Using cover crops and organic amendments to meet your farm’s soil health goals - Oahu Resource Conservation and Development Council

How can you tell if your soil health practices are working?

Workshop 3 of our WFN Summer Soil Health Workshop dives into this question, looking specifically at the soil health practices of cover cropping and organic fertilizers applications. In addition to demoing simple in-field tests, this workshop also demonstrates how to set-up a simple trial on your farm to measure the nutrient contributions of specific soil health practices to your crops. This workshop also discusses the selection of cover crop seed and organic fertilizer, application rates, and the multiple soil health benefits that these practices provide in addition to the contributions of nutrients, such as nitrogen. Workshop 3 concludes with the introduction and demonstration of online tools, such as the cover crop calculator.

The learning objectives for this workshop include:

Know how specific cover cropping systems and organic fertilizers can be selected to meet your soil health goals for your farm;
Understand how to account for the contributions of cover crops and organic fertilizers into your farm’s nutrient management system;
Be able to link improved soil health and nutrient management needs on your farm;
Be able to identify changes in soil health after implementation of new management practice, focusing on trials and improvements from using cover crops and organic fertilizers;
Become familiar with an in-field soil incubator test to determine the amount of microbial activity in your soil;
Learn how to setup a simple on-farm fertilizer trail and the results other farmers are seeing.

Please watch the videos below to learn how these practices and tools can be used on your farm.

During our workshop, Christian Zuckerman, farm manager of Kahumana Organic Farms, shared some of the soil health principles they apply on their farm, which include ‘keeping the soil covered’, ‘increasing biological diversity’, ‘keeping a living root in the ground’ and ‘integrating animals’ in order to feed and care for the biology in the soil. These principles are achieved through the practice of composting, green mulching (chop and drop), mulching with wood chips, crop-rotation, the application of organic fertilizers, conservation tillage, cover cropping and integrating grazing animals.

In the video above, Christian shares his on-farm composting system. Compost is a great DIY organic amendment for your soil. It improves soil, water holding capacity, nutrient availability, aeration, tilth, microbial diversity. In making your own compost: Aim for: 25-30:1 C:N, 50% moisture, and air access to prevent anaerobic microorganisms from taking over. Turning over piles is one method of keeping air introduced. Covering with a tarp is a good way to control how much rain gets into your pile. Be careful with what you compost and how you use it as certain compostable material can add food safety risks. Composting is a whole separate workshop -or several-on its own. In addition to applications of carbon-heavy, wood chip mulch, Christian also plants Glericidia, which he uses as a green-mulch, using a ‘chop-and-drop’ approach to mulch-in-place. Watch these videos to learn about some of the polycropping systems Christian is trying in their avocado orchard and how he’s working with HDOA, NRCS, HFUU and Healthy Soils Hawaii to support this effort through financial and technical support. (Please scroll down the page for additional resources for composting systems and organic fertilizers).

Besides the compost they make at Kahumana Organic Farms, Christian also uses bone meal and feather meal for organic nutrient amendments. He is reducing his bone meal in favor of feather meal because bone meal is rich in phosphorus. Phosphorus leaching and runoff can lead to the contamination of our ground water and negatively impact our reefs. Although phosphorus leaching is normally limited in most Hawaii soils due to their high P-fixing characteristics, phosphorus leaching can occur if the soil reaches maximum phosphorus holding capacity, especially when P fertilizers are overapplied. Sandy soils are most susceptible to phosphorus leaching. Erosion of soils that contain high amounts of phosphorus is another source of phosphorus runoff.

In establishing their avocado orchard, Christian shares how they amended with gypsum to provide better drainage in their heavy clay soil, since avocado trees require good drainage. In between the rows of avocado trees, Christian plans to use alley cropping to diversify his production. He plans to rotate to rows with cover and cash crops. Once the avocado trees mature, a perennial cover crop will be established.

When establishing his citrus orchard Christian put a heavy layer of wood mulch around the young plants for weed suppression and planted Pigeon Pea between the rows to provide ground cover while also introducing a continuous source of nitrogen into the soil. Over the years the heavy mulch has broken down into a finer compost that continues to help retain moisture, moderate soil temperature, and suppress weeds.

