Table 10.

Cumulative N balance sheet for lowland rice soil at 0.5 m depth after 27 continuous rice crops. IRRI field, 1985 wet season to 1998 dry season^a.

Fertilizer treatment	Crop (A)	Change in soil N (B)	Fertilizer input (C)	Other inputsb (D)	N balance (A+B) – (C+D)		Grain yield (t ha-1)
					Total	Per cropc	Total	Per crop
	-----------------------------------------------kg ha-1-------------------------------------------------------
Control	1656cd	-8bc	0	405	1244ae	46	111.1a	4.1a
Urea	2598b	-134c	1710	405	348be	13	152.1b	5.6b
Sesbania	2707ab	344ab	2001	405	646be	24	149.4b	5.5b
Azolla	2781a	541a	1782	501	1039ae	38	156.0b	5.7b
SEf	37.1	111.9			111.4

^aAdapted from Ladha et al. (2000).

^bOther inputs include N from rain and irrigation water, P fertilizer, pesticides, etc.

^cN gains per crop.

^dMeans in a column followed by a different letter are significantly different at the 0.05 probability level by Duncan’s Multiple Range Test (DMRT).

^esignificantly different from zero at the 0.05 and 0.01 probability level, respectively

^fStandard error