Soil Microbial Activity and Biomass in Semiarid Agroforestry Systems Integrating Forage Cactus and Tree Legumes

Dayanne Camelo,Erinaldo Viana de Freitas,José Carlos Batista Dubeux,Mércia Virginia Ferreira dos Santos,Mario Andrade Lira,Felipe José Cury Fracetto,Giselle Gomes Monteiro Fracetto,Márcio Vieira da Cunha

doi:10.3390/agronomy11081558

Abstract

Vegetation cover affects soil organic matter and activity of soil microorganisms. We investigated the intercropping effect of forage cactus with tree legumes on soil microbial biomass and organic matter in the semi-arid tropic, state of Pernambuco, Brazil. We assessed the following cropping systems: (i) Gliricidia sepium intercropped with cactus cv. IPA-Sertânia; (ii) Leucaena leucocephala intercropped with cactus cv. IPA-Sertânia; and (iii) Cactus cv. IPA-Sertânia in monoculture. Samples were collected during the dry and rainy seasons in the 0- to 0.10- and 0.10- to 0.20-m soil layers at 0, 1.5, 3.0, and 4.5 m in a perpendicular gradient from tree legume rows. The following responses were determined: δ13C and δ15N, C and N, microbial activity and biomass, and metabolic, microbial, and mineralization quotient. δ13C and δ15N varied with the distance from the trees. In the dry season and beginning of the rainy season, the cropping systems showed similar values for C, N, microbial activity, carbon, and nitrogen in the microbial biomass. The presence of tree legumes at the end of the rainy season favored soil microbiota, which showed a reduced loss of C-CO2, with no indication of metabolic stress and greater microbial biomass and microbial quotient in relation to forage cactus in monoculture.

Highlights

Forage cactus is an important feed source for herds in semiarid regions. It is utilized throughout the year in the tropical semiarid region of Brazil and in other countries, as it adapts to the edaphoclimatic conditions of these regions
The isotopic composition of soil organic matter near the legume plants indicate a differential effect from these species, both agroforestry systems and cactus monoculture had overall similar effects in increasing soil C and N levels, indicating that all systems might be considered sustainable in this tropical semiarid region
Microbial carbon was greater in the agroforestry systems at the end of the rainy season, but not in other sampling dates

Summary

Introduction

Forage cactus is an important feed source for herds in semiarid regions. It is adapted to semiarid regions, the reduced fiber and crude protein concentrations of forage cactus leads to a need to balance the diet of livestock. One of the alternatives to balance the diet of livestock with proteins and fibers when feeding cactus is intercropping cactus with tree legumes [1]. Gliricidia sepium and Leucaena leucocephala are important tree legume options for animal production in Northeastern Brazil. Both legume species are drought tolerant and nitrogen-fixers, and can be consumed (as a feed or hay) by ruminants, improving the diet of grazing animals and supplying high levels of protein [5,6]. Given the importance of soil organic matter, its evaluation using isotopic techniques (δ13C and δ15N) is a good indicator of the type of existing vegetation and the cycling of organic matter [8]

Methods

Results

Discussion

Conclusion