Action: Amend the soil with bacteria or fungi
Biodiversity: One randomized, replicated trial from India showed that adding soil bacteria and arbuscular mycorrhizal fungi resulted in higher microbial diversity.
Soil organic matter: One controlled, randomized, replicated trial from Turkey found increased soil organic matter content in soil under mycorrhizal-inoculated compost applications
Yield: Two randomized, replicated trials (including one also controlled) from India and Turkey found higher crop yields.
SOIL TYPES COVERED: clay-loam, sandy-loam.
Soil microbial biomass is the amount of tiny living organisms within a given area or amount of soil. Arbuscular mycorrhizal fungi are a group of fungi that live around the roots of plants. By living together, the fungi and host plant benefit each other: the fungi can live in a habitat without having to compete for resources and gain a supply of carbon from the plant, while they provide an enhanced supply of nutrients to the plant which improves plant growth, the ability to reproduce and tolerance to drought. Arbuscular mycorrhizal fungi colonise a wide variety of host plants, including grasses, herbs, agricultural crops and legumes (Bardgett 2005).
Bardgett R. (2005) The Biology of Soil: A community and ecosystem approach. Oxford University Press, Oxford.
Supporting evidence from individual studies
A controlled, randomized, replicated experiment in 2002-2004 on sandy-loam soil in Udham Singh Nagar, India (Srivastava et al. 2007) found that adding soil bacteria and arbuscular mycorrhizal fungi (see background section) increased soil microbial diversity (2.5 x 103 colonies/g soil), compared to the control (1.9 x 103 colonies/g soil). Crop yields in okra Hibiscus esculentus, pea Pisum sativa and cowpea Vigna unguiculata increased when bacteria (33, 25 and 8 kg/ha, respectively) and arbuscular mycorrhizal fungi (40, 28 and 11 kg/ha) were added, compared to the control (22, 21, and 4 kg/ha). Three crops were grown in rotation: okra, pea and cowpea. Each plot was 16 m2. AMF Glomus intraradices and a bacterium species Pseudomonas fluorescens were added to the soil as treatments. Only crop residues were added during the experiment. There were three replicates. Soil samples were taken and soil microbe numbers were measured. The effect of rotation was not reported.
A controlled, randomized, replicated experiment from 1996 to 2008 on clay-loam soil in southern Turkey (Celik et al. 2010) found 24% higher organic matter content in soil under mycorrhizal-inoculated compost applications compared to the control. The largest soil aggregations were found under mycorrhizal-inoculated compost (0.11 mm), manure (0.05 mm) and compost (0.07) applications. Crop yield was highest under mineral fertilizer (13720 kg/ha) followed by manure (10500 kg/ha), compost (8780 kg/ha) and mycorrhizal-inoculated compost (7630 kg/ha), compared to the control (5900 kg/ha). Within a wheat Triticum aestivum-maize Zea mays rotation were three replicates five 10 x 20 m treatments: control, mineral fertilizer (300-60-150 kg N-P-K/ha), manure (25 t/ha), compost (equal mixture of grass, wheat stubble and plant leaves, 25 t/ha), mycorrhizal Glomus caledonium-inoculated compost (10 t/ha). Soil samples were taken to 30 cm depth 2008.
- Srivastava R., Roseti D. & Sharma a.K. (2007) The evaluation of microbial diversity in a vegetable based cropping system under organic farming practices. Applied Soil Ecology, 36, 116-123
- Celik I., Gunal H., Budak M. & Akpinar C. (2010) Effects of long-term organic and mineral fertilizers on bulk density and penetration resistance in semi-arid Mediterranean soil conditions. Geoderma, 160, 236-243