Soil test to get the best

Warm weather makes farmers think about planting, and soil testing can ensure plants get what they need to thrive.

Crops, whether they’re fruit, field crops or garden vegetables, require proper nutrition for best results. Knowing what nutrients are needed, and how much, is a key to success. Soil testing provides a window into the soil’s nutrient status and the results address the plant’s needs. Testing also helps us manage our fertilizer dollars wisely and protect the environment from over application of nutrients. Nitrogen applied in excess of the plant’s needs can leach with rain, down to the groundwater. Over-application of phosphorus can lead to runoff or wind erosion moving it to surface water. Since phosphorus is commonly the limiting nutrient in our lakes and streams, this phosphorus addition can cause stimulation of unwanted algae and other aquatic plants, resulting in fish die-offs and loss of quality recreational waters.

Plants require at least 16 elements for growth. Carbon, hydrogen and oxygen come from air and water and make up over 90% of the fresh weight of plants. The rest of the plant’s weight is made up of the needed macronutrients (nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium) and micronutrients (zinc, copper, iron, manganese, boron, chlorine, molybdenum, and cobalt), which plants get from soil, compost or fertilizer. The macronutrients are needed in greater quantities while only very small amounts of the micronutrients are required. The chlorine requirement for example, was unrecognized for years, because the amount needed was so minute that enough was residual on the well-washed research glassware.

Nutrient recommendations have changed over the years. The changes are based on changes in crop varieties and research results in controlled field studies. For example, some new corn varieties provide high yields with less nitrogen than older varieties. However, it is still recommended for long-term nutrient management, that producers sample a field at the same time of year each time the field is sampled, and that fields be sampled regularly. For vegetables, sample at least every two years. For field crops, sample every three years. Sampling depth depends on the plow depth and type of crop.

In addition to nutrients, a soil test provides the pH. This indicates how acid or alkaline the soil is; pH affects nutrient availability. For example, plants growing in a high pH (alkaline) soil containing iron will be iron deficient because the iron is bound and unavailable to the plants. For good plant growth, the pH of this soil will need to be lowered.

Producers can take their own soil samples or hire someone to do it. If a field is uniform and has a uniform cropping history for the past two years, 20 samples can be taken from up to 40 acres, mixed up for a composite sample from which a representative subsample is submitted for testing. However, if there is variation in cropping history, soil type, slope, tillage practices, manure/fertilizer management, etc. the field needs to be subdivided and sampled based on site similarity and fertilizer application plans. Representative sampling provides meaningful information for fertilizer management. Soil testing can be obtained through the MSU Soil and Plant Nutrient Laboratory as well as some commercial laboratories.

Nitrogen, potash and phosphate fertilizer prices are up from last year. If the weather gradually warms across the United States, supply will match fertilizer demand as producers begin the planting season from south to north, and fertilizer prices will remain stable. If, however, the Corn Belt and the northern areas all have fertilizer demand at the same time, there could be an additional increase in prices. This would further boost the importance of soil testing to maximize fertilizer dollars.

Contact your county Extension office for soil testing services available from MSU

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