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Potassium Release Characteristics of Selected Peruvian Soils¹

ABSTRACT

To evaluate K release, 16 Peruvian soils were intensively cropped in growth chambers using the Stanford-DeMent technique, and K was extracted with sodium tetraphenylboron (NaTPB) for varying periods. When 1-g soil samples were equilibrated with solutions containing NaTPB for 0.25, 1, 10, 100, 1,000, and 2,000 hours, K extracted with NaTPB was linearly correlated with the logarithm of time from 10 to 1,000 hours. Rates of K release varied from –0.03 to 7.43 meq K/100 g soil per week. Large differences in the total amount of K removed in 2,000 hours (1.9 to 66.9 meq K/100 g soil) were related to the presence and apparent degree of crystallinity of illite in the clay fraction of the soils.

Amounts of plant-available K, as determined from cumulative K uptake by five successive 2-week-old oat (Avena sativa) crops, varied from 0.35 to 3.24 meq K/100 g soil, and rates of K uptake varied from 0.016 to 0.215 meq K/100 g soil per week. Omitting three soils which released relatively large amounts of K (two at low and one at high levels of exchangeable soil K), the uptake of K by the first oat crop was highly correlated with initial exchangeable soil K.

¹ Journal Article no. 7080, Michigan Agric. Exp. Sta., East Lansing. Presented in part before Div. S-4, Soil Science Society of America, Miami Beach, Oct. 1972.

² Visiting Assistant Professor of Soils, North Carolina State University, presently at CATIE, Turrialba, Costa Rica; Agronomist, International Fertilizer Development Staff, Tennessee Valley Authority, Muscle Shoals, Alabama, formerly Professor of Soil Science, Michigan State University and Head, Department of Soils, La Molina Agric. Exp. Sta., Lima, Peru, respectively.

Received for publication November 4, 1974. Accepted for publication June 6, 1975.