer, applied at 45 kg N/ha, on the incidence of take‐all and grain yield of wheat. The N fertilizers were ammonium sulphate, ammonium chloride, and sodium nitrate. Compared with the Nil N treatment, ammonium‐nitrogen fertilizer, either as ammonium sulphate (ASdr) or ammonium chloride (ACdr) drilled with the seed, lowered the severity of take‐all. Sodium nitrate topdressed (SNtd) to the soil surface reduced the severity of take‐all in three of five experiments, while ammonium sulphate topdressed (Astd) reduced the severity in four of the five experiments. Ammonium sulphate and ammonium chloride drilled with the seed were equally effective in reducing the severity of take‐all in three of the five experiments. However, ACdr was more effective than ASdr in reducing the severity of take‐all in one experiment whereas ASdr was more effective than ACdr in another experiment. In these two experiments (1 and 5), the effects of the reduction in take‐all severity between the ASdr and ACdr treatments did not affect grain yield. The results suggest that grain yield losses from take‐all are most severe where wheat plants are deficient in N. Chloride containing fertilizers are unlikely to control take‐all disease of wheat on soils of southwestern Australia.     

Influence of nitrate‐nitrogen and ammonium‐nitrogen on calcium (45Ca2+) absorption in sorghum root tips

Abstract

Root‐tip, 1‐cm of Sorghum bicolor (L.) Moench cv SC283, SC574, GP‐10, and Funk G522DR were exposed to calcium (⁴⁵Ca²⁺) at pH 5.5 for 2‐hr in the presence of nitrate‐nitrogen (NO3^?‐N) or ammonium‐nitrogen (NH4+‐N). Nitrate (0.1 mM) induced significantly increased ⁴⁵Ca uptake in Funk G522DR, SC283, and GP‐10 while 0.01 mM NO₃ ^?‐N induced significantly increased ⁴⁵Ca'uptake in SC574, but ⁴⁵Ca absorption was significantly decreased at 1 mM NO₃—N. In the presence of the NH4⁺ ion, ⁴⁵Ca uptake was increased up to 8X that of the NH₄ ⁺‐N untreated roots. When ammonium chloride (NH₄CI) was used, the Cl^? tended to induce an increased ⁴⁵Ca uptake. Cultivar variation was present.     

The effects of volcanic ash influenced soils and nitrogen fertilization on douglas‐fir seedlings

Abstract

An experiment was conducted to help understand the contributions of different soil layers to soil fertility, plant growth, and response to fertilization. Douglas‐fir (Pseudotsuga menziesii) seedlings were used in a pot bioassay to delimit the effects of volcanic ash soils, urea fertilization at 100 and 200 ppm, and the technique of using undisturbed soil as a growth medium. Volcanic ash horizons contained more available phosphorus and mineralized more nitrogen than underlying horizons. Best seedling growth occurred in ash horizons fertilized with 200 ppm of urea‐N. Fertilization decreased soil pH, mycorrhizae formation and foliar‐P levels but increased foliar‐N. The technique of using undisturbed soil had little effect on seedling growth in the weak structured ash horizons but did decrease root weights in the moderate structured sub‐ash layers.