Clay dispersion and its relation to surface charge in a paddy soil of the Red River Delta,Vietnam

Dispersion is an important issue for clay leaching in soils. In paddy soils of the Red River Delta (RRD), flooding with fresh water and relatively high leaching rates can accelerate dispersion and the translocation of clay. For the clay fraction of the puddled horizon of a typical paddy soil of the RRD, the effect of various cations and anions as well as humic acid (HA) at different pH values on the surface charge (SC) were quantified and the dispersion properties were determined in test tubes and described by the C₅₀ value. In the <2 µm fraction, dominated by illite, the proportion of 2:1 vs. 1:1 clay minerals is 5:1. The organic‐C content of the clay fraction is 2.2%. Surface charge was found to be highly pH‐dependent. At pH 8 values of –32 and at pH 1 of –8 mmol_c kg^–1 were obtained. Complete dispersion was observed at pH > 4, where SC is > –18 mmol_c kg^–1. The flocculation efficiency of Ca strongly depends on the pH. At pH 4, the C₅₀ value is 0.33, 0.66 at pH 5, and 0.90 mmol L^–1 at pH 6. At pH 6, close to realistic conditions of paddy soils, the effect of divalent cations on the SC and flocculation decreases in the order: Pb > Cu > Cd > Fe^II > Zn > Ca > Mn^II > Mg; Fe^II was found to have a slightly stronger effect on flocculation than Ca. An increase in concentrations of Ca, Mn^II, and Mg from 0 to 1 mmol L^–1 resulted in a change in SC from –25 to approx. –15 mmol_c kg^–1. In comparison, the divalent heavy‐metal cations Pb, Cu, Cd, and Zn were found to neutralize the SC more effectively. At a Pb concentration of 1 mmol L^–1, the SC is –2 mmol_c kg^–1. From pH 3 to 5, the dispersion of the clay fraction is facilitated rather by SO than by Cl^–, which can be explained by the higher affinity of SO to the positively charged sites. With an increase of the amount of HA added, the SC continuously shifts to more negative values, and higher concentrations of cations are needed for flocculation. At pH 3, where flocculation is usually observed, the presence of HA at a concentration of 40 mg L^–1 resulted in a dispersion of the clay fraction. While high anion concentrations and the presence of HA counteract flocculation by making the SC more negative, Fe^II and Ca (C₅₀ at pH 6 = 0.8 and 0.9 mmol L^–1, respectively) are the main factors for the flocculation of the clay fraction. For Fe^II and Ca, the most common cations in soil solution, the C₅₀ values were found to be relatively close together at pH 4, 5, and 6, respectively. Depending on the specific mineralogical composition of the clay fraction, SC is a suitable measure for the determination of dispersion properties and for the development of methods to keep clay particles in the soil in the flocculated state.     

Effect of sulfur source and rates on yield and yield components of soybean in subtropical soils

Abstract

The supply of sulfur (S) fertilizers, such as phosphogypsum, to new agricultural frontiers has been hindered by the high cost of freight. However, this problem could be resolved by utilizing deposits of rock in the affected regions. Accordingly, a greenhouse study was designed to evaluate the effect of S source and rate on soybean yield. Five S rates (0, 50, 100, and 200?mg kg^?1) and five S sources (S-phosphogypsum, S-Niquelândia rock, S-Araripina rock, S-Grajaú rock, and S-Sulfurgran [90% S0?+?10% bentonite]) were applied to soybean grown in two soil types (Typic Ultisol and Typic Oxisol), which differ in clay content. Regardless of soil type, the application of P-phosphogypsum resulted in a higher grain yield. However, application of the other S sources also improved grain yield as well as total dry weight; S application, in general, improved soybean yield components (number of grains per pod, number of pods per pot, and weight of pods per pot), photosynthetic rate, chlorophyll content, and the S levels of leaves and grains as well as the available sulfate (SO₄^2-) levels in the soil. Therefore, for soybean grown in Typic Ultisol and Typic Oxisol, different S sources effectively improve a variety of variables that ultimately improve grain yield.     

