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DIVISION S-6-SOIL & WATER MANAGEMENT & CONSERVATION

Biomass and Residue Cover Relationships of Fresh and Decomposing Small Grain Residue

^a USDA-ARS, 1420 Experiment Station Road, Watkinsville, GA 30677 USA
^b USDA-ARS, P.O. Drawer 10, Bushland, TX 79012 USA

jsteiner{at}arches.uga.edu

Maintaining residue cover provides diverse conservation benefits. Exponential relationships have been developed to estimate cover from biomass of randomly distributed, flat residues, but a large portion of crop biomass remains standing after harvest. Our objective was to determine how relationships between biomass and soil cover change in no-tillage small grain fields as residues decompose and shift from standing to flat. Winter and spring wheat (Triticum aestivum L.), winter barley (Hordeum vulgare L.), and spring oat (Avena sativa L.) were grown at Bushland, TX, on Pullman clay loam (fine, mixed thermic Torrertic Paleustoll) in 12 field plots in three randomized complete blocks. For each crop, differential seeding rate, fertilization, and irrigation produced a range of biomass. During decomposition, differential irrigation increased environmental variability (13, 5, and 0 applications to sub-sub-plots). Ash-free residue biomass was measured seven times in 14 mo, after taking photographs to determine soil cover of 1-m² sites. For crop-date combinations, coefficients were determined from total (k_t, m² g^-1) or flat (k_f, m² g^-1) biomass. Regression indicated k_t increased with time (P < 0.0001 for all crops, except spring wheat with P < 0.0041). Across crops, the relationship indicated that decomposition affects cover provided by total biomass. Across crops, the weak relationship indicated that cover could be estimated from flat biomass with k_f 0.0175 for extended periods. These findings can improve estimation of residue cover for no-tillage fields and indicate that residue orientation should be considered in biomass-to-cover relationships.

Abbreviations: DAH, days after harvest • k_f, flat biomass cover coefficient (m² g^-1) • k_t, total biomass cover coefficient (m² g^-1) • M, residue biomass (g m^-2)

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