Soil Nitrogen Mineralization in the Presence of Surface and Incorporated Crop Residues
- S. J. Smith and
- A. N. Sharpley
The increasing adoption of farming practices which maintain crop residues on the soil surface has created a need for more detailed information regarding associated soil N availability. This study examines the effects of crop residue placement and type on soil N availability for a range of soils. Representative field rates of alfalfa (Medicago saliva L.), corn (Zea mays L.), oat (Arena saliva L.), peanut (Arachis hypogaea L.), sorghum, (Sorghum sudanense (Pipe;:) Stapf.), soybean (Glycine max L.), and wheat (Triticum aestivum L.) crop residues were applied to eight Oklahoma surface soils. The experiment was conducted under aerobic laboratory conditions at 35 °C, and involved 2-mim soil particles and 0.25-mm crop residue materials. The N availability was measured on the basis of indigenous and fertilizer-derived soil N mineralized during short- (14 d) and long- (84 d) term incubation. Short-term, an initial depression (more than 80% with corn) in net mineralization occurred with nonlegume residue additions. The depression was enhanced when the residues were incorporated rather than left on the soil surface. The relative depression was greater with the newly formed, fertilizer-derived soil N than the older, indigenous soil N. On the other hand, N mineralization was enhanced more than 50% with the alfalfa addition. Effects of crop residue type on N mineralization showed ranges up to threefold or more and generally proceeded in the order alfalfa > peanut > soybean > oat ≥ sorghum > wheat > com. Long-term, N mineralization for all systems was more comparable to that without residue additions.
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