Wednesday, May 27, 2015

How much biogas production potential is there in Iowa?

 Are you interested in the potential anaerobic digestion holds in the state of Iowa? A new, easy to use tool, the Iowa Biomass Asset Mapping Tool (IBAM), may be just what you are looking for (available at IBAM is an economic analysis tool integrated with geographical information systems and was produced as a collaborative product of Dr. Mark Wright of Iowa State University and the Des Moines based company EcoEngineers. 

The model is an online, GIS, interactive map where a user can click on different layers of data to study  the biogas resource potential available or conduct an initial screening of where a potential project could be sited based on both feedstock and infrastructure availability. The IBAM tool provides estimates on production of a wide variety of biogas-based feedstock data including crop residues, manures, and industrial co-products.

The users can assess the potential availability of animal manure, crop residue and determine what co-location opportunities with existing biodiesel, ethanol, food and paper manufacturers exist. In addition to the feedstock data, there is also energy infrastructure data on the locations of natural gas pipelines, electric and gas service territories, and existing power plant locations. This helps users identify potential locations for optimizing substrates available for gas production and for best using the produced biogas.

A complementary tool to the GIS map is a preliminary economic assessment spreadsheet. The downloadable spreadsheet provides users the availability to modify inputs and assumptions to conduct a preliminary economic evaluation for a potential biogas project. Both the IBAM map and spreadsheet will require more robust analysis and engineering designs for any project moving forward, but these publically available tools can help users from the private and government sectors to conduct an initial project screen or quantify the potential for biogas projects in Iowa.

So that’s all great if you are a biogas expert, but really, what is anaerobic digestion?

Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material in an environment with no oxygen. As these microbes break down the organic matter they make a mixture carbon dioxide and methane with trace amounts of hydrogen sulfide, ammonia, water vapor, and other gasses that we call biogas. This occurs in a series of three steps: in the first large particles are brown down into things like carbohydrates. Acidogenic bacteria then convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids. Acetogenic bacteria turn those organic acids into acetate, which methanogens convert into methane and carbon dioxide. This is a naturally occurring process, its just when we do it in a digester we are trying to make it happen faster and control where the produced methane goes. So this organic material goes in and what comes out is the methane, which can be combusted to make heat or electricity and stabilized organic matter which still has the fertilizer value (the N, P, and K) it had when it went in.

This almost seems too good to be true right, we still get all our fertilizer value but we can get energy as too! Well, in some cases it can be a great deal, but anaerobic digesters can be expensive to build and sometimes challenging to manage, so they aren’t the right fit everywhere as often times we need an economy of scale to make them cost affordable. Thought not the final solution, hopefully more tools like the IBAM model will help us figure out where anaerobic digestion has the potential to be successful. 

Thursday, May 21, 2015

Bigger Pigs, More Manure – A Follow-up

On April 23rd I posted a blog entry called “Bigger Pigs: More Manure and Impact on Facility Design.” Though they didn’t all get shared on the post (note there are like zero comments there), but I did get a few helpful emails and had several good conversations about it with different colleges.

As I discussed there were a few (lots) assumptions that went into making that estimate, but a big one was the growth curve of the pig. I pulled a growth curve out of the literature and rolled with it, thinking it would probably be ok; I mean I needed something to work with, but after looking it over, that growth curve seemed low - I mean it wasn't bad, the average daily gain was 1.8 lb/day, but as several people pointed out not only are we growing bigger pigs, but finish times are often decreasing as well. As I got to thinking about it, I wondered what does this mean for manure production?

So to answer this question I needed some growth curve data to work with. As a starting point I found a table published in National Hog Farmer showing that in 1980 a typical finish pig (at least at the research site they found a useful study from) had an average daily gain of about 1.50 lb/day, took 105 days to get to market, and had in and out weights of 49 and 206 pounds respectively. The same report said that in 2001, a typical rate of daily gain was 1.95 lb/day, the pig took 102 days to get to market, and had in and out weights of 62 and 260 respectively. As a point of references, the latest PIC wean-to-finish manual suggested the expected performance of a grow-finish pig was 2.03 lb/day going from 60 to 270 lbs (103 days), with optimized performance at 2.36 lb/day going from 60 to 270 lbs (89 days)

So where does that leave us? Well, it seemed like the best place to start was with the model I developed in the last post, but modifying it with different growth curves and seeing what happened. In this work I’ll focus on just grow-finish average manure production and look at the four new cases, i.e., 1.5 lb per day, 1.95 lb per day, 2.03 lb/day, and 2.36 lb/day and going to finish weights of 206, 260, 270, and 270 lbs and using initial weights of 49, 62, 60, and 60 respectively. Just for fun I'll compare that to the manure production I estimated from the growth curve with 1.8 lb/day with a start and finish weight of 60 and 270 lbs.

