Skip to main content
ARS Home » Pacific West Area » Pendleton, Oregon » Columbia Plateau Conservation Research Center » Research » Publications at this Location » Publication #59246


item Rasmussen, Paul

Submitted to: Western Nutrient Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/9/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Farm managers need all possible information when making decisions on best management practices for their farm. Cropping practices that may offer immediate economic gain can have deleterious long-term effects of soil quality and future productive capability. Examples that occur quite frequently include tillage options (plow or mulch), residue disposition (incorporate in soil, use for feed, burn off), and crop rotation (fallow, grow a legume, grow another cereal). Long-term experiments with well-kept records and periodic evaluation of soil quality are perhaps the only way to quantify future effects. In semi-arid regions, residue management, fertilizer application, organic amendment addition, and crop rotation affect organic matter content, microbial biomass, acidity, and enzyme activity in soil. Changes develop very slowly, taking from 10-20 years before they become apparent. But many adverse changes affect water infiltration, soil tilth, nutrient release, and eventually reduce crop yield. Incorporating crop residue each and every year into soil is very beneficial for maximizing organic matter content and quality. Other uses (feed or fuel) often provide immediate economic return and are selected when long-term detrimental effects have not been defined. We are ever striving to define long-term effects, and attempting to develop meaningful indicators that can be used by farmers, environmentalists, and regulatory agencies as a measure soil quality.

Technical Abstract: Long-term experiments often provide the only method to determine if crop management practices will maintain soil organic matter and sustain future productive capability. We review some of the changes that have occurred in long-term experiments in semi-arid regions of the pacific Northwest. These involve residue return to soil, nitrogen (N) fertilizer application, organic amendment addition, and crop rotation effects on soil organic matter (OM), organic N, pH, microbial biomass, and enzyme activity in soil. The amount of crop residue return to soil has a long-term impact on its OM content; the higher the input, the greater the organic matter. Nitrogen application that increases crop residue yield also increases soil OM provided residue is incorporated rather than removed or burned. Ammonium based N fertilizer (practically all of present use) progressively decreases soil pH; increased soil acidity changes microbial populations and chemical reactions, with long-term implications on soil-borne disease severity and lime needs. Long-term recovery of N fertilizer through crop uptake and soil OM immobilization is good (75-90%) when the optimum rate of N is applied, but drops rapidly when the optimum N rate is exceeded. Some of the missing N is leached, but most is probably denitrified to the atmosphere. Soil microbial biomass or enzyme activity may be useful indicators of soil quality because they show up much more rapidly than changes in soil OM and are fairly easy to determine.