Table 3. Soil available nutrients content under different wheat straw incorporation treatments in 0–20 and 20–40 cm soil layers from 2008 to 2011.

Years	Treatments	AN (mg kg-1)		AP (mg kg-1)		AK (mg kg-1)
		0–20 cm	20–40 cm	0–20 cm	20–40 cm	0–20 cm	20–40 cm
2008	H	58±0.6 1 a 2	42±0.8a	21±0.6a	9.1±0.8a	163±2.9a	109±2.3a
	M	57±0.8a	41±0.8a	18±0.6a	8.7±0.3a	165±1.7a	103±1.9a
	L	53±0.8ab	38±0.5b	16±0.5ab	6.7±0.8ab	152±1.8b	101±2.3a
	CK	51±0.7b	33±0.8c	14±0.2b	5.8±0.6b	136±1.5b	94±1.4a
2009	H	61±0.7a	43±0.6a	22±0.6a	9.4±0.6a	165±1.9a	112±1.7a
	M	59±1.1ab	41±0.8a	19±0.7b	9.0±0.9ab	169±2.1a	106±1.6ab
	L	53±1.0bc	39±0.4b	16±1.0bc	6.7±0.5bc	152±1.5b	103±2.4abc
	CK	51±1.1c	32±0.4b	15±0.5c	5.9±0.7c	133±1.6c	95±1.5c
2010	H	62±0.7a	44±0.5a	24±0.2a	10.6±0.1a	171±2.3a	119±1.8a
	M	59±0.4ab	42±1.1a	21±0.6ab	9.7±0.4a	169±2.7a	111±1.1a
	L	53±1.3c	39±0.6a	18±0.8bc	6.9±0.3b	154±1.7ab	109±2.5ab
	CK	51±1.1c	31±0.8b	16±0.4c	6.2±0.9b	131±1.4bc	98±1.9c
2011	H	66±0.5a	45±0.6a	28±0.3a	12.3±0.7a	180±3.1a	128±1.6a
	M	62±0.7ab	42±0.7ab	24±0.5b	10.4±0.2ab	174±2.3a	121±1.4ab
	L	55±0.4c	39±0.3b	20±0.3c	7.3±0.5bc	160±1.8ab	117±2.1ab
	CK	53±0.8c	32±0.7c	17±0.7c	6.4±0.8c	138±2.2b	104±2.2b

Note: CK, no wheat straw incorporation; L, incorporation of straw at a low rate of 3 000 kg hm^-2 wheat straw; M, incorporation of straw at a medium rate of 6 000 kg hm^-2 wheat straw; H, incorporation of straw at a high rate of 9 000 kg hm^-2 wheat straw. AN, available nitrogen; AP, available phosphorus; AK, available potassium

¹ Means ± standard deviations

² Values within a column for the same year followed by different letters are significantly different (P<0.05)