ADSORPTION-DESORPTION CHARACTERISTICS OF HIGH LEVELS OF COPPER IN SOIL CLAY FRACTIONS

Copper adsorption and desorption under acid conditions by soil clay fractions separated from Vertisol, Planosol and Gleyic Acrisol has been studied in 0.01 M Ca(NO₃)₂. A Freundlich equation was appropriate to describe Cu adsorption. Within the range of 150 to 2600 mg of copper per kg of soil clay fraction the proportions of Cu not displaced during 5 successive 48-hour desorptions with 0.01 M Ca(NO₃)₂ decreased with increasing adsorption density and at the lower pHs. The proportions ranged from as high as 0.98 in th case of the Vertisol clay (pH 5.3) to as low as 0.12 (88% desorption) in the Planosol clay (pH 4.5). Measurement of separation factors (ga Cu/Ca) showed that the preference of the clay surface for Cu over Ca decreased in the order: Gleyic Acrisol > Planosol > Vertisol. A considerable amount of sorbed copper could be solubilized by decreasing pH values to 4 when in the Planosol clay 39% was desorbed and 45% was desorbed in the Gleyic Acrisol clay.     

Effects of Different Rates of Ca2+ Addition on Respiration and Sorption of Water-Extractable Organic C to a Vertisol Subsoil

It is well known that calcium (Ca²⁺) plays an important role in binding organic matter to clay. However, most previous studies were conducted with either topsoil or pure aluminosilicates. Less is known about the effect of Ca²⁺ on binding of organic matter to clay-rich subsoils, which have lower organic-matter contents than topsoils, and their clays are more strongly weathered than pure aluminosilicates. Two experiments were conducted with a Vertisol subsoil (69% clay): a laboratory incubation and a batch sorption. The mineral substrate in the incubation experiment was pure sand alone or sand amended with 300 g clay kg^?1. Powdered calcium sulfate (CaSO₄) at rates of 0, 5, 10, and 15 g Ca kg^?1 and mature wheat residue at a rate of 20 g kg^?1 were added to this mineral substrate and the water content was adjusted to 70% of water-holding capacity. Carbon dioxide release was measured for 28 days. Cumulative respiration per g soil organic carbon (C) (SOC from clay and residues) was increased by clay addition. Increasing Ca²⁺ addition rate decreased cumulative respiration in the sand with clay but had no effect on respiration in the pure sand. Clay and Ca²⁺ addition had no significant effect on microbial biomass carbon (MBC) per g SOC but clay addition reduced the concentration of potassium sulfate (K₂SO₄)–extractable C per g SOC. For the batch sorption experiment, the subsoil was mixed with 0 to 15 g Ca kg^?1 and water-extractable organic C (WEOC) derived from mature wheat straw was added at 0, 1485, 3267, and 5099 mg WEOC kg^?1. Increasing Ca²⁺ addition rate increased sorption of WEOC, particularly at the greatest concentration of WEOC added, and decreased desorption. This study confirmed the importance of Ca²⁺ in binding organic matter to clay and suggests that Ca²⁺ addition to clay-rich subsoils could be used to increase their organic C sequestration.     

Spatio-temporal variations in nutrient concentration in soil solution under greenhouse tomato

The aim of this trial was to study the spatio-temporal variability in solution nutrient concentration under intensive greenhouse tomato production, to determine the number of suction-cups needed to obtain a representative sample and the influence by the position in the greenhouses. Twenty sampling points were selected within the greenhouse with one suction-cup per sampling point. One soil solution were sampled per point at weekly intervals to analyze for pH, electrical conductivity, chloride, nitrate, phosphate, sulfate, sodium, potassium, calcium, and magnesium (EC, Cl^?, NO₃^?, H₂PO₄^?, SO₄^2—, Na⁺, K⁺, Ca²⁺, and Mg²⁺) concentrations. The pH, Cl^?, H₂PO₄^?, and SO₄^2? concentrations showed no spatio-temporal variation but EC, NO₃^?, and K⁺ showed temporal variation. The spatial variability in EC, K⁺_, Na⁺, Mg²⁺, and Ca²⁺ can be influenced by microclimate and topography. The numbers of suction cups required for a representative sample ranged from 1 to 10 depending on nutrient.     

