Advances in Life Sciences 2014, 4(1): 12-16 DOI: 10.5923/j.als.20140401.02 Concept of Soil Water Movement in Relation to Variable Water Potential Rajan Bhatt 1,* , Roopinder Singh Gill 2 , Arsh Alam Singh Gill 3 1 Department of Soil Science, Punjab Agricultural University, Ludhiana, 141004, India 2 Department of Agronomy, Punjab Agricultural University, Ludhiana, 141004, India 3 USF Naraingarh, Punjab Agricultural University, Ludhiana, 141004, India Abstract Soil water potential is the main driving force which causes the soil water to move from one point to other point in the soil depending upon it’s energy state. The total energy state of soil water is defined by its equivalent potential energy, as determined by the various forces acting on the water per unit quantity. In general, flow rates of water in soils is too small to consider kinetic energy. Therefore, the energy state of soil water is defined by its equivalent potential energy, that is by virtue of its position in a force field and which further has a scope to manage irrigation. Usually, farmers mostly apply flood irrigation but after properly monitoring soil water potential with the help of tensiometer helps us to save a significant amount of water. Thus, a proper understanding of soil water potential, it’s components and their relation with the soil water movement is a must for every soil scientist, agronomist and hydrologist for implementing effective plans towards the judicious use of water. Keywords Soil water potential, Water movement, Tensiometers, Matric potential 1. Introduction The complex nature of the pore space in soil and the water held therein makes it difficult to specify directly the force fields acting on the water. The description of movement of soil water on a microscopic scale depends upon not only the quantification of the force field but also on the dimensions of the soil matrix geometry. Water is must for all the ecological processes. In Indian Punjab, water scarcity is an emerging problem because of excessive withdrawal of water (13 Lakh ha-m/Year) for the irrigation purposes. With the result out of 141 blocks, 114 blocks in the state declared in the dark zone. Thus, there is urgent need to understand the concept of soil water potential so that some technique must be used for the efficient and judicious irrigation scheduling viz. tensiometer. which schedule applied the irrigation to crops as per soil suction. Tensiometer works on the principle of measuring the soil suction as when soil dries, water from inner of tensiometer porous cup moves out in the soil to make a balance in potential energy of water within cup of tensiometer and the surrounding drying soil. As a result, the potential reading increased in tensiometer and at a predetermined level of potential, irrigation applied to crops. After some time of irrigation, water again move back into the tensiometer from the irrigated soil as now potential is lower * Corresponding author: rajansoils@gmail.com (Rajan Bhatt) Published online at http://journal.sapub.org/als Copyright © 2014 Scientific & Academic Publishing. All Rights Reserved in tensiometer cup as compared to the surrounding soil. With this technique neither the grain yield affected (as water applied before the crop faces any water stress) nor excess water applied (as farmer knows that when to irrigate). Water availability in soils is governed by its movement because of the difference in soil water potential at different points, which occurs mainly in unsaturated conditions when only micro-pores are water filled while macro-pores are air filled. On the contrary, however under the saturated soil condition, both macro as well as micro-pores are water filled and conducting water from one place to other. Water under saturated soil conditions moves under the influence of gravity while under unsaturated conditions the difference in water potential is the principle driving force causing the water movement from one point to other point. Micropores of fine textured soils is capable of holding water for a longer duration of time even at higher value of suction while macropores drain out the water quickly at a smaller suction. Thus there is a need for frequent irrigation in coarse textured soil as compared to the fine textured soil. Soil water, like other bodies in nature, can contain energy in different quantities and forms. The potential concept to the soil water in relation to it’s movement was first given by[1] in his classical paper on the capillary potential while[2] showed the dependency of water potential on the water content and[3] prepared tensiometer for measuring it. The study of water movement from its potential (energy state) point of view is not a new concept, but still difficult to understand and is very important for the soil physicist, agronomist and even for the engineers working in the field of