472
root colonization. Our results demonstrate the strong effect of soil quality and crop
genotype on AMF- rhizobia- legume symbiosis, which affects overall crop growth
and production. These factors should therefore be critically considered during
the development of efficient low-cost inocula for enhanced smallholder farmers’
crop production.
1 Introduction
Over the last decade, agricultural productivity has continued to decline in many
smallholder agroecosystems, which are the main source of livelihood in developing
countries. This has been as a result of several underlying factors such as inherent
poor soil fertility, pests and diseases and increased human population, which has
consequently led to land fragmentation, degradation and water stress associated
with the changing climate (Mwendwa and Giliba 2012; Cozzolino et al. 2013).
Among these factors, low soil fertility presents one of the major challenges to sustainable crop production since most smallholder farmers cannot afford to invest in
chemical fertilizers (St.Clair and Lynch 2010). Recently, most research to improve
crop production has targeted plant breeding for crop cultivars that are high yielding,
drought tolerant and resistant to pests and diseases (Boon et al. 2013). However, the
widening gap between food production and increasing population has continued
unabated, which calls for concerted efforts to enhance sustainable agriculture practices. In this context, key strategies such as the utilization of soil biota for improvement of soil fertility and land productivity through biological processes have been
brought to the limelight (Oruru and Njeru 2016).
Nitrogen and phosphorus are the major limiting nutrients required for plant
growth (Antunes and Goss 2005). Due to its involvement in crucial plant processes such as respiration, energy transfer, phospholipid and nucleic acid synthesis, plants require phosphorus in large amounts compared to other nutrients (Chen
and Graedel 2016). Globally, phosphate-based fertilizer application has increased
fivefold from 5 million tons of phosphorous (P) per year in 1961 to 20 million
tons per year in 2013 (Chen and Graedel 2016). Most sub-Saharan Africa soils are
deficient of P in both inorganic and organic forms since most of the P is poorly
available for plant uptake, due to its immobilization and precipitation with other
soil minerals such as iron (Fe) and aluminium (Al) in acid soils and calcium (Ca)
in alkaline soils. Consequently, only a small percentage of P (<1%) is directly
available for plant uptake (Battini et al. 2017), resulting in a major limitation to
crop production.
Microorganisms associated with plant roots can be used sustainably in mobilizing P in the soil, thus making it available to the plants (Philippot et al. 2013).
These include arbuscular mycorrhizal fungi (AMF) which constitute a key functional group of soil microbiota that can greatly contribute to crop productivity and
E. M. Njeru et al.
root colonization. Our results demonstrate the strong effect of soil quality and crop
genotype on AMF- rhizobia- legume symbiosis, which affects overall crop growth
and production. These factors should therefore be critically considered during
the development of efficient low-cost inocula for enhanced smallholder farmers’
crop production.
1 Introduction
Over the last decade, agricultural productivity has continued to decline in many
smallholder agroecosystems, which are the main source of livelihood in developing
countries. This has been as a result of several underlying factors such as inherent
poor soil fertility, pests and diseases and increased human population, which has
consequently led to land fragmentation, degradation and water stress associated
with the changing climate (Mwendwa and Giliba 2012; Cozzolino et al. 2013).
Among these factors, low soil fertility presents one of the major challenges to sustainable crop production since most smallholder farmers cannot afford to invest in
chemical fertilizers (St.Clair and Lynch 2010). Recently, most research to improve
crop production has targeted plant breeding for crop cultivars that are high yielding,
drought tolerant and resistant to pests and diseases (Boon et al. 2013). However, the
widening gap between food production and increasing population has continued
unabated, which calls for concerted efforts to enhance sustainable agriculture practices. In this context, key strategies such as the utilization of soil biota for improvement of soil fertility and land productivity through biological processes have been
brought to the limelight (Oruru and Njeru 2016).
Nitrogen and phosphorus are the major limiting nutrients required for plant
growth (Antunes and Goss 2005). Due to its involvement in crucial plant processes such as respiration, energy transfer, phospholipid and nucleic acid synthesis, plants require phosphorus in large amounts compared to other nutrients (Chen
and Graedel 2016). Globally, phosphate-based fertilizer application has increased
fivefold from 5 million tons of phosphorous (P) per year in 1961 to 20 million
tons per year in 2013 (Chen and Graedel 2016). Most sub-Saharan Africa soils are
deficient of P in both inorganic and organic forms since most of the P is poorly
available for plant uptake, due to its immobilization and precipitation with other
soil minerals such as iron (Fe) and aluminium (Al) in acid soils and calcium (Ca)
in alkaline soils. Consequently, only a small percentage of P (<1%) is directly
available for plant uptake (Battini et al. 2017), resulting in a major limitation to
crop production.
Microorganisms associated with plant roots can be used sustainably in mobilizing P in the soil, thus making it available to the plants (Philippot et al. 2013).
These include arbuscular mycorrhizal fungi (AMF) which constitute a key functional group of soil microbiota that can greatly contribute to crop productivity and
E. M. Njeru et al.