 discussing the various methods of surface irrigation, gravity, all those irrigation methods which we have looked at so far, the border irrigation and the basin irrigation we have seen in details what are the various circumstances under which they are suitable. Today we will start looking at another method which belongs to the surface irrigation method which is known by Faro irrigation. You must have visualised that the previous two methods we had gone into the details and we found that the jack basin or the basin irrigation method is quite suitable when you have soils which are either very permeable soils or they are very impermeable soils, either they are fine soils or they are the light soils that that method can be used under those circumstances. But we also realised that there is a situation where you have some crops which are quite susceptible to decay or to injury under situations where the water is getting collected and is standing for a long duration. So to cater to those situations, in this method these methods are old age old methods we are trying to peep into what would have been the way these methods have came into existence. So far we are catering to those type of situations, it could have been felt that let us think of some ways and means by which we can we can ensure that the water is not made to stand over the surface of the soil but it can be still made available through the lateral movement because the water which is made available in the soil as we have seen that the deficit in the soil will ensure that the water moves from the with respect to the gradient the potential which is available in the soil, the water will move from a wetter area to a dry area. So that situation can be it can be made use of that is what is exactly happening in the case of furrow irrigation method. You construct the furrows let me plotter, there can be different shapes of these furrows not necessary that it has to be like this only it can be there can be another situation where you have another that type of cross section you might have something like this. In these furrows the water is what is made available in these channels these are the cross section the thing which I have plotted here there is the cross section view of these furrows say if I make the water available in this in these channels these channels are the channels which are created then the tendency of this water will be to move in the lateral direction the water can be spread in the lateral direction as well as they can be spread in the vertical direction. This movement of moisture from these channels into these areas will make this soil wet plants can be grown in these areas you can have the plants which can be grown in this on these ridges. Now this area is getting water not in the same manner as it was getting in the case of basin and the border irrigation situation this water is obtained this soil will the moisture level of this soil will increase because of the water available in this channel the adjoining channel and the movement of this moisture in the lateral direction that is the basic difference in the this method and the previous two methods which we have considered that in those methods the movement of the moisture is in the vertical direction because of the fact that the water is moving over those the fields in the form of a sheet of water whereas in this case the water is made to move in these channels and from these channels the water moves in these areas which are dry areas in the lateral direction as well as there will be some movement of moisture in the vertical direction also and the crop will be getting the moisture from this zone. This will give opportunity for the crop to have a better irrigation there would be any stage where the water will be choking the total soil the soil will always be having in the pores lot of air available so all those crops which are which were susceptible to the inundation of water in terms of their growth in terms of their quality of yield which they they can give all those crops now can be catered to using this specific method. So now also now let me also tell that the spacing between this now in the design which ultimately will be going in for what will be the various aspects of design the aspects of design will be what should be the size of these channels the size of these furrows the spacing between the two adjoining furrows that spacing will decide how much is the area available on the ridge. So depending on that you might be in a position to even have in some cases two rows of the crops instead of one all these things there are many other features which will decide whether you should have two rows because it will also have a function of what type of crop which crop is going to be grown here will be their requirement what type of soil you are having because the if you have the spacing between these two channels is too wide now if that happens let me say that you have a situation where you have you have created something like this the spacing in the two channels is too wide it might be difficult in this situation of the moisture to move in the later direction to an extent at least if you provide the water in both these channels at least the moisture from the sign should be able to reach up to this level from this channel it should be able to reach up to this level and there will be a function of what is the what are the characteristics of the soil. We have seen that the texture as well as the structure will decide how much what can be the possible movement of moisture and that is going to be the deciding factor in finding out how much is the possible spacing which you can provide that the same time the other parameters will be the size of the stream size again what stream size should be made to pass through the channels there will be a function of again what is the infiltration capacity characteristics of the soil was the gradient available how much opportunity time is required and all those things the characteristics of those design parameters will remain similar but they will be subject to some of these constraints which we are looking at. Having understood this now let us try to enumerate the suitable conditions under which this method can be suitable though we have already mentioned most of those things. First thing is that you can use this for row crops you can use this method for those crops which are sensitive in some cases if you if you do not use this method then it might be having the standing water available for a longer period and then because of that standing water it might influence the yield of the crop this can be used for from the soil concentration the medium to moderately fine these soils will normally have quite in comparison relatively they will be having high holding capacity the moisture holding capacity is much higher in these