Compost, Stockpiling, and Fresh Manure – What is happening?

Handling systems affect manure nutrient levels and forms by influencing gaseous emissions, exposure to runoff and leaching, and as a result can influence a manures ability to supply crop nutrients when land applied. Traditionally, on feedlots in Iowa, pens are cleaned periodically and then the manure is stockpiled, either near the lot or in a field and then eventually land applied. In some cases, lots might be scraped frequently and the manure land applied almost immediately. So what difference does each of these make to the manure properties?

 Freshly excreted manures are often very wet, which is especially true during wet periods of the year, like after rainstorms or snowmelt. These wet conditions generally make long-distance transport difficult or almost impossible. This also requires field be available for land application throughout the year, and as such, has generally fallen out of favor as it means the ground can’t be used to support crop production throughout the summer. Though in some cases, through the use of varied rotation, usually including some hay ground, land application can be accomplished. As a result, stockpiling manure becomes more prevalent. In this practice, manure is cleaned form the pen surface and then heaped into stacks, or stockpiles, to await reloading, hauling, and spreading. Stockpiling is generally a passive process but helps in matching manure application timing to better align with typical crop production practices. A third alternative is composting. Composting is an aerobic treatment where the manure is managed so the pile continues to have oxygen in it, providing conditions for microbes and bacteria to break down the material. Composting uses mixing to make a more uniform pile and causes the material to heat, often killing pathogens within the manure and inactivating weed seeds.

Figure 1. Stockpiled beef cattle manure.

When looking at the results, there are two things to look at. The first is the nutrient concentrations and the second is the mass balance.  When it comes to the concentrations, this tells us how far we can afford to move the manure. Higher concentrations mean we can afford to haul it a bit further as it is more nutrient dense. The results indicate that both stockpiling and composting increase the nutrient density relative to fresh manure. Much of this change is due to water loss, so we just aren’t hauling around as much water.

However, if you look at the results a bit closer, you’ll see we actually end up with less nitrogen and phosphorus to land apply from both stockpiling and composting. This occurs because some of the nutrients are lost due to volatilization of the nitrogen during the storage process.  Some of the loss of is due to dust and rainfall runoff during stockpiling and composting for phosphorus. Taken together, these results would show that if we need to transport manure long distances, composting might be a good option, but if we are using the manure on farm and want all those nutrients, stockpiling might be a better choice for your operation. Of course additional factors like consistency of the manure, killing pathogens, or inactivating weed seeds might be additional factors to consider. (these results are a summary of Larney et al., 2006 – Fresh, stockpiled, and composted beef cattle feedlot manure: nutrient levels and mass balance estimated in Alberta and Manitoba).

Table 2. Nutrient concentration of fresh, stockpiled, and composted beef cattle manure.

	Dry Matter	Water	Total Carbon	Total Nitrogen	Inorganic Nitrogen	Total P
	lb/ton	lb/ton	lb/ton	lb/ton	lb/ton	lb/ton
Fresh	698	1302	216	11.2	2.6	3.2
Stockpiled	856	1144	212	13.2	3.8	4.6
Composted	1280	720	208	18	1	6.6

Table 3. Mass comparison of fresh, stockpiled, and composted beef cattle manure.

	Initial Mass	Final Mass	Dry Matter	Water	Total Carbon	Total Nitrogen	Total P
	lb	lb	lb	lb	lb	lb	lb
Fresh	1000	1000	349	651	108	5.6	1.6
Stockpiled	1000	636	272	364	67	4.2	1.5
Composted	1000	328	210	118	34	3.0	1.1

Manure Application Uniformity

Maybe you have seen some tweets and pictures about manure application uniformity testing over the past years, or hopefully seen some information about upcoming field days where uniformity is going to be a key topic. You might be wondering why we are making a big deal about this, but when it comes to using manure as a fertilizer effectively, understanding how uncertainty impacts your decisions is critical for making the best management decision.

So why should we worry about manure application uniformity? Nitrogen for crop growth can come from multiple sources, the soil organic matter can mineralize and in doing so release mineral nitrogen for the plant. The remaining nitrogen needed to support crop growth comes from applied fertilizer. Years of research have gone into characterizing how crops would respond.  If you take a look at the Nitrogen Rate Calculator it will give you an idea of how a corn crop (in this case corn following soybeans) responds to the addition of nitrogen. What this graph (figure 1) shows is how the addition of nitrogen causes corn to respond. What the figure demonstrates is that we want to apply somewhere around 150 lb N/acre, if we are less than this the yield goes down, if we apply more than this we see minimal yield improvement.

