1. Can deep roots remove the N surplus? Main crops Catch crops Crop sequence Kristian Thorup-Kristensen Danish Institute of Agricultural Sciences Plantekongres 2006

2. 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

3. Root growth of barley, winter wheat, and beets - data from two soil types and two years Thorup-Kristensen and Berntsen 0 50 100 150 200 250 AugOctDecFebAprJunAugOct Rooting depth (cm) barley wheat beets

4. Differences in crop rooting depth Pea Potato 75 cm Winter cereals Sugar beet Winter rape > 150 cm > 250 cm Ryegrass Clovers? Spring cereals Seed grass ?? 100 cm Lucerne ?? White mustard Fodder radish Chicory Dyers voad Winter rye / oats

5. 0102030405060 0 100 200 0102030405060 0 100 200 - no cover Ryegrass Salad burnett Chicory Dyers voad Depth (cm) Root densityNitrate-N (kg/ha) New undersown catch crops with deep roots root density and N min in November

6. 0 50 100 150 200 250 300 augoktdecfebaprjunaugokt Rooting depth (cm) Fodder radish catch crop Rooting depth of winter wheat, spring wheat and a fodder radish catch crop - 3 years data Spring wheat Winter wheat

7. 04080120160 0 50 100 150 200 250 Depth (cm) N min (Kg N/ha pr. 50 cm soil layer) Winter wheat - uncovered Crucifer catch crop 247 261 35 N min Nov. under wheat, catch crop or no cover N min total to 250 cm: Cereal catch crop 78

8. 0306090 0 50 100 150 200 250 Depth (cm) N min (Kg N/ha pr. 50 cm soil layer) Winter wheat - uncovered Crucifer catch crop 144 248 109 N min April under wheat, catch crop or no cover N min total to 250 cm:

9. 0306090 0 50 100 150 200 250 Depth (cm) N min (Kg N/ha pr. 50 cm soil layer) Winter wheat Spring wheat after uncovered Spring wheat after crucifer catch crop 59 145 38 N min after harvest of winter or spring wheat N min total to 250 cm:

10. 020406080100120 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

11. 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

12. THANK YOU! Kristian Thorup-Kristensen Danish Institute of Agricultural Sciences Plantekongres 2006 Can deep roots remove the N surplus?