THE EFFECTS OF INTRASPECIFIC AND INTERSPECIFIC

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Intraspecific and interspecific competition between two species of plants were examined in this study to help a group of organic farmers determine the best planting arrangement, including the optimum density of seeds and the optimum combination of plants of different species. The farmers would like to maximize their crop of healthy seedlings in a limited amount of space. The purpose of this study was to find the balance between competition and healthy growth. Competition is a very important part of plant interactions. Plants undergo two types of competition: intraspecific, among their own species, and interspecific, with plants of another species. The two kinds of competition have distinct effects. Intraspecific competition is the most aggressive because plants of the same species have the same needs and same resource-obtaining structures (Alexander et al., 1970). There are three principle effects of intraspecific competition outlined in a series of papers by Yoda et al., 1963: the average size of a plant decreases as density increases, the size structure of the population becomes hierarchical and self-thinning or density dependent mortality occurs (Park et al., 2003). For interspecific competition, many different experimental designs have been employed, for researchers have different aims (Park et al., 2003). The replacement series is one design where the proportions of one plant to another are changed, but the total density is kept constant. According to Park et al., 2003, many argue this does not separate the effects of intra and interspecific competition, so is not an adequate design. Another design is the additive design where both density and proportion are altered, and this yields a simple hyperbolic relationship between the crop damage and number of weeds (Park et al., 2003). 2
However, in this study, the goal was not to study crop-weed interspecific competition, but intercropping, and whether two crops could be planted together to produce higher, healthier yields in smaller space. In his 2003 Agronomy Guide, Preston Sullivan said, “Intercrops can be more productive than growing pure stands.” He argues there is more stability in diversity established in having more than one crop. The reason to intercrop is to increase the productivity of the land, and when the density, maturity dates, and plant architectures are taken into account, it can be very successful (Sullivan, 2003). In 2003, Sullivan described a South Carolina trial where corn and peas were intercropped at three different corn densities. There was a definite yield advantage from intercropping than from growing the two crops pure stand, but the peas suffered from increased competition in the higher densities of corn (Sullivan, 2003). A balance must be attained. The specific purpose of this study was to find an optimum density for growing wheat and to find out whether wheat and peas could be grown together to maximize yield per area. It was hypothesized that there would be no difference in the stalk length (above ground height of the plants) or the root length between pure wheat grown at a density of two per pot and wheat grown at higher densities, and that there would be no difference between the control wheat and the wheat grown with pea seeds. The purpose of the experiment was to find out whether competition (intraspecific or interspecific) did indeed effect the growth of individual plants. Materials and Methods The experiment began on September 28, 2004. After planning out the experimental design, 42 small starting pots were obtained and filled three-fourths of the 3
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THE EFFECTS OF INTRASPECIFIC AND INTERSPECIFIC

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