NH4+ Fixation and Ionic Competition with K+ in a Clayey Soil from Ocumare Del Tuy, Venezuela

Abstract

Ammonium and potassium are essential for plant production, both share an ionic potential capable of entering the structure of some 2:1 type clay minerals, remaining fixed. Although, in Venezuela there are abundant areas with the presence of this type of clays, ammonium fixation (NH4f) has been little studied. The soil studied located in Los Valles del Tuy, Miranda State, presented clayey texture, some textural homogenization, and little differentiation in horizons, which is characteristic of Inceptisols. That soil also evidenced by XRD the abundant presence of nontronite / montmorillonite, resulting in a semi-quantification of 20% and 16.4% for the surface and subsoil horizons, respectively. The fixation of ammonium and the competition with potassium to occupy the fixed sites of these clays were studied by means of an incubation experiment, varying the concentration of K+ and keeping the concentration of NH4+ fixed, then extracting and determining the fixed ammonium by a photocolorimetry method. The soil presented a great ammonium fixing capacity, 49% of the total added was fixed in the absence of the competitive ion; however, NH4f fell drastically when both ions were added simultaneously, decreasing exponentially under increasing amounts of the competitive ion and staying constant around 8%. It seems possible that, the high toxicity induced by excessive fertilisation with ammonium sulfate could be counteracted in soils with capacity to retain K, if, at the expense of Kf, the levels of K in the soil solution are increased causing a decrease in the concentrations of N in the tissue.

Relation of several pedological characteristics to engineering qualities in expansive clays of Northern Venezuela

“…The values of the Atterberg limits were, in general, comparable with the information from the literature for expansive soils [6,9,11,20]. However, the scarce data presented in specialised journals on these parameters in tropical soils is striking.…”

“…These limits also provide information for interpreting a set of mechanical and physical properties of soils, such as shear strength, load capacity, compressibility, and shrinkage potential [5,6]. From the above it follows that AL have a dual practical use, since in soil science they generate valuable information for the genesis, classification and use of land, and in engineering sciences they are very useful in the design of infrastructures (construction of buildings and roads) [9]. Moreover, ALs have recently seen to play an important role as indicators of soil vulnerability to degradation processes due to natural and anthropic causes [10,11].…”

“…granulometry, cation exchange capacity) are useful in the study of their morphology, genesis and mapping; similarly, relatively easy-toobtain measures, such as Atterberg limits, help to complement that information. Therefore, these limits are widely used by geotectonic engineers in the evaluation of the properties and risks involved in the expansion-contraction of the sediments of their infrastructures, in particular those built on expansive clays (EC) [9].…”

“…In general, ECs are located in temperate, subtropical and tropical zones [9,[12][13][14] these clays are characterised because in their mineralogical composition present a significant proportion of 2:1 type phyllosilicates, which gives them a high capacity for expansion as a result of the location of water molecules between the silicate sheets [15]. ECs, due to their particular expansion-contraction characteristic with wetting, are susceptible to anomalous deformation due to the volumetric change induced by expansion, which, in turn, generates damage to infrastructure works as a result of harmful differential movements [16,17].…”

“…In Venezuela, in the Caribbean Region, northern part of the country, with a semi-arid climate with low rainfall, there are adequate conditions for the development of soils with the presence of expansive clays. Thus, the presence of expansive clays is the main pathology registered by the road infrastructure in some sectors, which its concomitant problems of deterioration and deformation of road arteries, and in surrounding infrastructures [9].…”