Effect of some herbicides on microbial activity in soil

The effect of 25 herbicides and herbicide combinations, in amounts comparable to those used in agriculture, on microbial activity in two soil types was determined in the laboratory. Herbicides did not affect respiration, assayed by CO₂ evolution and dehydrogenase activity, in either silty clay loam or loamy sand. Organic matter decomposition, determined by the amount of CO₂ evolved and inorganic N formed from decomposing alfalfa tissue, was also not affected. Alteration in soil pH or moisture content did not affect herbicide action. Addition of herbicides 3 weeks before amendment, or fertilizer application, also did not influence herbicide activity. Selected herbicides (trifluralin, linuron, dinoseb) at concentrations 100-fold higher than the recommended rates did not affect alfalfa decomposition. Solubilization of Ca₃(PO₄)₂ in soil was not affected by herbicides. S oxidation to SO^2?₄ in soil, however, was increased by most herbicides. In silty clay loam, 18 of the 25 herbicides and herbicide combinations increased S oxidation almost up to 3-fold. Results in loamy sand were similar. Dinoseb effectively reduced the algal population in loamy sand by more than 90%. Trifluralin, linuron, and metribuzin did not inhibit algal populations.     

Effect of temperature on biochar priming effects and its stability in soils

Recent studies have shown both increased (positive priming) and decreased (negative priming) mineralisation of native soil organic carbon (SOC) with biochar addition. However, there is only limited understanding of biochar priming effects and its C mineralisation in contrasting soils at different temperatures, particularly over a longer period. To address this knowledge gap, two wood biochars (450 and 550 °C; δ¹³C −36.4‰) were incubated in four soils (Inceptisol, Entisol, Oxisol and Vertisol; δ¹³C −17.3 to −28.2‰) at 20, 40 and 60 °C in the laboratory. The proportions of biochar- and soil-derived CO₂–C were quantified using a two-pool C-isotopic model.Both biochars caused mainly positive priming of native SOC (up to +47 mg CO₂–C g⁻¹ SOC) in the Inceptisol and negative priming (up to −22 mg CO₂–C g⁻¹ SOC) in the other soils, which increased with increasing temperature from 20 to 40 °C. In general, positive or no priming occurred during the first few months, which remained positive in the Inceptisol, but shifted to negative priming with time in the other soils. The 550 °C biochar (cf. 450 °C) caused smaller positive priming in the Inceptisol or greater negative priming in the Entisol, Oxisol and Vertisol at 20 and 40 °C. At 60 °C, biochar caused positive priming of native SOC only in the first 6 months in the Inceptisol. Whereas, in the other soils, the native SOC mineralisation was increased (Entisol and Oxisol) and decreased (Vertisol) only after 6 months, relative to the control. At 20 °C, the mean residence time (MRT) of 450 °C and 550 °C biochars in the four soils ranged from 341 to 454 and 732−1061 years, respectively. At 40 and 60 °C, the MRT of both 450 °C biochar (25−134 years) and 550 °C biochar (93−451 years) decreased substantially across the four soils. Our results show that biochar causes positive priming in the clay-poor soil (Inceptisol) and negative priming in the clay-rich soils, particularly with biochar ageing at a higher incubation temperature (e.g. 40 °C) and for a high-temperature (550 °C) biochar. Furthermore, the 550 °C wood biochar has been shown to persist in soil over a century or more even at elevated temperatures (40 or 60 °C).     

