Effect of Crop Residue Management on Nitrogen Loss and Balance from Applied Urea in a Lowland Rice Cropping System

News source: Department of Agriculture, Thailand, 2002-01-01

Field experiments were conducted in a rice-fallow-rice cropping sequence during consecutive dry and wet seasons (1997) at the Suphanburi Rice Experiment Station on a Phimai soil (Vertic Tropaquept) to determine the fate and efficiency of broadcast urea in combination with three crop residue management practices. These were:

• No residues;
• Burned residues; and
• Untreated rice crop residues which were incorporated into the soil one week before transplanting.

Losses from Broadcast Use

The results showed that the maximum rate of ammonia (NH₃) volatilization losses from urea (70 kg N/ha) broadcast into floodwater shortly after transplanting occurred 2 - 4 days after the fertilizer was applied. The cumulative NH₃ losses during the 11 days following urea application were 4.6, 8.1 and 5.6 kg N/ha from no residues, burned residues and residue treated plots, respectively. This corresponded to 7, 12 and 8% of the applied N. At around that time, N₂ + N₂O emissions due to urea addition corresponded to 62.5 kg/ha from no residues, 26.8 kg/ha from the field with burnt residues, and zero from the field where the residues were incorporated.

Nitrogen Balance

The ¹⁵N balance study when the dry-season rice crop was ready to harvest showed that the amount of fertilizer N recovered in the grain, straw and roots indicated that there was no significant difference between the different residue treatments. Fertilizer N recovery by the grain was low, only 9 to 11% of the N applied. Fifty to 53% of the applied ¹⁵N remained in the soil after the rice harvest, mainly in the upper 0 _ 5 cm layer. The unaccounted for ¹⁵N was probably lost by gasous N emissions, which ranged from 27 to 33% of the applied N and were not affected by the type of residue treatment.

Residual Effect

Only 4 - 5% of the initial ¹⁵N-labeled urea applied to the dry season rice crop was taken up the succeeding wet-season rice crop, to which no additional N fertilizer was applied. Grain yield and N uptake were significantly increased (P = 0.05) by N application in the dry season, but were not significantly affected by the type of residue treatment in either season.

For further information, contact Sakorn Phongpan, Nuclear Research in Agriculture Group, Institute of Research and Development in Agricultural Production Science, Department of Agriculture, Thailand.

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