|Douglas Jr, Clyde|
Submitted to: Nitrogen Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/1996
Publication Date: N/A
Interpretive Summary: The use of nitrogen fertilizer in the Pacific Northwest has acidified the soil. Continued use of fertilizers in this dry-land farming region will increase soil acidity, injure crops and cause a reduction in yields. The addition of lime, a common practice to decrease soil acidity, may affect the soil microorganisms and soil chemistry. It is unknown how liming of Pacific Northwest soils will influence residue decomposition and nutrient dynamics. The present study was begun to evaluate the effect of liming on nitrogen in soils of the Pacific Northwest. Samples of two local soils were collected and their acidity reduced by calcium carbonate addition. Soil samples, with and without wheat residue, were incubated at a constant temperature and humidity for up to 112 days. Changes in soil nutrients and acidity were monitored. The amount of nitrate nitrogen increased during the incubations, however, when residue is added to the system, the amount of nitrate nitrogen in the soil rapidly decreased as it was utilized by soil microorganisms. Decreasing the soil acidity slightly reduced the rate of nitrate production, but the pattern of nitrate uptake with added residue was similar to the nonamended soil. Both the nitrate nitrogen production and utilization potential of the soil was slightly reduced by decreasing soil acidity and suggests that the microbial activity in the soil microbial was reduced by this treatment.
Technical Abstract: Nitrogen fertilizer applications have acidified surface soils in the Pacific Northwest. Continued use of ammonium fertilizers in this dry- land farming region will continue to increase soil acidity. However, liming to decrease soil acidity might change the soil microbial population and impact soil quality. This study was begun to evaluate the effect of liming on mineralization and immobilization in the Pacific Northwest soils. The pH of two soils, a Walla Walla silt loam and a Cowsly silt loam were increased with calcium carbonate. Mineralization was determined by aerobic laboratory incubation, at 25 C, 100% relative humidity, and a soil water potential of -0.03 MPa, for up to 112 days. Nitrate, ammonia and soil pH were measured during the study. Liming increased the soil pH by approximately 1.0 unit in both soils. Without residue additions, nitrate concentration increased during the incubation. In both soils, at either pH, residue addition immobilized nitrate, the concentration remaining low, until nearly the 40th day of the incubation, at which time it gradually increased. The mineralization rate did not equal that of the soil without residue until about day 80 of the incubation. The pattern of immobilization in the calcium carbonate amended soil was similar to the nonamended soil. However, the change from immobilization to mineralization was delayed when compared to the nonamended soil and the rate of mineralization was likewise depressed. Both mineralization and immobilization potential of the soil was slightly reduced by liming in the pH range tested.