Tuesday, January 31, 2017

Manure Application Injectors - What do we need?

When it comes to selecting the right manure injection tool for the job there are many variables; the application rate, the amount of power to pull it, the soil type and conditions, the desired amount of residue cover left, or even the speed we can pull it through the field. All these constraints are important to consider, but the one we are going to discuss today is how much space do we need to create in the soil to have room to get the manure in.
It is intuitive that injection tools that create a larger cavity below the ground for the manure are capable of achieving good injection at higher application rates if the soil conditions are right, but they also require more power to pull, so trade-offs are required. One newer example injector is shown below. This one uses a fluted coulter to open an injection cavity.

Figure 1. A fluted disc manure injector followed by two concave discs. The fluted coulter opens the injection trench while the discs close and cover the injection furrow.

When it comes to injection, we want no overflow of manure out of the injection cavity. Two things are to achieve this, the first is that we must not have overflow manure. Overflow manure is when our injection furrow isn’t big enough to hold all the manure and as a result, it bubbles back to the surface. To avoid this the tool capacity has to be greater than the application rate (we’ll discuss in more detail below). The second thing we have to avoid is in-furrow manure; this manure stays in the injection furrow like we want, but we fail to cover up the furrow after putting the manure in it. Avoiding these two conditions limits the manure from air exposure, keeping odor and ammonia volatilization low. The example injector shown in figure 1 demonstrates both of these operations. In this case, the fluted coulter cuts the injection cavity. To be successful this cavity must be big enough to hold the manure we are putting down. The two concave trailing discs then cover the applied manure so we can’t see the furrow. To be successful both parts must be set correctly for the soil conditions and manure application rate we are trying to achieve. Below (in figure 2) you can see two examples of manure injection, the one on the left where the manure is covered, and the one on the right where we coverage of the injection furrow wasn’t achieved.


Figure 2. Good injections as compared to in-furrow manure injection.

So how can we determine how much injection capacity is needed for our manure? Well, it’s based primarily on two factors, the application rate you are trying to achieve and your tool spacing. Higher application rates require more capacity, while narrower spacing reduces required capacity (because each knife has to put down less manure per acre). Next, we will take a look at the requirement for two reasonable manure application rates, a swine finishing manure applied at 3,000 gallons an acre and a dairy manure applied at 12,000 gallons an acre. In both cases, we will assume the manure injector are on 30-inch centers.

The first thing we need to do is calculate the amount of manure each injector will receive. In the 3,000 gallon per acre case this is calculated by multiplying the application rate (3000 gallons per acre) by the tool spacing (2.5 feet), dividing by 43,560 to convert from acres to feet, multiplying by 0.134 to convert from gallons to cubic feet, and then multiplying by 144 to get the injection cavity cross-sectional area in feet. For the swine manure, we need about 3.3 square inches, as the dairy manure application rate was 4 times as much, four times this much area, almost 13.25 square inches, is needed.

What does this mean in practice? Let’s assume we are using the fluted disc (or similar to that shown in figure 1). Based on our soil conditions (current soil moisture, soil structure, residue cover, and the down pressure on our toolbar) it is cutting a cavity 4 inches deep by 2.5 inches wide, is our tool capacity sufficient for these application rates? The tool capacity is equal to the cross sectional area we are cutting so in this case it would be 4 inches times 2.5 inches, or approximately 10 square inches, which is enough for the deep pit swine manure example (3.3 square inches required), but not enough for the dairy manure example (13.25 square inches required).

So what options are there to increase capacity? A few things could be done: (1) We could reduce the manure application rate to be in line with what the equipment can handle (to achieve the desired application rate we would need to apply twice), (2) we could reduce the tool spacing as this reduces the amount of manure each tool needs to inject, (3) we could try running the tool deeper to get a larger cavity, or (4) we could use a tool with a larger area, potentially a knife or sweep.

Monday, December 19, 2016

Winter Manure Application – What’s the Science Tell Us?

Certainly one discussion point when we talk about using manure as fertilizer is that we want to try to match manure nutrient availability to crop nutrient need and demand. At first glance this might seem like well nothing is growing in the winter, why would we put manure on then? Although some reasons may exist, such as well its better than having a storage overflow, or it reduces some compaction risk especially if we’ve had a wet fall or may have a wet spring, but I think we can all recognize that it some ways the risk of nutrient loss may be higher. However, that means we need to really know and understand what causes the risk on how to best minimize it if winter manure application is necessary. So what science is out there?