Influence of deer exclusion on soil nutrients in oak forests of a central European low mountain range

High densities of red deer can have severe impacts on soil nutrient status by removing the ground vegetation and enhancing erosion of the fertile soil layers. We compared four fenced deer exclosures with adjacent unfenced sites to evaluate the effect of deer grazing and trampling on the soil nutrient status (C_org, N_t, PO₄³⁻, Ca²⁺, Mg²⁺, K⁺) in sloping oak forests of a central European low mountain range. The investigation was set up as a three‐factor randomized complete block design (RCBD) with the factors: ‘fencing’ (fenced/unfenced), ‘gradient’ (gentle/steep) and ‘aspect’ (windward/leeward). We hypothesized that exclusion of red deer by fencing would increase soil nutrient contents independent of slope gradient and aspect. Fencing increased the contents of C_org, N_t, Ca²⁺ and PO₄³⁻, but only at the windward sites. This effect was less pronounced at the gently sloping site than at the steep site, which exhibited the lowest contents of C_org, N_t and PO₄³⁻ of all sites. We did not find increased soil nutrients in the fenced exclosures at the leeward sites, neither at the steep nor at the gently sloping site. At both slope aspects nutrient contents (C_org, N_t, PO₄³⁻, K⁺) tended to be higher on the gentle than at the corresponding steep slopes. Our results suggest that red deer trampling and grazing enhance the loss of soil nutrients at predisposed sites such as windward locations with a high slope gradient. Only at such sites did the exclusion of red deer increase several soil nutrients. Copyright © 2005 John Wiley & Sons, Ltd.     

SO42-和Cl-对稻田土壤养分及其吸附解吸特性的影响

利用长期定位试验 ,比较了长期施用含SO₄^2-和Cl^- 化肥 22年后稻田土壤的 pH值、养分状况及其吸附解吸特性。结果表明 ,长期施用含SO₄^2-化肥 ,土壤有机质、速效氮和速效钾的含量较高 ,但全量氮磷钾的含量较低 ;长期施用含Cl^- 化肥 ,土壤全量氮磷钾和速效磷的含量较高 ,但pH值相对较低。长期施用含上述二种阴离子的化肥后 ,土壤对H₂PO₄^-的最大吸附量均较大 ,且在Cl^- 处理下土壤对H₂PO₄^-吸附的结合能较大 ,而SO₄^2-处理下土壤在同等吸附量时对H₂PO₄^-的解吸量相应较多。长期施用含SO₄^2-的化肥亦使土壤对钾素的供应强度较大 (ΔK0的绝对值较大 )、缓冲能力增强 (AR0值较高 ) ,而长期施用含Cl^- 的化肥时则与SO₄^2-相反     

第四纪红粘土发育的红壤在施用石灰和石膏后元素的淋溶特征

本文利用模拟土柱试验研究了施用石灰和石膏对第四纪红粘土发育的红壤中元素淋溶过程的影响。结果表明,施用石灰后１０ｃｍ土层中除Ｃａ＾２＋以外的阳离子元素的淋失量减少,而ＳＯ４＾２－和ＨＣＯ３＾－的淋失量增加;施用石膏后１０ｃｍ土层中所有阳离子元素,特别是ＡＩ＾３＋的淋失量增加。红壤中Ｃａ＾２＋的淋失以自由态为主,施用石膏后与ＳＯ４＾２－结合的比例增加,不同处理中３０ｃｍ土层处铝的淋失以自由态为离,１０     

Effect of ammonium sulfate pretreatment on ammonia volatilization after urea fertilization

Abstract

Urea applications to soil are subject to loss by ammonia (NH₃) volatilization, unless incorporated. It has been proposed that this loss can be reduced by stimulating populations of soil nitrifiers by an ammonium sulfate [(NH₄)₂SO₄] pretreatment two to four weeks before urea application. The objective of this laboratory trial was to evaluate this concept with five diverse soils, two North American Mollisols and three South American Oxisols. The soils were incubated untreated for two weeks, followed by pretreatment with 0 or 5 kg nitrogen (N) ha^‐1 as (NH₄)₂SO₄, on a soil surface area basis. After another two weeks of incubation, the soils were treated with the equivalent of 0 or 50 kg N ha^‐1 as urea. Ammonia loss was estimated after trapping into phosphoric acid (H₃PO₄). Ammonium sulfate pretreatment reduced NH₃ loss with the two Mollisols and a sandy Oxisol and increased the recovery of the urea application as mineral [ammonium (NH₄ ⁺) + nitrate (NO₃ ^‐)] N in these soils. Little NH₃ loss was detected from the two clay Oxisols, and (NH₄)₂SO₄pretreatment did not influence NH₃ loss or recovery of urea as mineral N. An example of a cropping system where this concept may have utility is discussed.     

