Transport and transformation of fertilizer solution in columns packed with puddled soil

A laboratory experiment was carried out to study the transport of major plant nutrients in rice soil. Five soil samples were collected from rice fields puddled to different intensities by country plough and puddler in presence or absence of organic matter and were packed separately to a bulk density of 1.5 Mg m⁻³ each. A solution pulse of 2.91×10⁻³ mL containing 893.7 mg L⁻¹ N, 904.32 mg ⁻¹ P and 1141 mg L⁻¹ K in the forms of urea and potassium hydrogen orthophosphate was displaced in each of these saturated soil columns by 0.01 N CaSO₄ solution under steady-state condition. Results indicated that the velocity of urea-N was faster than that of NH₄⁺-N,P,K and the displacing solution. The urea hydrolysis rate-constant ranged from 0.051 h⁻¹ to 0.097 ha⁻¹ in these five soils. The retention of P and NH₄⁺-N was confined to upper 0.03 m of soil column. During displacement, much of native K was released and the displacement of K was deeper than that of P. Presence of organic matter induced retention of K in upper soil layers.