Decomposition of sorghum residue in a double-crop sorghum and wheat system

Abstract

An understanding of crop residue decomposition patterns is fundamental to the efficient management of residue, particularly in double-cropping systems. In a 3-yr study conducted at Plains, Ga, decomposition of residue from three grain sorghum [ Sorghum bicolor (L.) Moench] cultivars buried in mesh (53-μm) bags at two different times was monitored for 160–225 d, depending on the year. No consistent differences in decomposition patterns among the cultivars were apparent. Residue dry matter and N loss from both Burial 1 (immediately after sorghum grain harvest) and Burial 2 [prior to planting wheat ( Triticum aestivum L. em Thell), about 50 d after Burial 1] followed exponential patterns. During the interval between Burial 1 and Burial 2, slower decomposition of the standing residue resulted in Burial 2 residue being reduced to means of 77 and 84% of the original dry matter and N values, respectively; whereas, mean values for the buried Burial 1 residue had declined to 50 and 76% for original dry matter and N, respectively. However, by 225 d after Burial 1, both residues had very similar relative dry matter and N values. At 225 d, the mean relative dry matter remaining for Burial 1 and Burial 2 residues were 36 and 33%, respectively. The mean relative N remaining at 225 d for Burial 1 and Burial 2 residues were 67 and 64%, respectively. The C-to-N ratio of the residue decreased linearly with time from an initial mean of 33.3 to a mean of 15.8 after 225 d of decomposition. The results demonstrate that sorghum residue is readily decomposed in soils of the southeastern U.S.A.