CROP RESIDUE DECOMPOSITION IN NO-TILLAGE SMALL-GRAIN FIELDS

Authors: Steiner, Jean; Schomberg, Harry; Unger, Paul; Cresap, James

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Management of crops in the U.S. has changed substantially from practices involving intensive tillage following harvest to practices such as no-tillage, ridge tillage, and other conservation tillage systems, that leave residues undisturbed following harvest. New systems have been adopted to increase production efficiency and reduce water and wind erosion. Residues impact erosion, water quality, integrated pest management, nutrient management, and other issues, so we need to understand residue persistence in conservation tillage systems. Much of our understanding of residue decomposition is based on controlled environment studies, but organisms that drive decomposition go through cycles of population dynamics and biological activity as field environments change and time progresses. We established a field study at Bushland, Texas, to analyze residue decomposition of four small grains for 14 months after harvest. Irrigation treatments during decomposition created a wide range of environmental conditions in this semi-arid location. Climate indices based on air temperature and precipitation (plus irrigation) were were used to normalize the time scale for analysis of decomposition rates. This strategy to relate field environments to conditions producing maximum decomposition rates accounted for irrigation effects. However, use of only climatic parameters was inadequate to account for the different environments found with different amounts of residue. Under the same climatic conditions, relative decomposition rate decreased as initial initial biomass increased. Climate-soil-residue interactions need further elucidation to understand impacts of residue density on decomposition and other agroecosystem processes.

Technical Abstract: Conservation tillage has been widely adopted in the USA to increase production efficiency and reduce water and wind erosion. Fields with surface residues provide different environments for soil biological and chemical processes than tilled fields, so we need to understand residue impacts and persistence to optimize production systems. Our understanding of decomposition is based largely on controlled environment studies, but field environments are highly variable. We conducted an experiment at Bushland, Texas, to determine residue density and climate impacts on decomposition, and to normalize field environments relative to environmental conditions that maximize decomposition rates. Four small grains were grown to produce three biomass densities by varying seeding rate, fertilizer, and irrigation. During decomposition, three irrigation treatments were imposed. Ash-free residue biomass was measured seven times sover 14 months. Climatic indices to normalize field environments (decomposition days, DD) were based on the daily minimum of temperature and moisture coefficients. First order decomposition coefficients, k, were determined for each plot using DD as the time variable. Irrigation did not significantly affect k (P < 0.53), indicating the moisture index accounted for irrigation effects. Crop affected k somewhat (P < 0.068). There was a strong inverse raltionship (P < 0.001, between k and biomass density. A few prior studies related density to decomposition rate, but this has not been explained. Climate indices appear promising to normalize field environments to conditions that maximize decomposition rate, however, atmosphere-soil-residue interactions need further elucidation to understand impacts of residue density.