Okay, hello everyone again, I want to continue our discussions about, soil testing. In our previous lecture we looked at soil test procedures and how they're developed and what they can do and, and what they can't do. And I alluded to the fact that there are some philosophical variations out there on how we interpret those index numbers, and how we convert them into a fertilizer recommendation. And I want to continue that discussion here today. And I guess I ought to give you a little bit of a warning, you know, we're, this, this is one of our longer lectures. I don't think it's going to go too much more than 30 minutes, so you know, if you need to have a drink or something with you go ahead and be my guest. Also this area of soil testing and fertilizer recommendations, is a little bit controversial, there are differences of opinion about how to go about this and these phil-, philosophical do, do lead to some fairly healthy discussions. And, just remember I'm the instructor, I'm the teacher and I'm the messenger. And I, I think it's going to be interesting to say how everyone out there on the discussion, in the discussion world discusses and looks at these, these differences in philosophical approaches to making fertilizer recommendations. Okay so last time we talked about the fertilizer recommendations, here's a exampel of a kind of report, that would come out of a lab. And I want you to look at this, so we won't dwell on it, otherwise the lecture will be, way too long. But just notice that for phosphorous, this is the, the big line right here is the phosphorous, you see that it's very high. So the number over here, the index, the 125 parts per million, milligrams per kilogram was interpreted by this lab using this procedure as being very high. The other part to go along with that is down here and you see the fertilizer recommendations. This particular lab is saying that the middle number is the phosphorous. The first number is the nitrogen recommendation and the middle number is the phosphorous and the potassium. You know that the middle number is zero. So this lab says this soil has enough phosphourius to supply that phosphorous nutrient requirement. So when you look at soil test reports, they generally have the soil test index, the interpretation of the index and the fertilizer recommendation. And as we get done today you'll be able to make some determinations about the lab as to what philosophical approach they make, they use when they make a fertilizer recommendation. So when we do soil testing we know something about the fertility level of our soil, they were going to grow corn in or tomatoes. And the lab is going to give us a recommendation for how to supplement that native fertility with fertilizer. So then the question is how do you go about making that final recommendation for, for that farmer. And there have been several approaches developed over the years, and typically, you know, I would have to admit to you that the private sector testing labs and the Land Grant universities take a little bit of a different approach. There is some crossover between the two for sure but generally there is differences in the approaches in which of these philosophical approaches the different labs take a look. And In my mind, it comes down to these, to a couple of ideas like this. There's differences in whether you approach the soil testing. And the recommendation, the fertilizer management part, fertilizing the soil or the plant as a, as a priority. And are you, probably even more importantly, are you comfortable with recommending or using a zero amount of nutrient. For example, as we saw, under a high or a very high Index are you comfortable with omitting the phosphorous in that scenario. So, the discussion about philosophies, again just like soil testing, it really revolves around these non-mobile nutrients. We're using a pre-fertilization soil test to Predict the, the nutrient requirements, that would re, we would apply as fertilizer under different, soil, test, scenarios. And so we'll talk, we'll, we'll focus most of our discussion on, phosphorus. And, as I said before, nitrogen is mobile. In most of our agriculture soils and in the United States, we do not do it pre, most labs do it pre-fertilization soil test for, for nitrogen. Okay, so here are the three, probably the three most widely used approaches to making a fertilizer recommendation. I'll call them philosophies. The build up and maintenance approach. The percent sufficiency ranges. It also goes by a couple other names depending on where you are in the country. The crop nutrient requirement approach or the sufficiency level of available, nutrients. All of them basically revolve around the idea, that's there's an index above which you do not need to fertilize the crop. And then there's another, probably older and, and less used, becoming more and more less used, the basic cation saturation ratios. So you'll need to recall your the information that we talked about on cation exchange when we get to that. So the soil test is a, is a starting point, and then we come to the point of making a fertilizer. My recommendation, do we simply just say no fertilizer when the soil is high or very high or do we hedge a, a little bit? And that's basically you know, what, what's happening here with these different. The philosophical approaches. It gets down to the comfort zone of the person making the recommendation or the farmer using the recommendation. Also fertilizer costs are coming more and more to the front in this decision making process because you'll see when we're done today that there are