For farmers, soil fertility is a high-stakes balancing act. Providing too little of a needed nutrient can lead to low yields or even crop failure. Adding too much increases your costs without improving your harvest. The stakes are also high for the environment. Runoff can carry excess fertilizer into streams, rivers, and coastal waters, where it feeds microbial activity that can suffocate fish, coral, and other animals.
Extension specialist Jonathan Deenik is helping farmers decide what inputs work best with their soils, crops, and budgets. For example, repeated applications of fertilizer containing both nitrogen and phosphorous can cause phosphorus to build up in the soil. Experiments to find the range of soil phosphorus concentrations required for optimal crop growth enable farmers to test their soil and, if their land is already phosphorus-sufficient, use a nitrogen-only fertilizer that saves hundreds of dollars per acre. On-farm trials allow growers to see for themselves the costs and benefits of different practices, and Deenik spreads the new knowledge further through collaborations with and workshops for agricultural extension agents, who named him their Outstanding Specialist for 2007.
Several of Deenik’s projects evaluate organic soil amendments. These include research to calculate the soil-specific rates at which animal manures release nitrogen to plants and to assess the ability of composts and cover crops to boost soil organic matter, improve soil fertility, and increase crop quality. Another amendment, flash-carbonized charcoal, was developed by UH Manoa professor Michael Antal. Flash carbonization locks carbon into a stable, biologically unavailable form, so flash carbonizing agricultural wastes prevents them from releasing greenhouse gasses. Charcoal can also improve a soil’s ability to retain water and minerals. However, student-turned-research assistant Tai McClellan has found that the degree of carbonization is critical: adding highly carbonized macadamia nutshell charcoal to soil can benefit plants, but poorly carbonized charcoal contains volatile compounds that inhibit plant growth. Through wide-ranging research, Deenik and colleagues are finding new ways to make farmers’ fields and pocketbooks greener.