Thursday, February 17, 2011

Soil testing a good idea

Now that the latest snow has melted, it's a good time to collect and submit soil for testing ahead of spring soil preparation and planting. Do be sure to air dry soil first before shipment.

I've seen both extremes over the years - too little fertility to produce good vegetables and over-fertilization that causes problems. Nationally studies show over-fertilzation is more of a problem in home gardens.

Excess nitrogen applied to tomatoes, squash and other "fruiting" vegetables produces luxuriant leaf growth and few fruit. With root crops such as carrot, turnips and parsnips you will see many leaves and small roots. Little nitrogen when corn tassels produces poor ear production.

Excess phosphorus tends to interfere with vegetables' ability to absorb iron and other micronutrients. The excess shuts down the roots production of phytochelates, organic molecules that increase iron uptake.

You can see that a general broadcast of a 5-10-5 or 10-10-10 fertilizer without knowing where you stand on fertility is likely a poor idea.

Sample prior to adding compost or fertilizer and send to the Soil Testing Lab at Colorado State University or another analytical lab for analysis. The soil test results will inform you about whether compost should be added and what type. For example a salt-affected soil with low organic matter will require low-salt compost (often plant-based and not containing manure).

Testing your soil on a three to four year cycle is usually enough to do a good job of managing the fertility and organic matter in Colorado soils. For more information check the Colorado State University Extension fact sheet Fertilizing the Vegetable Garden.

Photo credit: Collecting soil sample - Carl Wilson

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