Crop Residue Type and Placement Effects on Denitrification and Mineralization

Abstract

Nutrient release from legume and cereal crop residue is important to N cycling and the success of conservation and sustainable farming systems. Residue type, placement, and degree of incorporation, and soil water regimes largely control availability and loss of soil N and were evaluated in the laboratory. Four residues, i.e., vetch (Vida villosa Roth.), soybean (Glycine max [L.] Meir.), corn (Zea mays L.), and wheat (Triticum aestimm L.) having C/N ratios ranging from 8 to 82 were applied on the soil surface or incorporated in repacked cores of a NicoIIet loam (fine-loamy, mixed, mesic Aquic Hapludoll) and incubated for 17 or 35 d at 60 and 90% water-filled pore space (WFPS) with enriched "N-NO, (76.7%). Denitrification losses from all treatments were negligible at 60% WFPS. At 90% WFPS, total denitrification losses from residue-incorporated soils represented 87 to 127% of the initial soil NO 3 level (80.5 mg N kg-'); losses increased with decreasing residue C/N ratio. Denitrification was greatest during the first 8 d, as was CO 2 evolution. Initial denitrification with surface-placed residues was less than with incorporated residues, but cumulative losses over 35 d did not differ significantly. Substantial N immobilization occurred with incorporated or surface-placed wheat, corn, and soybean residue with wide C/N ratios at 60% WFPS, whereas, with low-C/N-ratio vetch, significant mineralization occurred. After 35 d, 51 and 36% of N in incorporated and surface-placed vetch residue, respectively, was mineralized. Residue C/N ratio was inversely related to initial rates of residue decomposition, and effects of residue type and placement and soil water on denitrification and mineralization were most important during early (8-10 d) decomposition. I NCREASED COSTS and environmental concerns promote research on agricultural production systems that reduce soil erosion and balance synthetic chemical use with renewable biological resources. With conventional tillage, crop residues are incorporated into the soil; in conservation farming (reduced-or ridgetillage management systems), residues are left on the soil surface or are partially incorporated just before

Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

“…N 2 O is emitted during microbial processes such as nitrification and denitrification (Aulakh et al 1991). Although the 1% default N 2 O EF from the decomposition of crop residues was determined independent of crop types (IPCC 2006), recent studies have suggested that crop residues with a low carbon to nitrogen (CN) ratio, including those derived from soybeans, are more likely to emit relatively larger amounts of nitrous oxide-nitrogen (N 2 O-N) per N input (Baggs et al 2000;Toma and Hatano 2007;Delgado et al 2010).…”

“…This was the period during which nodules were likely to be decomposing and producing N 2 O. Another soil incubation study showed a positive effect of increasing soil moisture on N 2 O emissions from soybean residues (Aulakh et al 1991). In that study, soybean residues were applied on the soil surface and the soil was incubated for 35 d at 60% and 90% WFPS.…”

“…During the 35-d experimental period, cumulative soil N 2 O emissions from soils incubated with soybean residues increased from < 1.4 to 16.7 mg N kg −1 soil when soil moisture was increased from 60 to 90% WFPS. Aulakh et al (1991), based on their measurements of total denitrification rates and inorganic N concentrations in soils, concluded that soybean residues were the source for nitrate-nitrogen (NO 3 À -N), and the consequent increase in denitrification rate was responsible for the increase in N 2 O emissions from soybean residues when soil moisture was increased. Ciarlo et al (2009) also conducted a laboratory incubation study using air-dried intact soil cores at 18 to 22°C.…”

“…In laboratory studies, high N 2 O emissions from soybean residues were observed when soil moisture conditions were > 50% WFPS (Aulakh et al 1991;Ciarlo et al 2009). In many of the field studies listed in Table 1, soil moisture levels in fields during the postharvest period in soybean ecosystems were relatively lower than those reported in laboratory studies.…”

How Important is the Quality of Organic Amendments in Relation to Mineral N Availability in Soils?

“…A large variation in C/N ratio can be expected from different sources of materials because of differences in species and age. The C/N ratio ranges from as low as 6.5 in composted chicken or pig manure to as high as 82 in cereal-crop residues [5] and 664 in sawdust [44]. It has been reported that crop residues with a C/N ratio of less than Agric Res (June 2013) 2(2): 99-110 101 33 will provide net N mineralization [8].…”