Phosphorus Fractions of Red Soils in Guangdong Province of South China and Their Bioavailability for Five Crop Species
2014
Ao, Junhua | Chen, Zhijian | Wu, Man | Lu, Xing | Huang, Zhenrui | Liao, Hong
Red soil, the main soil type in south China, has many limitations for crop production, especially low phosphorus (P) bioavailability. Currently, little is understood concerning P fractions and their bioavailability for crops. In the present study, P fractions were analyzed from 50 red soil samples collected from regions leading agricultural production in Guangdong Province of south China. The most abundant P forms were iron-bound P (Fe-P) and organic P (Org-P), which, combined, account for 64.4% ± 1.9% of total soil P. Both Org-P and Fe-P had less bioavailability for soybean in sand culture than the other sparingly soluble P forms tested, with growth reduced by 78.0% ± 4.2% or 35.4% ± 6.7% and P content reduced by 50.2% ± 8.4% or 68.7% ± 1.8% when P was supplied as Org-P or Fe-P, respectively, compared with plants supplied with KH2PO4. Further field experiment using five crop species showed that P bioavailability in red soils is very low, as reflected by an average of 53.9% ± 2.9% loss in shoot P content for all tested crops in soils without P fertilization compared with plots amended with P fertilizer. After evaluation of root-to-shoot ratio and specific root length, along with rhizosphere P depletion and acidification, it is reasonable to speculate that different crop species have evolved various strategies to overcome P deficiency in red soils. Among the tested crops, rapeseed displayed more rhizosphere acidification and lower carbon cost for maintaining root growth and subsequently possessed a superior ability to use and activate P from red soils than the other four crops.
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