Myths and facts about residue breakdown
Crop residue serves an important role in physically protecting soil by preventing soil erosion during rain events or high winds. Also, crop residue plays a significant role in enhancing the soil biological community by providing sources of organic carbon and nitrogen for its energy or food needs. To understand how residue decomposes or breaks down, we need to understand the processes and mechanisms that include both biological and chemical activities influenced by environmental and soil conditions, namely air and soil temperatures, soil moisture availability, soil pH, oxygen, and type of microbial community. The composition of crop residue includes lignin, cellulose, hemicellulose, and macro and micro nutrients. To release or breakdown and decompose most of these organic forms, certain biological and enzymatic processes controlled by a wide range of microorganisms influenced by other factors have to occur to these materials at various rates as influenced by the environment and soil conditions.
In agriculture, annual cropping systems and other ecosystems management can influence these factors that are critical to the process of residue breakdown. However, there is a common belief among many farmers and agronomists that the physical change in crop residue structure or orientation in the field by tillage can accelerate residue breakdown by cutting crop residue into small pieces or burying residue by tillage. Also, there is the belief that the application of nitrogen fertilizer on crop residue (i.e., corn residue) after harvest can speed up the process of residue breakdown. Both assertions are not correct.
click image to zoomFig. 1. Rate of CO2-C released as an indicator of residue breakdown/decomposition from control (bare soil) and Bt and non-Bt corn residue mixed into the soil or unmixed with soil (left on soil surface). Asterisk represents CO2-C released rates from treatments that were significantly different from control for the corresponding days at the 0.05 probability level using the least significant difference. Tillage Effects on Residue Breakdown
Recently, we conducted a study to examine the effect of three different tillage systems that include deep tillage (DT), strip-tillage (ST), and no-till (NT) on residue breakdown of both Bt and non-Bt corn residues. The results of this three-year field and laboratory incubation study show no signiﬁcant differences in the breakdown or percent of residue that remained among the three tillage systems of Bt and non-Bt corn hybrid decomposition. Also, in these studies after 12 months, there was no difference between tillage systems or Bt and non-Bt residue hybrids breakdown in the ﬁeld, where 34–49 percent of the corn residue still remained on the soil surface. The results of the residue decomposition study are presented in Figure 1, in which the residue decomposition rate is represented by CO2-C release. The results show no significant difference in the breakdown or decomposition due to tillage or type of residue (Bt or non-Bt).
Nitrogen Fertilizer Application Effects on Residue Breakdown
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