differences in cost associated with the these differences and philosophical approaches. And as we all know there's more and more emphasis now a days then there was 40 or 50 years ago, or 60 years ago when these philosophies were gaining ground there's more emphasis on the environmental impacts of different fertilizer recommendation strategies. And again, I want to present each of em to you and then I, I, I think it's healthy to have a good discussion about these approaches. So let's start with build up and maintenance philosophy. Under this philosophy you add fertilizer until you achieve your desired soil test level. So, for example, you want your soil to test high in phosphorus, so you're going to add fertiziler. Some promote adding it, building it up over a short period, two or three years. And then you grow your, your crops on this, and you're going to add back, each season, an amount of, of phosphorous in this case, let's say, that the crops, removed. So if you, if you sell your corn grain off the farm it's going to take some phosphorous away. It's going to remove that from the soil, bank, as it were. So under this, scenario, this approach relies on some very accurate and very important crop removal values. How much phosphorous was taken out of your field, given a certain yeild level? And that's a real tricky part. You have to have good numbers reliable numbers. This approach more or less treats the soil as a bank. So you hope that the, the phosphorous that you put into the bank, your bank account's going to stay relatively level over the years. So as you remove money from the bank, or phosphorous from the soil you need to add it back. So under this scenario, you usually are going to be adding phosphorous every year. Now, some proponents suggest not testing every year, because if you're always adding a little bit of phosphorus, chances are once you get away from that critical level between medium and high on the soil test, then perhaps you can back off of the need for a soil test every year. And maybe some farmers that own their own land may be they don't mind building up or, or may be they like building up the phosphorus for example in their soils. If they are renting landing and the chances are they are not going to have the land more, or for more than a short time, then there might be a little reluctance to practice this particular approach to fertilizer management. So I mentioned crop removal values, here is a chart of some, and there's many, many of these, kinds of charts, out there. Here's corn grain, and you can see that, for this certain level of yield. It was expected that 66 pounds of P205. Again, you know, that's, what, 20 or 30, pounds of, or, kilograms of, p, was removed from the from the field. If you are in, you know, producing using your corn stalks for bio-fuel, then you may remove another 40 pounds. So somewhere around 100 pounds of P2O5 would be a removal value that a farmer might add back, if they were practicing buildup and, and maintenance. So for these crop removal values, as I said, they're very important. You need to know where they came from. How were they developed? Do they reflect luxury consumption? So when they were developed. When the researcher was developing these numbers, did they apply a lot of fertilizer? Fertilizer such that the plant took up a lot of nutrients and therefore these numbers might be a little bit on the high side so you need to know a little bit about the crop removal values that the lab or the person making the recommendations where they cam from, In this regard if we just step aside a little bit The and, and touch on nitrogen. Typically for, for this procedure, for this philosophical approach nitrogen is recommended based on a yield goal. So a farmer would say I think I can produce. So many bushels per acre of corn, or so many pounds of potatoes in my crop. And I know that the matter of nutrients are associated in, in that amount of crop. And so for nitrogen the recommendation Might be 200 pounds per acre because that correlates with a particular yield goal. And so yield goals are used very commonly to make nitrogen recommendations. So again here, you need to Ask if you're not familiar with how the lab is, or the person making the recommendations if they're using yield goals. Where did those yield goals numbers come from? What research was used? The challenge here is to really have a good realistic yield goals. If your fertilizer recommendation is going to be based on yield goals Then, you need to think about what would be realistic for you. The average of the last five years, the average of the last ten years some people say you know, my average is 200, but I really would like to produce, 300 bushels of corn per acre is that realistic, for that farmer and for your growing region. There's been some research on yield goals and I've given you one of the citations here. These researchers studying yield goals and evaluating farmers found out that very few farmers, in fact about 20% of them were successful in achieving their yield goals. So that's another reality check that we all need to do with ourselves when we're using yield goals to set our nitrogen fertilizer rate. Here's the results from some studies evaluating yield goals over four years and many, many farms. You can see the numbers of farms that were involved in this. And you see that, on average depending on the year, farmers were overestimating their yields. In this particular year here, you can see that the overestimation was, you know, modest, only 16 bushels per acre. But also that year they had really, really good yields compared to the