 which influence the selection of various methods and the two major factors which we had talked about how the soil type influences the selection of method and then we looked at how the topography influences the irrigation methods. The other factors which have been included which have impact on the selection of irrigation methods include climate, in the case of climate how does it influence the irrigation method because as we have seen in the previous topics, the climate is the one which influences the evapotranspiration requirements. Now if your climate is such that the evapotranspiration requirement is very high because of the climate, you might not be in a position to choose a method which needs which needs sufficient amount of water or sufficient quantity of water because in the case where your frequency is high, the frequency of irrigation or the number of times the irrigation has to be provided because what you do is that you are replenishing the deficit and the rate at which the deficit is being created is quite high because of this high rate, the frequency at which the moisture has to be supplied will also be high so consequently you might not be in a position to choose a method which cannot be repeated very often so that is how the climate will influence the choice of the method because there are some methods where you have complete control on the application, the number of times the applications can be made whereas there are some methods where the control is not as good as with some other method. So these methods where you have to wait for the next application because of the complications in the layout of the system or the distribution network of the system, those methods might not be in a position to be getting the priority or getting the selection in terms of the climatic conditions. So climate can be at in some situations can be very very influencing factor in the selection. On the other side this is one aspect of the climate where we have said in general that those methods which are dependent on the gravity flow they might not be highly suitable in some situations, we correct generalize but let us see the other extreme. Let me say that if I have very windy conditions the wind velocities are very high in this climate where the wind velocities are very high you might find that the other methods which are suitable which are which are capable of having a very high level of frequency of irrigation. You might not be in a position to for example let me say that this you are using under windy conditions a method which is sprinkler irrigation method. Now if you use sprinkler irrigation method because of the wind effect there will be lot of moisture which will be drifted away from the target of the target level if your fields are somewhere here you might find that because of the wind conditions you might be applying you might want to apply water here in this area over this zone your water might be drifted and it might be getting applied some water might be getting applied here but there can be some portion the water might be getting drifted. There can be losses which are the spray losses which will deal with subsequently they might increase to an extent that this particular method under very high windy conditions might not become the natural choice you might have to look for some other method if the conditions are not suitable for this method because of the windy conditions. So you have to look at the various combinations in terms of the climate what is the what is the overall combination of the various factors which are influencing the climate and thereby in turn influencing the rubber transpiration and whether you can choose that specific method if you choose that method what will be the implied other implied factors which have to which will influence the various aspects of irrigation. Let us go to the other factors in influence selection of the method of irrigation. Water supply in any irrigation some factors related to the water supply which have to be looked into and these factors vary from the when you say water supply the three attributes of water supply which you will have to consider what is the quality of water quantity of water the relation for which that quantity of water is available. Now these three aspects different circumstances they can be very influencing factors in deciding what type of method should be suitable under those set of circumstances. Let us take the example that if your quality of water is not very good you might need a method where you can enhance the moisture level of the soil or you can keep the moisture level of the soil quite high because if you will be using that method which can be applied in small quantities where the water can be even you can afford to supply the water in small quantities then as we have discussed earlier that in those situations where the moisture content is very low the salt accumulation in the soil can be detrimental the ill effects of the salt accumulation of the uhh in the soil can be less detrimental if the moisture content of the soil can be kept at a higher level. So if you have that problem then it will be better to choose that method which can afford to let the moisture content of the soil be at a higher level or in some cases where you can have sufficient quantity of moisture so that the salts which have accumulated in the top layer of the soil can be depleted and they can be pushed into the lower levels. Similarly in the case of quantity of water now there are some methods where you cannot apply the water if the quantity of water is very low because of uhh the fact that the distribution of water over the field will be very poor if you are let us assume that if your quantity of water is small the quantity can be in terms of the total volume or it can be in terms of the rate at which the water is available that is where the duration comes into picture. Now when you look at the quantity you might have to scrub it along with the duration because if the rate at which the water is available is very low but is available for a very longer period you might have the same quantity covered in terms of volume if the rate of water uhh was very high but for a very short duration. So looking at the quantity in terms of volume as well as the duration for which is available your method of uhh your choice of method of irrigation might be constrained if there are some methods where you cannot go below a level in terms of the rate of water available. If the rate of water available is very very small some of the methods might not be suitable for the application of water onto the field. There is uhh this cannot be looked at as a standalone uhh criteria you have to look at the other parameters like what is the slope of the field, what is the soil type so it cannot be when you say quantity and duration you cannot look at these these attributes in isolation you will have to look at the other aspects of uhh the topography of the field, the slope of the field, the type of the soil which is available but the supply, the water supply in terms of quantity, in terms of its quality, in terms of uhh the rate