Remote-sensing algorithms for estimating nitrogen uptake and nitrogen-use efficiency in cotton

Figures & data

Table I. Monthly accumulated heat units, total monthly precipitation, and long-term (1973–2000) means at the experimental site, Mississippi State, Mississippi in 2001 and 2002.

	Heat units (°C days)			Precipitation (mm)
Month	2001	2002	Long-term mean	2001	2002	Long-term mean
Jan	0	15	0	173	193	145
Feb	11	0	0	165	107	129
Mar	1	40	2	198	174	159
April	134	139	52	55	73	152
May	244	186	198	57	90	128
June	315	310	311	111	16	102
July	378	377	387	66	140	109
Aug	369	371	365	212	67	87
Sep	227	311	251	103	236	87
Oct	63	140	67	157	164	88
Nov	30	9	1	91	148	127
Dec	6	2	0	149	122	131
Total	1778	1900	1634	1537	1530	1444
Heat units=[(Maximum Temp.+Minimum Temp.)/2] − 15. The heat units are considered as 0 if the values are negative.

Figure 1.  Temporal changes in cotton leaf photosynthetic rate during plant growth as affected by nitrogen fertilizer rates in 2001 and 2002. Data are means (±SD) of three replicates and five leaves in each replicate.

Table II. Above-ground biomass accumulation (kg ha⁻¹) of cotton plants during squaring and fruiting as affected by the four N fertilizer treatments of 0, 56, 112, and 168 kg N ha⁻¹ in 2001 and 2002. Each value is the mean of five (2001) or six (2002) replications.

		Nitrogen treatment
Year	DAS^†	0 N	56 N	112 N	168 N	LSD(0.05)
2001	28	67	85	87	88	NS^‡
	43	416	391	415	404	NS
	52	1140	1070	1110	1150	NS
	67	2510	2450	3040	2970	247
	84	5770	7620	7180	7230	613
2002	34	199	187	194	192	NS
	45	802	905	893	836	NS
	52	1480	1290	1470	1320	NS
	69	2610	3230	3150	3950	328
	83	3850	6200	6200	6530	772
^† DAS = days after seeding. ^‡ NS = not significant.

Figure 2.  Nitrogen concentrations of leaves (dashed lines), stems (solid lines), and fruits (dotted lines) during plant growth as affected by N-application-rate treatments of 0 N (circle), 56 N (square), 112 N (triangle), and 168 N (diamond).

Figure 3.  Accumulated nitrogen of leaves (dashed lines), stems (solid lines), and fruits (dotted lines) during plant growth as affected by N-rate treatments of 0 N (circle), 56 N (square), 112 N (triangle), and 168 N (diamond).

Figure 4.  Relationships between (A) N concentration of above-ground plant tissues and ratio of canopy reflectance at 715 and 405 nm (R ₇₁₅/R ₄₀₅) and (B) accumulated N and reflectance ratio of R ₇₉₅/R ₇₅₅. Linear regression equations are based on data pooled across years, N treatments, and measuring dates (P<0.001, n=176).

Figure 5.  The percentage of N partitioning in leaves (dashed lines), stems (solid lines), and fruits (dotted lines) during plant growth as affected by N-application-rate treatments of 0 N (circle), 56 N (square), 112 N (triangle), and 168 N (diamond).

Table III. Significance (P-values) of each source of variation for cotton lint yield (kg ha⁻¹), above-ground tissue accumulated N (kg ha⁻¹), fertilizer N uptake (kg N ha⁻¹) at 84 days after seeding, fertilizer N recovery (%), and fertilizer N-use efficiency (NUE) (kg lint kg⁻¹ N application).

Source	df	Lint yield	Accumulated N	df	Fertilizer N uptake	Fertilizer N recovery	Fertilizer NUE
Year (Y)	1	0.005	0.016	1	0.008	0.018	0.080
Treatment (T)	3	<0.001	<0.001	2	0.032	0.494	<0.001
Y×T	3	0.001	0.126	2	0.263	0.532	0.069
df = degrees of freedom.

Table IV. Cotton lint yield, above-ground tissue accumulated N, fertilizer N uptake 83 days after seeding, fertilizer N recovery, and fertilizer N-use efficiency (NUE) as affected by N-application rate and year. Data are means±S.D. of four (2001) or five (2002) replications.

Year	Treatment^†	Lint yield (kg ha^−1)	Accumulated N (kg ha^−1)	Fertilizer N uptake (kg ha^−1)	Fertilizer N recovery (%)	Fertilizer NUE (kg kg^−1)
2001	0 N	1369±45	92±5	—	—	—
	56 N	1411±77	117±6	25±6	45±12	25±1
	112 N	1464±64	112±11	20±11	18±10	13±1
	168 N	1450±75	131±15	39±15	23±9	9±1
	LSD(0.05)	NS^‡	30	NS	NS	3
2002	0 N	864±76	48±5	—	—	—
	56 N	1190±56	79±9	30±9	54±16	21±1
	112 N	1367±42	108±10	60±10	54±9	12±0
	168 N	1426±33	133±20	85±20	51±12	9±0
	LSD(0.05)	160	37	42	NS	2
^†The four N treatments are 0 (0 N), 56 (56 N), 112 (112 N), and 168 (168 N) kg N ha^−1. ^‡NS = not significant.