. Hello everyone, and welcome back to our next section of the course. Today I want to start talking a little bit about nutrient management. So far we've come a long way in, in learning about soil testing and soil management, and today I want to talk a little bit more about some specifics regarding fertilizer management in an agricultural setting. So we're going to start the, the discussion now a little bit more focused on best management practices. Specifically, now that we know a little bit about the fertilizer and how to determine how much fertilizer we need, I want to start talking a little bit about managing that fertilizer. Fertilizer is typically the largest input into our nutrient budget on a farm. So it makes a lot of sense to focus on our management strategies. And we know now that if not managed properly our nutrients that we use as fertilizer on our farms not only could result in reduced profits, but also in problems with environmental degradation. So understanding nutrient best management practices is really a key to helping out with farm profitability and water quality protection. I want to talk about nutrient management from the perspective of what we call the 4 Rs. The International Plant Nutrition Institute as well as all of our land grant institutions, and many in the private sector, including farmers I think understand some of these parts, or at least understand what they are. But in this course, we want to talk a little bit more in detail about what exactly we mean by the 4 Rs. And how do these various parts of nutrient management fit into a best management practice. So we're going to talk about the right rate. That's very important. I think that's pretty intuitive to everybody. How do we place the fertilizer most optimally for most efficient use of it? Timing of the application of fertilizer during the crop production season is very important for getting the best benefit. And also selecting the right fertilizer materials. We may need a certain suite of nutrients, and we want to select the materials that can supply those nutrients or maybe that single nutrient that we need. So are we making progress in fertilizer management in the agricultural world? Nitrogen management has always been a goal in agriculture. The acres of corn, for example, in this particular country that are excessively fertilized has been decreasing. The USDA conducted a study a few years ago taking a look at the adoption of best management practices. And despite the effort by many farmers to get a, get a handle on the 4 Rs there still was a significant amount, over half of the acreage of corn producers that were found to be deficient in one or more of those 4 Rs. So we're going to talk a little bit about the 4 Rs, and perhaps maybe we can reduce that number that are deficient in adopting best management practices. So how much fertilizer is needed to grow crops? Recall our discussion about soil testing, and how we use soil testing to determine the amount of the overall crop nutrient requirement that can be supplied from the soil, and the difference we would need to make up from fertilizer. So conceptually, we're looking at fertilizer to supplement the native soil fertility. Along the way, we learned that setting realistic yield goals is very important, particularly when we talk about nitrogen fertilization. We generally don't soil test in a pre-fertilization fashion for nitrogen, and so we rely on what kinds of crops do farmers expect. And usually that means setting yield goals. Or it could mean using our best available science on a region. So, for example, if a lot of research has been done with potato and a target nitrogen rate is suggested from that research, we might use that rate as our fertilizer recommendation. So the fertilizer rate is a very important part, and I emphasize the word part of a fertilizer BMP. Many times we get very concerned about the rate, as if it were the only aspect of a proper fertilizer management, best management practice. And so how do we determine the right rate of fertilizer? As I've eluded to before, much of this comes from significant detailed field research done in many, many areas over years, where we test crop response to a particular fertilizer nutrient of interest. So for example, we might look at nitrogen fertilization of tomatoes. And in this picture, you can see some of the plots that receive low amounts of fertilizer. You might even look at this row here, this first row, and say, well that doesn't look quite as lush green as this one. And, in fact, you'd be right. This, this row here received less nitrogen fertilizer than this row. But who knows? Until we actually finish the research and collect the tomato for yield, this row here may actually yield more and be a, a more economical and environmentally friendly nitrogen management practice. So this is the kind of research that has to be done with our fertilizer nutrients in order to come up with a best recommended nitrogen rate, for example. So here are some data from that particular experiment. And we mentioned before, on these very sandy soils, you get very low yields