Root mass for oilseed and pulse crops: Growth and distribution in the soil profile Y. T. Gan1, C. A. Campbell2, H. H. Janzen3, R. Lemke4, L. P. Liu5, P. Basnyat1, and C. L. McDonald1 Can. J. Plant Sci. Downloaded from www.nrcresearchpress.com by MICHIGAN STATE UNIV on 01/14/17 For personal use only.

1

Agriculture and Agri-Food Canada, Semiarid Prairie Agricultural Research Centre, Gate #3, Airport Road E., Swift Current, Saskatchewan, Canada S9H 3X2 (e-mail: [email protected]); 2Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, 960 Curling Ave., Ottawa, Ontario, Canada K1A 0C6; 3Agriculture and Agri-Food Canada, Lethbridge Research Centre, 5403 1st Ave. S., Lethbridge, Alberta, Canada T1J 4B1; 4 Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2; and 5Department of Plant Sciences, University of Saskatchewan, 51 Campus Rd, Saskatoon, Saskatchewan, Canada S7N 1A8. Received 13 August 2008, accepted 22 April 2009. Gan, Y. T., Campbell, C. A., Janzen, H. H., Lemke, R., Liu, L. P., Basnyat, P. and McDonald, C. L. 2009. Root mass for oilseed and pulse crops: Growth and distribution in the soil profile. Can. J. Plant Sci. 89: 883
893. Crop roots transport water and nutrients to the plants, produce nutrients when they decompose in soil, and provide organic C to facilitate the process of C sequestration in the soil. Many studies on these subjects have been published for cereal crops, but little is known for oilseed and pulse crops. This study was conducted at Swift Current, Saskatchewan, in 2006 and 2007 to characterize the root growth and distribution profile in soil for selected oilseed and pulse crops. Three oilseed [canola (Brassica napus L.), mustard (Brassica juncea L.), flax (Linum usitatissimum L.)], three pulse crops [chickpea (Cicer arietinum L), dry pea (Pisum sativum L.) lentil (Lens culinaris Medik.)], and spring wheat (Triticum aestivum L.) were grown in 100 cm deep 15 cm diameter lysimeters pushed into a silt loam soil. Crops were studied under rainfed and irrigated conditions. Lysimeters were removed from the field and sampled for above-ground (AG) and root mass at different depths at five growth stages. Root mass was highest for canola (1470 kg ha 1) and wheat (1311 kg ha1), followed by mustard (893 kg ha1) and chickpea (848 kg ha1), and was lowest for dry pea (524 kg ha1) and flax (440 kg ha1). The root mass of oilseeds and pulses reached a maximum between late-flowering and late-pod stages and then decreased to maturity, while wheat root mass decreased to maturity after reaching a maximum at boot stage. On average, about 77 to 85% of the root mass was located in the 0 40 cm depth. Canola, mustard, and wheat rooted to 100 cm, while the pulses and flax had only 4 to 7% of the root mass beyond the 60 cm depth. Irrigation only increased root mass in the 0
20 cm depth. Roots developed more rapidly than AG biomass initially, but the ratio of root biomass to AG biomass decreased with plant maturity. At maturity, the ratio of root biomass to AG biomass was 0.11 for dry pea, and between 0.20 and 0.22 for the other crops tested. Our findings on rooting depths and root mass distribution in the soil profile should be useful for modelling water and nutrient uptake by crops, estimating C inputs into soil from roots, and developing diverse cropping systems with cereals, oilseeds and pulses for semiarid environments. Key words: Root growth, root biomass, rooting depth, chickpea, lentil, pea, canola, mustard, flax, root:shoot ratio Gan, Y. T., Campbell, C. A., Janzen, H. H., Lemke, R., Liu, L. P., Basnyat, P. et McDonald, C. L. 2009. Masse racinaire des ole´agineux et des le´gumineuses : croissance et distribution dans le sol. Can. J. Soil Sci. 89: 883
893. Les racines apportent l’eau et les e´le´ments nutritifs aux plantes, libe`rent des compose´s organiques dans le sol quand elles s’y de´composent et procurent du C organique, ce qui concourt a` la se´questration de cet e´le´ment dans le sol. Maintes e´tudes sur ces aspects ont e´te´ publie´es pour les ce´re´ales, mais on sait peu de choses a` ce sujet sur les ole´agineux et les le´gumineuses. La pre´sente e´tude s’est de´roule´e a` Swift Current (Saskatchewan) en 2006 et en 2007. Elle devait caracte´riser la croissance des racines et la distribution de ces dernie`res dans le sol pour plusieurs ole´agineux et le´gumineuses. Les auteurs ont seme´ trois ole´agineux [canola (Brassica napus L.), moutarde (Brassica juncea L.), lin (Linum usitatissimum L.)], trois le´gumineuses [pois chiche (Cicer arietinum L), pois (Pisum sativum L.), lentille (Lens culinaris Medik.)] et du ble´ de printemps (Triticum aestivum L.) dans des lysime`tres de 100 cm de profondeur et de 15 cm de diame`tre, puis ont enfonce´s ceux-ci dans un loam limoneux. Les cultures ont e´te´ e´tudie´es sous re´gime pluvial et sous irrigation. Les lysime`tres ont e´te´ retire´s du champ, puis on les a e´chantillonne´s afin de mesurer la masse des organes ae´riens et celle des racines a` diverses profondeurs, a` cinq stades de croissance. Ce sont le canola et le ble´ qui enregistrent la plus forte masse racinaire (1 470 kg et 1 311 kg par hectare, respectivement). Suivent la moutarde (893 kg par hectare) et le pois chiche (848 kg par hectare), le pois et le lin arrivant bon derniers (524 kg et 440 kg par hectare, respectivement). La masse racinaire des ole´agineux et des le´gumineuses atteint un maximum entre la fin de la floraison et la fin de la production des gousses. Ensuite, elle diminue jusqu’a` ce que la plante parvienne a` maturite´. En revanche, la masse racinaire du ble´ commence a` diminuer apre`s le maximum atteint a` la fin de la montaison, et ce, jusqu’a` maturite´. En moyenne, 77 a` 85 % de la masse racinaire se trouvent a` moins de 40 cm de

