Phosphorus Management and the P-Index

Javed Iqbal and Rick Koelsch Author

03/05/2021 Added

16 Plays

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From "Benefits & Barriers to Manure Use" portion of Land Application Training 2021

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[00:00:00.620]So, hello everyone.
[00:00:03.400]My name is Javed Iqbal
[00:00:04.840]and I am a nutrient management and water quality specialist.
[00:00:07.860]I probably may have met, seen you last week as well.
[00:00:13.260]So in this presentation I am going to share some information
[00:00:17.340]about the Nebraska P-index.
[00:00:22.240]And before I proceed with this presentation,
[00:00:27.180]I would like to recognize the contribution
[00:00:30.070]of doctor Charles Wortmann
[00:00:33.430]who developed this tool
[00:00:36.180]for P-index for Nebraska.
[00:00:40.370]So, after my presentation
[00:00:43.290]then Dr.Rick Koelsch will take over
[00:00:45.920]and we go through some exercises.
[00:00:49.170]All right, so in this presentation I will just provide
[00:00:51.400]a very brief overview of the risk of phosphorous losses.
[00:00:57.020]And I would also share why we are using the P index.
[00:01:01.607]What's the purpose of using P index?
[00:01:04.620]And we would also share some of the management practices
[00:01:07.860]that we can use to reduce the risk of phosphorous loss
[00:01:13.020]by using the P-index.
[00:01:16.030]So, by the way...
[00:01:18.390]So, how does this phosphorus move to water?
[00:01:21.240]Because phosphorous is an important nutrient
[00:01:25.150]and it can move from agricultural landscapes
[00:01:30.070]to surface water, through water.
[00:01:34.330]And fortunately, phosphorous management is not as difficult
[00:01:40.840]as you would think of nitrogen management
[00:01:43.080]because nitrogen has the potential of losses
[00:01:47.620]through many pathways through denitrification, nitrification
[00:01:51.580]and other processes.
[00:01:52.660]But when you think about P, it just moves with the water.
[00:01:58.450]So, there are actually two processes through which
[00:02:01.930]the phosphorus can move with the surface water.
[00:02:06.850]It's erosion and runoff.
[00:02:10.050]It moves through erosion
[00:02:12.130]because this phosphorous particle is attached to the soil
[00:02:17.270]that usually erodes when you have this process.
[00:02:21.670]And it could also be lost through runoff
[00:02:24.810]because phosphorous is dissolved in the water.
[00:02:28.840]However, it hardly moves within the soil profile.
[00:02:33.240]But in some cases, it can move when there are large pores
[00:02:39.580]or some soil micropores that can drain some of that water
[00:02:44.590]containing phosphorous
[00:02:45.930]and that can drain out through tiles.
[00:02:48.660]If those are installed in the subsurface soil
[00:02:52.470]or if those are not installed,
[00:02:54.200]at least this phosphorous through the micropores
[00:02:57.512]can reach out
[00:03:00.910]down into the side profile
[00:03:03.273]and might not be in the root zone.
[00:03:06.670]So, however, if you are maintaining
[00:03:10.410]the agronomic soil P-levels
[00:03:12.680]as Rick mentioned earlier today in his presentation.
[00:03:17.020]So, we have some threshold values
[00:03:19.090]from 15 to 25 parts per million
[00:03:22.680]and above these values there is no crop yield response.
[00:03:26.680]So, if your soil P levels are within this range
[00:03:30.710]then there is no risk of soil phosphorous loss
[00:03:33.880]from your field.
[00:03:35.270]But as the soil test p-levels gets higher
[00:03:39.200]there is a more risk associated with P loss
[00:03:42.780]which can ultimately ends up in the surface water,
[00:03:46.870]on streams and rivers and cause many kind of problems.
[00:03:54.090]So, the question is why do we use P-index?
[00:03:57.590]Probably because NDEE says so.
[00:04:00.790]Nebraska Title 130 requires to conduct a field P loss
[00:04:05.350]assessment prior to initial land application of manure,
[00:04:09.270]which occurs...
[00:04:10.610]Which is required once every five years.
[00:04:12.960]And this actually applies to fields or application
[00:04:16.480]to the control by (indistinct).
[00:04:18.700]Though NDEE requires this
[00:04:21.320]but in reality we want to use this p-index
[00:04:25.150]because we do not want to lose phosphorus
[00:04:28.230]from our agricultural fields to the surface waters
[00:04:33.840]that we use for different purposes.
[00:04:36.790]And then...
[00:04:37.623]So, that's how like P-index can really help us
[00:04:41.070]to really assess
[00:04:43.630]if we can reduce the phosphorus losses.
