Fate of urea-N in floodwater |
| |
Authors: | J C Katyal A M Gadalla |
| |
Institution: | (1) International Fertilizer Development Center, P.O. Box 2040, 35662 Muscle Shoals, AL, USA;(2) Present address: Division of Soil Science and Agricultural Chemistry, IARI, New Delhi, India;(3) Present address: Atomic Energy Authority, Soil and Water Department, P.O. Box, 13759 Cairo, Egypt |
| |
Abstract: | One day after application, urea-N remaining in the floodwater and determined as water-soluble N (urea-N + NH4
+-N) was used to calculate the potential N loss from lowland rice soils. Actual N loss calculated from 15N balance measurements using forced air exchange (airflow rate: 20 L min-1) in greenhouse pots. Conditions for variable potential N loss were created by manipulating the method of urea application and duration of presubmergence or by selecting soils with diverse cation exchange capacities (CEC). Potential N loss tended to be lower than actual N loss; the differences were, however, nonsignificant. The method of urea application that led to the lowest potential N loss from a Guthrie silty clay loam (Typic Fragiaquult) also led to the least 15N loss and vice-versa (r=0.99**). Duration of presubmergence did not alter the relationship between potential and actual N loss although it influenced the rate of urea hydrolysis in floodwater. The primary depencence of actual N loss on water-soluble N was maintained in soils differing in CEC (r=0.83**). The association between potential and actual N loss was closer for high-CEC soils ( 20 cmol +] kg-1 soil, r=0.91**) than for low-CEC soils (<20 cmol +] kg-1 soil, r=0.85**). Ammonia volatilization could be more closely predicted by potential N loss than could apparent denitrification.The results of this study suggest that potential N loss calculated from one-time determination of water-soluble N in floodwater can be a good index of actual N loss from flooded, puddled rice soils. Notable exceptions are to be expected for soils in which water-soluble N gets lost from floodwater either before (soils with fast urea hydrolysis in floodwater) or after (soils with steady leaching) determination of potential N loss. |
| |
Keywords: | actual N loss flooded soils 15N balance potential N loss urea water-soluble N |
本文献已被 SpringerLink 等数据库收录! |
|