LONG TERM EFFECTS OF CROP MANAGEMENT IN A WHEAT/FALLOW SYSTEM: I. INPUTS, YIELD AND SOIL ORGANIC MATTER.

Authors: Rasmussen, Paul; PARTON WILLIAM J - COLORADO STATE UNIV

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Long-term experiments are perhaps the only method to determine if agricultural practices sustain or degrade the soil environment. Residue management effects on crop yield and soil organic matter in a semi-arid region were determined over a 56-year period, 1931-1986. Winter wheat was rotated with summer fallow, a common practice because it stabilizes crop yield, but is sometimes controversial because of declines in soil organic matter content and quality. Residue burning, which once increased yield of the following crop, now decreases yield. Both organic amendments and inorganic nitrogen fertilizer increased yield substantially. The organic matter content of soil declined steadily with time under all practices but manure addition. But, in recent years, inorganic nitrogen fertilization coupled with high-yielding semi-dwarf wheat produced higher yield, increased straw production and reduced organic matter decline to near manageable levels. Adequate residue return to soil was absolutely essential in this semi-arid region to maintain soil organic matter and sustain crop productivity.

Technical Abstract: Long-term experiments are one of very few methods to determine if agricultural practices sustain or degrade soil quality. The effects of several residue management practices on crop yield and soil organic matter (carbon and nitrogen) were determined over a 56 year period (1931-1986) for a semi-arid wheat/fallow system. Only manure addition (22 t ha-1 crop-1) maintained soil N and C at or above the 1931 level. Soil N and C declined linearly with time in other treatments (wheat residue burned, limited inorganic N fertilization, pea hay addition, and straw not burned but no N applied). The soil C and N decline was strongly related to residue input and to change in crop yield. Low-fertility treatment yield declined from 85% of manure yield in 1931 to <50% in 1986, reflecting the deterioration in the soil resource base. Repeated burning, which was once advantageous to crop yield, now results in both lower yield and less soil organic matter rthan in the comparable non-burn treatment. Over 50 years were required to fully quantify residue management effects on organic matter change in soil.