Table 2.

Studies that report effects of N deficiency on total root length and/or root length density (TRL-RLD) at field scale.

Reference	Crop	Soil	Factors	TRL-RLD
(Chen et al., 2020)	cotton	loamy	LEV	DECREASE
(Anderson, 1987)	maize	silty loam	DEV YEAR	DECREASE
(Anderson, 1988)	maize	silty loam	DEV YEAR	DECREASE
(Fang et al., 2022)	maize	loamy	LEV YEAR DEV	DECREASE
(Hadir et al., 2021)	sugar beet	silty loam	DEV	DECREASE
(Barraclough et al., 1989)	winter wheat	silty clay loam	IRR DEV	DECREASE
(Mehrabi et al., 2021)	winter wheat		PLAN IRR LEV	DECREASE
(Xue et al., 2014)	winter wheat		DEV LEV	DECREASE
(Feng et al., 2016)	maize	loamy clay, clay loam, sandy loam	SOIL YEAR LEV	VARIABLE
(Mackay and Barber, 1986)	maize	silty loam	GEN DEV	VARIABLE
(Peng et al., 2012)	maize	silty loam	DEV LEV YEAR	VARIABLE
(Sharifi et al., 2005)	potato		GEN DEV	VARIABLE
(Nakamura et al., 2002)	sorghum		GEN DEV	VARIABLE
(Comfort et al., 1988)	spring wheat	silty loam, clay loam	GEN SITE LEV	VARIABLE
(Eghball and Maranville, 1993)	maize	silty clay loam	LEV	INCREASE
(NaNagara et al., 1976)	maize	silty loam	TILL DEV	INCREASE
(Thom and Watkin, 1978)	maize	sandy loam	DEV LEV	INCREASE

DECREASE (in red): diminished TRL-RLD, VARIABLE (in yellow): diverse, inconclusive or no effects on TRL-RLD, and INCREASE (in green): large TRL-RLD in case of deficient as compared to non-deficient conditions. Factors refer to the variables studied in each manuscript. LEV: several levels of N applied, DEV: several development stages investigated, YEAR: several years investigated, IRR: water treatments applied (such as irrigation and drought), PLAN: several planting methods tested, SOIL: several soil types tested, GEN: diverse genotype tested, SITE: different sites tested, TILL: several tillage practices tested. For more details refer to SI Table 1 .