In the first case (that 1980 pig) I got an average manure production of 0.96 gallon per day, or about 100 gallons of manure being produced as I get that pig to market. In the second case (that 2001 pig) I got 1.15 gallons per day, or 117 gallons of manure produced in the time it took to get the pig to market. Finally, for the average 2015 pig I got 1.17 gallons per day, or 120 gallons of manure to get that pig to market. Finally, what about that optimized 2015 pig? I’d estimate about 1.17 gallons per day from that pig, but only 104 gallons to get it to market because of the more rapid finish time.

So, bringing it all back - what does this mean to us. To me, it still looks like bigger finish weights will lead to more manure, but improved genetics that are leading to larger daily gains and faster finish times. As a result, even though we are getting more manure on a daily basis, our total volume of manure per amount of pork produced seems to be going down.

Tuesday, May 19, 2015

Nutrient Management Spotlight - The Late Spring Nitrate Test

Don't feel neglected, the latest Manure Scoop has arrived. Hope everyone is having a successful planting season; may the leaves be green and your soils fertile (from that wonderful manure).
As you might have saw the new IMMAG newsletter just came out (you can find the complete newsletter at So I'm going to borrow one of the articles I wrote for the newsletter and post it here too. This one is on using the late spring nitrate test.

This year as part of the Manure Applicator Certification program, we asked you what you were doing as part of the Nutrient Reduction Strategy to reduce nutrient loses from your farm. One of the more popular answers was switching to split fertilizer application. Some potential benefits of split fertilizer application may include reduced opportunity for nitrate loss through leaching and denitrification, the potential to use less fertilizer, having less investment in the field if you are forced to replant to soybean after weather related losses or planting delays, or even slightly delaying to get additional information about this year’s markets and growing conditions. However, there can be concerns about the costs of making a second fertilizer application trip across the field, or even if the weather will permit this fertilizer application.
Often times when we switch to split application our general plan is be to apply 50-60% of the nitrogen recommendation in the fall or early spring, and then to sidedress the remaining 40-50% into the growing crop. An alternative approach is to determine our sidedress amount using the late spring nitrate test (LSNT). The late spring nitrate test is a nitrate only soil test where soil samples are taken to a depth of 12 inches when the corn plant is 6-12 inches tall. This test is supposed to inform us about available nitrogen concentrations in the soil just as our corn growth, and nitrogen need, is about to take off. In using the results you’ll want to break your field up into different management zone, parts of the field that have similar management histories and soil types (a management zone probably shouldn’t be any bigger than 10 acres). Within each management zone 16 to 24 soil cores should be collected. As these samples are collected you need to make sure that any banded fertilizer or manure isn’t biasing your results; sampling in a pattern relative to the corn (or banded fertilizer) row can help eliminate the effect of the banded application. For example, go to the first sampling location in your management zone and pull the first soil sample in the row, then move to your next sampling spot and pull the soil sample one-eighth the distance between rows, go to your next sampling location and pull the sample one-fourth the distance between rows, and continue this pattern.
Although this may seem a little complicated, the real difficulty starts in interpreting the results. Iowa State research says corn needs 25 ppm of nitrate-nitrogen in the top 12 inches of soil to produce maximum yield; however, the interpretation of the results vary with cropping system, manure history, and even weather conditions prior to and after sampling. Selecting the “critical” soil nitrate concentration (the one you are trying to achieve) is one of the more difficult parts of using the late-spring nitrate test to make management decisions.
Table 1. Nitrogen fertilizer recommendations for corn on manures soils.
Recommended N rate
Soil Test
Excess rainfall
Normal rainfall
ppm NO3-N
lb N/acre
lb N/acre
> 20
In fields that have received manure, a “critical” soil nitrate-nitrogen concentration of 15-20 ppm nitrate-nitrogen is recommended. You’ll note that this is lower than non-manured fields; this is because the manure application provided more organic nitrogen that will be mineralized throughout the growing season and become plant available, but isn’t detected by this test. Based on your sample results you can then calculate the amount of nitrogen that would be recommended to sidedress. The formula for calculating nitrogen application is if your soil test was greater than 20 ppm then 0, otherwise (20 ppm - soil test nitrate) * 8 = lbs of N/acre to apply. Alternatively, table 1 provides a way to select a sidedress nitrogen application rate. In this table excess rainfall would be May precipitation that exceeded 5 inches, normal rainfall should be used for other cases.
As with any new fertility management program, first-time users are encouraged to experiment with the test in small areas before using it to guide fertilization on all their fields. As with most recommendations this test is intended to maximize profits when used across many years and sites, not to give the “perfect” rate in a specific year.