Abbreviations: AG, above-ground plant parts 883

884 CANADIAN JOURNAL OF PLANT SCIENCE

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profondeur. Le canola, la moutarde et le ble´ e´tendent leurs racines jusqu’a` 100 cm de profondeur, tandis que chez les le´gumineuses et le lin, a` peine 4 a` 7 % des racines se retrouvent plus bas que 60 cm de profondeur. L’irrigation n’accroıˆ t la masse des racines que dans les premiers 20 cm de sol. Au de´part, la biomasse des racines se de´veloppe plus rapidement que celle des organes ae´riens, mais le ratio entre les deux diminue a` mesure que la plante s’approche de la maturite´. A` maturite´, le ratio entre la biomasse des racines et la biomasse des organes ae´riens s’e´tablit a` 0,11 pour le pois et varie entre 0,20 et 0,22 pour les autres cultures teste´es. Ces constatations sur la profondeur de l’enracinement et sur la distribution des racines dans le sol devraient faciliter une mode´lisation de l’absorption de l’eau et des e´le´ments nutritifs par les cultures, l’estimation de la quantite´ de C fournie par les racines et le de´veloppement de divers syste`mes agricoles pour la culture des ce´re´ales, des ole´agineux et des le´gumineuses en milieu semi-aride. Mots cle´ s: Croissance des racines, biomasse des racines, profondeur de l’enracinement, pois chiche, lentille, pois, canola, moutarde, lin, ratio racines:pousses

The primary tasks of crop roots are to provide anchorage and supply water and nutrients to the plants, but they also modify soil structure and help maintain soil organic matter (Cresswell and Kirkegaard 1995; Whalley et al. 2004). Therefore, crop roots are not only of critical importance to productivity, but also an important sink for photoassimilates and carbon input to soil. The decomposition of roots produces CO2 and N2O, two of the main greenhouse gases. Furthermore, current concerns about the contribution of agriculture to global climate change, and the fact that roots produce CO2 and N2O, make roots of significant interest to the scientific community. However, crop roots are very difficult to measure, and thus research on roots has lagged behind that on above-ground (AG) biomass. In the literature, there are many studies documenting root characteristics of field crops, but the vast majority of these studies have considered cereals (Campbell et al. 1977; Bolinder et al. 1997; Niu et al. 2004; Caires et al. 2008; Jordan-Meille and Pellerin 2008). To date, there are no detailed studies reporting root growth and biomass distribution profile in soil for oilseeds or pulses. Yet, during the past two decades, economic and environmental advantages of crop diversification have prompted a steady increase in the production of oilseed and pulse crops throughout the major production regions of the world, such as the northern Great Plains of North America (Campbell et al. 2002), northeast Eurasia and the Siberian steppes (Suleimenov 2006), northwest China (Gan et al. 2008b) and northwest Europe (Knights et al. 2007). In these regions, oilseeds and pulses have consistently been included in cropping systems. Rotating these broadleaf crops with cereals has shown both short- and long-term benefits. In the short term, diverse cropping systems improve nutrient- and water-use efficiency (Miller et al. 2003), increase grain yield and quality of subsequent crops (Gan et al. 2003), break disease cycles and provide more options for pest control (Krupinsky et al. 2002), and improve overall economic returns of cropping system (Zentner et al. 2001). In the longer term, crop diversification with pulses enhances the N supplying power of soil, leading to reduced requirements for inorganic fertilizers in subsequent crops (Campbell et al. 2004), and improves

