Availability to plants of phosphate from“biosupers” and partially acidulated phosphate rock

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Abstract
An 18-month greenhouse study using: uncalcined Christmas Island“C” grade ore (CC); Chatham Rise phosphorite nodules (CR); and North Carolina phosphate rock partially acidulated with phosphoric acid (PAPR) was conducted to evaluate CR/S and CC/S biosupers (phosphate rock/sulphur granules), and PAPR in comparison with superphosphate. Perennial ryegrass was grown as the test crop in a highly phosphate-retentive soil. The fertilisers were added 5 mm below soil surface at 5 rates and a control was also included. An additional set of pots with biosuper added was inoculated with Thiobacillus thioxidans bacteria. For the first 12 months the total dry matter yield indicated that CR/S was the most effective material then PAPR and superphosphate, then CC/S (Psuperphosphate>CC/S (P<0.01). The recovery values ranged from 13% to 57% for CR/S and 13 to 29% for PAPR. The values for superphosphate and CC/S were 12% and 4% respectively, again independent of the amount of fertiliser added.