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Title: RESPONSE OF MYCORRHIZAL SWITCHGRASS TO PHOSPHORUS FRACTIONS IN ACID SOIL

Author
item Clark, Ralph
item Baligar, Virupax
item Zobel, Richard

Submitted to: Communication in Plant and Soil Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2004
Publication Date: 5/1/2005
Citation: Clark, R.B., Baligar, V.C., Zobel, R.W. 2005. Response of mycorrhizal switchgrass to phosphorus fractions in acid soil. Communications in Soil Science and Plant Analysis. 36(9-10): 1337-1359.

Interpretive Summary: Acid soils occupy more than 4 billion hectares of land area in the world. Poor productivity of crops grown on acid soils is due to their low phosphorus status. There are beneficial fungi that grow inside the plant roots that are known to improve the plants' ability to take up phosphorus more efficiently. The described study compared the effectiveness of four different fungi in acquisition of phosphorus by switchgrass. For this study we used five different acid soils from the Mid-Atlantic region. The fungi enhanced plant growth, but no one fungal isolate was optimum or even best on all five soils. Specific fungal isolates and their compatibility with any given soil must be evaluated before a recommendation can be made of its suitability. Farmers of the Mid-Atlantic region will benefit greatly by inoculating grasses grown on acid soils with suitable fungi. Such practice will improve soil phosphorus supply and pasture yield potentials in acid soils.

Technical Abstract: In acidic soils, acquisition of phosphorus (P) by plants is limited due to low P availability and slight solubility. Arbuscular mycorrhial fungi (AMF) have the ability to access much of soil P and make it more available to plants. Therefore, pools of available P to mycorrhizal (AM) plants grown in acidic soil are usually higher than in nonmycorrhizal (nonAM) plants. Switchgrass (Panicum virgatum L.) was grown in five acidic soils (Lily, Porters, Tatum, Rayne, and Pacolet) containing various amounts of P with four different isolates of AMF in a glasshouse. The different fractions of P in each soil were determined to assess their importance to plant acquisition by AM and nonAM plants. Total and organic P fractions in soil were relatively high compared to other extractable P fractions. They are considered available to plants (extractable fractions), but differences among soils in total and organic P were relatively narrow compared to extractable fractions. With the exception of G. intraradices, each of the AMF isolates used (Glomus Clarum, Glomus etunicatum, Glomus intraradices, and Acaulospora mellea) enhanced growth to some extent when grown in each of the soils. However, the highest dry matter (DM) for each of the AM plants was soil dependent. Shoot concentrations of mineral nutrients generally increased in AM plants that enhanced growth. None of the AMF isolates was best for these acidic soils, nor for each P fraction or other soil characteristic measured. Extractable P fractions appeared to be more readily available to AM plants compared to non-extractable fractions.