of water availability they will certainly influence the uhh method of irrigation uhh to be selected. Then crop crops will also influence which crops you want to uhh cultivate which are the crops in question so depending on the type of crop which you which you want to irrigate the method of irrigation will be dependent on the type of crop also. For example let us there are the various aspects of uhh the crops how they influence the method the first thing you can uhh think in terms of uhh sensitivity of the crop to foundation of water. There are some crops which are very sensitive if the water stands on the ground for uhh a sufficient period and because the low irrigation available available if the water will be standing you will get the the saturation conditions or conditions which are close to saturation all the air will be displaced and it will be it will be replaced with water. So under those circumstances there are some crops which which get influenced in terms of reduction in the yield. Those crops if you have if you are uhh cultivating those crops then you you cannot choose a method of irrigation which can which can induce the conditions of saturation or which where the water might be standing for some time and reducing the irrigation in the soil. So uhh if you have if you have such crops you will go in for a method where you have the application done in such a manner that the water is not is not possible for the water to stand beyond a certain period which which is not detrimental for the the crop production. Similarly uhh the type of crop how how much they grow in uhh in horizontal direction and in vertical direction in terms of how much is the resistance they provide to the flow of water. Whenever you will have the crop grown into the field you will find that as the crop grows they will be spread off the their stem they will be uhh depends what type of crop it is. If it is uhh the the ford of crop it will be so close drawing that you might find that the resistance to the flow of water will be so much that it might be it might might not be possible for the water to move at a very very fast rate and go to the next subsequent areas in the field. In that situation you might choose a method where you do not have very elongated fields because otherwise you might find that most of the water which has been applied it just keeps on infiltrating onto the upstream ends of the if this is the if this is the field and if you are applying the water in the from upstream end and it is flowing towards the downstream end if there is lot of the density is very high you might find that the unevenness of the distribution of water will be too much. So you cannot choose a method of irrigation which needs very long fields you might have to go in for a method because when you say methods the methods are distinguished on the basis of the shapes of the fields, the sizes of the fields how they are laid all the methods which will be covering this immediately after this you will find that the methods are not the method of application only their differentiation is with respect to the shapes and sizes of the fields also. So this in this particular situation you will find that the crops can influence to an extent the the selection of the method what type of method should be suitable to the specific crops. In another aspect you can you can even consider that the value of the crops can also influence the method to be applied if the crop is value crop in that situation you might find it quite reasonable to invest more money, select the method which is more efficient but it needs more investment so you might be able to justify that investment depending on how much is the return from that crop because if you are using a method which is very sophisticated but the crop value is very low in that situation you might not be able to get the return from the crop which is commensurate with the investment which you have made. So that that aspect will be very important in some cases where your crop value has to be looked into it has to be taken into consideration because why you why you going for artificial irrigation because you want to have a security in terms of the water availability if the nature is not providing water you are trying to replenish the deficit the moisture deficit in the soil whenever it is it is going beyond a certain limit so you are trying to replenish that in artificial manner but the control with which you can have the security of this replenishment it goes very high with high level of investment but the same time you have to look at whether it is justifiable depending on what is the outcome from the total activity and that outcome is only through the final crop production. So if the crop is not very is not very highly you can say in the market you cannot get very high price from the crop it is a very low price crop you can take more risk because even if it fails you are not losing much. So from that angle it has bearing on the method of irrigation which method of irrigation you should use can also be factored by the type of crop you are having in question. Cropping machinery is another factor which with the more mechanization of the cropping activity we are finding that the requirements of these machines which you are using these appliances which you are using for the mechanization of various processes that has to be kept in mind. So sometimes depending on what type of implements you will be using you will have to take that into consideration while deciding on which method of irrigation you should be using. For example if you are using a method suppose you are having a tractor which is which is using an implement which has this much width or for in the end when you are using a combine for harvesting it will have some some width which is covering. So if you are using the sizes of the fields which are not multiples of these widths you might find that it will be either it will be a the operations will be more expensive because in some cases if suppose if you are having this is the size of your field in this case to cover this whole area you will have to go once and then the next time you will be only covering half the area. So it is not a multiple of the width of the implement which is being used. In the bigger itself when you are designing your method you will have to keep this in mind otherwise the operations will be more expensive you will have to put in more labour or more number of hours will have to be spent to cover the same area. So those things are also now becoming important when you are designing the method you are looking at these requirements also you will also look at what will be the where will be the turning strip where the machine will be taking a turn is that area available somewhere or not if it is not available then it has to be provided otherwise you might be in terms of the time taken in terms of the efficiency of the operation it might be creating problems. There are so many other factors which can influence for example the labour availability can also be a factor which can influence the type of method to be used. There are some methods which