Title: Effect of nitrogen fertilization and shade type in soil quality and nitrogen assimilation in Ecuadorian Amazon Coffea canephora agroecosystems.
Author: Rosa Elena Ibarra López (El Salvador).
Advisors: Carmen Alicia Parrado, Ph.D. Andrew Margenot Ph.D.
Department: Environmental Science and Development
In the Amazon basin, Robusta coffee (Coffea canephora) is produced in contrasting agroecosystems of low input, shade-based smallholder production, or in intensively managed monoculture plantations that differ in nitrogen (N) availability and productivity. This study aimed to determine whether the shade trees and proper addition of N-fertilizer in coffee plantations may provide soil fertility benefits and contribute to soil quality and crop productivity. Full sun had a positive effect on enzyme activities, potentially mineralizable N (PMN), available ammonium (NH4-N), leaf %N and leaf N:P. Enzyme activities as well as NH4-N were greater under low input, whereas high input yielded greater PMN, leaf N and leaf N:P. Protease was positively associated with PMN (R = 0.60, P = 0.003) but unrelated to the activities of the aminopeptidases, and carbon (C) mineralizing enzymes. Permanganate oxidizable C (POXC) and nitrate (NO3-N) were similar across input and shade management but more variable under shade relative to full sun. Low input offers limited improvements in soil N cycling increasing by 53% the enzymatic activity and N availability by 31% relative to high input under Robusta coffee production in this region, whereas high input improves PMN and Robusta N uptake (Leaf N). Relatively lower response in enzymatic activities, C and N stocks, and leaf N under shade management suggests that although it is a common smallholder practice in this region, leguminous tree-based agroforestry may not close N needs of Robusta as effectively as higher N inputs.
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