Straw Decomposition in Irrigated Soil: Comparison of Twenty-three Cereal Straws

The objective of this research was to evaluate field decomposition of 23 cereal grain straws. Straw samples of ‘Fieldwin’ and ‘Owens’ soft white spring wheats (Triticum aestivum L.); ‘Borah’ and ‘McKay’ hard red spring wheat; ‘Nugaines’, ‘Daws’, ‘Lewjain’, ‘Stephens’, and ‘Hill 81’ soft white winter wheats; ‘Weston’, ‘Manning’, ‘Neeley’ hard red winter wheats; ‘Advance’, ‘Steptoe’, ‘Lud’, ‘Pirolene’, and ‘Klages’ spring barleys (Hordeum vulgare L.); ‘Kamiak’, ‘Boyer’, and ‘Schuyler’ winter barleys; Waid durham wheat (Triticum durum Desf.); and ‘Flora’ and ‘Palouse’ triticales (Triticale hexaploide Lart.); were buried in field plots. The straw bags were removed at intervals during 1 yr and analyzed for the amount of decomposition, and C and N contents. Final decomposition ranged from 54% for the Borah wheat straw to 75% for the Lud barley straw with about half of the straws decomposing 64 or 65%. The hard red spring wheat and triticale straws decomposed the slowest and two spring barley straws decomposed most rapidly, but no completely systematic differences were observed for different genera of straws. The original straw N concentrations ranged from 2.2 to 12.5 g/kg. Nine straws lost N during the incubation period from September to November while eight increased in N concentration during this time. In the next three incubation periods, from November to the following October, nearly every straw sample increased in N concentration. The total N weight in the straw increased to the May sampling and then decreased thereafter. This pattern indicates that the straw was releasing N as it was mineralized and became available for utilization by the growing corn crop. Carbon/N ratios ranged widely in the initial straw samples, becoming more nearly uniform as the decomposition process developed. The C/N ratios remained fairly high avg 41 for the final sampling even though the straw in every case had released N into the soil during the last sampling period. Regression analysis of total decomposition and change in weight of N in the wheat straw samples for the first 67-d incubation in the field showed a linear relationship with decomposition during the year, decreasing with increasing N loss in the early stage.