Losses of Wheat Straw Residue Under Simulated Field Conditions

Wheat ( Triticum aestivum L.) straw residues contained in fiberglass screen envelopes were exposed to field conditions at Bozeman and Huntley, Mont. Samples from above‐soil, on‐soil, and buried exposures were taken periodically during an 18‐month period to measure weight losses and changes in N and P contents of the residues. Decomposition was more rapid at Huntley than at Bozeman, probably because air temperatures averaged 2.3C warmer at Huntley. Percentage losses were inversely related to residue amounts. After 18 months, on‐soil residue losses averaged 31% at Bozeman and 40% at Huntley. The 50% decomposition stage for buried straw occurred in 3 months at Huntley and 6 months at Bozeman, and after 18 months, losses of buried straw averaged 93% at Bozeman and 98% at Huntley. Compared to the original straw, both N and P percentages increased as much as sixfold in the buried samples during decomposition. For buried straw, maximum percent N was 1.18 at Bozeman and 1.46 at Huntley. Similar values for maximum percent P were 0.132 at Bozeman and 0.147 at Huntley. For buried straw, N and P immobilization was maximum after 3 months at both locations. At that time, N contents at the two locations exceeded original content by an average of 1.6, 2.9, 2.8, 2.9, and 5.3 kg/ha for straw rates of 1,121, 2,242, 3,363, 4,484, and 6,732 kg/ha. P contents exceeded original content by an average of 0.3, 0.5, 0.7, 1.0, and 1.7 kg/ha for the same straw rates.