AgDM newsletter article, September 1998

Swine manure management practices

Bruce Babcockby Bruce Babcock, Professor of Economics, 515.294.5769, babcock@iastate.edu

Farmers have long known that integration of livestock and crop production systems offers significant economic benefits. The manure from livestock was recycled back to the land as a source of crop nutrients and soil amendments.  The other benefit of an integrated system is that livestock producers have a place to dispose of accumulated manure in a cost-effective and environmentally sound manner.

Without ready access to cropland, two situations can arise:

Value of swine manure

Swine manure offers Iowa’s farmers both short and long-term benefits. 

Short-term benefits

In the short-run, manure nutrients can replace fertilizer applications. ISU researchers estimate the gross value of swine manure as a source of nitrogen, phosphate, and potash is often as high as $2.20 per hog. This amounts to about $5,500 per year per 1,000-head finishing house. 

The gross value of swine manure as a source of N, P, and K, is often as high as $2.20 per hog.

Long-term benefits

The long-term benefit of swine manure is maintenance of a soil’s productivity from the addition of soil organic material and nutrients. Most Iowa farmers do not include this value when evaluating their management strategies because the benefits of maintaining and/or enhancing soil tilth from a year’s application of manure are small and occur in future years. But annual applications of animal manure can maintain soil productivity in the long run even under intensive cropping systems. 

Capitalizing on manure’s value

Do Iowa’s farmers capitalize on the value of manure in their cropping programs?  It would not be surprising if many do not because of the obstacles to overcome before the potential value of manure can be realized. 

Current management practices

A survey of current swine manure management practices in Iowa was conducted recently by the Iowa Agricultural Statistics Service for the ISU Department of Economics.  Market hog manure generated from various types of manure handling systems is shown in Table 1.

Table 1.  Manure generated from market hogs by type of manure system.

Type of system

Percent

Solid manure

31%

Deep pit system

36

Outdoor earthen basins

7

Outdoor formed storage *

9

Anaerobic lagoons

7

Other systems **

9

*Concrete basins or above ground steel tanks
** Primarily pasture systems

Solid manure

Survey results indicate that 72 percent of Iowa’s hog producers handle some solid manure on their farms.  This represents about 31 percent of the total swine manure produced by market hogs in Iowa.

Solid manure is most often generated in open front feedlot systems where the manure is periodically scraped and transported to fields. Most producers who handle solid manure control runoff by creating barriers that trap the manure solids. These solids are then transported and spread on nearby fields. Typically, a producer handling solid manure land-applies the manure more frequently than a producer who uses a liquid system, which means producers using solid systems must have application fields that are available year round.  This is confirmed in Table 2.

Table 2. Time of application of solid manure

Time of year

Percent

Spring

30%

Summer

15

Fall

31

Winter

24

Are solid manure systems consistent with effective utilization of manure nutrients? Probably not, for two reasons.

Nutrient variability

The nitrogen content of solid manure depends quite significantly on how long it has been exposed to the elements and the type of weather that has occurred before it is scraped up. This means the nitrogen content of solids varies both within a year and between years. Thus, each time manure is hauled, it would have to be sampled and tested to determine proper application rates. No quick test yet exists for testing manure, although research and development continues. 

Timing of application

Manure nutrients applied in the summer cannot be utilized by growing corn and soybeans. Pastures can utilize the nutrients, although the efficiency of utilization is low because soil incorporation is not possible. Winter-applied nutrients also cannot be effectively utilized because incorporation in frozen, snow-covered ground is not practical. Waiting until spring to incorporate means the manure has been exposed to early-spring rain and snow, and freezing and thawing ground. The survey results indicate that 39 percent of solid manure in Iowa is applied in the summer and winter as shown in Table 2. 

Liquid manure

Are liquid systems more conducive to effective utilization of nutrients? As shown in Table 3, 20 percent of liquid manure is applied in the summer or winter, in contrast to the 39 percent of solid manure. This finding is consistent with the notion that farmers with liquid systems have greater manure storage capacity than farmers using solid systems.

Table 3. Time of application of liquid manure

Time of year

Percent

Spring

34%

Summer

9

Fall

46

Winter

11

Liquid systems also have the advantage that the nutrient content of liquid manure is less variable than solid manure, especially if the stored manure is mixed (agitated) prior to pumping. Testing costs should be lower than with solid systems both because the frequency of tests is lower (liquid is hauled less frequently than solids) and there is less variability in nutrient content across years. 

The advantages of liquid manure systems over solid systems in allowing farmers to utilize manure nutrients should lead to a greater proportion of farmers on liquid systems taking nutrient credits for their manure. One of the survey questions asked producers if they adjusted commercial fertilizer applications on their manure fields. Three out of four producers reported that they adjusted N, P and K application rates. This proportion was the same for producers using solid systems as for producers using liquid systems.