the biochemical and microbiological attributes of the soil (Biederbeck et al. 2005). With increasing interest regarding cropping system impacts on environmental sustainability, there is an urgent need to quantify root growth and its distribution in soil profile for pulse and oilseed crops, especially as they compare with cereals. Crop-specific information on root attributes will improve the estimation of water and nutrient uptake by plants, as well as determine subsequent effects of crop roots on soil properties. For crop modellers, this information will help to improve the ability of models to predict crop development, and carbon and nutrient dynamics. For producers, this information can help design appropriate crop rotation systems where crop species with different rooting systems can be arranged in a well-planned crop sequence. The objective of this study was to quantify the root production and distribution in soil profile for selected oilseed and pulse crops in comparison with spring wheat under rainfed and irrigated conditions in a semiarid environment. MATERIALS AND METHODS Experimental Design Field experiments were conducted at the Agriculture and Agri-Food Canada Semiarid Prairie Agricultural Research Centre, near Swift Current (lat. 50o15?N, long. 107o44?W), Saskatchewan, during the 2006 and 2007 cropping seasons. The soil was a Swinton loam Orthic Brown Chernozem (Ayers et al. 1985). In the surface 30 cm depth, soil organic carbon was 1.7% and pH (water paste) was 7.3, with average content of sand, silt, and clay of 28, 49, and 23 g kg 1, respectively. Three oilseed [canola (Brassica napus L.), mustard (Brassica juncea L.), flax (Linum usitatissimum L.)], three pulse crops [chickpea (Cicer arietinum L), dry pea (Pisum sativum L.) lentil (Lens culinaris Medik.)], and spring wheat (Triticum aestivum L.) were grown in 15-cm-diameter, 100-cm-deep, 24-guage iron lysimeters that were pushed into the soil at seeding time using a hydraulic system (Gan et al. 2008a). All crops were tested under rainfed and irrigated conditions with two replicates. Five lysimeters were used for each crop in each replicate; this allowed plant and root samplings at five

GAN ET AL. * ROOT MASS FOR OILSEED AND PULSE CROPS

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Table 1. Crop cultivars and seeding information for lysimeter experiments conducted at Swift Current, Saskatchewan, Canada, 2006 2007

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Crop

Cultivar

Seeds per lysimeter

Plants per lysimeter

Seed treatment

Rhizobium inoculant

11 11

3 3

Helix, 1.5 L 100 kg 1 Helix, 1.5 L 100 kg 1

NA NA

Oilseeds Canola Mustard

45H21 Cutlass

Pulses Chickpea Field pea Lentil

CDC Anna Eclipse CDC Glamis

5 5 7

2 2 3

Crown, 600 mL 100 kg 1 Apron FL, 16mL 100 kg1 Crown, 600 mL 100 kg 1

Liquid Liquid Liquid

Cereal Wheat

Lillian

7

3

Vitaflo, 330 mL 100 kg1

NA

developmental stages. Treatments were arranged in a randomized complete block design, with each lysimeter surrounded by a 2 m 6 m area of the same crop as grown within the lysimeter. Four additional lysimeters were installed and sampled for initial values of soil water and nutrients. Each year, the experiment consisted of 144 lysimeters (7 crops 2 water regimes 5 growth stages2 replicates4). Seeding and Plot Management Seed was pretreated with fungicides to minimize seedand soil-borne diseases. Legume seeds were inoculated with an effective Rhizobium strain (liquid form). Crops were planted in the lysimeters with seeding rates corresponding to the lysimeter area (Table 1). In 2006, the seedbed was very dry; therefore, 125 mL of water was added to each lysimeter 2 d before seeding. On the date of seeding, 2 cm of the top soil was removed, the seeds were placed on the firm seedbed, and then the soil was returned and packed. Two weeks after plant emergence the seedlings were thinned to the desired plant population (Table 1). Oilseeds and wheat received 80 kg N ha1 (fertilizer 46-0-0) and 27 kg P ha 1 (superphosphate 0-45-0) at seeding; pulse crops received P only. The fertilizers were applied through two handmade holes 10 cm deep within the lysimeter. Crops were grown using recommended agronomic practices. Irrigated treatments received natural rainfall plus 150 mm of additional water, which was equal to 3/4 of the longterm average rainfall at the experimental site (Table 2). Irrigations were applied to the plots during the both vegetative (2
3 app.) and reproductive (2
3 app.) growth periods. Sampling and Data Collection Above-ground plant parts and roots were sampled at each of the five developmental stages of the crop: seedling (Sd), early-flower (Ef), late-flower (Lf), latepod (Lp), and physiological maturity (Mat) for oilseeds and pulses. For wheat, the corresponding stages were seedling (Sd), boot (B), anthesis (Anth), soft-dough (D) and maturity (Mat). Detailed crop development stages and sampling times were summarized in Table 3. At each sampling time, the plants were cut off at ground

level and AG biomass was determined following oven drying for 5 to 7 d at 50oC. After AG biomass determination, lysimeters were lifted from field positions, transported to the laboratory, and stored at 2oC until processed. Lysimeters were sampled destructively with cross sectioned slices of soil made at 10-cm intervals to a depth of 60 cm and at 20cm intervals from 60 to 100 cm. Each slice of the soilroot matrix was individually dispersed in a dilute NaHCO3 solution in containers overnight, and the roots were separated by washing out the soil using an in-house semi-automatic root washing system. The root-soil matrix was first placed on a 4-mm-diameter sieve under running water to wash out the soil, followed by placement on a 2-mm-diameter sieve mounted about 1 cm below the water level in containers full of tap water. Foreign objects, straw residues, and dead root pieces were removed using tweezers. The roots were placed on paper towels to air-dry before being oven-dried at 50oC for 5 to 7 d and weighed. Both AG biomass and root dry matter (mg/lysimeter) were extrapolated to kg ha1 by multiplying 0.548, a factor determined based on the cube of the lysimeter (Campbell and Paul 1978). Statistical Analysis Data were analyzed using the MIXED procedure of SAS (Littell et al. 1996) with the option of KenwardRoger degree of freedom; this option used an adjusted estimator of the covariance matrix to reduce small sample bias (Kenward and Roger 1997). Crop, moisture, and year were considered fixed effects and replicates random effects, and the analysis was performed on all variables at each of the five development stages due to significant crop stage treatment interactions. When moisture crop species interaction was not significant for a variable, moisture was treated as additional replicates in determining the main effect of crop species (Hoshmand 2006). RESULTS Analysis of variance showed that year, crop species, time of sampling, and most of the two-way interactions had significant effects on AG biomass and root biomass for the 0 to 100 cm depth (Table 4). Year and year crop

