eChapters

Fracture healing is a specialized type of wound healing response in which the regeneration of bone leads to restoration of skeletal integrity. Though the process of fracture healing is usually considered to be biologically optimum; the healing of 5-10% is delayed or impaired. For management of these types of fractures, use of biological methods for the enhancement of fracture healing is essential. Furthermore, fracture-healing can be modified by almost any endogenous or exogenous factor that has an influence on the metabolic function of cells. These factors include transforming growth factor-beta, bone morphogenetic proteins, hormones, vitamins, prostaglandin and calcium containing feed supplement medicine.

Keeping in view the above, in this chapter, efficacy of herbal product-Magacal in promoting osteogenesis during fracture healing in experimental animals is discussed. Magacal optimizes absorption, bioavailability and utilization of dietary calcium, phosphorus and magnesium. It is claimed to have advanced chelating agent to form organic complex chelate with dietary Ca, P and Mg, besides containing natural Vitamin D metabolites in highly bioavailability organic form, naturally protected and stable biotin and modern delivery system for optimum translocation of Ca, P and Mg ions to the sites of requirements.

Clinically healthy, adult New Zealand White rabbits of either sex (10) are divided equally into two groups A and B each consisting of 5 animals. All animals are kept on standard diet and management throughout the experiment. In all animals, midshaft simple transverse fracture is created in both the ulnae under thiopental (2.5%) anaesthesia. In test group (Group A), Magacal is given @5ml/animal/ day, orally from day 5-20 post fracture, whereas, in group B, no drug is given which serve as control. Antibiotic dressing of the skin wound is done daily for one week with povidone iodine and himax ointment. All the animals are administered streptopenicillin @ 0.5 gm/animal/day for 5 days postoperatively. Skin sutures are removed on the10th postoperative day.

Clinically all the animals are observed for inflammation, pain and edema at the fracture site, surgical wound healing, appetite, general health, muscular atrophy of the limb, if any, at different intervals postoperatively.

Bone is the only tissue in the body able to heal without microscopical scarring. On the other hand fracture healing is a slow process causing long immobilization periods with consequently high costs for fracture healing giving rise to delayed healing, fibrous healing or non-healing with subsequent problems for both, the patient and the orthopedic surgeon. Fracture healing is complex phenomenon which involves numerous cells, regulators of cell function and biochemical interactions in the repair process. The healing potential of bone, in a fracture model is influenced by a variety of biochemical, biomechanical, cellular, hormonal and pathological mechanisms. A continuous occurring state of bone deposition, resorption and remodeling facilitates the healing process.

Biodegradable and bioinert ceramic materials such as hydroxyapatite (HA), tri-calcium phosphate (TCP), aluminum-calcium-phosphate (ALCAP) ceramics provides scaffold to support the attachment and migration of newly formed bone cells into the osseous defect and also help in formation of a vascular network through the newly formed bone. Bioceramic also act as a carrier to deliver stem cells for osteogenesis.

Specific bone-inductive proteins/growth factors can induce bone formation and healing in vivo. These morphogens are therefore, to be an ideal alternative to autogenous bone grafts. These findings initiating intensive research into bone regeneration orchestrated by putative soluble signals and lead to the discovery and identification of an entirely novel family of protein initiators collectively called the bone morphogenic protein (BMPs), which belong to transforming growth factors-ß (TGF- ß) super family. These growth factors might possess a biological activity that is site and tissue specific in the induction of bone formation. Different growth factors have been demonstrated to possess osteoinductive and fracture healing properties.

Stem cells have therapeutic potential in the realm of orthopaedic surgery because of their capacity to self-renew and differentiate into various types of mature cells and tissues, including bone. Embryonic stem cells (ESCs) are pluripotent cells derived from the inner cell mass of pre-implantation embryos and represent embryonic precursor cells that give rise to any cell type in the embryo. Specifically, it has been shown that ES cells can differentiate into osteogenic cells under selective culture conditions. These osteogenic cells are capable of in vitro producing bone nodules in three dimensional scaffolds.

