Soil microbial and nutrient properties in the rhizosphere of coffee under agroforestry management

Published Date

September 2015, Vol.93:40–46, doi:10.1016/j.apsoil.2015.04.003

Title 

Soil microbial and nutrient properties in the rhizosphere of coffee under agroforestry management

• Author 

• J.W. Munroe ^a
• G. Soto ^b
• E. de M. Virginio Filho ^c
• R. Fulthorpe ^d
• M.E. Isaac ^a,d,,

• aDepartment of Geography, University of Toronto, Toronto, Canada
• bUniversidad Nacional de Costa Rica, San José, Costa Rica
• cCentro Agronómico Tropical de Investigación y Enseñanza (CATIE), Turrialba, Costa Rica
• dDepartment of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada

Received 28 October 2014. Revised 27 March 2015. Accepted 3 April 2015. Available online 11 April 2015.

Highlights

• •
  We determined coffee rhizosphere soil nutrient concentrations and nitrifier populations.
• •
  Soil nitrates accumulate in rhizosphere of shade coffee compared to monoculture coffee.
• •
  Soil pH and AOB abundance positively correlate under shade and monoculture coffee.
• •
  Under monoculture coffee, ammonium:nitrate ratios vary with AOB abundance.

Abstract

The integration of shade trees in coffee production can positively contribute to increased yields in these cropping systems. However, little work has examined nutrient-microbial dynamics in the rhizosphere of coffee under shade trees. In this study, we compared nutrient concentrations and nitrifier populations in rhizosphere soil of coffee under shade and in monoculture as well as in rhizosphere versus bulk soils. Our study was performed in a low altitude, wet coffee zone of Costa Rica, at a 12-year-old agroforestry experimental farm with coffee (Coffea arabica) grown under full sun and under the commonly used dinitrogen (N₂) fixing shade tree, Erythrina poeppigiana. Rhizosphere and bulk soils were collected and analyzed for inorganic N, available P, exchangeable base cations and pH status. Real-time PCR was used to determine the relative abundance of ammonia oxidizing bacteria (AOB). We show a nutrient increase (11–158%), particularly nitrates, in the rhizosphere soil compared to bulk soil of coffee. Moreover, this accumulation was greater in the rhizosphere of coffee associated with E. poeppigiana than under monoculture. AOB abundance was strongly related to soil pH (r = 0.83; P = 0.002) across both treatments, while AOB abundance varied with soil ammonium:nitrate ratios (r = −0.82; P = 0.0420) exclusively under monoculture coffee. Our study, for the first time to our knowledge, illustrates soil nutrient differences and nutrient–microbial relationships under coffee in monoculture and in a N₂-fixing shade tree system.

Keywords

• Ammonia-oxidizing bacteria
• Coffea arabica
• Erythrina poeppigiana
• Real-time PCR
• Rhizosphere

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• ⁎ 
  Corresponding author at: University of Toronto, Physical and Environmental Sciences, 1265 Military Trail, Toronto, Ontario, Canada. Tel.: +1 416 287 7276; fax: +1 416 287 7279.

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