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Crop stagez 2006, rainfed Pl to Sd Sd to Ef Ef to Lf Lf to Lp Lp to Mat Total

Wheat

Canola

Mustard

Chickpea

Field pea

Lentil

Summer fallow

--------------------------------------------------------------------------------------------------- (cm) -------------------------------------------------------------------------------------------------------13.1 13.1 13.1 13.1 13.1 13.1 13.1 2.1 1.4 1.1 1.1 1.4 1.4 1.4 1.5 2.2 2.5 2.5 2.2 2.2 2.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1.2 1.2 1.2 1.2 1.2 1.2 1.2 18.0 18.0 18.0 18.0 18.0 18.0 18.0

2007, rainfed Pl to Sd Sd to Ef Ef to Lf Lf to Lp Lp to Mat Total

10.2 1.6 0.2 0.0 1.5 13.5

9.0 2.8 0.2 0.0 1.5 13.5

9.0 2.0 0.9 0.2 0.0 12.1

10.2 0.7 1.1 0.0 1.5 13.5

10.2 1.6 0.2 0.0 0.0 12.0

10.2 1.6 0.2 0.0 1.5 13.5

10.2 1.6 0.2 0.0 1.5 13.5

2006, irrigated Pl to Sd Sd to Ef Ef to Lf Lf to Lp Lp to Mat Total

15.6 5.9 2.8 1.4 2.4 28.1

15.6 3.9 4.7 1.4 3.7 29.3

15.6 3.6 5.0 1.4 2.4 28.0

15.6 3.6 5.0 1.4 3.7 29.3

15.6 3.9 4.7 1.4 2.4 28.0

15.6 3.9 4.7 1.4 2.4 28.0

15.6 3.9 4.7 1.4 3.7 29.3

2007, irrigated Pl to Sd Sd to Ef Ef to Lf Lf to Lp Lp to Mat Total

14.0 4.1 2.7 2.5 5.3 28.6

12.7 5.3 1.5 2.5 6.5 28.5

12.7 3.2 2.1 4.0 3.8 25.8

14.0 3.2 2.4 2.5 6.5 28.6

14.0 4.1 1.5 2.5 3.8 25.9

14.0 4.1 2.7 2.5 5.3 28.6

14.0 4.1 2.7 2.5 5.3 28.6

z

For oilseeds and pulses, the growth stages are planting date (Pl), seedling (Sd), early flowering (Ef), late flowering (Lf), late pod (Lp), and maturity (Mat); the corresponding stages for wheat are planting date, seedling, boot, anthesis, soft-dough, and maturity.

886 CANADIAN JOURNAL OF PLANT SCIENCE




Table 2. Precipitation on rainfed, and precipitation plus irrigation on irrigated treatments received between growth stages of six crops, at Swift Current, Saskatchewan, Canada, 2006 2007

GAN ET AL. * ROOT MASS FOR OILSEED AND PULSE CROPS

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Table 3. Julian dates of crop growth stages on which lysimeters were extracted from field positions, at Swift Current, Saskatchewan, Canada, in 2006 and 2007

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Year and crop stagez 2006 Seedling (Sd) Early-flower (Ef) Late-flower (Lf) Late-pod (Lp) Maturity (Mat) 2007 Seedling (Sd) Early-flower (Ef) Late-flower (Lf) Late-pod (Lp) Maturity (Mat)

Canola

Mustard

Dry pea

Lentil

Chickpea

Wheat

Summer fallow

178 191 207 214 233

178 187 207 214 223

178 191 207 214 223

178 191 207 214 223

178 188 207 214 233

178 199 207 214 223

178 191 207 214 233

173 190 197 204 219

173 184 193 204 214

177 190 197 204 214

177 190 201 207 219

177 186 197 204 219

177 193 201 207 219

177 190 201 207 219

z

For wheat,the corresponding stages were: seedling, boot, anthesis, soft-dough, and maturity, respectively. All crops were planted on Julian day 139 in 2006 and 138 in 2007.

species interaction did not have any effect on the ratio of root biomass to AG biomass. The three way interactions were not significant for any of the variables investigated. Root Biomass and Crop Development Root biomass for the 0- to 100-cm depth increased rapidly from seedling to early-flowering for all crop species (except flax), reached the maximum about the lateflowering to late-podding stages in oilseeds and pulses, and then decreased to maturity (Fig. 1 and Table 5). In wheat, however, after a rapid increase from seedling to flowering, root biomass tended to plateau from flowering to maturity instead of decreasing. At maturity, canola achieved a similar amount of root biomass as the wheat control; both being highest among the crop species tested. Flax had the lowest root biomass at any given crop stage. Table 4. Summary of variance analysisz for above-ground (AG) biomassy, root biomassy, and the ratio of root to AG biomass for oilseeds, pulses, and wheat grown under rainfed and irrigated conditions in Saskatchewan, Canada, in 2006 and 2007 Source of variationx