Despite the benefits that minimally invasive surgery and osteosynthesis have brought to fracture management and bone healing, there are still many circumstances where bone healing remains challenging. Large bone defects are serious complications that are most commonly caused by extensive trauma, tumour, infection, or congenital musculoskeletal disorders. In nonunion cases repairing of bone defects with composite biomaterials as defect filler can promote bone regeneration. Currently, the gold standard for bone regeneration is use of autogenous bone graft. In order to avoid morbidity at the donor site or if large amount of autogenous bone is needed, bone substitution materials can be used. Bone substitution materials can be combined with cells such as mesenchymal stem cells (MSCs) to increase bone formation. Bone-marrow derived mesenchymal stem cells (BMSCs) represent an attractive cell population for tissue regeneration. Bone marrow stem cells are pluripotent cells that have been used to facilitate bone repair because of their capability of differentiating into osteoblasts. Several studies on the regeneration of bone have shown that cultured BMSCs, seeded on different bioabsorbable implants are able to induce bone formation in vivo and lead to improved healing of critical-size defects.

Calcium phosphate bone substitutes such as hydroxyapatite (HA) and tricalcium phosphate (TCP) are currently used for bone substitution in many different clinical applications such as repair of bone defects after trauma or tumour and bone augmentation in spinal arthrodesis. Although these bone substitutes are osteoconductive, they often lack the osteogenecity needed to support bone healing in large defects and are slowly degraded in the body. Studies have shown that coating of hydroxyapatite with a calcium silicate layer could encourage cell proliferation and osteogenic differentiation of human bone marrow-derived stromal cells. Silica-calcium phosphate composite in comparison to calcium phosphate-rich biomaterials has a faster resorption rate owing to greater dissolution of Si ions. The use of several growth factors have been studied in bone repair and these factors are known to play a role in differentiation of mesenchymal progenitor cells specific lineages like endothelial cells or osteoblast. Bone morphogenetic protein-2 (BMP-2) has been shown to accelerate bone healing in humans and animal models. BMP-2 acts by osteoinduction and is involved in the differentiation of mesenchymal progenitor cells into osteoblasts. The addition of recombinant human BMP (rhBMP-2) to a self-cross linkable cellulose hydrogels/biphasic calcium phosphate granules construct promotes bone regeneration in a critical-size segmental defect model of non-union in dogs. It is also reported that protein, insulin-like growth factor (IGF-1) stimulates direct migration of human mesenchymal progenitor cells (MPC) and contributes to the recruitment of MPC in bone formation and bone healing.

The process of fracture healing is unique, in which damaged bone restores its original architecture but it does not form a poorly organized replacement matrix, otherwise known as scar tissue, rather it regenerates the original matrix and retains its mechanical properties. In order to repair bone defects, a combination of cells with osteogenic activity and appropriate scaffolding material can stimulate bone regeneration and its repair. A potential substitute for autologous transplantation should possess 3 elements: osteoprogenitor cells, osteoinductive factors, and an osteoconductive scaffold. Stem cells from adult tissues are attractive materials for cell therapy and tissue engineering. These cells generally have restricted lineage potential when compared to embryonic stem cells, and this may be advantageous in certain therapeutic applications. Bone-marrow-derived mesenchymal stem cells (BMSCs) have proven to be beneficial in bone regeneration. Bone marrow stem cells are pluripotent cells with the capability of differentiating osteoblasts so that they have been used to facilitate bone repair. Several studies have shown that seeding of cultured BMSCs on bioabsorbable implants can induce bone formation in vivo and lead to improved healing of critical-size bone defects.

Mesenchymal stem cells (MSCs) because of their self replication and osteogenic differentiation capabilities are regarded as an excellent source of cells for bone tissue engineering. Autologous stem cells are not always preferable since the quality and quantity of such cells will be affected by metabolic diseases, old age, and osteoporosis. Allogenic BMSCs might be preferable to xenogenic, but they are always not readily available. In addition, allogenic MSCs have the potential for carrying some diseases. The use of non-autologous stem cells isolated from healthy donors offers a major advantage since these stem cells can be thoroughly tested and formulated into off-the-shelf medicine in advance. Major attractive advantage of BMSCs as a source of cell transplantation is their low immunogenecity. It is now well established that BMSCs are immune-privileged cells that do not elicit immune responses due to an absence of their immunologically relevant cell surface markers.