when you do not put nitrogen fertilizer out. Some of you maybe familiar with soils in your growing region, where you might get 50% or 60% relative yield or more, with no nitrogen, because your soils can supply a significant amount of nitrogen for mineralization, for example, of the organic matter. The other takehome principle that we've already learned is that the response, to nitrogen happens very rapidly. And pretty soon, you reach a peak in terms of crop response. And this term, in this particular situation yield in terms of boxes of fruits per acre. And then after that, if we continue to add more and more nitrogen, we do not see a positive return on investment. In fact, those responses out here on the curve might mean that excess nitrogen is being left behind in the soil. So many, many studies need to be done testing this rate of a particular nutrient. And you'll see a zone of response at the lower rates, and then a peak, and then a leveling off of the crop response to the, to the nutrient. So once you've done several of these kinds of studies, then you can, you can hone in on what would be a good target nitrogen, in this case, nitrogen fertilizer recommendation. And I've said here that you, you do need to have numerous, studies. Varieties differ in their yield potential, and may differ in the fertilizer requirements. Locations might cause variations in fertilizer requirements. Years seasons. Seasons here in Florida is very important, because we grow tomatoes almost year round. And so a tomato crop grown in the spring may have a different fertilizer, nitrogen, for example, recommendation than a tomato crop grown in the fall. Now, even though these studies point out where the nitrogen rate is maximized, we still don't know, or we would want to know what that researcher did to manage that nitrogen. Those are going to be topics like placement and timing that we'll study in a little bit. But just keep in mind that right now we're going to focus on the right rate of a, of fertilizer. Now, the right rate may result in optimal biomass production. But we also, particularly this is true in the horticultural area like vegetables, we also want to evaluate the quality of the, of the fruits. So for example, tomato fruit size, crisp head lettuce, head size. These are all very important quality aspects that the scientist would want to factor into their research studies. So when they look at their response of the crop across a range of fertilizer rates, they're not only evaluating total marketable yield, but they're also looking at quality aspects, maybe, maybe even chemical quality, sugar content things like that would be important. Fertilizer rate, when we talk about rates there is a communication issue here that we need to be aware of. How, depending on where you are in the world, how are the rates expressed? Typically, a fertilizer rate is simply an amount of fertilizer material over an area of ground or a field. And usually, we, and depending on where you are in the world, you'll express this as pounds per acre, as we do here in the United States, or kilograms per hectare in many other places in the world. So if we're operating or making advice in, in many places that have different ways of expressing units how do we convert from one to the other? It's very important for us to understand. And you might want to prove to yourself that pounds per acre times 1.12 equals kilograms per hector. We won't belabor the time of going through that, but just prove to yourself that, that's true. I grew up on a, on a vegetable farm here in America. And I learned pounds per acre. And then when I went to college and, and in the position where I am now to publish research in the scientific journal, we use the metric system. And so I've had to learn to go back and forth in the scientific world. Well if I go out to the farms, and talk about fertilizer management, I have to switch back to pounds per acre when I'm talking to American farmers. So many of us around the world that are in the area of science development, and particularly in extension and working with growers, we have to be able to go back and forth. And maybe some of you, maybe many of you out there understand what I'm talking about. The fertilizer rate assumes a broadcast area in essence, ie, we spread the fertilizer uniformly over an area of land. And that's tradition. That, that's mostly tradition because in the old days, that's essentially how fertilizer, or manure was applied. So we think about a length and a width of an area. It could be a rectangular, you know. Not all acres are, are square so to speak. So, in this particular case 200 pounds per acre would equal 224 pounds or kilograms, sorry, 200, 200 pounds per acre would equal 224 kilograms per hectare. So, if we're talking about nitrogen rate we might have a field that's shaped as I've, presented here. And we would spread that amount of fertilizer. Or think, at least in terms of spreading that amount of fertilizer uniformly over that area. Even though our actual placement, which we'll talk about a little bit later, may not be broadcast. And, in fact, in