need less amount of labour there are some methods which need more labour there are some methods which need unskilled labour there are some methods which need skilled labour. So if you if you go in for a method which needs skilled labour and if the skilled labour is not available in the near vicinity of that area then you have problem. You might find that your operations are hampered or you might have to invest more money in terms of getting skilled labour, labour from far of places which might not be available at the appropriate time because in many situations whenever the labour is in demand the cropping seasons are same when the cropping season is prevalent in one area the other area joining area will also have a similar because we are our seasons are the same season where the crops are grown we have the rubbish season we have the curry season. So if the labour requirement is in one area the labour requirement is also in the same time in another area so you would not find that the labour will be possible to be obtained from the other adjoining areas if the labour is not available it is not available. So from those angles is very essential that whenever you design a method you have to look at these requirements you have to look at whether the labour will be available during that time or the kind of labour which you require will it be available or not. If it is not available you might find that ultimately your operations might suffer the timing might have to be changed and changing the timings you have seen that they have their own impacts you might have some permanent irreparable damage done to the crop yield. So if the irrigation is delayed then the yield is going to be affected which you cannot repair by providing more water later on that is not possible. So this becomes a very important requirement to be looked at when you are looking at which method you are going to imply. Then the local customs and preferences of the farmers invariably you will find that you may you may keep on saying that yes this particular crop is very good for the area there will be many other factors which will influence what is being grown in the area. The factors can vary from the individual requirement of the farmer because most of the farmers in India they are marginal farmers, they are farmers with very small land holdings and most of them are doing farming to fulfil their own requirements along with them if there is some surplus production they might select but basic requirement is what is a major factor in most of their cases as the areas are very small the holdings are very small. So in that situation they will try to go in for those crops which they can use themselves and the additional surplus can be sold. These are the customs have developed from those requirements so they do not want to leave the customs, they do not want to listen to the various advices which are given to them. They will take their own time, they might take once the irrigation water has been made available to them they might have to wait for 2-3 years before they get a full confidence that yes whatsoever is being recommended it can fetch them more money, it can be more useful they can they can get a better return only then they might change. So many a times it might be there might be a gap between what is the best and what is being grown in the specific area. Those factors also many a times they are the influencing factors they do not want to change the methods of irrigation because in some cases either it requires more investment because the method of irrigation is such that it needs the grade to be very smooth, the grade to be very good the when we say grade to be very good means that the leveling of the area should be very perfect. So in that situation they they have to invest more they will have to go in for may be land farming which will require some more investment and they do not want to indulge in that. So they will stick to their old methods because they know that though they might be using more water they might be using some water they are not bothered because of various reasons may be because of the fact that the water is available at a hardly any price they do not have to pay anything for that water. So there are many factors which go into the socio-economic factors the factors which are beyond the scope here you might not know what are the rare reasons but there are many different factors which influence the actual prevailing methods what methods are being used how they I mean whether they even if you will tell them that yes these are not the good methods either they do not have the money to invest or they do not want to invest that money because there is there is no benefit direct benefit they feel because if their water is getting wasted they are not paying much for that so it is not it is not a situation where they are losing lot of money directly. So you have to and that is not the scope of this particular subject right now we are only looking at what is scientifically true whether we can implement that or not those are things which are beyond the scope here but in general it has been felt that people are people have started understanding they have seen that in some cases where more water is being applied there are some problems which are popping up the problems of water clogging the problems of salinity and because of that they have started understanding these things because they are interested in in question now. So now let us go to the various methods at this level what are the various methods of irrigation which are let us try to look at the classification of irrigation methods there are many different nomenclatures which have been put forward the various ways people will classify these methods there is no not a unique method or unique way by which you will you can club these methods various methods I am just using one which I feel is quite a reasonable one under the present circumstances with the availability of the methods which we have which we have been which are being practiced we can club them into surface surface or gravity irrigation. So this will include all those methods which use this phenomena of the gravity flow and the water is being applied on the surface of the field. In the second category we can put those methods where we are not applying the water on the surface of the field we are putting the water in such a manner that is coming through the sub surface source so that we can call that group of methods we can term them as sub surface irrigation. In the other category where we are using the water the water which is being supplied to the fields is under pressure we will call them pressurized irrigation and in this situation I will like to differentiate a situation where you might be pumping some water and putting into the canal and that in that case it would not become a pressurized irrigation because ultimately the water is taken to the fields under the flow of gravity. You might be only tapping that water from a lower point and pumping it to take it to the the head end of the canal or may be augmenting the water into the canal by the pumping that