soils. So these soils wherever you have these soils we have seen that the method like border irrigation method was not a very suitable method under these circumstances and though the check basin method was quite suitable but then in that case you are having smaller areas you are having smaller fields where you are making the water stand for a longer period for letting the water penetrate into the soil so infiltration whereas in this case if you have such a situation that your crops are not suitable to that those environments which you are creating by adopting the basin method then you should use this method for those similar soils. There are some situations where you have the problem of crust formation so if crust formation crust formation is in some soils if the water is standing for some period when it dries up then the top soil will be you will have the crust formation it will have a tendency to just hold together and there will be cracks on the soil and it will have a tendency to just break up in the form of thick cakes. So that crust formation is quite bad if it is if it is being formed in the areas because that might influence the later on infiltration. For those soils this method can be used because when you are wetting the partial area in this case the only method of surface irrigation is utilizing the gravitational flow where you are not wetting the whole soil you are wetting part of the soil. So from that angle the crust formation problem can be tackled by using this method then this is also suitable where you have problem of surface drainage. In some situations if the area is having lot of rainfall the natural rainfall occurs quite frequently and with the conventional methods with the other methods which we have discussed so far the basin as well as the border irrigation methods using those layouts you might find it relatively difficult to drain the whole area of that water which is accumulating because of the rainfall the excess rainfall whereas in this method the drainage the natural drainage will be very fast all that water which is being collected it has a tendency to drain off the area in a much better manner than with the previous two methods. Now here again it may not be so in all the layouts we are going to discuss the various layouts which are possible under the forward irrigation method but if you have an area which is flat area which is not having any grade which is not having any slope then there would not be any difference much difference in the two even in this situation then the drainage might not be very very fast and very good whereas if you have the slight grade then this method the furrow the way you have constructed those channels those channels will help in draining of the area very fast but there has to be some grade some minimum grade which will ensure that the water is not standing there for a long period it should be drained off the surface. So in general the surface drainage facilities naturally are much better when you go in for the furrow irrigation system. In terms of the limitations or the various limitations which might be encountered the limitation of erosion has because this erosion hazards will be of the same order of magnitude because it is a function of the slopes. So in this method also if the slopes become very steep then in that case the erosion problems can be faced and your design will be constrained with respect to the erosion problems. Those limitations are the same as we have in the case of the previous two methods. Let us look in terms of the labour the labour requirements they are high in comparison to the previous two methods which we have looked at because in this case one is that you have to ensure that the grades are quite proper because in each individual channel how the water moves that is going to decide how much water will be penetrating into the beds of those furrows. So you have to take care of each individual channel and moreover the water is also being supplied to each individual channel whereas in the previous case you were supplying the water in a sheet to the whole area. So that way the simply the application requirement the labour requirement from the application point of view is also going to be more in comparison to the previous two methods. The land grading also better than the other two methods. The grades in the furrows they should be quite uniform so that you can the lengths which you are selecting for the furrows they have to be they can only be relevant lengths the design lengths which we have come out with through the design methods those can only be applicable if the grades are proper throughout the length. Otherwise if the grade is not proper in the other case may be that if the grade was not proper in the case of border it might create a hump where you do not have a patch where you do not have the water reaching only at one point or if there is a low depression you might get excess water whereas in this case if the grade is not proper if the grade is not maintained it might not the water might not reach in the remaining part of the furrow. So though you are handling each individual channel separately but the same time that channel is providing water to the total may be couple of rows on both sides of the channel it will have its own repercussions if the grades are not given properly and you have to look at those requirements very closely. Then let us look at the various layouts which are I just mentioned that under various different conditions under different situations you might feel like adopting different layouts. So what are the various layouts possible? Before we go in for the layouts let us try to look at that what they depend on why you require these layouts why you require different formations of these furrows they are basically influenced by topography, soil type these are the three major factors which will influence which will dictate which layout is better than the other layout. In some cases if the existing topography is such that you do not want to unnecessarily spend money on changing the layout if the topography is such that you can utilize the existing layout or the existing slopes the prevailing slopes then I think there is nothing like that because by that by doing that you are saving lot of effort unnecessary effort you are also ensuring that the soil is not disturbed because in these land forming processes it will take lot of time for the soil to replenish its fertility if the soil is disturbed the top soil has been replaced by the soil which is from the lower horizons or the lower layers those lower layers are not as fertile as the top layer was as we had discussed earlier also whenever you go in for land forming you are cutting the soil from some area and dumping it on to the other area so at both the places let me make this point clear we had discussed that if we