many cases most efficiency is achieved by banding or some other placement, rather than broadcasting. Let's step aside a little bit here and do some, do some math. And I put the non-smiley face up there, because I understand a lot of people, when you use the word math that causes consternation. And many of my students when you start talking about math problems in class, you can see their, you can see their excitement dwindle considerably. But I think we need to understand a little bit about the math and conversions and calculations with fertilizer, because everyone, sooner or later when you use fertilizer, you're going to be faced with doing some kind of a calculation. Because we are talking about numbers and we are talking about rates and areas. So, fertilizer analysis is expressed here in the United States as N P2O5 and K2O. And I'm talking about, I'm thinking about mostly a dry blend of material. So this particular fertilizer might be composed of several materials to be able to supply all three of those nutrients. In fact, there may be other nutrients, plant needed nutrients in that fertilizer, for example, magnesium or sulfur. But for our purposes with this lecture, we'll focus on N, P and K. So those are the three numbers that you at least see on all fertilizer packages. So as an example, let's say that we have a 26-4-12. So we have 26% of that material, that fertilizer, is nitrogen. And 4% is P2O5. And 12% is, is K2O, sometimes called potash or potassium. So that's what those numbers mean, and those numbers could vary depending on the analysis of fertilizer that the farmer might need and the materials that are used to make it up. So you'll recognize that the fertilizer material is only partially made up of those plant nutrients N, P and K. And as I eluded to before, because of the materials that there, are used to make those materials those fertilizers, you might have some other nutrients in there. Particularly sulfur might be another example. And sometimes there are materials are added in to fill, called filler, to bring that total, total mass up to, say, 100 pounds. So, if I had a 100 pound bag of fertilizer, and it was 26, 4, 12. It would be 26% Nitrogen, 4% P2O5 and 12% K2O. So hopefully that gives everybody a sort of a basic starting point as we go, go forward with some calculations. So let's take our fertilizer material, and again, this particular analysis could, I've just, I just made up the numbers. It doesn't refer to any particular fertilizer for any particular purpose. But just to illustrate the numbers as we go through here. Let's say that we take that fertilizer material, and we apply it to a crop at a 100 pounds per acre of that material. So we take 100 pounds of that 26,4,12, and we're going to apply it to an acre of crop. So when we get done, we will have applied 26 pounds of nitrogen per acre. So, the 100 pounds is 26% nitrogen. So we will have applied 26 pounds of nitrogen. You can do the same math for the P2O5 and the K2O. And you'll see that in this particular case, because we used 100 pounds it was pretty straightforward to come up with the numbers, and they equal the numbers in the analysis. But what if we applied this fertilizer at 80 pounds per acre, or 70, or 95, or 120? So using this example here, why don't you try to see what kinds of numbers you would come up with as far as the total nutrient that you apply if you use that fertilizer material at varying rates on that acre. Now the fertilizer that we've talked about is a blend. It's a blend of materials, that when put together, supply nitrogen, phosphorous and potassium for the crop. And as I said, there might be also something else in there, like sulfurs is very commonly found because of the sulfate containing materials that we might use to supply for example nitrogen or potassium. But recall back when we talked about soil testing. We might find out that our soil is very high in a particular nutrient, maybe phosphorus. And we might decide that we don't need to put phoshporus out as a fertilizer. So that particular blend may not be for us, in that case. In this case, we might only need nitrogen. And this would be especially true if we were adding nitrogen through the season because remember, nitrogen has a tendency to move in our soils. And so we'll learn a little bit later that split applications of nitrogen are very important for improving efficiency. So put that aside, but just think in terms of situations where we might need only nitrogen. We may choose a, a single nutrient or a single yeah, a single nutrient material like urea for example. It's 46% nitrogen. Other materials that are, that can, will, will provide only phosphoruous or provide only potassium, there are lots of those to, to choose from out there. So if we only need one of the nutrients, then we can find materials, fertilizer materials, that will supply only that nutrient. And why supply other nutrients if they're not needed? So what if we needed 30 pounds of N, and we were going to use urea to do that? Remember, we talked about urea being a relatively inexpensive source of nitrogen. Now we know