The role of nitrogen forms on solubilisation and utilisation of rock phosphate by tomato plants
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Date
2005
Authors
Onyango, Gweyi
Neumann, G.
Romheld, V.
Journal Title
Journal ISSN
Volume Title
Publisher
African Crop Science Society
Abstract
The role of nitrogen forms on solubilisation and utilisation of rock phosphate was investigated on tomato (Lycopersicon esculentum) crops grown in minirhizotrons to assess root-induced chemical changes in the rhizosphere. Two tomato cultivars Cal-J and Moneymaker were supplied with rock phosphate as P source, ammonium (plus DIDIN-nitrification inhibitor) and nitrate as Nforms.NH4+ treatment significantly reduced rhizosphere pH while nitrate led to alkanization. Shoot P content increased with declining rhizosphere pH due to rock phosphate solubilisation. P nutrition was sufficient for NH4-N (intense rhizosphere acidification)
but critical under NO3- supply. Shoot Ca contents were in the deficiency range under NH4+ supply, despite increased Ca availability due to rock phosphate solubilisation. Also Mg2+ and K+ uptake declined with decreasing rhizosphere pH. These findings suggest NH4
+ and H+ competition with cation uptake, limiting shoot growth. Acid soils low in Ca and Mg, NH4 + in combination with NO3- may improve rock phosphate utilisation
Description
Keywords
Ammonium, nitrate, rock phosphate, tomato cultivars
Citation
African Crop Science Conference Proceedings, Vol. 7. pp. 1029-1032 2005