have this is the layout the existing layout you want to give a grade you want to give a grade in such a manner that this is the grade which you want to get this is the slope which you want to get the uniform slope in this area so what you can do is that you can remove this soil from the top dump it on this because this is the filling area where you want to do some filling this is the area from where you want to cut this is also the area from for cutting remove these soils and keep on dumping on this so after some time you will find that to reach this grade you have removed the soil from this zone which is the last strip and that has come on the top of this this is the most in fertile soil which belong to a lower depth that has been put here so the existing soil which was fertile in this part the existing soil which was fertile in this top part both have been dumped on to this area here you have exposed the lower soil here you have dumped on to the fertile soil at both the places you have problem so whenever you go in for any such land forming procedure you are indulging in this process that if possible it should be avoided because that is also from the angle of soil fertility which is very important and if you cannot avoid that then there is no other way because you want to get this grade to ensure that your applications the water application efficiencies and those other related things they can be enhanced you can have better management of the distribution of water but the first priority is to be given to anything which can be done using the same existing topography. So if the endulation is not very excessive if you can use some method by which you can avoid any alteration in the land topography you can you should use appropriate method so there are some furrow layouts which use the topography in the same form in which it is available on that location then the soil type again depending on the soil type depending on the variation of soil type if you have soils which are having very low infiltration capacities you will have to make a layout which is having very minimal grade or even a flat you should lay the furrows in such a manner that they are almost on the flat land there is no grade given to that so that you can let the water be blocked into this the total length of the furrow you will fill the furrow block the water and let it infiltrate taking the long period which is required because the soils are very fine soils. So from that angle you will then lay the furrow in that manner this soil type can also dictate how the furrows should be laid the crop type this parameter can also be sometimes they can influence the layout of the as I had discussed that in some cases the crop is such that you can have close spacing between the two plants or more than two plants then you will try to try to keep the spacing between the furrows with the higher towards the higher side so that you can have more than three rows or more than two rows of the same crops the crop can sometimes or in some cases the crop is such that it it can be best grown if there is only a single row and they should there is a spacing between those two rows then that case you can have the furrows laid in such a manner that you should have only the minimum spacing between the two furrows and there will be only one plant put on each range or the bed of the the the the crown part of the furrow all those parameters put together will decide what should be the appropriate appropriate most appropriate layout of furrows in a particular area what these layouts can be now let us have a look at the common layout there can be many there is no end to that because at different location you might find that there is there is one which can be most appropriate but some of them are the ones which have known to be the common layouts which are being experienced which are being used by the farmers in general these are the graded graded furrows level furrows to a furrows these three are the most common layout as the name suggests the graded furrows are those which have a long longitudinal slope slope these will have a longitudinal in this case the soil type since you are giving a grade to the furrow you will have those soils these will be suitable to those soils which are moderately having moderate infiltration rates so in that case you will be in a position to get some water infiltrated from the channels into the later areas even though the slope is there they can be open-ended open-ended means that you are not having a blockage in the downstream side you let the water flow continuously but for that you have to have a very proper grade you cannot you cannot go in for open-ended furrows if the grade is not proper so for those areas where the where you want to use the open-ended furrows the length again the length how much length you can go in for is a function of the grade is a function of the soil type is a function of what is the stream size which you are using and those are the features which we will look at when you are going for the design because the design is nothing but the combination of these parameters that if you have these parameters for example stream size is something which may or may not be in your control as a farmer in our situation in India a farmer will be getting a stream size which is the prevailing stream size which is being made available by the irrigation department or by the the specific project what is the stream size available and this stream size you might not have any control on if you want a bigger stream size you might not be able to get that stream size unless he has the water availability is within his control he has a tube well which the size the capacity of that tube well if that can be weighed and if he can the maximum capacity if it is known and that is the maximum level of stream size he can choose below that he can always choose that stream size by wiping the water into two different streams so he can reduce the stream size provided he has the the control over the maximum available. Similarly there are some other situations where some of the things might not be under his control so if the stream size becomes a fixed thing then the remaining components of designs are that if the stream size is fixed knowing the type of soils he might have to find out how much is the length of the the furrow he can go in for and that also will be influenced by that what type of crop he is using. He might have to he might like to know that what should be the spacing between the two furrows which will give him the dust results he might be interested in knowing what should be the best grade to be provided because if he wants to go in for the grading of the area what slope should be given so in case the slope is a prevailing slope he wants to use the prevailing slope then the design will be having a constraint on