Christian also rotates sheep through existing fields as a method of weed control and to provide a nutrient rich manure source. The sheep are also utilized for their grazing and nutrient cycling services, which assist in preparing future fields. In this video, Christian describes his full set-up and some of the sources where he purchased his perimeter and electric fencing, sheep and the rotation schedule they are trialing.

We also demoed how to set up a simple fertilizer trail on your farm to assess and monitor the results of any new soil health practices you begin to integrate into your operation. This process involves sectioning off your growing field with transects and testing the amount of plant available nitrogen (PAN) that the fertilizer provided. During our workshop, Josh Silva of CTAHR delved into how he setup a fertilizer trial with Kahumana Organic Farms to test the amount of nitrogen provided from organic fertilizers, such as compost, feather meal and bone meal (tankage). In testing the results of this new fertilizer treatment, Christian is able to determine how much nitrogen the new fertilizer contributes to his crops. This information can be used to adjust his nutrient management regime. As Josh explains in this video, the same process for setting up the trial of organic fertilizers could also be used to test the nitrogen contribution from cover crop treatments. Josh also gives some great tips and applications for setting-up transects in this video. Some considerations he mentions include: distributing your ‘treatment’ evenly across your trial area, keeping all other variables constant other than the one you’re testing, marking your transects clearly, and keeping good records.

How much nitrogen did my cover cropping or organic fertilizer treatments provide for my crops? Can I start reducing the amount of nitrogen fertilizers I purchase and apply? After learning how to set-up a simple on-farm trial to test the nitrogen contribution from cover cropping systems and/or organic fertilizers, Josh and Koon-Hui helped answer these questions by demonstrating how to use the SolVita CO2 test to assess the amount of microbial activity in the soil. Josh also explains how organic fertilizers don’t release nutrients very quickly unless there are adequate moisture conditions and microorganisms present to break down the stored nutrients. The populations of soil microorganisms present in a soil fluctuate with moisture conditions. To test microbial activity present, Josh used Solvita CO2 test kit. He put a color changing test strip that is sensitive to carbon dioxide into the container, added the dry soil being tested, added water, and closed the container to measure the amount of respiration over a 24 hour period. The resulting color corresponds to a level of microbial activity from low to high. Low indicates that there aren’t many microbes present while a high reading would signify overactive populations that are rapidly breaking down organic matter and are emitting carbon dioxide. Repeating this measurement over time is useful for monitoring how the management of a field is affecting microbial populations and provide insight into the nutrient cycling rates occurring.

To determine how much nitrogen the cover crops contributed and the amount available for their cash crops to uptake, Josh and Koon-Hui also demonstrated a simple soil nitrate test. Using calculations provided in our Cover Crop and Organic Fertilizer handouts, workshop participants were able to determine the nitrate levels required by different types of cash crops. In this case, Kahumana planned to plant their K6 field with pak choi, which required a nitrate level of at least 100 lb/acre. In conducting the soil nitrate test, we were able to observe that their field had a nitrate level of 80 lb/acre, so they only needed to apply 20 lbs/acre of nitrogen, opposed to a full 100 lbs/acre of nitrogen. This translated into a reduced cost of the fertilizer they needed to apply before planting their crop. In addition to these cost savings, using the cover crop seeds as their nitrogen source provided the extra benefit that contribute to the health of their soil ecosystem.

Koon-Hui provided a wealth of information on the various properties of different types of cover crops and based on specific soil health goals. For instance, Oil radish, Sorghum, or other species with tap roots are efficient at reaching nutrients and minerals that leach down through the soil while also breaking through compacted layers. Oil radish also provides biofumungant properties, which kills off non-beneficial soil organisms and helps to return the balance in the soil of more beneficial organisms. Sugars and compounds that increase microbial diversity are also exuded from living plant roots. Clover varieties provide nitrogen, but some varieties, like yellow sweet clover, also form deep roots that can tolerate drought and reach additional nutrients. These nutrients can be released into the topsoil by cutting them down and using them as mulch. Please watch our the video above to learn more about Koon-Hui’s tips in choosing cover crops that meet your farm’s productivity and soil health goals.