Figure 1. Corn response to added nitrogen for Iowa conditions for a corn crop following soybean.

So what does this all have to do with manure application uniformity? When we are trying to hit 150 lb N/acre does that mean we just need to average that for the field? Probably not, it’s about getting a condition where it’s uniform over the whole field (yes, there might be some soil variations and every field has a bit different response to nitrogen, and weather conditions matter so some year’s crop response to nitrogen is much more drastic than others, but for the sake of argument, let’s work with this curve to see what it means).

For fun as we think about the math behind this problem, let’s assume we have corn planted on 30-inch spacing, our manure toolbar also has 30-inch spacing, and that corn roots only get their nitrogen from the manure application band that was placed next to that corn row. Then let’s figure we applied 150 lb N/acre from liquid swine manure that tested 50 lb available N/1000 gallons, so we were applying 3000 gallons an acre.

Now think about two pieces of equipment, one has a knife-to-knife coefficient of variation of 35% at this application rate, the other has a coefficient of variation of 10%. In both cases let’s figure an 8-knife setup. To give you an idea what this looks like in terms of nitrogen application rates achieved by the different knives and the impact different levels of uniformity have on crop yield let’s run through an example. Both of the tools in this example hit the right application rate on average, but how they do it, in terms of evenness across the toolbar is very different. What I want you to start thinking about is what would this mean for your crop yield from row-to-row and nitrogen leaching.

Table 1. Nitrogen and manure application rates for two pieces of application equipment that that achieve different levels of manure application uniformity.

Knife #	N Application (lb N/acre)	N Application (lb N/acre)	Application Rate (gallons/acre)	Application Rate (gallons/acre)	% of Desired Rate	% of Desired Rate
1	100	150	2000	3000	67	100
2	135	160	2700	3200	90	107
3	165	170	3300	3400	110	113
4	210	160	4200	3200	140	107
5	220	150	4400	3000	147	100
6	180	140	3600	2800	120	93
7	120	120	2400	2400	80	80
8	70	150	1400	3000	47	100
Average	150	150	3000	3000	100	100
St. Dev.	53	15	1060	302	35	10
COV	35	10	35	10	35	10

So let’s do a nitrogen example, using figure 1 (the nitrogen response curve) you can make an estimate of the corn yield that would be achieved from each of the knives (and if you assume a maximum yield of around 200 bushels an acre) can figure out what the field level yields would be.  So if you work through this math, you can find a few interesting results (table 2). Even though we were putting on the same amount of nitrogen on in both cases, because of variation from knife-to-knife we get different average yields per acre. In the case of corn following soybean, yields increased by 2 extra bushels per acre yield from the improved distribution and in the case of continuous corn about 4 extra bushels per acre. But there are other things to notice, the coefficient of variation in corn yield is always much lower than that in the nitrogen application rate. The soil supplies some of the nitrogen and this dampens out the response making everything a bit more uniform, but one thing to keep in mind is that early in the growing season the response might be more visually drastic than what final yields end up showing. Overall I think this asks an interesting question -how good is uniform enough, how does application uniformity uncertainty compare with other uncertainties in crop production, and how does this information help us make better manure decisions?

Table 2. Impact of nitrogen application uniformity on crop yield in corn-soybean (CS) and continuous corn (CC) rotations for machines with coefficients of variation in their application of 35% (left) and 10% (right)

Knife #	Corn Yield (CS) (bu/acre)	Corn Yield (CS) (bu/acre)		Corn Yield (CC) (bu/acre)	Corn Yield (CC) (bu/acre)
1	187	194		162	179
2	193	195		175	182
3	196	196		183	184
4	198	195		190	182
5	198	194		191	179
6	197	193		186	177
7	191	191		170	170
8	178	194		146	179
Average	192	194		175	179
St. Dev.	7	2		16	4
COV	4	1		9	2

To learn more about this topic and how you can get the most benefit from your manure make sure you register for one of our four field days, get a free lunch, get your manure questions answered, and learn how to set yourself up to maximize the benefit of manure on your farm this fall.