Reducing Pacific Island Growers’ Reliance on Of...

Reducing Pacific Island Growers’ Reliance on Off-island Fertilizer Sources

Reducing Pacific Island Growers’ Reliance on Off-island Fertilizer Sources

hawaii compost

The Challenge

At the Western SARE Hawaii sub-regional conference held in 2008, stakeholders identified replacing imported fertilizers with local resources as the highest research, education, and development priority. The cost of commercial fertilizer has risen along with oil prices, and thus, growers in the Pacific region are increasingly interested in obtaining locally available by-products that can be used as agricultural inputs. According to Theodore Radovich, University of Hawaii, possible inputs include commercial green-waste composts, rendered animal products (tankage), and invasive algae from coral reef remediation projects. These by-products are readily available, but bottlenecks exist that inhibit use and adoption by growers. Radovich identified the bottlenecks as  1) commercial composts vary significantly in quality, often have low nitrogen content, and frequently very high C:N ratio, 2) rendered meat product quality also varies depending on feedstock source, and we have yet to fully understand its effects on plant growth under different Hawaiian soils and microclimates, 3) invasive algae is available in large quantity and can be an important source of K and other plant nutrients, but nutrient content depends on species, and potential salinity concerns need to be addressed. Due to these issues, Radovich found that growers were “unaware of resources available to them and unsure of their ability to profitably utilize the local resources they are aware of.”

To address these problems, Radovich developed the Western SARE funded project “Reducing Pacific Island Growers’ Reliance on Off-island Fertilizer Sources (SW11-055)” to conduct a series of greenhouse and on-farm trials in cooperation with university faculty, commercial growers, and industry partners.

Searching for a Solution

Radovich and project team evaluated quality, maturity, nitrogen release pattern, and crop growth for 10 composts through lab incubation and greenhouse trials. They collected samples of major algae invasive species and of tankage. This research was conducted to meet the following objectives: 

  1. Enhance the capacity of at least 300 growers, compost producers and other agricultural professionals in Hawaii, American Samoa, and elsewhere to evaluate compost quality.
  2. Identify the most important variables influencing the effect of rendered meat products (tankage) on plant growth and mineral nutrition in Hawaii and American Samoa.
  3. Quantify the independent and interactive effect of species, collection location and simple processing on nutrient content and availability of three algae species collected from multiple sites on Oahu, Molokai and Hawaii islands.
  4. Ensure dissemination of information from this project to producers and agricultural professionals throughout the Pacific region beyond the project duration.

Cost analysis of inputs and practices were conducted throughout all activities.

What was Learned

In the greenhouse trials, Radovich confirmed “1) common quality parameters (C:N ratio and maturity) are not sufficient to evaluate the quality of a compost; 2) the rate of N mineralization from different organic amendments has a narrow range of 0.02–0.03/day; and 3) there is a potential for long-term improvement in soil fertility and quality due to compost applications, especially for composts contain 2% N and more.”  Using the algae samples, he was able to “1) establish bio-security protocol (drying the samples at 190OF for 72 hours) to ensure reduce viability of the invasive algae species into new locations in Hawaii; 2) confirm the K content in the three algae species were about 15-20% from samples collected over two years period; 3) establish an application rate of 200-250 lbs K/acre for sweet potato and pak choi crops form dried algae; and 4) draw a K release pattern from different algae species under peat moss and different soils (results are still in the analysis stage).” He found through the tankage sampling “1) average N content in the samples was 10%; 2) tankage can be a good source of other nutrient (such as P average 3%); 3) there is a chance of N loss from tankage between 10-15% annually of the initial N during storage, the decline depends on the storage condition, especially temperature and humidity; 4) in a lab leachate studies about 20% of total N was mineralized/released in the first two weeks of the incubation. Also, the total mineralized N after 90 days of incubation reached up to 75% of total N applied."


Due to the project’s findings, Radovich asserts,

  • Bio-security protocols have reduced concerns of algae spread to other areas.
  • There is an increased demand for locally produced tankage. The increased reliance on the local inputs will reduce demand for off-state fertilizers.
  • Farmers utilizing the invasive algae, mainly taro and sweet potato farmers, are reporting increase in the yield and quality of their crops.
  • There is increased incorporation and utilization of locally produced composts among small-farm holders. This may lead to increase net-benefits, due to reduction in production cost.

Want more information? See the related SARE grant(s) SW11-055, Reducing Pacific Island Growers’ Reliance on Off-island Fertilizer Sources .

Product specs
Location: Hawaii | West

2016 Annual Report

For the first time, we are sharing a yearly snapshot of our work. The stories provided here typify the creative, participatory and integrated research Western SARE annually funds – led by land grant institution researchers and graduate students, Extension and other ag professionals, and nonprofit leaders in full partnership with producers.