other year. So weather may have played a bigger role in the yields across these years than fertilizer nitrogen, for example. So again just to drive home the point, that yield goals, need to be, set realistically. So in the build-up and maintenance approach, is building up the soil nutrient level okay? Where might this work? Think about soil texture, Where might this be a challenge? Think about soil texture. Again, why, some people will ask why add fertilizer, even a little bit, if a soil is already at a level where it can supply the requirements for that crop. I think that's a valid question, why would you add more fertilizer, particularly in today's age with the extra cost, increasing cost of fertilizer. And also the potential that extra fertilizer that's not used by the plant is going to end up in, in someones water body. So that's a valid question. Also, if you remember as you change from medium to the high on the. The, soil test, calibration. If you're far out to the right of the high in the very high category. Maybe you have enough phosphorus in the soil to grow several crops years. You can essentially mine the phosphorus. So, again, a question as to why you might be inclined to add more phosphorus, in that situation. Environmental and economic considerations, as I said can have, should have an impact on this decision making process. And even though traditionally labs have recommended to add back 100% of the crop removal value, some labs are starting to back off of that. And recommending under those high and very high soils to add back only a portion of the crop removal value. So if you remember our example, where we talked about possibly adding 100 pounds of P 205, maybe some labs would back off and say Add half of that. Or maybe even a quarter. I saw some labs, recommendations that are for adding back a quarter, of the crop removal value. So we're moving in that direction of, reducing the amount of fertilizer that's recommended, by this, philosophical approach. And what we'll, we'll, I'll have a few more words about that as we get, towards the end. The other, major approach, or phi-, philosophy is that percents/g efficiency or the crop nutrient requirement approach. This relies on the idea that there is a soil test index there in a well correlated, calibrated, soil testing procedure. Above which we can, we can be sure we do not need to add fertilizer, in our case phosphorus. And so if our soil tests at or above that index then the recommendation under this philosophical approach would be zero phosphorus. This relies very heavily on a well calibrated Soil test procedure and it relies particularly or if you're in the high, just into the high category is going to rely on more frequent testing to make sure that you're remaining in the high category and that you haven't slit, your soil hasn't slipped into the, the medium category which is where you might start adding some fertilizer. This particular approach is generally favored by the land grant institutions who are still in the, the soil fertility testing and, and recommending business. The percent sufficiency, many people say it fertilizes the crop, because now we just add the nutrients that the crop needs to make up for those nutrients that Are already there in the soil, so we focus more on the crop with this approach. And some argue that other soil testing philosophies focus more on the soil. We need to build the soil up to a level And even though that level is higher than the critical level and the crop would do just fine without fertilizer. So here for the example, the University of Florida and I've highlighted in green, the high and the very high So here, this example happens to be for vegetables and as you can see our fertilizer recommendations for P2O5 go all the way from 150 to 0. And so once we've crossed that threshold and our soil is high then We recommend zero phosphorous to the farmer. And so you can see that for watermelon, potato, and tomato for, for phosphorous, we're confident that the soil test can predict no crop No crop increase or advantage to adding more phosphorus. There's been lots and lots of studies comparing these philosophical procedures. Here's our philosophies, here's one here done in, in Kentucky where they had eight years of trials and in this column here they had the percent sufficiency and over here the buildup in maintenance. And you can see the fertilizer recommendations, and in this particular case, the soil tested high and phosphorus and potassium so, they recommended 0. Over here under the maintenance philosophy these farmers had a recommendation to add some amount of phosphorus and potassium and you can see that resulted in a difference in the, the total cost of the fertilizer program and the interesting aspects to this is that the corn yields over all of these trials were exactly the same. With these 2 philosophical approaches. So under one approach more money was spent for fertilizer but it did not return an increase in, in yield. So it's interesting that in this particular case in one of those studies there was a significant difference and it was towards the advantage of the percents efficiency approach. The third philosophical approach is basic cation saturation's ratios and so you think back to your discussion on cation exchange capacity, you can see where this one is built from. So here is cation exchange capacity illustrated. Here's our colloid either organic or clay, and it has calcium and mag-, magnesium, and sodium associated with it. And in the soil solution, the blue, that can be exchanged, in the soil solution. Under this, basic cation