Improving Nitrogen Synchronization of Local Fertilizers, Soil Fertility, and Crop Quality with Biochar Application

2016 Annual Report for SW16-021

Project Type: Research and Education
Funds awarded in 2016: $259,816.00
Projected End Date: 12/31/2019
Grant Recipient: University of Hawaii at Manoa
Region: Western
State: Hawaii
Principal Investigator:
Dr. Nguyen Hue
University of Hawaii at Manoa

Improving Nitrogen Synchronization of Local Fertilizers, Soil Fertility, and Crop Quality with Biochar Application


It is hypothesized that a combination of biochar and compost when applied to nutrient-poor soils would enhance soil fertility and plant growth more than when biochar or compost is applied separately. To test this hypothesis, a greenhouse experiment was conducted, consisting of two wood-based biochars at 0 and 2% and 2 composts (a vermi- and a thermos-compost) at 0 and 2%, factorially applied to two highly weathered, acid soils (an Oxisol and a Ultisol) of Hawaii. Two additional treatments: 2 cmolc/kg lime + 2% vermi-compost and 2 cmolc/kg lime + 2% thermo-compost were included for comparison. Chinese cabbage (Brassica rapa cv. Bonzai) was used as the test crop. Table 1 shows cabbage fresh weight and N uptake as affected by the various treatments.

Table 1. Cabbage fresh weight and N uptake as affected by biochar, compost, and lime amendments.

                                                   Leilehua Ultisol                                                 Wahiawa Oxisol

                                Shoot fresh weight          N uptake             Shoot fresh weight          N uptake

Treatment                          g/plant                 mg N/plant         g/plant                                 mg N/plant

Lactree wood                     6.0                          21.0                        16.0                                        40.0

Hilo wood                           4.9                          10.5                        17.0                                        33.0

Vermicompost                  13.5                        37.0                        17.5                                        41.0

Thermocompost              12.5                        29.0                        14.5                                        33.0

Lactree + vermi            23.0                       68.0                       17.0                                       44.0

Lactree + thermo             12.0                        29.0                        21.0                                        41.0

Hilo wood + vermi           18.0                        52.0                        16.5                                        58.0

Hilo wood + thermo         14.0                        40.0                        21.5                                        46.0

Lime + vermi                     14.5                        31.0                        23.0                                        49.0

Lime + thermo                  7.0                          27.0                        6.5                                          26.0


Our preliminary findings were: (1) the use of biochar in combination with compost improved soil fertility and increase plant growth, and (2) the effect varied with types of biochar, compost, as well as with plant nutrient studied: Lactree wood biochar + vermi-compost seemed to be the best soil amendment in terms of nutrient availability and plant growth.

Objectives/Performance Targets

The objectives of our experiment are

(1) to examine the effect of biochar on N dynamics (i.e., potential loss and rate of mineralization) of organic fertilizers over time and

(2) to evaluate the combined effect of biochar and compost on vegetable growth.


See summary.

This is the beginning year of the project, and the reported experiment was the first of a series of up-coming experiments. A field work with similar set-up/treatments is underway.

Impacts and Contributions/Outcomes

High-N organic fertilizers could be more efficiently utilized when applied in combination with certain biochars than when applied alone. This finding/recommendation would provide organic farmers some good management tools in improving their soil fertility/quality. Further more, our work suggests that good knowledge about biochar and organic fertilizer is required in their selection for a specific usage.


Dr. Theodore Radovich
Associate Specialist
Univerisity of Hawaii at Manoa
3190 Maile Way
St. John 102
Honolulu, Hawaii 96822
Office Phone: 808-956-7909
Dr. Amjad Ahmad
Junior Researcher
University of Hawaii at Manoa
3190 Maile Way
St. John 102
Honolulu, Hawaii 96822
Office Phone: 808-956-7909