Plant Science

First, Last name Lab session / hours

The Effect of Density on Radish (Raphanus sativus) Growth

ABSTRACT

When plants compete for resources, such as space, water and light, plants will try and

absorb as much recourses as it possibly can, but when there are less resources for it to

use, there will be noticeable effects on its health (xavior.edu, 2015). This experiment was

designed to compare the effects of radish density on the growth of radishes, seeing if

competition for space really does affect the plant health/ size. Three pots were taken with

different amounts of radish seeds planted in each (2 in one pot, 4 in one pot, 8 in one pot,

two being the control) and were grown until the plant was ready to pick (6 week period).

At that time, the radishes were then picked and measured. The measurements for the

radish root dry weight, root diameter, leaf surface area, and leaf dry weight were taken.

Results showed that the average effects of competition for space decreased the root size,

leaf (wet) area, and root fresh weight, but didn't have a significant decrease on the leaf

(dry) weight. The objective of this experiment is to see the effects of density on the

growth of radishes (Raphanus sativus).

Introduction

Plants, just like most living organisms, compete against one another. This

competition derives when there is a necessity that the individual needs. For plants, water,

minerals, light and space are important resources they need to live. When these resources

are limited plants compete in order to survive (xavior.edu, 2015). When plants compete,

each plant will regulate its intake and use what resources it can. Since each plant will

consume what it can, and there are more plants in one area, it will cause each plant to

collect fewer resources then it could.

This experiment is a good way to test just how close plants should be in a

particular area to be more efficient for farmers who want to utilize as much space as they

can, but still have good growth results from their crops. Plant competition on space can

affect the plants growth and can result in a smaller overall product if it is unable to get the

amount of nutrients needed (Bianco de Carvalho, 2011). Carrots (Daucus carota) and

radishes (Raphanus sativus) are prime candidates to experiment on due to the fact they

have taproots and the effects can be seen more visibly. When carrots (Daucus carota) are

planted too close to one another, the resulting diameter is significantly smaller than if it

was planted further apart (Salter, Currah, Fellows, n.d.). In comparison radishes

(Raphanus sativus) will also produce smaller specimens when more competition is

presented.

The purpose of the experiment was to test whether or not plant density has any

effect on the competition of radish plants. The prediction is that the density did effect the

radish growth in size, leaf area and root density; the radish with fewer competition would

DESNSITY STUDIES, RADISH 2 have had the most success growing while the one with the most would have had the least

success in these fields.

The objective of this experiment is to see the effects of density on radish

(Raphanus sativus) growth. The null hypothesis is that the density will have no effect on

the growth of the radishes. The alternative hypothesis is that the density of the radishes

will effect the growth of the radishes.

Materials and Methods

The experiment was carried out at the California State University, Chico Farm in

Chico, CA. The researchers involved were current students at California State University,

Chico’s Plant Science 101 class. The section three class participated in the radish density

growth study as a whole and were divided into six different groups.

The experiment will be conducted to demonstrate the effect of the radish density

on the (dependent variables) root dry weight root diameter, leaf surface area and leaf dry

weight and the independent variable will be the density. Radishes were grown in 6-in.

pots with three densities of 2, 4, and 8 plants per pot. The pot with two plants was used as

the control, the pot with four was used as treatment 1 (T1) and the pot with eight was

used as treatment 2 (T2).

By placing each plant in different density situations, the plants were be able to

formulate different density growths. When the plants completed the 6 weeks,

measurements were made. Each group measured the diameter of the largest root from

each pot (in cm.), the total leaf area (wet/ dry) from each pot (in cm.) using a leaf meter,

and finally the root fresh weight (in g.). Each group’s measurements were taken from the

control, T1 and T2 and the average, range and standard deviation for all were calculated

to give the class average results.