[00:04:52.200]So again, what is the p-index?
[00:04:54.530]This is a tool that is used to assess
[00:04:59.110]the risk of phosphorus loss
[00:05:01.150]or to assess the potential of phosphorous delivery
[00:05:04.970]from individual lands to near surface waters.
[00:05:09.160]This tool is used for land application planning
[00:05:14.280]and is also used for education of different factors
[00:05:18.850]that contribute to phosphorous loss.
[00:05:21.380]So, in this P-index tool
[00:05:22.820]there are different components including the sources
[00:05:25.670]and the transport factors that contribute
[00:05:28.380]to phosphorous loss.
[00:05:30.620]Today I'm not going in detail
[00:05:33.090]but we will be looking at the final results there
[00:05:36.330]which is the p-index value.
[00:05:39.610]So, once you enter all those components
[00:05:42.520]you'll fill out all those components
[00:05:45.000]in the phosphorous index tool
[00:05:47.970]then you would get these results.
[00:05:49.367]For example, here I'm...
[00:05:51.520]You can see p-index value of 6.28.
[00:05:54.890]And then when you get these results,
[00:05:56.520]you may not only want to look at this.
[00:05:58.250]You also want to look at the two components
[00:06:00.770]that makes this P value, P-index value.
[00:06:03.710]So, runoff P value is one other component.
[00:06:07.520]And then when this runoff P value is higher,
[00:06:11.900]you may want to consider some of the practices
[00:06:15.100]that can reduce this runoff.
[00:06:16.720]For example, cover crop is one of the practice
[00:06:19.760]that can reduce this P value.
[00:06:23.490]But if you have got higher erosion P value
[00:06:27.170]that we have got in this case,
[00:06:28.680]then you may want to consider
[00:06:30.870]some of the management practices
[00:06:32.570]that can reduce the erosion P value.
[00:06:36.380]So, when you look at the here the text high.
[00:06:40.760]This indicates something about
[00:06:43.063]this P-index value that we will look in at the next slide.
[00:06:48.010]How do we interpret this?
[00:06:50.330]So,
[00:06:53.530]once you get the P....
[00:06:55.413]Once you run the P-index then would get a value
[00:06:59.880]and those values can range from zero to 15 plus.
[00:07:05.140]What that we call the P-index value.
[00:07:07.290]And there are different levels of those P-index
[00:07:09.540]or there are different risk levels associated with P-index.
[00:07:14.800]For example, if you get...
[00:07:16.750]If your result is between zero to two P-index value
[00:07:20.890]that means that there is a lower risk of phosphorous loss.
[00:07:24.840]And in that case you're not likely
[00:07:26.640]contributing to water quality problems.
[00:07:29.530]And that the individual management practices
[00:07:32.920]on your farm are likely okay.
[00:07:35.520]So in that case, you can apply manure
[00:07:39.420]based on the nitrogen rate
[00:07:41.420]as long as it is sufficient for your crop nitrogen needs.
[00:07:46.530]If your P-index value is between two and five
[00:07:50.220]this indicates a medium risk level of phosphorous loss.
[00:07:55.940]So that means that your field is contributing
[00:08:00.370]somewhat to the impairment of the surface water.
[00:08:04.690]And then you may want to consider...
[00:08:06.250]You may not need to change a lot
[00:08:08.060]but you may tend to consider some practices
[00:08:11.680]that can reduce this P value or early scan.
[00:08:17.110]Reduce the risk associated with phosphorous loss.
[00:08:19.990]So in this case, you can still apply manure
[00:08:23.560]using nitrogen-based rate
[00:08:25.590]as long as you are not moving to the next category
[00:08:30.680]or high risk level category.
[00:08:35.760]How if you get a P-index value between five and 15.
[00:08:39.470]This means that you have a higher risk of phosphorus loss
[00:08:43.490]and your field is
[00:08:46.487]contributing a lot
[00:08:48.850]to the surface water quality problems.
[00:08:50.870]So you need to seek some alternative conservation
[00:08:53.710]management practices to reduce those phosphorus losses.
[00:08:57.920]So in this case, you may apply manure
[00:09:01.900]based on the phosphorus rate,
[00:09:04.290]if you know the management practices
[00:09:06.060]that you are looking to implement
[00:09:08.540]would reduce the risk associated with phosphorous loss
[00:09:11.780]within the next five years.
[00:09:15.110]However, if your P-index value is above 15
[00:09:19.330]that means a very high risk of phosphorous loss.
[00:09:22.900]So, your field is contributing
[00:09:26.530]all sorts of water quality impairment problems
[00:09:30.370]or water quality problems in the surface water.
