Myths and facts about residue breakdown
The results of corn residue decomposition with different N rates in the no-tillage system under field conditions are presented in Figure 2a of the two-year study. Corn residue decomposition was evaluated by applying three N rates (UAN 32 percent), 0, 30 and 60 lb N/acre to corn residue immediately after harvest, in which specific amounts of corn residue were weighed and placed in nylon mesh bags and left in the field immediately after harvest for decomposition evaluation. The rate of residue decomposition was evaluated every three months for the entire year (12 months).
Fig. 2. Nitrogen (N) effect on (a) residue breakdown in the field, (b) residue breakdown in the laboratory under 32 degrees F and (c) residue breakdown in the laboratory at 90o F room temperatures. The results showed that corn residue decomposition increased with time with lesser amounts of residue remaining after each evaluation period. There were no differences in the rate of residue decomposition as a result of N application of different N rates. These results show that applying N fertilizer to facilitate residue decomposition is not effective. The timing of N application for corn residue decomposition immediately after harvest, as practiced, is not an effective strategy, as the soil and air temperatures decrease over time after fall harvest. The decomposition of crop residue is highly controlled by soil moisture and temperature as essential factors for microbial activity for the residue decomposition. Therefore, from economic and environmental perspectives, N application has little effect in achieving the intended results of facilitating residue decomposition.
The same results were observed with laboratory evaluation of corn residue decomposition that was conducted with the same residue treated with different N rates in the field study. Corn residue samples from the field were incubated in the laboratory under constant temperatures of 32 degrees F and 90 degrees F for approximately 30 days each (Fig. 2b and 2c). The rate of corn residue decomposition under laboratory conditions followed a similar trend as that in the field. Similar to the results of the field study, no differences in residue decomposition/breakdown with different N rates were found. The laboratory study results confirmed the field results and demonstrated the role of temperature in controlling corn residue decomposition rather than N rate, in which a slower rate of residue decomposition was observed at the low temperature (32 degrees F) and increased at the higher temperature (90 degrees F) (Fig. 2b and 2c) without any effect of N application on residue breakdown.
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