Incorporation of urea in puddled rice soils as affected by tillage implements

Abstract

Thorough incorporation of urea into the soil is known to reduce the high N losses associated with the traditional practice of broadcasting urea onto puddled lowland rice fields. Few studies have, however, examined the effectiveness of farm-level implements for incorporating broadcast urea during final land preparation in small rice fields. A field experiment was conducted at two sites in the Philippines to compare the effectiveness of several commonly available and experimental tillage implements for basal incorporation of urea. The relative effectiveness of N incorporation and relative susceptibility of N to ammonia volatilization losses were assessed from floodwater (urea + ammoniacal)-N and partial pressure of ammonia (pNH3) following urea application to puddled, unplanted soil. Conventional water buffalo- and single axle tractor-drawn comb harrows were equally, but only partially, effective in reducing floodwater (urea + ammoniacal)-N andpNH3 by 42 to 56% of the values for broadcast prilled urea (PU) without incorporation. Removal of the comb harrow from the single axle tractor did not reduce the effectiveness of PU incorporation, indicating that the cagewheel rather than the comb harrow was largely responsible for fertilizer incorporation. An experimental conical puddler was slightly more effective than the conventional comb harrow. The movement of transplanters through the field did not effectively incorporate PU. A power weeder, frequently used by researchers to incorporate fertilizer in small experimental plots, was less effective than traditional comb harrows, reducing floodwater (urea + ammoniacal)-N by only 35%. No tillage implement for incorporating urea reducedpNH3 as effectively as did the liquid urea band injector. Results suggest that sizeable losses of fertilizer N still occur following incorporation of PU with tillage implements commonly used by small rice farmers. Considerable scope remains for the improvement of fertilizer incorporation in puddled rice soils.