Spacing between plants

Tillers plant-1 20 DAP

Standard error

Tillers plant-1 28 DAP

Standard error

Tillers plant-1 51 DAP

Standarderror

Tillers plant-1 72 DAP

Standard error

< 1 cm (AC)

1.2 0.17 1.3 0.19 1.3 0.18 1.4 0.19

2.5 cm (LC)

0.9 0.18 1.2 0.19 1.1 0.18 1.1 0.19

10 cm (SC) 1.7 0.18 1.6 0.19 1.5 0.18 1.4 0.1925 cm (USP)

1.8 0.23 2.3 0.25 2.3 0.24 2.1 0.25

Spacing between plants in clumps

Number of tillers clump-

1

Standard error

Plant height in cm

Standard error

Number of observations

< 1 cm (AC) 0.6 0.21 79.1 0.89 362.5 cm (LC) 0.7 0.21 80.1 0.89 3610 cm (SC) 2.1 0.21 76.6 0.89 36

Planting density Tillers plant-1 20 DAP

Tillers plant-1 28 DAP

Tillers plant-1 51 DAP

Tillers plant-1 72 DAP

1 plant by itself 2.2 2.5 3.3 4.82 plants in clumps

1.0 1.7 1.6 1.8

4 plants in clumps

0.6 0.9 0.8 0.8

6 plants in clumps

0.3 0.5 0.4 0.5

Factors Affecting the Extent of Tillering in Dryland Grain Sorghum Clumps

Srirama R. Krishnareddy1, B.A. Stewart1, W.A. Payne2, C.A Robinson1, and R.C. Thomason1

1West Texas A&M University, Canyon, TX. and 2Texas Agricultural Experiment Station, Bushland, TXAbstract

Tillering is an important morphological component of grain sorghum (Sorghum bicolor L. Moench) development because it affects light capture, water use, grain yield, plant competition and other physical and biological processes. Our objective was to determine the differences in genotype and environmental factors associated with different tillering patterns when grain sorghum plants grown in clumps were compared with uniformly spaced plants. Six sorghum lines were studied for their tillering abilities using two water conditions in a greenhouse at Canyon, TX. Also, four planting geometries and four plant densities were tested in two separate experiments at Bushland, TX in 2005. In experiment I at Bushland TX, four plants seeded (adjacent to each other, 2.5 cm apart from each other in a square pattern, and 10 cm apart from each other in a square pattern) were compared to uniformly spaced plants (25 cm apart) in rows. In experiment II, four plant densities (clumps spaced 75 cm apart in 75 cm rows with one, two, four, and six plants per clump) were studied. Red/far-red (R:FR) light ratio, temperature, tiller number, crop phenology, and leaf number were measured in both experiments. Results of both experiments in the field showed no treatment effects on plant temperature, due to an absence of water stress associated with good soil moisture conditions after the five-leaf stage. Number of tillers plant-1 and R:FR ratio increased with increasing distance between plants in clumps. Additionally, the number of tillers plant-1 and R:FR ratio decreased with increasing plant density. Planting dryland grain sorghum in clumps of four plants with plants 2.5 cm or less apart from each other reduced tillering, apparently due to lower R:FR ratio sensed by the phytochrome system.

Introduction The Texas High Plains are characterized by limited precipitation, low humidity, and high evaporative demand due to high radiation, wind speed, and temperature.

Sorghum often uses stored soil moisture early in the growing season, when conditions are favorable, and produces one to several tillers leading to high amounts of aboveground biomass and leaf area (Fig. 1).

Severe stress conditions during later stages of the crop result in fewer tiller-producing heads, or heads with fewer grains (Fig. 2).

Studies at Bushland, TX and Tribune, KS found that planting sorghum in clumps (Fig. 3) reduced tillers and increased yield under water stress conditions (Bandaru et al., 2006).

Jones (1985) reported that reduced plant competition for light, nutrients and water favors tiller production, whereas low temperature and short day lengths result in fewer tillers in grain sorghum.

Gautier et al. (1999) showed that R:FR ratio regulates tillering in perennial grasses. A reduction in R:FR ratio decreases tillering.

Objectives

The objectives for the study were to investigate:

1) how close together plants need to be in clumps to reduce tillering,

2) how the number of plants in a clump affects tillering, and

3) how the differences in light, water, temperature and genotype are associated with disparity in tiller number when sorghum grown in clumps are compared with uniformly spaced plants.

Fig. 1. Uniformly spaced plants (USP) during early growth stage

Fig. 2. One of USP during later growth stage

Fig. 3. Plants in clumps during later growth stage

Results

Greenhouse study: At 31 days after planting (DAP), number of tillers produced per clump increased with increase in spacing between plants in clumps and at 34 DAP plant heights increased with decrease in spacing between plants in clumps (Table 1).

The number of tillers produced varied with lines and spacing between plants (Fig. 4).