[00:09:33.410]So, there is need to be a change,
[00:09:36.810]bigger changes in management practices
[00:09:40.310]to reduce this risk associated with phosphorous loss.
[00:09:44.320]And then no phosphorous, in this case,
[00:09:46.750]could be applied to that field.
[00:09:50.860]Okay.
[00:09:51.870]So from here, I will turn this over to Dr. Rick Koelsch
[00:09:56.867]who will be going through some of the exercises.
[00:10:02.100]The first thing we're gonna ask
[00:10:03.710]about these three fields is
[00:10:05.190]what is driving the phosphorus risk?
[00:10:08.690]Is it
[00:10:11.570]the P levels?
[00:10:16.090]And can we bring those P levels down to a lower level?
[00:10:20.600]Can we limit erosion?
[00:10:23.680]Can we limit runoff?
[00:10:26.860]And is there a need for a better buffer
[00:10:30.310]between the field and surface water?
[00:10:33.410]So, let's begin putting this into application.
[00:10:37.960]Here's our three fields.
[00:10:41.870]Field A you can see it's a terraced field.
[00:10:44.300]It sets just to the South of a stream.
[00:10:48.950]Looks like there's a reasonably good buffer
[00:10:51.840]between that stream and the field.
[00:10:57.794]Field B is a field that if you look over here
[00:11:01.170]on the topo map has some slope to it.
[00:11:03.850]You can see by these topographic lines that are pretty close
[00:11:09.110]and it looks like we're farming right up to the stream
[00:11:14.330]that's flowing around along the North edge of that.
[00:11:17.460]Field C you can see that irrigated pivot
[00:11:21.230]as a draw through the field within an intermittent stream
[00:11:24.660]whenever you see dotted lines on a topo map,
[00:11:27.890]topographic map to intermittent stream.
[00:11:31.790]And so, some connection to the surface water
[00:11:35.420]through that intermittent stream.
[00:11:40.240]Below that you've got a summary of what we just presented
[00:11:43.640]in the slide in terms of what's the interpretation.
[00:11:46.450]I'm gonna skip by that.
[00:11:48.670]And we're gonna look at activity one.
[00:11:52.780]And what I'd like you to do in activity one
[00:11:56.790]is to tell me what you think are the drivers
[00:12:01.790]to the P-index that we're seeing.
[00:12:04.610]So, field A in its current...
[00:12:08.620]What I'm suggesting here...
[00:12:10.520]What I've shown here, here's our P-index value
[00:12:15.330]and our text value down here at the bottom.
[00:12:17.530]So field A, we have a medium risk,
[00:12:20.880]field B has a high to medium risk
[00:12:22.870]and fields C as a high risk.
[00:12:25.810]So, what's the drivers?
[00:12:28.610]And we're gonna use a little worksheet down below
[00:12:31.970]and we're just gonna decide whether each of these ideas
[00:12:36.304]or topics are important or less important.
[00:12:42.290]So we'll...
[00:12:43.720]Let's just take an example.
[00:12:46.110]We'll do our first field, field A.
[00:12:49.990]Is the soil P level
[00:12:53.920]important or less important?
[00:12:56.730]So I've highlighted that here
[00:12:58.440]soil P level 200 parts per million for A,
[00:13:04.150]for B it's 25 for C it's 200.
[00:13:09.040]So, what would you like me to label?
[00:13:12.100]I'm assuming field A it's an important factor
[00:13:17.000]probably would do less important here.
[00:13:19.630]I'll let you label the third field.
[00:13:25.430]Now that you've done that let's look at the erosion risk
[00:13:31.230]and you'll remember that that P-index value
[00:13:35.200]has a component that's for runoff
[00:13:38.600]and a component that is for erosion.
[00:13:42.730]So for erosion,
[00:13:43.850]and then below that runoff risk
[00:13:46.450]label them either important or less important
[00:13:50.290]and do it for all three fields.
[00:14:06.710]Less important,
[00:14:09.390]low erosion factor.
[00:14:12.720]Looks like for field B it's important
[00:14:19.610]and for field C it's certainly important.
[00:14:23.140]Okay, I see an I
[00:14:27.080]And continuing a cross
[00:14:30.560]kind of a somewhere between I
[00:14:32.740]and an L here for the field B.
[00:14:35.007]And it's not a big contributor
[00:14:37.750]but it's partial
[00:14:40.220]and we'll call it less important for now
[00:14:43.330]and then run off for field C.
[00:14:45.360]Looks like that's pretty comparable to erosion
[00:14:48.240]so it's important.
[00:14:52.146](indistinct)
[00:14:53.520]Is the buffer an important factor to consider
[00:14:59.570]for field A, B and C?
[00:15:02.060]And to find that we need to go up here
[00:15:06.530]to filter with.
[00:15:14.560]35 to 75 on field A, 10 to 20,
[00:15:20.110]zero to 10 on field C.
[00:15:24.060]So, probably less important field A, important on B and C.
