Preparing Hawai‘i agriculture for rising soil salinity and water scarcity challenges to improve food self-sustainability

Commodities

• Agronomic: peas (field, cowpeas), radish (oilseed, daikon, forage), sunflower
• Vegetables: onions, taro

Practices

• Crop Production: cover crops, water management, other
• Education and Training: demonstration, extension, on-farm/ranch research, workshop
• Natural Resources/Environment: habitat enhancement, soil stabilization, other
• Pest Management: mulches - general
• Production Systems: agroecosystems, dryland farming, organic agriculture, transitioning to organic
• Soil Management: composting, green manures, organic matter, soil analysis, soil microbiology, soil physics, soil quality/health
• Sustainable Communities: local and regional food systems, sustainability measures

Soil salinization from water scarcity and the use of reclaimed water has become a threat to farms on the Leeward side of Hawai'i. Many cash crops, including bulb onions and taro, are susceptible to high soil salinity, leading to substantial yield losses. Instead of relying on using scarce freshwater to leach salts from topsoil, this project explores the use of salt-tolerant cover crops (STCC) to improve soil microbial activity, water infiltration, and other soil health properties. Some STCC can host plant growth-promoting rhizosphere microbes (PGPMs) with induced salt tolerance (IST) properties on crops they associate with. Research objectives of this proposed project are: 1) evaluate the ability of sunflower, cowpea, and daikon radish to function as salt tolerant cover crops that improve soil health and mitigate salinity stress on subsequent cash crops; 2) identify PGPMs with IST properties associated with STCC; and 3) integrate STCCs with sheet mulching (SM) on cash crops to preserve the PGPMs. Education objectives of this project include: 1) support early adoption of STCC/SM through field demonstration; 2) develop site-specific recommendations; and 3) organize community events to broaden public awareness of salinity management strategies. The graduate student will work with soil ecologists, an extension agent and a taro farmer to conduct field trials, and laboratory and greenhouse bioassays. Extension outputs of this project include outreach to farmers and new farmers' training program in Hawai'i. This project would have a significant environmental and social impact on small family farms and food self-sufficiency in Hawai'i.

Research objectives:

• Evaluate the ability of sunflower, cowpea, and daikon radish to function as salt‑tolerant cover crops (STCCs) that improve soil health and mitigate salinity stress on subsequent cash crops.
• Identify STCC‑associated plant growth‑promoting rhizosphere microbes (PGPMs) that stimulate induced salt tolerance (IST) in salt-susceptible crops.
• Integrate STCCs with sheet mulching (SM) to enhance PGPM abundance and activity.

Education objectives:

• Support early adoption of the integrated STCC/SM system by farmers through hands‑on demonstrations and practical guidance.
• Develop site‑specific recommendations that help producers optimize these practices for their own fields.
• Broaden public awareness of low‑input salinity‑management strategies through community events and outreach to non‑farmer audiences.