EFFECTS OF NITROGEN FIXING PEA PLANTS (Pisum sativum)
ON GROWTH OF CORN (Zea mays)
Interactions among plant species, particularly negative ones, have been a concern in agriculture (Levene 1926, Russell 1961). Novoa (1981) suggested that it would be advantageous to rotate certain crops by season, grow certain crops together, or avoid growing certain crops on the same land. Observations indicated that some crops require specific types of nutrients in contrast to other crop species, and plants within the Legume Family actually “fix” nutrients, for example nitrogen, within surrounding soils. Nitrogen is a key plant nutrient, and has been shown to be both increase plant growth and development (Russell 1961), but is often deficient in many western U.S. soils (Novoa 1981). Thus Legumes could provide high community trophic “service” (Aprison et al. 1954, Hiroshi 2010).
The common pea plant (Pisum sativum), a member of the Legume family, and a robust dicot flowering plant (i.e., an Angiosperm) native to the western U.S., enjoys a symbiotic relationship with Rhizobium bacteria (Hiroshi 2010). These bacteria grow inside nodules located on the roots of pea plants and convert atmospheric nitrogen (N2) into ammonia (NO3-), which is a molecular form the pea plant, and neighboring plants, can use for numerous physiological functions (including production of DNA, proteins, and plant hormones (Russell 1961, Novoa 1981, Hiroshi 2010). It has become a common practice to rotate crops within fields, alternating Legumes with various other plant species to maintain high soil nitrogen levels.
Our research was conducted in the BIO170 Lab (107 Lewis Hall, Montana State University [MSU]), and was focused on potential effects of pea plants on the growth and development of corn (Zea mays). Our objective was to vary growth environments, with some plants of different species type grown in close proximity, under the same conditions, and other treatments with single plant species, thus allowing us to address the primary research questions: Will the presence of pea plants, in close proximity to corn, positively affect corn shoot height, root length, shoot mass, and overall seedling growth rate? We formulated the primary research question into the following formal hypotheses: H1: pea plants grown in close proximity to corn plants will increase the height of the corn plants; H2: pea plants grown in close proximity to corn plants will increase the root length of the corn plants; H3: pea plants grown in close proximity to corn plants will increase the shoot mass of the corn plants; and H4: pea plants grown in close proximity to corn plants will increase the seedling growth rates of corn plants. For each stated research hypothesis (i.e., H1 thru H4), the null (H0) hypothesis was: the presence of pea plants growing in close proximity to corn plants will have no effect on the corn plant response variables (i.e., shoot height, root length, shoot mass, and overall seedling growth rate). The explanatory, or treatment variable, in all cases, was presence or absence of a pea plant within the growth cells of our measurement units (see below).
The plant experiments were conducted in Lewis Hall, room 107, on the campus of Montana State University. The lab’s room temperature is typically 65 to 70 degrees F (celsius scale thermometer). We set up our experiment in the NW corner of the lab on the counter. We used three polyurethane growth trays (Carolina Biological Supply Company, Savannah, GA), where each tray contained 36 cells 15cm X 10 cm X 10 cm (depth). Each cell was filled with organic soil to the rim of the cell (soil type: Sunshine Mix; Plant Growth Center, MSU). Each growth tray was divided into two sections, with 18 cells containing two corn plants; and 18 cells each containing one Alaska variety pea plant and one corn plant; for a total of 108 corn plants alone and 54 corn plants grown with pea...
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