Methodology One greenhouse study at West Texas A&M Univ., and two experiments were conducted at Texas Agricultural Experiment Station, Bushland, TX during 2005. Experiment I: Equal plant populations (53,333 plants ha-1) were maintained in 75-cm rows with four planting geometries. All treatments had four plants for every meter. Adjacent clumps (AC) seeded with all four plants close to each other, loose clumps (LC) with plants seeded 2.5 cm apart in a square, scattered clumps (SC) with plants seeded 10 cm apart in a square, and individual plants seeded 25 cm apart in rows (USP). Experiment II: For every 0.56 m2 there were one plant, or two, four, and six plants per clump in four different treatments. Two hybrids used in the study were Pioneer 8699 and NC+5C35. Light (R:FR ratio) was measured on selected days at hourly intervals using a Skye 660/730 sensor on the shaded and the sunlit sides of plant base. Experimental design – randomized split-plot design with hybrids as main plots and planting geometry as subplots with three replications Data taken related to light and tillers are presented here. Other measurements not presented include crop phenology, temperature, leaf count, and plant height. Grain yields were not determined due to bird damage on heads. In greenhouse, six sorghum lines (BTx 642, BTx 3197, BTx 2752, RTx 430, Tx 2880, Tx 7078) were planted at AC, LC and SC in wet and dry water treatments. Measurements were taken on tiller number and plant height are presented here. Other measurements taken on cumulative water, above ground biomass, grain yields, harvest index, and water use efficiency are not presented. The statistical analysis was performed using analysis of variance procedure using SYSTAT software (version 10.0).

Table 1. Number of tillers and plant height as influenced by spacing between plants

Experiment I: Tiller numbers (Table 2) were directly related to spacing between plants. When plants were 2.5 cm, or less, apart there were 1.5 tillers plant-1. In contrast, there were 2.3 tillers plant-1 for plants 25 cm apart as USP in rows. Pioneer 8699 produced more tillers (P>F=0.05) than NC+5C35. The R:FR ratio on the shaded side in clumps (Fig. 5) with plants 2.5 cm, or less, apart was 0.20. In contrast, the R:FR ratio in clumps with plants 10 cm, or more, apart was greater (R:FR=0.26, P>F=0.05).

Planting geometry (Spacing between plants in cm)

0 5 10 15 20 25

Lig

ht

(R:F

R)

rati

o (

660/

730

nm

)

0.00

0.15

0.20

0.25

0.30

Pioneer 8699 NC+ 5C35

Fig. 5. Light (R:FR) ratio by planting geometry and hybrid (37 DAP)

Spacing between plants in clumps

<1 cm (AC) 2.5 cm (LC) 10 cm (SC)

Num

ber

of ti

llers

clu

mp-1

of f

our

plan

ts

0

1

2

3

4

5BTx 642 BTx 3197 BTx 2752 RTx 430 Tx 2880 Tx 7078

Fig. 4. Tiller number by planting geometry and lines (21 DAP)

Plant density

1 plant 2 plants 4 plants 6 plants

Lig

ht

(R:F

R)

rati

o (

660/

730

nm

)

0.000.15

0.20

0.25

0.30

Pioneer 8699 NC+ 5C35

Fig. 6. Light (R:FR) ratio by planting density and hybrid (37 DAP)

Discussion and ConclusionsThe plants in clumps perceive more far-red light (or reduced amount of transmitted red light) reflected by neighboring plants leading to changes in plant architecture.

The R:FR light ratio reaching the base of the plants decreases as plants grow in closer proximity to one another due to mutual shading.

The lower amount of R:FR light sensed by phytochome system in clumped plants resulted in fewer tillers and taller plants compared to USP.

Number of tiller produced per plant varied with genotype and decreased with increase in plant density.

A clump spacing of 2.5 cm or less is effective in reducing tiller production.

References

• Bandaru, V., B.A. Stewart, R.L. Baumhardt, S. Ambati, C.A. Robinson, and A. Schlegel. 2006. Growing dryland grain sorghum in clumps to reduce vegetative growth and increase yield. Agron. J. 98:1109-1120.

• Casal, J.J., R.A. Sanchez, and V.A. Deregibus. 1986. The effects of plant density on tillering: the involvement of R/FR ratio and the proportion of radiation intercepted per plant. Environ. Expl. Agric. 29:61-76.

• Gautier H., C.V. Grancher, and L. Hazard. 1999. Tillering responses to the light environment and to defoliation in populations of Perennial ryegrass (Lolium perenne L.) selected for contrasting leaf length. Ann. Bot. 83:423-429.

• Jones A.C. 1985. C4 grasses and cereals - growth, development and stress responses. p. 80-82.

Acknowledgements West Texas A&M University, Canyon, Texas and the Texas Agricultural Experiment Station, Bushland, Texas for research facilities.

Texas A&M University Water Resources Institute and the Texas Water Development Board for partial funding of this research.

Table 2. Number of tillers as influenced by planting geometry

Experiment II: Tiller number (Table 3) decreased with increase in number of plants per clump and with increase in density. Light (R:FR) ratio decreased with increase in number plants per clump resulting due to increased mutual shading with increase in number of plants per clump (Fig. 6).

These results are similar to those by Casal et al. (1986) who found that the number of tillers per plant in grasses decreased with increase in plant density.

Table 3. Number of tillers as influenced by planting density