Back yard sample - this is as close to "native" soil as I have, though the native top soil was likely scraped off and fill dirt added when the subdivision was built in the late Sixties. When Jack bought the house in 2004, the "lawn" was a mix of Bermuda, St. Augustine and weeds. Much of the turf has died off, and horse herb and oxalis have moved in. This clay soil has not been amended in a decade.
The soil test results - iron was low. Nitrate and phosphorus were moderate. Potassium, magnesium, sulfur, zinc and copper were high. Manganese, boron and calcium were very high, and pH was moderately alkaline at 8.0. Organic matter content was good at 5.89% (despite no added amendments). If I had turf grass growing here, the Aggies would recommend fertilizing with nitrogen and phosphorus three times a year during the growing season, plus foliar iron every 4-6 weeks, particularly if the grass was noticeably yellow.
Veggie garden sample - this soil is mostly Hill Country Garden Soil trucked in from The Natural Gardener, amended yearly since 2009 with Ladybug brand Revitalizer compost, and fertilized spring and fall with Ladybug 8-2-4 fertilizer according to directions on the bag. I mulched these beds with Sylvan mulch in the spring. I tested the soil after harvesting summer crops, before doing any fall preparations.
The soil test results - compared to the back yard sample, the nitrate levels were much lower - virtually nil - and the phosphorus levels were much higher: so high, in fact, that the Aggies recommended I add no additional phosphorus for five years before retesting! Organic matter was about 2% higher than the "native" soil, and pH was a little lower at 7.7, though still in the moderately alkaline range. All the micronutrients were elevated, including iron; manganese, boron and sulfur were very high. The Aggies recommended only one additive: 1.3 pounds of nitrogen to every 1000 sq ft every 4-6 weeks during growing season (my eight 4' x 6' raised beds total about 200 sq ft).
Finding a fertilizer that contains only nitrogen and nothing else may prove to be a challenge, particularly one that's fast-acting, organic, and reasonably priced! Blood meal contains iron, while manures, fish products and plant-based "meals" contain 1-4% phosphorus and/or potassium. But clearly, the soil in my vegetable garden is nutrient-rich and needs no additional phosphorus, potassium or micronutrients. Planting cover crops and nitrogen-fixing legumes would be another way to boost the nitrogen content of the soil.
Have you ever had your soil tested? What were your results, and did testing change the way you fertilize? Leave a comment and share your soil test stories.
Words and photos © 2009-2013 Caroline Homer for "The Shovel-Ready Garden". Unauthorized reproduction is prohibited.