the slope also so the slope is fixed the stream size is fixed he will he can only play with the size of the length of the furrow and the spacing between the furrows so that way there are different combinations even in the case of designs there is no fixed thing is always subject to what are the constraints available under the specific circumstances. Now the level furrows let me first show you the the graded furrows this is a picture of the furrows in this case you might not be able to make out very much whether is the grade is there or not so this picture may be of a level furrow or graded furrow but this is how they have been put these are the channels which are where the water is to be made available and these are the ridges where the crop will be growing okay this is what I had shown I had only shown the sectional view of this so in general this will be the length of this is going in this direction and the water is to be made available this is the supply ditch the water can be made available from this ditch into each of the individual furrows. In the case of the level furrows these are the furrows where there is no longitudinal slope the grade is 0 you do not have any is practically level furrows and will be normally close ended so that you can check the water once the furrow the total length is filled with water since the water will take long time to infiltrate you give that opportunity by blocking the water and letting it stay within that channel that opportunity time will ensure that there is lot of movement, lateral movement of water from the channel into the soil and for that purpose since the soils are fine soils the rate of infiltration are very low you make this provision to have the level furrows. Then the contour furrows are those furrows where you are making use of the natural topography and you lay the furrows along the contours by the same time you give slight grade in the longitudinal direction of the furrows so that the water can move from the upstream end to the downstream end. This here a picture of this contour furrow you will see here that is using the natural topography of the area and in this in these situations the topography has to be very very mild mildly undulating topography you cannot use it on highly undulating topographic areas. So if there is very mild natural slopes you can avoid doing any land forming on that by going along the contours and laying your furrows along the contours by the same time giving slight grade that means you might not be going exactly along the contours you will be slightly going away also so that you can get the grade the desired grade. So you will be going while going in the longitudinal direction you will be slightly going to the lower part of the contour so that that grade is can be obtained again that the level of grade which is required will be a function of the soil type how much infiltration rate is desirable and that can be obtained that is what the contour furrow irrigation system looks like and there you can the main idea is the main advantage is that you can try to make use of the natural topography thereby reducing the chances of losing the fertile area and also avoiding the unnecessary labour or the infrastructural or the land forming expenses which have to be made if you have to go in for the grade to be to be required in the graded furrows or even in the case of level furrows. With that I have given you enough idea about what we do in the case of furrow irrigation but there is one there is one class of furrow irrigation which is sometime put to use and is known as corrugations. These corrugations are nothing but they are the furrows of smaller size the cross section area of these furrows is very small in comparison this is a picture of that in which you have these these corrugations which are nothing but they are small furrows and they are spaced quite far apart where we use these corrugations in some situations you will find that either the crops which you want to grow using the furrow method they are close growing crops so you want a wider bed where you can grow the crop instead of having grow crops you want to use it for the close growing crops then you go in for corrugations or sometime where you feel that the amount of water availability is very small it is quite scarce but at the same time you can your soils are such that you can cover a wider area the soil can penetrate in the lateral direction up to a wider spacing then you can use this corrugation method. In some cases when the soil salinity is a problem the water which you are using is creating low salinity problems again the the corrugation method can be quite handy because by by doing that you can reduce the quantity of water to be used and in some situations you are also calling them is not the nomenclature remains same basically there is there is a way in the other furrow irrigation methods there are sometimes situations where you do not supply the water in every channel in all the irrigations you supply the water in alternate channels. So example what I am trying to say is that because when I mentioned about the salinity problem that salinity problem can also be tackled in some situations by ensuring that if these are the channels in the normal furrow irrigation method you are supplying water to this channel in one irrigation in the next irrigation you do not supply water in this channel you supply the water in the other channels which were which were not supplied earlier. So once the water is moving from this end to this side and the other irrigation is moving from this side to this side that can also be is also one way of managing your resource in such a way it can be used when the water is scarce you do not want to but at the same time you have to look at is it sufficiently satisfying the requirement of the crop? How much is the deficit which is still remaining? So all those things can be looked into but this this way of supplying water is called alternate method. And the corroboration the order of magnitude of these corroboration the size can be you can get an order of magnitude feeling about the size is 6 centimetre bottom width 10 to 15 centimetres of these furrows or the corroboration which you use and the side slopes can be 1 is to 1 which you normally use in the case of corroborations. So with that I think we will conclude the topic on corroboration what the furrows are what the corroboration method involves into and we will deal with the remaining 2 method which are not very common method but at some in some situations they are being used which is the the contour levee or the contour ditch method we will discuss them and then we will go on to the other methods of irrigation which are the 2 classes one is the sub surface irrigation and the pressurized irrigation methods. Any question at this stage? Ok thank you very much.