Short-term tillage practices on soil organic matter pools in a tropical Ultisol
David Sotomayor-Ramírez A D , Yusmary Espinoza B and Rafael Rámos-Santana CA Agronomy and Soils Department, College of Agricultural Sciences, University of Puerto Rico – Mayagüez Campus, PO Box 9030, Mayagüez 00681-9030, Puerto Rico.
B Centro Nacional de Investigaciones Agropecuarias – Instituto Nacional de Investigaciones Agrícolas (Ceniap-INIA); Maracay, Venezuela.
C Agronomy and Soils Dept., College of Agricultural Sciences, Agricultural Experiment Station, Corozal, Univ. of Puerto Rico – Mayagüez Campus, Puerto Rico.
D Corresponding author. Email: dsotomayor@uprm.edu
Australian Journal of Soil Research 44(7) 687-693 https://doi.org/10.1071/SR06049
Submitted: 14 April 2006 Accepted: 25 September 2006 Published: 20 October 2006
Abstract
In tropical regions, pasture establishment involves tillage operations. Adoption of conservation tillage practices could result in lower costs and in improved soil quality by decreasing soil organic carbon (SOC) losses. This study investigated the effects of 3 tillage practices on the establishment of Brachiaria decumbens and on the total SOC and soil organic nitrogen (SON) content and its fractions in an Ultisol from the humid mountain zone of Puerto Rico that was previously under pasture. The treatments evaluated were no-tillage, minimum tillage, and conventional tillage (CT). At 120 days after planting (DAP), plant cover and density was improved in the CT treatment compared with the other treatments. At 180 DAP, there were no significant differences in the SOC, SON, aggregate size distribution, distribution of C within aggregate size classes, and labile C physical fractions among tillage treatments. Approximately 60% of the total SOC associated with aggregates was found within macroaggregates. About an equal proportion of the particulate organic matter (POM) was associated within aggregates and nonaggregate-protected free light fraction, and these were not affected by tillage management. Lower amounts of C mineralised after disruption of macroaggregates containing POM with high C/N ratio was probably due to immobilisation of the more labile protected C (iPOM). Labile forms of C were greater in macroaggregates than in microaggregates, yet comprised a lower proportion of total SOC, suggesting that macroaggregates have a greater proportion of C physically protected from microbial attack. The results indicate that there are no short-term changes in the tendency of the soil to lose C and N as a result of tillage practices for the establishment of pastures in this soil.
Additional keywords: soil organic matter fractions, soil tillage practices, soil aggregates, soil organic matter protection.
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