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Title: Phosphorus Depletion From Rhizosphere Solution by Maize Grown in Compost-amended Soil

Author
item BORTOLON, LEANDRO - University Of Rio Grande Do Sul
item Kovar, John
item GIANELLO, CLESIO - University Of Rio Grande Do Sul

Submitted to: Plant Nutrition Colloquium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2009
Publication Date: 7/1/2009
Citation: Bortolon, L., Kovar, J.L., Gianello, C. 2009. Phosphorus Depletion From Rhizosphere Solution by Maize Grown in Compost-amended Soil. Plant Nutrition Colloquium Proceedings. Available: http://escholarship.org/uc/item/1cc397f1

Interpretive Summary: Phosphorus (P) fertilizer is essential for maintaining high yields of grain crops, such as corn. Organic amendments, such as manure and compost, are an economical alternative to commercial fertilizers for supplying P to crops. To better understand how plants capture P from soil amended with compost, rather than fertilizer, we must get a handle on the dynamics of P in soil solution around roots. In this study, we used a micro-sampling technique to measure spatial and temporal changes in soil solution P in the rhizosphere of young corn plants. At the end of five days of measurements with roots growing in both topsoil and subsoil, we found that the corn roots were able to acquire more than enough P from solution to prevent significant P depletion. This suggests that the long-term application of compost will not only supply sufficient P for the corn plants, but also limit the effect of P stratification that often occurs when P fertilizer is applied to the soil surface. These results should be of value to commercial growers and conservationists, as well as the fertilizer industry.

Technical Abstract: Knowledge of rhizosphere processes is essential for characterizing soil nutrient availability. Our objective in this controlled-climate study was to evaluate phosphorus (P) dynamics in the rhizosphere of juvenile maize (Zea mays L.) grown in soil amended with compost. Maize seedlings were transplanted at the two-leaf stage, and grown for five days. Soil (550 g) collected from the 0-5 cm layer of field plots was placed in one chamber of a vertically divided mini-rhizotron, and soil from the 5-10 cm layer was placed in the other chamber. Micro-suction cups (15 per chamber) were used to collect rhizosphere soil solution that was subsequently analyzed for P and pH. Initially, P concentrations in rhizosphere solution did not differ with distance from the root surface and were similar in the two soil layers. These results reflect the high levels of available P in both soil layers. Solution pH also was similar among the soil layers and distances from the root surface. The soil used in this study was calcareous and strongly buffered against changes in solution pH. After five days, both soil solution P and pH had decreased in both soil layers. However, only soil solution P was affected by distance from the root surface, confirming the pH buffering of the soil. Maize shoot dry matter production was similar in the two soil layers (0.65 g plant-1 in the 0-5 cm layer and 0.60 g plant-1 in the 5-10 cm layer), suggesting that soil P stratification in this soil under no-tillage had little effect on plant growth.