Thursday, November 8, 2007 - 9:45 AM
344-4
Carbon Decomposition Patterns of 13C Labeled Rice and Wheat Roots and Shoots under Field Conditions.
A study was conducted using the stable isotope 13C to pulse label the rice (Oriza sativa L.) and wheat (Triticum aestivum L.) crops to examine root and straw residue decomposition in soil under no-till (NT) and conventional tillage (CT) management under field conditions. Two existing tillage experiments (3-5 years old; permanent bed vs CT at Ranighat and NT vs CT at Baireni) in the central terai region of Nepal were utilized for this study. Both rice and wheat crops were grown in microplots and after 4-6 weeks of growth, plants were pulse labeled with 13CO2 a total of six times at 7-10 day intervals. Initially straw decomposition was slower in the NT treatment, where straw was placed as mulch, than in the CT treatment. However, after 16 months and 3 crops straw C remaining in the NT treatment (7-13%) was significantly less than that in the CT treatments (13-17%) for both rice and wheat residue types. Root C decomposed more slowly than straw C for both rice and wheat under both NT and CT treatments. However, significant effects of tillage were only found for rice root derived 13C after 12 and 16 months. Higher levels of rice root 13C were observed under NT (43-57%) than CT (37-38%). Overall, decomposition of straws of rice and wheat was faster under NT compared to CT, and only the decomposition of rice roots was slower under NT. Possibly the change to NT in these degraded soils, leads first to accelerated decomposition of residues before later building aggregates that protect organic matter from decomposition. It is expected that root derived C will be the most important contributor to C sequestration under long-term NT in the rice-wheat system.
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