DF

AG biomass

Root biomass

Root/AG biomass

Year (Y) Crop (C) YC Stages (S) YS S C YS C

1 6 6 4 4 24 24

*** *** *** *** *** *** NS

*** *** *** *** NS *** NS

NS * NS ** *** *** NS

z

Because moisture effects on root biomass were not significant we used the two moisture treatments as additional reps (for a total of 4 reps) before doing the ANOVA. y Biomass units are in kg ha 1 and roots are from 0- to 100-cm depth. x Crops are oilseed (canola, mustard, flax), pulses (chickpea, dry pea and lentil), and spring wheat; the stage of sampling are seedling, earlyflower, late-flower, late-pod and maturity for oilseeds and pulses, and seedling, boot, anthesis, soft-dough and maturity for wheat. *, **, ***Significant at P B0.05, PB0.01, and PB0.001, respectively; NS, not significant.

Between the two Brassica species, canola always had significantly greater root biomass than mustard. The three pulses had greater root biomass than flax, but lower than canola. The growing season in 2007 was drier than in 2006 (Table 2), and had a significant impact on room mass responses among crop species (Table 5). At the stage when crop achieved the maximum root mass, canola, mustard, wheat, and chickpea had, respectively, 36, 33, 13, and 19% greater root mass in the drier 2007 than in 2006. The opposite was observed for dry pea and lentil, with root mass 7 and 50% lower, respectively, in 2007 than in 2006. Flax performed similarly both years. Root Biomass Distribution in Soil Profile Root biomass was greatest near the soil surface and decreased steadily with soil depth for all crop species tested (Fig. 1 and Table 6). At maturity, chickpea had 52% of its total root biomass in the 0- to 20-cm depth, while all other crops had between 61 and 67% of total root biomass in this depth. Furthermore, all crops had 77 to 85% of their root mass in the 0- to 40-cm depth. Except for canola, mustard, and wheat, the other crops had very little root mass in the 80- to 100-cm depth. The pulse crops and flax had less than 40 kg ha1 of roots below the 60-cm depth. Root development patterns were similar in the 0- to 20-cm (Fig. 1B), 60- to 80-cm (Fig. 1E), and 80- to 100cm depths of the soil profile (Fig. 1F) where roots increased to a maximum near late flowering and then plateaued. However, in the 20- to 60-cm depth (Fig. 1C and 1D), root mass tended to decrease after reaching a maximum. In most depth segments, wheat and canola had the highest root mass and dry pea and flax the lowest. Analysis of variance of root mass in the various depths showed that irrigation had a significant effect (P B0.01) on root mass in the 0- to 20-cm depth, but no effect in the other depths. In the 0- to 20-cm depth, root

888 CANADIAN JOURNAL OF PLANT SCIENCE 2000

2000

A

1800

1600

Lp -1

Lf

Mustard

Root Mass (0-20 cm; kg ha )

Root Mass (0-100cm; kg ha-1)

Canola

1400

Mt

Flax

Ef

Wheat

1200

Chickpea Field Pea

1000

Lentil 800 Sd

600

1400

210

220

180

190

200

220

230

Date Sampled (Julian Days)

Date Sampled (Julian Days) 300

210

Sd

0 170

230

Mt

600

200

200

Lp

Ef

800

200

190

Lf

1000

400

180

SE

1200

400

0 170

300

C

D

SE 250

Lp Ef

Lf

Root Mass (40-60 cm; kg ha-1)

-1

Root Mass (20-40 cm; kg ha )

250

Mt

200

150

Sd

100

SE

Lp

Ef

200

Lf Mt

150

100 Sd

50

50

0 170

180

190

200

210

220

0 170

230

180

Date Sampled (Julian Days)

190

200

210

220

230

Date Sampled (Julian Days)

300

E

250

F

250

SE

SE

-1

-1

Root Mass (80-100 cm; kg ha )

300

Root Mass (60-80 cm; kg ha )

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1800

SE

1600

B

200 Lp Lf 150 Mt Ef 100

200

150

100

Lp

Mt

Lf 50

50 Sd

Ef Sd

0 170

180

190

200

210

220

230

0 170

Date Sampled (Julian Days)

180

190

200

210

Date Sampled (Julian Days)

Fig. 1 (Continued)

220

230

GAN ET AL. * ROOT MASS FOR OILSEED AND PULSE CROPS

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Table 5. Root biomass in the 0- to 100-cm depth for pulses, oilseeds and wheat measured at various growth stages in Saskatchewan, Canada, in 2006 and 2007 Growth stagez Crop

Year

Seedling

Early flower

Late flower

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----------------------------------------------------- (kg ha Pulses Chickpea Dry pea Lentil Chickpea Dry pea Lentil Oilseeds Canola Mustard Flax Canola Mustard Flax

1

Late pod

Maturity

) -----------------------------------------------------

2006 2006 2006

y

112 290 207

316 612 752

568 803 994

759 540 944

812 545 916

2007 2007 2007

273 315 183

613 559 400

793 646 633

936 507 594

668 463 690

2006 2006 2006

110 186 48

659 514 195

1189 835 371

1146 714 511

955 751 479

2007 2007 2007

571 448 66

1296 918 122

1615 928 349

1794 1072 368

1571 836 412

Cereal Wheat 2006 211 991 1058 1217 Wheat 2007 669 1445 1308 1405 LSD (0.05)53 between years; 98 between crops; 140 cropyear interaction; 83 between stages; and 220 crop stage interaction.

