Surface-applied or incorporated biochar and compost combination improves soil fertility, Chinese cabbage and papaya biomass

Justine Cox,Nguyen V. Hue,Kent D. Kobayashi,Amjad Ahmad

doi:10.1007/s42773-020-00081-z

Justine Cox, Nguyen V. Hue + Show 2 more

Open Access

https://doi.org/10.1007/s42773-020-00081-z

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Abstract

Many Hawaiian agricultural soils are acidic with low-nutrient retention; therefore, organic soil amendments are often used to improve soil properties and increase yields. Amendments can be incorporated for annual crops, but perennial orchards need surface application to avoid damaging surface roots. Pot trials compared responses to incorporated (IBC) or surface-applied (SBC) combination of hardwood biochar and chicken manure compost (4% v/v of each amendment) added to an Andisol and Oxisol. Soil pH was increased by 0.4–1.1 units in IBC and by 0.2–0.5 for SBC in the 0–10 cm soil layer. Both SBC and IBC increased soil total N, extractable P, Ca and Mg in the 0–10 cm soil layer. Soil pH, total C and extractable Ca were also higher in the 10–20 cm soil layer for IBC soil, indicating movement and/or leaching of amendments. Chinese cabbage biomass was 18–70% higher in the IBC and 14–47% higher in the SBC than that in the unamended soil, while papaya biomass was 23% and 19% higher in SBC and IBC, respectively. There was a greater response in the more acidic Andisol soil, with larger improvements in soil pH, plant nutrient uptake and root biomass than the Oxisol. Surface application was as effective in increasing plant growth as the incorporated amendment, providing evidence for farm scale assessment. Biochar and compost are recommended for use in tropical soils, and surface application may be beneficial to annual and perennial crops.

Highlights

Many Hawaiian agricultural soils are constrained by low fertility and lack of nutrient retention due to weathering in the tropical climate
The results of this study indicate that the combination of biochar and compost is an effective amendment to increase Chinese cabbage and papaya biomass and improve soil chemical properties, and that surface application is an option for perennial horticulture
There is evidence of downward movement of the amendments possibly in soluble or particulate form, with increased soil pH, total C, extractable P and Ca in the layer below application. These changes were found in the 10–20 cm layer below the incorporated amendment and in the 0–10 cm layer below the surface-applied amendment

Summary

Introduction

Many Hawaiian agricultural soils are constrained by low fertility and lack of nutrient retention due to weathering in the tropical climate. Andisols (developed from volcanic ash, pumice and cinder) typically have a high organic matter content, very high P sorption capacity and are low in Ca, Mg and K, creating a potentially P- and Ca-deficient soil, whereas Oxisols (developed from basaltic lava) are low in nutrients, and have high Fe and Al oxides, which reduce cation retention (Uehara and Ikawa 2000).

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