Nitrogen Efficiency of Urea Amended With Inhibitors and Cations Applied to Rice
Shah, Shree Chandra (1994) Nitrogen Efficiency of Urea Amended With Inhibitors and Cations Applied to Rice. PhD thesis, Universiti Pertanian Malaysia.
Urea, the major source of nitrogen (N), is subjected to extensive gaseous N losses to the atmosphere. Ammonia (NH3)volatilisation and denitrification losses are important mechanisms for N losses from urea and are causes of poor fertilizer use efficiency by lowland rice. The study was undertaken in a series of five experiments to evaluate means of increasing the efficiency of urea-N under flooded rice soil conditions. A laboratory incubation experiment of different rice soils was conducted to study the kinetics and transformations of urea in flooded soils. A greenhouse experiment was carried out on marine and riverine alluvial soils to evaluate urea-N efficiency in direct-seeded (DS) rice and transplanted (TP) rice under similar N management practices using lSN-Iabelled urea. Two greenhouse and one field studies were conducted to evaluate the effectiveness of inhibitors and cations on marine and riverine alluvial rice soils on the efficiency of urea-N using 15N recovery techniques. Urea hydrolysis followed the first-order kinetics and rate constants ranged from -0.032 to -0.076 ha-1 A lag phase existed in flooded soil conditions and it varied from 6 to 15 hours. The half-life of urea ranged from 12 to 26 hours. Urea conversion to NH4 -tN was initially rapid with about three-fourths being converted within 48 hours of incubation and total conversion completed within 108 hours.
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