Seasonal P uptake by corn under no‐till and conventional‐till management

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Abstract
This study was conducted to measure season‐long uptake of P by corn grown under no‐till and conventional‐till management at three levels of P supply‐low, adequate, and high as defined by grain yield‐to test the feasibility of using whole‐plant P uptake as an indicator of the P supply in soil; and to calibrate soil P extractable with both Mehlich No. 1 (HC1 + H2SO4) and Mehlich No. 2 (HC1 + H2SO4 + NH4F) versus whole‐plant P uptake over the response region. Rates of P uptake were essentially linear over about 10 weeks of the growing season. P uptake rates were consistently higher under no till than conventional till, and these uptake rate differences were magnified under low moisture conditions. The critical P uptake rate for corn on this Matapeake soil was between 25 and 30 mg P/plant/week. Rates below these resulted in significant grain yield reductions in a good growth year. The soil P extractant containing F was a more consistant indicator of soil P sufficiency.