The knowledge and principles from interconnected disciplines of bioengineering, material science and life sciences are combined in tissue engineering with the aim of developing a construct, that can wholly or partly restore/maintain/augment the function of a damaged tissue or organ. Tissue engineering construct generally comprises cells on a suitable scaffold. The ultimate functionality of a tissue engineering construct is mainly dependent on the cell behavior on scaffolds. The proliferation and cell viability on scaffolds varies from one cell type to another and from one species to another. So it is important to investigate individual cell-scaffold combinations. The similarity in structure and composition to bone mineral, osteoconducive properties, ability to integrate with the bony tissue and absence of immune response makes hydroxyapatite [Ca₁₀ (PO₄)₆(OH)₂] the choice of calcium phosphate biomaterial with only disadvantage of slow rate of resorption. On contrary, silica–calcium phosphate composite in comparison to calcium phosphate is rich biomaterials having a faster resorption rate. Studies have shown that coating of hydroxyapatite with a calcium silicate containing layer encourages cell proliferation and osteogenic differentiation of human bone marrow-derived stromal cells. So in this chapter, a triphasic composite scaffold (calcium silicate, hydroxyapatite and tricalcium phosphate), namely HASi with elements in the following percentages: 66.36 % - calcium, 25.35 % - phosphorus and silicon - 8.29 % and porosity of 50 – 500 µm is reported to evaluate the rBMSC proliferation and differentiation properties in vitro.

The present chapter is therefore, included with the aim of assessing cytocompatibility of HASi and rBMSC in terms of cell attachment, cell morphology, cell proliferation and osteogenic differentiation.

Bone differs from other tissues not only in physio-chemical structure, but also in its extraordinary capacity for growth, continuous internal remodelling and regeneration throughout post fetal life. Bone formation is a complex process regulated by diet, vitamins, hormones and growth factors. Growth factors are polypeptides that increase cell replication and have important effects on differentiated cell function. Growth factors are initially considered as systemic agents, but current evidence indicates that they act primarily as local regulators of cell growth. The transforming growth factor-β family of proteins, which comprises polypeptide growth factors that have diverse effects on the growth, differentiation, and function of cells, is receiving considerable attention for potential clinical applications and is likely of physiological and orthopedically significance.

Transforming growth factors

It is one of the most important growth-promoting osteo-inductive substances, which have been identified at the site of fractures and other places. Transforming growth factors (TGFs) have been categorized into TGF-β (alpha) and TGF-β (beta). TGF-α has not been isolated from bone tissue and cannot be considered a local regulator of bone remodelling, although it is mitogenic for bone cells and stimulates bone resorption. TGF-α shared amino acid sequence, receptor-binding and functional activity with epidermal growth factors but had only weak transforming growth factors activity. Furthermore, TGF-β by itself is completely ineffective, but together with TGF-α, it potently induced growth of colonies of cell-line.

In 1965, Urist demonstrates that the implantation of demineralized bone at extra skeletal sites induced de novo formation of cartilage and bone and proposed that the decalcified bone matrix possess high osteoinductive property and the inductor is a unique chemical that differentiates mesenchymal type cells (pericytes) into new bone. Urist and Starates (1971) reported that the inductor is a protein and termed it bone morphogenetic protein (BMP) . BMP is the bone induction principle.

Sources: Bone morphogenetic protein isolate from bovine as well as human bone and designated as bBMP and hBMP respectively. The molecular cloning of the bone morphogenetic proteins and their subsequent expression in recombinant system, resulted recombinant bone morphogenetic protein designated as rhBMP. BMP has been extracted from dentin and bone matrix, as well as from bone tumours, by enzymatic and nonenzymatic methods. The sources of BMP, thus far explored are rabbit dentin, rat, rabbit and bovine bone, human bone, mouse or human osteosarcoma and human placenta.

BMP circulates in the blood and it can be detected by BMP-radioimmunoassay. BMP levels higher in growing children (20-72 ng/ml) and patients with Paget’s disease (over 259 ng//ml) than in normal adults (14-18ng/ml). Crude and partially purified BMP has been extracted with the aid of collagenase, ethylene glycol, calcium chloride urea and Guanidine hydrochloride (GuHCL) solution. Wang et al (1988) purified BMP factor that induces bone formation> 300,000 fold from Guanidine chloride extracts of demineralized bone. As littlie as 50ng of this factor can induce the formation of cartilage and bone in an in vivo assay, though only 40µg could be obtained from 400kg of bovine bone powder.

Fracture in animals occur frequently and is a concern of economic importance to the owner. The practice of keeping them as pets in households rather than in sheds or in confinements have increased the chance of encountering accidents like fall from coat, terrace, limbs being trapped in drains, being hit by vehicles, dog bites etc. leading to fracture. Fracture management in small animals/small ruminants can be successfully achieved owing to their light weight; they tolerate external coaptation relatively well and can ambulate in three limbs well in order to spare the injured limb. Fracture can be repaired successfully with regional anaesthetic techniques which they can tolerate very well. The constraint of cost effectiveness can be balanced by carefully selecting the appropriate technique according to the weight and limb involved. Many economical skeletal fixation technique have been evolved which can well fit into the budget of the owner. Knowledge of simple techniques can enhance healing in cases of bone loss and management of infection.

