Table 4.

Studies that report effects of N deficiency on the root-to-shoot ratio (R_S) and root length per shoot biomass (LENG_SHOOT) at the field scale.

Reference	Crop	Soil	Factors	R_S	LENG_SHOOT
(Sharifi et al., 2005)	potato		GEN DEV	INCREASE	INCREASE
(Xue et al., 2014)	winter wheat		DEV LEV	INCREASE	INCREASE
(Eghball and Maranville, 1993)	maize	silty clay loam	LEV	INCREASE	VARIABLE
(Hadir et al., 2021)	sugar beet	silty loam	DEV	INCREASE	DECREASE
(Welbank and Williams, 1968)	barley		DEV LEV	INCREASE
(Anderson, 1988)	maize	silty loam	DEV YEAR	INCREASE
(Myers, 1980)	sorghum	clay loamy	GEN DEV	INCREASE
(Wang et al., 2005)	winter wheat	clay loamy	IRR LEV YEAR	INCREASE
(Feng et al., 2016)	maize	loamy clay, clay loam, sandy loam	SOIL YEAR LEV	VARIABLE	VARIABLE
(Otto et al., 2014)	sugarcane	Typic Kandiudox, Rhodic Eutrudox	SOIL LEV DEV	VARIABLE
(Fang et al., 2022)	maize	loamy	LEV YEAR DEV	DECREASE	DECREASE
(Louvieaux et al., 2018)	oilseed rape		DEV		INCREASE
(Nakamura et al., 2002)	sorghum		GEN DEV		INCREASE
(Comfort et al., 1988)	spring wheat	silty loam, clay loam	GEN SITE LEV		INCREASE
(Peng et al., 2012)	maize	silty loam	DEV LEV YEAR		VARIABLE

DECREASE (in red): diminished R_S, LENG_SHOOT, VARIABLE (in yellow): diverse, inconclusive or no effects on R_S, LENG_SHOOT, and INCREASE (in green): higher R_S, LENG_SHOOT 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 .