Let’s start with this, if it is risky why might we still practice winter manure application? In my mind there are probably three driving factors for this: 1. Reduced manure storage structure size/management of the storage structure, 2. Time available for manure application, and 3. Compaction risk. Constructing a storage is an expense, it may offer vale in that it improves our manure application timing, but accounting for this value can be difficult. Spring and fall are busy times on the farm and in sometimes we find ourselves in a situation with more hours than work and as winter generally has less demands on our time, it becomes a manure application window. Finally, frozen soils offer more support for heavy equipment and thus reduce compaction risk.
The downside of winter manure is risk of nutrient transport. Nutrient movement is always driven by water movement – so what makes winter application riskier? Well, given the last week winter might seem cold, but generally winter is a mix of freezing and thawing, and these freeze-thaw cycles affect soil structure, infiltration, and water movement. Often what you see happen is freezing and thawing break up surface soil aggregates increasing crusting (or even getting the top layer of soil filled with water and freezing solid).  This make is more difficult for water to move through the soil and makes it harder to resist erosion. But it’s really not as cut and dried as that, way back in 1955 they identified four types of frozen soil structures: concrete, honeycomb, stalactite, and granular. Of these structures, it’s the concrete structure that really slows water infiltration. Unfortunately, this is also one of the more common structures to develop especially if soils are wetter when they freeze. This is one of the reasons that if winter manure application is necessary, earlier application (in the winter) is safer, because after several freeze-thaw cycles soils tend to be wetter from the snow water they have infiltrated.

One thing that all the studies of manure application to frozen ground have in common is variability. Every situation is different – the weather, the soil, the manure characteristics all play a role. However, what we do know is that the response is typically driven by the hydraulic conditions. If rapid snowmelt or rainfall is imminent, don’t apply. Runoff will move manure nutrients.  Anticipate problems early in the winter and get manure on then, especially before snow cover develops or before freeze-thaw cycles cause the soil to get wetter and refreeze. If applications must be made later in the winter, choose fields that get the manure closer to the soil surface and look for weather conditions when rain and melt is not imminent.

Tuesday, December 6, 2016

IMPACT: Utilizing Manure Value



Manure - An important part of the fertility puzzle. ISU is working hard to and hopefully help make a positive impact on how farmers are using manure.

Tuesday, November 22, 2016

Update! Yield Goal compared to Maximum Return to Nitrogen

A few years ago I wrote a post discussing both of these methods for determining nitrogen needs. Since then we've had a few more crop years. This means county yields have been updated and there are newer records in the Maximum Return to Nitrogen calculator so I figured it was time for another look.

A manure management plan is a tool for animal farmers that describes how they plan to place and use their manure nutrients for crop production. The process of filing out a manure management plan makes producers identify the amount of manure they expect their farm to produce, estimate the nutrient concentration in the manure, determine the number of acres that are required for land application, and then detail the amount of manure that will be applied to each available acre. In Iowa these plans are based both on the nitrogen needs of the crop as well as the phosphorus index for each field.

Current Iowa law states, “Nitrogen-based application rates shall be based on the optimum crop yields and crop nitrogen usage rate factor values or from other credible sources. Nitrogen-based manure rates shall account for legume production in the year prior to growing corn or other grass.” Therefore, I’m going to take a minute to compare these options to try to better understand what they mean for manure nutrient management. The first approach to calculating the nitrogen application rate desired to support crop production is the yield goal method. In this approach, the farmer determines the optimum yield of the crop and then multiplies the yield times a crop nitrogen usage rate factor for the specific crop. The required nitrogen rate is then adjusted for ammonia losses during application, the nitrogen availability of the manure, and any previous legume crops grown in the field. The optimum yield for each crop may be set to either the average of the last 5-year county yields plus 10 percent or the average of the highest 4 out of the last 5-year county average.

The other approach is the maximum return to nitrogen. This approach uses economic return to N application found in research trials as the basis for the suggested N rate. The average of N responses accumulated from a population of N rate trial sites is used to estimate the point where net return is the greatest (an example of yield response curves shown below). That is, it identifies the nitrogen the point where the next added unit of fertilizer results in a yield increase that based on the value of corn is equal to the price of that unit of nitrogen. This may sound complicated, but a tool to help with these calculations is available at: http://cnrc.agron.iastate.edu/. Input a corn price, a nitrogen fertilizer price, select your crop rotation (corn-soybean or continuous corn), and select which state or fertilizer region you are in, and the program generates an estimate of what fertilizer rate will give you your maximum return to nitrogen.


So now we get to the important part, how do these two methods compare.
To determine the maximum return to nitrogen we have to estimate a nitrogen price (I used $0.36 per pound) and a corn price (I used $2.82 per bushel) for both a continuous corn rotation and a corn soybean rotation (fertilizer recommendation for the corn phase).

