How Burning and Other Methods of Removing Irrigated Crop Residues Affect Yields and Soils

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Burning crop residues has long been discouraged for many reasons . It pollutes t he air, leaves the soil surface exposed to wind and water erosion and possibly volatilizes some nitrogen at the time of burning. Now, with crop residues proposed as a source of energy, we need to know how residue removal affects not only crop yields but also soil physical and chemica l characterist ics.
Several methods of managing residues have been studied f or ten years at the Garden City Experiment Station. The treatments included removing the residue: 1) by burning; and 2) by physi cally removing as much top growth as possible; and incorporating either normal or twice no rmal quantities of res idue. In addition, nitrogen was applied at 50 and 100 lb/A rates.
Yields did not differ significantly the first eight years of the experiment (Table 1}. However, in the past three years removal and burning t reatments have begun to produce lower yields than the other treatments. In 1979, yields from the two plots with residue removed were lower than from plots with residues incorporated. T hese results are consistent with other experiments which indicate that it may take as long as ten years to begin to observe yield reductions from burning.
The plots were sampled to a depth of 6-feet in the fall of 1979 to evaluate the soil chemical properties under these management practices. Chemical anal yses included pH, organic mater, P, K, Zn, Na, Mg, and Ca on t he surface 6 inches and residual N03and total Non the entire 6 foot profile. Analyses of the data showed no differences in P, Zn, Na, Mg, or Ca due to the residue management treatments. However, there were significant differences in pH, organic matter (O.M.) and potassium (K) (Tabl e 2). Continuously removing residues (physically or by burning) d ecreased soil O .M. as expected because resi· dues were not being returned to the soil. In addition, pH increased where the res idue was removed. Both the pH and O.M. are very important in managing soi ls. O rganic matter helps to maintain stability of soils by acting as a cementing agent for soil part icles so granular structure of the surface soil is maintained . Organic matter also supplies s.ome micronutrients needed for p lant growth.
Soil pH affects the availability of some nutrients; as pH increases, the availability of nutrients such as P, Fe and Zn decreases. In addition, pH and O.M. are critical in some herbic ide programs. The levels found after ten years' burning and removal (Table 2) are approaching these critical levels, so they may affect the rate herbic ides are degraded.
Potassium is also declining where residues have been removed (Table 2). This is expected since residues are high in K. However, the concentrations observed in this experiment are still in the very high soil test category and will no t limit c rop production.
Nit ra te-nitrogen (NO)-NJ analyses showed no statistical differences in the total quant ity of this nutrient accumu lated in the six-foot profile. However a higher percentage of NO)-N has been leached deeper in the physical removal and burning treatments, (See figure  below). This may reduce N03availability to plants if it is leachedbelow the zone of greatest root activity. We attribute the greater leaching to incorporating reduced quantities of residues on t he two removal treatments. In these situations there is little Ue-up of N during residue decomposition and it remains susceptible to leaching as N03during high rainfall or irrigation. %of total N03 accumulated Although no immediate deleterio us effects on crop yields or soil properties were observed due to residue burning or removal, the continual long-term practice of these residue management treatments w ill have negative effects on soi l pH, O .M ., K and N03-N . These c hanges may eventually have negative effects on c rop yields. This publication from Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information: http://www.ksre.ksu.edu.