in general is known as lift irrigation but that is not a method of irrigation that lifting is only a part of augmenting the water which is which is being made available in the irrigation network. At some point you might put some more water into the canal if the canal water which you are getting from the other sources if it is coming from under diversion from a river or if it is coming from a dam if that is not sufficient we are augmenting that water by putting some water from a lower and lower level into this canal through a lift irrigation or through a through the lifting of that water through the pumping that is that is not that would not be called the pressurized irrigation pressurized irrigation where here we mean those methods where we are using the the pressures the water and the pressure is being made available when it comes to the field level okay. So the the category of methods which we are having under this pressure irrigation is the drip irrigation and the sprinkler irrigation. Under these three broad categories which we have which are just listed we will start with the surface irrigation surface irrigation methods the various methods which are available under surface irrigation methods, now again the list can be very long, there can be some local practices which are being followed because the surface irrigation methods are age old methods but now looking at those methods which have survived the vagaries of time and they have proven to be very useful those methods are border, border irrigation method, basin irrigation method or sometime is there is another class of irrigation it is called corrugation. These three are the major methods but they can be some local methods for example the above methods but we will have a look at them also but the first three are the major the major categories of surface irrigation methods which are most popular all over the world. Now in general when you talk of the methods which are belonging to the surface irrigation or the gravity irrigation methods category there are some common characteristics of these methods which in general this requirement is also not very high low maintenance but the same time the attributes there are some attributes which you must look at before you decide for these methods in general you will find that the requirement of what should be have adequate water you might find that these methods are not suitable so there are the requirements in terms of the quantity of water will be comparatively high smoothness of whenever you want to methods the fields the surface on which you are applying the water should be smooth only then these methods can be used you cannot use these methods on undulating areas unless they are they are leveled they are graded properly and those whether they whether you should use a level area or a graded area will be a function of other parameters of the other characteristics of the area. Let us start looking at these methods one by one then we can discuss their their suitability and we go within the within the surface irrigation methods and we look at these various forms of surface irrigation methods where they are suitable right now we will be only looking at their characteristics and having covered all these methods having got some feel got some idea what these methods are about then we will go to their design that how we can design these methods because each method you will have to consider some you will have to come out with the various parameters of those designs in which parameters are important is a function of which method you are using. So let us first look at border irrigation you are using long strips of long strips of areas which are laid parallel to each other and these long strips are termed as borders they will look something like this this is the field ditch canal which is providing water and let me say that then this is the ridge which is which you can call the cross ridge so each of these strips is called this is a border which is surrounded by the ridges on all the sides of the cross ridge the collection channel this collection channel in some cases it may not be there depending on whether there is any surplus water which is coming into the density area or not and that will be a function of what is the slope of the borders. In addition to such that you are supplying the water from the field edge into the each of these borders either by providing this and letting the water flow into the the border through the the side connection and have some some control structure here. So through this opening the water can move into the through the border over these two methods is always preferable to use the number of pipes because of the fact that in case you are you are using this method you might find that the the waterfront the way the water will move it will have uneven front the water will be moving in the middle of the the border and in the sides the waterfront and the waterfront would not be in a form where in this case you might be able to have a waterfront which is preferable because all these areas as you go along in the in the direction of the field all these area cross they will get the same opportunity time. So this is the arrangement which you have in the case of border irrigation and have some slope situation you might find it necessary to have a collection ditch also which will collect that is a surplus water at case the water might not be sufficient period and that will be decided by what type of soil you have if you have clay soils you might like to give more opportunity time or the water to infiltrate into the soil. By in general if you try to try to look at the various in general you will find that there will be a moving from the upstream end to the downstream end a recession curve water recedes from various locations of the who curves are very important how much is the location of the field how much is the opportunity time this is what is called infiltration decides how much infiltration will take place at a specific location of the field turns from upstream end to downstream end and this is the time a question is that also this is the typical which might change when you go from one soil to another soil so this is I have just given a typical but it will belong to some soil the shape of these two curves the advanced curve and recession curve will change with respect to the other characteristics like what is the slope of the field what is the type of soil which you are and but in general you will find that this is what will be absorbed in the field also the shape and the exact the other many of the properties that will see when that is what is the basic crux of the whole design when you are saying that you want to design the irrigation method under a specific irrigation method what you want to design you want to design the basic aspect that the infiltration opportunity time should be uniform along the length of the field that is the basic crux of the basic requirement of the design if you can keep that infiltration opportunity time as uniform as possible throughout the length of the field then you have achieved the best possible design.