Whether Iowa producers are taking proper credits is not known however.  But 32 percent of the producers surveyed indicated they have prepared a manure management plan. This number is surprisingly high because only the largest Iowa hog producers are required to file formal manure management plans.

Effect of size of operation

Survey results show that 93 percent of producers who reported that they marketed more than 2,000 hogs in 1996 adjusted commercial fertilizer rates and 76 percent of these producers indicated that they had prepared manure management plans. These results suggest that as hog producers get larger, they pay more attention to the nutrient content of their manure and make adjustments in their commercial fertilizer rates.

As hog producers get larger, they pay more attention to nutrient content of their manure and make adjustments in their commercial fertilizer rates.

This conclusion should not be surprising.  Iowa law mandates that the largest producers obtain a permit from the Iowa Department of Natural Resources (DNR). The permitting process requires filing a manure management plan 1/.  Also, it is likely that larger producers have more resources available to devote to manure management.  If larger producers manage manure more effectively than smaller producers, then a greater proportion of nutrients from Iowa swine manure will be utilized effectively by crops as the proportion of Iowa’s hogs being produced in large-scale facilities increases.

Environmental effects of size of operation

As hog operations get larger, what does this imply about environmental costs and benefits? 

There are beneficial environmental effects from large-scale operations. One reason is that the movement to large scale hog operations in Iowa will likely result in greater utilization of manure nutrients in crop production. There are two justifications for this conclusions.

Cost advantage

The development of a manure management plan costs about the same whether a producer has 300 hogs or 3,000 hogs on a site. The steps required to create a plan are identical for both operations. 

But the cost per-hog or per-acre of cropland is less for the large operator than the small operator, which implies that the large operation can justify the cost more easily. This is particularly true for contract operations where the company that issues the contract may supply the contractor with a ready-made manure management plan.

These cost advantages also exist for testing the nutrient content of manure. It costs about the same to test nutrients whether a pit holds manure from 300 hogs or 3,000 hogs. Thus, a larger operator will more likely test the nutrient content of manure.

Is size alone an inducement to take proper credit for manure nutrients? Consider two hog producers who both handle slurry from finishing hogs. The first producer raises 1,000 hogs per year. The second raises 10,000 hogs per year. The cost of delivering nutrients from these hogs, if the nutrients are applied at agronomic rates, is approximately $1,400 for the smaller producer. The cost of delivering the nutrients for the large producer depends on how far the slurry must be hauled. A hauling distance of two miles is not uncommon in Iowa. At this distance, the total cost of delivering nutrients is about $19,000. 

The potential value of the nutrients in corn production is typically around $2.00 per hog.  To realize this potential value requires some investment of time and money in developng and implementing a manure management plan.  If this cost is $300 per year, the small farmer can cover the costs of hauling manure and have $300 left over ($2.00 x 1,000 - $1,400 - $300 = $300).  The larger producer can also cover delivery costs and will have $700 left over ($2.00 x 10,000 - $19,000 - $300 = $700).  Because the delivery costs are much higher for the larger producer, he has more incentive to take the time and effort needed to capture the value of nutrients.

More liquid storage

Larger operations will result in increased utilization of manure nutrients because, as the scale of operation increases, so does the likelihood that the operation will store manure as a liquid. The ISU survey indicates that 69 percent of manure from market hogs is handled as slurry on farms where more than 2,000 hogs are produced on a site. This compares with 52 percent of manure for all of Iowa.  As discussed earlier, manure nutrients are more likely to end up being utilized in crop production when manure is handled as slurry. 

Harmful effects

The conclusion that larger hog operations will better utilize manure nutrients does not necessarily mean that larger operations will be beneficial to the environment overall. Odor problems, the risk of catastrophic spills, and possible links between greater concentration of manure stocks and an increased risk of pathogen contamination of water supplies all suggest that large-scale hog operations can be more environmentally damaging than smaller operations. 

If these steps are taken, there is no environmental reason to fear the industrialization of the hog industry in Iowa.

But odor problems can be significantly reduced by adopting relatively inexpensive practices, if producers have the incentive to adopt them. Examples of these practices include soil incorporation of manure at the time it is applied and the use of straw to cover outdoor manure storage basins. And the risk of catastrophic spills and pathogen contamination of water supplies can be reduced through added investment in manure storage structures. 

If these steps are taken, there is no environmental reason to fear the industrialization of the hog industry in Iowa. Rather, the future of pork production in Iowa could be one where manure nutrients are again viewed as a valuable resource to be used to lower crop production costs and to maintain the long-term health of Iowa’s cropland.

1/  DNR permits are required if a producer has more than 625,000 lbs. liveweight of livestock at any one time. This amounts to producers who have more than 4,167 market hogs on site at any given time. This level decreases to 200,000 lbs., or 1,333 hogs if the producer uses an earthen basin or anaerobic lagoon.

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