By Rob Sirrine
Nitrogen is an essential plant nutrient required for optimum cone production. The nitrogen replacement value, or the amount needed to replace what has been taken up by the plant biomass for fully-grown bines, is approximately 110 lbs/ac/year (cones-45 lbs/ac, crop residue-65 lbs/ac). By the end of July, hops have generally accumulated 80-150 lbs of N/ac. Depending upon site-specific characteristics like soil quality and management practices (fertilizer type, application method, cultural practices, etc.), the nitrogen use efficiency (NUE) for hops is roughly 50 percent.
This suggests that roughly half of the actual nitrogen applied is not taken up by the hop plant, but is instead lost to the environment; usually through leaching or volatilization. If the replacement value is 110 lbs/ac/yr and only 50 percent is taken up by the hop plant, then producers should be applying 220lbs of actual N/ac/yr. However, this does not account for the method or timing of nitrogen application. Nitrogen that is banded into the hop rows in one spring application, prior to the optimum period of uptake, is likely lost at a higher percentage than liquid nitrogen (ex. 28n solution) fertigated on a daily basis throughout the primary vegetative growth period in May and June.
Hop sites on sandy soils have low soil organic matter levels and may need to apply the higher rate of Nitrogen to optimize growth. Based on our experience, it is recommended that hop growers apply at least 200 lbs of actual N/acre/yr to mature hop plants. (See Figure). Near the end of June, internode length should measure around 8 inches in length. If length is less than 8 inches, growers need to increase N. If greater than 8 inches, growers should back off on N. At the same time. growers should calculate cumulative lbs. of actual N applied YTD. It should be at least 150 lbs. or more by the end of June when plants begin to transition from vegetative to reproductive growth. If the early summer has been overly wet and growers have not had the opportunity to fertigate this amount, granular N should be band applied and lightly tilled. For organic options growers can continue with composted manure and should account for this N when developing their seasonal N budgets, but should be diligent about not over applying Phosphorous. Other organic options include granular products like Nature safe 13-0-0, feathermeal, and blood or bone meal that should be applied in early spring. Cover crops can also provide significant quantities of N, but cover crops must be tilled in for N to be released.
Source:msu.edu