1074 1423

z

Growth stages for wheat are seedling, boot, anthesis, soft dough, and maturity, respectively. Values are averages across moisture treatments, which were not significant.

y

mass averaged 389 kg ha1 under rainfed conditions and 435 kg ha1 under irrigation. Ratio of Root to AG Biomass All variables (year, crop species, and crop growth stage) and their interactions had highly significant impacts on AG biomass except for the year cropstage interaction (Table 4). Since we have previously discussed AG biomass in detail (Gan et al. 2008a), here we only discuss AG biomass briefly as it relates to the ratio of root to AG biomass. The AG biomass increased steadily with crop development, and reached a maximum at about late-pod stage in most crops (Table 7). This pattern of AG biomass accumulation was parallel to the pattern of root growth. On average, AG plant biomass was greater in 2006 (the wetter year) than in 2007, and was greater in irrigated than in rainfed treatments. Wheat AG biomass was greater than pulse crop AG biomass, which was greater than oilseed AG biomass (Table 7). Among the pulses, dry pea had the highest AG biomass, and among the oilseeds, flax the lowest. Fig. 1. Root mass patterns of oilseeds, pulses, and spring wheat measured at the growth stage of seedling (Sd), early-flowering (Ef), late-flowering (Lf), late-podding (Lp), and maturity (Mt) for pulses and oilseed. For wheat, the corresponding stages are seedling, boot, anthesis, soft-dough, and maturity, respectively. Root mass distribution in the depths of (A) 0
100, (B) 0
20, (C) 20
40, (D) 40
60, (E) 60
80, and (F) 80
100 cm. The vertical bars are standard errors of the means.

The ratio of root to AG biomass decreased with plant development in wheat and pulses, but was nearly constant across various growth stages for oilseeds (Fig. 2A). The ratios of root to AG biomass were greater in 2007 than in 2006 (Fig. 2B), but as crops matured the ratio declined more steeply in 2007 than in 2006. The differences in the absolute values of the ratios were substantial among crop species measured at any given stage of crop development (Table 8). During the period from late-pod to maturity, the ratio was about 0.20 for chickpea and lentil, and was 0.11 for dry pea in both years. For canola, the ratio was between 0.22 and 0.36, which was greater than mustard Table 6. Proportion of the roots in the 0- to 100-cm depth that is present in each soil segment at maturity, in Saskatchewan, Canada Soil depth (cm) Crop Canola Mustard Flax Wheat Chickpea Field pea Lentil SEy

0
20

20
40

40
60

60
80

80
100

-----------------------------------(%)---------------------------------11.8 10.2 7.6 3.6 66.9z 66.5 13.5 10.8 7.4 1.8 62.3 21.3 11.0 4.8 0.5 61.5 16.4 12.7 7.3 2.1 52.0 24.6 16.1 6.2 1.0 61.4 21.3 12.3 4.5 0.5 62.3 22.5 11.8 3.3 0.1 1.9 1.8 0.7 0.6 0.5

z Values averaged over 2 yr (2006 and 2007), two moisture levels, and two replicates. y Standard error of the mean.

890 CANADIAN JOURNAL OF PLANT SCIENCE Table 7. Above-ground biomass for pulses, oilseeds and wheat grown in 2006 and 2007, measured at various growth stages, in Saskatchewan, Canada Growth stagez Crop

Year

Seedling

Early flower

Late flower

Late pod

Maturity

---------------------------------------------------- (kg ha1) -----------------------------------------------------

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Pulses Chickpea Field pea Lentil Chickpea Field pea Lentil Oilseeds Canola Mustard Flax Canola Mustard Flax

2006 2006 2006

462y 1393 508

1466 3683 2291

2463 5391 3772

4284 4835 5286

3681 5194 4307

2007 2007 2007

588 970 445

1210 2329 1152

2493 3189 2415

4251 4128 2507

3137 4110 3192

2006 2006 2006

1181 1526 293

4161 3669 1351

4064 4394 2235

5451 3880 3492

3965 3661 2636

2007 2007 2007

1721 1473 295

4044 2580 603

5077 3506 2515

4492 4036 2096

4959 3850 1662

Cereal Wheat 2006 763 4890 5502 6969 6712 Wheat 2007 1365 3654 5507 5253 6110 LSD (0.05)115 between years; 347 between crops; 489 yearcrop interaction; 289 between stages; 413 yearstage; and 773 crop stage interaction. z

Growth stages for wheat are seedling, boot, anthesis, soft-dough, and maturity, respectively. All values were averages over two moisture levels, and two replicates.

