Nitya Goel, Year 2 Research
Acidic soil affects many people living in coastal British Columbia, impacting farming, wildlife and plant growth. Using natural and artificial soil conditioners can reduce acidity and help raise the pH of soil to a neutral range. This experiment tested the effectiveness of natural fertilisers, including wood ash and mushroom manure, as well as artificial fertilisers such as dolomite lime, in reducing soil acidity and optimising the growth and health of bean plants. Bean plants were grown in acidic soil with a pH of 5.86 collected from Delta, BC, each with one of the three soil conditioners to see which would be the most effective. It was found that the beans grew best in the natural mushroom manure, which raised the pH of the soil by 0.36 and yielded healthy plants.
Soil condition plays a significant role in the growth of plants. As soil is the primary medium from which plants obtain the nutrients necessary for growth, it’s essential for gardeners to understand what makes soil effective. One of the most important properties of soil is its pH (Allaway 2010). Soil with a pH of 6 and below is considered abnormally low, and is normally considered too acidic for common garden plants (Gentili et al. 2018). Acidic soil decreases plant growth in many ways, often by causing deficiencies in phosphorus and calcium as well as toxicities in aluminium and hydrogen ions (Gentili et al. 2018). It has been estimated that acidic soil is a challenge for nearly 40% of the world’s total arable land (Yadav et al. 2021).
Several factors contribute to the acidity of the soil in BC. Excessive rainfall can strip soil of essential ions such as potassium, calcium, magnesium, and sodium (Zhang 2017). Another factor is organic matter decay, which produces hydrogen ions (Zhang 2017). Fir and pine tree needles are found across BC and are also acidic, with a pH of between 3 and 4 (Savonen 2015). When fir and pine tree needles fall to the ground, they form an acidic mulch covering the garden bed, making it a poor environment for plants (Savonen 2015). Lowering soil acidity with chemical fertilisers like dolomite lime is often expensive and can be harmful due to high magnesium content (McKibben 2012). Mushroom manure is a natural blend of leftover mushroom wastes that is known to contain nutrients that are beneficial for photosynthetic plant growth and lower soil acidity (Fasadi et al. 2010). Wood ash is another natural soil conditioner that can help raise the pH of acidic soils as well (Demeyer 2010).
This experiment aims to test the effects of artificial and natural soil conditioners on the growth and health of bean plants, which were chosen due to their fast growth and quick germination. The plants will be grown in either dolomite lime, mushroom manure, or wood ash over the period of a month to investigate the impact each soil conditioner has on the health of the plants and effects it has on the soil’s acidity.
Materials and Methods
Six experimental groups and two controls of soil were prepared. Four groups were made using backyard soil from Delta, BC. The other four were made using potting mix (Promix). Both soils were tested for pH using a calibrated pH metre prior to the addition of the soil conditioner. Each soil conditioner was mixed with the soils using suggested ratios. The mushroom manure (WaytoGrow) was mixed with each soil in a ratio of 1:1. The wood ash (Gardeners Luv) was mixed with each soil in a ratio of 1:3. The dolomitic lime (Golfgreen) was mixed with each soil in a ratio of 1:5.
A total of eight 8cm seed starter pots were planted. Six of the pots included added materials while two were controls with only soil. Each pot was filled with its respective soil halfway. One bean seed was planted and the pot was topped off with more soil until the pot was full. Each pot received ¼ cup of water after planting. All pots were placed on a metal tray which was then placed on a seed warming mat (VIVOSUN) in a room with a north facing window and an artificial tube light. The beans were watered at 8:10 am each morning with around two tablespoons of water.
Over the course of a month (January 30-February 28, 2022), the bean plants were observed daily. Once they had germinated, the plants were moved off the warming mat and the size of the plant was measured daily. Soil pH was estimated using a soil pH metre (VIVOSUN) on the day of planting, and again on February 28, 2022. Final qualitative observations of the bean plants were made on February 28, 2022.
Table 1: Raw data of plant heights collected from Feb 12-Feb 28
From the eight groups, five grew and three remained empty during the growth period of one month. The garden soil with wood ash was the first to germinate 13 days after planting, the potting mix control, garden soil with lime, and garden soil with mushroom manure germinated in 15 days, followed by the potting mix with mushroom manure in 18 days. The potting mix with wood ash, potting mix with dolomite lime, and the garden soil control never germinated.