[00:15:30.810]So now we have some idea as to practices
[00:15:35.700]that might help us out.
[00:15:36.980]So, for field B and C,
[00:15:39.530]it looks like things that control erosion
[00:15:42.140]might be pretty valuable to us.
[00:15:45.010]Also, adding to the buffers might be valuable.
[00:15:49.380]So, we can begin to see where to put our emphasis
[00:15:53.010]in that P-index.
[00:15:55.210]All right?
[00:15:56.860]So, these are examples of the kind of report
[00:15:59.790]you will get...
[00:16:00.623]You will see in your permit application for the P-index
[00:16:07.610]We all use the same tool here in Nebraska,
[00:16:11.010]so your reports will look very much like this.
[00:16:15.280]All right, I'm gonna skip on to field A
[00:16:18.920]and what I want you to do with field A
[00:16:22.860]is look at the baseline scenario here.
[00:16:29.950]And for the baseline I actually have a medium level of risk.
[00:16:36.280]And next to it, I have a lower soil P level
[00:16:40.510]just to give you an idea of what the benefit results
[00:16:45.920]from lowering that P level from 200 to 25 part per million.
[00:16:52.890]Oops, 25.
[00:16:55.010]And it helped us out,
[00:16:56.920]it got us out of that medium category.
[00:17:00.370]Now, what I want you to do is ask
[00:17:03.590]of those scenarios below there, the three.
[00:17:06.820]Which of those conservation practices might cause you
[00:17:11.480]some real headaches if you were to give them up?
[00:17:14.270]I was to start farming through those terraces
[00:17:16.830]or start farming without...
[00:17:19.220]Just going around the field
[00:17:21.010]rather than following the contour
[00:17:23.540]or getting rid of my filter strips.
[00:17:27.570]Which of these really hurt
[00:17:32.900]the P index for this field?
[00:17:40.770]There's two of these practices,
[00:17:42.610]it looks like I would not like to give up.
[00:17:46.380]Right?
[00:17:48.630]I gave up my terraces, I jumped into the high category.
[00:17:59.310]And if I gave up my contouring
[00:18:01.390]I guess I have not jumped into the high category,
[00:18:05.360]I'm still medium.
[00:18:06.450]But my value is 4.6 and five is my cutoff.
[00:18:11.460]So I'm pretty close to jumping into that high category.
[00:18:16.470]So I'd add very little cushion for any future increases
[00:18:22.350]in soil P levels or anything such as that.
[00:18:26.290]So, the worst thing to do
[00:18:27.900]would be to give up the terraces.
[00:18:29.930]So, that's one way you can use the P index
[00:18:33.360]is evaluating what's the benefit
[00:18:35.230]of some of those conservation practices.
[00:18:39.270]Now, I'd like to wrap this up, we...
[00:18:41.710]What I want you to do is skip down to field C.
[00:18:47.370]So, I have a high-risk field
[00:18:49.560]and C
[00:18:52.160]in my baseline scenario
[00:18:55.410]and I want you to find a practice that you might try,
[00:19:00.020]be willing to implement
[00:19:03.180]that would get that soil P index
[00:19:08.230]down into the medium category.
[00:19:11.720]So, I'll let you look through those, pick something out.
[00:19:16.020]Your consultants provided you with a set of P-indexes
[00:19:19.600]for the fields receiving manure.
[00:19:22.260]You need to go through that data
[00:19:24.660]and decide where the red flags
[00:19:26.750]that you need to pay attention to in the future.
[00:19:29.530]So, anything high or very high certainly has a red flag.
[00:19:33.290]If you see something in that medium category,
[00:19:36.380]potential for trending up, you need to be aware of that.
[00:19:43.670]Then, once you establish those red flag fields,
[00:19:49.150]for those red flag fields, we need to ask,
[00:19:51.970]can I reduce that P index by reducing the runoff potential,
[00:19:56.880]the erosion potential?
[00:19:59.470]Can I reduce soil P levels?
[00:20:01.250]And that's a slow, difficult process.
[00:20:05.710]It's probably gonna be very difficult to drop soil P levels
[00:20:10.250]by more than, let's say,
[00:20:12.650]probably at the max and maybe 10 parts per million
[00:20:16.376]on a high-performing corn field that's performing very well.
[00:20:23.700]Or am I gonna want to add some buffers
[00:20:26.940]to create some buffer between the field and surface water?
[00:20:31.340]So, which of those approaches might help me get
[00:20:35.350]out of a high risk situation?
[00:20:38.840]So, that's where we'll leave it.
[00:20:41.840]There're some resources
[00:20:42.980]if you want those in the PowerPoint.

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Phosphorus Management and the P-Index

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