Influence of Catchment Characteristics and Flood Type on Relationship Between Streamwater Chemistry and Streamflow: Case Study from Carpathian Foothills in Poland

The study aimed to determine the influence of catchment characteristics and flood type on the relationship between streamflow and a number of chemical characteristics of streamwater. These were specific electrical conductivity (SC), pH, the concentrations of main ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO ₃ ^? , SO ₄ ^2? , and Cl^?), and nutrients (NH ₄ ⁺ , NO ₂ ^? , NO ₃ ^? , and PO ₄ ^3? ). These relationships were studied in three small catchments with different geological structure and land use. Several flood types were distinguished based on the factors that initiate flooding and specific conditions during events. Geological factors led to a lower SC and main ion concentrations at a given specific runoff in catchments built of resistant sandstone versus those built of less resistant sediments. A lower concentration of nutrients was detected in the semi-natural woodland catchment versus agricultural and mixed-use catchments, which are strongly impacted by human activity. The strongest correlation between streamflow and the chemical characteristics of water was found in the woodland catchment. Different types of floods were characterized by different ion concentrations. In the woodland catchment, higher SC and higher concentrations of most main ions were noted during storm-induced floods than during floods induced by prolonged rainfall. The opposite was true for the agricultural and mixed-use catchments. During snowmelt floods, SC, NO ₃ ^? , and most main ion concentrations were higher when the soil was unfrozen in the agricultural and mixed-use catchments versus when the soil was frozen. In the case of the remaining nutrients, lower concentrations of NH ₄ ⁺ were detected during rain-induced floods than during snowmelt floods. The opposite was true of PO ₄ ^3? .     

Soil colloids-bound plasmid DNA: Effect on transformation of E. coli and resistance to DNase I degradation

The adsorption and binding of plasmid p34S DNA on four different colloidal fractions from a Brown soil and clay minerals in the presence of various Ca²⁺ concentrations, the ability of bound DNA to transform competent cells of CaCl₂-treated Escherichia coli, and the resistance of bound DNA to degradation by DNase I were studied. DNA adsorption on soil colloids and clay minerals was promoted in the presence of Ca²⁺. Kaolinite exhibited the highest adsorption affinity for DNA among the examined soil colloids and clay minerals. In comparison with organo-mineral complexes (organic clays) and fine clays (<0.2 μm), DNA was tightly adsorbed by H₂O₂-treated clays (inorganic clays) and coarse clays (0.2-2 μm). The transformation efficiency of bound DNA increased with increasing concentrations of Ca²⁺ at which soil colloid or clay mineral-DNA complexes were formed. DNA bound by kaolinite showed the lowest transformation efficiency, and especially no transformants were observed with kaolinite-DNA complex prepared at 5-100 mM Ca²⁺. Compared to organic clays and fine clays, DNA bound on inorganic clays and coarse clays showed a lower capacity to transform E. coli at different Ca²⁺ concentrations. The presence of soil colloids and minerals provided protection to DNA against degradation by DNase I. Montmorillonite, organic clays and fine clays showed stronger protective effects for DNA than inorganic clays and coarse clays. The protection mechanisms as well as the differences in transforming efficiency of plasmid DNA molecules bound on various soil colloidal particles are discussed. The information obtained in this study is of fundamental significance for the understanding of the horizontal dissemination of recombinant DNA and the fate of extracellular DNA in soil environments.     

