Spring wheat nitrogen-use indicators responses to cropping sequence and nitrogen fertilization

Figures & data

Figure 1. Monthly average air temperature and total precipitation as well as growing season (April–August) and annual average air temperature and total precipitation and from 2012 to 2019 at the study site.

Table 1. Analysis of variance for spring wheat straw N concentration and N uptake, N harvest index (NHI), and grain N concentration, N uptake, N-use efficiency (NUE) and N recovery index (NRI) with sources of variance for cropping sequence (CS), N fertilization rate (NR), and year (YR).

Source	Straw N conc.	Straw N uptake	Grain N conc.	Grain N uptake	NRI	NUE	NRI
	p values	———————————————————————————————————–————————————————————
CS	0.030	0.008	0.001	<0.001	0.937	0.027	0.206
NR	<0.001	<0.001	<0.001	<0.001	0.022	0.001	0.001
CS × NR	0.639	0.579	0.005	0.002	0.587	0.007	0.123
YR	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001
CS × YR	0.025	0.002	<0.001	<0.001	0.011	<0.001	<0.001
NR × YR	0.813	0.261	<0.001	<0.001	0.292	0.018	0.034
CS ×NR × YR	0.999	0.962	0.306	0.246	0.893	0.497	0.641

Table 2. Interaction between cropping sequence, N fertilization rate, and year on spring wheat straw N concentration and N uptake, N harvest index (NHI), and grain N recovery index (NRI) averaged across N fertilization rates and cropping sequences.

Cropping sequence^a	N fertilization rate (kg N ha^−1)	Year ———————————————————————————-
		2012	2013	2014	2015	2016	2017	2018	2019
		Straw N concentration (g N kg^−1)
CTWF		12.6	15.3a^b	12.6	28.1a	13.8a	15.2a	13.1	5.7
NTWF		11.9	13.4ab	11.9	25.3b	13.0ab	14.2ab	11.5	5.4
NTWP		12.3	13.2b	12.7	24.6bc	11.5b	12.6b	12.8	5.0
NTCW		12.1	13.2b	12.1	23.0c	13.3ab	12.8b	12.5	5.7
		Straw N uptake (kg N ha^−1)
CTWF		34.3a	37.7a	64.0a	72.0	96.3a	58.9a	34.5	27.8
NTWF		35.7a	32.5ab	49.1ab	66.6	89.0a	56.7a	33.1	26.7
NTWP		28.1ab	27.2ab	55.4a	68.3	99.6a	39.7b	31.5	19.3
NTCW		16.9b	22.1b	35.3b	69.4	71.3b	26.0b	26.3	12.7
		NHI
CTWF		0.78	0.76ab	0.61b	0.53b	0.59a	0.69	0.75	0.84a
NTWF		0.75	0.77a	0.67a	0.54ab	0.56ab	0.69	0.75	0.84a
NTWP		0.77	0.75ab	0.65ab	0.58a	0.54b	0.67	0.74	0.84a
NTCW		0.78	0.72b	0.67a	0.62a	0.58ab	0.68	0.75	0.79b
		NRI (%)
CTWF		37.4	2.8b	44.3a	33.2ab	29.0c	−16.9c	45.9b	38.2b
NTWF		44.2	22.6a	35.7b	16.0b	12.4c	6.0b	−1.7c	42.6c
NTWP		30.0	24.2a	22.6b	46.1a	48.4b	16.0ab	49.0b	55.3a
NTCW		45.1	34.1a	45.9a	23.7b	74.7a	31.0a	76.9a	41.3ab
		NRI (%)
	50	47.7a	13.6	34.9ab	29.2ab	53.5a	7.6	34.6	28.8b
	100	40.5ab	31.2	47.4a	45.5a	37.6b	7.6	51.4	60.1a
	150	29.2b	18.1	29.0b	14.8b	32.8b	11.8	42.0	44.2ab

^aCropping sequences are CTWF, conventional till spring wheat-fallow; NTWF, no-till spring wheat – fallow; NTWP, no-till spring wheat-pea; and NTCW, no-till continuous spring wheat.

^bNumbers followed by different letters in a column (year) within a set are significantly different at p ≤ 0.05 by the least square means test.

Table 3. Effect of N fertilization rate on spring wheat straw N concentration and N uptake and N harvest index averaged across cropping sequences and years.

N fertilization rate	Straw N conc.	Straw N uptake	N harvest index
kg N ha^−1	g N kg^−1	kg N ha^−1
0	12.6d^a	36.2c	0.67b
50	13.3c	43.5b	0.69ab
100	14.0b	49.9a	0.71a
150	17.9a	53.4a	0.69ab

^aNumbers followed by different letters in a column are significantly different at p ≤ 0.05 by the least square means test.

Figure 2. Relationship between N fertilization rate and spring wheat grain N concentration for cropping sequences from 2012 to 2015. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.

Figure 3. Relationship between N fertilization rate and spring wheat grain N concentration for cropping sequences from 2016 to 2019. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.

Figure 4. Relationship between N fertilization rate and spring wheat grain (a) N concentration, (b) N uptake, and (c) N-use efficiency (NUE) averaged across years. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.

Figure 5. Relationship between N fertilization rate and spring wheat grain N uptake for cropping sequences from 2012 to 2015. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.

Figure 6. Relationship between N fertilization rate and spring wheat grain N uptake for cropping sequences from 2016 to 2019. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.

Figure 7. Spring wheat grain N-use efficiency (NUE) as affected by cropping sequence and N fertilization rate from 2012 to 2019. Cropping sequences are CTWF, conventional till spring wheat-fallow; NTCW, no-till continuous spring wheat; NTWF, no-till spring wheat-fallow; and NTWP, no-till spring wheat-pea. Markers accompanied by different letters at a N fertilization rate are significantly different at p ≤ 0.05 by the least square means test.