Linking carbon inputs to sustainable agriculture in Canadian and Costa Rican agroforestry systems

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Authors

Oelbermann, Maren

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University of Guelph

Abstract

Alternative land management practices, including agroforestry, can rejuvenate marginal soils and increase soil C sequestration to help mitigate atmospheric CO2 emissions. The objective of this study was to quantify C inputs in temperate and tropical alley cropping systems. In Costa Rica 18, 9 and 3-year old 'Erythrina poeppigiana' (Walp.) O. F. Cook and 'G. sepium' (Jacq.) Walp. were combined with maize and beans ('Phaseolus vulgaris' L.), and in Canada 12-year old hybrid poplar ('Populus deltoides' x 'nigra' DN 177) was alley cropped with maize ('Zea mays' L.) and soybeans [('Glycine max' L. (Merr.)]. The 18 and 9-year old tropical system, with either tree species, had an input of 2365 and 3960 kg C ha -1 y-1 from maize and bean residues, where maize roots contributed approximately 14% of total residue C input and bean roots contributed 12%. Comparatively crop C input in Canada was 2118 kg C ha-1 y-1 for maize and 826 kg C ha-1 y-1 for soybeans, where roots contributed 10 to 14% of the total C inputs. A higher C input from crop residues in the tropical biome results from two cropping seasons per year compared to a single crop in the temperate system. Carbon input from 18-year old tree prunings was 4003 kg C ha-1 y-1, and 1038 and 1038 kg C ha-1 y-1 for 9 and 3-year old trees. Annual C input from hybrid poplar prunings was 1407 kg C ha-1 y-1 with an additional contribution of 816 kg C ha-1 y-1 from autumnal litterfall within 3.5 m of the tree row. Soil organic C (SOC) ranged from 139, 101 to 96 Mg C ha-1 y-1 for 18, 9 and 3-year old tropical systems, whereas the temperate system SOC pool was 125 Mg C ha-1 y-1. The proportion of C derived from C4 plants to a 20 cm depth in tropical alley crops was 35% (18-yr) and 24% (9-yr), with similar values (23%) in the temperate system. These results suggest that the rate of SOC turnover in tropical soils (14 yrs) is greater than that of temperate soils (45 years).

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Keywords

Canada, Costa Rica, agroforestry systems, carbon inputs, sustainable agriculture

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