For more information related to using the Late Spring Nitrate Test please see, ISU PM1714-Nitrogen Fertilizer Recommendations for Corn in Iowa. More information on best management practices for reducing nutrient loss from agriculture can be found in SP435 - Reducing Nutrient Loss: Science Shows What Works.

Tuesday, May 5, 2015

Manure chemistry: What’s happening to my phosphorus

What happens to manure from the time it is excreted until it is land applied? Well, that’s simple right, we put it in some sort of storage (a pit, a lagoon, a Slurrystore, a concrete or earthen basin, or store it dry on a stacking pad) and it just stays there, waiting for us to land apply it and take advantage its fertility. Of course, it is not really that simple; manure waits for no man (or woman), while it is sitting there waiting it is changing (it is alive after all – it’s filled with microbes). Because of this, almost no matter how we store the manure, these microbes will be doing something – breaking down some of the organic material in the manure, converting elements from one form to another, or just causing things to be different.

This process can be complex and still isn’t completely understood, but we can give some generalities about what is happening and understand at least some of the jargon that gets thrown around. There are many ways to cover this topic, but what I am going to try to do is break it down by element, carbon, nitrogen, phosphorus, ect. In this post, I’m going to turn my attention to phosphorus.

When we think of phosphorus we are probably most familiar with it in some of the fertilizer compounds we can purchase, such as mono-ammonium phosphate, di-ammonium phosphate, or triple super-phosphate. Otherwise we might think of it as the plant-available ion orthophosphate. Regardless of the actual chemical form of phosphorus we purchase, the analyses of phosphorus fertilizer is usually given as phosphate (P2O5).

Alright, so back to phosphorus in manure. As we’ve discussed previously, about 70% of the phosphorus consumed by the animal will be excreted, so it ends up in the manure. The actual amount is dependent on lots of things, animal age, species, diet composition, and numerous others, but the majority of the P we feed, will be in the manure. At the time of excretion, virtually all the phosphorus is associated with the fecal, or solid, material ( > 90%), but as the manure ages and the organic material in it breaks down from microbial action, more and more of the phosphorus becomes dissolved in the liquid fraction. For example in swine manure from a deep-pit, a good guess is that around 75% of the phosphorus will be dissolved reactive phosphorus (ortho-phosphate).

Although numerous fractionations schemes can be used to fractionate the manure phosphorus into pools of different characteristics and availabilities, the use of this information remains academic. From a practical standpoint, there are really four basic types of phosphorus in manure: dissolved inorganic phosphorus, precipitated inorganic phosphorus, and dissolved organic phosphorus, and particulate organic phosphorus.

Essentially all the dissolved, inorganic P in manure exists in the form of orthophosphate (or other derivatives of phosphoric acid (H3PO4, H2PO4-, HPO42-, and PO43-). The exact form of this phosphate is dependent on the pH of the manure, but most of it will be either H2PO4- or HPO42- under normal pH conditions. This phosphorus is essentially equivalent to what would be purchased if you were to buy a mineral phosphorus fertilizer. As we store manure, two things can happen to this phosphorus, it can undergo biological immobilization and be incorporated into an organic molecule or it can react with something in the manure (often iron or calcium) and become a solid material (it is precipitated).

When we focus on the organic phosphorus, there are again two types, particulate phosphorus and dissolved organic phosphorus. In general, the flow is from organic phosphorus towards dissolved reactive phosphorus, this happens through a process called mineralization. Mineralization is just a way of saying broken down from an organic form (associated with carbon) to an inorganic from (usually H2PO4- or HPO42-). This process is mediated by micro-organisms living in the manure, as these “bugs” eat carbon to provide themselves with energy they break off the phosphorus and either use it to grow their cells, or release it into as dissolved phosphorus into the manure.

The final type of phosphorus is precipitated phosphorus. This is inorganic phosphorus that has reacted with something else in the manure and formed a particle. In general, I tend to think of this of being of less importance in manure, but in some cases we might add iron to our manure (as a way to acidify it – think for instance alum or ferric sulfate as amendments in poultry litter) and this makes it so our manure can hold less phosphorus in dissolved forms.

So now that we have talked about forms, where does this leave us? What we have seen is that phosphorus can change forms, but all these forms stayed in the liquid. This means that if the phosphorus was there to start with, it will be there when we land apply it (unless we spill some or if rainwater leaches through it and then flows away). However, just because it is there, doesn’t mean we’ll be able to capture it an land apply it. Since the particulate phosphorus is attached to solids, it is distributed like the solids. This means that the sludge rich manure often will have higher phosphorus contents and watery manure from the surface will have less. To get uniform phosphorus concentration we want to either get those solids evenly mixed in the manure, or to get as much of the phosphorus as possible into a dissolved form.