exchange, capacity, which was developed, a long time ago. It's an idea that says that there are certain favored percentages of our cation exchange capacity that will be occupied by these various cations. So therefore we can develop a ratio of one cation to the other. And the idea here is, is that you can modify those amounts, those percent saturation or those ratios by changing your fertilizer. And new analytical lab equipment that can analyse a lot of different cantions. And computers that can cacluate these ratios and make recommendations has made this approach easy to do. So here's an example of some of the original research promoted that the cation exchange capacity of a, a soil should be roughly in these kinds of percentages. And this is used for, obviously for potassium, magnesium, calcium, some of the other cations for making fertilizer recommendations. So if your soil is sort of not in these kinds of, of numbers or is so-called out of balance, then you would change the amounts of fertilizer that you added. And so you can think back to our soil textural triangle, and you might think that, well, you know, in these kinds of soils up here that have some significant, cation exchange capacity, maybe this could be managed. But think about out sandy soils, with low cation exchange capacity. Maybe you have the ratio and the balance correct but the amount that, that low[INAUDIBLE] exchange capacity could hold maybe in, in sufficient to supply the nutrition for the crop. And in fact in those kinds of scenarios potassium for example could be leached. If you added a lot of potassium in an effort to achieve a, a certain balance or, or ratio. So I hope you see that. That this, this particular approach is, is rather cumbersome and, and rather difficulte to manage particularly when you go to our south eastern coastal plain soils and here in Flordia where we're dealing with sandy soils this approach or this phylisophical apprach is probably very difficult to It's, to justify. Again here's some research that's been done with this approach. In this particular study, this scientist, looking at corn and soy beans over several years, took the highest, the highest five, sites and the lowest five sites in terms of yield. And then looked at the ratio of calcium to magnesium in the soil. And you can see that for the highest yielding site and the lowest yielding site this range and ratio is almost exactly the same. You know, as you go from year to year so the take home lesson here is that the ratios were the same in the low and the high yielding sites. So there must have been some other factor going on there, controlling yield across those sites rather than the basic cation saturation ratios in the soil. So why the lack of relationship, that more modern researchers, have determined about this, philosophical approach? Well, it turns out that most plants are pretty good scroungers. I use the word scroungers because, plants can do a pretty good job of To obtaining nutrients if they're, if they're out there in the, in the neighborhood. They can do a, a very good job over a wide range of ratios on the on the cation exchange. And we've eluded to some of the problems with this approach particularly for sandy soils with low cation exchange, capacity. Well, what about calcareous soils that are high, very high in calcium? Could you ever achieve, a desired, ratio in those soils? What about farming scenarios like we have in Florida where we're irrigating with high calcium carbonate irrigation water, we're adding calcium every time we irrigate. So we might start out with what we might think will be our ideal or desired ratio, but pretty soon, as soon as we start irrigating, that ratio is gone. And this approach like in large way, like the build up in maintenance typically results in adding a fertilizer, because you rarely have that ideal. Ratio when you do the soil test and you start. So in summary, with these philosophies, the buildup and maintenance. You determine a point a soil test index, high or very high that we, you would like to get to, if your soil isn't already there, and then you're going to maintain that level of fertility. You may allow some draw-down if you're out at the very high, periodically, maybe not so attest, maybe reduce greatly the amount of fertilizer that you add, but you typically, in accordance with this philosophical approach, you're going to add back fertilizer based on what the crop, the previous crop, removed. So many people say that this approach fertilizes the soil. Because you're more concerned about the soil test, result and situation, so you typically always add, some fertilizer. The research with this particular approach compared to say for example the percent sufficiency. You know, shows rarely where there are differences and/or enhancements in, in yield by following this approach but the fertilizer costs typically went up, what about soils with erosion we talked about rolling topography and soils that might erode and think about continually building up phosphorus in those soils if you are not also controlling soil erosion and using good soil conservation techniques, then this approach which might risk at putting larger amounts of, of phosphorus and risking it to, to erosion. The basic cation saturation ratio, again is that there's some best ratio or amount or balance of cations occupying the cation exchange in the soil. This usually results in adding fertilizer to change or to recalibrate those ratios to some desired levels. And it usually results in adding fertilizer and we've eluded to the fact that this has problems with very sandy low