. 2016 Feb 9;7:53. doi: 10.3389/fpls.2016.00053

Table 1.

Criteria used to divide the continuous variables grain yield g plant⁻¹ (GY_P), whole plant N at R6 g plant⁻¹ (R6N_P), grain yield kg ha⁻¹ (GY_A), whole plant N at R6 kg ha⁻¹ (R6N_A), and NNI into categorical variables.

Categorical variable	Continuous variable	Criteria	N Rates Included
			Range	Mean
			— — –kg ha⁻¹— — –
CatGY_A-1	GY_A	<7184	0–492	104
CatGY_A-2	GY_A	7184–9540	0–492	142
CatGY_A-3	GY_A	9540.1–11800	0–630	202
CatGY_A-4	GY_A	>11800	0–834	246
CatR6N_A-1	R6N_A	<136	0–492	79
CatR6N_A-2	R6N_A	136–179	0–450	148
CatR6N_A-3	R6N_A	179.1–225	0–450	194
CatR6N_A-4	R6N_A	>225	0–834	263
LowStress	NNI	>1.1	0–834	311
MedStress	NNI	1.1–0.8	0–450	182
HighStress	NNI	<0.8	0–492	106
			— — –g plant⁻¹— — –
CatGY_P-1	GY_P	<124	0–8.2	1.5
CatGY_P-2	GY_P	124–153	0–8.2	2.6
CatGY_P-3	GY_P	153.1–181	0–9.1	3.4
CatGY_P-4	GY_P	>181	0–13.9	4.8
CatR6N_P-1	R6N_P	<2.2	0–8.2	1.2
CatR6N_P-2	R6N_P	2.2–2.8	0–6.6	2.3
CatR6N_P-3	R6N_P	2.81–3.67	0–9.1	3.3
CatR6N_P-4	R6N_P	>3.67	0–13.9	4.8

GY_P, R6N_P, GY_A, and R6N_A categories (Cat) were divided into four groups (1–4) using the quartiles and the mean of each variable across both the Old and New Era. NNI was divided into three stress categories (Low, Med, High) using the interquartile range. The range and mean of N rates represented in each category are also reported.