Can deep roots remove the N

surplus?Main cropsCatch crops

Crop sequence

Kristian Thorup-KristensenDanish Institute of Agricultural SciencesPlantekongres 2006

Why look at root depth?

• Few field studies– very few related to N uptake

• Environmental regulation and evaluation– depth of rooting zone 100 cm?

• Much larger rooting depth frequently shown– concequences for the legislation?– can we use deep root growth to increase N

utilization?– use of main crops or catch crops

Root growth of barley, winter wheat, and beets- data from two soil types and two years

Thorup-Kristensen and Berntsen

0

50

100

150

200

250Aug Oct Dec Feb Apr Jun Aug Oct

Roo

ting

dept

h (c

m)

barleywheat

beets

Differences in crop rooting depth

PeaPotato

75 cm

Winter cerealsSugar beet

Winter rape

> 150 cm

> 250 cm

RyegrassClovers?Spring cerealsSeed grass ??

100 cm

Lucerne ??

White mustardFodder radish

ChicoryDyers voad

Winter rye / oats

0 10 20 30 40 50 60

0

100

200

0 10 20 30 40 50 60

0

100

200

- no coverRyegrassSalad burnettChicoryDyers voadD

epth

(cm

)

Root density Nitrate-N (kg/ha)

New undersown catch crops with deep rootsroot density and Nmin in November

0

50

100

150

200

250

300aug okt dec feb apr jun aug okt

Roo

ting

dept

h (c

m)

Fodder radish catch crop

Rooting depth of winter wheat, spring wheat and a fodder radish catch crop

- 3 years data

Spring wheat

Winter wheat

0 40 80 120 160

0

50

100

150

200

250

Dep

th (c

m)

Nmin (Kg N/ha pr. 50 cm soil layer)

Winter wheat - uncoveredCrucifer catch crop

247261 35

Nmin Nov. under wheat, catch crop or no cover

Nmin total to 250 cm:

Cereal catch crop 78

0 30 60 90

0

50

100

150

200

250

Dep

th (c

m)

Nmin (Kg N/ha pr. 50 cm soil layer)

Winter wheat - uncoveredCrucifer catch crop

144248109

Nmin April under wheat, catch crop or no cover

Nmin total to 250 cm:

0 30 60 90

0

50

100

150

200

250

Dep

th (c

m)

Nmin (Kg N/ha pr. 50 cm soil layer)

Winter wheatSpring wheat after uncoveredSpring wheat after crucifer catch crop

59145 38

Nmin after harvest of winter or spring wheat

Nmin total to 250 cm:

0 20 40 60 80 100 120

Winter wheat

Spring wheat

Spring wheat after crucifer catch crop

Spring wheat after cereal catch crop

Yield (dt/ha)

N Uptake (kg N/ha)

Yield and N uptake in winter or spring wheat

Konklussioner• The root zone othen deeper than 100 cm! • Significant differences among crops

– winter wheat has deeper roots than spring cereals– large differences among catch crops

• Deep roots can be used actively in rotations– after previous leaching of N– before shallow rooted crops

• Deep roots can be used to reduce N losses and N surplus

THANK YOU!

Kristian Thorup-KristensenDanish Institute of Agricultural SciencesPlantekongres 2006

Can deep roots remove the N surplus?