『Abstract
In order to better understanding the role of crop residues in
soil protection, soil organic matter, nutrient conservation and
cycling in Mediterranean agro-ecosystems, it is necessary to develop
research since only limited information is available. Few studies
have compared the decomposition rates of legume and cereal residues
in the field, particularly under soil conservation practice with
respect to residue management. In disturbed and undisturbed Portuguese
light soils amended with mature lupine and oat labelled 15N
residues, nitrogen, carbon and microbial activity dynamics were
investigated in situ using undisturbed soil cores in completely
randomized blocks with three replications. Crop residue labelled
with 15N allowed the estimation of N mineralization/immobilization
and nitrification and the level of leaching losses. Most nitrates
were produced in summer, especially in buried top soil with legume
residue, and leaching (about 7% of residue-N) occurred mostly
in October. A preferentially labile C loss by an intense CO2 emission by microbial respiration was observed
in oat residue managed soil after September, with the consequent
increase of greenhouse gas concentration in the atmosphere, overall
a 2% of organic C was accumulated in this soil after six months.
Legumes, with smaller C:N and total lignin:total N ratios resulted
in a more efficient conversion to stable soil organic matter than
cereals. Changes in soil microbial activity were largely controlled
by the quantity and quality of available C and by N in soil, and
less affected by soil disturbance. A more intensive activity was
observed in cereal amended plots, especially in the top soil caused
by a greater organic N level (r = 0.38, p<.05), although the decomposition
rate of oat residue was slower when compared with legume residue.
Keywords: Dehydrogenase activity; Gross N immobilization; In situ
incubation; Leaching; Mineralization/nitrification; 15N』
1. Introduction
2. Materials and methods
2.1. Site description and experimental layout
2.2. Crop residue
2.3. Soil cores
2.4. Chemical methods
2.5. Statistical analysis
3. Results
3.1. Organic C
3.2. Organic N
3.3. Gross mineralization and nitrification
3.4. Nitrate leaching
3.5. Microbial activity
4. Discussion
4.1. Pattern of residue decomposition
4.2. Pattern of nitrate leaching
4.3. Pattern of soil microbial activity
4.4. Summary
5. Conclusions
Acknowledgements
References