Organic Amendments and Growth of Phaseolus vulgaris

Introduction

Composting on the farm makes sense from several perspectives. Composting reduces farm waste by turning it into a soil nutrient. Adding compost to the soil allows plants to utilize this waste, improving productivity and yield. The type of compost needed depends on the needs of the particular crop and the conditions of the native soil. This research explored the effects of four different soil and compost combinations on the germination, growth, and yield of yellow beans (Phaseolus vulgaris).

Compost can contain a number of ingredients to meet the needs of the crop being produced. Common components of compost include leaf matter, weeds (without seed heads), straw, and manure. Sugar stimulates growth in plants and can be added to an organic mixture as well. Legumes, such as the beans used in this experiment, have nitrogen-fixing bacteria growing in nodules on their roots. Other plants have specialized nutritional components as well. Finding the proper compost mixture for the type of plant is the key to healthy growth. Healthy plants are more productive and resistant to disease than plants that lack the proper nutrients for their particular growth needs.

This study examined four different soil amendments on the growth of yellow beans (Phaseolus vulgaris). The four soil amendments were sugar, cow manure, leached leaf litter (leaf litter tea), and straw. This study tested the following hypotheses:

H1: Soil amended with sugar will produce more vigorous Phaseolus vulgaris plants than soil alone.

H2: Soil amended with cow manure will produce more vigorous Phaseolus vulgaris plants than soil alone.

H3: Soil amended with leached leaf litter will produce more vigorous Phaseolus vulgaris plants than soil alone.

H4: Soil amended with straw will produce more vigorous Phaseolus vulgaris plants than soil alone.

The null hypothesis states that no difference in growth will be found between plants grown in any of the four amendments when compared with soil alone.

Methods and Materials

The objective of this project was to examine differences in bean growth among the different soil amendments. This study furthered our understanding of how these four soil amendments affect plant growth. The findings are useful for increasing production of legumes and for improving operational efficiency by reducing waste in farm production.

The study design tested the effect of four different organic materials on plant growth. The four materials were: (1) Sugar (designated SS); (2) Cow manure (designated SM); (3) Leached leaf litter (designated SL); and (4) Straw (designated SW).

The independent variable consisted of soil only (the control). The dependent variable consisted of soil in combination with one of the four soil amendments. The soil mixture consisted of a standard commercial blend of humus, peat moss, perlite, and limestone. Additional perlite and vermiculite were added to the soil mixture to make seedling emergence easier, creating a mixture similar to standard commercial seed-starter mixes.

The study consisted of five different soil treatments. Ten samples of each treatment were used. Growing media for the SM, SL, and SW treatments were a volumetric mixture of 50% soil and 50% compost. The SS mixture was made by adding 20 g of refined white sugar to the surface of the soil. Leaching action carried the sugar to the roots of the plant, much as rain washes nutrients to roots in the field.

Pots were filled with approximately 400 ml of growth medium in each of the 50 plastic pots. Initially, four beans were placed in each pot, positioned in the corners to minimize crowding as the plants matured. Pots were placed on a table at room temperature under fluorescent lights. Seedlings were misted with standard tap water for five consecutive days.

Seedlings began to emerge on day 5. A 430 W high-pressure sodium lamp was suspended 50 cm above the tops of the pots. The light was set on a regime of 16 hours on and 8 hours off to simulate light conditions at the height of the growing season for this zone. As the plants grew, the lamp was raised to facilitate proper leaf and stem development. Watering was changed to 50 ml per day, once per day by sprinkler. Pot positions were changed randomly after each watering to ensure equal light exposure. After 12 days, the pots were thinned to one plant per pot; the strongest plant was retained and the three weaker ones were removed. The watering and light routine continued for the entire 45-day growing period.

Recording of plant growth began on day 15 after planting. Canopy width and stem height were recorded every five days through day 45. After 45 days the plants had reached their maximum growth in the pots. Canopy width was measured as the horizontal distance between the farthest leaf extremities. Height was defined as the distance from the soil surface to the highest stem dichotomy. Flower bud development was recorded after day 30, as buds began to appear, and was measured by counting them.

After 45 days of growth, all roots and shoots were separated at the soil line and placed in bags. They were dried at 70°C for two days. Roots and shoots were then cooled in a desiccator and weighed to determine oven-dry mass.

Data were analyzed using a two-way Analysis of Variance based on time and the treatment applied (SC, SS, SM, SL, and SW). This was followed by Tukey's Multiple Comparisons test to separate significantly different treatments. Dry masses of roots were analyzed using a one-way Analysis of Variance, also followed by Tukey's Multiple Comparisons test.