Table 3.

Studies that report effects of N deficiency on root biomass (RBIO) at field scale.

Reference	Crop	Soil	Factors	RBIO
(Welbank and Williams, 1968)	barley		DEV LEV	DECREASE
(Fang et al., 2022)	maize	loamy	LEV YEAR DEV	DECREASE
(Schneider et al., 2017)	maize	silt loam, clay loam	SOIL	DECREASE
(Sharifi et al., 2005)	potato		GEN DEV	DECREASE
(Nakamura et al., 2002)	sorghum		GEN DEV	DECREASE
(Myers, 1980)	sorghum	clay loamy	GEN DEV	DECREASE
(Otto et al., 2014)	sugarcane	Typic Kandiudox, Rhodic Eutrudox	SOIL LEV 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 LE	DECREASE
(Chen et al., 2020)	cotton	loamy	LEV	VARIABLE
(Sainju et al., 2005)	cotton	sandy loam	TILL LEV	VARIABLE
(Anderson, 1987)	maize	silty loam	DEV YEAR	VARIABLE
(Anderson, 1988)	maize	silty loam	DEV YEAR	VARIABLE
(Feng et al., 2016)	maize	loamy clay, clay loam, sandy loam	SOIL YEAR LEV	VARIABLE
(Thom and Watkin, 1978)	maize	sandy loam	DEV LEV	VARIABLE
(Hadir et al., 2021)	sugar beet	silty loam	DEV	VARIABLE
(Wang et al., 2005)	winter wheat	clay loamy	IRR LEV YEAR	VARIABLE
(Eghball and Maranville, 1993)	maize	silty clay loam	LEV	INCREASE

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