y

(0.20 to 0.25) or flax (0.17 to 21). Wheat possessed a ratio of root to AG biomass between 0.17 and 0.25. DISCUSSION Crop roots play an important role in the development of sustainable agricultural ecosystems because of their large carbon input to the soil. There are considerable root data related to cereal crops (Bolinder et al. 1997; Niu et al. 2004; Caires et al. 2008; Jordan-Meille and Pellerin 2008), especially some of the studies conducted in the 1970s and 1980s (Wellbank et al. 1974; Campbell et al. 1977; Gregory et al. 1978; Buyanovsky and Wagner 1986). However, very limited literature exists in which extensive measurements of roots have been taken for oilseed and pulse crops under field conditions. The data generated from the present study partly fill that gap. Root Biomass and Dstribution In pulses and oilseeds, root biomass increased rapidly from seedling to flowering, reached a maximum at lateflowering to late-podding stage, and then decreased to maturity. The rapid decrease after podding was probably due to their role in nutrient uptake diminishing soon after the formation of sufficient number of pods on the plant. In pulses, active nitrogen fixation through symbiosis during flowering may have accumulated a large pool of N source in both root and above-ground plant parts, while in oilseeds the remobilization of photosynthates from existing plant parts to growing sinks may be dominant after podding. In wheat, plants

developed slowly but maintained vigorous root growth until later in the growing season. In some earlier studies with spring wheat, root mass reached its maximum at boot stage and then decreased from anthesis to maturity (Campbell et al. 1977; Campbell and De Jong 2001). Similar results have also been reported for winter wheat (Wellbank et al. 1974; Gregory et al. 1978). Campbell et al. (1977) noted that the decrease in root mass occurred in the 0- to 75-cm depth, but remained constant below 75 cm. In the present study, the pattern of root development varied with soil depth. At 20- to 40-cm depth, root mass decreased after reaching a maximum, while root mass below 60 cm remained constant after reaching a maximum. Gregory et al. (1978) reported that the root decrease after reaching a maximum occurred in the 0- to 40-cm depth, while, at the same time, root mass increased below the 40-cm depth. In barley (Hordeum vulgare L.), Xu and Juma (1992) found root mass increased until heading then decreased or remained constant thereafter, while the AG plant biomass kept increasing to maturity. The loss of root mass after reaching a maximum (flowering to podding) is probably due to a transfer of assimilates into the developing grains (Campbell et al. 1983). It is also possible that older roots decay after plants complete their flowering (Xu and Juma 1992). These results indicate root mass will change during plant development, and the intensity of the change will depend largely upon crop species as well as soil and environmental conditions.

GAN ET AL. * ROOT MASS FOR OILSEED AND PULSE CROPS 0.50

more water. In addition, our data show that canola, mustard, and wheat had greater root mass in drier than wetter years, whereas the three pulses and flax possessed similar root mass across years. These results suggest Brassica species and wheat may possess greater resilience to droughts than pulse crops and flax. The greater root mass at 0 to 20 cm under irrigation than rainfed conditions indicates surface soil moisture encourages shallow root growth.

A

0.45 0.40

Wheat

0.35 Pulses

Ratio of root- to AG-biomass

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0.30 0.25

Oilseeds

0.20 0.15

B 0.45 0.40

891

2007

0.35 0.30 0.25 2006

0.20 0.15 r r g d dlin owe e-flowe ate-po urity ly-fl L Mat Lat Ear

See

Growth stage

Fig. 2. The ratios of root to above-ground biomass measured at various growth stage of crop development for (A) comparing among pulses, oilseeds and spring wheat averaged over 2 yr, and (B) comparing differences between 2006 and 2007 averaged across crop species. The corresponding stages for wheat are seedling, boot, anthesis, soft-dough, and maturity, respectively. The vertical bars are standard errors of the means.

In the present study, about 77 to 85% of the total root mass was in the 0- to 40-cm depth. The three pulse crops and flax had very little roots beyond 60-cm depth, while canola, mustard, and wheat had a larger portion of roots in the 80- to 100-cm depth. Pietola and Alakukku (2005) found 59 to 80% of the total root biomass for cereal and summer rapeseed crops was concentrated in the upper 20 cm of soil. Similar results have been obtained for cereals (Campbell et al. 1977; Buyanovsky and Wagner 1986; Xu and Juma 1992; Bolinder et al. 1997). Based on our results, the three pulses and flax can be regarded as shallow-rooting crops and are more likely to suffer from water deficiency in top soils than Brassica species and wheat in drought years. Among pulses, dry pea usually has greater seed yield than lentil and chickpea (Miller et al. 2003). Our results on root growth and biomass indicate that the improved productivity of dry pea over lentil and chickpea is mainly due to improved water use efficiency rather than extraction of

