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Flowers, Fruits, and Frass

Local and statewide information on a variety of current topics for home gardeners and market growers.
PH and Nutrient Availability

Soil Testing

Posted by Kelly Allsup -

Have you tested your soil lately?

By Kelly Allsup

Horticulture Extension Educator

Have you tested your soil lately?

By Kelly Allsup

Horticulture Extension Educator

A soil test can be an excellent addition to a gardener's tool box. Individual plants require a specific soil pH and nutrient level. The proper soil fertility and texture provided by the gardener can improve plant health and productivity. The soil test is a scientific way of gathering pH and nutrient information. With information gained from a soil test, a gardener can make decisions on what plants to grow and what amendments to make to the soil to optimize its potential. A soil test also enables a gardener to apply only what the plant needs and minimizes fertilizer run off and its impact on the environment. It is a rule of thumb to always test soil after first crop production to test to see if pH has been altered or nutrients have been depleted. For instance, potassium (K) is incorporated back into the soil but phosphorous (P) is taken into the structure of the plant and may need to be amended.

A standard soil test tests the soil pH, phosphorous, potassium and organic matter. The pH level is important information for a gardener to know because some vital nutrients are unavailable if the pH is too high or too low. The ideal pH for garden soils is 5.8 to 6.8 and 6.0 to 7.0 for turf. A neutral pH is a 7, an acidic pH is below 7, and a pH above 7 is basic. A soil that is too acidic has a build up of soluble salts (burn plant roots) and could have been caused by heavy fertilizer applications or soil leaching from rain and irrigation. Leaching is the loss of water-soluble nutrients due to water run off. A soil that is too basic can be caused by an over abundance of lime, the inherent properties of the soil, or the alkalinity of irrigation water. Knowing your pH will allow you to choose the proper amendments and amounts to use.

Phosphorous and potassium are macronutrients vital to plant growth. Phosphorous is responsible for root development in establishing new turf. If you have a pH higher than 7.5 it is possible to have a phosphorous deficiency in your lawn. A phosphorous deficiency is expressed by slightly stunted plants, blue green discoloration of older leaves, and the purpling of the margins. Garden soils require a slightly higher level of phosphorous than turf. In garden soils, phosphorous promotes root growth, flower and fruit development, and is beneficial to root crops and flowering bulbs.

Potassium is responsible for healthy plant development, improving tolerance to water stress and disease resistance. It is not common to have potassium deficiency. A potassium deficiency is expressed by interveinal chlorosis (veins of the leaf remain green and the leaf edges turn yellow), drooping soft leaves and leaf rolling.

Phosphorous and potassium application to garden soil is most often minimal because of our fertile soils and because high fertilizer treatments can cause nutrient deficiencies and imbalances and kill of beneficial mycorrhizal fungi in the soil. Mycorrhizal fungi have a symbiotic relationship with the plant where the plant supplies the fungi with carbohydrates and fungi supplies the plant with increased water uptake and nutrients in available form. Mycorrhizal fungi are a crucial element in the natural ecosystem.

The best method of applying phosphorous and potassium to garden soil is applying organic matter to soil prior to planting in the form of humus, manure, or compost. Therefore you would only be able to apply liquid fertilizer in small amounts frequently with little or no phosphorous or potassium to ensure plants get the nitrogen they need.

Soil tests also measure organic matter. Organic matter has numerous beneficial effects on a soil profile. It improves soil structure, increases efficiency of fertilizers, aids in soil productivity, buffers soil against pH change, and ties up toxic ions. A test result of 3-6% is acceptable. The best time to apply soil amendments to alter pH, add phosphorous and potassium, and incorporate organic matter is in the early spring or fall. Follow up 6-12 months later with another soil test.

Steps to testing your soil

1.Obtain a sample bag from a soil testing lab or participating nursery

 2. Take 3 to 6 small core samples from your garden 6" deep (4" Turf) with a bulb digger or trowel. It is better to collect fewer samples made of several cores than more samples made of fewer cores to ensure accuracy.

3. Mix all cores in bucket then fill soil testing sample bag

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