Nitrogen Dynamics and Sweet Potato Production under Indigenous Soil Moisture Conservation Practices in the Leeward Kohala Field System, Hawai’i Island

William C L Sirabis,Noa K Lincoln,Michael B Kantar,Theodore Radovich

doi:10.3390/soilsystems6010016

William C L Sirabis, Noa K Lincoln + Show 2 more

Open Access

https://doi.org/10.3390/soilsystems6010016

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Journal: Soil Systems	Publication Date: Feb 2, 2022
Citations: 1	License type: CC BY 4.0

Affiliation: University of Hawaiʻi at Mānoa

Abstract

Intensive cultivation of ‘uala (sweet potato) in the Leeward Kohala field system on Hawai’i Island supported substantial populations of Native Hawaiians prior to its abandonment in the 19th century. Productivity is influenced by the heterogeneity of the climate and biogeochemical soil characteristics across the substantial ecological gradient. Agricultural infrastructure and associated practices were developed to manage crop production eventuating from the variation in inter- and intra-annual rainfall. Mechanisms of sustaining soil nitrogen (N) are still unclear; however, a pronounced source of N is soil organic matter decomposition. This study investigated in situ the effects of indigenous Hawaiian mulching practices against two control treatments on soil moisture and temperature dynamics to facilitate N mineralization in soil mounds cultivated with ‘uala. Field experiments were set in two agricultural restoration plots with distinct climatic and soil characteristics. Data included soil moisture and temperature, soil and plant N, growth and development of ‘uala, and real-time weather data. Concurrently, N mineralization was also investigated under controlled conditions. All indigenous mulching treatments were found to significantly increase soil moisture, regulate temperature variation, and improve N availability compared to control. Differences in soil properties between treatments translated to significant differences in above-ground biomass. The data suggest that these differences would extend to tuber production, but the use of a long-gestation variety limited tuber production in the study. Increased temperatures in the controlled experiments were observed to increase inorganic N significantly, but less substantially than soil moisture. Indigenous practices in the region could have greatly mitigated plant stress due to moisture, temperature, and N availability, increasing productivity and reducing the variability of the Leeward Kohala Field System.

Highlights

For at least four centuries, commencing in the 1400s, a vast agricultural system occupied the central elevations of the Leeward Kohala landscape on Hawai’i island and produced food for populous communities [1]
The ~6500-hectare system, known as the Leeward Kohala Field System (LKFS) (Figure 1), was a dense network of infrastructure used for rain-fed cultivation [1,2,3,4]
Site Description In July 2019, we established replicated field experiments within experimental māla within the ahupua’a of Puanui (Figure 1) managed by Ulu Mau Puanui—a nonprofit organization focused on promoting research, awareness, and education of the cultural and historical prominence of the LKFS

Summary

Introduction

For at least four centuries, commencing in the 1400s, a vast agricultural system occupied the central elevations of the Leeward Kohala landscape on Hawai’i island and produced food for populous communities [1]. The ~6500-hectare system, known as the Leeward Kohala Field System (LKFS) (Figure 1), was a dense network of infrastructure used for rain-fed cultivation [1,2,3,4]. The system spans a broad ecological range—extending from sea level to ~750 masl and encompassing ~750 to ~2200 mm/y in rainfall—with the productivity of the systems influenced by rainfall, temperature and soil nutrient levels [5,6]. 2022, 6, 16 x FOR PEER REVIEW Soil of 13 22 of Kohala Figure

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