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Response by Paddy Rice to Rates and Sources of Applied Phosphorus¹

A series of greenhouse pot experiments with flooded rice (Oryza sativa L. var. ‘Nato’) was conducted on Mountview silt loam, a soil found to be very low in available P for upland crops. Marked yield response by rice was obtained to applied P, but maximum yields were obtained at much lower rates of applied P than is true for most upland crops. Response to applied P decreased with liming of the soil and with increasing levels of acid-soluble soil P. Granular water-soluble P sources were most effective for increasing tillering and yields of rice; granular dicalcium phosphate was ineffective. Effectiveness of several fine phosphate rock sources increased with increase in content of AOAC-available P. The P in S-coated concentrated superphosphate was not available to a first crop of rice but after degradation of the coating became available for a second crop. The P in Fe phosphates was more available than that in A1 phosphates in the flooded soil. These phosphates were more available as fines than as granules and in colloidal form than as fine crystals.

Key Words: Phosphate rock • Superphosphate • Ammonium phosphates • Fe and Al phosphates

² Agronomists.

Received for publication October 23, 1969.