Measuring Soil Health Before Converting To Deep-Zone Tillage
Jude Boucher, University of Connecticut
reprinted from Croptalk v5.1
In a recent article on ĎSoil Health and Deep Zone Tillageí (Vol. 4,No. 1, May 2008), I defined a healthy soil as one that is capable of sustaining crop productivity. I also mentioned how it is a balance of soil chemical, biological and physical attributes that makes a soil productive. Cornellís Soil Health Team has refined this concept further by creating a new Soil Health Test which uses 12 different critical indicators to help measure and quantify a healthy soil.
Cornellís Soil Health Test
For chemical indicators Cornell uses pH, extractable phosphorus and potassium, and minor elements; for biological indicators they use organic matter content (%), active carbon, mineralizable nitrogen, and a root health rating system; for physical indicators they measure aggregate stability, water (holding) capacity, and surface and subsurface hardness/compaction. Although many more potential indicators (39) were investigated to come up with this list, these 12 were determined to be the most critical and most practical to measure.
You are familiar with many of these 12 indicators already and others are self-descriptive, but a few require a brief explanation. Active carbon is the portion of the organic matter that is available to feed beneficial soil organisms. Beneficial organisms (such as earthworms, fungi, bacteria, etc.) are important to provide deep soil channels for drainage and root growth, to help hold soil clods together and maintain soil structure and porosity (provide air to roots), and to help decompose organic matter.Mineralizable nitrogen is the amount of N that can be made available to plants by microbes in the near future. The root health rating is conducted after actually growing beans in the soil for 4 weeks and then washing and checking the roots for disease, size and color. This Soil Health Test became available to New York growers in 2007 and to non-residents in 2008 for $45 per sample.
The Soil Health Test sampling is similar to a conventional soil test except that it includes penetrometer measurements for compaction (see related ďCompaction & OM SurveyĒ article) and involves collecting more soil (1.5 quarts) which must then be kept shaded and cooled, both in the field and during shipping, to preserve the microorganisms. You receive two pages of results: a standard soil test results (pH, P, K, CA, Mg, micros) is returned to you in a week or so, while the actual Soil Health Report takes 6-12 weeks to process (they have to grow beans in your soil for the root rating).
The Soil Health Report lists the 12 indicators in the first column, followed by actual lab measurements and then a rating for each result on a scale of 1-10. The ratings column is colored with red for poor soils (inpaired/constrained) rated <3, yellow for medium soils rated between 3-8, and green for healthy soils that score >8 to 10. The next column lists the soil constraint or problem (e.g. water retension, plow pan, biological activity), while the final column tells how your soilís score compared with all other soils previously tested (as a percentage) and generates an overall soil health score for your field (also a percentage).
Grant to promote deep zone-tillage
As part of our recent Sustainable Agriculture Research and Education (SARE) Program Partnership Grant, we used Cornellís new Soil Health Test to provide preliminary soil status data for the two Connecticut farms that were converting to deep zone-tillage. Our hope is that we can re-test the soil on these farms 5 or 10 years from now and detect some of the soil improvements that are expected to take place using this reduced-tillage system.
Nelson Cecarelli, who farms in Northford, and Tom Scott, who farms in East Lyme, have now both converted to deep zone-tillage and are participating partners on our SARE grant to help educate others about the benefits of this reduced-tillage system. As part of this educational effort, Nelson and Tom have helped conduct a farmer-to-farmer discussion group on reduced-tillage in Connecticut (Jan 08), a twilight meeting on zone-tillage at Nelsonís farm (June 08), and a Conference in Sturbridge (Dec. 08). Nelson also spoke at the Connecticut Vegetable & Small Fruit Growersí Conference in Vernon (January 09), and both growers will be participating in a zone-till session and discussion group at the next New England Vegetable & Fruit Conference in Manchester, NH (Dec. 09). We also hope to write up case studies of their transition from conventional tillage to deep zone-tillage, which will be published in Crop Talk and posted on the UConn IPM Web Site to help others with a smooth transition.