Ratio of Root to AG Biomass Roots developed more rapidly than AG initially, but the proportion of root mass in total biomass decreased with plant maturation. The decrease was more substantial in oilseeds and pulses than in wheat. Similar observations were reported for spring wheat (Campbell et al. 1977) and winter wheat (Wellbank et al. 1973). Our study also revealed that the ratio of root to AG biomass was greater in the drier year of 2007 than in 2006, suggesting AG plant biomass was depressed proportionally more by drier conditions. Among three pulse crops tested, dry pea had the lowest root mass, but had the highest AG plant biomass, resulting in a much lower root to AG biomass ratio than other crops. For example, at maturity the ratio for dry pea was 0.11 compared with 0.22 for chickpea and lentil. For oilseeds and wheat this ratio varied, but averaged 0.20. These ratios are different from some of the estimates in the literature. For example, Janzen et al. (2003) estimated the ratios to be 0.15 for wheat, barley, flax, canola, corn and mustard; 0.20 for dry pea, lentil and oat (Avena sativa L.); and 0.25 for soybean. In many studies, shoot biomass is measured at crop maturation and shoot-to-root ratios established are used to estimate annual carbon inputs to the soil (Bolinder et al. 1997). In the present study, we found root mass of spring wheat was at its maximum at anthesis, in agreement with Pietola and Alakukku (2005), while the maximum root mass in oilseeds and pulses was at their late-flowering to late-podding stages. Sampling roots at these stages may provide more accurate estimates of root mass and carbon contribution to the soil by oilseeds and pulses. CONCLUSIONS Roots are difficult to measure under field conditions. Although there is some information on the root growth of cereals in the scientific literature, there is a paucity of such data for oilseeds or pulse crops. In the present study, we measured root mass of selected oilseed and pulse crops that are commonly grown in the northern Great Plains of the North America, and compared them with the predominant crop, spring wheat. Our results showed that Brassica oilseeds (napus canola and juncea mustard) had greater root mass than pulses. Canola had the greatest root mass among the specialty crops tested, with root mass equivalent to that of wheat. Dry pea had the greatest above-ground biomass among the pulse

892 CANADIAN JOURNAL OF PLANT SCIENCE Table 8. The ratio of root to above-ground plant biomass for pulses, oilseeds, and wheat measured at various growth stages in Saskatchewan, Canada, in 2006 and 2007 Crop

Growth stagez

Year Seedling

Early flower

Late flower

Late pod

Maturity

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——————————————————————————— (%)————————————————————————— Pulses Chickpea Field pea Lentil Chickpea Field pea Lentil

2006 2006 2006 2007 2007 2007

0.24 0.21 0.41 0.46 0.32 0.41

Oilseeds Canola Mustard Flax

2006 2006 2006

Canola Mustard Flax

2007 2007 2007

y

0.22 0.17 0.33 0.51 0.24 0.35

0.23 0.15 0.26 0.32 0.20 0.26

0.18 0.11 0.18 0.22 0.12 0.23

0.22 0.10 0.21 0.21 0.11 0.22

0.09 0.12 0.16

0.16 0.14 0.14

0.29 0.19 0.17

0.21 0.18 0.15

0.24 0.21 0.18

0.33 0.30 0.22

0.32 0.36 0.20

0.32 0.26 0.14

0.40 0.27 0.18

0.32 0.22 0.25

Cereal Wheat 2006 0.28 0.20 0.19 0.17 Wheat 2007 0.49 0.40 0.24 0.27 LSD (0.05)0.30 between crops; 0.25 between stages; 0.36 yearstage interaction; and 0.67 cropstage interaction.

0.16 0.23

z

Growth stages for wheat are seedling, boot, anthesis, soft-dough, and maturity, respectively. All values were averages over two moisture levels, and two replicates.

y

crops tested, but it had the smallest root mass. Flax had the smallest root mass among the seven crop species tested. The root mass of the oilseeds and pulses reached a maximum between late-flowering and late-podding stages, and then decreased to maturity, suggesting that the best time for sampling roots in these crops can be at late-flowering to podding stages. Further, the major proportion of the roots of all crops was located in the 0to 40-cm depth (77 to 85% of the total root mass) with over 60% in the 0- to 20-cm soil layers, regardless of moisture conditions. Future assessment of crop roots could be made by sampling roots at the top 40-cm depth. Canola and mustard rooted to 100 cm depth as did the wheat control; the pulses and flax had very little root mass beyond 60 cm depth and could, therefore, be prone to moisture stress in drought years. Moisture influenced root mass largely in the 0- to 20-cm depth, indicating that irrigation encourages shallow root development and growth. Although the roots developed more rapidly than AG plant biomass initially, with crop maturation the ratio of root- to above-ground plant mass decreased. The detailed root data collected from this study should prove useful to scientists modelling water and nutrient uptake by crops and estimating crop root carbon inputs to soils. Producers can use the information on rooting depth of oilseeds and pulses for designing crop rotations for more efficient use of soil water and nutrients in a well-planned crop sequence.

ACKNOWLEDGEMENTS We are grateful to technical support of Greg Ford, Lee Poppy, Ray Leshures, and Kevin Siever, and to summer students Brian Bohrson, Heather Krahn, Stacey Spenst, Rebecca Heur, Kristi Wall, Kara Heinrichs, and Raquel Dyck for washing roots, and to financial support by Novozymes, Saskatchewan Pulse Growers, and Agriculture and Agri-Food Canada Matching Investment Initiative. Ayers, K. W., Acton, D. F. and Ellis, J. G. 1985. The soils of the Swift Current map area 72J Saskatchewan, Saskatchewan Institute of Pedology, Publ. 86. Extension Division, University of Saskatchewan, Saskatoon, SK. Extension Publ. 48. Biederbeck, V. O., Zentner, R. P. and Campbell, C. A. 2005. Soil microbial populations and activities as influenced by legume green fallow in a semiarid climate. Soil Biol. Biochem. 37: 1775
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