Adaptive Soil Management : From Theory to Practices by Amitava Rakshit Purushothaman Chirakuzhyil Abhilash Harikesh Bahadur Singh & Subhadip Ghosh

Author:Amitava Rakshit, Purushothaman Chirakuzhyil Abhilash, Harikesh Bahadur Singh & Subhadip Ghosh
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

14.5 Microbial Integrity for Plant Fitness Under Acid Stressed Soil

Soil acidity is a global problem in crop production. About 40% cultivated land is greatly affected by soil acidity. Despite ample N, P, K supplementation in soil, crop productivity in acid soils is still below average. This is due to ionic toxicity, particularly Al toxicity which is a yield-limiting factor in acid soil (Marschner 1991). Availability of phosphorus is also restricted due to formation of relatively insoluble Al and Fe phosphate in acidic soil.

Acid soil is not at all problem soil. Rather it is the nature of soil as those of other soil types. Reclamation of acidic soil with the application lime stone is conventional mitigation option. But it is not a permanent solution. It recurres within year or two, thus, involves a recurring cost—unaffordable to poor farmers of universally inhabitant of acidic locality in the globe. Moreover, lime induced CO2 production as a source of greenhouse gas is claimed by the environmentalists. Under this context, adaptive soil management that will help the crop plant to acclimatize in existing system without hampering the current environmental health. Encroaching deep soil by selecting deep rooted crop plants, root-induced changes in rhizosphere such as pH increase, release of chelator like amino acids, organic acids for aluminium and augmentation of autochthonous acidophilic beneficial microorganisms, particularly mycorrhizae for increased root surface are the possible adaptive management options for acid soil.

Fungi by acidophilic in nature can improve the plant fitness to an acid soil. Especially mycorrhizal association with crop plants in acidic soil evolves adaptive mechanisms to improve plant fitness in acidic soils having low plant available phosphorus (Marschner 1995; Dodd 2000). Plant-mycorrhizal symbiotic association enhances plant ability to exploit more soil nutrient, particularly, phosphorus and zinc by virtue of extended root surface due to fungal mycelial envelop on plant root (Dodd 2000; Marschner 1998). It is interesting to note that the length of mycorrhizal fungal thread in each centimeter of root may be in the range of 10–100 m in P-deficient soils (McGonigle and Miller 1999). Benefits derived from plant-fungal association are more conspicuous in soil generally poor in nutrients. 70–80% more phosphorus; 50 and 60% more Zn and Cu uptake were recorded in a pot experiment with mycorrhizal inoculated white clover (Li et al. 1991).

Mycorrhizal colonization of plants enhances their ability to explore the soil for P through the action of the fungal mycelium. This results in increased exploration of the soil for available nutrients and delivers more mineral nutrients, particularly P, to plant roots (Dodd 2000; Marschner 1998). It is estimated that the extent of fungal mycelium may be in the range of 10–100 m per cm root or per gram of soil under field conditions in P-poor soils (McGonigle and Miller 1999). In general, the contribution of mycorrhizal associations to the plant nutrient supply is larger in soils with poor availability of mineral nutrients than in soils rich in nutrients. In pot experiments, mycorrhizal colonization contributed to the total P uptake with between

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