that urea, 46% nitrogen, is only partially nitrogen. So intuitively, we know that we're probably going to need more than 30 pounds of urea to get 30 pounds of actual nitrogen. So, taking the calculation further I've divided 30 pounds per acre, that is our desired rate of actual N, by 0.46, and come up with 65 pounds of urea is needed. Now when we look at that number, we say 65, that makes sense because urea is almost half nitrogen. And so it makes sense that almost twice as much, twice 30 is probably where we're going to be with our overall rate. And you can prove this to yourself by going backwards. Take 65 and multiply it by 0.46, and you'll come up with 30. So if we're going to need 30 pounds of nitrogen and we're going to use urea we will need 65 pounds of urea to supply that 30 pounds of nitrogen per acre. Now we've talked about dry materials. There are liquid fertilizers out there. And I don't want to spend a lot of time going through all of the calculations with them, but just realize that liquids canned liquid mixtures of fertilizer can be used to supply these nutrients for crops. And in fact, in some situations that we'll talk about later they might be the preferred way of delivering nutrients to a crop, because they're easy to handle in the, in the field. If we need to know the nutrient content of nutrients supplied from liquid forms, then we're going to need to know, and the fertilizer dealers can supply the amount of nutrients that would be in a volume uh,of the final solution. So in terms, you know, for example, pounds of nitrogen per gallon of liquid fertilizer, and then we can go and do our, our calculations, and we can determine how many gallons of a liquid fertilizer that we have in hand, we would need to supply a certain rate of nitrogen fertilizer. So just recall that with fertilizers we've gone through a process with soil testing to determine those nutrients that are required in our in our cropping scenario. And then you'd want to supply, or select, or ask a fertilizer dealer to blend a fertilizer that will meet those requirements. And for example you may want a fertilizer that supplies the, the correct nutrients for a pre-plant fertilizer application to get, maybe if you need phosphorous and some of the nitrogen and some of the potassium. And then later on in the season, you'll want another fertilizer that will supply, for example, nitrogen and potassium. That's a typical program that we would use here in Florida on our very, very sandy soils because nitrogen and, and potassium we've already acknowledged can be lost or can be leached. So we want to keep some of those fertilizers back in the bag, or in the tank, or in the barn as it were, and spoon feed the crop with those. So we'll, we'll talk a little bit more about this. And also, we'll practice a little bit through your discussion sections with some calculations and determinations of fertilizers so that you get a little more practice with how to determine fertilizers and how to, how to calculate rates of fertilizers from given fertilizer formulas. Now this idea of fertilizer rate is fairly straightforward for some crops. And that would be like sod production, where pounds per acre really is pounds per acre. We broadcast that amount of fertilizer over an acre of soil, because our sod is uniformly growing over that acre. Another example might be where we grow corn or soy beans or cotton. And all of the farmers use the same row spacings, and so pounds per acre with one farmer really means the same with another farmer. So here the rate expression, pounds per acre and kilograms per hectare is, is more intuitive and, and straightforward. But then you come to places like Florida and areas that are growing vegetable crops and particularly those vegetable crops that are grown in plastic mulch systems, where we put all of the fertilizer under the mulch beds. And especially in situations where a tomato grower might be using one particular row spacing and another tomato grower another. And so what does pounds per acre mean, and how do you interpret, in, interpret that for those two particular growers? So for example, potatoes, upper left hand picture. Sweet corn, lower left hand. Pretty standard practices in row spacings. So if I have five potato growers, and I talk about 200 pounds per acre of nitrogen for all of those growers, I pretty well know that they probably understand and will get, get the application correct in those, across those different farmers. The sod grower on the upper right hand corner, pretty straightforward. Pounds per acre, kilograms per hectare spread over that uniformally over the surface of the soil is going to be the appropriate, we're going to get it right when we say 100 pounds per acre. But, what about the watermelon grower in the lower right-hand corner? Here's a situation where you might have a watermelon grower who's growing watermelons on plastic mulch with six or seven, say six feet between bed spacings. And then I've got a neighbor down the road who's spacing is now eight feet. What does that cause to the expression, pounds per acre? So plastic mulch