Evaluation of phosphorus availability from three phosphorus sources in Nigerian soils

Abstract

In an attempt to search for a cheaper source of phosphorus (P), both for direct application and industrial use, three P fertilizers were evaluated in incubation and greenhouse studies. Indigenous Sokoto rock phosphate (SRP) imported, Togo rock phosphate (TRP), and conventional single superphosphate (SSP) were applied on three soil types namely Oxisol, Ultisol, and Alfisol at rates ranging from 0–800 mg P kg^‐1 soil. Evaluation of the P sources was conducted for 12 weeks in incubation study, and five weeks in the greenhouse using maize as test crop. Evaluation of direct application of SSP and SRP on an oxic paleudult was carried out in the field for three years. The results of incubation studies revealed in general, that P availability increased as fertilizer rates increased. The P availability was, however, greater when SSP was applied on the Alfisol than on the Oxisol and Ultisol. The rock phosphates on the other hand were more efficient on acid soils than on soils neutral in pH. Optimum P availability from the fertilizers was observed to occur predominantly between four and eight weeks of incubation. In the greenhouse study, SSP gave the highest cumulative P uptake and optimum rate of application was 200 mg P kg^‐1 soil, while optimum rate for rock phosphate was 400 mg P kg^‐1 soil. The agronomic effectiveness (EA) of the rock phosphates was about 40% relative to SSP on the Alfisol. The EA, however, for TRP and SRP was 120% and 160%, respectively, on the Oxisol, while on the Ultisol, SRP was equally effective as SSP and TRP had 65% effectiveness. The results of the field trial indicated that the SRP had 54%, 83%, and 107% agronomic effectiveness of SSP, respectively, in the first, second, and third year of cropping. Optimum rate for SSP and SRP application was considered to be 50 and 75 kg P₂O₅ ha^‐1, respectively.     

Evaluation of calcium dihydrogen phosphate solution as an extractant for inorganic sulfate applied to soils

Abstract

To evaluate conventional calcium dihydrogen phospahte [Ca(H₂PO₄)₂] solution containing 500 mg P/L as an extractant for soluble plus adsorbed sulfate (SO₄), we added known amounts of SO₄ to 10 soil samples differed in clay mineral composition and extracted with Ca(H₂PO₄)₂ solution. The experimental results showed that the five successive extractions at a soihsolution ratio of 1:10 could quantitatively recover the added SO₄, and there was little effect of air‐drying the soils after addition of SO₄. Based upon these experimental results, we concluded that the Ca(H₂PO₄)₂ extraction is an excellent method for determining soluble plus adsorbed inorganic SO₄ in soils.     

The nature and composition of amorphous material and free oxides in some temperate region and tropical soils

Abstract

Amorphous clay separated from pedons of a highly weathered soil previously classified as Oxisol and an Ultisol of the Southern States and, from the surface horizons of an Oxisol and two Andepts of the tropics were studied by chemical, DTA, infrared and X‐ray analysis.

Considerable amounts of amorphous material, 20–37% in temperate region and 29–40% in tropical soils, were extracted by differential dissolution using 0.5 N NaOH. The molar SiO₂/Al₂O₃ ratios of the dissolved material varied from sesquioxidic to siliceous (0.36–9.1) in temperate region soils, whereas those of the Andepts were allophonic (1.5–1.7). DTA and infrared analysis confirmed these results, however the strong gibbsite peaks in the X‐ray analysis of temperate region soils suggested that the aluminum fraction dissolved was in part, if not all, crystalline in nature. Indications were obtained with DTA and infrared that Na‐dithionite treatment might have altered the nature of the clay.     

Amorphous Aluminum Hydroxide Control on Sulfate and Phosphate in Sediment-Solution Systems

We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)₃ for SO₄ and PO₄. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO₄ prior to acidification experiment; this sorbed PO₄ was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)₃ appears to be an important control on dissolved PO₄ concentration in surface waters, unless there is a large excess of PO₄. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO₄. Maximum SO₄ adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO₄ ⁺ inhibited the increasing SO₄ adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)₃ substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)₃, or in Al(OH)₃-rich sediment, PO₄ mobility will be severely restricted. Suspended Al(OH)₃ in acidified surface waters cannot strongly influence SO₄ concentrations because of the considerably higher total SO₄ concentrations compared to the available surface area.     

