Effects of Nitrogen on Pea Plants
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 ate? 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). Methods 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 plants.
All seeds were also obtained from Carolina Biological Supply Company. The trays were placed under full spectrum UV grow lights (also from Carolina Supply Co. , Model: XPV-230 Lum. ), and received 12 hours of light per day (using a light timer [Home Depot: Model ISZ210/120). We planted seeds at 0. 5 inch depth, and maintained moist (but not “wet” or muddy) soil for 3 days, or until the onset of germination. We used tap water, with approximately 50 ml per growth cell each morning and evening during germination. After germination, we reduced watering to 50 ml once per day, typically in the late afternoon (to acilitate overnight availability of water per cell and prevent drying). After 10 days, when seedlings were well established, we increased daily water to 100 ml per cell. After 2 weeks of seedling growth, we began measuring the response variables, including height of shoot (soil level to apical tip) using a standard metric ruler, and the Precision Balance (room 106) to measure mass to the nearest 0. 01 grams. We compared height, and mass using mean values per treatment, including the standard deviation to assess variation. We used percent growth per week as an estimate of growth “rate”.
Roots were washed, and then dried, prior to mass measurement. Results The average shoot height (Fig. 1) of corn grown in close proximity to pea plants, compared to the height of the corn grown alone, indicated that pea plants may have increased the height of neighboring corn. At the end of three weeks, the average height of corn grown with peas was 35. 4 cm, whereas corn plant grown alone reached an average height of approximately 33 cm, which represented a 6. 78% difference between treatments (Fig. 1). Figure 1. Average height of corn plants grown in Lewis Hall Lab 107 (MSU).
The upper line was on the graph shows the height of corn grown with peas. The lower line represents the corn grown alone. Figure 2. Shows average root mass (dry weight) of corn in the two treatments, i. e. , with or without the presence of Pea Plants. The average mass of the corn grown with peas was 1. 2 grams while the average mass of the corn alone was 1. 07 grams. This represents a 10. 8% difference between treatments (Fig. 2). Figure 3. Average root length of corn plants between treatments. Our observation result also showed that average root length for corn grown with peas was 11. 5 cm and the length for corn grown alone to be 9. 69 cm, a 16. 8% difference between treatments. Figure 4 shows germination rates for the two treatments, with 37% increase per week for corn grown with peas, slightly higher than the corn grown alone (35. 2%). Table 1 shows the various percent differences between the two treatments, and in each contrast, the values for corn grown with peas was greater than corn grown alone. Discussion Overall, in summarizing our key results, we observed corn grown with peas showed a trend of 6. 78% taller and 10. % heavier than corn grown alone. We also observed the roots of corn grown with peas were on average, 16. 8% longer than the roots of corn grown alone. Finally, we found that the corn grown with peas had a 4. 86% higher germination rate than corn alone. Figure 4. Average germination rate of corn plants estimated between treatments. Table 1. Percent difference between the treatment, showing increases in all variables in treatment with both plants together. Height6. 78% Mass10. 80% Root length16. 80% Germination rate4. 86% Our results, reviewed together (e. . , Table 1), strongly suggested that our ideas concerning facilitation were correct, and supported our research hypotheses that corn grown with peas would be taller, heavier, have longer roots, and have a higher germination rate than corn grown alone. Upon reflection, we believed that it made sense that the corn grown with peas tended to outperform the corn grown alone for the variables we tested, because clearly nitrogen is an essential component of chlorophyll (Tam 1935), amino acids, ATP, and nucleic acid (Levine 1926).
Since pea plants are nitrogen fixers, their presence increases the amount of usable nitrogen in the soil. Thus, the corn grown with the peas would have had more nitrogen available to it to aid in the production of chlorophyll, amino acids, ATP, and nucleic acid, all of which probably aided the corn growth, mass, and also the higher germination rate (percent) that we observed.
Furthermore, our results tend to agree with other research findings, for example a study presented at the 2010 World Congress of Soil Science found that corn rotated with soy, also a nitrogen fixer (Aprison 1954), tended to grow taller and have higher yields than corn rotated with corn (Yin 2010). Another study found that along with the correct row spacing and plant density, corn plants grew best when given moderate levels of nitrogen (Cox 2000).
Further, a study done in Europe noted that nitrogen deficiency in plants tended to inhibit plant growth and rates of photosynthesis (Zhao 2005, Bradshaw et. al 2010, Cox et al. 2010). The positive effects nitrogen has on plants are well documented and have been studied for decades, but we think our replications of pea plant facilitated growth were well worth the efforts, and also allowed us to see first-hand, how experiments can be powerful tools for learning and for confirmation of research ideas.
It is well known by both plant scientists and amateur backyard gardeners that plants need nitrogen to grow to their full potential, so perhaps our work offered little new information, but it was still quite fascinating to conduct the research, learn the steps of the scientific process, and apply them ourselves, rather than simply read about experimentation. Those wishing to grow corn, or other important, or popular house plants, might use our outcomes to enhance growth production of desired species.
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