Recently, the Corn Nitrogen Rate Calculator split the state of Iowa into two regions – Main Iowa area, which includes majority of the state, and a Southeast Iowa area, which includes Soil Regions 21, 22, and half of 17 (generally south of highway 92). In the main Iowa area, the results indicated in a corn soybean rotation my maximum return to nitrogen would occur at an application rate of 126 (112-140) lbs N/acre and at  176 (159-190) lbs N/acre in the continuous corn rotation (numbers in parenthesis produce a profit estimated to be within $1 per acre of the maximum return to nitrogen). In the Southeast Iowa region, my maximum return to nitrogen would happen at 142 (129-159) lbs N/acre in a corn soybean rotation and at 192 (179-211) lbs N/acre in a continuous corn rotation. I compared this to the amount of nitrogen that would be applied if the yield goal method was used (the ideal yield was set to the higher of the average of the last 5-year county yields plus 10 percent or the average of the highest 4 out of the last 5-year county average). The manure application you’d pick based on yield goals is summarized in the table below (end of the post).

When I compared the results of the maximum return to nitrogen and yield goal approaches for nitrogen application rates, I found that in 82 of Iowa’s 99 counties the maximum return to nitrogen resulted in a lower nitrogen application rate than the yield goal method in a corn soybean rotation. In these cases, the yield goal method resulted in a nitrogen application rate within $1 of the profit produced at the maximum return to nitrogen in 18 of the counties, a lower nitrogen application rate in 11 of the counties, and a higher application rate in 70 of the counties as compared to the maximum return to nitrogen approach. Similarly, in the continuous corn rotation the results showed that 15 counties produced application within the $1 max profit nitrogen application bracket, a lower nitrogen application rate in 15 of the counties, and a higher application rate in 69 of the counties as compared to the maximum return to nitrogen approach. These comparisons are summarized in the figure of Iowa shown. In the counties left white, the maximum return to nitrogen recommended nitrogen application rate was less than that calculated for the yield goal approach for both continuous corn (CC) and corn soybean (CS) rotations. In the green-shaded counties, the yield goal method predicted a nitrogen application rate within the range provided by the maximum return to nitrogen concept for either the CC, CS, or both, depending on the shade of green as specified in the figure. Finally, in the counties shaded orange or red the maximum return to nitrogen approach suggested a higher nitrogen application rate than what would be estimated based on the yield goal approach.


  

 So which method should you use? I think both methods have some strengths and limitations. Conceptually the yield goal method seems really nice as it’s essentially a mass balance approach where we try to supply the amount of nitrogen we will be removing with the harvested portion of the plant as well as what we might be losing to other places. However, in practice, its accuracy is limited by our ability to accurately estimate increased nitrogen cycling resulting from a rotation effect with a legume (especially soybean in the corn-soybean rotation) and in general it doesn’t predict the application rate that will maximize our profit in using nitrogen. On the other hand, in the maximum return to nitrogen approach we have a much better chance of applying at the rate that maximizes the nitrogen value of the manure. However, in addition to just nitrogen, manure also supplies other nutrients like phosphorus, potassium, and organic matter which may impact how we value this nutrient source. Additionally, in some high yield cases, the maximum return to nitrogen approach may recommend nitrogen application rates below what is being removed with the harvested corn grain (about 175 bu/acre in a corn soybean rotation and 232 bu/acre in a continuous corn rotation).

So that’s a fair amount of discussion with no solid answer about which method to use. I think that the maximum return to nitrogen concept is preferable as it attempts to make better use of our nitrogen resources. In general, I’d prefer to write my manure management plan with using the yield goal method, but when it comes time to apply my manure, I’d collect my manure sample, determine its nitrogen content, and adjust my application rate to try to achieve an application within the range the maximum return to nitrogen approach suggests. One benefit of doing this is if it looks like a great growing season we'd still be able to consider side dressing some nitrogen onto our crop and being within the bounds we set in our manure management plan.

Additional resources for selecting your nitrogen application rate can be found at:
PM-1714 “Nitrogen Fertilizer Recommendations for Corn in Iowa” available at: https://store.extension.iastate.edu/Product/Nitrogen-Fertilizer-Recommendations-for-Corn-in-Iowa
PM-2015 “Concepts and rationale for regional nitrogen rate guidelines for corn” available at: https://store.extension.iastate.edu/Product/Concepts-and-Rationale-for-Regional-Nitrogen-Rate-Guidelines-for-Corn