Figure 1: Graph of plant growth from sprout date
The plant grown in garden soil with wood ash was the first to sprout and the tallest overall at 28.0cm, but did not make it to the end of the growing period. From the plants that made it to the final day of the growing period, the garden soil with mushroom manure was the tallest at 20.5cm. The shortest plant was the garden soil with dolomite lime at 9.5cm. The last plant to sprout was the potting mix with mushroom manure.
Figure 2: Graph of the general rate of plant growth
The plant with the fastest rate of growth was the garden soil with wood ash. The potting mix with mushroom manure began steady but had a sudden increase in height around the 8 day after germination. The slopes of the other three pots on the graph remained low through the entire period.
Table 2: Change in pH of each soil group from January 30 to February 28, 2022
Table 3: Qualitative observations made throughout growth period
Figure 3: Photo of plants taken February 20, 2022
This experiment aimed to determine whether dolomite lime, mushroom manure, or wood ash was the most effective acidity-reducing soil conditioner. From the eight original groups of soil, 5 germinated while 3 remained empty for the duration of the growing period (table 1). As expected, nothing grew in the control pot of garden soil as it was too acidic for bean plants, which are sensitive to low pH and grow best in neutral soil (ph 6-7) (MacKenzie 2018). The plants in the potting mix with dolomite lime and the potting mix with wood ash did not grow either, which could be due to the drastic change in pH (table 2) making the soil too alkaline for growth. The garden soil with dolomite lime, mushroom manure, and ash all germinated, their pH’s becoming more neutral (between 6-7) with the help of the soil conditioners.
The results of the experiment demonstrated that wood ash was the most effective soil conditioner in terms of change in pH (table 2). It also yielded the tallest bean plant when paired with the acidic garden soil (figure 1). However, observations of the plant throughout the growth period revealed that it was not healthy or robust. While the growth was almost exponential (figure 2), the plant was unable to support its own weight as the stem was thin and weak. Near the end of the growth period, the plant became shrivelled and brown. This suggests that the wood ash may have been too harsh on the soil overall. The plant also died 13 days after the initial germination (table 1), bringing wood ash’s effectiveness into question. This may also be due to too much ash being added to the soil, as detrimental effects are observed at extremely high application rates (Gaskin & Risse 2010). When taking the qualitative observations of health into consideration, mushroom manure was the most effective soil conditioner for both the garden soil and potting mix (table 3). The garden soil with mushroom manure also produced the second tallest plant overall, growing at a quick steady rate with limited plateaus (figure 2). In terms of height and change in pH, the least effective soil conditioner was the dolomite lime (figure 1, table 2). This came as a surprise since lime is often used industrially to increase soil pH.
The results of this experiment suggest that for small-scale gardening in the household, mushroom manure would be the most effective way of reducing acidity. As mentioned earlier, mushroom manure is a very natural fertiliser made from mushroom wastes (Fasadi et al. 2010). While it is generally more expensive than mineral fertilisers in terms of nutrient content per unit weight, it releases nutrients in a slower, more effective manner (McEntee 2021), making it more effective than artificial conditioners like dolomite lime in household gardening. It is important to note that this conclusion cannot directly apply to industrial farming techniques, as the methods are much different and not replicable in a household setting.
It was not possible to verify whether the seed that was planted in each would be able to germinate or not, even in favourable conditions. Planting several seeds for each type of soil would be beneficial when repeating the experiment to ensure the soil is the only thing impacting growth. Human error was also introduced in the data collection and care of the plants during the 30-day growth period. Since the length of the plants was measured by hand, inaccurate measurements are possible. The amount of water given to the plants daily was estimated to be around two tablespoons, but may not have been exactly the same for each plant. The plants were also kept indoors with limited sunlight as the weather was extremely cold, which could have impacted their growth. It is also difficult to measure pH of soil accurately, as different samples taken from the same general area can vary greatly. Adjustments to the amount of soil conditioner, temperature, plant type, and water given would all be beneficial in any future replications.
With the results obtained from this experiment, small-scale gardeners from B.C. can better understand which types of soil conditioner would be most suited for their needs. In the case of acidity reducing conditioners, this experiment identifies mushroom manure as the most effective one that maintains the health of plants while improving the health of the soil.
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