Fracture site stabilization

Fracture repair is usually elective, hence initial support and care of the fracture is necessary to prevent further trauma and complications like communication of fracture site to the exterior through wound or sinus and chances of infection. Initial support to splint the bone not only limits the movements but also supports the soft tissues from untoward consequences. Limb splinting reduces edema and pain, preserves neurovascular supply to the limb till the day of operation and helps to transport the animal safely. Fracture to limbs caudal to mid radius ulna/ tibia can safely be stabilized by splints or full limb casts. Wood, pliable bamboo or split poly vinyl chloride pipes positioned on the caudal and lateral aspects of the limbs and supported firmly with tapes or bandages can serve the purpose. Fracture proximal to mid radius ulna or tibia should not be stabilized using splits since the fulcrum effect created due to this can augment soft tissue injury. Careful assessment of the viability of the structures caudal to fracture site should be assessed prior to a decision regarding surgery, devitalized tissue hamper healing and is a subject to be considered for amputation.

Repairing fractures in small animal’s presence challenges to the veterinarians in their day to day service. These challenges include properly repairing fractures, each of which is unique, choosing the right fixation device, keeping an extensive inventory of costly instruments, and providing high standards of care for fracture repair. But fracture repair also gives veterinarians the opportunities to do something a little unusual in daily practice and to experience the immediate gratification of easing pain and promoting activity in injured animals.

Successful management of fractures mainly depends upon early diagnosis, type of fracture, timing of surgery and selection of proper method of fixation. The fixation of fractures can be achieved either by external or internal fixation methods. An ideal method of fracture fixation is one that can maintain early anatomical reduction, minimal soft tissue trauma, rigid stability and early motion of bone and joint. Restoring a fractured bone’s normal shape is important for return to function because it contributes to normal alignment of adjacent joint surfaces. Whereas, rigid stability of fracture fixation eliminates fragment movement and reduces pain. Soft tissue trauma adjacent to fractured bone should be minimum, which play a vital role in early vascularisation and prevents infection. Finally, early return to function maintains muscular tone of the limb allows normal weight mobility and joint nutrition and uses normal weight bearing forces to maintain bone density. These can be achieved with use of internal fixation devices.

1. Bone grafts

Bone grafting represents one of the earliest devised reconstructive approaches to the musculoskeletal system and remains among the most commonly used orthopedic procedures. Bone is the second most frequently transplanted tissue. The first recorded attempt to use bone graft is by the Dutch surgeon Job Van Meek’ren in 1668.

Definition

A graft is a living tissue that is transplanted to another site either within the same individual or into another individual for repair of a defect. An implant is a non viable material placed in a living system. Implants are composed of bone cement, metal or ceramic material. Grafts are structurally important for mechanical stability, but their use evolved to include the stimulation and enhancement of bone in response to injury.

Indications

Bone grafts are used, in general as framework, both to provide stability and to augment healing. It is used in the management of non union, delayed union, treatment of pseudoarthrosis, filling of osseous defects or cavities, arthrodesis, stabilization of spinal segments and addition of bone stock in total joint displacement.

Fracture healing is a specialized type of a wound healing response in which the regeneration of bone leads to a restoration of skeletal integrity. Because healing of a fracture in a living organism is accomplished by cells, it can be modified by almost any endogenous or exogenous factors like nutrients, vitamins, hormones, growth factor etc. that has an influence on the metabolic function of bone cells. Fracture healing may be induced by malnutrition that involves certain nutrients, notably calcium (Ca), phosphorus (P) and vitamin D, but also iodine (I), copper (Cu), zinc (Zn), manganese (Mn), fluorine (F), silicon, vitamin A and perhaps vitamin C as well as different endocrines. The number of these nutrients and their interaction is so large that dietary intervention in fracture management is likely to be the most effective if directed at consumption of a good diet that is completely balanced for growth, maturity, old age or stress. Substitution of a good diet for a bad one is also likely to be more convenient and safer than most attempts at partial supplementation of a faulty diet in order to bring it into balance. Underfeeding a good diet decreases size-for-age of bones during growth and delayed fracture healing. Underfeeding may engender osteoporosis in older animals. Underfeeding of Ca, P and vitamin D, causes delayed fracture healing. Over feeding a balanced diet induces rapid growth of newly formed bone and sometimes-accelerated fracture healing but it also causes obesity in adults.

