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Chapter 3- Residue Management, No. 1, October-November 1984

The Value of Crop Residue is Going Up In Smoke?

Roger Veseth

The value of crop residues for long-term productivity is well known, but too often overlooked. A few important benefits include providing and recycling plant nutrients, maintaining soil organic matter levels, aiding in water conservation and preventing soil erosion. Wheat stubble burning may seem like a cheap and easy way of handling a residue problem but what are the hidden costs? USDA-ARS soil scientist Robert Ramig and other STEEP researchers at the Columbia Plateau Research Center near Pendleton, OR, have been involved in crop residue management research for over 15 years. A few of their results are presented here as food for thought in respect to wheat stubble burning.

Ramig estimates the value of plant nutrients in 1 ton of wheat residue to be about $10 at current fertilizer prices. Burning wheat residue results in a loss of nearly all the nitrogen and approximately half of the sulfur and phosphorus. This means about $5 worth of nutrients are lost for every ton of residue burned. If the wheat residue level is 4 tons per acre, that is a loss of $20 per acre.

The value of crop residue for soil water storage is also important. Pendleton research shows that standing wheat stubble helps store 76 percent of overwinter precipitation compared to 57 percent when the stubble is burned in the fall. If 9 inches of overwinter precipitation is received, this storage potential difference results in 1.7 inches additional soil water for the following crop. Generally, every inch of water stored produces from 5 to 7 bushels of grain per acre. For example, assume 6 bushels per acre and $3.50 per bushel wheat. The additional water stored by leaving the stubble stand overwinter could increase yield of a wheat crop by 10 bushels per acre and increase gross returns by $35 per acre over fall burning.

Results of Ramig long-term, residue management research on wheat-pea rotations indicate standing wheat stubble stores 20 percent more water during the winter months than clean fall tillage. The additional 2 inches of stored soil water increased green pea yield about 20 percent and the yield of the following wheat crop about 5 percent. In a reduced tillage system where 1,500 pounds of residue per acre remained on the soil surface after winter wheat was seeded, 10 percent more water was stored during the winter than where the stubble was burned or plowed. These results illustrate how good use of crop residue for improved water storage allows a potential increase in gross returns with no additional cost. The savings from reducing tillage operations can also reduce costs at the same time.

The value of crop residue for preventing soil erosion is important in terms of continued soil productivity. Erosion in the greater Palouse region is ranked as the second most serious in the United States. The average soil loss is about 7 tons per acre, but losses over 100 to 200 tons per acre are not unusual in some years. At Pendleton, soil erosion of 6 to 40 ton per acre has been measured on slopes of 14 to 18 percent. Ramig's research indicates that erosion can be reduced about 2 tons per acre for every 100 pounds of residue left on the soil surface. They recommend a minimum of 1,000 to 2,000 pounds per acre of crop residue slightly mixed in or on the soil surface to provide adequate soil erosion protection under most conditions. Residue needed varies with slope and soil texture.

Rarnig estimates the value of major plant nutrients (nitrogen, phosphorus and potassium) at $1 per ton of average topsoil. However, the value of nutrients lost is small compared to the permanent loss of soil productivity in terms of lower crop yields. The loss of 150 tons of soil per acre is equivalent to the loss of about 1 inch of topsoil. As soils become shallower, the loss of each additional inch of topsoil results in an increasingly larger proportion of yield loss as rooting depth, water-holding capacity and other important soil productivity factors are reduced. The low yields on eroded knobs and ridges are good reminders of this loss in productivity. The size of these less productive, eroded soils is growing every year.

Ramig and Darrell Maxwell, STEEP Extension area agronomist at Pendleton, are authors of Oregon State University Extension publication SR699, Small Grain Residue Management. It reviews some important tillage considerations in residue management for soil erosion prevention. Crop residue is a valuable tool in maintaining soil productivity and conserving soil and water resources.


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