Mycorrhizas and tropical soil fertility
Irene M. Cardoso a,*, Thomas W. Kuyper b
b a Department of Soil Sciences, Federal University of Vicosa, Vicosa 36570-000, Minas Gerais, Brazil ¸ ¸ Department of Soil Quality, Wageningen University, P.O. Box 8005, 6700 EC Wageningen, the Netherlands
Available online24 May 2006
Abstract Major factors that constrain tropical soil fertility and sustainable agriculture are low nutrient capital, moisture stress, erosion, high P ﬁxation, high acidity with aluminium toxicity, and low soil biodiversity. The fragility of many tropical soils limits food production in annual cropping systems. Because some tropical soils under natural conditions have high biologicalactivity, an increased use of the biological potential of these soils to counter the challenges of food production problems is proposed. Most plant species (including the major crops in the tropics) form beneﬁcial associations with arbuscular mycorrhizal (AM) fungi. These fungi could be the most important and poorly understood resource for nutrient acquisition and plant growth in agriculture.This review treats the role of AM fungi in enhancing physical, chemical, and biological soil quality. It focuses on the roles of AM in maintenance and improvement of soil structure, the uptake of relatively immobile elements, both macronutrients (phosphorus) and micronutrients (zinc), the alleviation of aluminium and manganese toxicity, the interactions with other beneﬁcial soil organisms(nitrogen-ﬁxing rhizobia), and improved protection against pathogens. Mycorrhizal associations enable a better use of sparingly soluble phosphorus pools, thereby increasing the efﬁciency of added phosphorus fertilizer and of the large relatively immobile phosphorus pools. Mycorrhizal management through agroforestry, reduced soil disturbance or crop rotation, is often a better option than mycorrhizalinoculation, considering the problems and costs of large-scale inoculum production. Research directions that are needed to increase understanding of mycorrhizal associations in tropical cropping systems and to increase mycorrhizal beneﬁt are indicated. # 2006 Elsevier B.V. All rights reserved.
Keywords: Arbuscular mycorrhizal fungi; Tropical soils; Soil structure; Soil fertility
1. Introduction Manysoils in the tropics are fragile and prone to degradation. Some characteristics of tropical soils put severe constraints on food production. Sanchez et al. (2003) proposed a fertility capability soil classiﬁcation that identiﬁes the major attributes that constrain plant production. These constraints include soil moisture stress (a dry season lasting longer than 3 months makes year-round cropproduction difﬁcult), low nutrient capital, erosion risks, low pH with aluminium (Al) toxicity, high phosphorus (P) ﬁxation, low levels of soil organic matter, and a loss of soil biodiversity.
* Corresponding author. E-mail address: email@example.com (I.M. Cardoso). 0167-8809/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2006.03.011
In the last century, the so-calledGreen Revolution technologies, such as the use of pesticides, synthetic fertilizers and high-yielding cultivars, were used to overcome these constraints (Dalgaard et al., 2003). With this technology the global food supply increased, reducing hunger and improving nutrition. Nevertheless, a billion people have no food security and many rural communities in the tropics and subtropics are persistentlyaffected by a decline in household food production (Stocking, 2003). The Green Revolution techniques also increased natural resource degradation, raising questions about the sustainability of current agricultural practices (Dalgaard et al., 2003). Yields have stagnated in several regions for 15–20 years. The challenge for the next 50 years is to double food production in a way that does not...