Straw Management and Crop Rotation Alternatives to Burning Wheat Stubble: Assessing Environmental Trade-Offs.

Farmer incentives for burning wheat residues include facilitating the establishment of the next crop, decreasing incidence of soil-borne disease, decreasing nutrient tie-up from decomposing cereal residues, and positive response of crop growth and yield.  Conversely, potential disincentives of residue burning to growers can be difficult to quantify, particularly in the short-term, and include negative impacts on overall soil organic matter levels, loss of nutrients (e.g. N, P and S), and increased hazard of soil erosion if burning is combined with too much tillage.  Our objectives are to: (1) assess wheat residue burning effects on SOM, soil erosion estimates, soil condition, and residue C and nutrient (N, P, S) losses; (2) identify crop rotations and beneficial sequences from retaining winter wheat residues in direct-seed systems; and (3) convey findings through media and outreach efforts.

In assessing environmental trade-offs whether to burn crop residues, finding from an on-going four year study, after a 2-year cycle, include:

1. Reduced surface winter wheat residue mass by 62% (fall burn) and 55% (spring burn).
2. Total C losses of 2,010 lbs C/ac (fall burn) and 1,271 lbs C/ac (spring burn).
3. Average N losses of 12 lbs N/ac (fall burn) and 11 lbs N/ac (spring burn).
4. Loss of winter wheat residue N was 40% (spring burn) and 33% (fall burn); these values were appreciably lower than previously reported laboratory residue burning studies of nearly 100%.
5. Residue burning had little impact after the first year on the following soil properties: N%, C%, C/N ratio, bulk density, and pH.
6. Increased early season soil N availability, spring wheat development, and N uptake with burning.
7. Aboveground spring wheat N uptake at tiller stage was 112% greater for fall burn plots.
8. Field deployed PRS probes had 40% more µg N 10 cm^-2 7 days^-1 in fall burn plots; a linear relationship exists between plant N uptake and the PRS probe data.