cation exchange capacity soils, for example, what we have here in Florida. And again you know, we pointed out the idea that plants are pretty good at obtaining nutrients over a wide concentration in the soil. And also the fertilizer research comparing this technique, or this philosophical approach does not document that it has a benefit over say for example the crop nutrient requirement or percent sufficiency. In the crop nutrient requirement or percent sufficiency philosophical approach we have a calibrated, a good calibrated soil test procedure, that will tell us when and how much we need to add fertilizer to. We may actually end up. Over years following this philosophical approach with soils that are higher or maybe even a little bit higher than high, very high. But at least we're going to move that soil test index from the medium to the high category because that's where we need it to be to get a maximum yield fertilizer in this particular situation, is seen as a material to supplement the native nutrients in the soil, and that's a very, very important distinction and concept with this particular philosophical approach. We're looking at both of those sources, the native soil fertility and fertilizer to supply the nutrients that the, the crop needs to give us the, the good response. And most of the research that's done comparing these philosophical approaches shows that this is typically the most appropriate one, particularly when you factor in environmental issues and costs. So just a few more points to, to make here. You know the percent sufficiency and the build up may end up in the same place sooner or later. That is soils that test high in phosphorous for example. So at that point these two are, are fairly similar in that regard. They have, in, in essence, built the soil up to a, a high category. We're not going to use percent sufficiency or crop nutrient requirement and always farm soils that are in the medium or medium-low category. Because we know that they need fertilization. The main difference between these two is what happens after you get to that high category. The percent sufficiency would say we're OK for now, we can confidently grow that crop without added PTO5. And the other approach would say maybe we're not quite that confident and we're going to add what we remove because we want to keep our bank account full. And those are decisions that. Farmers and people making recommendations need to confidently and, and, and with a lot of good science behind them make those decisions because they do have implications for. The return on investment and the economics of the farm, and also, potentially, and environmentally. These so attest philosophies came along when fertilizer, was increasing in use, synthetic fertilizer back in the 40s and 50s. Many of these soil test procedures, these extraction solutions and these philosophical approaches to making fertilizer recommendations were born out of that time of the last century. That's when large benefits were seen by Making fertilizer applications and no one wanted to be on the low side of fertilization of our crops because we saw the drastic improvements in yield and quality by adding fertilizer. And fertilizer, you know, during those years was a fairly small, maybe a few percent of the total cost of producing a crop, so it was seen as relatively inexpensive insurance to make sure that we had enough fertilizer out there. And the research had not progressed, enough to really show farmers and help them get confidence that when the soil tests said high we could get by with no, with no, fertilizer. So this was all prior to more recently in the last, say two decades, when fertilizer costs have been increasing and, more and more emphasis now on. The environmental, implications of this, and in the 70's and 80's, we had far enough, we'd come far enough along that scientists were very interested in comparing soil test, extracting solutions and philosophical approaches, and there's been a fair amount of, Research done on that. Unfortunately we have not done very many of those kinds of studies in the last say decade really so word about yield goals. Some degree of measured yields needs to be incorporated in this whole process. So, if you're going to use yield goals, those numbers need to be based on some good experience that the farmer has in terms of the productivity level on their farm or some good research. The goals should be to have realistic yield goals because if your yield goals are not realistic then chances are you're going to be applying more fertilizer than your crop could, could use. And our studies of the fates and flows of nutrients, particularly nitrogen, which is where yield goals really come into play very heavily. You know, we've learned now what can happen to nutrients that are beyond the capacity of the crop to, to assimilate and return in terms of yields. So in today's world, the, the idea of yield goals needs to be really more, more thoughtfully approached. I'm not saying that yield goals do not constitute an important part of making a good fertilizer recommendation. I think in many cases, they do but they need to be very carefully considered. I want to finish with just a minute here to let you know that, you know, over the years there has been some studies done on comparing these different philosophical approaches. There's one fairly detailed and complete study, by Doctor Olson, and his colleagues. Unfortunately it's the early 80's, and we just have not done very many of these studies. But it involved growing corn over several years. And what the scientists did was to take samples