Three major component of bone are osteogenic cells, organic matrix and inorganic matrix (mineral). The osteogenic cells include osteoblasts, osteocytes and osteoclasts, while the matrix consists predominantly of collagen and proteoglycans and constitutes approximately one-third of bone mass (on dry basis). The inorganic/mineral component that makes up approximately two-third of bone and it performs two essential functions : it serves as an ion reservoir and it gives bone most of its stiffness and strength. Bone is a reservoir for 99% of body calcium, 85% of body phosphorus and 40-60% of body sodium and magnesium. The main mineral composition of a long bone is: 85% calcium phosphate as hydroxyapatite, 12% calcium carbonate and 3% magnesium phosphate, calcium fluoride and magnesium carbonate and trace amount of chloride, potassium and sodium. For collagen synthesis, hydroxylase enzymes requires ferrous ion and vitamin C. Impaired collagen synthesis also occurs during deficiencies of vitamin D and E and zinc. The organic intercellular bone matrix is rich in mucoplysaccharide. Their synthesis involves enzymes that require manganese, zinc and vitamin A.

A. Definition

A fracture is a break in the continuity of hard tissues like bone, cartilage, etc.

B. Etiology

(a) Extrinsic causes

Direct violence

Indirect violence

Bone is an integral part of musculo-skeletal system of body. In the living animal it is bluish pink, whereas, fresh dead bone is yellowish-white in colour. It is hard and resistant to pressure but also have certain amount of elasticity. Its tensile strength is equal to the cast iron, though bone three times lighter and ten times flexible to cast iron.

Number of bones: The number of bones of the skeleton varies with age and species. Number of bones in cattle-210; Horse-208; Dog-271; Fowl-166 and human-208 (207-212)

Composition of bone: Bone contains different bone cells, organic and inorganic matrix and water. Organic matrix is about one-third and Inorganic matrix is two-third weight by volume. The organic material consists of 90% collagen [type-I (maximum), type V and type XII] and 10% non-collagenous glycoprotein and bone specific proteoglycans (osteocalcin, osteonectin, sialoprotein, bone phosphoproteins and small proteoglycans) and bone growth factors [TGF-beta family; Insulin-like growth factor-1, 2; bone morphogenetic protein (BMP); platelet derived growth factor (PDGF); Interleukin -1 (IL-1); Interleukin-6 (IL-6); colony stimulating factor]. Organic matrix of bone resembles the matrix of dense fibrous tissues such as tendons, ligament and joint capsule. It is not certain whether all of these proteins are synthesized by bone cells or whether they are synthesized by cells outside of the bone and then incorporated into the bone matrix. However, their presence within bone and their potential to affect the activity of bone cells suggests they have important role in controlling bone cell functions. Inorganic matrix of bone or mineral component of bone serves as an ion reservoir and gives bone of its stiffness and strength. It reserves 99% of body calcium, 85% body phosphorus and 40-60% body sodium and magnesium. Inorganic matrix of bone is composed of 85% calcium phosphate, 12% calcium carbonate, 3% of magnesium phosphate, calcium fluoride and magnesium carbonate. It also contains traces of chlorine, sodium, potassium. These minerals remain as hydroxyapatite crystal form within bone. However, bone mineral crystal is not pure hydroxyapatite, instead they contain both carbonate and acid phosphate groups (HPO₄) and bone crystal does not contain OH groups. Bone matrix has such great durability and stability that it can remain essentially unchanged and retain much of its strength for centuries after death. Removal of organic matters renders the bone fragile, brittle and shattered, whereas, decalcification renders bone soft and pliable and resistant to fracture.

11.1 Performance of Farm Irrigation Systems

The performance of farm irrigation systems is determined by the efficiency with which water is delivered to the field and utilized to the fullest amount possible with minimum losses due to seepage and percolation, runoff, evaporation and other operational losses. The efficiency of the irrigation system will increase if the conveyance losses, application losses and other losses are reduced to a great extent.

11.1.1 Overall Efficiency

The overall efficiency of a farm irrigation system is defined as the percent of water applied to the farm that is used for irrigation on the farm. Irrigation efficiency otherwise called as overall system efficiency is defined.

