|Douglas Jr, Clyde|
Submitted to: Proceedings of the Pacific Northwest Conservation Farming Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/7/1998
Publication Date: N/A
Interpretive Summary: Soil quality is important to the agricultural community. Many changes in soil quality require 10-20 years to identify. Long-term experiments can benefit agricultural productivity by depicting the effects of farming practices. The Pendleton Agricultural Research Center has several ongoing long-term experiments that are representative of regional farms. The loss of soil organic matter has a substantial effect on soil quality in the Pacific Northwest. Maintaining or increasing soil organic matter will offer long-term productivity and reduce erosion. The two major factors influencing changes in soil organic carbon and nitrogen are the frequency of summer fallowing and the amount of carbon input by crop residue. Most of the organic matter is lost during the fallow year of a crop cycle. Soil organic matter light fraction can provide an indication of soil quality. The light fraction, isolated from several of the long-term experiments, differed distinctly among management systems. Soils from experiments where the residue is retained showed greater organic matter light fraction content than soils from systems incorporating summer fallow and residue burning. The loss of carbon dioxide from the soil to the air can offer information about the soil carbon cycle. Carbon dioxide production was elevated following plowing but remained relatively stable in plots that were not tilled. Soil organic matter can be maintained or increased in most semi-arid soils if they are cropped every year, the residues are returned to the soil, and erosion reduced or eliminated. Crop management practices, such an nitrogen fertilization, increase residue production and improve soil carbon and nitrogen levels and improve soil quality.
Technical Abstract: The long-term experiments at the Pendleton Agricultural Research Center are representative of cropping systems in the Pacific Northwest. Long-term experiments are beneficial because changes in some soil parameters can require 10-20 years to identify. The loss of soil organic matter is a major problem for maintaining soil quality in the Pacific Northwest. The two major factors influencing changes in organic carbon and nitrogen are the frequency of summer fallow and the amount of carbon input by crop residue. Most of the organic carbon is lost during the fallow year of a crop cycle. Although decreasing tillage intensity reduces soil carbon and nitrogen loss, it is not as effective as eliminating summer fallow. Soil organic matter light fraction can be used as an indicator of the status of soil quality. The light fraction differed distinctly among the management systems found in the long-term experiments. Soils from management systems where the residue is retained on the surface showed greater organic matter light fraction accumulation than soils from systems incorporating summer fallow and residue burning. Carbon dioxide flux from soils provides an insight to soil carbon cycling Carbon dioxide flux was greatest following moldboard plowing and least from no-till plots. Soil organic matter can be maintained or increased in most semi-arid soils if they are cropped every year, the residues are returned to the soil, and erosion reduced or eliminated. Most of the loss of organic carbon and nitrogen is due to biological oxidation and the lack of carbon input into soils. Yearly crop production with a reduction in tillage would be advantageous for maintaining soil quality in the soils of the Pacific Northwest