In the experiment, each group filled three 6-inch pots with porting mix

(greenhouse media). Each pot was labeled, one being control (2 plants) another T1 (four

plants), and a T2 (eight plants). Next, the radish seeds were planted in each pot. To

ensure that the plants would grow, more extra seeds were planted. For example the

control had five, T1=seven and T2=fourteen. (After a week trimming was needed so

there was only two in control, four in T1 and eight in T2). Depending on the seed size,

each seed should have a depth was 3-5 times the largest seed length. So the radish (1mm)

was planted at 4-6 mm depth incision made by a pencil. After the seeds were planted they

were covered up with a layer of soil. Once done, the pots were placed on a tray with the

other groups’ pots in the greenhouse. Each week observations were made on the radish

growth, and after six weeks the final measurements were made.

Results

DESNSITY STUDIES, RADISH 3 The experiment was designed to see the effects of plant density on the growth of

radishes and to determine whether or not competition would affect the size of the plants.

When calculated, results showed that the average root circumference ARC, the leaf area

LA, and the fresh root weight FRW declined as the density increased. As shown in (Table

1), the control had an average of 8.6 cm. ARC, a 276.2 cm2 in LA, and 22.6 g in FRW.

For T1 the averages were 8.3 cm ARC, 188cm2 LA, and 13.5 FRW. In T2, ARC was 6.3

cm., LA was 121.2 cm.2 and FRW was 6.0 g. Although the ARC, LA, and FRW all

indicated that the measurements decreased with more density, the average for the leaf dry

weight LDW stayed at relatively the same rate. All this supports the previous hypothesis.

Graph 1: Average and STD for control (C), T1, and T2.

Discussion

Results have shown that the denser pots (T1 and T2) struggled more to grow than

the control, which grew better due to less competition to gain the provided nutrients in the

pot. With limited space, the plants in T1 approximately got half the nutrients than that of

the control, and T2 got approximately a forth of the possibility of resources than the control.

The study had a few limitations that had the possibility of altering data received.

The seeds in which were planted, were randomly spread out. To ensure a more valid result,

measurements should be made so that each seed is equally separated from one another.

Another error can be found in the tools of measurement. There must be an agreed upon

amount of significant figures used to record data, to avoid any calculation errors. Using the

leaf meter also adds error to the experiment. By removing every particle of dust or dirt

from the machine after each use will help get a more accurate reading.

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

Average St. Dev Average St. Dev Average St. Dev

C T1 T2

Largest Root Circumference (cm)

Leaf area (cm2) Mean /plant

Leaf area (cm2) Sum / Pot

Root fresh weight (g) Mean /plant

Root fresh weight (g) Sum / Pot

DESNSITY STUDIES, RADISH 4 This evidence supports the previous research going into the experiment, and

provides an evidence that plants with more competition will not grow as well as those that

are in less competitive environments. The competition fro the resources, as shown from

this experiment, adds to the theory that competition leads to less availability of resources

and stunts the growth of plants in competitive space and further helps approve that spacing

is key to result with a healthy, well-nourished plant.

To conclude the null hypotheses, that density would not affect the growth of the

radish, was rejected and the alternative hypotheses, that density would affect the growth of

the radish, was accepted instead.

DESNSITY STUDIES, RADISH 5 References

Bianco de Carvalho, L. (2011). Effects of Plant Density and Proportion on the

Interaction between Wheat with Alexandergrass Plants, 70(1). Retrieved March 23, 2015,

from http://www.scielo.br/scielo.php?pid=S0006-

87052011000100007&script=sci_arttext

Plant Competition. (n.d.). Retrieved March 23, 2015, from

http://site.xavier.edu/blairb/eco/ecology_biol_250/lab_reprints_biol_250_-

_spr/ecolabs/plant-competition/plant-competition.pdf

Salter, P., Currah, I., & Fellows, J. (n.d.). Further studies on the effects of plant density,

spatial arrangement and time of harvest on yield and root size in carrots. The Journal of

Agricultural Science, 465-465.

Effects of Mechanical Stress and Plant Density on Mechanical Characteristics, Growth,

and Lifetime Reproduction of Tobacco Plants. (2005, December 1). Retrieved April 19,

2015, from http://www.jstor.org/stable/10.1086/497442