10.1 Application Efficiency and Irrigation Uniformity

All irrigation systems have some non-uniformity. This non-uniformity influences yields and irrigation efficiency especially application efficiency. If the net amount of water applied during irrigation is the same as that required to fill the soil water deficit, then because the distribution of water is never perfect, half of the field will receive too much water while the other half will receive too less water. In such a context, a farmer will try to apply more irrigation water to his field so that a larger fraction of the field has an adequate amount. This will tend to have higher percolation and runoff and thereby declining the application efficiency. An alternative to adding extra water is to improve the uniformity of water application. A major advantage when the uniformity is improved is that the amount of deficit in the area under irrigation is reduced and the potential for water logging and salinization is also reduced.

9.1 Introduction

After knowing when to irrigate and how much to irrigate, next important thing is how to irrigate the crop field. Methods of irrigation plays a very crucial role in deciding how to irrigate the crop fields since all the crops do not require same methods of irrigation. Depending on the sources of water available for irrigation, type of crop to be irrigated, quantity and quality of water to be applied and other economic considerations, methods of irrigation will vary. Irrigation water may be applied to the crops by flooding it on the field surfaces as surface irrigation, by applying it beneath the soil surface as sub irrigation, by spraying it under pressure as sprinkler or overhead irrigation or by applying it in drops around the root zone of the crop as trickle irrigation. The commonly used methods of irrigation are described in schematic diagram as follows

8.1 Introduction

For maximization of yield of crops, it is essential to provide irrigation to crops. When either the natural sources like rainfall, dew, snowfall and other forms of precipitation or when the capillary rise of groundwater is not sufficient to meet the crop water demand, then there is need to supply irrigation. This irrigation water is a precious resource and need to be used cautiously. There are three important things need to be understood for optimum utilization of irrigation water with basic purpose to maximize the yield and returns. 

7.1 Introduction

The entire amount of water that is diverted at the canal head regulator does not reach at the field for use of irrigation. Major amount of it is lost on way during its movement in the canal systems. During the passage of water from main canal to outlet at the head of the water course, water may be lost either by evaporation from the surface or by seepage through the peripheries of the channel. These losses are sometimes very high, and may go up to 50 % of the total water diverted into the main canal. Evaporation losses are low and may go to a maximum of about 7 percent of total losses. The major loss of water in the conveyance system is the seepage loss. Seepage loss depends on the channel geometry and evaporation loss is proportional to the area of free surface. In determining the designed channel capacity, a provision of these water losses must be made. The provision for the water lost in the watercourses and in the field however, already made in the outlet discharge factor, and hence no extra provision is made on that account. However, excluding the above two losses, there is operational loss which when added to the evaporation and seepage losses, the total losses goes up the maximum 50 percent level. The operational loss includes spillage, over-toping, leakage through rodent holes, dead storage, initial infiltration and evapotranspiration from the vegetation along the watercourse. Evaporation and seepage losses of the canals are discussed below.

6.1 Introduction

In order to increase the production and productivity of crops, provision of irrigation system is highly essential. A project that makes use of weir or a barrage for providing irrigation to fields is called as direct irrigation system. On the other hand, a storage irrigation system makes use of storage reservoir by construction of dams. In order to provide irrigation by both the schemes, it is necessary to have a network of canal systems. A canal is an artificial channel, generally trapezoidal in shape constructed on the ground to carry water to the fields. The canal systems that provide water to the fields include main canals, branch canals, distributaries, minors and watercourses. It is imperative to design the canal systems properly for a certain realistic value of peak discharge that must pass through them so as to provide sufficient irrigation to the command areas. The flow irrigation that provides irrigation water to the fields may be of two types i.e. Inundation irrigation and Perennial irrigation.

5.1 Soil

Soil and water are the two most important natural resources required for crop production. Without soil, no crop can be produced even if there is availability of plenty of water. It is vital not only for agriculture but also very vital for sustenance of life. No building can stand on any place without soil. Soil gives foundation support for any building. The term ‘soil ’is defined in various ways depending on the general professional field in which it is used. However to an agriculturist, soil is the substance existing on the earth surface, which grows and develops plant life. It contains all vital elements including its inherent fertility contents that support the growth of plants. For an engineer, soil is the unaggregated deposits of mineral and organic particles covering major part on the earth crust. It includes widely different materials like boulders, sand, gravel, clays and silts. Soil is produced by the weathering of solid rocks. The formation of soil is due to geologic cycle continuously taking place on surface of the earth. The geologic cycle comprises weathering or denudation, transportation, deposition and upheaval, again followed by the above mentioned processes. Weathering may be natural or artificial. In natural weathering, physical processes like temperature changes, flow of water, ice, wind and rain play the role. In artificial weathering animals especially human beings interference causes soil erosion and formation. It is obvious that it takes hundreds of years to form one inch of soil.