Changes in Chemical Properties of an Oxisol Due to Gypsum Application

The increasing demand for fertilizers and the fact that the world reserves of phosphorus (P) and potassium (K) are depletable make appropriate soil management a critical factor in agriculture. Techniques for the fertilizer use and soil acidity corrective are becoming increasingly necessary to minimize the cost of yield and increase the nutrient efficiency. In view of the aforementioned, the present study aimed to assess the effects of gypsum application on the leaching of cations in the soil profile. A completely randomized design in a 5 × 4 factorial arrangement, with five replicates, was used. The treatments corresponded to five gypsum rates (0, 1, 2, 4, and 8 magnesium (Mg) ha^?1) applied on broadcast of soil and at four depth sampled (0–5, 6–10, 11–15, and 16–20 cm). Gypsum application increased the fertility in depth, with the leaching of cations. There was an increase in soil pH, exchangeable K⁺ and calcium (Ca²⁺), sulfur (S–SO₄^2?), P, boron (B), and manganese (Mn) concentration, cation exchange capacity (CEC), K⁺ and Ca²⁺ saturation, Ca²⁺/Mg²⁺, Ca²⁺/K⁺, and K⁺/(Ca²⁺ + Mg²⁺) ratios, and electrical conductivity in soil depth. On the other hand, there was a decrease in exchangeable Mg²⁺ and potential acidity hydrogen and aluminum (H⁺ + Al³⁺), available silicon (Si), Mg²⁺ saturation, and Ca²⁺/K⁺ and Mg²⁺/K⁺ ratio. These results demonstrate that the gypsum application in an Oxisol with 690 g kg^?1 of clay improves the root system with a significant increase in the soil fertility in the profile.     

Evaluation of the Nutrients Variability in Sap of Different Petiole Samples in Tomato Plant

The aim of this trial was to study the variability of anions and cations concentrations in the different petiole samples: young leaves (YL), mature leaves (ML) and aged leaves (AL). The experimental design consisted of four blocks and four plants per block being each plant one replication. In each plant, petiole samples were collected at 135 days after transplanting (DAT) to determine chloride, nitrate-nitrogen, phosphate-phosphorus, sulfate-sulfur, sodium, potassium, calcium, and magnesium (Cl^?, NO₃^–N, H₂PO₄^–P, SO₄^2–S, Na^+, K⁺, Ca²⁺ and Mg²⁺) concentrations. Our results showed that the selection of sample petiole in the tomato crop did not modify the Ca²⁺, Cl^?, SO₄^2–S and Na⁺ concentrations, while NO₃^–N, K⁺, Mg²⁺ and H₂PO₄^–P concentrations showed a great variability due to the selection of the sample petiole, therefore it is necessary to be careful with the sample selection.     

Diurnal Macronutrients Uptake Patterns by Lettuce Roots under Various Light and Temperature Levels

In order to reduce nutrient wastes to the environment the supply should be in accordance to the demand for these. Two experiments were conducted to study and quantify the effect of temperature, irradiance, and plant age on the uptake of nitrate (NO₃^?), ammonium (NH₄⁺), dihydrogen phosphate ion (H₂PO₄^?), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and sulfate (SO₄²). In the first experiment, various levels of temperature and irradiance were applied to plants in a growth chamber, while in the second experiment the uptake was studied along the crop season under greenhouse conditions. The uptake rates were calculated at 2-hour intervals through sampling the nutrient solution and analyzing it by inductively coupled plasma atomic emission spectrometry (ICP-AES). Increasing light and temperature enhance the uptake rates, while the rates decrease with plant age. Nitrogen absorption was similar during the day as during the night. No differences were found in the absorption of H₂PO₄^?, K⁺, Ca²⁺, Mg²⁺, and SO₄^2? between day and night. Nitrate absorption was found to have a positive correlation with the absorption of all the ions except for NH₄⁺.