Soil types and the plants and crops grown on them are highly variable. Soils can be heavy (clays), light sandy loams or somewhere in between. Soils can have varying amounts of organic matter (4% to 10% is the desirable range), various pH readings, as well as different amounts of the major nutrients, Nitrogen, Phosphorous and Potassium (NPK) - which are needed in sufficient quantities for plants to grow and prosper.
Bear Path Compost highly recommends for all of our customers to consider having routine testing of the soils from the important growing areas on their property. Perennial beds, vegetable gardens, lawns, fruit trees, and for farmers individual crops, all have specific nutrient needs for healthy and productive growth. The initial soil test is a good base of information to determine what you need to add to your soil to make it work well for your plants. We have for years used the soil lab at UMass for both soil tests and compost nutrient analyses. The information provided is very thorough and includes nutrient recommendations for general plant categories (vegetable garden, perennial beds) or specific categories such as apples, butternut squash, turf (lawns), roses etc. These tests are very affordable and are considerably more accurate than the soil test kits sold by gardening supply stores.
Once you have the results of the initial tests of your various growing plots, it’s important to save these analyses, and in the future refer to them to determine what progress has been made in improving your soil fertility. Future soil tests will either confirm that your growing plots are in peak condition or you might have to make some additional adjustments. Since compost is generally not a significant source of nitrogen, you might find that you need to occasionally add supplemental nitrogen from a different organic source high in nitrogen such as fish emulsion, dried blood etc. You also might find that all of the required nutrients are where they should be and your soil organic level is approaching 10%. It’s then ok and even recommended to take a year or two off from adding more compost or other organic amendments to your soil.
Remember compost is not a panacea for all of your growing needs. Compost is highly useful and desirable in many applications. However, without accurate information about the condition of your soil, adding more compost may or may not make a difference. This of course applies to other nutrients and amendments as well. The soil lab warns on their soil analyses – “avoid over-fertilizing which can cause plant toxicity and can contribute to insect and disease problems.” The end result of all of this is that professional soil tests are a road map to productive growing and satisfied gardening. Enjoy the ride!
Every year samples of finished compost are taken to the UMass Soil Testing Lab for comprehensive analysis. Each analysis includes the following information: % total nitrogen (N), nutrient levels of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg), % organic matter, micronutrients and extractable heavy metals. This information is intended to supplement professional soil tests that specify the fertility needs of plants and crops. Open this .pdf file to a sample analysis from March, 2016. Interpreting Your Compost Test Results (.pdf file)