production, especially where growers have different ways of producing, particularly with bed spacing causes some concern about our language. Remember I said communication is very important. In this particular situation with plastic mulch we're usually putting the fertilizer under the mulch. We might be incorporating it with a rotor tiller, as we're doing in the upper picture and then covering it with plastic mulch. So, what we did years ago, here in Florida, was develop a system so that the extension service would know when we're talking about pounds per acre with our various vegetable producers, particularly watermelon and tomato and pepper growers, who are, tend to, to have more variation in their row bed spacings, we developed what we call the linear bed foot system. And quite simply, we were trying to address this issue of being able to be sure that when we said pounds per acre no matter what the bed spacing was used by various growers, they would get the rate and correct, especially as it pertains to the fertilizer under the plastic mulch. So the objective is to fertilize the, the crop, and have the same amount of fertilizer in that root zone under the plastic mulch. And I've give you a citation here, for those of you that want to read, a, a little bit more on this. And it really was an attempt to bring some consistency to the rates for these for the same crop where growers are using different bed spacings. And let's illustrate this a little bit more. Here would be a tomato crop, where from bed center to bed center is four feet, perhaps. Here's another scenario where the distance between centers is wider, six feet. If I tell this grower pounds per acre, and this grower the same pounds per acre, which one is going to have more fertilizer under the plastic mulch? This one? That's the one. That's, that's the correct answer, because this particular person has fewer linear bed feet of crop per acre. So this person has more. So that fertilizer is going to get spread over, over more linear bed feet of, of crop. So I hope you see the, the potential issues here, when we talk about pounds per acre, which is a broadcast expression, and we try to apply it to this bedded kind of production practice that we use with, with vegetables, and particularly if they're using different bed spacings. So again, the bed spacing is this from center to center. Here is one that might be four feet. This on an acre basis, this production scenario is going to have more linear bed feet of plastic or crop per acre, right? This one less. If we say the same amount per acre here as we give the grower here, this grower is going to have a higher concentration, or higher amount of fertilizer, under the beds. So, this particular system has to start somewhere. And what we chose to do was to take sort of, the standard or typical bed spacing, which happens to be six feet between centers. Most of the research like this was done with six foot bed centers, you know, approximately 1.8 meters, as the predominant production system. Once we determined, say for example, 200 pounds as the optimal rate of nitrogen per acre, under this bed system, then we can convert to so many pounds of nitrogen as it were, as we decided per hundred linear bed feet. And now we can convert back and forth between production systems. So just to give you an example, and here's, you know, a little bit a little bit of the math. So, tomatoes on six feet centers. How many linear bed feet in an acre grown in, in this fashion? Okay. Here's the calculation that we would do to get that. And growers are very, very familiar with this particular calculation, because it so happens that plastic mulch comes in rolls. And they might use three rolls per acre for example. So this is, this is intuitive to most vegetable producers. So we weren't doing anything really, really strange here when we came up with this system for expressing fertilizer. We made it a little bit simpler by expressing it on a 100 linear bed feed. And the reason we did this is because most farmers are used to using some kind of a 100 foot track or raceway to, to calibrate their fertilizers spreaders. So as I said, you know, the, the farmers are familiar with this kind of a setup. So if we do this then, on six foot bed centers, we know we're going to have approximately 7,300 linear bed feet sections, 100 foot sections in an acre. Our nitrogen recommendation, determined from our research that I just showed you, is 200 pounds. So what we're going to do is to take 200 pounds of nitrogen fertilizer, and we're going to spread it evenly over 7,260 linearbed feet, or 72.6 100 linear bed feet. So here's a simple calculation. 