How does dairy manure compare with swine manure?After reading demonstration results in the December issue of Water Watch, a dairy producer who lives near Postville called to ask if there was a difference in the results when dairy manure was compared to swine manure.
There is a difference. Our suggestion is that livestock producers get to know their manure by having a manure spreader calibration and analysis of a manure sample, especially now as the growing season approaches.
We looked at all the dairy manure sample information, specifically the dairy gutter manure samples, and found that the average first year manure nitrogen (N) credit on the dairy gutter manure demonstrations was 70 pounds of N per acre.
Comparing the corn yield results of the plots with 70 pounds of manure N credit, we found that an additional 50 pounds of nitrogen, in the form of ammonium nitrate, resulted in significant yield increases. However, with 100 pounds of additional N, there was no significant yield response.
With that in mind, all 24 manure demonstrations, including swine, dairy and beef feedlot, were divided into two groups, low and high. We used 120 pounds of manure N credit as the dividing point.
The next step was to average each group. The low manure N rate average was 83 pounds of N per acre; the high manure N rate average was 174 pounds of N per acre. Of interest, most of the sources in the low group were dairy gutter or cattle shed bedded pack and most of the sources in the high group were swine.
| Manure | ––––– Corn yield, bu/acre –––––– |
––– Cornstalk nitrate NO 3 , ppm ––– |
|||||||
| credit* | Check | Manure only | M+50 | M+100 | Check | Manure only | M+50 | M+100 | |
| Overall average (24) | 136 | 129 | 143 | 148 | 148 | 464 | 1,896 | 2,703 | 3,855 |
| High manure (14) | 174 | 132 | 157 | 160 | 158 | 346 | 2,677 | 3,375 | 4,675 |
| Low manure(10) | 83 | 112 | 124 | 130 | 133 | 612 | 1,058 | 2,117 | 3,209 |
*Manure credit is in pounds of N per acre. Manure sources were dairy, swine and beef.
When we looked at the yield results for the low group, an additional 50 pounds of N per acre produced a significant yield increase, just as it had in previous examinations of the results. The addition of 100 pounds of N per acre over the manure did not improve yield significantly.
Looking at the yield results for the high N group, we found no response to additional N (see table above). The first year manure N contribution was enough to provide the N needs of the corn plant.
Finally, the results of the end-of-season cornstalk nitrate nitrogen test (NO3) were evaluated. In all cases, the check plots, which received no manure and no additional nitrogen, showed that additional N would likely produce a yield increase. The addition of manure in all cases brought the plots into the "comfort range," where there was adequate N for the corn plant.
Some producers are confident in taking a 100 percent contribution the first year after a manure application. For farmers who are not confident in the nitrogen calculations for manure applications, the addition of 50 pounds of N will meet the N needs of the rop. The additional 50 pounds of N compensates for problems such as spreading uniformity, and it is an easy first step for producers who have never credited for manure.
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