Re-Evaluating Diagnostic Phosphorus Tests for Rice Systems Based on Soil Phosphorus Fractions and Field Level Budgets
- Bruce Linquist *a and
- Matthew Ruarkb
The efficient management of P fertilizer in rice (Oryza sativa L.) systems is essential in ensuring optimal yields while also avoiding problems related to over application. Identifying P deficient soils is critical to developing efficient P recommendations. The objectives of study were to determine the extent of P deficiencies in California rice systems, evaluate diagnostic P tests, and identify soil P fractions that contribute to crop P nutrition. On-farm P-omission experiments were conducted at 64 sites where we measured Y-leaf P concentration, P uptake, and grain yield. Soil samples were collected and analyzed for Olsen and Bray-P as well as being subjected to a sequential P fractionation scheme to determine NaHCO3, NaOH, and HCl inorganic (Pi) and organic (Po) P. From grower interviews, an annual input/output P budget was constructed for each site that accounted for P fertilizer inputs and outputs (P removed at harvest) over the previous 5 yr. Olsen-P (critical value: 6 mg kg−1) and Y-leaf P tests (critical value: 0.2%) were reasonable at predicting P deficiencies across a wide range of soil types. The P budget, correlated with Olsen and Y-leaf P, was also helpful in determining if the grower applied P rates were adequate as the only P deficient sites had a P budget of 0.5 kg P ha−1 yr−1 or less. Sodium bicarbonate inorganic P (NaHCO3–Pi), NaOH-, and HCl-Pi and -Po fractions were all correlated with Y-leaf P concentrations. The only Po fraction correlated with Y-leaf P and the P budget was HCl-Po. The primary sinks for excess applied P fertilizer were the NaHCO3–Pi and NaOH-Pi fractions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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