VOL. 15, NO. 15, AUGUST 2020 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences ©2006-2020 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 1666 RELATIONSHIP OF WATER PARAMETERS WITH THE OPTIMUM MOISTURE CONTENT IN CLAY SOILS Euriel Millan-Romero and Carlos Millan-Paramo Faculty of Engineering, Universidad de Sucre, Sincelejo, Colombia E-Mail: euriel.millan@unisucre.edu.co ABSTRACT A compacted soil shows a deterioration in physical properties, affects the availability of water and the growth of plants. The amount of useful water in the soil is a characteristic of it that defines its agricultural aptitude and corresponds to the water that can be absorbed by the plants. This study aims to evaluate the relationship of water parameters, field capacity (FC) and permanent wilting point (PWP), with the optimum moisture content (OMC) in clay soils. The physical properties of the soil, such as texture, real and bulk density, maximum dry density (MDD) value and OMC are analyzed. The Proctor compaction test is used to determine the MDD and its OMC; a Richards Pressure Chamber is utilized to obtain the FC and PWP and a tension table to acquire other moisture retention parameters. The results indicated that in Latossolos (oxisols) of Brazil (LV, LVA) soils, the ratio for FC with water retention value of -100 hPa is 100% of OMC, and in Vertisol soil for -300 hPa is 100% of the OMC. For Latossolos (LV, LVA) soils, the PWP (-15000 hPa) is 80% of the OMC and for Vertisol soil 80% of the OMC. With statistical analyze a polynomial regression model is obtained to relate the water contents to OMC. This regression shows that exist a direct relationship between water retention and OMC values. Keywords: proctor compaction test, compaction index, soil properties, soil water retention. 1. INTRODUCTION The growth and development of plants are influenced by the environment, especially by the availability of water because it plays a vital role since it is practically involved in all physiological processes [1]. According to [2], the water deficit is due to the drought that triggers metabolic and physiological responses in plants affecting breathing, photosynthesis, both anatomical and metabolic reactions, nutrient absorption, development, growth, production, among others. The knowledge of the different ecophysiological strategies in the use of water by the species of the diverse communities is vital to be able to predict their response to fluctuations in the hydrological cycle susceptible to change by human activities, to establish programs of sustainable forest and livestock management [3]. Field capacity (FC) is the water content that is retained in the soil after being saturated with water [4]. In the case of non-saline soils, the water potential at field capacity varies between -0.1 to -0.3 bar. Water content is more significant than field capacity in fine textures with high clay and organic matter content [4]. In contrast to the field capacity, the permanent wilting point (PWP) is the most negative soil water potential at which the leaves of the plants do not recover their turgidity. The PWP is close to -15 bar (pF 4.2), although it depends on the type of plant [5]. Globally, the water potential of many plants has been investigated and related to the moisture present in the soil to properly plan irrigation, which allows the rational use of water. The amount of useful water in the soil is a characteristic of it that defines its agricultural aptitude and corresponds to the water that can be absorbed by the plants. Its limit is located between the field capacity (CC) and the wilting point (PM). The behavior of these clayey soils, with their mineralogy, determines the development and distribution of the root system of the crops that are established in them. Maintaining adequate levels of water in the soil is essential to ensure the success of crops in the field, together with factors of soil management, improved seeds and fertilizers. According to [6], the availability of water is the factor that governs the development of crops, because it strongly affects the rate of oxygen diffusion, temperature and mechanical resistance of the soil. Soil compaction is one of the main problems for soil degradation in agriculture, and it is a severe problem due to the interaction between physical properties and plant growth and productivity, which leads to the need to have a parameter that integrates soil-plant interactions. When the compaction increases to excessive levels, the aeration can be affected if the humidity is high and on the other hand, in dry soil conditions, the soil resistance can restrict the growth of the plants [7]. Significant changes that occur in the soil structure in response to compaction, among others, will cause changes in the soil-water-air relationship and the mechanical resistance and, consequently, in the growth of plants in response to the physical characteristics of the soil [8]. The moisture content is important in compaction since it depends on the amount of water in the soil mass so that the particles and group of mineral particles can be rearranged under specific compaction energy, also determines the properties of the soil. Compaction humidity has a dominant effect on many properties of compacted soils [9] and dramatically affects soil infiltration. The compaction test, given its relative simplicity concerning equipment and procedures, represents a potential methodology to estimate the susceptibility or risks of soil compaction in the agricultural field [10]. Studies related to the compaction process have used tests frequently developed for use in soil mechanics [11]. An example of this is the application of the Proctor compaction test that is still rarely used in studies of tropical agricultural soils.