from several sites, and they split those samples. And sent some of them to various labs including private soil testing labs and also the University lab and they followed those recommendations coming out of those labs for fertilizer explicitly for their crops. So the treatments in these experiments consisted of the fertilizer programs that were recommended by the, the crops. The commercial labs and one way or another use the canine exchange, capacity, the ratio approach, or the buildup approach. The University Lab subscribed to the percent sufficiency approach. And when they got done, and manage the fertilizer according to the lab recommendation they. They found no differences in grain yield. Amongst the different philosophical approaches with the different, resulting in different fertilizer amounts. They were great differences in the amount of fertilizers used to grow the corn crop but, but no difference in the yield. So the scientists concluded and I've added a few words to this but basically they concluded the conservative approach with the percent sufficiency and most people recognize or put the moniker on the percent sufficiency as being very conservative. And depending on how you define conservative maybe, maybe that's, maybe that's a good thing But the conservative approach with the percents efficiency no fertilizer for soils that tested high seem to be the most appropriate given considerations for social economic and the environment and I've inserted. As I have warned you all, uh,[LAUGH] through this course, the Triple Bottom Line, because that's very important and I think, comes out, shining, clear in studies like this, because the economics and the potential, impacts on environment, are very important. So still today, these, philosophies are out there. There in terms of making fertilizer recommendations. But as I said, there's been some changes and some moderations to some degree and some amalgamations, if you will, between different approaches, and so I think we're moving forward with understanding a little bit more about making fertilizer recommendations, and How our philosophical approach, should, will impact, those. And particuarly you know with regard to over fertilization, we surely don't want, to make, fertilizer recommendations based on a philosophy that results in, excessive fertilization. Because the economic impacts on the farmer even though fertilizer today is still relatively small compared to other impacts, it's still not, it, it is not a trivial part of the overall production costs and budgets. Fertilizer might still be seen in some sectors as relatively inexpensive insurance against low yields. So, if I put a little extra on, I can sleep at night based from my fertilizer aspects. I can worry about other things on my farm like weather disasters and, and labor costs and, and pest management and marketing and things like that so sometimes that plays a role in the decision making process. As I said before, fertilizer, you know, Twenty or thirty years ago demand was few percent but now increase in cost of fertilizers hmm, it becoming a non trivial part of our cost of production and I am giving you some papers on this subject if you want to do little bit more reading on this subject hmm, you know again there. You know, they're 20 years old now. And I wish that we had the wherewithal and the, the resources to continue to study these kinds of aspect with soil testing, because we all say that its an important BMP for nutrient management. And as we move forward as crops change, as variety change, as production practises change and become more intensive We really need to keep up with doing research on fertilizer and nutrient requirements and calibrating soil testing. So a couple take home pages here for you. Soil testing is still a very important first step in a nutrient management BMP. With all its potential problems and challenges that we've talked about now it's still very important because without it we really are moving in, in the dark. We need to have an idea, of the nutrient supply and capacity of our soils. Even though you have a good soil testing result and a recommendation, you need to think about, the, basis for the recommendation and you need to, to do some, spend some, some time, quizzing the, the lab and the person making those, recommendations. So that the farmers can understand the differences, amongst those approaches, and also the potential economic and maybe even environmental implications. Not all philosophical approaches are, are going to apply to your farming situation. The environmental part of the triple bottom line in this regard is becoming increasingly important and is going to continue to drive decisions about fertilizer use and management. Cost of fertilizer today, much more expensive than it was two or three decades ago. These two aspects at least in my mind, seem to be driving the decision more towards a sort of percents efficiency approach, applying less fertilizer at least on those soils that are high and very high. But soil tests, you know, in the final analysis, soil tests that are properly developed and properly executed and properly interpreted can, can, can go a long ways to helping us manage nutrients on the farm. And we'll talk a little bit more next time, you know we'll get a little more detailed about some of those nutrient management procedures but I thought it was very important to really cover this aspect of soil testing fairly thoroughly because it is so important, to our understanding of best management practices and being able to move forward, with managing nutrients, on our farms.
