Friday, March 19, 2021

Manure Scoop: The Value of Real Time Nutrient Sensing

 

A few years ago, I became interested in the value of manure sampling and how obtaining good information helped us make better nutrient management decisions. I tried to use the theory of value of data to determine how much a manure sample was worth. Read a summary here.

 

Many factors cause variations in manure's average nutrient concentration: diet, housing type, manure storage type, environmental conditions, management techniques, and treatment practices. Just as critically, our ability to agitate and create a uniform, homogeneous mixture is often limited by our ability to stir manure storages.

 

A repeated sampling at five manure storages was used to assess the average, standard deviation, and coefficient of variability. The data were summarized as averages across the sampling data set to determine the variability in manure concentrations from each manure application event. Average manure nutrient concentrations were 28, 16, and 21 pounds of N, P, and K, respectively, per 1,000 gallons with standard deviations of 4, 7, and 3.

 

In determining the manure test's value, it is essential to understand how a farmer can use the information gained from the test results, i.e., how having this information alters the farmer's nutrient management and affects the farm profit. This is a complex topic, as almost limitless possibilities exist. This evaluation assumed the manure application method would be either injection or immediate incorporation to maximize N utilization. Additionally, we assumed best management practices for manure application timing were followed. As a result, the yield response to available N (defined here as the sum of ammonia N and organic N expected to mineralize in the first growing season) would be the same as the yield response to mineral N fertilizer. Finally, we limited crop rotation choices to continuous corn and corn-soybean rotations, as these represent the dominant rotations in the upper Midwestern U.S.

 

Our methodology was to estimate the profit that would have been made if the manure was assumed to have a "typical" nutrient composition and then to compare this to the profit generated if the actual nutrient composition was known. To make this evaluation, an economic model was developed as an Excel spreadsheet. The model compared the costs and revenue of corn production. Corn yield was calculated as the product of maximum yield and the estimated percent yield that was achieved.

 

For a corn-soybean rotation where the manure is going to corn, this means that the real-time nutrient correction for manure would be worth approximately $3.13 per acre. However, in a continuous corn rotation, which is more sensitive to nitrogen application in terms of crop response, it would be worth around $4.29 per acre. However, understanding just how big this variability is from load-to-load or pass-to-pass is critical for putting value to this technology.

Wednesday, January 20, 2021

Manure Nitrogen Availability from Manures and N Application Recommendations Around the Midwest

 

How much nutrient is there? While it seems a simple question, with manures where the only thing consistent about them is inconsistency, the answer isn't always easy. The place I like to start is what does 'availability' mean.

 I define availability as nitrogen present in a form able to be used. When talking about manures, we typically mean that this percent of the nutrient will cycle through a form that plants can use.

I'll use the term supply to specify how much is added; less the fractions are lost to volatilization, leaching, denitrification.

 Within the state of Iowa, our go-to document on the subject of nutrient availability is "Using Manure Nutrients for Crop Production," specifically table 1. A second correction is made for ammonia volatilization losses based on the type of manure (as this impacts the amount of nitrogen that is in the ammonium at the time of application) and the application method (as this influences how long the manure it's on the surface and is exposed for potential losses.

Table 1. Iowa Suggested Manure Nutrient Availability.

Manure Source

1st Year

2nd Year

3rd Year

Beef Cattle (solid or liquid)

30-50

10

5

Dairy (solid or liquid)

30-50

10

5

Liquid swine

90-100

0-10

0

Poultry

50-60

0-10

0

Table 2. Iowa Suggested Manure Nitrogen Volatilization Correction Factors.

Application Method

Incorporation

Volatilization Correction Factor

Direct Injection

-

0.98-1.00

Broadcast (liquid/solid)

Immediate Incorporation

0.95-0.99

Broadcast (liquid)

No Incorporation

0.75-0.90

Broadcast (solid)

No Incorporation

0.70-0.85

Irrigation

No Incorporation

0.60-0.75


Iowa nitrogen management recommendations either come from the Yield Goal Method or the Maximum Return to Nitrogen concept. In the Yield Goal Method. As a base case for comparison, I will look at deep-pit swine manure testing at 50 lbs/N per 1000 gallons. In Iowa, the average yield times 1.1 is 215 bushels/acre of corn and 56 bushels/acre of soybean. Assuming a nitrogen use factor of 1.2 lb N/expected bushel of corn and a soybean credit of 50 lb N/acre, nitrogen application rates would be 208 lb N/acre to the corn phase of a corn-soybean rotation and 258 lb N/acre in a continuous corn rotation. The Corn nitrogen calculator would be 140 lb N/acre in a corn-soybean rotation and 188 lb N/acre in a continuous corn rotation. I'll show a figure of these results in just a second, but I also wanted to compare them to two neighboring states, Illinois and Minnesota. Second-year N availability was estimated in the continuous corn rotation as what didn't mineralize the first year.

 Illinois uses the same nitrogen volatilization recommendations as Iowa (they come from Midwest Plan Service) and uses the Midwest plan service method to estimate nitrogen availability from the manure. For swine manure with approximately 70% of the nitrogen in the ammonia form and a 35% mineralization factor, 80% of the nitrogen will be available in the first year. The second-year availability for the continuous corn rotation is estimated to be half of the amount mineralized from the organic nitrogen fraction, which amounts to approximately 2 pounds. The desired Nitrogen application rate for Illinois is selected using MRTN, but rather than the optimum value, the maximum within a $1 profit is recommended.

Minnesota suggests that 150 plant available pounds of N per acre should be applied in a corn-soybean rotation and 195 in a continuous corn rotation. In Minnesota, they don't separate corrections for availability and loss but incorporate both into a correction factor. They also provide a second-year availability factor of 15% for swine manure.

What does this mean? I put together this figure of nitrogen application rate recommendations, two for Iowa (Yield Goal and MRTN), to compare the suggested rates for Minnesota and Illinois. Note this is only for nitrogen and doesn't consider any phosphorus limitations that may restrict manure application.



Figure 1. Summary of recommended manure application rates for the corn phase of a corn—soybean rotation. Swine manure with 50 lb N per 1000 gallons, 70% ammonium with error bars set based on high and low suggestions for nitrogen availability and volatilization losses suggested within each state.

 
Figure 2. Summary of recommended manure application rates for a continuous corn rotation. Swine manure with 50 lb N per 1000 gallons, 70% ammonium with error bars set based on high and low suggestions for nitrogen availability and volatilization losses suggested within each state.

 As we look at this data, I came home with a few takeaways. The first being, the factor ammonia loss with broadcast application in Minnesota is much higher than in Iowa and Illinois, based on the Midwest Plan Service Methods. Iowa and Illinois have volatilization factors of 15-30%, while Minnesota uses ~45%. The difference in volatilization assumption makes a substantial change in the recommended application rate.

The two recommendations for Iowa make an interesting comparison. When using the yield goal approach, Iowa's recommendations are similar to those provided with the Illinois method. In the case of continuous corn, the Yield Goal method for Iowa tends to be slightly higher, while in the corn-soybean rotation marginally lower, but overall, the results are similar.

When we look at the recommendations resulting from using the MRTN for Iowa, the results are more comparable to the Minnesota recommendations. In the corn-soybean phase, Iowa's MRNT recommendation would be lower thanks to both the lower mineralization suggestion and the slightly higher N application recommendation.

Overall, these results indicate that Iowa's approaches place us within the context of the surrounding states.