Extraction of phosphorus from the major agricultural soils of Alaska

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Abstract
The crop land in Alaska has increased five‐fold in the past ten years. The state includes a relatively large geographic area and the agricultural soils vary considerably from volcanic ash to loess derived soils. The P‐sorption capacities of the soils also are known to vary widely but little data is available on the nature of soil P and the performance of P extractants on these soils. A laboratory and growth chamber study was conducted to investigate the suitability of seven P extractants for use on Alaska agricultural soils. Ten representative soils were collected from the agricultural regions of Alaska, five were volcanic ash derived and five were loess derived. Response of barley (Hordeum vulgare L. var. ‘Weal') to soil test P‐levels was determined in the growth chamber. Soil P levels were established from P‐isotherm curve data and soil P levels were determined using Morgan, Bray 1, Bray 2, Mehlich 1, Mehlich 2, Mehlich 3, and Olsen extracting reagents. The volcanic ash soils contained 47% more native P and had P‐sorption maximas 157% higher than the loess soils. The volcanic ash soils required over four times the P applied for maximum yield than the loess soils. Oxalate extractable (amorphous) Fe plus Al was highly correlated to P‐sorption among the ten soils. The Mehlich 3 extractable P at maximum yield was most highly correlated with oxalate Fe plus Al followed by Bray 1 and Mehlich 2. The Morgan extractable P was the lowest of all extractants for all soils and P addition levels. Mehlich 3 extractable P correlated well with yield for the soils. Mehlich 3 test levels to attain maximum yield were highly correlated to oxalate extractable Fe plus Al. Extractable P by Olsen and Bray 1 extractants was most variable over the ten soils. It was concluded that the Mehlich 3 extractant is both suitable and desirable for use due to its high correlation to percentage maximum yield and the predictability of desired soil test P levels with soil oxalate extractable Fe plus Al. Additionally, Mehlich 3 holds potential for future use as a multi‐element extractant.