Early Attention to Soil Fertility Will Save

Feature Story Early Attention to Soil Fertility Will Save Time and Money in the Long Run

by Bill Errickson, Agriculture Agent - Rutgers Cooperative Extension of Monmouth County

Photo: NJAES

For landscape plants to reach their full potential, proper soil fertility is essential. Just as nutrition is key to human health, when soil nutrition is optimized, your plants will be healthier, more disease resistant and more stress tolerant. Focusing on soil fertility before establishing your plantings will save you time and money in the long run and will support plant performance that results in customer satisfaction.

Soil Fertility Testing

Before adding any fertilizers or liming materials to the soil, it is important to take a soil fertility test. This is the most accurate way to determine the nutritional needs of the soil, and testing is required to apply any fertilizers containing phosphorus to turfgrass. Soil samples are best taken in the fall or in the spring before fertilizer application. Soil testing should be repeated at least every 2 to 3 years, but testing every year is preferable when possible. Your results will also be most accurate if you sample at the same time each year. Testing the fertility levels in your soil early and often will allow you to supply the nutrition that is required for next level plant growth, before any deficiencies or other problems develop during the growing season.

How to test your soil: Soil test kits can be obtained from your local Rutgers Cooperative Extension County Office or from the Rutgers Soil Testing Laboratory. To take a soil sample, collect 10 to 15 cores randomly selected from the landscape where you are planning to fertilize. Place all the cores into a bucket and mix them together, being sure to break up any clods. Take approximately 2 cups of soil from the bucket and place it into the plastic bag that comes with the soil test kit. Fill out the questionnaire and mail the sample to the laboratory or drop it off at your county extension office. After the sample is analyzed, you will receive a soil test report with lime and fertilizer recommendations specific to the plants you plan to grow.

Soil pH

In addition to providing nutrient recommendations, your soil test report will include information about pH. Soil pH affects the availability of nutrients for plant uptake. While individual plant species have different optimum pH ranges, most plants in the landscape thrive in a slightly acidic to

Soil pH influences the availability of nutrients for plants. Wider bands indicate that nutrients are more available and narrow bands indicate that nutrients are less available at different pH levels. Chart: Purdue Extension

neutral pH around 6.2 to 6.8. If soil pH is too low, it will limit the availability of most nutrients and plant growth will be reduced. So, even if the nutrients are present in the soil, they will not be fully taken up by the plants if the pH deviates from the optimum range. Soil pH can be raised by adding liming materials such as calcitic and dolomitic lime to the soil. Calcitic lime will only supply calcium to the soil, while dolomitic lime will supply both calcium and magnesium. Both of these soil amendments will effectively raise soil pH, but dolomitic lime should only be used if a soil test determines that magnesium is required. Some plants, such as azaleas and rhododendrons, grow best at a lower pH. If soil pH needs to be lowered, elemental sulfur (S) can be added to the soil. If calcium is deficient in the soil, but pH is already in the optimum range, gypsum (calcium sulfate) can be added to supply the necessary calcium without raising the pH. Soil pH will tend to decline over time, as plants use the available calcium, magnesium, and other cations in the soil. Regular soil testing will determine when to add lime and how much is required to bring the soil pH back into the optimum range. It should also be noted that it can take some time for lime additions to have their desired effects on raising soil pH, so any applications should be made early in the spring or in the fall to prepare for the following season.

Plant Nutrition

Plants are mostly composed of carbon, hydrogen, and oxygen, which they obtain from the air and water. The soil must supply fourteen additional essential elements for optimum plant growth. This includes 6 macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg) and Sulfur (S), and 8 micronutrients: Boron (B), Chlorine (Cl), Copper (Cu), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), and Zinc (Zn). Macronutrients are required in larger quantities than micronutrients; however, all are required for plant growth.

Nitrogen (N) is the most abundant plant nutrient that is supplied by the soil. It is essential for vegetative growth and is a component of proteins, amino acids, and the chlorophyll pigment that is involved in photosynthesis, giving plants their green color. Nitrogen deficiency will result in stunted growth, yellowing of the leaves, and weakened plants. However, excess N can also create problems. The rapid, lush, green vegetative growth that results from too much N can result in plants that have thinner and weaker cell walls. This can make plants more susceptible to attack by insects, such as aphids and fungal pathogens.

Optimum phosphorus (P) levels are important for energy transfer in plants, as well as root, flower, and fruit development. Many “bloom booster” fertilizers will be

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high in P due to its effects on promoting abundant flower production. While a certain level of P is required for healthy plant growth, applying excess P beyond the recommended amount can have serious environmental impacts, in addition to wasting time and money.

Potassium (K) is another well-known macronutrient that is required for proper movement of water, nutrients, and carbohydrates throughout plant tissues. Insufficient K levels will result in weakened and stunted plants in the landscape. On a cellular level, K is also involved in regulating the opening and closing of stomata, which play an important role in photosynthesis, gas exchange, and water relations in the

plant. As such, there is a growing body of research showing that adequate K levels are critical for improving abiotic stress tolerance and resistance to insect and fungal pathogens.

Environmental Impacts

Excess N and P can have negative environmental impacts, including contamination of ground and surface water. When more fertilizer is applied to the landscape than can be taken up by plants, it can leach into groundwater or run off into surface waterways and stimulate algae blooms. In addition to unnecessarily increasing your fertilizer costs, this leads to additional impacts on the aquatic environment, including depleted oxygen in the water and the resulting death of fish and other organisms. New Jersey’s Fertilizer Law restricts the application of N and P on turf before March 1 and after December 1 for commercial applicators. The law also requires any P applications to turf to be justified by a soil test. Proper N and P management must take into consideration the amount of fertilizer required to support plant growth in the landscape without impacting the surrounding waterways.

Additional steps to reduce the chances of fertilizer applications affecting the water include: 1. Do not apply fertilizer near water, storm drains or drainage ditches. 2. Do not apply fertilizer if heavy rain (water runoff) is expected. 3. Apply fertilizer only to the intended lawn or garden beds, and sweep any fertilizer particles that land on the driveway, sidewalk or street back onto the lawn.

Remember, routine soil tests will help you identify the appropriate types of fertilizers to apply each season. Targeted applications to improve soil fertility will maximize plant health while minimizing costs by reducing unnecessary fertilizer applications and decreasing the likelihood of plant pests and disease presence later in the season. By providing the macronutrients and micronutrients your plants need, and maintaining optimum soil pH, you will be setting your plants up for season-long success.

For more information visit: https:// njaes.rutgers.edu/soil-testing-lab/ or contact your local Rutgers Cooperative Extension County Office: https://njaes. rutgers.edu/county/

Aphids are attracted to succulent growth caused by excess nitrogen. Photo: NJAES Bill Errickson is the Agriculture and Natural Resources Agent for Rutgers Cooperative Extension of Monmouth County with a focus on sustainable nursery production, turfgrass, and agricultural innovation. He has worked in various aspects of the horticultural sector for the past 16 years, including operating his own diversified farm in coastal Maine and growing bare-root nursery stock for Fedco Trees. He has led courses focused on sustainable horticulture and soil fertility for commercial growers, homeowners, and college students throughout New Jersey and New England.