Meanwhile, I have been recording benefits and challenges they encounter, writing newsletter articles on deep zone-tillage (such as this), and speaking at meetings from Massachusetts to Washington D.C. to help supplement Nelson and Tomís educational efforts.Nelson uses his 2-row, Unverferth Zone Builder to plant all his sweet corn, winter squash and pumpkins, while Tom uses his 4-row Zone Builder to plant all his crops, including sweet corn, pumpkins, squash, peppers, eggplant, beans, Brassica, Swiss chard, spinach, strawberries and apple trees.
Tom transplants most crops on his farm and even uses the Zone Builder before preparing raised, plastic-mulched beds. He makes a single pass with the Zone Builder to loosen soil and make a narrow mulched bed, or two passes side-by-side to loosen enough soil to make a standard 3-foot wide, raised, bed, using 4-foot wide plastic mulch. Nelson bought his Zone Builder for the 2007 season and Tom used his for the first time in 2008.
In the spring of 2007, before Nelson used his Zone Builder for the first time, we recorded compaction and OM levels only. In the spring of 2008, when the Cornell Soil Health Test became available, we used the new test to gather preliminary data on 12 individual fields at Nelsonís farm and 8 fields at Tomís farm. In 2008, we took care to take penetrometer readings on Nelsonís farm from between rows of the previous seasonís crop, so that we were not testing for compaction in soil loosened by the sub-soiling shank on the Zone Builder the previous season.
Soil Health Test Results on Nelson Cecarelliís FarmThe soil organic matter in Nelsonís fields ranged from 1.6-3.5% (all low), with most of them in the very low range (<2.5%). His fields scored an average of 4.1 (yellow = medium health) on the Soil Health Test for organic matter. However, his soils rated low (2.1 = red) in soil health for two indicators: subsurface hardness and active carbon. All 12 of Nelsonís fields had a plow pan between 9-13 inches deep, which was listed as constraining root growth and drainage on the test results. The lack of deep roots can cause crops to be less drought tolerant, and poor drainage can lead to disease problems, such as Phytophthora, or soil erosion problems as water runs off the land because it canít penetrate the plow pan. The good news was that half of the indicators on Nelsonís tests averaged above 8 (high soil health) and he had 5 fields (42%) which had an overall Soil Health Score in the high range >70% (average across all 12 indicators).
Soil Health Test
Results on Tom Scottís Farm
The soil organic matter in Tomís fields ranged from 1.7-3.1% (all low), with 75% of them in the very low range (<2.5%). Tomís fields scored an average of 3.4 (yellow = the low end of the medium range for soil health) for organic matter. His fields scored 4.6 (medium = yellow) for subsurface hardness, which indicated that his plow pan was not as consistent and compacted as that in Nelsonís fields, but was still detected in all fields. Tom had two indicators which averaged a low (red) score: active carbon (1.0) and mineralizable nitrogen (2.6). Low ratings for active carbon mean that his soils have limited biological activity (the soil is a dead media instead of a healthy, functioning ecosystem) and low mineralizable nitrogen means that his soils have very low fertility levels (almost no organic matter that can be converted to N).
Again, the good news was that 5 of the 12 indicators on Tomís tests averaged above 8 (high soil health), and he had one field with an overall Soil Health Score >70 (high soil health = green), and 4 more fields that averaged in the high 60ís (yellow = high end of the medium health range). So Tom had 62% of his fields that averaged, or almost averaged, a high overall soil health rating.
Improving soil health
Interestingly, results from these 20 fields all showed similar soil deficiencies (same indicators rated low or medium-low). So, how does Cornellís Soil Health Assessment Training Manual suggest Nelson and Tom manage their fields to eliminate crop production constraints that were identified by the test?
A recent Soil Compaction and Organic Matter Survey on CT Vegetable Farms indicated that plow pans and low organic matter levels are the normal situation on conventionally-tilled farms throughout the state. Nelson and Tom have already implemented corrective measures for these soil health deficiencies on their farms: they have both transitioned to deep zone-tillage.
What are you doing to reverse the damage caused by 100-300 years of excess tillage and improve soil health on your farm?
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