200 divided by 72.6 equals 2.75 pounds of nitrogen per 100 linear bed feet. So in our standard production system, 200 pounds per acre is the broadcast expression now can be converted for the plastic mulch system to 2.75 pounds per 100 feet of plastic across a, a field. So now, let's say we have growers that are using a different production system. Here's a four foot. I, I'm a grower. I say, I don't use six foot centers. I use four foot centers. So now, instead of doing all of the mental calculations of what, how 200 pounds per acre equates in that scenario we just tell the growers, no matter what kinds of bed spacings they're on, they put down 2.75 lbs of nitrogen per 100 linear bed feet. I, I'm not going to worry about the, the various production systems. So if I'm a four foot grower, my answer is 2.75 pounds of N per 100 linear bed feet. I've got the same concentration of fertilizer under my mulch beds, in my mulch beds, as that grower with the six foot centers. So if I came along and I told this particular grower 200 pounds per acre, and they have many, many more linear bed feet in an acre, they're probably going to be a little bit shy on the amount of nitrogen, because they've gotta make that 200 pounds go further. I hope, I hope this is clear as mud to everyone. But remember, the, the main goal is to achieve the same amount of fertilizer under that plastic mulch because now all of our fertilizer is in that bed, under that mulch. So the concentration of the soil in the, the fertilizer in the, in the soil under the bed is going to remain the same. And so all of those tomato plants, no matter the production system, are going to have access to the same amount of fertilizer. So now, what is the per-acre rate for somebody on four foot bed centers? So if we take our calculations that we did before. And you can go through these. Remember, it's still the same, 2.75 per 100 linear bed feet. But with four foot beds, we have almost 11,000 linear bed feet in an acre of land. So now if we want to express this on a per acre basis, we simply multiply 2.75 times 108.9, and we find out that this particular farmer is actually applying 300 pounds per acre. So I would have made a big mistake if I came along and told this grower on four foot centers without knowing, maybe I talked to him over the phone and that information didn't get relayed. I would say 200 pounds per acre. I'd be off, seriously. So the linear bed foot system helps solve that particular problem. So here's a few math questions, and we'll post some more for you to, to try, and to see if see if, if you can follow along and see if this makes some sense for those of you that deal with these kinds of production practices, where you are. There's a lot of information on the right rate of fertilizer. You know, I've listed a few of the places here. If I were getting started on searching out for some of this information in my area, I would look for sites that had the edu in them because those are going to come from the land grant institutions. And more than likely, those are the institutions and the scientists that will have done the research on determining the right rate. There are a lot of private advisors and private research institutions out there that can also do this work. And perhaps they've derived some of the recommendations that they have from the land grant institutions. So there's a lot of information out there. And just you know, just be, be careful about where you go to look for the information because right rate is a, is very, very important. So just a few take-home lessons from this, this part of the course. The right rate of fertilizer is very, very important. It's a part, and I emphasize again, a part of a good nutrient management best management practice. The right rate is determined, or should be determined by rigorous field research with crops and soils and production practices that you know, would be typical of the, of the farms in that area. The recommended rate is part of what we might call a BMP train. I think we introduced this terms earlier in the course. And there are other Rs involved on that train. And we'll talk a little bit about them. So the recommended rate is an amount of fertilizer that is going to let the farmer achieve his, his best yield that is possible, and also from an economical standpoint. And so we've talked about the importance of yields and yield potentials. And so as long as they're set realistically, and a good realistic recommended fertilizer that, rate that's research based goes along, then the economics will be satisfied and also the environmental aspects will be satisfied. And growers and everyone making advice to growers needs to understand about fertilizer and the calculations that go along with it, so that we get the right rate out for those production practices. Sometimes, I will just add parenthetically here, sometimes the rate will need to be adjusted through the season. And we'll talk a little bit about some of those instances. So even though you have the right rate that is a target rate that should work in most situations during that growing season. But we also know that mother nature plays a role in the right rate. And we may need to supplement the right rate with extra fertilizer if we lose fertilizer to leaching rains for example, that may not be under our control. So there are some adjustments that need, that can go along with this, and logically should go along with this. And we'll talk about some of the other aspects in fertilizer management, some of the other Rs in our next lecture.