County
Corn
Soybean
N use factor
Nitrogen Application -Corn-Soybean
Nitrogen Application - Continuous Corn
(bu/acre)
(bu/acre)
(lb N/bu)
(lb N/acre)
(lb N/acre)
Adair
163
50.8
1.2
146
196
Adams
165
50.6
1.2
148
198
Allamakee
185
57.1
1.2
172
222
Appanoose
139
42.3
1.2
125
167
Audubon
181
55.4
1.1
149
199
Benton
181
57.3
1.2
167
217
Black Hawk
184
55.6
1.2
171
221
Boone
189
53.4
1.2
177
227
Bremer
191
57.2
1.2
179
229
Buchanan
189
56.9
1.2
177
227
Buena Vista
190
54.1
1.2
178
228
Butler
187
51.6
1.2
174
224
Calhoun
183
51.6
1.2
170
220
Carroll
161
54.5
1.2
143
193
Cass
181
54.0
1.1
149
199
Cedar
195
62.0
1.2
184
234
Cerro Gordo
181
52.7
1.2
167
217
Cherokee
201
60.8
1.1
171
221
Chickasaw
186
53.7
1.2
173
223
Clarke
138
44.4
1.2
121
166
Clay
196
56.1
1.1
166
216
Clayton
196
61.0
1.2
185
235
Clinton
196
62.1
1.2
185
235
Crawford
188
57.0
1.1
157
207
Dallas
181
53.2
1.2
167
217
Davis
143
42.6
1.2
129
172
Decatur
146
43.1
1.2
132
175
Delaware
192
58.1
1.2
180
230
Des Moines
183
56.3
1.2
170
220
Dickinson
186
53.1
1.2
173
223
Dubuque
201
62.6
1.2
191
241
Emmet
192
52.3
1.2
180
230
Fayette
194
58.1
1.2
183
233
Floyd
183
54.1
1.2
170
220
Franklin
195
54.6
1.2
184
234
Fremont
180
53.2
1.1
148
198
Greene
180
51.0
1.2
166
216
Grundy
197
61.6
1.2
186
236
Guthrie
169
51.0
1.2
153
203
Hamilton
181
52.1
1.2
167
217
Hancock
191
53.8
1.2
179
229
Hardin
192
56.5
1.2
180
230
Harrison
182
51.3
1.1
150
200
Henry
174
55.4
1.2
159
209
Howard
187
54.5
1.2
174
224
Humboldt
189
53.2
1.2
177
227
Ida
199
59.7
1.1
169
219
Iowa
190
57.4
1.2
178
228
Jackson
186
58.7
1.2
173
223
Jasper
192
57.5
1.2
180
230
Jefferson
161
49.4
1.2
144
193
Johnson
189
55.9
1.2
177
227
Jones
186
60.1
1.2
173
223
Keokuk
175
54.3
1.2
160
210
Kossuth
195
54.3
1.2
184
234
Lee
156
49.4
1.2
138
187
Linn
184
56.5
1.2
171
221
Louisa
185
56.5
1.2
172
222
Lucas
138
45.6
1.2
120
166
Lyon
199
61.2
0.9
129
179
Madison
160
49.0
1.2
143
192
Mahaska
186
55.7
1.2
173
223
Marion
170
53.3
1.2
154
204
Marshall
192
60.4
1.2
180
230
Mills
179
51.9
1.1
147
197
Mitchell
188
53.5
1.2
176
226
Monona
170
51.4
1.1
137
187
Monroe
142
44.9
1.2
126
170
Montgomery
173
51.8
1.1
140
190
Muscatine
185
59.1
1.2
172
222
O'Brien
204
61.9
1.1
174
224
Osceola
202
57.9
1.1
172
222
Page
166
51.2
1.1
133
183
Palo Alto
193
53.9
1.2
182
232
Plymouth
188
56.9
1.1
157
207
Pocahontas
196
53.5
1.2
185
235
Polk
181
54.4
1.2
167
217
Pottawattamie
188
54.8
1.1
157
207
Poweshiek
193
57.1
1.2
182
232
Ringgold
139
44.8
1.2
122
167
Sac
185
55.7
1.1
154
204
Scott
190
63.5
1.2
178
228
Shelby
192
56.9
1.1
161
211
Sioux
199
63.7
1.1
169
219
Story
179
52.6
1.2
165
215
Tama
188
59.1
1.2
176
226
Taylor
158
47.1
1.2
143
190
Union
153
48.4
1.2
135
184
Van Buren
155
46.9
1.2
139
186
Wapello
159
49.1
1.2
142
191
Warren
158
50.9
1.2
140
190
Washington
183
58.3
1.2
170
220
Wayne
145
43.4
1.2
131
174
Webster
191
53.9
1.2
179
229
Winnebago
190
53.0
1.2
178
228
Winneshiek
191
55.4
1.2
179
229
Woodbury
187
54.2
1.1
156
206
Worth
187
53.6
1.2
174
224
Wright
194
53.7
1.2
183
233