PUTTING
MANURE IN ITS PLACE
Greg Stewart, OMAFRA Corn
Specialist
If you have liquid manure, you probably
like to get the most nutrient bang for your buck. Injecting the manure directly
into the ground is an approach that may have a significant impact on the amount
of nitrogen available for next year's corn crop. Consider an example of some of
the decision making that is associated with manure application systems. In the
process of improving manure use efficiency, the first step is to get a manure
sample that is representative of your manure supply and have it analyzed for nutrient
content. In this example, the manure analysis tells you that the total nitrogen
content is 50 Ibs of N per 1,000 gallons of manure. This includes both the organic
fraction (20 lbs N/1,000 gallons) and the ammonium fraction (30 lbs N/1,000 gallons).
The rather stable organic fraction will not be affected by the method of application,
as these organic compounds breakdown gradually to release nitrogen in a plant-available
form. The ammonium fraction of the manure will start to volatilize into the air
as soon as it has been applied to the field. If this manure was applied in the
late fall and incorporated within 24 hours the OMAFRA estimates indicate that
40% of the total N would be available to next year's corn crop. If the application
rate is 3,000 gallons per acre, the math looks like this: 3,000 gal x 50 Ibs N
11,000 gal x .40 = 60 lbs N/acre (available to corn crop) This estimate is based
on several assumptions, one of which is the loss of N through
ammonia volatilization in the 24 hour period between application and incorporation.
For late fall applications, this loss is estimated at 25% of the ammonium N in
the manure.
Figure 1. Injection system on Van Arenthals' manure
tanker (Nuhn Industries)
Figure 2. Setting up manure injection strips to be
compared with surface applications.
If the manure was injected rather than broadcast and incorporated,
this loss could be virtually eliminated. In this example, it would represent reduced
nitrogen losses of about 23 lbs N/acre. Of course not all of this available nitrogen
will make it to next year's corn crop, but assume that 70% does. If this is the
case, an additional 16 Ibs of N would be supplied to next year's corn crop. Remember,
nitrogen losses from the ammonium form can vary widely with conditions at the
time of manure application. For example, if conditions were warm (> 25 C) and
the soil was dry, the volatilization losses may reach 50% of the ammonium fraction
rather than the 25 % used in this example. Middlesex Soil and Crop Improvement
Association has a research and demonstration project underway that is attempting
to verify some of these estimates. Dean Van Arenthals, from Lucan, is one of the
co-operators in this project, and he is Continued using his new manure tanker
to set-up plots which compare broadcasting
and incorporating to direct injection. Figure 1 shows Van Arenthals' unit with
the s-tine injecting system.
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Figure
3. Injector knives (Yetter) with covering discs on Doug Schneider's manure
tanker. |
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Figure
4. Shallow injection and covering of manure with Schneider's unit |
Research from Ohio has also been comparing manure injection systems. E. Oekler and G. Graham summarized their 2003 results by indicating significantly higher corn yields where manure was injected compared to surface application. In this trial, fall injection of manure produced corn yields of 169 bu/ac, surface manure application yielded 152 bu/ac, and fertilizer N applied through the planter (120 Ibs N/acre) yielded 167 bu/ac. It should be pointed out that in this study, the fall surface applied manure was not incorporated. The manure application rate in this study was selected so as to meet all of the corn crop N requirements, as no supplemental fertilizer N was applied to the plots that received manure.
Other factors to consider in regard to manure injection systems:
1) It does not appear that manure must be buried deep into the soil profile to minimize N losses. A shallow (5-10 cm) injection and covering of the manure appears to prevent most of the N loss.
2) Corn Belt research indicates that injection systems tend to provide more reliable manure N credits than surface applications with later incorporation.
3) Odour concerns and the reduction in odour provided by injection may be a significant motivating force for adopting injection technology.
4) The tillage action of the injection system may be all the tillage (other than leveling, perhaps) that is required for subsequent crop production. Some injection toolbar designs may also be used as a sidedress toolbar if your circumstances present some opportunities for sidedressing manure in corn in June. Doug Schneider of Fullarton has been sidedressing manure in corn for years with Yetter knives on the back of his tanker; closing discs mounted on the back of these knives do a reasonable job of covering manure in fall application situations as well (See Figure 3 and 4).